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Details for Half-High Concrete Masonry Units

August 2018

INTRODUCTION

Concrete masonry offers numerous functional advantages, such as structural load bearing, life and property protection, durability and low maintenance. Half-high concrete masonry units offer the additional advantages of a veneer-like appearance in economical single wythe construction. As for all concrete masonry units, integrally colored half high brick-like units provide enduring strength and lasting resistance to fire and wind while maintaining a virtually maintenance-free façade. These attributes are appealing for both new construction and renovations in historic districts.

Many designers are turning to half-high masonry because of its economy. As an alternative to a traditional cavity wall, these walls offer the same finished appearance, exterior durability and low maintenance coupled with a shorter construction time because of the single wythe loadbearing design. This TEK describes the use of half high units for single wythe masonry construction. For veneer applications, see Refs. 1 and 2.

HALF-HIGH UNITS

Half-high concrete masonry units are produced to the same quality standards as other concrete masonry units. ASTM C 90 (ref. 3) governs physical requirements such as minimum compressive strength, minimum face shell and web thicknesses, finish and appearance, and dimensional tolerances.

Like other concrete masonry units, half-highs are produced in a variety of sizes, unit configurations, colors and surface textures. In addition, special shapes, such as corners and bond beam units are also available.

WALL PERFORMANCE

Structural design considerations for half-high construction are virtually the same as those for conventional concrete masonry units. One aspect that may be different for half-high units is the unit strength. Typical nonarchitectural concrete masonry units have a minimum unit strength of 1,900 psi (13.10 MPa), corresponding to a specified compressive strength of masonry, f’m, of 1,500 psi (10.34 MPa). Half high and other architectural units, however, are typically manufactured to a higher unit strength. Designers should check with producers about the strength of locally available units, with the intent of taking advantage of these higher strengths in their designs when available.

Section properties for half-high units are essentially the same as for full-height units, and the same design aids can be used for both (see Ref. 4). In addition, because the core sizes are also typically the same as for full-height units of the same thickness, considerations for maximum reinforcing bar size as a percentage of the cell area are the same as well. See Ref. 5 for more detailed information.

Because there are more horizontal mortar joints in a wall constructed using half-high units, there is slightly less concrete web area in the wall overall. Although this theoretically reduces the wall weight, in practice the wall weights of walls constructed using half-high units are within 1 psf (0.05 kPa) of those for full height units (see Ref. 6).

To facilitate the construction of bond beams, half-high bond beam units are typically available with depressed webs to accommodate horizontal reinforcement. Grouting two half-high units provides an 8 in. (203-mm) deep bond beam, as shown in Figures 1 through 3. Note that the bottom unit of the bond beam should have depressed webs to accommodate the horizontal reinforcement, but the top unit need not have depressed webs.

Performance criteria for fire resistance, energy efficiency and acoustics of half-high units can be considered to be the same as for similar full height units. See Refs. 7 through 11 for further information. In addition, detailing window openings, door openings, etc., is the same as for single wythe masonry walls constructed using full-height units.

CONSTRUCTION

Construction with half-highs is very similar to that for conventional units. Some differences include: an increased number of courses laid per wall height, greater amount of mortar needed, as well as the difference in bond beam construction noted above. Crack control considerations are the same as for full height units.

As an alternative to supporting trusses by means of a pocket in the masonry wall or by joist hangers, Figure 4 shows a unique application where half-high units have been corbelled out to provide bearing for a wood truss floor. This also provides continuous noncombustible bearing thickness without the need to stagger the joists. See Ref. 12 for additional floor and roof connection details.

As for any single wythe construction, particular care should be taken to prevent water from entering the building interior. Dry walls are attained when both the design and construction address water movement into, through and out of the wall. Considerations include potential sources of water, unit and mortar characteristics, crack control, workmanship, mortar joint tooling, flashing and weeps, sealants, and water repellents. For single wythe masonry, an integral water repellent in both the units and mortar, as well as a compatible post-applied surface water repellent are recommended. See Refs. 13 -18 for more information.

Figure 1 shows a proprietary flashing system that collects and directs water to the exterior of the wall and out weep holes, without compromising the bond at mortar joints in the face shells (see Ref. 15 for recommended flashing locations). There are a number of generic and proprietary flashing, drainage, weep, mortar dropping control, and rain screen systems available. Single wythe flashing details using conventional flashing are included in Ref. 14.

Solid grouted single wythe walls tend to be less susceptible than ungrouted or partially grouted walls to moisture penetration, since voids and cavities where moisture can collect are absent. As a result, solid grouted walls do not require flashing and weeps, although they do require other moisture control provisions, such as sealants and water repellents. For partially grouted walls, flashing should be placed in ungrouted cells.

REFERENCES

Concrete Masonry Veneers, TEK 03-06C. Concrete Masonry & Hardscapes Association, 2012.
Crack Control Strategies for Concrete Masonry Construction, CMU-TEC-009-23, Concrete Masonry & Hardscapes Association, 2023.
Standard Specification for Loadbearing Concrete Masonry Units, ASTM C 90-06b. ASTM International, Inc., 2006.
Weights and Section Properties of Concrete Masonry Assemblies, TEK 14-01B. Concrete Masonry & Hardscapes Association, 2023.
Steel Reinforcement for Concrete Masonry, TEK 12-04D. Concrete Masonry & Hardscapes Association, 2006.
Weights and Section Properties of Concrete Masonry Assemblies, TEK 14-01B, Concrete Masonry & Hardscapes Association, 2023.
Fire Resistance Ratings of Concrete Masonry Assemblies, TEK 07-01D. Concrete Masonry & Hardscapes Association, 2018.
R-Values for Single Wythe Concrete Masonry Walls, TEK 06-02C. Concrete Masonry & Hardscapes Association, 2013.
Sound Transmission Class Ratings for Concrete Masonry Walls, TEK 13-01D. Concrete Masonry & Hardscapes Association, 2012.
Noise Control With Concrete Masonry, TEK 13-02A. Concrete Masonry & Hardscapes Association, 2007.
Outside-Inside Transmission Class of Concrete Masonry Walls, TEK 13-04A. Concrete Masonry & Hardscapes Association, 2012.
Floor and Roof Connections to Concrete Masonry Walls, TEK 5-7A. Concrete Masonry & Hardscapes Association, 2001.
Water Repellents for Concrete Masonry Walls, TEK 19-01.
Concrete Masonry & Hardscapes Association, 2006.
Design for Dry Single-Wythe Concrete Masonry Walls, 19-02B. Concrete Masonry & Hardscapes Association, 2012.
Flashing Strategies for Concrete Masonry Walls, TEK 19-04A. Concrete Masonry & Hardscapes Association, 2008.
Flashing Details for Concrete Masonry Walls, TEK 19-05A.
Concrete Masonry & Hardscapes Association, 2008.
Joint Sealants for Concrete Masonry Walls, TEK 19-06A.
Concrete Masonry & Hardscapes Association, 2014.
Characteristics of Concrete Masonry Units With Integral
Water Repellents, TEK 19-07. Concrete Masonry & Hardscapes Association, 2008.
Intelligent Design, Half-High Architectural CMU. Illinois Concrete Products Association.
Building Code Requirements for Masonry Structures, ACI 530-08/ASCE 5-08/TMS 402-08. Reported by the Masonry Standards Joint Committee, 2008.

Concrete Masonry Hurricane and Tornado Shelters

August 2018

INTRODUCTION

Extreme windstorms, such as hurricanes and tornadoes, can pose a serious threat to buildings and their occupants in many parts of the country. Hurricanes and tornadoes produce wind pressures and generate flying debris at much higher levels than those used to design most commercial and residential buildings. Hence, these storms require residents to either evacuate the area or seek protection in dedicated shelters. Storm shelters are buildings, or parts of buildings, that are designed and built specifically to provide a highly protected space where community members or occupants can seek refuge during these events.

The newly-developed standard ICC-500, Standard on the Design and Construction of Storm Shelters (ref. 1), provides design and construction requirements for hurricane and tornado shelters. The standard covers structural design requirements for these shelters, as well as requirements for ventilation, lighting, sanitation, egress and fire safety.

ICC-500 covers both hurricane and tornado shelters, and includes requirements for two types of shelters: community shelters, buildings specifically dedicated to provide shelter during a storm; and residential shelters, which are typically reinforced rooms within a home, where the occupants can safely seek refuge during a hurricane or tornado.

Prior to the publication of ICC-500, builders and homeowners seeking storm shelter guidance have used the FEMA 320 publication Taking Shelter From the Storm: Building a Safe Room Inside Your House, and the FEMA 361 publication Design and Construction Guidance for Community Shelters, (refs. 2, 3). Research performed at the Texas Tech University Wind Science and Engineering Research Center (ref. 4), however, found that the FEMA recommendations were overly conservative for concrete masonry for impact resistance. Concrete masonry walls have been tested to withstand the ICC500 criteria, resulting in more economical wall designs than those previously recommended by FEMA.

