Analysis of cable-stayed bridges to earthquake loads

. The aim of this study is to analyze cable-stayed bridges subjected to seismic ground motions by means of computer. A computer program is developed using the Newmark-f3 method as one of the numerical methods to evaluate the general equations of motion based on the linear acceleration concept. Ghamra cable-stayed bridge is selected as a case study to be dynamically analyzed and its _ stability is examined during ground motions. To perform such analysis, the bridge is modeled as a 2-D multi-degree of freedom system where cables are modeled as link members with equivalent modulus of elasticity. The general equations ofmotion are formulated in such away to make it possible to take into consideration the uniform earthquake input.The parameters of the bridge elements are computed referring to the general property matrices for multi-degree of freedom systems. These parameters are the global stiffness matrix, the global mass matrix, the damping matrix and the eigenvalues. The analysis of the bridge is performed by the application of five earthquake records. The peak acceleration and the frequency content of these earthquakes are different and they are scaled so that they all have the same peak acceleration.By the application of the five earthquakes it was possible to judge the behavior of the bridge under seismic ground motions by comparing the resulting straining actions of its different elements and their nominal capacities.A computer program is developed to obtain the response of cablestayed bridges as a multi-degree of freedom system using the Newmark-13 method. Ghamra Cable-Stayed Bridge is used as a case study to be analyzed and to check its stability against ground motions by the computer program. The natural periods of the bridge are obtained and the forces in certain elements are computed.Based on the analysis process performed on Ghamra Cable-Stayed Bridge using different earthquake records, the following conclusions and remarks can be made:1. The bridge in General:• Using the frrst principles and the PCACOL program to determine the nominal capacities of the bridge elements under the effect of earthquakes only and comparing them with the resulting straining