fire resistance and protection of structures · pdf filefire resistance and protection of...

31-1

31Fire Resistance and

Protection of Structures

Mark B. Hogan, P.E.*

Jason J. Thompson**

31.1 Introduction ......................................................................31-1Balanced Design for Fire Safety and Property Protection • Design, Construction, and Material Requirements

31.2 Fire-Resistance Ratings .....................................................31-5Heat Transmission in Slabs • Fire-Resistance Ratings of Single-Wythe Masonry Walls • Single-Layer Concrete Walls, Floors, and Roofs • Multiple-Layer Walls, Floors, and Roofs

31.3 Fire Protection of Joints ...................................................31-9Masonry Elements • Precast Concrete Wall Panels and Slabs

31.4 Finish Treatments............................................................31-1131.5 Fire Resistance of Columns ............................................31-11

Reinforced Masonry Columns • Reinforced-Concrete Columns

31.6 Steel Columns Protected by Masonry ...........................31-1331.7 Fire Resistance of Lintels ................................................31-14References ...................................................................................31-14

31.1 Introduction

Life safety and property protection are critical functions of all structures, particularly as they relate tofire safety. Further, the functionality of these structures is influenced by their design, construction, andmaintenance. Key elements of the design, which have an impact on both the life safety and propertyprotection functions, include the principles of balanced design that incorporate compartmentation tolimit the spread of fire, early detection to alert occupants when a fire occurs, and automatic suppressionto control a fire until it can be extinguished. Concrete and masonry materials are inherently fire resistant,noncombustible, and durable and maintain structural integrity under fire conditions. These features areused in the design of compartments to contain fire and in the design of structural elements to maintain

* Vice President of Engineering, National Concrete Masonry Association, Herndon, Virginia; active member ofcommittees in several professional societies, including ACI/TMS Committee 216 on Fire Resistance and Fire Protec-tion of Structures.** Director of Engineering, National Concrete Masonry Association, Herndon, Virginia; active member of severalprofessional societies and codes and standards development committees, including ACI 530/ASCE 5/TMS 402, BuildingCode Requirements for Masonry Structures, and ACI 530.1/ASCE 6/TMS 602, Specification for Masonry Structures.

© 2008 by Taylor & Francis Group, LLC

31-2 Concrete Construction Engineering Handbook

structural integrity during a fire. The durability and permanence of concrete and masonry can be reliedon for life safety and property protection throughout the life of the structure, with minimal investmentin maintenance or repair. This chapter presents criteria for the design of concrete and masonry elementsto ensure both property protection and life safety functions during fire conditions.

31.1.1 Balanced Design for Fire Safety and Property Protection

Fire safety requires an awareness and understanding of the hazards so both the potential for fire occur-rence and the threat to life and property during a fire are minimized. Death and injury from fire arecaused by asphyxiation from toxic smoke and fumes, burns from direct exposure to the fire, heart attackscaused by stress and exertion, and impact due to structural collapse, explosions, and falls. Life safety andproperty protection are influenced by the design of the building, its fire-protection features, and thequality of construction materials, building contents, and maintenance. Balanced design relies on threecomplementary systems to reduce the risk of death and the threat to property due to fire:

• A detection system to warn occupants of the fire• A containment system to limit the extent of the fire• An automatic suppression system to control the fire until it can be extinguished

Each of these essential systems contributes to lowering the risk of death and injury from fire as well asto protecting property. The three balanced-design components complement each other by providing fireprotection features that are not provided by the other components. Some features of each balanced-design component are intended to be redundant so if one system is breached or fails to perform, thenthe other components continue to provide safety. Although not a tangible element in fire protection, astrong education and training program should be an integral part of any good fire-protection plan inaddition to the physical components of a balanced-design system.

31.1.1.1 Automatic Detection

Accurate early warning is the first line of defense against slow smoldering fires with low heat release ratesthat do not activate sprinkler heads. Detectors that respond to light smoke are important from a life-safetystandpoint because they alert occupants near the origin of the fire to evacuate. Other detection or alarmsystems may be used to notify the fire department, thus decreasing response time, expediting rescueoperations, and limiting the resulting fire spread and property damage. Detectors wired to a central alarmand installed in corridors and common areas notify all building occupants, allow timely and orderlyevacuation, and decrease the potential for injury and death. The most common detector installed is thesmoke-sensing fire detector. Ideally, detectors should be wired into a continuous power supply and beprovided with a battery backup in the event of a power failure. Their location is determined by judgmentand in accordance with the requirements of the general building code. Each dwelling unit in residentialconstruction should be equipped with detectors in all sleeping rooms, in areas adjacent to all sleepingrooms, and on each level of the building, including the basement. The amount of air movement, obstruc-tions within the space, number of stories, and other factors will guide the proper selection of detectorlocations. The performance of detectors is vulnerable to many unpredictable malfunctions, among whichare those due to acts of sabotage, lack of maintenance due to human error and neglect, and faulty powersupply. Young children, the incapacitated, or the elderly may not be able to respond to alarms. All smokedetectors require regularly scheduled maintenance and, in some cases, periodic replacement.