TEK 05-11, Residential Details for High-Wind Areas (ref. 5), provides prescriptive requirements for reinforced concrete masonry homes in hurricane-prone areas, based primarily on providing a continuous load path from roof to foundation. These are general residential details, and do not address storm shelters. In contrast, the requirements described in this TEK apply only to dedicated shelters, or to shelter areas within a home, meant to provide temporary protection during a storm. Concrete masonry walls capable of meeting the ICC-500 requirements are presented, as well as the results of impact testing on concrete masonry walls. Note that this TEK does not address all requirements of ICC-500.

ICC-500 WIND DESIGN CRITERIA FOR SAFE ROOM WALLS AND FLOORS

General design considerations for storm shelters include:

adequate wall and roof anchorage to resist overturning and uplift,
walls and ceiling, as well as openings such as doors and windows, must withstand design wind pressures and resist penetration by windborne objects and falling debris, and
connections between building elements must be strong enough to resist the design wind loads. Figure 2 shows a typical detail for connecting a concrete roof slab to concrete masonry shelter walls, using reinforcing bars to provide adequate load transfer. ICC-500 defines design tornado wind speeds across the United States, and hurricane design wind speeds for applicable coastal areas. When the shelter is to provide shelter from both hurricanes and tornadoes, the most restrictive of the two design criteria should be used for design. The reader is referred to the standard (ref. 1) for maps defining these speeds. Note that wind speeds in ICC-500 are much higher than wind speeds in ASCE7 (ref. 6) or the International Building Code (refs. 7, 8), and are considered to provide the maximum or ultimate tornado or hurricane design wind speed at a site. Therefore, the wind load contribution in the load combinations is adjusted accordingly.

For example, 1.0W rather than 1.6 W is used as the factored wind load in strength design combinations. In allowable stress design, 0.6W is used instead of W. Wind pressures are to be based on exposure C, although exposure B is permitted if it exists for all wind directions.

In addition to being designed for these design wind speeds, shelter walls and ceilings must be able to withstand impact from flying debris, whose projectile speed varies with the design wind speed. The ICC 500 design criteria vary with location. The concrete masonry walls tested at Texas Tech were tested at the most stringent of the ICC-500 wind speeds and impact requirements, as follows. For tornado shelters, the highest design wind speed prescribed by ICC-500 is 250 mph (402 km/h). Corresponding walls and ceilings must withstand impact from a 15 lb (6.8 kg) wooden 2 x 4, propelled at 100 mph (161 km/h) and 67 mph (108 km/h), respectively.

These conditions will more than satisfy the less stringent requirements for hurricane shelters. For hurricane shelters, the highest design wind speed in ICC-500 is 237 mph (381 km/h) (with the exception of Guam, which has a design hurricane wind speed of 256 mph (412 km/h)). In addition, walls subject to this 237 mph (381 km/h) design wind speed must be capable of withstanding impact from a 9 lb (4.1 kg) wooden 2 x 4 propelled at 100 mph (161 km/h). Ceilings and other horizontal surfaces must withstand impact from the same projectile propelled a 25 mph (40 km/h).

In addition to these requirements, ICC-500 defines requirements for tie-down to the foundation and adequate foundation sizing to resist the design overturning and uplift forces.

CONCRETE MASONRY ASSEMBLIES FOR STORM SHELTERS

A typical concrete masonry storm shelter design is shown in Figure 1. Several concrete masonry systems have been successfully tested to withstand the 15 lb (6.8 kg) 2 x 4 propelled at 100 mph (161 km/h) (ref. 4). Solidly grouted 8-in. (203-mm) concrete masonry walls with No. 5 (M #16) reinforcement at 48 in. (1,219 mm) o.c., with one horizontal No. 5 (M#16) min. at the top of the wall and in the footing or bottom of the wall, can withstand these conditions. All weight classes of concrete masonry meet the strength and impact-resistance requirements. The engineer will use the masonry weight in the shelter design to resist overturning. Regardless of the concrete masonry density, the weight of the grouted masonry assembly provides increased overturning resistance compared to low-mass systems.

Although solidly grouted 6-in. (152-mm) concrete masonry walls with No. 4 (M #13) bars at 32 in. (813 mm) o.c. successfully passed the impact test, they may not have enough weight to resist overturning for the most severe tornado loading, based on a 250 mph (402 km/h) wind speed. Hence, the details included in this TEK show 8-in. (203 mm) storm shelter walls. Solidly grouted 6-in. (152-mm) walls may be adequate for lower wind requirements, however.

A ceiling system using 7-in. (178-mm) deep bottom chord bearing steel joists infilled with concrete masonry units and grout to a nominal 8-in. (203-mm) depth was also tested and found to withstand the 15 lb (6.8 kg) 2 x 4 at 67 mph (108 km/h) protocol (ref. 4). No. 4 (M #13) reinforcing bars were placed perpendicular to the joists, at 8 in. (203 mm) o.c. Note that all assemblies were successfully tested using standard masonry grout per ASTM C 476 (ref. 9). Some previous references recommend the use of concrete to fill the masonry cores, rather than grout, but this is contrary to the building code and is highly discouraged.

RESIDENTIAL SHELTERS

The purpose of an in-home shelter is to provide an area where the occupants can safely shelter during a high wind event. In flood prone areas, the shelter must not be built where it can be flooded. The shelter should be accessible from all areas of the house and should be free of clutter to provide immediate shelter. If not within the residence, the shelter needs to be within 150 ft (45.72 m) of the residence (ref. 1). FEMA (ref. 2) suggests a basement, an interior room on the first floor on a foundation extending to the ground or on top of a concrete slab-on-grade foundation or garage floor as good locations for an in-home shelter.

Below-ground safe rooms provide the greatest protection, as long as they are designed to remain dry during the heavy rains that often accompany severe windstorms. When shelters are located below grade, the soil surrounding the walls can be considered as protection from flying debris during a high wind event, as long as the wall is completely below grade and soil extends at least 3 ft (914 mm) away from the wall, with a slope no greater than two inches per foot (167 mm/m) for that 3 ft (914 mm) distance. When these conditions are met, the walls do not need to meet the missile impact requirements described above. Below-grade ceilings must have a minimum of 12 in. (305-mm) of soil cover to be exempt from the impact testing requirements.

Sections of either interior or exterior residence walls that are used as walls of the safe room must be separated from the structure of the residence so that failure of the residence, which is designed for a much lower loading, will not result in a failure of the safe room.

RESIDENTIAL RETROFIT

Special consideration must be given when retrofitting a shelter into an existing home. Figures 3 through 5 illustrate typical details for connecting shelter elements to an existing basement wall.

The results of recent testing (ref. 4) has improved the economy of constructing retrofits. Previously, a concrete masonry storm shelter would have required a large dedicated foundation. Research confirms, however, that considering the weight of fully grouted concrete masonry, a large foundation is not required to adequately resist the uplift and overturning forces.

Accordingly, ICC-500 allows concrete masonry storm shelters to be constructed within one and two family dwellings on existing slabs on grade without a dedicated foundation, under the following conditions:

the calculated soil pressure under the slab supporting the storm shelter walls does not exceed 2,000 psf (95.8 kPa) for design loads other than the design storm events and 3,000 psf (143.6 kPa) for design storm shelter events,
at a minimum, the storm shelter is anchored to the slab at each corner of the structure and on each side of the doorway opening (see Figure 4), and
the ICC-500 slab reinforcement requirements are waived if the slab dead load is not required to resist overturning.

COMMUNITY SHELTERS

Requirements for community shelters are similar to those for residential, but require a larger area and additional features in anticipation of sheltering more people. For example, community storm shelters require: signage to direct occupants to storm shelter areas; wall, floor and ceiling assemblies with a minimum 2-hour fire resistance rating; as well as additional ventilation and sanitation facilities.

REFERENCES

Standard on the Design and Construction of Storm Shelters, ICC-500. International Code Council and National Storm Shelter Association, 2008.
Taking Shelter From the Storm: Building a Safe Room Inside Your House, FEMA 320. Federal Emergency Management Agency, 2004.
Design and Construction Guidance for Community Shelters, FEMA 361. Federal Emergency Management Agency, 2000.
Investigation of Wind Projectile Resistance of Concrete Masonry Walls and Ceiling Panels with Wide Spaced reinforcement for Above Ground Shelters, CMHA Publication MR 21. Texas Tech University Wind Science and Engineering Research Center, 2003.
Residential Details for High-Wind Areas, TEK 05-11, Concrete Masonry & Hardscapes Association, 2003.
Minimum Design Loads for Buildings and Other Structures, ASCE 7-02 and ASCE 7-05. American Society of Civil Engineers, 2002 and 2005.
2003 International Building Code. International Code Council, 2003.
2006 International Building Code. International Code Council, 2006.
Standard Specification for Grout for Masonry, ASTM C 476-07. ASTM International, Inc., 2007.

Rolling Door Details for Concrete Masonry Construction

August 2018

INTRODUCTION

Openings in concrete masonry walls utilize lintels and beams to carry loads above the openings. When openings incorporate rolling doors (also referred to as overhead coiling doors or coiling doors), wind loads on the door are transferred to the surrounding masonry through the door guides and fasteners.

