Antoine N. Gergess

Cold Curving Steel Bridge Girders

Horizontally curved steel girders are extensively used in bridge construction. An overview on a new, innovative cold bending technique for curving steel girders, specifically developed to meet the tight construction tolerance requirements of the Miami, Florida, Metromover, is presented. The curving procedure used by the fabricator was retained and detailed analyses were developed to provide closed-form solutions relating loads to deformation for curving symmetrical, asymmetrical, stiffened, and unstiffened girders. This eliminates the trial-and-error nature of the operation in the steel shop. Limits are imposed on the maximum load and corresponding plastic strain to prevent damage. Numerical examples illustrate the application of the proposed method and suggestions for future work are made on how cold bending may be adapted for bridge use.

Simplified Analysis of Heat-Curved Steel Girders

Heat curving is commonly used in the fabrication of curved structural steel bridge girders. A two-dimensional superposition analysis known as the Duhamel Analogy was used for numerical modeling in the development of the AASHTO code provisions. This iterative analysis can take into consideration multiple heating–cooling cycles, initial residual stresses, temperature-dependent material properties, and the nonlinear temperature distribution across the girder cross section. A simplified analysis based on the Duhamel Analogy that can be carried out by using hand calculations is described. The curvatures obtained by this method are within 15% of the measured curvatures, which are very comparable to the results obtained by using the Duhamel Analogy or the three-dimensional, nonlinear, finite element solution. The background, basis, and steps required for the proposed analysis are described; and an illustrative numerical example is presented. The proposed analysis may be used to estimate curvatures or to determine the maximum fabrication temperature and the heating width for a single heating–cooling cycle for steels such as high-performance steel not covered by the current AASHTO provisions.

Numerical analysis of heat-curved I-girders

Abstract Heat curving is a practical and economical process used by steel fabricators for curving structural steel. In this method, the flange edges of a fabricated straight girder are asymmetrically heated to induce residual curvature on cooling. Available analytical methods for predicting the resulting residual stress, strain and curvature are complex and iterative because of the need to account for material and geometric non-linearity. This paper presents a single-step, non-iterative, numerical procedure for determining the effects of heat-curving on residual stress and strain based on a previously developed simplified analysis. Thermal equilibrium equations for idealized heating profiles are first recast in a general parametric form and then solved numerically for standard heating width and temperature using modern technical computing. The resulting solutions are expressed as polynomial functions to allow the solution space for the residual curvature to be graphically represented. Curvature predictions using this simplified approach are shown to be within 11% of measured values and within 5% of values obtained using more rigorous numerical methods.