31.1.1.2 Automatic Suppression

The function of automatic sprinkler systems is to control a fire at the point of origin. Although notdesigned to extinguish a fire, residential sprinklers have been shown to be reliable and effective incontrolling a fire in the room of origin until it can be extinguished. Automatic sprinklers reduce thelikelihood of flashover, the near instantaneous ignition of volatile gasses within a confined space whichcan be a particularly hazardous event. Suppression of a fire allows access to the building to permit rescue


Fire Resistance and Protection of Structures 31-3

and fire suppression efforts to proceed. Through the years, sprinklers have been credited with preventinghundreds, possibly thousands, of injuries and deaths.

The National Fire Protection Association (NFPA) maintains minimum standards for the design andinstallation of sprinkler systems. Sprinkler systems for general application are covered by NFPA 13,Standard for the Installation of Sprinkler Systems (NFPA, 2007a), whereas NFPA 13R, Standard for theInstallation of Sprinkler Systems in Residential Occupancies up to and Including Four Stories in Height(NFPA, 2007b), specifically address residential applications. Ideally, when the interior construction orbuilding contents contain a large amount of combustibles, sprinkler systems should meet the require-ments of NFPA 13, regardless of height, to ensure protection in attics, closets, and other concealed spacesbuilt with combustible materials and to provide additional suppression in all areas due to the higher fuelloadings.

The NFPA standards cover the design, installation, testing, and maintenance of sprinkler systems.Obviously, to be effective, automatic sprinklers require an adequate water supply and piping system todeliver sufficient water to the sprinkler head. Sprinkler head requirements ensure proper water coveragebased on the room dimensions, area to be covered, and fuel loading. The standards also list exceptionsfor specific spaces that are not required to be sprinklered. When installation is complete, the standardsrequire inspection and acceptance of the piping valves, pumps, and tanks of the system. Testing alsoincludes verification of adequate water flow to the sprinkler heads. Finally, after the sprinkler system isin use, it must be maintained; however, specific maintenance requirements and frequency of maintenanceare not specified by the standards.

Performance of automatic sprinklers can be vulnerable to system failures due to inadequate mainte-nance and inspection or inadequate water supply. Sprinklers are not intended to control electrical andmechanical equipment fires or fires of external origin, such as fires from adjacent buildings and brushfires. Fires in concealed spaces, including some attics, closets, flues, shafts, ducts, and other spaces wheresprinkler heads are not required to be installed, can compromise life safety due to the spread of toxicfumes and smoke. An inadequate water supply can result from low pressure in the municipal watersystem, broken pipes due to earthquakes or excavation equipment, explosions, freezing temperatures,closed valves due to human error, arson or vandalism, corrosion of valves, pump failure due to electricaloutage, and lack of system maintenance.

31.1.1.3 Compartmentation

Compartmentation limits the extent of fire by dividing a building into fire compartments enclosed byfire walls or fire separation wall assemblies and by fire-rated floors and ceilings. Compartments alsominimize the spread of toxic fumes and smoke to adjacent areas of a building. Conflagrations beyondthe fire compartment are prevented by limiting the total fuel load contributing to the fire. Compartmen-tation provides safe areas of refuge for handicapped, young, elderly, incapacitated, and other occupantswho may not be capable of unassisted evacuation. Compartmentation also provides safe areas of refugefor extended periods when evacuation is precluded due to smoke-filled exit ways or blocked exits.Compartmented construction provides protection for fire and rescue operations. Highly hazardous areas,such as mechanical, electrical, or storage rooms, can be isolated from other occupied areas of a buildingby fire walls. Fire separation walls and floor and ceiling assemblies between dwelling units in multifamilyhousing afford protection from fires caused by the carelessness of other occupants. Refuge areas withina building provide protection for occupants by allowing fire fighters to concentrate on extinguishing thefire rather than on rescue efforts.

Compartmentation serves to contain a fire until it can be brought under control by firefighters. Eachconcrete or masonry element forming the boundary of a compartment should have a fire-resistancerating as defined by the general building code and should be capable of preserving the structural integrityof the building throughout the duration of the fire. In multifamily housing, each dwelling unit shouldform a separate compartment. In addition, interior exit ways, as well as storage, electrical, and mechanicalrooms, should be separate compartments. Exterior walls should be fire rated to form a barrier to thepenetration of exterior fires and to contain interior fires.



The value of compartmentation may be reduced when joints between floors and walls, typically exteriorcurtain walls, or between walls and ceilings are not properly fire-stopped. As such, openings throughcompartment boundaries should be protected to prevent the migration of smoke and fire. Damage causedby equipment, abuse, or the installation of utilities that are not properly sealed can allow the passage ofsmoke and gas. Unsealed openings around penetrations can also allow the spread of smoke. Self-closingmechanisms on doors in compartment walls may fail if not maintained or if blocked open.