In some instances, the rolling doors have been designed for specific wind load applications, and are heavily dependent on the structural integrity of the door jamb members as they are attached to building walls at jamb locations. This TEK discusses the forces imposed on a surrounding concrete masonry wall by rolling doors, and includes recommended details for jamb construction. Lintel design, to carry the loads imposed on the top of the opening, are covered in Allowable Stress Design of Concrete Masonry Lintels and Precast Concrete Lintels for Concrete Masonry Construction (refs. 1, 2).

LOADS EXERTED BY ROLLING DOORS

Architects and building designers should determine the loads that rolling doors exert on the wall around the opening. Dead loads include the weight of the door curtain, counterbalance, hood, operator, etc., that is supported by the wall above the opening. Live loads result from wind that acts on the door curtain. Rolling doors are available with windlocks, which prevent the door curtain from leaving the guides due to wind loading. On doors without windlocks, the only wind load force that the curtain exerts on the guides is normal to the opening. For doors with windlocks, there is an additional load parallel to the opening (see Figures 1 and 2 for face-mounted and jambmounted doors, respectively). This load is the catenary tension that results when the curtain deflects sufficiently to allow the windlocks to engage the windbar in the guide. This force acts to pull the guides toward the center of the opening. The door is exposed to a additive wind loads, from both inside and outside the building.

Calculating the parallel force involves several variables, the most prominent of which are the width of the opening and the design wind load. It is also important to note that the door must withstand both positive and negative wind loads. Including these forces in the design of the jamb and its supporting structure can help prevent a jamb failure and allow the building to fully withstand its specified wind load requirements. The rolling door manufacturer can provide a guide data sheet for quantifying the loads imposed by the overhead coiling doors due to the design wind load.

The following conditions need to be considered:

The wall above the door opening must be designed to support the total hanging dead load. The face of wallmounted doors may extend above the opening for 12 to 30 in. (305-762 mm). The door guide wall angles must be mounted to the wall above the opening to support the door. When the door has a hood to cover the coiled door and counter-balance, some provision must be made to fasten the top of the hood and hood supports to the masonry wall. See also Fasteners for Concrete Masonry (ref.3).
Reinforcement in jambs is recommended to adequately distribute the forces imposed by the door.
Reinforcement locations should be planned such that the reinforcement does not interfere with expansion anchor placement.

ACCOMODATING MASONRY REINFORCEMENT AND DOOR FASTENERS

Rolling door contractors and installers sometimes encounter reinforcement in walls at locations where door jamb fasteners have been specified. Arbitrarily changing either the reinforcement location or the fastener location is not recommended, as either can negatively impact performance. Changing the door manufacturer’s recommended jamb fastener locations may reduce the structural performance of the rolling door or possibly void the fire rating.

The typical masonry jamb detail shown in Figure 3 indicates recommended vertical reinforcement locations for concrete masonry jambs to provide an area for the door fasteners. The detail shows a “reinforcement-free zone” to allow for fasteners of either face mounted or jamb-mounted rolling doors. The Door and Access Systems Manufacturers Association International (DASMA) recommends that vertical reinforcement should be within 2 in. (51 mm) of either corner of the wall at the jamb (ref. 4).

EXISTING CONSTRUCTION

Before installing fasteners in existing masonry construction, the following steps should be followed to locate the reinforcement, to avoid interference:

If structural drawings are available, the project engineer should review the drawings to determine whether or not the jamb reinforcement locations conflict with the specified door jamb fastener locations.
If the building’s structural plans are not available, either drill
representative “pilot holes” or use a device similar to an electronic stud locator to determine the steel reinforcement locations.

Once the steel reinforcement has been located, if it is concluded that the reinforcement will interfere with installing jamb fasteners, DASMA recommends that one of the following courses of action be taken:

Consider an alternate door jamb mounting or door size to assure that the reinforcement will not interfere with jamb fasteners.
If an alternate door jamb mounting or alternate door size cannot be accomplished, consult a structural engineer to determine a workable solution. One possible solution is to contact the door manufacturer to obtain an alternate conforming hole pattern for the mounting, which would not interfere with the existing reinforcement. Another solution may be to bolt a steel angle to the concrete masonry jambs, which allows the door guides to then be welded or bolted to the steel angle.

FIRE-RATED ROLLING DOOR CONNECTIONS

When installed in a fire-rated concrete masonry wall, rolling steel fire doors must meet the code-required fire rating corresponding to the fire rating of the surrounding wall. For fire testing, the doors are mounted on the jambs of a concrete masonry wall intended to replicate field construction. The fire door guides must remain securely fastened to the jambs and no “through gaps” may occur in the door assembly during the test. Figure 4 shows a representative jamb construction and guide attachment details for a four-hour fire rated assembly. Note that guide configurations and approved jamb construction will vary with individual fire door manufacturer’s listings. Consult with individual manufacturers for specific guide details and approved jamb constructions.

REFERENCES

Allowable Stress Design of Concrete Masonry Lintels
Based on 2012 IBC/2011 MSJC, TEK 17-01D, Concrete
Masonry & Hardscapes Association, 2011.
Precast Concrete Lintels for Concrete Masonry
Construction, TEK 17-02A, Concrete Masonry &
Hardscapes Association, 2000.
Fasteners for Concrete Masonry, TEK 12-05, Concrete
Masonry & Hardscapes Association, 2005.
Metal Coiling Type Door Jamb Construction: Steel
Reinforcement In Masonry Walls, TDS-259. Door and
Access Systems Manufacturers Association International,
2005.
Architects and Designers Should Understand Loads
Exerted By Overhead Coiling Doors, TDS-251. Door and
Access Systems Manufacturers Association International,
2005.
International Building Code 2003. International Code
Council, 2003.
International Building Code 2006. International Code
Council, 2006.
Common Jamb Construction for Rolling Steel Fire Doors:
Masonry Construction—Bolted and Welded Guides, TDS-
Door and Access Systems Manufacturers Association
International, 2005.
Steel Reinforcement for Concrete Masonry, TEK 12-04D,
Concrete Masonry & Hardscapes Association, 2006.

Modular Layout of Concrete Masonry

August 2018

INTRODUCTION

Although concrete masonry structures can be constructed using virtually any layout dimension, for maximum construction efficiency and economy, concrete masonry elements should be designed and constructed with modular coordination in mind. Modular coordination is the practice of laying out and dimensioning structures and elements to standard lengths and heights to accommodate modular-sized building materials. When modular coordination is not considered during the design phase, jobsite decisions must be made—often in haste and at a cost. This TEK provides recommendations for planning masonry construction to minimize cutting of masonry units or using nonstandard unit sizes.

When a project does require non-modular layout, further design and construction issues need to be addressed, including:

Placement of vertical reinforcement—In construction containing vertical reinforcing steel, the laying of units in other than running (half) bond or stack bond interrupts the vertical alignment of unit cells. As a result, reinforcement placement and adequate consolidation of grout becomes difficult, and partial grouting of walls is virtually impossible.

Interruption of bond pattern—In addition to the aesthetic impact a change in bond pattern can create, building codes often contain different design assumptions for masonry constructed in running bond versus other bond patterns. Walls incorporating more than a single bond pattern may present a unique design situation.

Locating control joints—In running bond, control joint construction can be accomplished using only full and half-size units. Similarly, stack bond construction only requires full-size units when control joints are properly spaced and detailed. However, with other bond patterns units may need to be cut if specially dimensioned units are not used or are not available.

MODULAR WALL ELEVATIONS

Standard concrete masonry modules are typically 8 in. (203 mm) vertically and horizontally, but may also include 4-in. (102 mm) modules for some applications. These modules provide overall design flexibility and coordination with other building products such as windows, doors, and other similar elements as shown in Figures 1 and 2.

MODULAR WALL OPENINGS

The rough opening dimensions illustrated in Figure 1 apply to the layout and construction of the masonry. To allow for fastening windows and doors to the masonry, however, the nominal heights and widths of these elements are slightly less.

For conventional construction methods, the widths of masonry openings for doors and windows should generally be 4 in. (102 mm) larger than the door or window width. This allows for 2 in. (51 mm) on each side of the opening for framing. The heights of masonry openings to accommodate windows are typically 8 in. (203 mm) greater than the window height. This opening size allows for 2 in. (51 mm) above and below for framing and 4 in. (102 mm) for installation of a sill at the bottom of the window. Masonry openings for doors are commonly either 2 or 4 in. (51 or 102 mm) greater than the door height, allowing for the door framing as well as the use of a standard sized door.

