THICKNESS DETERMINATION FOR SPRAY-APPLIED FIRE …

1 Following The World TradeCenter disaster, a review ofcurrent design practices hascommenced with hope thatout of the tragedy somethingmay be gleaned that could influencemore effective new building is a legitimate area offocus. There is little debate that a morerational approach to fire protection ispossible than our current reliance onthe prescriptive method using testedassemblies. Efforts are being expend-ed to formulate a rational approach forevaluating the performance of steelstructures in a fire environment and amore rational performance basedapproach to fire protection is certainlyon the horizon.

2 Nonetheless, thedesign team is faced with providingfire-safe buildings under currentguidelines. This paper addresses themethod for determining the thicknessof SPRAY-APPLIED fire resistive materialbased on the current prescriptive the material properties, theyield strength and elastic modulus ofconstruction materials (steel and con-crete), the properties that influencestrength and deformation, are reducedat elevated temperatures. Therefore,insulation is applied to extend the timethat steel structures can sustain load atelevated temperatures.

3 The time thestructural system is required to endurea fire is influenced by building area,height, use and occupancy and isdirected by the applicable buildingcode. The amount and type of insula-tion is determined through testing, ormore commonly by referencing exist-ing test data for assemblies similar tothose intended in the can be provided in manyforms including masonry or concreteencasement, gypsum board wrap-pings, insulation board enclosures,intumescent coatings and SPRAY-APPLIED fire resistive materials. Themost common form of insulation for astructural steel assembly is a SPRAY-APPLIED fire resistive material.

4 SPRAY-APPLIED fire resistive materials use abinder, generally gypsum or Portlandcement, that is mixed with insulatingmaterials to form a slurry or mixed at anozzle and SPRAY-APPLIED . Cafco300 , manufactured by Isolatek and Monocote MK-6 , manufactured byW. R. Grace, are examples of slurrybased insulating materials. BlazeShield , manufactured by Isolatek, isan example of a nozzle mixed SPRAY-APPLIED THICKNESS of SPRAY-APPLIED fireresistive material needed to producethe building code dictated duration offire endurance is determined by test-ing.

5 Beams supporting slab construc-tion representing the constructionintended in the actual building arecoated with a specific THICKNESS ofspray-applied fire resistive materialand tested over a furnace. Since itwould be impractical to test all thesteel sections to be used in the actualbuilding along with a full range ofspray-applied fire resistive materialthicknesses, procedures have beendeveloped that facilitate adjusting thespray-applied fire resistive materialthickness used on the tested beam todetermine the THICKNESS required inthe real structure.

6 The purpose here isto clarify the correct application of theequation for adjustment of SPRAY-APPLIED fire protection material thick-ness. STANDARD FIRE TESTFire tests are performed in accordancewith ASTM E-119 [1]. A slab system,the same as anticipated in the building,is constructed over supporting beamsabove a furnace. The beams are instru-mented with thermal couples, protect-ed with SPRAY-APPLIED fire resistivematerial and shimmed tight to aperimeter frame and the assemblyplaced over the furnace. All assem-blies are tested fully loaded andJohn L.

7 Ruddy is Chief OperatingOfficer and Principal, StructuralAffiliates International, Inc., Nashville, A. Ioannides is President,Structural Affiliates International, Inc.,Nashville, DETERMINATION FOR SPRAY-APPLIED FIRE RESISTIVE MATERIALSM odern Steel Construction April 2002 Preview!restrained against the test , a single test is used to deter-mine two conditions of thermalrestraint of the structural system,restrained and unrestrained . Thermalrestraint is defined as the conditionwhen the surrounding or supportingstructure is capable of resisting sub-stantial thermal expansion throughoutthe range of anticipated elevated tem-peratures.

8 The supports of a thermallyunrestrained condition are free torotate and expand. Except in unusualconditions, steel framed structures arethermally restrained [2].A fire is ignited within the furnaceand controlled to follow a standardtime temperature relationship (stan-dard fire). The fire is continued and thethermal couple readings are time when either the average steeltemperature reaches 1100 F or any onelocation reaches 1300 F is time establishes the unrestrainedassembly and unrestrained beam rat-ing as long as the temperature on thenon-fired side has not been raisedmore than 250 F or cotton balls on thenon-fire side have not ignited.

9 Thestandard fire is continued and a secondtime recorded when any one of the fol-lowing conditions occurs; the load canno longer be supported, the tempera-ture on the non-fired side has raisedmore than 250 F or cotton balls on thenon-fire side have ignited. If this sec-ond time exceeds twice the unre-strained time then twice the unre-strained time is recorded as therestrained assembly rating otherwisethe second time is recorded as therestrained assembly rating. A provi-sion in establishing the restrained rat-ing of an assembly is that the tempera-ture limits (1100 F and 1300 F) not beexceeded at one-half the restrained rat-ing time or one hour whichever isgreater.

10 Therefore, for the case of aone-hour fire resistance rating, thespray-applied fire resistive materialthickness is independent of arestrained or unrestrained rating. The plot of temperature versus timedepicted in Figure 1 is a simplifiedgraphic of the application of ASTME119 in determining the fire resistancerating for restrained and SUBSTITUTIONThe beams used in the fire test will sel-dom match the steel sections used inthe actual building. However, thethickness of SPRAY-APPLIED fire resis-tive material applied to the test beamcan be used as a basis for calculatingthe THICKNESS to be used on the substi-tute beam.