Theoretical And Methodological Research On Improving Seismic Reliability Of Ancient Pagodas Applying Shape Memory Alloys

The architectural form pagoda combined itself with Chinese cultural as it came to China. After thousand years’development, it became a representative ancient Chinese architectural form. The pagodas recorded the history, materials, architectural technology of ancient china. As the ancient pagodas were the witnesses of our long history, culture, architectural, religions, politics, diplomacy, society and economy, they are very important and irreplaceable in the historic and cultural researches of our country.Most of the pagodas existing in our country are of great age, they suffered serious natural disasters and manmade damages in the long history and most of them were seriously injured. So the researches on protecting those ancient pagodas became an important work of cultural relic preservation.The purpose of this paper was to find out a method to evaluate the seismic reliability of a historic building, and search a feasible and effective method on seismic reinforcement of it.First, a detailed inquiry was made to acquire the changes in its history and the present situation of Guang Minaret in Huaisheng Mosque through reviewing of the literature and field testing. Through the inquiry, the material composition, structural form, bank and crack amount were acquired in detail. Then, the dynamic characteristics and the seismic performance of Guang Minaret in frequently-occurred earthquake and rarely-occurred earthquake was studied in detail through finite element method, and the key point of Minaret’s weighted behavior and seismic protection for it were also discussed.As most historic buildings had worn down by the years and their material strengths were low, the probability that they can work in elastic stage when an earthquake happened was little, and so, the seismic reliability analysis method based on random vibration theory was not fit the historic buildings. So, in this paper, the seismic reliability method based on earthquake resistant design code was applied. This analysis method mainly contains two parts, one is the strength-checking calculation in frequently-occurred earthquake, and the other is the deformation-checking calculation in rarely-occurred earthquake. The seismic reliability of Guang Minaret in frequently-occurred earthquake and rarely-occurred earthquake were separately analyzed according to its material characteristics, the structural form and weighted behavior.The sample space of Guang Minaret was built up according to its present situation; the key section, failure criteria and performance function was defined and the seismic response of each sample was calculated separately and the seismic reliability of Guang Minaret in frequently-occurred earthquake and rarely-occurred earthquake were concluded.Through the seismic reliability analysis of Guang Minaret, it was found that the minaret’s seismic reliability was low and it needed some seismic protection and reinforcement urgently. The protection plan using shape memory alloys to build up a passive seismic response control system for Guang Minaret was suggested in this paper.The passive seismic response control system was designed applying the pseudo-elasticity of shape memory alloys. Some experimental researches were made on the pseudo-elasticity of shape memory alloys, and the impact that working temperature, maximal strain value and loading rate may make on the mechanical properties of shape memory alloys were paid special attention. A data fitting was made on the material tensile test curve under specific working condition applying the bilinear model. The bilinear restoring force model can be used as the simplified pseudo-elasticity restoring force model of shape memory alloys in following theoretical analysis and calculation.Two type shape memory alloy dampers were made according to the minaret’s structural features and weighted characteristics. And some tensile experiment researches were made to acquire the performance data of those dampers. A data fitting was made on the dampers’tensile test curve under specific working condition applying the bilinear model. The bilinear restoring force model can be used as the simplified super-elasticity restoring force model of shape memory alloy dampers in following theoretical analysis and calculation.Seven protecting plans were made for Guang Minaret using the shape memory alloy dampers and the seismic response of reinforced minaret was calculated. Comparing the results of each protecting plans, a most suitable protecting plan was chosen, and according to this reinforcement, the sample space of reinforced minaret was built up. The key section, failure criteria and performance function were chosen for the reinforced minaret and the seismic reliability of Guang Minaret under frequently-occurred earthquake and rarely-occurred earthquake were calculated using Monte-Carlo method.Through the seismic reliability analysis of Guang Minaret, it was known that the seismic reliability was low and there were some internal defects and weak points in the minaret, and it needed some protection urgently or it may not survive a strong natural disaster such as an earthquake or a hurricane. Shape memory alloys were metals with very unique mechanical property, the pseudo-elasticity, and the shape memory alloy dampers had very good energy absorbing capability according to the experimental researches. The protecting plan applying shape memory alloy dampers suggested in this paper was proved to be an effective seismic reinforcement for ancient pagodas. The seismic response of Guang Minaret reduced a lot and the seismic reliability improved obviously with this protecting plan using shape memory alloy dampers.The passive seismic response control system applying shape memory alloy dampers in this paper was proved to be with good energy dissipating effect and can effectively improve the seismic reliability of Guang Minaret, and this reinforce method using shape memory alloys in the ancient pagodas’seismic reinforcement need more developments, spread and exploitations. The conclusions in this paper can not only provide some theory evidence and technical support to the seismic protecting and seismic reliability analysis of Guang Minaret, but also, it can provide references to protecting and repairing of other ancient buildings.