OPTIMUM DESIGN OF CONTINUOUS PLATE GIRDER WITH VARIABLE DEPTH

The need to protect our global environment, and to decrease the amount of embodied air emissions (carbon, sulphur and nitrogen oxides) for new steel structures, has called for the effective use of steel in construction. These besides the importance of plate girders in structural engineering for upholding high significance structures necessitate the must to find the best plate girder design in terms of both performance and economy. These can be accomplished by design optimisation. Hence, this work deals with the optimum design of continuous plate girder with variable depths. A nonlinear optimisation technique relied upon a Generalised Reduced Gradient method, embedded in Microsoft Excel Solver was utilised to find the minimum weight of continuous plate girder. This was achieved by finding the optimum web depth, span length and area of the continuous steel girder satisfying the ultimate and serviceability limit state requirements of BS 5950-1:2000 for different loads. A formulated optimisation procedure was applied in a case study in order to evaluate the efficiency of the proposed structural design formulation. The study results demonstrated that an increase in web plate depth translates to reduction in the girder cross sectional area, and by inference decrease in the girder weight. It was excitingly found that optimisation of continuous plate girder design can be more economical with a benefit of 18.81% reduction in the weight compared to the conventional design. This clearly illustrates the exciting promises of optimisation in continuous plate girder design. The study produces various design charts that can be utilized by structural engineers when designing long span buildings. Recommendations for future investigations were suggested.