Load factor calibration for the proposed 2005 edition of the National ...

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438 Can. J. Civ. Eng. Vol. 30, 2003Table 8. Summary of statistical parameters for loads.Load type Bias CoV Distribution typeDead load 1.050 0.100 NormalUse and occupancy live load50 year maximum load 0.900 0.170 GumbelPoint-in-time load 0.273 0.674 WeibullTransformation to load effect 1.000 0.206 NormalWind load (1 in 50 year specified)50 year maximum velocityRegina 1.039 0.081 GumbelRivière du Loup 1.054 0.112 GumbelHalifax 1.049 0.103 GumbelPoint-in-time velocityRegina 0.156 0.716 WeibullRivière du Loup 0.064 1.149 WeibullHalifax 0.084 1.001 WeibullTransformation to load effect 0.680 0.220 Log-normalSnow load (1 in 50 year specified)50 year maximum depth 1.100 0.200 GumbelPoint-in-time depth 0.196 0.882 WeibullDensity 1.000 0.170 NormalTransformation to load effect 0.600 0.420 Log-normalquate unless the dead load is dominated by thin, cast-inplaceconcrete toppings. Statistical parameters for live loaddue to use and occupancy were derived that pertain specificallyto the live reduction factor equation used in the NBCC.Statistics for snow and wind loads were normalized usingthe 1 in 50 year values that will be specified in the 2005NBCC. New statistical parameters were determined for thefactors that transform wind or snow loads to the force effectbecause of these loads.AcknowledgementsPrimary funding for this study from the National ResearchCouncil of Canada Institute for Research in Construction isgratefully acknowledged. Additional funding from the NaturalSciences and Engineering Research Council of Canadaand the Steel Structures Education Foundation is also acknowledged.The Engineering Climatology Section of theCanadian Meteorological Centre in Downsview providedenvironmental data and very helpful assistance concerningtheir interpretation. The authors gratefully acknowledgecomments and suggestions from the National Building Codeof Canada Part 4 Task Group on Snow and Wind Loads:D.E. Allen (Chair), P. Chan, P.A. Irwin, P. Jarrett,D.J.L. Kennedy, J.G. MacGregor, A. Metton, R.S. Riffell,R.G. Sexsmith, C. Taraschuk, and A. Wong. The opinionsexpressed in this paper are those of the authors, however,and not necessarily those of the Task Group.ReferencesAISC. 1986. Specification for structural steel buildings — load andresistance factor design. American Institute of Steel Construction(AISC), Chicago, Ill.Allen, D.E. 1975. Limit states design — a probabilistic study. CanadianJournal of Civil Engineering, 2: 36–49.ASCE. 2000. Minimum design loads for buildings and other structures(ASCE7-98). American Society of Civil Engineers(ASCE), Reston, Va.CEB. 1976. Common unified rules of different types of constructionand material. Vol. 1. Bulletin d’Information No. 116-E,Comité Euro-International du Béton, Paris, France.Chalk, P.L., and Corotis, R.B. 1980. A probability model fordesign live loads. ASCE Journal of the Structural Division,106(ST10): 2017–2033.CSA. 1995. Limit states design of steel structures. Standard CSA-S16.1-95, Canadian Standards Association, Rexdale, Ont.CSA. 2000. Concrete materials and methods of construction. StandardCSA-A23.1-00, Canadian Standards Association, Rexdale, Ont.Davenport, A.G. 1981. Some attributes of the wind load requirementsof the National Building Code of Canada. In Proceedingsof the Canadian Conference on Wind Engineering, Vancouver,B.C., 13–14 April. pp. 1–12.Davenport, A.G. 1982. On the assessment of the reliability of windloading on low buildings. In Proceedings of the 5th Colloquiumon Industrial Aerodynamics, Aachen, Germany, 14–16 June.Davenport, A.G. 2000. A comparison of seismic and windstormhazards. In Proceedings of the 6th Environmental SpecialtyConference of the Canadian Society for Civil Engineering, 7–10June 2000, London, Ont. Canadian Society for Civil Engineering,Montréal, Que. pp. 504–509.Ellingwood, B.R. 1999. A comparison of general design and loadrequirements in building codes in Canada, Mexico and theUnited States. In Proceedings of the North American Steel ConstructionConference, Toronto, Ont., 19–21 May. American Instituteof Steel Construction Inc., Chicago, Ill. pp. 12-1–12-27.Ellingwood, B.R., and Culver, C. 1977. Analysis of live loads inoffice buildings. ASCE Journal of the Structural Division,103(ST8): 1551–1560.Ellingwood, B., and O’Rourke, M. 1985. Probabilistic models ofsnow loads on structures. Structural Safety, 2: 291–299.Ellingwood, B.R., and Tekie, P.B. 1999. Wind load statistics forprobability-based structural design. ASCE Journal of StructuralEngineering, 125(4): 453–464.© 2003 NRC Canada
