Practical Optimization of Steel Highway Bridge Beams.

WITH DIGITAL COMPUTERS, THE NUMBER OF STRUCTURAL CONFIGURATIONS THAT CAN BE INVESTIGATED HAS BEEN GREATLY INCREASED, AND THE DEVELOPMENT OF OPTIMUM DESIGNS HAS BECOME PRACTICAL. A COMPUTER PROGRAM REFERRED TO AS GIRDER AUTOMATED DESIGN-I (GAD-I) IS AVAILABLE FOR THE DESIGN OF NONCOMPOSITE WELDED PLATE GIRDER BRIDGES. THERE EXISTS THE POSSIBILITY, PARTICULARLY IN THE CASE OF RELATIVELY SHORT SPANS, THAT A MORE ECONOMICAL STRUCTURE COULD BE CONSTRUCTED BY USING ROLLED STEEL BEAMS WITH COVER PLATES, IF REQUIRED, IN COMPOSITE OR NONCOMPOSITE CONSTRUCTION. THE COMPUTER PROGRAM DESCRIBED IN THIS PAPER WAS DEVELOPED FOR DESIGNING SUCH ROLLED-BEAM BRIDGES FOR REQUIRED STATIC AND FATIGUE HIGHWAY LOADS. THE PROGRAM WILL HANDLE EITHER SIMPLE-SPAN GIRDERS OR CONTINUOUS STRUCTURES UP TO FOUR SPANS. THE ANALYSIS IS CARRIED OUT BY CALCULATING INFLUENCE COEFFICIENTS AT A SPECIFIED NUMBER OF ANALYSIS POINTS, EQUALLY SPACED IN EACH SPAN. INITIALLY, A CONSTANT MOMENT OF INERTIA THROUGHOUT THE LENGTH OF THE BRIDGE IS ASSUMED. LOADINGS CONSIDERED INCLUDE AASHO TRUCK AND LANE LOADINGS, INTERSTATE MILITARY LOAD, PEDESTRIAN WALKWAYS IF PROVIDED, AND DEAD-LOAD CONDITIONS. THE SHEARS AND MOMENTS AT THE ANALYSIS POINTS ARE USED FOR DETERMINING THE GOVERNING SHEAR AND MOMENT FOR THE ELEMENTS OF THE MEMBER BETWEEN EACH PAIR OF ADJACENT ANALYSIS POINTS. INITIALLY, STRESSES ARE COMPUTED FOR EACH ELEMENT BY USING THE HEAVIEST AVAILABLE ROLLED SECTION. IF THE STRESSES VIOLATE THE AASHO SPECIFICATION, AN ATTEMPT IS MADE TO ELIMINATE THESE VIOLATIONS BY THE ADDITION OF COVER PLATES. IN THE ADDITION OF COVER PLATES, REQUIREMENTS ON EXTENSION BEYOND THEORETICAL CUTOFF POINTS AND MINIMUM COVER-PLATE LENGTH REQUIREMENTS ARE CONSIDERED. THE COMPUTER PROGRAM FOR THE DESIGN OF ROLLED-SECTION BEAM BRIDGES CONSISTS OF A MAIN PROGRAM AND 34 SUBROUTINES. THE MAIN PROGRAM CALLS THE SUBROUTINES IN THE CORRECT SEQUENCE FOR READING DATA, PERFORMING AN INITIAL ANALYSIS, AND SELECTING THE MOST ECONOMICAL SECTION. AFTER THE FINAL DESIGN IS OBTAINED, DEFLECTIONS ARE CALCULATED, AND DESIGN DETAILS ARE PRINTED ALONG WITH THE ESTIMATED COST. AN OPTION IS AVAILABLE TO DESIGN ON THE BASIS OF EITHER LEAST COST OR LEAST WEIGHT.