| The prefabricated building structure has become the main development trend of China’s construction engineering due to its advantages of less wet field operation,faster construction speed and environmental protection.The beam-column joint is an important part that determines the stability of the prefabricated building structure.When the structure is subjected to pre earthquake,the damage at the beam-column joints will lead to the overall instability of the structure and bring serious potential safety hazards to the building structure.Therefore,it is particularly important to study the reinforcement of beam-column joints damaged by earthquakes.In this thesis,four seismically damaged frame beam-column edge joint specimens were strengthened by using high ductility concrete(HDC)by increasing the section method.The quasi-static loading test is carried out on the strengthened joint specimens,and compared with the pre earthquake damage specimens,the performance of HDC in structural reinforcement and the seismic performance of the strengthened joint specimens are analyzed,it provides theoretical basis and practical cases for node reinforcement in engineering.The main content and conclusions of this paper are as follows:(1)The seismic damaged frame beam column edge joint specimens are strengthened with HDC by increasing the section method,the pseudo static test of HDC reinforced specimens is carried out by using the same loading system as the pre-seismic damage specimens.Comparing the failure mode and seismic performance index of the strengthened specimens and pre-seismic damage specimens,it is found that the good tensile performance of HDC can increase the peak load of the strengthened specimens by 47.7%,and the ductility deformation capacity and energy dissipation capacity by 51.5%and 68.8%;Compared with prefabricated reinforced specimens,the reinforcement effect of cast-in-place specimens is more significant,thanks to the bridging effect of PVA fibers,the integrity of the beam end surface is better after the reinforced specimen is damaged.(2)In the fabricated reinforced specimens,the specimens with angle steel ribbed and thickness of 12mm are compared with the specimens with angle steel ribbed and thickness of 10mm and without angle steel ribbed and thickness of 10mm,the cumulative energy dissipation capacity is increased by 19.4%and 108.8%,the positive peak load is increased by 54.4%and 190.8%,and the negative peak load is decreased by 16.4%and 23.4%,respectively;Ribbed and increased thicKNess of angle steel for prefabricated reinforced specimens,the cracks on both sides of the steel cover plate and angle steel on the surface of the beam end tend to be evenly distributed,the position of the main failure crack is transferred from the bottom of the beam to the end of the beam,it shows that adding angle steel ribs and increasing angle steel thicKNess can realize the design principle of strong joints.However,the degree of pre-shock damage between the fabricated specimen and its angle steel weakens the recovery effect of the seismic performance of the strengthened specimen;When HDC is recommended to reinforce the seismic damaged structure,the pre-shock degree of the steel of the component itself should be considered in the reinforcement of the fabricated specimen,the joint surface of old and new concrete should be avoided to be set in the part with complex force,the joint surface must take corresponding chisel measures,in order to increase the bonding capacity of the joint surface and improve the overall performance of the reinforced structure.(3)Ultrasonic nondestructive testing can quickly and qualitatively detect the damage of concrete,based on the ultrasonic velocity,the damage model of concrete material performance degradation is deduced,and the calculation results show that,the damage results obtained by the ultrasonic damage model are similar to the law of the final failure mode of the specimen,it can better reflect the damage and degradation of concrete,but the evaluation of the overall damage degree of the fabricated specimen is low.The damage calculation of nodes by introducing a two-parameter damage model shows that,HDC can effectively improve the damage resistance of pre-seismic damage specimens,the damage resistance of cast-in-situ reinforced specimens is the highest;Through the Park-Ang damage model to evaluate the damage of the nodes,the damage states of the node specimens in different loading stages are obtained. |
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