AISC LRFD 1.pdf

88 EVALUATION BY LOAD TESTS [Sect. N4.N4. EVALUATION BY LOAD TESTS1. Determination of Live Load Rating by TestingTo determine the live load rating of an existing floor or roof structure by testing, atest load shall be applied incrementally in accordance with the Engineer of Record’splan. The structure shall be visually inspected for signs of distress or imminentfailure at each load level. Appropriate measures shall be taken if these or anyother unusual conditions are encountered.The tested design strength of the structure shall be taken as the maximum appliedtest load plus the in-situ dead load. The live load rating of a floor structure shall bedetermined by setting the tested design strength equal to 1.2D + 1.6L, where D is thenominal dead load and L is the nominal live load rating for the structure. The nominallive load rating of the floor structure shall not exceed that which can be calculatedusing applicable provisions of the specification. For roof structures, L r , S,orRas defined in the Symbols, shall be substituted for L. More severe load combinationsshall be used where required by applicable building codes.Periodic unloading shall be considered once the service load level is attained andafter the onset of inelastic structural behavior is identified to document the amountof permanent set and the magnitude of the inelastic deformations. Deformations ofthe structure, such as member deflections, shall be monitored at critical locationsduring the test, referenced to the initial position before loading. It shall be demonstrated,while maintaining maximum test load for one hour, that the deformation ofthe structure does not increase by more than 10 percent above that at the beginningof the holding period. It is permissible to repeat the sequence if necessary to demonstratecompliance.Deformations of the structure shall also be recorded 24 hours after the test loadingis removed to determine the amount of permanent set. Because the amount ofacceptable permanent deformation depends on the specific structure, no limit isspecified for permanent deformation at maximum loading. Where it is not feasibleto load test the entire structure, a segment or zone of not less than one complete bay,representative of the most critical conditions, shall be selected.2. Serviceability EvaluationWhen load tests are prescribed, the structure shall be loaded incrementally to theservice load level. Deformations shall be monitored for a period of one hour. Thestructure shall then be unloaded and the deformation recorded.N5. EVALUATION REPORTAfter the evaluation of an existing structure has been completed, the Engineer ofRecord shall prepare a report documenting the evaluation. The report shall indicatewhether the evaluation was performed by structural analysis, by load testing or by acombination of structural analysis and load testing. Furthermore, when testing isperformed, the report shall include the loads and load combination used and theload-deformation and time-deformation relationships observed. All relevant informationobtained from design drawing, mill test reports, and auxiliary material testingshall also be reported. Finally, the report shall indicate whether the designstrength of the structure, including all members and connections, is adequate towithstand the load effects.LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION