Design And Seismic Performance Evaluation Of A High-rise RC Structure After Excavating And Adding Story Of The Basement

Under the influence of relatively scarce land resources, the large socialdevelopment requirements and other factors, most existing buildings face the urgentneed to improve its using functions which cannot be solved simply by the blinddemolition and reconstruction. A part of these building have adopted the lowerseismicfortificationcriterion than the existing standard with some even ignoring it.Therefore, the transformation of reinforcement and adding storey for these buildingsmeans a lot to mitigate the shortage of land resource, improve the using function ofbuildings, and enhance seismic performance.This paper takes a renovation project for storey-adding shopping mall ofChongqing as an example. It presents the appropriate and specific construction plan fordeep excavation and adding storey for the basement based on the actual conditions ofthis project and the characteristics of storey-adding basement. The paper alsodemonstrates the feasibility of the deep excavation and adding storey program in termsof bearing capacity of pile foundation after excavation, the overall anti-floating stabilityand the bearing capacity of exposed pile. Meanwhile, it uses the finite element analysissoftware to conduct static analysis and dynamic time-history analysis for theconstruction after excavation and the structure after transformation which is to evaluatethe seismic performance of the construction in different stages. Conclusions can bedrawn out as follows:①To use the method of top-down construction to excavate the storey-addingbasement under the existing structure. Firstly to upload the structure, then use theretaining piles to support the structure during construction, and pour the negative onefloor as the ancillary and horizontal support system for the one-time completion of theexcavation to the design surface.②The demands shall be met when it comes to check calculation of bearing capacityof pile foundation after excavation, the overall anti-floating stability and the bearingcapacity of exposed pile, then the program of deep excavation and adding story forbasement can be carried out feasibly and effectively.③The structure after excavation is in the elastic stage with the action of frequentearthquake, which can effectively avoid the damage to non-structural elements, andgood seismic performance can ensure the safety at the stage of construction. ④All the seismic performance indicators of the retrofitted structure are able to meetthe requirements of the current design codes, thus the structure can achieve the target ofseismic fortification “No damage after weak earthquake, being repairable after moderateearthquake, and no collapsing after strong earthquake”. Meanwhile, this paper proposesto regard the1st and8th floor as the weak floor, and the seismic fortification measuresshould be strengthened in the design of adding storey and strengthening works.