Experimental Study On Anchorage Performance Of Steel Bars With FRP Confined Rings

At present,China is vigorously advocating the sustainable development idea for buildings,such as green low-carbon,energy saving and environmental protection,Therefore,the new-type fabricated building mode,as a representative of building industrialization,is the product of this development theory.Precast concrete structures are the effective ways to implement the industrialization of construction,and the technical development of component connections with simple-construction,reliable-quality and reasonable prices is the key to ensure structural safety of precast buildings.Based on the two basic connection techniques,such as "sleeve grouting connection" and 'slurry anchor lap joint",which are recommended in the Technical Specification for Precast Concrete Structures(JGJ1-2014),this paper presents a new method of reinforcement connection which is called "the Overlapping Connection of Steel Bars with FRP Confined Rings"(Utility model publication number:CN205116564U).The method is to use the fiber reinforced polymer(usually referred to as FRP)materials in the field of prefabricated concrete connections to shorten the lengths of reinforcement connection by providing hoop restraints.Meanwhile,the FRP materials can also give a loose centering space,which reduces the demands of construction precision.More importantly,the presented connection has a greater price advantage over "sleeve grouting connection".Similarly,it overcomes the "hole-collapse"difficulty as widely exists in the method of "slurry anchor lap joint".Therefore,it must be appreciated that this new-type reforcement connection is to better adapt the developing construction level in China.The node connection techniques for precast concrete structures usually verify reliability of itself through a series of experiments including three parts,i.e.,the reinforcement anchorage performance tests,the reinforcement connection performance tests and the pseudo staticafter bond performance test of steel bar anchorage steel bar connection performance test and the pseudo static tests of joint structures.Considering these experimental processes,this paper mainly carries on the reinforcement anchorage tests of precast concrete components based on the proposed FRP-confining joint connection techniques,which can determine the basic reinforcement anchorage performance for the new connection method and further provide the prerequisite for the subsequent research.Specifically,the content of this paper is as follows:(1)The design of the new-type FRP-confining vertical connection joint for precast concrete structures was developed,which includes geometric sizes and surface shapes of the FRP ring.During the design process,the important joint-connection characteristics,such as safety,reliability and economy,should be kept;(2)The reinforcement anchorage performance tests were performed.In the experimental process,the influence of different factors,such as steel bar types,concrete grades,geometric parameters of the FRP-confining rings,on the bonding performance of the presented technique was analyzed to verify the basic anchorage reliability of itself;(3)The ABAQUS-based finite element analyses on the connection performance of connection joints with "FRP-confining rings”were implemented,which includes:?For steel bars with different diameters,when the anchorage length is 0.8la(lais the anchorage length of tensioned reinforcement specified in the code for design of concrete structures),the bond-slip value of the steel bar in the grouting material was calculated and the bonding reliability was analyzed,?For steel bars with different diameters,when the overlap lengths are 0.7ll,0.5ll and0.3ll,(ll is the lap length of longitudinal tensioned reinforcement specified in the code for design of concrete structures),respectively,the bond-slip value of the steel bars was also calculated,and the reliability of lap bond was similarly analyzed.In this paper,a large number of basic reinforcement anchorage performance tests were carried out in terms of the presented connection technique for precast concrete structures.According to the different matching modes of the relevant parameters,a total of 66 sets of test schemes were designed to carry out the comparative studies.Test results show that:?The minimum anchorage length of steel bar is 0.8la,which can still ensure the bond performance of steel bars;? There is no relative slip and local failure between the FRP-confining ring and the circumferential concrete.Therefore,the anchorage and bond performance of this new type of joint connection is elementarily reliable,which lays an important foundation for the subsequent study of the connection.The study conclusions also prove that the proposed technique is a reinforcement connection method for fabricated concrete structures with many good performances including the reliable performance,simple construction process and good economic benefit,which is suitable for construction industrialization of prefabricated reinforced concrete structures.