Thus, door and window widths of 28, 36, 44, and 52 in. (711, 914, 1,118 and 1,321 mm) (and so on in 8 in. (203 mm) increments) do not require the masonry to be cut. Modular window heights are any multiple of 8 in. (203 mm), with a masonry window opening 8 in. (203 mm) greater than the height of the window if a 4-in. (102 mm) sill will be used. Similarly, door heights 2 in. (51 mm) less than any even multiple of eight can be installed without the need for cutting the masonry. For the commonly available 84-in. (2,134 mm) high door, a 4-in. (102 mm) door buck can be placed at the top of the opening. In addition, precast lintels are available in some areas containing a 2 in. (51 mm) notch to accommodate 80-in. (2,032 mm) doors.

Hollow metal frames for doors should be ordered and delivered
for the masonry before the other door frames in the project are scheduled for delivery. For economy, the frames should be set before the walls are built. If the walls are built before the frame are set, additional costs are incurred to set special knock down door frames and attachments.

MODULAR WALL SECTIONS

For door and window openings, the module size for bond patterns and layout are nominal dimensions. Actual dimensions of concrete masonry units are typically 3/8 in. (9.5 mm) less than nominal dimensions, so that the 4 or 8-in. (102 or 203 mm) module is maintained with 3/8 in. (9.5 mm) mortar joints. Where mortar joint thicknesses differ from 3/8 in. (9.5 mm) (as may be specified for aesthetic purposes or with brick construction), special consideration is required to maintain modular design. Figure 3 illustrates this concept.

Typically, concrete masonry units have nominal face dimensions of (height by length) 8 by 16 in. (203 by 406 mm), and are available in nominal widths ranging from 4 in. to 16 in. (102 to 406 mm) in 2-in. (51 mm) increments. In addition to these standard sizes, other unit widths, heights and lengths may be available from concrete masonry producers. The designer should always check local availability of specialty units prior to design.

Incorporating brick into a project, either as a structural component or as a veneer, can present unique modular coordination considerations in addition to those present with single wythe construction. Brick most commonly have a nominal width of 4 in. (102 mm), length varying from 8 to 16 in. (203 to 406 mm) and height from 2 1/2 to 6 in. (64 to 152 mm). The specified dimensions of modular concrete and clay brick are typically 3 5/8 by 2 1/4 by 7 5/8 in. (92 by 57 by 194 mm), but may be available in a wide range of dimensions.

Because of their unique dimensions, concrete and clay brick are usually laid with bed joints that are slightly larger (or sometimes smaller depending upon the actual size of the brick) than the standard 3/8 in. (9.5 mm) mortar joint thickness. For example, common modular brick are laid with a 5/12 in. (11 mm) thick bed joint, thereby providing a constructed height of 2 2/3 in. (68 mm) for one brick and one mortar joint. (Note that a 5/12 in. (11 mm) thick bed joint is within allowable mortar joint tolerances (refs. 1, 2).) The result is that three courses of brick (including the mortar joints) equals one 8-in. (203 mm) high module, thereby maintaining modular coordination (see Figure 3).

MODULAR BUILDING LAYOUTS AND HORIZONTAL COURSING

In addition to wall elevations, sections and openings, the overall plan dimensions of a structure also need to be considered, especially when using units having nominal widths other than 8 in. (203 mm).

Ideally, the nominal plan dimensions of masonry structures should be evenly divisible by 8 in. (203 mm). This allows constructing each course of a wall using only full-length or half length units, which in turn reduces labor and material costs. In addition, maintaining an 8-in. (203 mm) module over the length of a wall facilitates the turning of corners, whereby half of the units from one wall interlock with half of the units from the intersecting wall. As an alternative to cutting units or changing building dimensions, corner block can be used if available. These units are specifically manufactured to turn corners without interrupting bond patterns. Concrete Masonry Corner Details,TEK 05-09A (ref. 4) contains a variety of alternatives for efficiently constructing corners.

METRIC COORDINATION

One additional consideration for some projects is the use of standard sized (inch-pound) masonry units in a metric project. Similar to inch pound units, masonry units produced to metric dimensions are 10 mm (13/32 in.) less than the nominal dimensions to provide for the mortar joints. Thus, the nominal metric equivalent of an 8 by 8 by 16 in. unit is 200 by 200 by 400 mm (190 by 190 by 390 mm net unit dimensions). Since inch-pound dimensioned concrete masonry units are approximately 2% larger than hard metric units, complications can arise if they are incorporated into a structure designed on a 100 mm (3.9 in.) metric module, or vice versa.

REFERENCES

International Building Code. International Code Council,
2003 and 2006.
Specification for Masonry Structures, ACI 530.1-05/ASCE
6-05/TMS 602-05. Reported by the Masonry Standards
Joint Committee, 2005.
Building Code Requirements for Masonry Structures, ACI
530-05/ASCE 5-05/TMS 402-05. Reported by the Masonry
Standards Joint Committee, 2005.
Concrete Masonry Corner Details, TEK 05-09A, Concrete
Masonry & Hardscapes Association, 2004.

Residential Details for High Wind Areas

August 2018

INTRODUCTION

High winds subject buildings to large horizontal forces as well as to significant uplift. Reinforced concrete masonry is well suited to resist the large uplift and overturning forces due to its relatively large mass.

High wind provisions generally apply to areas where the design wind speed is over 100 mph (161 km/hr) and over three second gust as defined by ASCE 7 (ref. 10). The enclosed details represent prescriptive minimum requirements for concrete masonry buildings, based on Standard for Hurricane Resistant Residential Construction (ref. 3).

CONTINUOUS LOAD PATH

Connections between individual building elements—roof, walls, floors and foundation—are critical to maintaining structural continuity during a high wind event. The critical damage to buildings in such events typically occurs due to uplift on the roof, resulting in the loss of crucial diaphragm support at the top of the wall. A primary goal for buildings subjected to high winds is to maintain a continuous load path from the roof to the foundation. This allows wind uplift forces on the roof to be safely distributed through the walls to the foundation. If one part of the load path fails or is discontinuous, building failure may occur.

Proper detailing and installation of mechanical connectors is necessary for maintaining continuous load paths. Note that in order for connectors to provide their rated load capacity, they must be installed according to the manufacturer’s or building code specifications. In coastal areas, corrosion protection is especially important due to the corrosive environment. Note that water penetration details are not specifically highlighted in the following details. The reader is referred to references 7 through 9 for more information on preventing water penetration in concrete masonry walls. In addition to a continuously reinforced bond beam at the top of the wall around the entire perimeter of the building, vertical reinforcement must be placed throughout a wall to resist the high uplift loads and provide continuity, including: at corners and wall intersections; on each side of openings wider than 6 ft (1,829 mm); at the ends of shear segments; and where girders or girder trusses bear on the concrete masonry wall (refs. 3, 4). Each of the exterior walls on all four sides of the building and all interior walls designed as shear walls must have at least one 2 ft (610 mm) minimum section of wall identified as a shear segment to resist the high lateral loads. Longer shear segments are more effective and are recommended where possible or required by design. See Figure 1 for a summary of reinforcement requirements (ref. 3).

Reinforcement must be properly spliced to provide load path continuity. Using allowable stress design, a splice length of 40 bar diameters is required by Building Code Requirements for Masonry Structures (ref. 1) for Grade 40 reinforcement and 48 bar diameters for Grade 60 reinforcement. If the wall was designed assuming Grade 40 and Grade 60 was used for construction, however, the 40 bar diameter lap splice may still be used. See Steel Reinforcement for Concrete Masonry, TEK 12-04D (ref. 5) for standard hook requirements.

DETAILS

Exterior Loadbearing Wall

Figure 2 shows a typical loadbearing wall with a floating floor slab. Vertical reinforcement should be placed in the center of the concrete masonry cores to adequately resist both positive and negative wind pressures. Bond beam depth and minimum horizontal reinforcement varies with design wind velocity, ceiling height, roof truss span and spacing of vertical wall reinforcement. Since wind suction forces on the leeward side of a building can be essentially as high as the pressure forces on the windward side, limitations are placed on the height above grade. However, if the slab is laterally supported and tied to the concrete masonry foundation wall as shown in Figure 3, the foundation wall may be extended to 8 ft (2,440 mm) above grade (ref. 3).

Roof Truss Anchor

Figure 4 shows a typical roof truss anchor cast into the bond beam of a concrete masonry bearing wall. The required anchor load capacity depends on the design wind speed as well as the roof truss span. In addition to being rated for uplift, the anchor must be rated for horizontal forces parallel to the wall (in-plane) and perpendicular to the wall (out-of-plane).

Often, the direct embedded roof truss anchor method of connecting the roof to walls is preferred over the bolted top plate and hurricane clip method, as it generally has greater capacity and fewer connections. Additionally, the nail area available for the hurricane clip is limited by the thickness of the top plate.

Bolted Top Plate

As an alternate to the roof truss anchor, a bolted top plate may be used for the roof to wall connection (see Figure 5); however, anchor bolt spacing must be reduced (24 in. (610 mm) maximum) because the top plate is loaded in its weak direction. The detail illustrates several different connector types that are commonly used to connect the truss to the top plate.