31.1.1.4 Property Protection

The initial cost of providing fire safety can be significant; however, balanced design offers advantagesthat offset costs. The higher level of protection for both the structure and its contents limits the potentialloss due to fire. Immediate and long-term savings will be reflected in lower insurance rates for both thebuilding and its furnishings. Balanced design limits both fire and smoke damage to the contents of thebuilding to the compartment of fire origin. Noncombustible compartment boundaries limit damage tothe structure itself and reduce repair time following a fire. Repair is generally nonstructural but mayinclude the replacement of doors and windows; electrical outlets, switches, and wiring; heating ductsand registers; and floor, wall, and ceiling coverings.

31.1.1.5 State of the Art in Designing for Fire Safety

Fire-protection engineering is as much an art as it is a science. The number of unknowns and potentialfire propagation scenarios are numerous. Fire protection is therefore generally based more on risk assess-ment than on precise calculation. Currently, building code prescriptive criteria, along with an under-standing of the science of fire protection, guide the designer in addressing fire safety (ACI Committee216, 1997, 2001; ICC, 2006; NIST, 1993). Some of the more significant fire safety issues requiringconsideration are listed in Table 31.1, along with a relative ranking of the effectiveness of each componentin contributing to balanced design. As shown by the table, more than one component may be consideredeffective in mitigating a particular hazard. Because none of the components is fail safe, overlappingfunctions are required to provide a necessary level of safety. In addition, some functions listed in the tableare addressed by only one component of balanced design. There is general agreement among the firesafety and regulatory communities that computer modeling will serve to continue improving fire safetyin the built environment. Widespread access to complex analytical models and computing equipment isgiving fire safety engineers new and ever-evolving tools to bolster fire safety requirements in buildings.

TABLE 31.1 Fire-Safety Functions of Balanced Design

Function Automatic Detection Compartmentation Automatic Suppression

Controls fire/limits fire growth ❍ ● ●

Provides smoke, toxic-fume barrier ❍ ● ❍

Provides fire barrier ❍ ● ❍

Limits generation of smoke/toxic fumes ❍ ■ ●

Allows safe egress ■ ● ■

Provides refuge ❍ ● ❍

Assists fire-fighting efforts ❍ ■ ■

Reduces response time ● ❍ ❍

Difficult to vandalize or arson ❍ ● ❍

Performance requires little maintenance ❍ ● ❍

Property protection functions and costs of balanced design componentLimits the extent of contents damage ■ ■ ■

Limits the extent of structure damage ■ ● ■

Low installation costs ● ■ ❍

Low maintenance costs ■ ● ❍

Limits repair time due to fire damage ■ ● ●

Note: ●, Considered to be effective; ■, considered to be partially effective; ❍, considered to be ineffective or only slightlyeffective.



31.1.2 Design, Construction, and Material Requirements

The fire-resistance ratings of concrete and masonry assemblies assume that the design and constructionof these elements comply with the provisions of the Building Code Requirements for Masonry Structures(ACI Committee 530, 2005) and the Building Code Requirements for Structural Concrete (ACI Committee318, 2005) for masonry and concrete elements, respectively. These codes stipulate material requirementsby reference to ASTM standards and establish quality assurance provisions for the construction of theseelements.

31.2 Fire-Resistance Ratings

Two major factors have to be considered in ratings: fire endurance and fire resistance. The definitions ofthese two terms, per ACI 216, are as follows:

• Fire endurance—A measure of the elapsed time during which a material or assembly continues toexhibit fire resistance under specified conditions of test and performance; as applied to elementsof buildings, it shall be measured by the methods and to the criteria defined in ASTM E 119.

• Fire resistance—The property of a material or assembly to withstand fire or to give protectionfrom it; as applied to elements of buildings, it is characterized by the ability to confine a fire orto continue to perform a given structural function, or both.

Building codes establish the minimum level of required fire resistance for specific elements within thestructure based on the type of occupancy of the building, the function of the element, the importanceof the structure, its contents, and other fire-protection considerations. When the required fire-resistancerating of a concrete or masonry element has been established, this chapter can assist the designer inmeeting that requirement.

The fire-resistance rating criteria presented here are based on the provisions of the ACI 216.1/TMS0216, Standard Method for Determining Fire Resistance of Concrete and Masonry Construction Assemblies(ACI Committee 216, 1997). This consensus standard, which is referenced by model building codes, isbased on current practice in determining the fire ratings of concrete and masonry elements. The standardcovers two methods of determining the fire-resistance rating of an element. The most common methodfor determining the fire-resistance rating is based on a calculation procedure that has established acorrelation between the physical properties of the concrete or masonry member and the measured fireendurance as determined through testing in accordance with ASTM E 119, Standard Test Methods forFire Tests of Building Construction and Materials (ASTM, 2005b). The second method allows for directmeasurement of the fire resistance of an element or assembly through testing in accordance with ASTME 119. A third option, which is not explicitly covered by existing codes and standards, is to establish thefire-resistance rating through a listing service, such as Underwriters Laboratory.

