SOIL STRUCTURE INTERACTION IN A CABLE STAYED BRIDGE

Abstract

A 4-lane cable stayed bridge having a tower in the middle of 100 m span was considered. A box section was assumed for deck. Four different arrangement- two radial and two harp were considered. Parametric study was carried out using 2-D static analysis, while soil structure interaction was carried out using 2-D dynamic analysis. Four different soil were considered- soft clay, silty clay, loose sand and dense sand. In each soil five different spring properties were adopted. Geometric non-linear behavior of cable was considered in each case. The static analysis parameters were taken, height of tower to total span ratio, effect of cable area, effect of flexural rigidity of girder and effect of flexural rigidity of tower. A total of 16 cases were studied for static analysis and total of 20 cases of soil stiffness variation, 16 cases of change in cable area and 16 cases change in flexural rigidity of deck were studied for dynamic analysis. Radial arrangement of cable is maximum optimum in view of minimum forces and deflection in the bridge. It is found girder deflection (19.8%), pylon moment (27.79%), cable tension (34.87%), negative girder moment (4.19%), positive girder moment (9.3%) are reduced. The area of all cable is increased from 0.01 m2 to 0.022 m2 and it was noticed that moment in tower and deck deflection are reduced. Flexural rigidity of deck_was changed from -25% to +25% and it was noticed that deck deflection reduced by 30.93%. and tower moment decreased by 31.80%. Flexural rigidity of tower was changed from -25% to +25% and it was noticed that tower moment increased by 43.47% and negative moment of deck increased by 31.44%.The effect of increase in soil stiffness as the frequency of vibration of tower in the first six modes is to increase it by about 20%. The effect of soft clay, silty clay, and loose sand is not significant on the frequency of vibration of the tower.