Bartlett et al. 439Ellingwood, B.R., Galambos, T.V., MacGregor, J.G., andCornell, C.A. 1980. Development of a probability based loadcriterion for American National Standard A58. NBS SpecialPublication 577, National Bureau of Standards, U.S. Departmentof Commerce, Washington, D.C.European Committee for Standardization. 1994. ENV 1991-1:1994 Eurocode 1: basis of design and actions on structures —Part 1: basis of design. European Committee for Standardization,Brussels, Belgium.Kariyawasam, S.N. 1996. Development of probability based resistancefactors and companion-action load factors for concrete designin Canada. Ph.D. thesis, University of Alberta, Edmonton,Alta.Kariyawasam, S.N., Rogowsky, D.M., and MacGregor, J.G. 1997.Resistance factors and companion-action load factors for reinforcedconcrete building design in Canada. Canadian Journal ofCivil Engineering, 24: 593–602.Kemp, A.R., Mahachi, J., and Milford, R. 1998. Developing LRFDcodes in South Africa. In Proceedings of the Structural EngineersWorld Congress, San Francisco, Calif. 19–23 July. ReferenceP315-3.MacGregor, J.G. 1976. Safety and limit states design for reinforcedconcrete. Canadian Journal of Civil Engineering, 3: 484–513.MacGregor, J.G., Kennedy, D.J.L., Bartlett, F.M., Chernenko, D.,Maes, M.A., and Dunaszegi, L. 1997. Design criteria and loadand resistance factors for the Confederation Bridge. CanadianJournal of Civil Engineering, 24: 882–897.NBCC. 1995. National Building Code of Canada. Institute for Researchin Construction, National Research Council of Canada,Ottawa, Ont.Newark, M.J. 1984. A new look at ground snow loads in Canada.In Proceedings of the Eastern Snow Conference, 41st AnnualMeeting, Washington, D.C. Vol. 29, pp. 37–48.Newmark, M.J., Welsh, L.E., Morris, R.J., and Dnes, W.V. 1989.Revised ground snow loads for the 1990 National Building Codeof Canada. Canadian Journal of Civil Engineering, 16: 267–278.Nowak, A.S., and Lind, N.C. 1979. Practical code calibration procedures.Canadian Journal of Civil Engineering, 6: 112–119.O’Rourke, M.J., Redfield, R., and Von Bradsky, P. 1982. Uniformsnow loads on structures. ASCE Journal of the Structural Division,108(ST12): 2781–2798.Peir, J.C., and Cornell, C.A. 1973. Spatial and temporal variabilityof live loads. ASCE Journal of the Structural Division, 99(ST5):903–922.Rosowsky, D.V., and Cheng, N. 1999. Reliability of light-frameroofs in high-wind regions. ASCE Journal of Structural Engineering,125(7): 725–733.South Africa Bureau of Standards. 1989. The general proceduresand loadings to be adopted in the design of buildings: SABS0160:1989. South Africa Bureau of Standards, Pretoria, SouthAfrica.Standards Association of Australia. 1985. Guidelines for conversionto limit states codes, Committee BD16 — Loading ofStructures. Standards Association of Australia, Canberra, Australia.Tabsh, S.W. 1997. Safety of reinforced concrete members designedfollowing ACI 318 building code. Engineering Structures,19(10): 843–850.Taylor, D.A., and Allen, D.E. 2000. Statistical variation and durationof snow load on flat roofs in Canada. Institute for Researchin Construction, National Research Council of Canada, Ottawa,Ont. Unpublished study.Turkstra, C.J. 1972. Theory of structural design decisions. SolidMechanics Study 2, University of Waterloo, Waterloo, Ont.Wen, Y.K. 1990. Structural load modelling and combination forperformance and safety evaluation. Elsevier, Amsterdam, TheNetherlands.List of symbolsA I influence areaB tributary areaC a snow accumulation factorC b basic roof snow load factorC e exposure factor for wind loadC g gust factor for wind loadC gr ground-to-roof snow load transformation factorC p external pressure coefficient for wind loadC s slope factor for snow loadC w wind exposure factor for snow loadCoV coefficient of variationCoV a coefficient of variation of annual maximum loadd snow depthE wind exposure factorL live load due to use and occupancyI max mean 50 year maximum live load due to use and occupancyn number of roofs in the samplep wind pressureP effect due to permanent loadq reference velocity pressureq T reference wind pressure with T year return periodS snow loadS i principal transient loadS j companion-action transient loadS r rain load associated with ground snow loadS s ground snow loadT return period or thermal characteristic factorV T wind velocity with 50 year return periodV max mean 50 year maximum wind velocityV 50 with 50 year return period wind velocityα load factorα i load factor applied to the effects due to the principaltransient loadα ij load factor applied to the companion-action transientloadsα P load factor applied to the effects due to permanent loadsuch as dead loadγ unit weight of snow∆ maximum excess thickness of cast-in-place toppingε error term in ground to roof snow load transformationfactorρ density2σ Lmax variance of 50 year maximum live load due to use andoccupancy© 2003 NRC Canada
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