| In the recent earthquakes,a large amount of reinforced concrete(RC)frame structures have experienced serious damage or even collapsed due to the failure of columns which were lack of enough ductility and energy dissipation capacity.These non-ductile frame columns which were designed without considering seismic load or could not satisfy the requirements of the current seismic code.Under the potential strong earthquakes,all these RC frames have to face the high risk of damage and collapse and therefore need to be retrofitted before earthquakes.Fiber Reinforced Polymer(FRP)has been widely applied in structural engineering reinforcement and reconstruction due to its lightweight,high strength,good durability and convenient construction.According to recent research results,the FRP retrofitting can obviously improve the seismic performance of the non-ductile frame columns.In real earthquakes,the angle between earthquake and the strong axis of rectangular columns is random.Many existing research were conducted by pseudo static test and numerical simulation under unidirection cyclic loading.However,the shake table test considering the structural dynamic characteristics under bi-directional earthquake is extremely scarce.Therefore,aiming at non-ductile RC rectangular columns which are widespread in China,the shake table test of FRP retrofitted RC rectangular columns has been conducted and the parameter studies about the dynamic characteristics have been investigated based on the Opensees software.The above work will provide the basic test data and suggestions for the revision of design code for FRPretrofitted RC structures.The main contents of this research are as follows:(1)Shake table test of three FRP retrofitted RC rectangular full scale columns have been conducted under different lateral earthquake direction(0,30 and 60 angle).The cross section of specimens is 150mm×225mm.Based on test results,the discussion has been carried on the failure mode,response and seismic performance of FRP retrofitted RC rectangular columns under different earthquake levels and directions.The test results showed that the acceleration,displacement,and damage degrees of RC rectangular columns were increased with the increase of earthquake input angles.The torsion effect leaded to the decrease of seismic performance FRP retrofitted RC rectangular columns and the final failure modes were controlled by the combination of bending,shearing and torsion effect.(2)The finite element model of FRP-retrofitted RC rectangular columns based on Open Sees software has been developed and built.Then,the dynamic time response analysis of FRP-retrofitted RC rectangular columns has been carried out.The numerical analysis and shake table test results are in good agreement.The applicability and accuracy of modeling method have been verified in order to carry out next parameter studies.(3)Based on the verified modeling and analysis method,the plastic static pushover analysis and the dynamic time response analysis of FRP retrofitted RC rectangular columns have been conducted to investigate the influence of earthquake input directions,the aspect ratios,axial compression ratios and the layers of FRP wraps.The results showed that the seismic performance of FRP retrofitted RC rectangular columns is expected to decrease with the increase of earthquake input direction,the aspect ratio and axial compression ratio and the decrease of the layer of FRP wraps.The calculation formular of bi-directional shear capacity of RC rectangular columns used in the current concrete structure design code will overetimates the shear performance.Based on the test and analysis results,the modification was made in terms of the bi-directional shear capacity of FRP retrofitted RC rectangular columns. |
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