Keywords: finite element, heat curving, HPS485W, three-dimensional, temperature.

Heat curving is commonly used for fabricating structural steel girders in horizontally curved bridges. In this method, the top and bottom flanges of a straight fabricated girder are continuously or intermittently (V-heating) heated along one edge at temperatures above the re-crystallization or work-hardening range.

Current US criteria (AASHTO) is outdated; it is based on research conducted more than thirty years ago for steels having yield stress of 345 MPa and lower, thus precluding newly developed high performance steel (HPS 485W) that has a yield stress of 485 MPa, and has been successfully used in many bridge projects in the US. This criteria limits the maximum heating temperature to 621^oC and the heated width to 1/4 of the flange width. The "Guide for Highway Bridge Fabrication with HPS 70W Steel" recommends investigating heat curving of HPS 485W steel at 705^oC.

The main objective of this paper is to evaluate the validity of this higher temperature limit for HPS girders on the basis of previous numerical analysis and experimental results. Three-dimensional finite element modelling incorporating geometric and material non-linearity is used for this purpose by NASTRAN (MSC/NASTRAN 2000) computer software. The model built accurately idealizes the girder geometry, stiffness, initial residual stresses, support conditions, temperature loading and temperature-dependent material properties. First, the finite element model is calibrated based on the parameters of the earlier test results for the Grade 250 test girder. Second, the calibrated model is used to investigate the effect of recommended increased temperatures on a geometrically identical HPS girder.

The results from this paper clearly point to the need for using higher temperatures for heat curving HPS 485W sections. The analysis suggests that the optimal maximum temperature to be set at 649^oC, (larger than the current limit of 621^oC, but smaller than the AASHTO recommended limit of 705^oC). As this temperature does not affect base strength, consideration should be given to its future adoption for use in HPS 485W sections.

1

American Association of State Highway and Transportation Officials (AASHTO), "Standard Specifications for Highway Bridges", 16th Edition, Washington, DC, 1996.

2

American Association of State Highway and Transportation Officials (AASHTO), "Guide for Highway Bridge Fabrication With HPS 70W Steel" Adopted by AASHTO Subcommittee on Bridges and Structures, San Diego, CA, 2000.

3

Brockenbrough, R.L., "Theoretical Stresses and Strains from Heat-Curving". ASCE, Journal of Structural Division, July, vol. 96, no. ST7, pp. 1421-1444, 1970.

4

Brockenbrough, R.L., "Experimental Stresses and Strains from Heat-Curving". ASCE, Journal of Structural Division, July, vol. 96, no. ST7, pp. 1305-1331, 1970.

5

MSC/NASTRAN for Windows, The MacNeal-Schwendler Corporation, "Finite Element Modeling and Postprocessing System", Los Angeles, California, 2000.

6

Brockenbrough R.L., Merrit F.S., "Structural Steel Designer's Handbook", 3rd Edition, McGraw-Hill, NY, NY, 1999.

7

Brockenbrough, R.L., "Investigation of Heat-Curved Girders". American Association State Highway Officials, December, pp. 209-253, 1968.

8

Gergess A., "Curving of Structural Steel Girders", PhD Dissertation in preparation, Department of Civil and Environmental Engineering, University of South Florida, Tampa, FL, 2001.

9

Sen R., Gergess A. and Issa C., "Finite Element Modelling of Heat-Curved I-Girders", ASCE, Journal of Bridge Engineering, Vol.8, No. 3, May/June 2003, pp. 153-161, 2003. doi:10.1061/(ASCE)1084-0702(2003)8:3(153)

10

Gergess A. and Sen R., "Simplified Heat Curving Analysis", Journal of the Transportation Research Board, No. 1861, pp. 101-114, 2003. doi:10.3141/1861-11

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