Fire testing of wall assemblies in accordance with ASTM E 119 defines four performance criteria thatmust be met:

• Resistance to the transmission of heat through the wall assembly• Resistance to the passage of hot gases or flame through the assembly sufficient to ignite cotton

waste on the non-exposed side• Loss of load-carrying capacity of load-bearing walls• Resistance to the impact, erosion, and cooling effects of a hose stream on the assembly after

exposure to fire

The fire-resistance ratings of concrete and masonry elements are typically governed by the transmissionof heat through the assembly, which is measured by temperature rise on the non-fire-exposed side of thewall. This consistent mode of failure allows for a standardized calculation procedure to be derived asdescribed below. Conversely, the fire-resistance rating of other construction assemblies, particularly thoseconsisting of combustible materials, is often governed by one of the other performance criteria.



31.2.1 Heat Transmission in Slabs

The structural fire endurance of simply supported concrete slabs as affected by the constituent materialscan be interpolated from Figure 31.1 by an effective concrete cover parameter (u) as a function of themoment ratio M/Mn, where M is the design moment and Mn is the nominal moment strength. In theusual case of continuous slabs and beams, a shift in the moment distribution develops, thereby increasingthe stresses in the negative reinforcement resulting from the increase in the bending moments at thesupports. During a fire, however, the negative reinforcement remains cooler than the positive reinforce-ment as it is often farther from the source of the fire. This in turn allows for an increase in the negativemoment that can be accommodated (ACI Committee 216, 1997). Although the moment redistributionthat results can be sufficient to result in yielding of the negative reinforcement, the resulting decrease inthe positive moment in effect permits the beam or slab span to endure higher temperatures. The negativemoment reinforcing bars must be long enough to accommodate the complete redistributed momentsand the change of the location of the inflection points. At least 20% of the maximum negative momentreinforcement must be extended throughout the span (CEB/FIP, 1990). The fire-resistance rating ofconcrete slabs can also be increased through the use of undercoating, as described in ACI 216.1/TMS0216 (ACI Committee 216, 1997).

31.2.2 Fire-Resistance Ratings of Single-Wythe Masonry Walls

The fire-resistance rating of masonry walls, including single-wythe walls, multi-wythe walls, and wallswith finish treatments, is based on the following criteria, which includes the effect of grouting and theeffect of filling the cores of hollow units with recognized loose fill materials.

FIGURE 31.1 Fire resistance of concrete slabs. (From ACI Committee 216, Guide for Determining the Fire Enduranceof Concrete Elements, ACI 216R, American Concrete Institute, Farmington Hills, MI, 2001.)

2

1

00.0 0.2 0.4 0.6

Carbonate AGG.reinforcing bars

Carbonate AGG.cold-drawn steel

Siliceous AGG.cold -drawn steel

Lightweight AGG.cold-drawn steel

Siliceous AGG.reinforcing bars

Lightweight AGG.reinforcing bars

ω* = 0.1ω = 0.3

ωp** = 0.1

* Reinforcement index for concrete beams reinforced with mild reinforcement: ω = Asfy /bdfc

** Reinforcement index for concrete beams reinforced with prestressing steel: ωp = Aspfy /bdfc

ωp = 0.3

4 hr

3

2

1

3

4hr4 hr

3

2

1

2

1

0.0 0.2 0.4 0.6 0.0 0.2 0.4 0.6

40

20

0

60

40

20

0

u, i

n.

u, i

n.

u, m

mu

, mm

M/Mn

M/Mn M/Mn M/Mn

M/Mn M/Mn

4 hr

4 hr

3

2

1

3

2

1

3

2

1

00.0 0.2 0.4 0.6 0.0 0.2 0.4 0.6 0.0 0.2 0.4 0.6

4 hr

3

2

3

´

´



31.2.2.1 Single-Wythe Concrete Masonry Walls

The calculated fire-resistance rating of single-wythe concrete masonry assemblies is determined in accordancewith Table 31.2. These calculated fire-resistance ratings are derived from the requirements of ACI 216.1/TMS0216. The equivalent thickness (Tea) of concrete masonry assemblies is based on the equivalent thickness ofthe masonry unit (Te) plus the equivalent thickness of any recognized finish materials (Tef) as follows:

(31.1)

The equivalent thickness (Te) of a concrete masonry unit is the net volume of the unit divided by theface area of the unit (length times height). The equivalent thickness (Te) of solid grouted masonry wallsis the actual thickness of the unit. The equivalent thickness (Te) of hollow masonry unit walls that arecompletely filled with loose fill is the actual thickness of the unit when the loose fill materials are sand,pea gravel, crushed stone, or slag that meet ASTM C 33 (ASTM, 2003) requirements; pumice, scoria,expanded shale, expanded clay, expanded slate, expanded slag, expanded fly ash, or cinders that complywith ASTM C 331 (ASTM, 2005a); or perlite or vermiculite meeting the requirements of ASTM C 549and ASTM C 516, respectively (ASTM, 2002, 2006).

