Study On The Integration Of Stress State And Strength Of Concrete Beam By Core-drilling Method

The in-situ stress and strength in the structure are the two main factors to judge its bearing capacity.On the one hand,accurately measuring the in-situ stress and strength of the structure can check whether the stress and strength of the new structure meet the design requirements.On the other hand,the stress and strength loss of the service structure can be evaluated,so as to provide the basis for the maintenance and reinforcement of the structure.At present,the in-situ stress measure of concrete at home and abroad mainly has non-destructive and micro-loss methods.The method of nondestructive testing is to detect concrete by physical method,and the method of microdamage mainly refers to the stress release method.This paper studies the stress release method,which was first used to measure the residual stress of metal materials.For a component with initial constraint stress,the stress generated by the constraint can be released through cutting methods such as grooving and drilling core,and the released strain can be measured.Then the initial stress of the component can be obtained according to the constitutive relation of the material.In this paper,the integrated measurement of stress and strength is realized by means of drilling core sampling.Through theoretical and test system research,the drilling core testing theory,concrete material characteristics,fiber Bragg grating sensing mechanism and a test system are studied.The finite element software MIDAS FEA was used to simulate three sizes of reinforced concrete beams with simple supports.Under different mid-span concentrated loads value,100 mm,75mm and 50 mm apertures were used to simulate the drill cores on the front and back sides respectively.The stress release trend is obtained by simulation.The analysis shows that the size and load have little influence on the 0 point value of stress release.The smaller the aperture,the faster the stress release,and the smaller the influence area of saint-venant.The core can be released on both sides of the positive side.By pouring three reinforced concrete beams of the same size,the core test is carried out.The rest conditions are the same as the finite element model.The results show that the accuracy of stress measurement can reach less than 10%.The measuring effect is good when the strain gauge is arranged in the ring.The measurement stability of bare fiber grating is good,but the accuracy is low.The aperture is not directly related to the measurement accuracy,but too small aperture will cause the test failure,too large aperture is not easy to release completely,the aperture used in this test can meet the measurement requirements of 50-100 mm.