The Application Of Concrete Local Stress Release Method In The Identification Of Residual Prestress

The residual pre-stressed force of the pre-stressed concrete structure is not only very important to the safety assessment of the structure,but also an important indicator to reflect the state of structure technology.It has a great influence on the formation and development of the cracks and the size of the deflection in the component.And if the loss of pre-stressed force is serious,it will affect the normal use and life of the component,and even have a safety accident.Therefore,only by accurately obtaining the value of residual pre-stressed force of existing bridges,the existing bearing capacity and provide reliable basis for maintenance and reinforcement of bridges can be evaluated,and provide guarantee for the safety of structures.On the basis of consulting the relevant literature at home and abroad,concrete stress relief method is used.By using the ANSYS software to make numerical calculation and study the factors that affect the effect of stress release and do stress-releasing experiment on a pre-stressed concrete T beam with a span of 24.6 m.In order to find a simple and reliable stress testing method to get the release depth of the stress zero,and then estimate the residual pre-stressed value of the structure according to the stress difference before and after the stress release.The paper mainly includes the following contents and conclusions:Firstly,establishing a three-dimensional solid finite element model,the release of stress curves are simulated in three cases,including opening ring hole,square hole and grooving method at the bottom of the middle span.The results show that: the result of cutting two transverse slots have the same effect as cutting four slots came into being a square hole,and also agree substantial effect as the ring-hole method of document,when the slots depth was 33 mm,the stress on the concrete surface can be released to zero.Secondly,According to the slotting method,has studied the cutting spaced,the cutting width t as well as cutting position separately which have influence on the stess release rate.The results indicate that the width and the position of the cutting slot have little effect on the force release,and the cutting spacing d directly affects the stress release rate of the measuring point.Thirdly,Establish the estimate formulate for the cutting spaced and the cutting depth which the stress can be released to zero in the cutting press,that is h?(0.32~0.34)d.Fourthly,According to the simulation results,slotting tests are performed on 1/4 cross,1/2cross and 3/4 cross at the bottom of the beam.Measure and record the change of strain before and after the stress relese,and then calculated the residual prestress value of the structure by the simplified mechanical formula.At the same time,in order to verify the reliability of the simulation results,the residual prestress obtained from the test is inversely integrated into the finite element model to obtain the stress value when the measuring point is not slotted,comparing with the test value,the error is within 10%,which verifies the reliability of the slotting test.