Axial Compressive Behavior Of Square-section Concrete Columns Transversely Reinforced With FRP Grids

In this work,aiming to meet the great demand of construction in oceans,the structural behaviors of the fiber reinforced polymer(FRP)grids and the square-section concrete columns transversely reinforced with FRP grids are investigated through experimental and analytical studies.FRP grid,as a new type of lateral reinforcement,has the advantages of high corrosion resistance,low maintenance cost,and ease of installation.In addition,FRP grid permits an improved concrete cover and confinement to concrete core when compared to those conventional stirrups in similar form.Therefore,FRP grid has a great potential to be widely employed in ocean constructions.Nonetheless,few studies have been conducted to address the mechanical properties of the FRP grid.In addition,no research regarding the axial compressive behavior of concrete columns transversely reinforced with FRP grids is seen in available literature.In this regard,the primary objective and motivation of this work are to investigate the behaviors of FRP grids made of two types of materials(carbon fiber reinforced polymer,also referred to as CFRP,and basalt fiber reinforced polymer,also referred to as BFRP)and the performance of the square-section concrete columns transversely reinforced with FRP grids.This work directly provides theoretical and experimental basis for the researches in the future.Detailed organizations of this work are as follows.Firstly,the mechanical behaviors of FRP girds were investigated.Conventional coupon test method cannot be used to assess the behaviors of FRP grids.Thus,two new test methods were proposed,including diagonal grid burst test and straight-line grid burst test.Failure modes of FRP grid were obtained using diagonal burst test.With the proposed test method,the strength of joint of FRP gird can be ensured,permitting the most effective use of the FRP rod.On the other hand,the strain state of FRP rod could be obtained by straight-line burst test.Based on the results of straight-line burst test,a simplified model was proposed to predict the performance of FRP grids in concrete columns.Secondly,an experimental study was conducted on 17 short columns transversely reinforced by CFRP/BFRP grids,welded reinforcement grids and steel hooops to investigate their performances under monotonic axial compression.The typical failuremodes of concrete columns as well as FRP grids are obtained.The measured strain of FRP grids showed the average efficiency value in columns was higher than the predicted value.Through comparison of concrete columns having different reinforcement,the FRP grid is found to be an effective transverse reinforcement in concrete columns.Finally,an analytical model for predicting the stress-strain behavior of nine-cell grid was proposed.This model was developed on the basis of the effective area model.The proposed model shows a good agreement with the experimental results obtained in this work as well as those in available literature.Additionally,a simplified model was proposed,which is readily applicable to practical designs.