Fire Resistance and Protection of Structures

Transcription

1 1 Fire Resistance and Protection of Structures Mark B. Hogan, P.E. * Jason J. Thompson ** 1.1 Introduction Balanced Design for Fire Safety and Property Protection Design, Construction, and Material Requirements 1. Fire-Resistance Ratings Heat Transmission in Slabs Fire-Resistance Ratings of Single-Wythe Masonry Walls Single-Layer Concrete Walls, Floors, and Roofs Multiple-Layer Walls, Floors, and Roofs 1. Fire Protection of Joints Masonry Elements Precast Concrete Wall Panels and Slabs 1.4 Finish Treatments Fire Resistance of Columns Reinforced Masonry Columns Reinforced-Concrete Columns 1.6 Steel Columns Protected by Masonry Fire Resistance of Lintels References Introduction Life safety and property protection are critical functions of all structures, particularly as they relate to fire safety. Further, the functionality of these structures is influenced by their design, construction, and maintenance. Key elements of the design, which have an impact on both the life safety and property protection functions, include the principles of balanced design that incorporate compartmentation to limit the spread of fire, early detection to alert occupants when a fire occurs, and automatic suppression to 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 are used 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 of committees in several professional societies, including ACI/TMS Committee 16 on Fire Resistance and Fire Protection of Structures. ** Director of Engineering, National Concrete Masonry Association, Herndon, Virginia; active member of several professional societies and codes and standards development committees, including ACI 50/ASCE 5/TMS 40, Building Code Requirements for Masonry Structures, and ACI 50.1/ASCE 6/TMS 60, Specification for Masonry Structures. 1-1

2 1- Concrete Construction Engineering Handbook structural integrity during a fire. The durability and permanence of concrete and masonry can be relied on for life safety and property protection throughout the life of the structure, with minimal investment in maintenance or repair. This chapter presents criteria for the design of concrete and masonry elements to ensure both property protection and life safety functions during fire conditions Balanced Design for Fire Safety and Property Protection Fire safety requires an awareness and understanding of the hazards so both the potential for fire occurrence and the threat to life and property during a fire are minimized. Death and injury from fire are caused by asphyxiation from toxic smoke and fumes, burns from direct exposure to the fire, heart attacks caused by stress and exertion, and impact due to structural collapse, explosions, and falls. Life safety and property protection are influenced by the design of the building, its fire-protection features, and the quality of construction materials, building contents, and maintenance. Balanced design relies on three complementary 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 as to protecting property. The three balanced-design components complement each other by providing fire protection features that are not provided by the other components. Some features of each balanceddesign component are intended to be redundant so if one system is breached or fails to perform, then the other components continue to provide safety. Although not a tangible element in fire protection, a strong education and training program should be an integral part of any good fire-protection plan in addition to the physical components of a balanced-design system Automatic Detection Accurate early warning is the first line of defense against slow smoldering fires with low heat release rates that do not activate sprinkler heads. Detectors that respond to light smoke are important from a life-safety standpoint because they alert occupants near the origin of the fire to evacuate. Other detection or alarm systems may be used to notify the fire department, thus decreasing response time, expediting rescue operations, and limiting the resulting fire spread and property damage. Detectors wired to a central alarm and installed in corridors and common areas notify all building occupants, allow timely and orderly evacuation, and decrease the potential for injury and death. The most common detector installed is the smoke-sensing fire detector. Ideally, detectors should be wired into a continuous power supply and be provided with a battery backup in the event of a power failure. Their location is determined by judgment and in accordance with the requirements of the general building code. Each dwelling unit in residential construction should be equipped with detectors in all sleeping rooms, in areas adjacent to all sleeping rooms, and on each level of the building, including the basement. The amount of air movement, obstructions within the space, number of stories, and other factors will guide the proper selection of detector locations. The performance of detectors is vulnerable to many unpredictable malfunctions, among which are those due to acts of sabotage, lack of maintenance due to human error and neglect, and faulty power supply. Young children, the incapacitated, or the elderly may not be able to respond to alarms. All smoke detectors require regularly scheduled maintenance and, in some cases, periodic replacement Automatic Suppression The function of automatic sprinkler systems is to control a fire at the point of origin. Although not designed to extinguish a fire, residential sprinklers have been shown to be reliable and effective in controlling a fire in the room of origin until it can be extinguished. Automatic sprinklers reduce the likelihood of flashover, the near instantaneous ignition of volatile gasses within a confined space which can be a particularly hazardous event. Suppression of a fire allows access to the building to permit rescue

