Experimental Study On Seismic Behavior Of Modified RAC Frame Interior-joints With Hybrid Fiber

Recycled Concrete Technology not only be able to reduce the exploitation ofnatural sand and gravel resources, but also can solve a large number of constructionsolid waste resulting from the deteriorating ecological environment problems,and it hasa very important significance for the sustainable development of economic constructionand the improving of the ecological environment. The special formation process ofrecycled concrete often makes it exist in some internal defects, compared with commonconcrete, there are some differences in the mechanical properties of recycled concrete.Therefore, in order to compensate for the lack of recycled concrete, expanding itsapplication in practical engineering, researching on the modified recycled concrete andthe seismic performance of modified recycled concrete components is imperative.This text, using the silica fume, polypropylene fibers and steel fibers mixed binaryfiber as admixture to make modified recycled concrete, studied the mechanicalproperties of binary hybrid fiber-modified recycled concrete test blocks, and on thisbasis, designed and made three modified RAC frame interior-joints with differentcontent of hybrid fiber, through its quasi-static test, studied the seismic performance andbearing properties of the fiber modified RAC frame interior-joints. The main work andresearch are as follows:?1?Using the content of silica fume and hybrid fiber as the main parameters,designed and made15sets of45concrete blocks. By mechanical testing, comparativestudied the silica fume and hybrid fiber effect on cube compressive strength, axialcompressive strength and modulus of elasticity of RAC, analysis the mechanism ofsilica fume and hybrid fiber affect the mechanical properties of RAC, and also gives the ascent curve equation of the modified RAC constitutive curve.?2?Using "strong component weak joint" approach to design three frameinterior-joints model, then make it happen the core area of shear failure, according to theratio of1/1prototype the test model of frame joint, its pseudo-static test. Studied thefailure mode, stiffness degradation, ductility and energy dissipation properties of frameinterior-joint with different hybrid fiber content under the same recycled coarseaggregate replaced rate with100%, comparative analysis of the test results, probed thegeneral rules that the seismic performance of each changes with the content of hybridfiber, obtained some conclusions and recommendations for reference.?3?Based on the existing cracking capacity formula of concrete frame joint andanti-shear bearing capacity formula in concrete specification, using the test results andcombining existing research results, by introducing the impact parameter and added thefiber action items, summed up cracking and shear capacity formula which suitable forthe modified RAC frame interior-joints with fiber.?4?Using the constitutive relation of corresponding modified RAC with fiber,simulation analysis the testing process of the joints specimens by the finite elementsoftware ABAQUS, obtain its failure modes, hysteresis curves and skeleton curves,compared with the test results, and both are in good agreement, these results provedthat the joint model are reasonable in the text, also can be more accurately simulate themechanical performance of the fiber modified concrete frame joints witch are undercyclic loads.Through the work and the content of the above study reached the followingconclusions:?1? incorporation of silica fume can significantly increase the compressivestrength of RAC, the binary hybrid fibers ?steel fibers, polypropylene fibers? used inthis article, when in low content the compressive strength of the RAC enhancing small,and when the dosage is increased its compressive strength is significantly improved;steel fiber is a high modulus of elasticity of the hybrid fiber, making the modulus ofelasticity of the RAC improve.?2? the destruction process of the fiber modified RAC frame joints are same tothe ordinary RAC frame joint, the main difference is that when the fiber joints eventually destroyed the core area of the concrete showing broken without falling "Fractured but not Separated " phenomenon; The incorporation of hybrid fiber cansignificantly improve the seismic performance of the RAC frame joints, enhance itsductility and energy performance, it also improves the crack resistance and shearcapacity of the RAC frame joints, is an effective way to improve the performance ofthe RAC materials.