فهرست مطالب مهدی فرج محمدیه

Excavation of tunnels can cause the earth to move, which is significant in the static and dynamic response of structures. In this study, the effect of a tunnel excavation in Tehran city on the dynamic and static response of structures in three section has been investigated. In the first part, PLAXIS software calculates the following two step session before and after excavating. The second part of PLAXIS also performs dynamic analysis for both stages and the following acceleration response is calculated. The purpose of the second part is to investigate the impact of excavating on acceleration response and its use in SAP 2000 software as input for structural analysis. In the third part, structure in modeled in SAP 2000 software and the results of the first part of the displacements of footing are applied and by using accelerating response, the structure`s nonlinear dynamic analysis is performed in two stages (PLAXIS output). The results of the analysis show that the tunnel excavation has increased the subsidence of foundation subsurface and the highest subsidence is in 6th model (Operation stage), which is 1.2 times the average of the previous one. The excavation has increased and the impact of the supporting structures during the execution phase compared to the operation stage where the concrete side walls are executed, has been effective in reducing the subsidence by 4% and maximizing the acceleration below 1.5 times and also in the structures the displacement increased by 1.25 times compared to the pre excavation phase response.

In this paper the effects of deep excavation on seismic vulnerability of existing buildings are investigated. It is well known that deep excavations induce significant changes both in stress and strain fields of the soil around them, causing a displacement field which can modify both the static and dynamic responses of existing buildings. A FEM model of a real case study, which takes into account geometry, non-linear soil behavior, live and dead loads, boundary conditions and soil–structure interaction, has been developed in order to estimate the soil displacements and their effects on seismic behavior of a reinforced concrete framed system close to deep excavation. Along with increasing urban activities, and developing underground facilities, subway stations, parking spaces and other underground structures, excavations made with various depths in urban areas around existing structures has been turn into an inevitable issue. The excavations cause significant changes in the stress and strain fields of the soil under the existing building foundations and finally result in horizontal and vertical displacements under the foundation as well as large changes in static and dynamic response of existing structures. The main objective in the present study is in particular to investigate the above-mentioned problems using a study performed on 4 types of soil as classified in 2800 earthquake regulations with a model of deep excavation in the vicinity of a steel framed building. In this study in order to evaluate the effect of deep excavation on seismic vulnerability of existing buildings, the required analyses has been carried out in three parts and using PLAXIS and SAP 2000. Nonlinear dynamic analysis of soil has been performed using PLAXIS software in which due to its inability to perform nonlinear dynamic structural analysis, the SAP 2000 software is used for nonlinear dynamic analysis. In the first part of the study, using PLAXIS software for conducting the static analysis horizontal and vertical displacements under the foundation subjected to dead and live load have been calculated in two stages before and after the excavation. In the second part, using PLAXIS software, dynamic analysis has been conducted for both mentioned stages with the application of ten scaled records which are chosen based on the model of each site. Afterwards, the acceleration response under the foundation is calculated. This part aims to evaluate the effect of excavation on the acceleration response and use it as an input for structural analysis in SAP 2000 software. In the third part, the structure is modeled in SAP 2000 software, the displacements resulted from the first part are applied to the foundation and using the acceleration response (output of PLAXIS), nonlinear dynamic analysis of the structure is conducted in two stages. The results indicate that the excavation made in all models causes the increased horizontal and vertical displacements. Therefore, both increasing the excavation depth and performing struts, vertical displacements and horizontal displacements increase by a smaller and bigger percentage change, respectively. The acceleration response under the foundation in soil types 1, 2, 3, and 4 increases 51%, 35%, 66% and 27%, respectively. In addition, the maximum displacement of the structure increases 1.6, 1.3, 1.9 and 2.5 times more compared to that before excavation, respectively.