Study On Bonding Performance Of Reinforcement Interface Of Fabricated Bridge

In recent years,prefabricated prefabricated structures have been widely promoted due to their short construction period,controllable construction quality,and temporary land occupation and labor savings.The effective bonding and anchoring of prefabricated prefabricated bridge connecting bars is a guarantee of service for prefabricated bridge structures The key to performance.Based on the innovation-driven "5511" project in Jiangxi Province,this paper studies the bond and anchoring performance of the precast concrete member connecting steel bars and the corrugated pipe grouting and overlapping steel bars through the central pull-out test,and obtains the main influencing factors of their bonding and anchoring properties.The interface stress distribution and development law of reinforced steel and bonding materials provide design suggestions for anchoring of prefabricated bridges connecting reinforced steel and grouting overlapped steel.Based on the experimental research,a corresponding finite element mesoscopic model is established,and the failure mode and failure mechanism of the bonding interface are analyzed in depth,as well as the continuous distribution and development characteristics of the bonding stress.Finally,based on the experimental and finite element analysis results,the recommended values for the anchoring of the connecting bars are given.The main work and conclusions of the paper are as follows:1.Through the pull-out test of the pre-cast concrete members connected to the reinforcing bars,the influence of factors such as the diameter of the reinforcing bar,the strength of the concrete,and the anchor length on the failure mode,bearing capacity,and interfacial bonding stress of the test piece was studied.The results show that: for prefabricated connecting bars,the bearing capacity is positively related to the strength of the concrete,the diameter of the bar,and the anchorage length;the interface bond strength is positively related to the strength of the concrete,negatively related to the diameter of the steel bar,and less related to the anchoring length.The influence of anchor length and protective layer thickness can be ignored when calculating its bond strength.2.Based on the measured distribution characteristics of the interface bonding stress along the anchorage length of the interface connecting the reinforcing steel and concrete,a load transfer unit assumption related to the interface stiffness was proposed,and the distribution of the interface bonding stress along the anchorage length from a single peak to a bimodal or multiple peak was analyzed The evolution of the peak distribution.3.Establish a meso-scale finite element model of the bonded interface between the reinforced concrete and the ordinary concrete,and analyze the zigzag stress distribution dominated by the mechanical occlusion force in the bond length direction and the stress development,failure and backward of the bond interface.During the transfer process,the distribution of the bonding stress in different failure modes is analyzed through the nonlinear change of the axial displacement of the reinforcing bar,and the formula for calculating the bond strength based on the interface displacement is given.4.According to the results of experiment and finite element,the fitting of the bond strength of steel bar and reinforced concrete prefabricated connection empirical formula,and deduces the corresponding critical anchorage length,at the same time comparative analysis at home and abroad related norms,presenting the basic anchorage length of precast concrete bridge connection reinforced recommended values: for ribbed steel bar HRB400 and below,when the concrete strength grade is C35 and below,suggest off for18 d;When the concrete strength grade is C40 or above,it is recommended to take 15 d.5.Based on the test results and test phenomena of the steel pipe overlap test for corrugated pipe grouting,analyze the failure mode,bearing capacity and reinforcement grouting interface of the steel bar,the diameter of the corrugated pipe,the overlap length,the grout and the external concrete strength The influence law of bonding stress provides basis for the establishment of corrugated pipe grouting finite element model and the anchoring design of grouting connection.The results show that all the specimens suffered from tensile failure of the steel bars,and there were no forms of steel bar pull-out,concrete cone failure,and adhesive interface failure.The interface between steel bars and grout,grout and corrugated pipe,and corrugated pipe and concrete were bonded and anchored.It is sufficient,which shows that the connection method using corrugated pipe grouting steel reinforcement in the connection of precast concrete members is more reliable.6.Based on the results of corrugated pipe grouting test,and considering the effect of the grouting pipe on the reinforcement and reinforcement of the grouting connection,the diameter of the corrugated pipe is recommended to be 4 times the diameter of the reinforced steel bar.The analysis found that the bonding stress at the interface between the steel bar and the grouting was distributed unimodal along the anchorage length,and the unloaded steel bar at the lap section was compressed and then tensioned.7.Based on the test results,a meso-finite finite element model of the grouting connection of the corrugated pipe is established.The analysis results show that the bearing capacity of the specimen is positively related to the anchoring length,grouting strength,and external concrete strength;when the anchoring is insufficient,the specimen is reinforced When pulling out damage,the bearing capacity of the specimen is inversely related to the diameter of the reinforcement and the diameter of the bellows.When the test piece is broken and pulled out,the bearing capacity of the test piece is positively related to the diameter of the bellows.When the steel bar is fully anchored,the test piece’s bearing capacity is positively related to the diameter of the steel bar.8.Comparative analysis found that the stresses at the three bonding interfaces of steel bars and grouts,grouts and corrugated pipes,and corrugated pipes and external concrete showed a zigzag distribution of alternating tension and compression along the anchor length.With the increase of the load,the distribution pattern of the main compressive stress at the interface of the reinforced concrete changed from a unimodal distribution to a multimodal distribution.The main compressive stress at the interface between the grout and the corrugated pipe still showed a unimodal distribution,and the corrugated pipe and concrete were bonded The interface compressive stress showed a unimodal distribution and gradually moved backward.9.Combining the results of the test and finite element analysis with a safety factor of 1.6 times,it is recommended that the overlap length of the corrugated pipe grouting connection bar is 12d.