Research On The Mechenical Properties Of Planting-bar Concrete Beams Under Cyclic Loading

As an anchoring technology,planting technology has been widely used in the reconstruction,reinforcement and expansion of building structure.At present,the researches on the planting-bar components mainly concern the mechanical properties under drawing and static load;whereas,there is not many research on the performance of planting-bar components under complex stress state.In the study of the mechanical properties of planting-bar beams under fatigue load,the researches found that the residual strain of the planting-bar beams after loading and unloading was greater than the residual strain of the preset reinforcement.They also put forward the theory of fatigue damage of the planting-bar components,while there is not many specific research on it.With the wide application of planting bar technology in concrete beams,it is significant to study the degradation of the planting-bar beams under the fatigue load.This paper analyzes the deflection,reinforcement strain,concrete strain,crack,bearing capacity and the degradation characteristics of stiffness-bearing capacity through the experiments on ten panting-bar concrete beams under fatigue load.The results show that the increase of the depth of the planting bars can improve the ultimate bearing capacity to a certain extent.As the depth of the planting bars is increased and the growth of bearing capacity gets slow,when the depth of planting bar increases from20 d to 25d(d for the diameter of embedded steel bars),the bearing capacity increases by22.3%.If the depth of planting bar increases to 30 d,the bearing capacity increases by only3.9%.With the increase of the depth of planting bar,the failure form of the beam transits from the concrete peeling on the bottom to the concrete being crushed on the top.As the depth of the planting bar increases,the degradation of stiffness-bearing capacity gets low,which indicates that increasing the depth of embedded bar can reduce the cyclic loading’s fatigue damage on the beams.Moreover,the beams with different depths and diameters of the planting bars are mainly damaged in the first 500,000 cycles,while they are slightly damaged after 500,000 times.Additionally,the smaller the depths and the diameters of the planting bar are,the greater the residual deformation of the beams is,and the more serious the degradation of the stiffness-bearing capacity is.The results also indicate that fatigue loading has a bad effect on the compressive zone of the concrete.Finally,stiffness-bearing capacity mainly degrades in the first 100,000 times of thefatigue loading,when the deflection rapidly increases;after 500,000 times loading,the alternation of stiffness-bearing capacity becomes stable and the degradation gets slow,when the deflection increases because of the fatigue damage accumulation.