Experiment And Performance Analysis Of Novel UHPC-Based Sandwich Structures

The fast development of bridge structures and the surge of traffic volume make the collision contradiction between bridge structures and means of transportation(e.g.,ships and vehicles)increasingly prominent.The sharp increase in the number of bridge structures in mountainous areas also further leads to the increase in collision risk between bridge structures and rockfall disasters.Bridge engineers put forward various impact protection strategies,to deal with the impact load that bridge structures may suffer under different environments.The traditional steel protective structure is widely used in the anti-collision of bridge structures because of its low cost,good ductility,and stable energy absorption.However,due to its low impact resistance of the facing panel,the steel panel is prone to local deformation or even puncture under the high-energy level impact,which is difficult to protect the bridge structures.Compared with the steel protective structure,fiber reinforced polymer protective structure has lighter weight and higher unidirectional strength.However,due to the characteristics of high cost,low shear strength,and low fracture strain,it has the disadvantages of easy damage and low energy absorption efficiency..The UHPC-steel protective structure utilizes the UHPC with high impact strength as the impact panel to solve the puncture of the impact facing panel in the traditional steel protective structure,and retains the excellent energy absorption performance of the steel core layer.Based on the combination of the UHPC and steel,this study investigated the crushing behavior and energy absorption performance of sandwich structures with different core configurations,and applied the sandwich structure with bestperforming comprehensive performance to the impact protection of bridge structures.The main work contents and conclusions are as follows:(1)The five types of sandwich structures named traditional frame(TF)type,ectopic frame(EF)type,corrugated plate(CP)type,horizontal tube(HT)type,and vertical tube(VT)type were developed.The quasi-static crushing test and crushing behavior analysis of UHPC-steel-PU foam sandwich structures have been carried out.It was found that the TF,CP,and VT configuration have large initial crushing force,while the EF and HT configuration have no initial peak crushing force.Compared with all other types of sandwich structures,the VT configuration had massive crushing force,which indicated that the stiffness of such an configuration is large,and it is difficult to give play to its cushioning and energy absorption characteristics in the application of structural energy absorption.Thus,it was reasonable to exclude it in the comprehensive performance evaluation of the sandwich structures.Besides,the present of polyurethane(PU)foam can significantly enhance the energy absorption of sandwich structures under quasi-static crushing test.The comprehensive performance evaluation results of sandwich structures using technique for order preference by similarity to an ideal solution(TOPSIS)method showed that the comprehensive performance of sandwich structures obtained under different design purposes will be different.(2)Based on the quasi-static test,the impact tests of 19 sandwich structures were carried out.The drop hammer impact test results further showed that the VT type is difficult to absorb energy under impact loads because of its excessive stiffness,so it is no longer recommended to be used in practical protection.Compared with other configurations,the sandwich structures with EF and HT configuration had lower initial peak force,plumper impact force platform,and more uniform deformation mode,which were the recommended structures.(3)The drop hammer impact test also showed that the PU foam filled sandwich structures absorbed the impact energy lower than that of the unfilled foam sandwich structures.The dynamic responses and crushing behaviors of sandwich structures with and without polyurea layer were almost the same.The sandwich structure without UHPC panel had high secondary peak impact force,and its mean crushing force is smaller,showing insufficient protection capacity.Under impact loading,sandwich structures with the same configuration had higher peak crushing force(PCF),mean crushing force(MCF),energy absorption(EA),and specific energy absorption(SEA)than those under quasi-static loading,but their crushing force efficiency(CFE)was lower than that under quasi-static loading.(4)According to the quasi-static crushing tests and drop hammer impact tests,the refined numerical models of sandwich structure were established.By comparing the crushing force-displacement results and the damage mode of sandwich structures,the effectiveness of the numerical modeling method used in this study was verified.Using the numerical modeling method verified in this study,the dynamic responses and protection of bridge structures subjected to rockfall impact and ship impact were investigated.(5)The investigation on the impact resistance of the bridge structure protected by UHPC-steel protective structure showed that such a protective structure can effectively reduce the dynamic responses of the bridge structures induced by rockfall impacts,and the UHPC panel played a important role in improving the impact resistance of the protective structure.The impact results of barge to fender showed that the protective capacity of rubber and GFRP fender under high-energy level barge impact was insufficient,while the UHPC-steel protective structure had sufficient protective capcatity.