3 Fire Resistance and Protection of Structures 1- and fire suppression efforts to proceed. Through the years, sprinklers have been credited with preventing hundreds, possibly thousands, of injuries and deaths. The National Fire Protection Association (NFPA) maintains minimum standards for the design and installation of sprinkler systems. Sprinkler systems for general application are covered by NFPA 1, Standard for the Installation of Sprinkler Systems (NFPA, 007a), whereas NFPA 1R, Standard for the Installation of Sprinkler Systems in Residential Occupancies up to and Including Four Stories in Height (NFPA, 007b), specifically address residential applications. Ideally, when the interior construction or building contents contain a large amount of combustibles, sprinkler systems should meet the requirements of NFPA 1, regardless of height, to ensure protection in attics, closets, and other concealed spaces built with combustible materials and to provide additional suppression in all areas due to the higher fuel loadings. 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 to deliver sufficient water to the sprinkler head. Sprinkler head requirements ensure proper water coverage based on the room dimensions, area to be covered, and fuel loading. The standards also list exceptions for specific spaces that are not required to be sprinklered. When installation is complete, the standards require inspection and acceptance of the piping valves, pumps, and tanks of the system. Testing also includes verification of adequate water flow to the sprinkler heads. Finally, after the sprinkler system is in use, it must be maintained; however, specific maintenance requirements and frequency of maintenance are not specified by the standards. Performance of automatic sprinklers can be vulnerable to system failures due to inadequate maintenance and inspection or inadequate water supply. Sprinklers are not intended to control electrical and mechanical equipment fires or fires of external origin, such as fires from adjacent buildings and brush fires. Fires in concealed spaces, including some attics, closets, flues, shafts, ducts, and other spaces where sprinkler heads are not required to be installed, can compromise life safety due to the spread of toxic fumes and smoke. An inadequate water supply can result from low pressure in the municipal water system, 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 electrical outage, and lack of system maintenance Compartmentation Compartmentation limits the extent of fire by dividing a building into fire compartments enclosed by fire walls or fire separation wall assemblies and by fire-rated floors and ceilings. Compartments also minimize the spread of toxic fumes and smoke to adjacent areas of a building. Conflagrations beyond the fire compartment are prevented by limiting the total fuel load contributing to the fire. Compartmentation provides safe areas of refuge for handicapped, young, elderly, incapacitated, and other occupants who may not be capable of unassisted evacuation. Compartmentation also provides safe areas of refuge for 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 building by fire walls. Fire separation walls and floor and ceiling assemblies between dwelling units in multifamily housing afford protection from fires caused by the carelessness of other occupants. Refuge areas within a building provide protection for occupants by allowing fire fighters to concentrate on extinguishing the fire rather than on rescue efforts. Compartmentation serves to contain a fire until it can be brought under control by firefighters. Each concrete or masonry element forming the boundary of a compartment should have a fire-resistance rating as defined by the general building code and should be capable of preserving the structural integrity of the building throughout the duration of the fire. In multifamily housing, each dwelling unit should form a separate compartment. In addition, interior exit ways, as well as storage, electrical, and mechanical rooms, should be separate compartments. Exterior walls should be fire rated to form a barrier to the penetration of exterior fires and to contain interior fires.