31.2.2.2 Single-Wythe Clay Masonry Walls

The calculated fire-resistance rating of single-wythe clay masonry assemblies is determined in accordancewith Table 31.3. The equivalent thickness (Te) of clay masonry assemblies is determined as follows:

(31.2)

As with concrete masonry assemblies, when solid grouted or when completely filled with approved loosefill materials, the equivalent thickness (Te) of a clay masonry assembly is the actual thickness of the unit.

TABLE 31.2 Fire-Resistance Rating Period of Concrete Masonry Assemblies

Aggregate Type in the Concrete Masonry Unitb

Minimum Required Equivalent Thickness (in.) for Fire-Resistance Ratinga

4 hr 3 hr 2 hr 1.5 hr 1 hr 0.75 hr 0.5 hr

Calcareous or siliceous gravel 6.2 5.3 4.2 3.6 2.8 2.4 2.0Limestone, cinders, or slag 5.9 5.0 4.0 3.4 2.7 2.3 1.9Expanded clay, shale, or slate 5.1 4.4 3.6 3.3 2.6 2.2 1.8Expanded slag or pumice 4.7 4.0 3.2 2.7 2.1 1.9 1.5

a Fire-resistance ratings between the hourly fire-resistance rating periods listed are determined by linear interpolation basedon the equivalent thickness value of the concrete masonry wall assembly.b Minimum required equivalent thickness corresponding to the hourly fire-resistance rating for units made with a combi-nation of aggregates is determined by linear interpolation based on the percent by volume of each aggregate used in themanufacturing of the unit.

TABLE 31.3 Fire-Resistance Rating of Clay Masonry Assemblies

Material Type

Minimum Required Equivalent Thickness (in.) for Fire-Resistance Ratinga,b

1 hr 2 hr 3 hr 4 hr

Solid brick of clay or shalec 2.7 3.8 4.9 6.0Hollow brick or tile of clay or shale, unfilled 2.3 3.4 4.3 5.0Hollow brick or tile of clay or shale, grouted or filled with perlite,

vermiculite, or expanded shale aggregate3.0 4.4 5.5 6.6

a Fire-resistance ratings between the hourly fire-resistance rating periods listed should be determined by linear interpolation.b Where combustible members are framed into the wall, the thickness of solid material between the end of each member andthe opposite face of the wall or between members set in from opposite sides should not be less than 93% of the thickness shown.c For units in which the net cross-sectional area of cored brick in any plane parallel to the surface containing the coresshould be at least 75% of the gross cross-sectional area measured in the same plane.

T T Tea e ef= +

T V LHe n=



31.2.3 Single-Layer Concrete Walls, Floors, and Roofs

The fire-resistance rating of plain and reinforced concrete walls, floors, and roofs that are a single layerin thickness are determined in accordance with Table 31.4 and are based on the equivalent thickness ofthe element. The equivalent thickness of solid concrete elements with flat surfaces is the actual thicknessof the element. The equivalent thickness of hollow-core panels with a constant cross-section throughouttheir length is determined by dividing the net cross-sectional area by the panel width. The equivalentthickness of elements in which all of the core spaces are filled with grout or loose fill material, such asperlite, vermiculite, sand or expanded clay, shale, slag, or slate, should be the same as that of a solid wallor slab of the same type of concrete. The equivalent thickness for flanged elements in which the flangestaper is determined at the location of the lesser distance of two times the minimum thickness, or 6 in.from the point of the minimum thickness of the flange. The equivalent thickness of elements with ribbedor undulating surfaces is determined as follows:

• Where the center-to-center spacing of ribs or undulations is not less than four times the minimumthickness, the equivalent thickness is the minimum thickness of the panel.

• Where the spacing of ribs or undulations is equal to or less than two times the minimum thickness,calculate the equivalent thickness by dividing the net cross-sectional area by the panel width. Themaximum thickness used to calculate the net cross-sectional area should not exceed two times theminimum thickness.

• Where the spacing of ribs or undulations exceeds two times the minimum thickness, but is lessthan four times the minimum thickness, calculate the equivalent thickness as follows:

(31.3)

where:

s = spacing of ribs or undulations (in.).t = minimum thickness (in.).te = equivalent thickness calculated in accordance with Equation 31.2.

