The Study On Static Performance Of Concrete Beam With Embedded Steel-bars By Fasteners

At present,reinforced concrete structure is the most widely used structural type in the world. In the construction process, whether it is a new construction or an existing engineering reinforcement and reconstruction, are closely related with the anchoring technology. Because some details will not be considered before placing concrete such as fixing location, post-installed fastenings technology can speed up the construction progress, improving efficiency. Its application is becoming increasingly prevalent. Planting-bar technique is a post-installed fastenings technology whose application is very broad. Planting-bar in the usual sense is chemically bonded rebar. It means that drilling holes with appropriate depth in the sites which needs rehabilitation according the reqired steel-bar in the project, then using chemical plastic binder to make the additional reinforcing steel bar bonded firmly with the concrete and make the new steel (which is usually called planting-bar) to play the expected performance in design.The method of planting steel bar used in the paper is mechanical planting rebar. It means that the steel fasteners (expansion anchor) are used to achieve the connection between the embedded reinforcing steel bar and the existing concrete. Its principle is that holes are drilled in the existing concrete and then the steel fasteners are installed, with connectors the implanted steel bar is connected with the reinforced concrete member. To achieve the purpose of embedded steel bars, expansion force of the steel fasteners generated in the process of fastening is used to each bite with the concrete hole wall, the load is transferred by friction between the fastener and concrete. We call the manner of planting steel bar Embedded Steel-bars by Fasteners in this paper.In this paper, we design three concrete beams with embedded steel-bars by fasteners and test them to study the static performance of them, including failure mode, ultimate bearing capacity, deformation properties and crack development etc. For the purposes of contrast, we also design two common reinforced concrete beams and test them together with the concrete beams with embedded steel-bars by fasteners. The results show that there is huge difference about the static performance between concrete beams with embedded steel-bars by fasteners and common reinforced concrete beams with the same reinforcement.From the results of tests and the finite element analysis of in this paper, the characteristics of the static performance of concrete beams with embedded steel-bars by fasteners, comparing with that of common reinforced concrete beams with the same reinforcement, are as follows:1. Failure mode is brittle fracture. The failure surface of concrete beams with embedded steel-bars by fasteners is in the interface of old and new concrete. Basically it damages as soon as beams crack, the failure mode is brittle fracture. Common reinforced concrete beams have a certain sign before they destroy, the upper pressure concrete is crushed and the lower tensile reinforcement reaches the yield strength, which is ductile failure.2. The ultimate bearing capacity is low. The test failure load maximum of concrete beams with embedded steel-bars by fasteners is 18KN, which is 20% of that of common reinforced concrete beam. After analysis we consider that it may be due to several reasons as follow: 1) Section agent is not used in the interface of old and new concrete, when connecting beams with embedding steel bar, concrete is poured only when chiseling on old concrete section is finish, which reduces the bond strength between the both, affects the integrity of concrete beams with embedded steel-bars and leads to measured capacity lower; 2) When drilling on the concrete, due to the impact effect and small margins, the concrete produces micro-crack, which affects the anchorage action of expansion anchor; 3) discreteness of concrete itself is larger etc.3. The deformation is larger. In concrete flexible work stage, the deflection of fastener bonded rebar concrete beam is consistent with that of common reinforced concrete beam basically, load is proportional to deflection. When achieving a certain load, the deflection of fastener bonded rebar concrete beam is larger than that of common reinforced concrete beam with load at the same level: when the load reaches 18KN, the mid-span deflection of L4 is 2.74mm, is larger than the mid-span deflctions of L1 and L2, which are 0.27mm,0.28mm respectively in the same load.In addition, the ANSYS software is used in this article to do finite element analysis about test components and tensile capacity of anchor bolts in concrete, selecting unit,material properties,modeling and setting solution are described in detail, the results of finite element analysis on element stress,crack development and ultimate bearing capacity are given. By analysis, it is obtained that the results of finite element analysis on ultimate bearing capacity and deformation of common reinforced concrete beam are closed to those of experimental results, both is in good agreement. When a single bolt in tension, if it is far from the edge, the concrete stress can form more complete cone zone. If the margin is small, stress proliferation is restricted by the edge, the concrete stress can not form more complete cone zone, tension capacity of that is smaller than that of anchor bolts capacity not affected by margins. When the two bolts in tension, due to the impact of spacing, concrete stress proliferation can not form a complete cone area, the capacity of which is smaller than that of the two single bolt not affected by margin and spacing.The results of this study can provide advice and information on selecting the manner of embedding steel bar about expansion anchor in the future practical engineering. We hope that it can guide the construction preferably and make contributions to the research of post-installed technique.