Gable End Walls

Because of their exposure, gable end walls are more prone to damage than are hipped roofs unless the joint at the top of the end wall and the bottom of the gable (see Figure 6b) is laterally supported for both inward and outward forces. Figure 6a shows a continuous masonry gable end wall using either a raked concrete bond beam or a cut masonry bond beam along the top of full height reinforced concrete masonry gable end walls.

As an alternative, a braced gable end wall can be constructed as shown in Figure 6b by stopping the masonry of the gable end at the eave height and then using conventional wood framing to the roof diaphragm. However, unless the end wall is properly braced to provide the necessary lateral support as shown in Figure 6b, this results in a weak point at the juncture of the two materials with little capacity to resist the high lateral loads produced by high winds. The number and spacing of braces depends on design wind speed, roof slope and roof span (ref. 2, 3, 6).

Gable End Wall Overhangs

Figure 7a shows a continuously reinforced castin-place concrete rake beam along the top of the gable end wall. The beam is formed over uncut block in courses successively shortened to match the slope of the roof. A minimum of 4 in. (102 mm) is needed from the highest projected corner of block to the top of the beam. Reinforcement that is continuous with the bond beam reinforcement in the side walls is placed in the top of the beam. In this detail, an outlooker type overhang is shown where the rake beam is constructed 3½ in. (89 mm) lower than the trusses so that a pressure treated 2 x 4 (38 x 89 mm) can pass over it. A ladder type overhang detail also can be used with the concrete rake beam where the beam is constructed to the same height as the trusses similar to that shown for the cut masonry rake beam in Figure 7b.

Figure 7b shows a continuously reinforced cut masonry rake beam along the top of the gable end wall. Masonry units are cut to conform to the roof slope at the same height as the roof trusses. A 2 ¾ in. (70 mm) deep notch is cut into the tops of the concrete masonry webs to allow placement of reinforcement that is continuous with the bond beam reinforcement in the side walls. A minimum of height of 4 in. (102 mm) is needed for the cut masonry bond beam. In this figure, a ladder type overhang is shown. However, an outlooker type overhang detail can be used similar to that shown for the cast-in-place concrete rake beam in Figure 7a.

REFERENCES

Building Code Requirements for Masonry Structures, ACI
530-02/ASCE 5-02/TMS 402-02. Reported by the Masonry
Standards Joint Committee, 2002.
The Guide to Concrete Masonry Residential Construction
in High Wind Areas. Florida Concrete & Products
Association, Inc., 1997.
Standard for Hurricane Resistant Residential Construction,
SSTD 10-99. Southern Building Code Congress
International, Inc., 1999.
2000 International Building Code. International Code
Council, 2000.
Steel Reinforcement for Concrete Masonry, TEK 12-04D.
Concrete Masonry & Hardscapes Association, 2002.
Annotated Design and Construction Details for Concrete
Masonry, CMU-MAN-001-23. Concrete Masonry &
Hardscapes Association, 2003.
Design for Dry Single-Wythe Concrete Masonry
Walls, TEK 19-02B. Concrete Masonry & Hardscapes
Association, 2012.
Flashing Strategies for Concrete Masonry Walls, TEK 19-
04A. Concrete Masonry & Hardscapes Association, 2003.
Flashing Details for Concrete Masonry Walls, TEK 19-05A.
Concrete Masonry & Hardscapes Association, 2008.
Minimum Design Loads for Buildings and Other
Structures, ASCE 7-02. American Society of Civil
Engineers, 2002.

Concrete Masonry Radial Wall Details

August 2018

INTRODUCTION

Concrete masonry units are uniquely suited to distinctive aesthetically-pleasing architectural features. The almost limitless variety of sizes, shapes, textures, colors and surface treatments has made concrete masonry one of the most versatile and sought after building materials today. In addition, the relatively small unit size lends itself to unique applications, such as radial walls.

The use of concrete masonry in the design and construction of radial walls presents a unique challenge to the design professional. Where curved walls once were formed from handhewn stone carved to fit a predetermined radius, radial walls of concrete masonry are usually formed from rectangular units of fixed shape and dimension. The end result is a series of short chords rather than a smooth arc. The greater the radius, the more closely the surface formed by the chords approaches that of a true arc.

The curvature of these walls depends on variables such as the length and thickness of the concrete masonry unit, the width of the vertical head joints at the interior and exterior wall faces and whether the units will be used as is, beveled at the ends, or cut to conform to the desired radius.

The bond pattern also impacts the overall appearance of a curved wall section. Curved walls laid up in stack bond (i.e., with vertical head joints aligned) possess the geometric properties of a regular polygon (Figure 1). Walls laid up in running bond (with offset head joints), on the other hand, exhibit a similar geometric configuration at the individual courses with the exception that the ends of units in alternating courses project out beyond the faces of the units immediately above and below (Figure 2). These projections create a basketweave effect which may or may not contribute to the aesthetic value of the wall.

This TEK contains information to help the designer determine the best way to construct a curved concrete masonry wall, based on factors such as: desired radius, unit size, mortar joint size, projection size for running bond and the effect of cutting the units. Note that these recommendations apply to the physical limitations and geometry of constructing radial walls.

The designer must ensure any radial wall design complies with all applicable building code requirements.

Although this TEK focuses on the construction of radial walls using conventional concrete masonry units, note that beveled units or other special shapes may be available to facilitate masonry radial wall construction as well.

MINIMUM WALL RADIUS

The minimum radii for curved or circular walls constructed of concrete masonry units is determined through iterations of the plane rectilinear geometric formulae for regular polygons. These equations are:

β = 2 (Tan -1 [(S1 S2)/2t]) Eqn. 1
n = θ/β Eqn. 2
r = Sl /(2 Tan β/2) Eqn. 3

Example

Nominal 8 x 8 x 16-in. (203 x 203 x 406-mm) concrete masonry units are being considered for use in a circular wall. Actual unit dimensions are 155/8 in. (397 mm) length and 75/8 in. (194 mm) width, and the exterior mortar joint is to be 3/8 in. (9.5 mm). The width of the interior mortar joint is to be 1/8 in. (3.2 mm). What is the smallest radius the circular wall can be constructed to without cutting the units?

Although the equations remain the same, there are several practical methods to vary the minimum radii of curved or circular concrete masonry walls:

Reduce the length of the units. Changing from a 16-in. (406-mm) long unit to an 8-in. (203-mm) long unit will reduce the minimum radius by half.
Vary the mortar joint width. An increase in the mortar joint width at the exterior wall face, with or without a decrease in mortar joint width at the interior wall face, reduces the radius as well as the number of units required. Although it is generally recommended that the width of the mortar joint at the interior face not be less than 1/8 in. (3.2 mm), this may be acceptable under certain circumstances.
Shorten the length of the units at the interior face. Cutting the units is practical if stretcher units with flanged ends are used. Cutting is less practical for double corner units with plain ends (see Figure 3).

Projections

For a curved masonry wall laid in running bond, it may be desirable to limit the projections of the unit corners beyond the unit faces in the courses above and below for reasons of aesthetics. Generally, projections of approximately 1/8 in. (3.2 mm) for nominal 8 in. (203 mm) long units and 1/4 in. (6.4 mm) for nominal 16 in. (406 mm) long units are considered acceptable. If the wall surface is to be stuccoed or otherwise covered, projections of 1/2 in. to 3/4 in. (13 to 19 mm) may be acceptable. Minimizing projections to less than 1/8 in. (3.2 mm) is usually not practical because of construction tolerances.

The projection of the unit corners for the previous example is found by using Equation 4.

DESIGN TABLES

Tables 1 through 6 list the minimum radii, number of units and length of projection for circular concrete masonry walls, based on using either a 3/8 in. (9.5 mm) or 1/2 in. (13 mm) wide exterior head joint. Using the larger exterior head joint width allows for smaller radii. All tables assume that the interior head joint width is 1/8 in. (3.2 mm). Tables 1 and 2 present this data for 8 in. (203 mm) and 16 in. (406 mm) long units which have not been cut (as shown in Figure 3), respectively.

Similar data for units cut as shown in Figure 3 are listed in Tables 3 through 6.

Table 7 should be consulted when the size of the projection is a prime consideration. These tables list the minimum radii and number of units required to limit projections to 1/8 in. (3.2 mm) and 1/4 in. (6.4 mm) for nominal 8-in. (203 mm) and 16 in. (406 mm) long units.

Construction and unit manufacturing tolerances are such that the radii provided in the Tables may vary by + 1 in. (25 mm).

NOTATIONS

n = Number of concrete masonry units to complete the arc for the central angle θ. The number of units for the arc should be a whole number.
p = for masonry laid in running bond, projection of masonry unit corners beyond the faces of the units in the courses above and below (see also Figure 2), in. (mm)
r = radius to the exterior face of the wall, measured to the midpoint of a unit, in. (mm)
S1 = length of each side of the polygon forming the exterior face of the wall (length of the unit plus the width of one exterior mortar joint), in. (mm)
S2 = length of each side of the polygon forming the interior face of the wall (length of the unit plus the width of one interior mortar joint), in. (mm)
t = actual unit thickness, in. (mm)
β = the angle subtended by one side of a polygon (length of one concrete masonry unit), see AOB in Figure 1, degrees
θ = central angle subtended for the complete arc of the curved wall (equals 360o for a complete circle), degrees

Concrete Masonry Corner Details

August 2018

INTRODUCTION

A building’s corners are typically constructed first, then the remaining wall section is filled in. Because they guide the construction of the rest of the wall, building the corners requires special care. It is essential that the corner be built as shown on the foundation or floor plan to maintain modular dimensions.

