Load and resistance factors for prestressed concrete girder bridges
There has been a considerable progress in the reliability-based code development procedures. The load and resistance factors in the AASHTO bridge design code were determined using the statistical parameters from the 1970's and early 1980’s. Load and resistance factors were determined by first fixing the load factors and then calculating resistance factors. Load factors were selected so that the factored load corresponds to two standard deviations from the mean value and the resistance factors were calculated so that the reliability index is close to the target value. However, from the theoretical point of view, the load and resistance factors are to be determined as coordinates of the so-called “design point” that corresponds to less than two standard deviations from the mean. Therefore, the optimum load and resistance factors are about 10% lower than what is in the AASHTO LRFD Code. The objective of this paper is to revisit the original calibration and recalculate the load and resistance factors as coordinates of the “design point” for prestressed concrete girder bridges. The recommended new load and resistance factors provide a consistent reliability and a rational safety margin.
design point; design formula; prestressed concrete girders; resistance factor; reliability index; bridge live load; safety margin
AASHTO, Bridge Design Specifications, American Association of State Highway and Transportation Officials, Washington, D.C., 2014.
AASHTO, Bridge Design Specifications, American Association of State Highway and Transportation Officials, Washington, D.C., 2002.
AASHTO, Bridge Design Specifications, American Association of State Highway and Transportation Officials, Washington, D.C., 2016.
ACI 318-14, Building Code Requirements for Structural Concrete, American Concrete Institute, Farmington Hills, Michigan 2014.
AISC LRFD, Manual of Steel Construction: Load and Resistance Factor Design, 14th edition, American Institute Of Steel Construction Inc., Chicago, IL, 2011.
ASCE Standard 7, Minimum Design Loads for Buildings and Other Structures, American Society of Civil Engineers, Reston, VA, 2016.
National Design Specification for Wood, American Wood Council's (AWC), Leesburg, VA, 2015.
Ellingwood B., Galambos T. V., MacGregor J.G. and Cornell C.A., Development of a Probability Based Load Criterion for American National Standard A58. National Bureau of Standards, NBS Special Publication 577, Washington, D.C. 1980.
Nassif H. and Nowak A. S., “Dynamic Load Spectra for Girder Bridges”, Transportation Research Record, no. 1476, 1995, pp. 69-83.
Nowak A. S. and Collins K. R., Reliability of structures. CRC Press, New York 2013.
Nowak A. S. and Rakoczy A. M., “Statistical Resistance Models for R/C Structural Components”, in ACI SP-284-6, vol. 248, 2012, pp. 1-16.
Nowak A. S., “Calibration of LRFD Bridge Design Code, NCHRP Report 368”, in Transportation Research Board, Washington, DC 1999.
Nowak A. S., Rakoczy A. M. and Szeliga E., “Revised Statistical Resistance Models for R/C Structural Components”, in American Concrete Institute, SP-284, 2012, pp. 6-16.
Nowak A. S., Szerszen M. M., “Calibration of Design Code for Buildings (ACI 318) Part 1: Statistical Models for Resistance”, ACI Structural Journal, vol. 100, no. 3, 2003, pp. 377-382.
SHRP2 R19B, “Bridges for Service Life Beyond 100 Years: Service Limit State Design Final Report”, in Transportation Research Board, Washington, D.C., 2015.
Szerszen M. M. and Nowak A. S., “Calibration of Design Code for Buildings (ACI 318) Part 2: Reliability Analysis and Resistance Factors”, ACI Structural Journal, vol. 100, no. 3, 2003, pp. 383-391.
Rackwitz R. and Fiessler B., “Structural Reliability under Combined Random Load Sequences”, Computer and Structures, vol. 9, 1978, pp. 489-494.
Agarwal A. C. and Wolkowicz M., “Ontario Commercial Vehicle Survey 1975”, in Ontario Ministry of Transportation and Comunications, Interim Report, Engineering Research and Development Branch, 1976.
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Budownictwo i Architektura supports the open science program. The journal enables Open Access to their publications. Everyone can view, download and forward articles, provided that the terms of the license are respected.
Publishing of articles is possible after submitting a signed statement on the transfer of a license to the Journal.