Study On Short-term Stiffness Of Fly Ash Reinforced Concrete Beams

Fly ash is one of the most abundant and widely used concrete mineral admixtures in the world.The use of fly ash can not only save resources,but also improve the performance of concrete.At present,the research on the basic performance of fly-ash concrete is quite mature.When we apply the fly-ash concrete in the structural engineering,we should consider the influence of Fly-ash on the bearing capacity safety and service performance of the structure.Fly ash has a direct impact on the modulus of elasticity of concrete,the bond performance of reinforcement and concrete and the crack resistance under load,which all affect the stiffness of the structure.The calculation of short-term stiffness of reinforced concrete beams with cracks has always been a key and difficult point in the structural design.The short-term stiffness formula in the code for design of concrete structures(GB50010-2010)in China was analyzed and obtained by the research group of the code in the 1970 s on the basis of experiments.With the rapid development of engineering material performance,the applicability of short-term stiffness formula of the code to fly ash concrete is still worth discussing.Therefore,this paper studies the influence of fly ash on the short-term stiffness of reinforced concrete beams.In this paper,the short-term stiffness of flyash reinforced concrete beams is studied by three ways of experimental research,theoretical derivation and software simulation.The experimental research is based on the calculation of the short-term stiffness of the beams in the bending stage,and discusses the internal force arm coefficient,the height coefficient of the compression zone,the comprehensive coefficient of the concrete compression zone,the coefficient of the crack nonuniformity,etc.of the beams to verify the formula of the code Applicability of short-term stiffness of concrete beams with coal ash stiffness.In the theoretical derivation part,two new methods for calculating the short-term stiffness of reinforced concrete beams and fly ash reinforced concrete are given.Firstly,by simplifying the short-term stiffness formula of the code,two main factors influencing the short-term stiffness of the beam in this method are obtained,and then the new formula is obtained by linear regression analysis of the data.Secondly,according to the moment curvature graph,based on the elastic assumption of concrete compression zone,the characteristic moment value and the characteristic curvature of the beam are calculated,and a new short-term stiffness formula is obtained.The software simulation uses ABAQUS simulation analysis,compares the load deflection curve of test and simulation,as well as the basic information of concrete and reinforcement strain at the moment of characteristic bending moment,determines the reliability of ABAQUS simulation analysis,then analyzes the load deflection curve of fly ash with different substitution rate,and explores the influence of fly ash on the short-term stiffness of beam.Through the above analysis,we can get the following main conclusions: when the replacement rate of fly ash is about 20%,it can improve the short-term stiffness of the beam,and when the replacement rate of fly ash is about 40%,it has little effect on the short-term stiffness of the beam.When calculating the short-term stiffness of 40% fly ash replacement rate beam,the calculation value of the code formula is low,which may reflect the influence of strength if it is too high,but ignore the influence of elastic modulus if it is too low.For this reason,this paper gives the code correction formula suitable for the short-term stiffness of 40% fly ash reinforced concrete beam.The stiffness reduction method based on the stiffness analysis method given in this paper is more concise than the standard formula in calculating the short-term stiffness of beams,and the basic error is small.The stiffness graph analysis method based on the elastic theory given in this paper is very consistent with the test,and it is also consistent with the test in other literature,which can meet the design use requirements.The results of ABAQUS simulation analysis are in good agreement with the test data,which proves the reliability of the test.The influence of fly ash on the short-term stiffness of the beam is consistent with the test.