For maximum construction efficiency and economy, concrete masonry elements should be designed and constructed with modular coordination in mind. Corners, however, present unique situations, because the actual widths of standard units are 3 5/8, 5 5/8, 7 5/8, 9 5/8 and 11 5/8 in. (92, 143, 194, 244 and 295 mm). In order to maintain an 8-in. (203-mm) module, special corner details have been developed to accommodate most typical situations.

Figures 2 through 6 show how corners can be constructed to minimize cutting of units while maintaining modularity of the construction. Vertical steel, while not always required, is often used at corner intersections.

UNITS

Unlike stretcher units, units used in corner construction have square ends (see Figure 1). In addition, all-purpose or kerf units are available, with two closely spaced webs in the center that allow the unit to be easily split on the jobsite, facilitating corner construction. Other special units may also be available, such as bevelled-end units, forming a 45° angle with the face of the unit, which are used to form walls intersecting at 135° angles. Units in adjacent courses overlap to form a running bond pattern at the corner. Architectural units, such as those with split or scored faces, are often available with the architectural finish on two sides to accommodate corner construction.

Local manufacturers should be contacted for information on unit availability.

CODE PROVISIONS FOR INTERSECTING WALLS

Building Code Requirements for Masonry Structures (ref. 3) stipulates three options to transfer stresses from one wall to another at wall intersections, each requiring the masonry to be laid in running bond. These three options are via: running bond; steel connectors; and bond beams. Corner construction lends itself to providing shear transfer by relying on running bond.

Running bond (defined as the placement of masonry units such that head joints in successive courses are horizontally offset at least one quarter the unit length) ensures there is sufficient unit interlock at the corner to transfer shear. When any of these conditions are not met, the transfer of shear forces between walls is required to be prevented.

REFERENCES

Annotated Design and Construction Details for Concrete Masonry, CMU-MAN-001-03, Concrete Masonry & Hardscapes Association, 2003.
Reinforced Concrete Masonry Inspector’s Handbook, 4th edition. Masonry Institute of America, 2002.
Building Code Requirements for Masonry Structures, ACI 530 02/ASCE 5-02/TMS 402-02. Reported by the Masonry Standards Joint Committee, 2002.

Detailing Concrete Masonry Fire Walls

August 2018

INTRODUCTION

Concrete masonry, due to its inherent durability, reliability and superior fire resistance characteristics, is well suited to a range of fire protection applications.

The International Building Code (IBC) (ref. 1) defines three wall types for fire protection— fire wall, fire barrier and fire partition—depending on the level of protection provided for the type of occupancy and intended use. Of the three defined fire-rated assemblies, a fire wall is generally considered to provide the highest level of robustness and fire safety. As such, it is intended to provide complete separation and must be structurally stable under fire conditions.

Generally, fire barriers and fire partitions are required to provide the minimum protection necessary to assure that building occupants can evacuate a structure without suffering personal injury or loss of life. In addition to these requirements, fire walls reduce the likelihood of fire spread into the adjoining space, thus minimizing major property loss. Potentially significant architectural and economic advantages can be gained from using fire walls since each portion of a building separated by fire walls is considered a separate building for code compliance purposes.

Designing and detailing fire walls is a complex task with many facets, including structural criteria, fire resistance, vertical and horizontal continuity, and criteria for protecting openings and joints. It is beyond the scope of this TEK to include every code provision and exception for fire wall design for all project conditions. While much of the information in this TEK is applicable to both the IBC and the NFPA 5000 (ref. 2) building codes, the provisions are based on the 2003 IBC, so certain provisions may be different from NFPA 5000 requirements. Hence, the information may or may not conform to local building code requirements and should be carefully reviewed to ensure compliance. In addition, the details shown here are not the only ones that will comply, but are included as examples. Project specific needs will dictate the final detailing decisions.

FIRE WALLS

By Code (ref. 1), fire walls are required to have the minimum fire-resistance rating acceptable for the particular occupancy or use group which they separate and must also have protected openings and penetrations. A fire wall must have both vertical and horizontal continuity to ensure that the fire does not travel over, under or around the fire wall. In addition, the wall must have sufficient structural stability under fire conditions to remain standing for the duration of time indicated by the fire-resistance rating even with the collapse of construction on either side of the fire wall.

Fire-Resistance Rating

Because fire walls provide a complete separation between adjoining spaces, each portion of the structure separated by fire walls is considered to be a separate building. Fire walls in all but Type V construction must be constructed of approved noncombustible materials. Table 1 shows minimum required fire-resistance ratings. Information on determining the fire-resistance ratings of concrete masonry assemblies is contained in Fire Resistance Rating of Concrete Masonry Assemblies, TEK 07-01D and Standard Method for Determining Fire Resistance of Concrete and Masonry Construction Assemblies (refs. 3, 4).

Protected Openings and Penetrations

The IBC states that fire walls must have closures such as fire doors or shutters which automatically activate to secure the opening in the event of a fire. Further, openings in fire walls are restricted to a maximum size of 120 ft2 (11.2 m2). An exception permits larger openings provided both buildings separated by the fire wall are equipped throughout with automatic sprinkler systems. In all cases, the aggregate width of all openings at any floor level is limited to 25 percent of the wall length.

Through-penetrations in fire walls must utilize either fire-resistance rated assemblies or a firestop system which is tested in accordance with either ASTM E 814 (ref. 5) or UL 1479 (ref. 6). The annular space between steel, iron or copper pipes or steel conduits and surrounding concrete masonry fire walls may be filled with concrete, grout or mortar for the thickness required to provide a fire-resistance rating equivalent to the fire-resistance rating of the wall penetrated. In addition, the penetrating item is limited to a 6-in. (152-mm) nominal diameter and the opening is limited to 144 in.2 (92,900 mm2). Openings for steel electrical outlet boxes are permitted provided they meet the Code specified requirements.

Combustible members, such as wood, are permitted to be framed into concrete masonry fire walls provided that, when framed on both sides of the wall, there is at least 4 in. (102 mm) between the embedded ends of the wood framing. The full thickness of the fire wall 4 in. (102mm) above and below, as well as in between, the combustible member must be filled with noncombustible materials approved for fireblocking.

Voids created at the junction of walls and floor/ceiling/ roof assemblies must be protected from fire passage by using fireresistant joint systems tested in accordance with ASTM E 1966 or UL 2079 (refs. 7, 8). Control joints in fire walls must have fire-resistance ratings equal to or exceeding the required rating of the wall. Recommendations for locating and spacing control joints in concrete masonry walls also apply to concrete masonry fire walls. Crack Control Strategies for Concrete Masonry Construction, CMU-TEC 009-23 (ref. 9) includes control joint spacing criteria and illustrates control joint details for various fire-resistance ratings.

Vertical and Horizontal Continuity

The IBC mandates vertical continuity of a fire wall by requiring that the wall extend continuously from the foundation to a termination point at least 30 in. (762 mm) above both adjacent roofs. Exceptions permitting the fire wall termination at the underside of the roof deck or slab are listed in the Code. These exceptions require the use of Class B roof coverings (minimum), no openings within 4 ft (1.22 m) of the fire wall and other criteria for roof assembly protection. Buildings located over parking garages and stepped buildings are subject to additional requirements and permitted exceptions.

Horizontal continuity limits the spread of fire around the ends of a fire wall. The IBC requires that fire walls be continuous from exterior wall to exterior wall and that they extend at least 18 in. (457 mm) beyond the exterior surface of exterior walls. As with the vertical continuity requirements, there are criteria for terminating the fire wall at the interior surface of an exterior wall based on the types and fire resistance ratings of the intersecting wall constructions and on the presence of an automatic sprinkler system installed per Code requirements.

Structural Stability Under Fire Conditions

While concrete masonry remains structurally stable during the extreme temperatures experienced under fire conditions, steel framing undergoes a reduction in strength as the surrounding temperature and duration of exposure are increased. This decreased structural capacity is evidenced by a dramatic increase in the deflection and twisting of steel members. Wood framing may burn, collapse, shrink and/or deform under fire exposure and it too loses its load-carrying capability. For these reasons, concrete masonry firewalls should be designed and detailed to withstand any loading imposed by fire-compromised framing systems or detailed so that those loads are not imparted to the fire wall during a fire. This is perhaps the most difficult detailing provision in fire wall design.

DETAILING CONSIDERATIONS FOR STRUCTURAL STABILITY

Because most fire wall criteria relating to fire-resistance rating, protected openings and penetrations, and vertical and horizontal continuity are prescriptive, the designer’s primary challenge when engineering and detailing a concrete masonry fire wall relates to maintaining the structural stability of the wall under fire conditions.