4 1-4 Concrete Construction Engineering Handbook TABLE 1.1 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 component Limits 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 slightly effective. The value of compartmentation may be reduced when joints between floors and walls, typically exterior curtain walls, or between walls and ceilings are not properly fire-stopped. As such, openings through compartment boundaries should be protected to prevent the migration of smoke and fire. Damage caused by equipment, abuse, or the installation of utilities that are not properly sealed can allow the passage of smoke and gas. Unsealed openings around penetrations can also allow the spread of smoke. Self-closing mechanisms on doors in compartment walls may fail if not maintained or if blocked open Property Protection The initial cost of providing fire safety can be significant; however, balanced design offers advantages that offset costs. The higher level of protection for both the structure and its contents limits the potential loss due to fire. Immediate and long-term savings will be reflected in lower insurance rates for both the building and its furnishings. Balanced design limits both fire and smoke damage to the contents of the building to the compartment of fire origin. Noncombustible compartment boundaries limit damage to the structure itself and reduce repair time following a fire. Repair is generally nonstructural but may include the replacement of doors and windows; electrical outlets, switches, and wiring; heating ducts and registers; and floor, wall, and ceiling coverings 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 potential fire propagation scenarios are numerous. Fire protection is therefore generally based more on risk assessment than on precise calculation. Currently, building code prescriptive criteria, along with an understanding of the science of fire protection, guide the designer in addressing fire safety (ACI Committee 16, 1997, 001; ICC, 006; NIST, 199). Some of the more significant fire safety issues requiring consideration are listed in Table 1.1, along with a relative ranking of the effectiveness of each component in contributing to balanced design. As shown by the table, more than one component may be considered effective in mitigating a particular hazard. Because none of the components is fail safe, overlapping functions are required to provide a necessary level of safety. In addition, some functions listed in the table are addressed by only one component of balanced design. There is general agreement among the fire safety and regulatory communities that computer modeling will serve to continue improving fire safety in the built environment. Widespread access to complex analytical models and computing equipment is giving fire safety engineers new and ever-evolving tools to bolster fire safety requirements in buildings.

5 Fire Resistance and Protection of Structures Design, Construction, and Material Requirements The fire-resistance ratings of concrete and masonry assemblies assume that the design and construction of these elements comply with the provisions of the Building Code Requirements for Masonry Structures (ACI Committee 50, 005) and the Building Code Requirements for Structural Concrete (ACI Committee 18, 005) for masonry and concrete elements, respectively. These codes stipulate material requirements by reference to ASTM standards and establish quality assurance provisions for the construction of these elements. 1. Fire-Resistance Ratings Two major factors have to be considered in ratings: fire endurance and fire resistance. The definitions of these two terms, per ACI 16, are as follows: Fire endurance A measure of the elapsed time during which a material or assembly continues to exhibit fire resistance under specified conditions of test and performance; as applied to elements of 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 protection from it; as applied to elements of buildings, it is characterized by the ability to confine a fire or to continue to perform a given structural function, or both. Building codes establish the minimum level of required fire resistance for specific elements within the structure based on the type of occupancy of the building, the function of the element, the importance of the structure, its contents, and other fire-protection considerations. When the required fire-resistance rating of a concrete or masonry element has been established, this chapter can assist the designer in meeting that requirement. The fire-resistance rating criteria presented here are based on the provisions of the ACI 16.1/TMS 016, Standard Method for Determining Fire Resistance of Concrete and Masonry Construction Assemblies (ACI Committee 16, 1997). This consensus standard, which is referenced by model building codes, is based on current practice in determining the fire ratings of concrete and masonry elements. The standard covers two methods of determining the fire-resistance rating of an element. The most common method for determining the fire-resistance rating is based on a calculation procedure that has established a correlation between the physical properties of the concrete or masonry member and the measured fire endurance as determined through testing in accordance with ASTM E 119, Standard Test Methods for Fire Tests of Building Construction and Materials (ASTM, 005b). The second method allows for direct measurement of the fire resistance of an element or assembly through testing in accordance with ASTM E 119. A third option, which is not explicitly covered by existing codes and standards, is to establish the fire-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 that must 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 transmission of heat through the assembly, which is measured by temperature rise on the non-fire-exposed side of the wall. This consistent mode of failure allows for a standardized calculation procedure to be derived as described below. Conversely, the fire-resistance rating of other construction assemblies, particularly those consisting of combustible materials, is often governed by one of the other performance criteria.

