| A large number of existing structures have suffered damage due to the material aging,earthquakes,fire and explosion,causing serious economic losses to the society.Except the severely damaged buildings which need to be demolished and rebuilt,many lightly and moderately damaged structures can be retrofitted after damage assessment,in order to ensure those structures meet the requirements of subsequent service function and bearing capacity.It is well known that fiber reinforced polymer(FRP)has been widely applied in strengthening/retrofitting structures due to its excellent performance,such as high strength,light weight,corrosion resistance and ease of installment.Most recently,basalt fiber reinforced polymer(BFRP)has gained popularity in retrofitting structures because of its good tensile properties and relatively low material cost.However,existing studies mainly focused on the use of carbon fiber reinforced polymer(CFRP),while few studies have investigated the repair effect of structures retrofitted with BFRP.Most importantly,it should be pointed out that existing studies mainly focused on the compressive behavior of FRP-confined undamaged concrete,while few studies have considered the effect of initial damage of concrete on the compressive behavior of FRP-confined pre-damaged concrete.However,the existing structures might have suffered damage due to their own weight,earthquakes,environmental corrosion or accidental loads such as explosion and collision.In addition,existing research on the size and slenderness effect of FRP-confined pre-damaged concrete is quite limited;for existing models based on small-scale tests,the applicability of these models in FRP retrofitted actual structures is still unclear.In the light of that a large number of damaged concrete structures need to be repaired and the related research is quite limited,this study focuses on the axial compressive behavior and slenderness ratio effect of BFRP-confined pre-damaged concrete under monotonic and cyclic compressive loadings.The main research contents are written as follows:(1)Based on three experimental factors including the slenderness ratio,pre-damage level and BFRP layer,42 BFRP-confined undamaged/pre-damaged concrete cylinders were tested under monotonic axial compressive loading to investigate their monotonic compressive properties and slenderness ratio effect.Subsequently,based on the test results in the current study and the experimental data collected from literature,a strength model,ultimate strain model and monotonic stress-strain model were proposed for BFRP-confined undamaged concrete.(2)Based on three different damage indices,the damage evolution parameters were introduced to describe the initial damage of concrete quantitatively.A modified strength model,ultimate strain model and stress-strain model were proposed for BFRP-confined pre-damaged concrete with considering the adverse effect of the pre-damage levels of concrete.(3)The intuitive analysis and statistical multi-factorial analysis were applied to analyze the slenderness ratio effect of BFRP-confined concrete.Subsequently,the influences of slenderness ratio effect on the strength and ultimate strain were investigated.Considering the influences of BFRP layer and pre-damage level on the slenderness ratio effect,a modified strength model and ultimate strain model were developed for BFRP-confined pre-damaged concrete.(4)Cyclic axial compressive loading test was carried on the BFRP-confined pre-damaged concrete cylinders,in order to investigate the influences of the pre-damage level and cyclic loading on their compressive properties.A modified cyclic compressive stress-strain model was established for BFRP-confined pre-damaged concrete with considering the adverse effect of concrete pre-damage.A new material of BFRP-confined pre-damaged concrete was developed and embedded in OpenSees,which provided a numerical constitutive model for the seismic performance analysis of damaged concrete structures retrofitted with BFRP. |
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