Analysis, design & cost comparisons of simply supported and continuous bridges

This study was undertaken to compare the design and -cost of simply supported and continuous bridges. Type of bridge selected is deck girder bridge where the girders are precast, prestressed of pretension system. All the spans in a given bridge were of equal length. Three different spans namely 20, 30 & 40m were considered. Different load cases were considered and analyzed using Finite Element Method to identify both, the critical load cases, in which the maximum forces occur, and the maximum design forces on which the design is based. Design of pretensioned SY- beams, slabs and diaphragms were carried out either using ready-made packages or manually. The cost of the bridges was estimated manually. The effect of temperature differences & non-uniform support settlements on the design and cost of these bridges were examined at seven levels of temperature differences and six settlement conditions. It was observed that for a given span, moments in both simply supported and continuous bridges were maximum at similar loaded spans. If the bridges are designed for the primary force effects induced due to dead and live loads only, the continuous types are of lower cost compared to the simply supported types. The cost difference between the two types decreases as bridge span increases. In a continuous beam deck, non-linear temperature distribution across the deck depth and differential settlement of supports, cause additional sagging & hogging moments as well as shear forces, resulting in higher costs, and the economical superiority of continuous types vanishes at a certain temperature change or support settlement level. The effect of differential settlement is more pronounced than that of temperature changes.

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