There are various methods of designing, detailing and constructing fire walls for structural stability during a fire. Among the systems recommended for use as fire walls are: (a) cantilevered or freestanding walls, (b) laterally supported and tied walls, and (c) double wall construction.

Cantilevered or Freestanding Walls

Cantilevered walls (Figure 1) do not depend on the roof framing for structural support. The wall is cantilevered from the foundation by grouting and reinforcing, or by prestressing. Freestanding walls may also be designed to span horizontally between pilasters or masonry columns integral to the wall.

It can be difficult to design a cantilevered single wythe loadbearing fire wall. Thermal stresses may cause deformation in steel or wood joists or framing systems which can eccentrically load the top of the fire wall. Designing the wall to remain stable under that loading condition may be difficult especially for tall or slender walls. For this reason, cantilevered single wythe fire walls are often designed as nonbearing walls with the primary roof framing system running parallel to the fire wall. Column lines on either side of the wall support the roof framing. Details for cantilevered/freestanding fire walls are similar to those for laterally supported walls (shown in Figures 2, 3 and 4) with the exception that cantilevered walls do not include through-wall ties or break-away connectors.

Laterally Supported or Tied Walls

Laterally supported or tied walls rely on the building frame for lateral stability. The fire wall is laterally supported on each side by the framing system. As such, forces due to the collapse of the structure on one side of the fire wall are resisted by the structural framework on the other side of the wall. Adequate clearance, as listed in Table 2, between the framing and the concrete masonry fire wall is necessary to allow framing expansion or deformation without exerting undue pressure on the wall.

Laterally supported fire walls may utilize break-away connectors
manufactured with metals having melting points lower than structural steel (generally about 800° F (427° C)), so that, in the event of fire, the connectors on the fire side of the wall will give way before those on the non-fire side. In Figures 2 and 3, the structural diaphragm on the side of the wall opposite the fire provides the stability. The connections between the roof and wall must be designed to resist these forces. If the diaphragms occur at different elevations, the wall must be designed to withstand the anticipated flexural forces that will be generated as well. Figure 4 shows a laterally supported fire wall with combustible framing supported by metal joist hangers. Joist hanger manufacturers may have alternate details as well. Note that there may be code limitations on the use of combustible framing.

Figure 5 shows design and detailing options for tied fire walls. Tied fire walls are a type of laterally supported fire wall where the roof structure is not supported by the fire wall, but rather by the roof structure on the other side of the fire wall, thus the two roof structures are tied together across the fire wall. Figure 5a illustrates one choice for a “double column” detail which uses a through-wall tie to connect the primary steel on both sides of the fire wall. In this detail, the primary roof framing steel is parallel to the fire wall and supported on fireproofed columns. One column is used on each side of the fire wall to support the roof system for that building. Both steel columns and primary support beams/trusses should be aligned vertically and horizontally with the columns and beams/trusses on the opposite side of the wall and should be fireproofed. If the primary steel is not parallel to the fire wall Figure 5b shows a through-wall tie which can be used.

As an alternative to using two steel columns, Figure 5c shows one steel support column encased entirely within the concrete masonry fire wall. Fire protection requirements for steel columns are included in Steel Column Fire Protection, TEK 07-06A (ref. 11). This system creates a single column line tied at the top of the wall to horizontal roof framing. Detailing the connection of the steel beams to the concrete masonry fire wall varies based on the framing layout, but the wall must be supported at the top and the connection must be fire protected.

Double Wall Fire Wall

Double wall construction (Figure 6) is generally easy to design and detail for loadbearing conditions, especially for taller walls. It utilizes two independent concrete masonry walls side by side, each meeting the required fire-resistance rating. In the event one wall is pulled down due to fire, the other wall remains intact, preventing fire spread. Floor and roof connections to each fire wall are the same as for conventional concrete masonry construction. These walls are often cantilevered or freestanding but may be tied or laterally supported as well if so detailed and designed. This system is also easy to use when a building addition requires a fire wall between the existing structure and the new construction.

REFERENCES

International Building Code 2003. International Code Council, 2003.
Building Construction and Safety Code – 2003 Edition, NFPA 5000. National Fire Protection Association, 2003.
Fire Resistance Rating of Concrete Masonry Assemblies, CMHA TEK 07-01D. Concrete Masonry & Hardscapes Association, 2018.
Standard Method for Determining Fire Resistance of Concrete and Masonry Construction Assemblies, ACI 216.1-97/ TMS 0216-97.
American Concrete Institute and The Masonry Society, 1997.
Standard Test Method for Fire Tests of Through Penetration Fire Stops, ASTM E 814-02. ASTM International, 2002.
Fire Tests of Through-Penetration Firestops, UL
Underwriters Laboratory, 2003.
Standard Test Method for Fire-Resistive Joint Systems, ASTM E 1966-01. ASTM International, 2001.
Tests for Fire Resistance of Building Joint Systems, UL
Underwriters Laboratory, 2004
Crack Control Strategies for Concrete Masonry Construction, CMU-TEC-009-23. Concrete Masonry & Hardscapes Association, 2023.
Criteria for Maximum Foreseeable Loss Fire Walls and Space Separation, Property Loss Prevention Data Sheets 1-22. Factory Mutual Insurance Company, 2000.
Steel Column Fire Protection, CMHA TEK 07-06A. Concrete Masonry & Hardscapes Association, 2003.

Concrete Masonry Curtain and Panel Wall Details

August 2018

INTRODUCTION

Steel and concrete structural frames often rely on nonloadbearing masonry curtain or panel walls to enclose the structure. Panel and curtain walls are distinguished by the fact that a panel wall is wholly supported at each story, while a curtain wall is supported only at its base, or at prescribed interims. Both are designed to resist lateral wind or seismic loads and transfer these lateral loads to the structural frame. They typically do not carry any vertical loads other than their own weight. Curtain and panel walls differ from anchored masonry veneer in that veneer is continuously supported by a backup material.

Curtain and panel walls must be isolated from the frame to prevent the unintentional transfer of structural loads and to allow differential movement between the frame and the masonry. Anchorage between the concrete masonry and structural frame must also account for different construction tolerances for each building material.

Concrete masonry curtain and panel walls should incorporate flashing and weep holes as for other concrete masonry construction. Design for Dry Single-Wythe Concrete Masonry Walls, Flashing Strategies for Concrete Masonry Walls and Flashing Details for Concrete Masonry Walls (refs. 3, 4 & 5) provide detailed information.

PANELWALLS

Concrete masonry panel walls are supported at each building story by means of concrete beams, concrete slabs or steel members.

Supports must take into account the strains and deformations in both the concrete masonry panel wall and the structural frame. Steel supports, often in the form of shelf angles, can be attached to the frame either by welding or bolting, although bolting is often preferred because slotted bolt holes permit adjustments to be made for proper alignment with the masonry. In addition, bolted connections are inherently more flexible than welded connections, allowing a limited amount of movement between the masonry and the frame. Care should be taken, however, to ensure proper bolt tension to avoid slipping once positioned.

For high-rise construction, allowance should be made for differential movement between the shelf angle and the panel wall below due to creep of the frame and/or masonry thermal expansion. This is accomplished by leaving an open (mortarless) space between the bottom of the shelf angle and the masonry below or by filling the space with compressible material. The joint is then sealed with caulking to prevent moisture intrusion. The horizontal movement joint below the shelf angle also helps prevent vertical loads from inadvertently being transferred to the concrete masonry panel wall below the shelf angle.

Flashing and weep holes should be installed immediately above all shelf angles to drain moisture. In multi-wythe panel walls, wall ties between the exterior and interior masonry wythes should be located as close to the shelf angle as possible. Figures 1 and 2 show steel shelf angle attachments to concrete and steel, respectively.

CURTAIN WALLS

Concrete masonry curtain walls can be designed to span either vertically or horizontally between supports. They can also incorporate reinforcement to increase lateral load resistance and the required distance between lateral supports.

Anchors used to provide lateral support must be sufficiently stiff in the out-of-plane direction to transfer lateral loads to the frame and be flexible enough in-plane to allow differential movement between the curtain wall and the frame. In addition, Building Code Requirements for Masonry Structures (ref. 1) includes specific corrosion-resistance requirements to ensure long-term integrity of the anchors, consisting of AISI Type 304 stainless steel or galvanized or epoxy coatings.

Anchors are required to be embedded at least 11/2 in. (38.1mm) into the mortar bed when solid masonry units are used (ref.1) to prevent failure due to mortar pullout or pushout. Because of the magnitude of anchor loads, it is also recommended that they be embedded in filled cores when using hollow units. As an alternative to completely filling the masonry core, this can be accomplished by placing a screen under the anchor and building up 1 to 2 in. (25 to 51 mm) of mortar into the core of the block above the anchor.

For both concrete and steel frames, the space between the column and the masonry should be kept clear of mortar to avoid rigidly bonding the two elements together.