31.2.4 Multiple-Layer Walls, Floors, and Roofs

ACI 216.1/TMS 0216 (ACI Committee 216, 1997) offers several alternatives to calculating the fire-resistance rating of multi-wythe and multi-layer walls, floors, and roofs using graphical, analytical,and numerical solutions. Each alternative considers various possible combinations of normal weight,semi-lightweight, and lightweight concretes; sandwich panels and insulation systems; and the use ofconcrete and clay masonry assemblies as part of a veneer or multi-wythe system. In addition to thematerial properties, the resulting fire-resistance rating is influenced by the use of finish materials,exposure conditions, and reinforcement cover distances. The user is referred to ACI 216.1/TMS 0216for additional information on determination of the fire-resistance properties of multiple-layer concreteand masonry systems.

TABLE 31.4 Fire-Resistance Rating of Single-Layer Concrete Walls, Floors, and Roofs

Aggregate Type

Minimum Equivalent Thickness (in.) for Fire-Resistance Rating

1 hr 1.5 hr 2 hr 3 hr 4 hr

Siliceous 3.5 4.3 5.0 6.2 7.0Carbonate 3.2 4.0 4.6 5.7 6.6Semi-lightweight 2.7 3.3 3.8 4.6 5.4Lightweight 2.5 3.1 3.6 4.4 5.1

Equivalent thickness = + ( )− −( )t t s t te4 1/



31.3 Fire Protection of Joints

31.3.1 Masonry Elements

Expansion or contraction joints in fire-rated concrete masonry wall assemblies and in clay brick wallassemblies are shown in Figure 31.2, Figure 31.3, and Figure 31.4. Figure 31.2 illustrates a standard controljoint detail for a 2-hour fire-resistance rating, and Figure 32.3 and Figure 32.4 offer alternatives for 4-hourfire-resistance ratings.

31.3.2 Precast Concrete Wall Panels and Slabs

In wall panels where openings are not permitted or where it is required that openings be protected, jointsmust be insulated. Joints between panels that are not insulated are considered unprotected openings.Where the percentage of unprotected openings is limited in exterior walls, the area of uninsulated jointsis added to the area of other unprotected openings to determine the total area of unprotected openings.Protected joints between precast concrete wall panels are filled with ceramic fiber blankets, the minimumthickness of which is calculated in accordance with ACI 216.1/TMS 0216 (ACI Committee 216, 1997).Other approved joint treatment systems that maintain the required fire-resistance rating are also used.Alternatively, joints between adjacent precast concrete slabs may be ignored when calculating the equiv-alent slab thickness, provided that a concrete topping not less than 1 in. thick is used. Where a concretetopping is not used, joints should be grouted to a depth of at least one third the slab thickness at thejoint, but not less than 1 in., or the fire-resistance rating of the floor or roof must be maintained by otherapproved methods.

FIGURE 31.2 Two-hour control joint.

Joint reinforcement,as required

Vertical reinforcement,as required

SealantBacker rod

Preformedgasket

Concrete masonrysash unit

Stop jointreinforcement at

control joint

Backer rod

Sealant



FIGURE 31.3 Four-hour control joint.

FIGURE 31.4 Four-hour control joint.



SealantBacker rod


control joint

Sealant

Backer rod

Ceramic fiberfelt (alumina–

silica fiber)



SealantBacker rod


control joint

Sealant

Building paperor other

bond break

Backer rod

Building paperor other

bond break

Raked mortarjoint



31.4 Finish Treatments

Finish treatments on concrete and masonry elements include gypsum drywall, terrazzo, or plaster. Thesetreatments increase the fire-resistance rating of the element by delaying the temperature rise within orthrough the element when exposed to fire. The effect of this increase is based on whether the finish isapplied to the side of the element being exposed to the fire or to the side that is not exposed to the fire.The fire-resistance rating of elements that may be exposed to fire from either side is determined basedon the lower rating determined from assuming that the fire exposure is from one side or the other. Thefire-resistance rating of the element including the effect of finish treatments is limited to twice the firerating of the element excluding the effect of finish treatments. Further, the effect of finish treatmentsfrom the non-fire-exposed side of the wall is limited to one half the fire-resistance rating of the elementexcluding the effect of finish treatments. Finishes that are assumed to contribute to the total fire-resistancerating of an assembly must meet the minimum installation requirements as prescribed in ACI 216.1/TMS 0216.

Some finishes deteriorate more rapidly when exposed to fire than when installed on the non-exposedside of an assembly. For this reason, ACI 216.1/TMS 0216 requires two separate calculations assuming,first, that the fire exposure is on one side of the wall and then again assuming that the fire is on the otherside of the wall. Table 31.5 applies to finishes on the non-fire-exposed side of the wall, while Table 31.6applies to finishes on the fire-exposed side. The resulting fire rating of the wall assembly is the smallerof the two calculated ratings. Note that in some situations the fire is assumed to occur only on one sideof the wall. For finishes on the non-fire-exposed side of the wall, the finish is converted to equivalentthickness of concrete or masonry by multiplying the thickness of the finish by the factor given in Table31.5. This is then added to the base equivalent thickness per Equation 31.1. For finishes on the fire-exposed side of the wall, a time is assigned to the finish per Table 31.6, which is added to the fire-resistancerating determined for the base wall and non-fire-side finish. The additional times listed in Table 31.6 areessentially the length of time the various finishes will remain intact when directly exposed to fire.