6 1-6 Concrete Construction Engineering Handbook u, in. 1 Carbonate AGG. reinforcing bars ω* = 0.1 ω = 0. 4 hr 1 Siliceous AGG. reinforcing bars 4hr 1 Lightweight AGG. reinforcing bars 4 hr u, mm u, in. 1 M/M n Carbonate AGG. cold-drawn steel ω p** = 0.1 ω p = 0. 4 hr 1 Siliceous AGG. cold -drawn steel 4 hr 1 M/M n M/M n Lightweight AGG. cold-drawn steel 4 hr u, mm M/M n M/M n M/M n * Reinforcement index for concrete beams reinforced with mild reinforcement: ω = A sfy /bdf c ** Reinforcement index for concrete beams reinforced with prestressing steel: ω p = A spfy /bdf c FIGURE 1.1 Fire resistance of concrete slabs. (From ACI Committee 16, Guide for Determining the Fire Endurance of Concrete Elements, ACI 16R, American Concrete Institute, Farmington Hills, MI, 001.) 1..1 Heat Transmission in Slabs The structural fire endurance of simply supported concrete slabs as affected by the constituent materials can be interpolated from Figure 1.1 by an effective concrete cover parameter (u) as a function of the moment ratio M/M n, where M is the design moment and M n is the nominal moment strength. In the usual case of continuous slabs and beams, a shift in the moment distribution develops, thereby increasing the stresses in the negative reinforcement resulting from the increase in the bending moments at the supports. During a fire, however, the negative reinforcement remains cooler than the positive reinforcement as it is often farther from the source of the fire. This in turn allows for an increase in the negative moment that can be accommodated (ACI Committee 16, 1997). Although the moment redistribution that results can be sufficient to result in yielding of the negative reinforcement, the resulting decrease in the positive moment in effect permits the beam or slab span to endure higher temperatures. The negative moment reinforcing bars must be long enough to accommodate the complete redistributed moments and the change of the location of the inflection points. At least 0% of the maximum negative moment reinforcement must be extended throughout the span (CEB/FIP, 1990). The fire-resistance rating of concrete slabs can also be increased through the use of undercoating, as described in ACI 16.1/TMS 016 (ACI Committee 16, 1997). 1.. Fire-Resistance Ratings of Single-Wythe Masonry Walls The fire-resistance rating of masonry walls, including single-wythe walls, multi-wythe walls, and walls with finish treatments, is based on the following criteria, which includes the effect of grouting and the effect of filling the cores of hollow units with recognized loose fill materials.

7 Fire Resistance and Protection of Structures 1-7 TABLE 1. Fire-Resistance Rating Period of Concrete Masonry Assemblies Aggregate Type in the Concrete Masonry Unit b Minimum Required Equivalent Thickness (in.) for Fire-Resistance Rating a 4 hr hr hr 1.5 hr 1 hr 0.75 hr 0.5 hr Calcareous or siliceous gravel Limestone, cinders, or slag Expanded clay, shale, or slate Expanded slag or pumice a Fire-resistance ratings between the hourly fire-resistance rating periods listed are determined by linear interpolation based on 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 combination of aggregates is determined by linear interpolation based on the percent by volume of each aggregate used in the manufacturing of the unit. TABLE 1. Fire-Resistance Rating of Clay Masonry Assemblies Material Type Minimum Required Equivalent Thickness (in.) for Fire-Resistance Rating a,b 1 hr hr hr 4 hr Solid brick of clay or shale c Hollow brick or tile of clay or shale, unfilled Hollow brick or tile of clay or shale, grouted or filled with perlite, vermiculite, or expanded shale aggregate 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 and the opposite face of the wall or between members set in from opposite sides should not be less than 9% 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 cores should be at least 75% of the gross cross-sectional area measured in the same plane Single-Wythe Concrete Masonry Walls The calculated fire-resistance rating of single-wythe concrete masonry assemblies is determined in accordance with Table 1.. These calculated fire-resistance ratings are derived from the requirements of ACI 16.1/TMS 016. The equivalent thickness (T ea ) of concrete masonry assemblies is based on the equivalent thickness of the masonry unit (T e ) plus the equivalent thickness of any recognized finish materials (T ef ) as follows: Tea = Te + Tef (1.1) The equivalent thickness (T e ) of a concrete masonry unit is the net volume of the unit divided by the face area of the unit (length times height). The equivalent thickness (T e ) of solid grouted masonry walls is the actual thickness of the unit. The equivalent thickness (T e ) of hollow masonry unit walls that are completely 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 (ASTM, 00) requirements; pumice, scoria, expanded shale, expanded clay, expanded slate, expanded slag, expanded fly ash, or cinders that comply with ASTM C 1 (ASTM, 005a); or perlite or vermiculite meeting the requirements of ASTM C 549 and ASTM C 516, respectively (ASTM, 00, 006) Single-Wythe Clay Masonry Walls The calculated fire-resistance rating of single-wythe clay masonry assemblies is determined in accordance with Table 1.. The equivalent thickness (T e ) of clay masonry assemblies is determined as follows: T = V LH e n (1.) As with concrete masonry assemblies, when solid grouted or when completely filled with approved loose fill materials, the equivalent thickness (T e ) of a clay masonry assembly is the actual thickness of the unit.