Figures 3 through 5 show curtain wall attachments to concrete and steel frames.

CONSTRUCTION TOLERANCES

Tolerances are allowable variations, either in individual component dimensions or in building elements such as walls or roofs. Construction tolerances recognize that building elements cannot always be placed exactly as specified, but establish limits on how far they can vary to help ensure the finished building will function as designed.

When using masonry with another structural system, such as steel or concrete, construction tolerances for each material need to be accommodated, since construction tolerances vary for different building materials.

In general, masonry must be constructed to tighter tolerances than those applicable to steel or concrete frames (refs. 2, 7). Particularly in high-rise buildings, tolerances can potentially affect anchor embedment, flashing details and available support at the shelf angle. To help accommodate these variations in the field, the following recommendations should be considered.

Use bolted connections with slotted holes for steel shelf angles to allow the shelf angle location to be adjusted to meet field conditions. Steel shims can be used to make horizontal adjustments to the shelf angle location. Figure 6 shows an example of a shelf angle connection which is adjustable in all three directions. For connections like this, the bottom flange needs to be evaluated for adequate load carrying capability as does the beam for torsion.
When shimming shelf angles, use shims that are the full height of the vertical leg of the shelf angle for stability. Shimming is limited to a maximum of 1 in. (25 mm) (ref. 7).
Provide a variety of anchor lengths to allow proper embedment over the range of construction tolerances.
Use two-piece flashing to accommodate varying cavity widths.
Cut masonry units only with the permission of the architect or engineer (this may be proposed when the frame cants towards the masonry, making the cavity between the two materials too small).
Include instructions for handling building element misalignment in the construction documents.

REFERENCES

Building Code Requirements for Masonry Structures, ACI
530-99/ASCE 5-99/TMS 402-99. Reported by the Masonry
Standards Joint Committee, 1999.
Specification for Masonry Structures, ACI 530.1-99/ ASCE
6-99/TMS 602-99. Reported by the Masonry Standards
Joint Committee, 1999.
Design for Dry Single-Wythe Concrete Masonry Walls,
19-02B, Concrete Masonry and Hardscapes Association,
2012.
Flashing Strategies for Concrete Masonry Walls , TEK
19-04A, Concrete Masonry and Hardscapes Association,
2003.
Flashing Details for Concrete Masonry Walls, TEK 19-05A,
Concrete Masonry and Hardscapes Association, 2008.
Laska, W. Masonry and Steel Detailing Handbook. The
Aberdeen Group, 1993.
Code of Standard Practice for Steel Buildings and Bridges,
American Institute of Steel Construction, Inc., 2000.

Integrating Concrete Masonry Walls With Metal Building Systems

August 2018

INTRODUCTION

Metal buildings are used extensively for warehouses and other structures requiring large, open floor spaces. Part of their design flexibility comes from the ability to clad metal buildings with a variety of materials to provide different appearances or functions to the buildings. Concrete masonry walls are popular enclosure systems for metal buildings because of masonry’s aesthetic appeal, impact resistance, strength, and fire resistance. The durability of concrete masonry resists incidental impacts from hand carts and forklifts, provides maximum protection in disasters such as earthquakes and hurricanes, as well as superior security, fire resistance, and noise control.

Concrete masonry walls used for metal buildings can include: exterior full-height walls, either with or without a parapet; exterior partial-height or wainscot walls; and interior loadbearing walls or nonloadbearing walls or partitions. Architectural concrete masonry units, such as colored, split faced, burnished, or scored units, can be used to provide an almost limitless array of textures and patterns to the walls. These units can be used for the entire facade or for banding courses to achieve specific patterns or highlight certain design aspects of the building.

A more detailed discussion of the system, along with structural design and construction considerations, is included in Concrete Masonry Walls for Metal Building Systems (ref. 1). The manual is intended to
bridge the gap between the engineer who designs the metal building system and the engineer who designs the concrete masonry walls to unify their respective knowledge.

DETAILS

A typical metal building clad with masonry is shown in Figure 1. Figures 2 – 6 show some typical details used for exterior concrete masonry cladding on a metal building. These details may need to be modified to meet individual design conditions.

Because of the inherent material differences between steel and masonry, careful consideration must be given to accommodating differential movement between the two materials and their assemblies. In Serviceability Design Considerations for Low-Rise Buildings (ref. 2), a lateral drift limit of H/100 for a ten year recurrence wind loading based on main wind force resisting system loads is suggested for low rise buildings with exterior masonry walls reinforced vertically. See Table 12.12.1 of ASCE 7 (ref. 3) for the allowable story drift for seismic loading. Most reinforced masonry walls for metal buildings are designed to span vertically, supported by a steel spandrel at the top and by the foundation at the bottom.

WALL BASE

Because of stiffness and deformation incompatibilities between flexible steel and rigid masonry assemblies, and consequently to control the location of cracking in the masonry walls that may result from relatively larger steel frame deflections at the top of the structure, a “hinge” can be incorporated at the base of the masonry assembly to allow out-of-plane rotation.

Two such hinge connections are shown in Figures 2 and 3. The construction shown in Figure 2 uses through-wall flashing to break the bond at the base of the wall providing a simply supported condition allowing shear transfer but no moment for out-of-plane loading. In many cases the shear force can be adequately transferred by friction through the flashed bed joint. However, it is recommended that a positive shear connection be provided by extending foundation dowels across the joint. It is recommended that the number of bars extended across the horizontal joint be minimized, and that the extension be limited to 2 in. (51 mm), to ensure that the joint will behave as assumed. Therefore, every vertical bar otherwise required for strength at critical sections does not necessarily need to be extended through the joint.

Masonry shear walls are very strong and stiff and are often used to resist lateral loads. However, masonry wall sections used as shear wall segments must have vertical reinforcement continuous into the foundation as shown in Figure 3. Flashing is also incorporated at the floor level to allow the wall some out-of-plane rotation due to building drift. Design aids are included in Concrete Masonry Walls for Metal
Building Systems (ref. 1) for inplane and out-of-plane reinforced masonry walls as well as for lintels and anchor bolts. Appendix C also presents design examples. As shown in Figure 4, these walls normally span vertically and are laterally supported by a spandrel at the top of the masonry portion of the wall.

When the masonry is designed with a base hinge, it is important to properly detail the building corners to accommodate the movements.

A vertical isolation joint should be placed near the building corner and proper consideration should be given to the masonry and steel connections at corner columns. Flexible anchors and/or slotted connections should be used.

WAINSCOT WALLS

Although full height masonry walls provide the most benefit particularly when the masonry is used for shear walls, partial-height walls, or wainscots, are sometimes used. These walls are commonly 4 to 10 ft (1.2 to 3.0 m) high with metal panel walls extending from the top of the masonry to the roof. The masonry provides strength and
impact resistance for the portion of the wall most susceptible to damage.

COLUMN DETAIL

Figure 5 shows the connection of a rigid frame column to concrete masonry sidewalls with a coincident vertical control joint. The details show vertically adjustable column anchors connecting the wall to the column. For walls designed to span vertically, it is good practice to provide a nominal number of anchors connecting the wall to the column to add stiffness and strength to the edge of the wall. If rigid enough, these anchors can assist in laterally bracing the outside column flange. For larger lateral loads, more substantial connections may be required. Anchorage to end wall columns is very similar.

SPANDREL DETAIL

A typical spandrel detail is shown in Figure Spandrels should be placed as high as possible to reduce the masonry span above the spandrel, especially on walls with parapets. Depending on the rigid frame configuration used, rigid frame connection plates and diagonal stiffeners may restrict the spandrel location. The spandrel is designed by the metal building manufacturer. If the inner flange of the spandrel needs to be braced, the metal building manufacturer will show on the drawings where the braces are required along with the information needed for the masonry engineer to design them and their anchorage to the wall.

Shim plates should be used at spandrel/masonry connections to allow for camber in the spandrel and other construction tolerances (see Figure 6). The steel spandrel should never be pulled to the masonry wall by tightening the anchor bolts.

CONSTRUCTION SEQUENCE

Typically, construction of metal buildings with concrete masonry walls proceeds as follows: concrete footing and column placement; concrete masonry foundation wall construction to grade; concrete slab placement; steel erection; and concrete masonry wall construction. Note, however, that this sequence may need to be modified to meet the needs of a particular project. For example, this construction sequence changes when loadbearing end walls are used. In this case, the steel supported by the masonry is erected after the masonry wall is in place.

Coordination between the various trades is essential for efficient construction. Preconstruction conferences are an excellent way for contractors and subcontractors to coordinate construction scheduling and to avoid conflicts and delays.

REFERENCES

Concrete Masonry Walls for Metal Building Systems, CMU-MAN-003-11. Concrete Masonry & Hardscapes Association, Metal Building Manufacturers Association, International Code Council, 2011.
Serviceability Design Considerations for Steel Buildings, AISC Steel Design Guide #3. American Institute of Steel Construction, 2003.
Minimum Design Loads for Buildings and Other Structures, ASCE 7-05. American Society for Civil Engineers, 2005.