31.5 Fire Resistance of Columns

31.5.1 Reinforced Masonry Columns

The fire-resistance rating of reinforced concrete and clay masonry columns is based on the least plandimension of the column in accordance with the requirements of Table 31.7. The minimum cover forlongitudinal reinforcement, measured from the outside surface of the reinforcement to the nearest outsidesurface of the masonry, is not permitted to be less than 2 in.

TABLE 31.5 Multiplying Factors for Finishes on the Non-Fire-Exposed Side of Concrete Slabs and Concrete and Masonry Walls

Type of Finish Applied to Slab or Wall

Type of Material Used in Slab or Wall

Siliceous or Carbonate Aggregate Concrete or

Concrete Masonry Unit; Solid Clay Brick Masonry

Semi-Lightweight Concrete;

Hollow Clay Brick; Clay Tile

Lightweight Concrete; Concrete Masonry Units of Expanded Shale, Expanded Clay, Expanded Slag, or

Pumice Less Than 20% Sand

Portland cement–sand plastera or terrazzo

1.00 0.75 0.75

Gypsum–sand plaster 1.25 1.00 1.00Gypsum–vermiculite

or perlite plaster1.75 1.50 1.25

Gypsum wallboard 3.00 2.25 2.25

a For Portland cement–sand plaster 5/8 in. or less in thickness and applied directly to concrete or masonry on the non-fire-exposed side of the wall, the multiplying factor is 1.0.



31.5.2 Reinforced-Concrete Columns

The fire-resistance ratings of reinforced-concrete columns, both circular and rectangular, are determinedin accordance with the requirements of Table 31.8. When a concrete column is exposed to fire on twoparallel sides, additional requirements as prescribed in ACI 216.1/TMS 0216 (ACI Committee 216, 1997)must be met. The minimum thickness of concrete cover to the longitudinal reinforcement in concretecolumns should not be less than 1 in. times the number of hours of required fire resistance, or 2 in.,whichever is less.

TABLE 31.6 Time Assigned to Finish Materials on Fire-Exposed Side of Concrete and Masonry Walls

Finish Description Time (minutes)

Gypsum wallboard3/8-in. 101/2-in. 155/8-in. 20Two 3/8-in. layers 25One 3/8-in. layer and one 1/2-in. layer 35Two 1/2-in. layers 40

Type X gypsum wallboard1/2-in. 255/8-in. 40Direct applied Portland cement–sand plaster —a

Portland cement–sand plaster on metal lath3/4-in. 207/8-in. 251-in. 30

Gypsum–sand plaster on 3/8-in. gypsum lath1/2-in. 355/8-in. 403/4-in. 50

Gypsum–sand plaster on metal lath3/4-in. 507/8-in. 601-in. 80

a The fire-resistance rating of elements with Portland cement–sandplaster finish treatment is determined by adding the actual thicknessof the plaster or 5/8 in., whichever is smaller, to the equivalent thick-ness of the element.

TABLE 31.7 Reinforced Masonry Columns

Fire Resistance (hr)

1 2 3 4

Minimum column dimension (in.) 8 10 12 14

TABLE 31.8 Minimum Concrete Column Size

Aggregate Type

Minimum Column Dimension for Fire-Resistance Rating (in.)

1 hr 1.5 hr 2 hr 3 hr 4 hr

Carbonate 8 9 10 11 12Siliceous 8 9 10 12 14Semi-lightweight 8 8.5 9 10.5 12



31.6 Steel Columns Protected by Masonry

Because of its inherent fire-resistant properties, masonry is often used as a nonstructural fire-protectioncovering for structural steel members. The fire endurance of steel column protection is determined asthe period of time for the average temperature of the steel to exceed 1000°F or for the temperature atany measured point to exceed 1200°F (ASTM, 2005b). These criteria depend on the thermal propertiesof the column cover and of the steel column. Accurate predictions of the fire endurance of protectedsteel columns are made possible by a numerical technique based on heat-flow analyses and researchinformation on the thermal and rheological properties of masonry and steel at elevated temperatures(Lie and Harmathy, 1972). Using this technique, an empirical formula was developed to predict the fireendurance of masonry-protected steel columns in accordance with ACI 216.1/TMS 0216 (ACI Committee216, 1997). The fire-resistance rating of structural steel columns protected by masonry is determined asfollows:

(31.4)

where:

R = fire-resistance rating of the protected column assembly (hr).Ast = cross-sectional area of the structural steel column (in.2).D = density of the masonry protection (lb/ft3).p = inner perimeter of the masonry protection (in.).ps = heated perimeter of steel column (in.), per Equations 31.5, 31.6, or 31.7.Tea= equivalent thickness of the concrete masonry protection assembly (in.)k = thermal conductivity of the masonry protection (BTU/hr·ft·°F).