8 1-8 Concrete Construction Engineering Handbook TABLE 1.4 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 hr hr 4 hr Siliceous Carbonate Semi-lightweight Lightweight Single-Layer Concrete Walls, Floors, and Roofs The fire-resistance rating of plain and reinforced concrete walls, floors, and roofs that are a single layer in thickness are determined in accordance with Table 1.4 and are based on the equivalent thickness of the element. The equivalent thickness of solid concrete elements with flat surfaces is the actual thickness of the element. The equivalent thickness of hollow-core panels with a constant cross-section throughout their length is determined by dividing the net cross-sectional area by the panel width. The equivalent thickness of elements in which all of the core spaces are filled with grout or loose fill material, such as perlite, vermiculite, sand or expanded clay, shale, slag, or slate, should be the same as that of a solid wall or slab of the same type of concrete. The equivalent thickness for flanged elements in which the flanges taper 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 ribbed or undulating surfaces is determined as follows: Where the center-to-center spacing of ribs or undulations is not less than four times the minimum thickness, 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. The maximum thickness used to calculate the net cross-sectional area should not exceed two times the minimum thickness. Where the spacing of ribs or undulations exceeds two times the minimum thickness, but is less than four times the minimum thickness, calculate the equivalent thickness as follows: ( ) Equivalent thickness = t + ( 4t / s) 1 te t where: s = spacing of ribs or undulations (in.). t = minimum thickness (in.). t e = equivalent thickness calculated in accordance with Equation 1.. (1.) 1..4 Multiple-Layer Walls, Floors, and Roofs ACI 16.1/TMS 016 (ACI Committee 16, 1997) offers several alternatives to calculating the fireresistance 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 of concrete and clay masonry assemblies as part of a veneer or multi-wythe system. In addition to the material 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 16.1/TMS 016 for additional information on determination of the fire-resistance properties of multiple-layer concrete and masonry systems.

9 Fire Resistance and Protection of Structures 1-9 Joint reinforcement, as required Stop joint reinforcement at control joint Vertical reinforcement, as required Preformed gasket Concrete masonry sash unit Backer rod Sealant Backer rod Sealant FIGURE 1. Two-hour control joint. 1. Fire Protection of Joints 1..1 Masonry Elements Expansion or contraction joints in fire-rated concrete masonry wall assemblies and in clay brick wall assemblies are shown in Figure 1., Figure 1., and Figure 1.4. Figure 1. illustrates a standard control joint detail for a -hour fire-resistance rating, and Figure. and Figure.4 offer alternatives for 4-hour fire-resistance ratings. 1.. Precast Concrete Wall Panels and Slabs In wall panels where openings are not permitted or where it is required that openings be protected, joints must 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 joints is 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 minimum thickness of which is calculated in accordance with ACI 16.1/TMS 016 (ACI Committee 16, 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 equivalent slab thickness, provided that a concrete topping not less than 1 in. thick is used. Where a concrete topping is not used, joints should be grouted to a depth of at least one third the slab thickness at the joint, but not less than 1 in., or the fire-resistance rating of the floor or roof must be maintained by other approved methods.

10 1-10 Concrete Construction Engineering Handbook Joint reinforcement, as required Stop joint reinforcement at control joint Vertical reinforcement, as required Ceramic fiber felt (alumina silica fiber) Backer rod Sealant Backer rod Sealant FIGURE 1. Four-hour control joint. Joint reinforcement, as required Stop joint reinforcement at control joint Raked mortar joint Vertical reinforcement, as required Building paper or other bond break Sealant Backer rod Backer rod Building paper or other bond break Sealant FIGURE 1.4 Four-hour control joint.

