Study On Working Mechanism And Mechanical Behaviors Of Fiber-Reinforced Polymer Bars Reinforced Engineered Cementious Composite Link Slab

Expansion joints are used in multi-span simple beam bridge to meet the structural deformation need.Affected by temperature and humidity change,acid salt erosion and vehicle load,expansion joints are easily damaged,which deteriorates the driving condition,resulting in impact to bridge deck on both sides of the expansion joint.Moreover,the safety of the bridge structure will decline due to steel and substructure corrosion caused by water leakage.Frequent damage to expansion joints seriously affects the life of the bridge and greatly increases the maintenance cost of the bridge.Researchers proposed jointless bridge design and built link slab to replace traditional expansion joint and reduce the damage of bridge expansion joint.However,steel erosion and great stiffness existing in traditional reinforced concrete link slab reduce its service life and restrain deformation of the main structure.It has been shown that engineered cementitious composites(ECC)have tensile strain-hardening characteristic and multi-crack development ability,which can effectively solve the problem of concrete brittleness and large crack width.However,the high elastic modulus of steel bar itself and high reinforcement ratio in current design method lead to excessive stiffness of the link slab,which adversely affects the deformation of the link slab and the stress of the main structure.The corrosion of the reinforcing bar is inevitable at the same time.Fiber-reinforced polymer bars(FRP bars)with higher tensile strength,better corrosion resistance and lower elastic modulus compared to steel bars,will help to solve the high stiffness and erosion problem if applied to link slab.In this paper,the working mechanism and the mechanical behaviors of the steel bars reinforced ECC link slab and FRP bars reinforced ECC link slab will be studied through structural tests and finite element analysis.The main research contents are as follows,(1)According to the working requirements of the link slab,carry out the research on the mixture ratio of ECC and select the mix proportion which meets the need of link slab by testing the fluidity,compressive strength,bending performances and tensile properties.The test results show that the formulated ECC material has stable strain-hardening characteristic,high bending toughness and crack width control ability.(2)Cyclic loading tests were carried out on four link slab to study the working mechanism of the structure,and analyze the effect of the types of reinforcement bars(steel bars,GFRP bars and BFRP bars)and reinforcement ratio(GFRP-1.44% and GFRP-0.72%)on structural mechanical behaviors.The test results show that FRP bars can effectively reduce the stiffness of the link slab and the influence on the main structure.The impermeability is better in FRP bars reinforced ECC link slab than steel bars reinforced ECC link slab for its more uniform distribution of crack and lower crack width due to the better synergistic deformation ability between the FRP bars and ECC.The high residual deformation of the steel link slab under large deformation restrain its deformation ability while the FRP bars reinforced ECC link slab still performs well.(3)Specimens of ECC,concrete and bars were tested to obtain the physical parameters of the materials,and the link slabs were simulated by the finite element method using software ABAQUS.The calculated results of FEM,reflecting the stress and deformation state of the link slab,are in good agreement with the experimental results.Parametric analyses based on GFRP bars reinforced ECC link slab show that the increase of height-to-span ratio of link slab greatly increases the stiffness of the link slab,which is unfavorable to the stress and deformation of the structure.The increase of the debonding area improves the deformability of the link slab,but will cause the disengagement between link slab and bridge deck and influence stress performances while excessively increase.Deformation ability reduces and compressive stress increases while the reinforcement ratio of link slab increases,and the smaller spacing of the reinforced bars will help to transfer the stress at mid-span,leading to lower tensile strain of ECC.