Seismic Reliability of Bridge With Considering Soil-Structure Interaction

رشید جابلو, علی and محبی, دکتر محتشم and رحمن شکرگزار, دکتر حامد and ایمانی, دکتر هوشیار (2019) Seismic Reliability of Bridge With Considering Soil-Structure Interaction. Masters thesis, University of Mohaghegh Ardabili.

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Abstract

Research Aim: Bridges are considered as important structures, so studying the seismic behavior of bridges is essential and may be more vulnerable in soft soil conditions. The uncertainty of the structural parameters and the indeterminacy of the earthquake force is a reason to consider the uncertainty in members of the structure, soil and earthquake. In this research, the reliability of the bridge structure is investigated considering the interaction of the soil-structure with the actual soil behavior. Due to the fact that under earthquake and uncertainty, important parameters in structure behavior and parameters in the soil can lead to different responses of the structure, therefore, using probabilistic theory and reliability, evaluated the effect of these parameters on the behavior of the bridge. Research method: In this study, a cable with a 640 meter span length modeled in the Opensees software, in three models with linear and nonlinear materials with fixed support and non-linear model with soil-pile-structure interaction in three dimensions. Dynamic time history analysis performed by a series of artificial earthquake records with the consideration of uncertainty in structural parameters including uncertainty in members of the cables, girders, towers, pile diameter and uncertainty in soil parameters including friction angle, shear strength, unit weight of the soil. Samples produced for each of the parameters were generated by the Latin Hyper Cube method, and the dynamic analysis time histories, and the serviceability limite state and the strength limit state were performed. Findings: Based on the analysis, it can be concluded that in linear model with fixed support compared nonlinear model with fixed support and non-linear model with soil-pile-structure interaction due to the high stiffness of the deck in members such as cable and girder during the earthquake, there is not a lot of force, but the towers will bear a lot of force. In the nonlinear model, with the interaction of the soil-pile-structure, the stiffness of cable stayed bridge is reduced and more force is applied to the cables and girders, and instead the force applied to the tower during earthquake reduce compare with the model with fixed support. Also, with the reduction of the stiffness and ductility of the cable-stayed bridge, it becomes more sensitive to severe earthquakes. The results of the sensitivity analysis indicate that the important parameters affecting the cable-stayed bridge are the modulus of elasticity and the cross section of the cables and the density of the concrete slab and the important parameters in the soil, including the angle of friction and shear strength. Conclusion: The results show that the probability of failure of the system and component in the nonlinear model with the interaction of soil-pile-structure is greater than fixed support models. Also, linear model with fixed support, has lowest the probability of failure. In general, the results show that the cable bridge has a low seismic reliability versus earthquake.

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