Research On The Retrofit Performance Of Existing Buildings

With the issue and implementation of “Seismic ground motion parameter zonation map of the 5th generation in China”,the seismic fortification intensity in many areas across the country should be upgraded in the future.It is sure that there must be a large amount of existing buildings that could not meet the current seismic fortification standards specified in the related design codes.Moreover,some of the existing buildings have reached or have been near the design life,which also need to be reconstructed to meet the needs of safety.The retrofitting of buildings with seismic isolation technology can not only improve the safety of the structures,but also have significant economic benefits compared with the retrofitting of buildings or retrofitting with traditional methods.The research works in the past about seismic isolation retrofitting were mainly concentrated on structural performance,while it lack detail research work about comparison and analysis of the seismic time history responses,and lack the comparison and analysis of construction costs.It is clear that further and overall research work should be done about seismic isolation retrofitting for existing buildings.One RC frame buildings with 4 layers respectively,were selected as the research target structures for seismic isolation retrofit research.The existing seismic fortification intensity is 7 degree(0.15g),and the target seismic fortification intensity is 8 degree(0.20g).Due to the limitation of frame column section and construction method,it is determined that seismic isolation retrofitting be applied to meet the needs in many ways.The numerical structural models were established with Etabs and YJK software respectively and the storey shears were computed,according to the structural natural periods before and after seismic isolation.Its seismic mitigation efficiency was evaluated with comparison of storey shears.The tensile stresses,compressive stress,restoring force,wind load resisting capacity,inter-storey displacements and etc.of the rubber bearings,were analyzed to decide their requirements specified code for seismic design of buildings GB 50011-2010(2016 Edition).The seismic retrofitting efficiency of existing buildings on different storeys under the same fortification intensity is calculated to evaluate and summary the seismic performance.By comparing the construction cost of two structural building systems with different storeys under the same fortification and traditional retrofiting buildings,the economic efficiency of the existing buildings were analyzed.With comparison of the structural performance before and after the isolation retrofitting,it shows that the structural natural periods could increase r3.3 times;both the overall structural storey shears and inter-storey rotations have been notably improved which could meet the requirements of fortification intensity 8 degree(0.2g).It also shows that all the other indexes are in line with the requirements specified in “Code for seismic design of building” GB50011-2010(2016 edition).On the other hand,it shows through the cost study for seismic isolation retrofitting of existing buildings,the initial cost of seismic isolation retrofitting is slightly higher than that of traditional seismic retrofitting.However,seismic isolation retrofitting for existing buildings will exhibit better economic benefit considering structural safety and cost of post earthquake repairment.Figure 28;Table 38;Reference 51...