For a W-section steel column, the heated perimeter (ps) is determined as follows:

(31.5)

For a pipe-section steel column, the heated perimeter (ps) is determined as follows:

(31.6)

For a square-tube steel column, the heated perimeter (ps) is determined as follows:

(31.7)

where:

bf = width of flange (in.).dst = column depth (in.).tw = thickness of web of W-section (in.).

For use in Equation 31.4, the thermal conductivity of concrete masonry is:

(31.8)

Likewise, the thermal conductivities of clay masonry are equal to:

k = 1.25 BTU/hr·ft·°F for a density of 120 lb/ft3.k = 2.25 BTU/hr·ft·°F for a density of 130 lb/ft3.

Steel Column Fire Protection (NCMA, 2003) contains a comprehensive list of fire-resistance ratings for awide variety of structural steel sections.

R A p T kst s ea cm= ( ) + ( )

0 401 0 285 1

0 7 1 6 0 2. . .. . . 00 42 7 0 25

0 8+ ( ) +( ){ }

. ..

A DT p Tst ea ea

p b d b ts f st f w= +( )+ −( )2 2

p ds st= π

p ds st= 4

k eD= 0 04170 02. .



31.7 Fire Resistance of Lintels

The fire-resistance rating of masonry lintels (beams spanning openings) is based on the nominal thicknessof the lintel and the minimum provided cover for the longitudinal reinforcement as shown in Table 31.9.The cover is measured from the outside surface of the reinforcement to the nearest outside surface ofmasonry, which may consist of masonry units, grout, or mortar.

References

ACI Committee 216. 1997. Standard Method for Determining Fire Resistance of Concrete and MasonryConstruction Assemblies, ACI 216.1/TMS 0216. American Concrete Institute, Farmington Hills, MI.

ACI Committee 216. 2001. Guide for Determining the Fire Endurance of Concrete Elements, ACI 216R.American Concrete Institute, Farmington Hills, MI.

ACI Committee 318. 2005. Building Code Requirements for Structural Concrete, ACI 318. AmericanConcrete Institute, Farmington Hills, MI.

ACI Committee 530. 2005. Building Code Requirements for Masonry Structures, ACI 530/ASCE 5/TMS402. The Masonry Society, Boulder, CO.

ASTM. 2002. Standard Specification for Vermiculite Loose Fill Thermal Insulation, ASTM C 516. ASTMInternational, West Conshohocken, PA.

ASTM. 2003. Standard Specification for Concrete Aggregates, ASTM C 33. American Society for Testingand Materials, West Conshohocken, PA.

ASTM. 2005a. Standard Specification for Lightweight Aggregates for Concrete Masonry Units, ASTM C 331.American Society for Testing and Materials, West Conshohocken, PA.

ASTM. 2005b. Standard Test Methods for Fire Tests of Building Construction and Materials, ASTM E 119.American Society for Testing and Materials, West Conshohocken, PA.

ASTM. 2006. Standard Specification for Perlite Loose Fill Insulation, ASTM C 549. American Society forTesting and Materials, West Conshohocken, PA.

CEB-FIP. 1990. Model Code for Concrete Structures. Comite’ Euro-International du Beton-FederationInternacionale de Precontraite, Paris.

ICC. 2006. International Fire Code (IFC). International Code Council, Falls Church, VA.Lie, T.T. and Harmathy, T.Z. 1972. A Numeral Procedure to Calculate the Temperature of Protected Steel

Columns Exposed to Fire. National Research Council of Canada, Division of Building Research,Ottawa, Ontario.

NCMA. 2003. Steel Column Fire Protection, NCMA-TEK 7-6. National Concrete Masonry Association,Herndon, VA.

NIST. 1993. HAZARD I—Fire Hazard Assessment Method, NIST Handbook 146. National Institute ofStandards and Technology, Gaithersburg, MD.

NFPA. 2007a. Standard for the Installation of Sprinkler Systems, NFPA 13. National Fire ProtectionAssociation, Quincy, MA.

NFPA. 2007b. Standard for the Installation of Sprinkler Systems in Residential Occupancies Up to andIncluding Four Stories in Height, NFPA 13R. National Fire Protection Association, Quincy, MA.

TABLE 31.9 Reinforced Masonry Lintels

Nominal Lintel Width (in.)

Minimum Longitudinal Reinforcement Cover for Fire-Resistance Rating (in.)

1 hr 2 hr 3 hr 4 hr

6 1.5 2 Not permitted Not permitted8 1.5 1.5 1.75 3.0010 or more 1.5 1.5 1.5 1.75


fire resistance and protection of structures · pdf filefire resistance and protection of...

Documents