11 Fire Resistance and Protection of Structures 1-11 TABLE 1.5 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 Siliceous or Carbonate Aggregate Concrete or Concrete Masonry Unit; Solid Clay Brick Masonry Type of Material Used in Slab or Wall Semi-Lightweight Concrete; Hollow Clay Brick; Clay Tile Lightweight Concrete; Concrete Masonry Units of Expanded Shale, Expanded Clay, Expanded Slag, or Pumice Less Than 0% Sand Portland cement sand plaster a or terrazzo Gypsum sand plaster Gypsum vermiculite or perlite plaster Gypsum wallboard a For Portland cement sand plaster 5/8 in. or less in thickness and applied directly to concrete or masonry on the nonfire-exposed side of the wall, the multiplying factor is Finish Treatments Finish treatments on concrete and masonry elements include gypsum drywall, terrazzo, or plaster. These treatments increase the fire-resistance rating of the element by delaying the temperature rise within or through the element when exposed to fire. The effect of this increase is based on whether the finish is applied 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 based on the lower rating determined from assuming that the fire exposure is from one side or the other. The fire-resistance rating of the element including the effect of finish treatments is limited to twice the fire rating of the element excluding the effect of finish treatments. Further, the effect of finish treatments from the non-fire-exposed side of the wall is limited to one half the fire-resistance rating of the element excluding the effect of finish treatments. Finishes that are assumed to contribute to the total fire-resistance rating of an assembly must meet the minimum installation requirements as prescribed in ACI 16.1/ TMS 016. Some finishes deteriorate more rapidly when exposed to fire than when installed on the non-exposed side of an assembly. For this reason, ACI 16.1/TMS 016 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 other side of the wall. Table 1.5 applies to finishes on the non-fire-exposed side of the wall, while Table 1.6 applies to finishes on the fire-exposed side. The resulting fire rating of the wall assembly is the smaller of the two calculated ratings. Note that in some situations the fire is assumed to occur only on one side of the wall. For finishes on the non-fire-exposed side of the wall, the finish is converted to equivalent thickness of concrete or masonry by multiplying the thickness of the finish by the factor given in Table 1.5. This is then added to the base equivalent thickness per Equation 1.1. For finishes on the fireexposed side of the wall, a time is assigned to the finish per Table 1.6, which is added to the fire-resistance rating determined for the base wall and non-fire-side finish. The additional times listed in Table 1.6 are essentially the length of time the various finishes will remain intact when directly exposed to fire. 1.5 Fire Resistance of Columns Reinforced Masonry Columns The fire-resistance rating of reinforced concrete and clay masonry columns is based on the least plan dimension of the column in accordance with the requirements of Table 1.7. The minimum cover for longitudinal reinforcement, measured from the outside surface of the reinforcement to the nearest outside surface of the masonry, is not permitted to be less than in.

12 1-1 Concrete Construction Engineering Handbook TABLE 1.6 Time Assigned to Finish Materials on Fire-Exposed Side of Concrete and Masonry Walls Finish Description Time (minutes) Gypsum wallboard /8-in. 10 1/-in. 15 5/8-in. 0 Two /8-in. layers 5 One /8-in. layer and one 1/-in. layer 5 Two 1/-in. layers 40 Type X gypsum wallboard 1/-in. 5 5/8-in. 40 Direct applied Portland cement sand plaster a Portland cement sand plaster on metal lath /4-in. 0 7/8-in. 5 1-in. 0 Gypsum sand plaster on /8-in. gypsum lath 1/-in. 5 5/8-in. 40 /4-in. 50 Gypsum sand plaster on metal lath /4-in. 50 7/8-in in. 80 a The fire-resistance rating of elements with Portland cement sand plaster finish treatment is determined by adding the actual thickness of the plaster or 5/8 in., whichever is smaller, to the equivalent thickness of the element. TABLE 1.7 Reinforced Masonry Columns Fire Resistance (hr) 1 4 Minimum column dimension (in.) TABLE 1.8 Minimum Concrete Column Size Aggregate Type Minimum Column Dimension for Fire-Resistance Rating (in.) 1 hr 1.5 hr hr hr 4 hr Carbonate Siliceous Semi-lightweight Reinforced-Concrete Columns The fire-resistance ratings of reinforced-concrete columns, both circular and rectangular, are determined in accordance with the requirements of Table 1.8. When a concrete column is exposed to fire on two parallel sides, additional requirements as prescribed in ACI 16.1/TMS 016 (ACI Committee 16, 1997) must be met. The minimum thickness of concrete cover to the longitudinal reinforcement in concrete columns should not be less than 1 in. times the number of hours of required fire resistance, or in., whichever is less.

13 Fire Resistance and Protection of Structures Steel Columns Protected by Masonry Because of its inherent fire-resistant properties, masonry is often used as a nonstructural fire-protection covering for structural steel members. The fire endurance of steel column protection is determined as the period of time for the average temperature of the steel to exceed 1000 F or for the temperature at any measured point to exceed 100 F (ASTM, 005b). These criteria depend on the thermal properties of the column cover and of the steel column. Accurate predictions of the fire endurance of protected steel columns are made possible by a numerical technique based on heat-flow analyses and research information on the thermal and rheological properties of masonry and steel at elevated temperatures (Lie and Harmathy, 197). Using this technique, an empirical formula was developed to predict the fire endurance of masonry-protected steel columns in accordance with ACI 16.1/TMS 016 (ACI Committee 16, 1997). The fire-resistance rating of structural steel columns protected by masonry is determined as follows: 07. R Ast p s Tea k cm ( A DT ). p+ T = ( ) + ( ) { st ea ( ea )} where: R = fire-resistance rating of the protected column assembly (hr). A st = cross-sectional area of the structural steel column (in. ). D = density of the masonry protection (lb/ft ). p = inner perimeter of the masonry protection (in.). p s = heated perimeter of steel column (in.), per Equations 1.5, 1.6, or 1.7. T ea = 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 (p s ) is determined as follows: 08. (1.4) p = ( b + d )+ b t ( ) s f st f w (1.5) For a pipe-section steel column, the heated perimeter (p s ) is determined as follows: p s =πd st (1.6) For a square-tube steel column, the heated perimeter (p s ) is determined as follows: where: b f = width of flange (in.). d st = column depth (in.). t w = thickness of web of W-section (in.). p s = 4d st (1.7) For use in Equation 1.4, the thermal conductivity of concrete masonry is: k = D. e (1.8) Likewise, the thermal conductivities of clay masonry are equal to: k = 1.5 BTU/hr ft F for a density of 10 lb/ft. k =.5 BTU/hr ft F for a density of 10 lb/ft. Steel Column Fire Protection (NCMA, 00) contains a comprehensive list of fire-resistance ratings for a wide variety of structural steel sections.

14 1-14 Concrete Construction Engineering Handbook TABLE 1.9 Reinforced Masonry Lintels Nominal Lintel Width (in.) Minimum Longitudinal Reinforcement Cover for Fire-Resistance Rating (in.) 1 hr hr hr 4 hr Not permitted Not permitted or more Fire Resistance of Lintels The fire-resistance rating of masonry lintels (beams spanning openings) is based on the nominal thickness of the lintel and the minimum provided cover for the longitudinal reinforcement as shown in Table 1.9. The cover is measured from the outside surface of the reinforcement to the nearest outside surface of masonry, which may consist of masonry units, grout, or mortar. References ACI Committee Standard Method for Determining Fire Resistance of Concrete and Masonry Construction Assemblies, ACI 16.1/TMS 016. American Concrete Institute, Farmington Hills, MI. ACI Committee Guide for Determining the Fire Endurance of Concrete Elements, ACI 16R. American Concrete Institute, Farmington Hills, MI. ACI Committee Building Code Requirements for Structural Concrete, ACI 18. American Concrete Institute, Farmington Hills, MI. ACI Committee Building Code Requirements for Masonry Structures, ACI 50/ASCE 5/TMS 40. The Masonry Society, Boulder, CO. ASTM. 00. Standard Specification for Vermiculite Loose Fill Thermal Insulation, ASTM C 516. ASTM International, West Conshohocken, PA. ASTM. 00. Standard Specification for Concrete Aggregates, ASTM C. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 005a. Standard Specification for Lightweight Aggregates for Concrete Masonry Units, ASTM C 1. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 005b. Standard Test Methods for Fire Tests of Building Construction and Materials, ASTM E 119. American Society for Testing and Materials, West Conshohocken, PA. ASTM Standard Specification for Perlite Loose Fill Insulation, ASTM C 549. American Society for Testing and Materials, West Conshohocken, PA. CEB-FIP Model Code for Concrete Structures. Comite Euro-International du Beton-Federation Internacionale de Precontraite, Paris. ICC International Fire Code (IFC). International Code Council, Falls Church, VA. Lie, T.T. and Harmathy, T.Z 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. 00. Steel Column Fire Protection, NCMA-TEK 7-6. National Concrete Masonry Association, Herndon, VA. NIST HAZARD I Fire Hazard Assessment Method, NIST Handbook 146. National Institute of Standards and Technology, Gaithersburg, MD. NFPA. 007a. Standard for the Installation of Sprinkler Systems, NFPA 1. National Fire Protection Association, Quincy, MA. NFPA. 007b. Standard for the Installation of Sprinkler Systems in Residential Occupancies Up to and Including Four Stories in Height, NFPA 1R. National Fire Protection Association, Quincy, MA.