Research On The Existing Stress Detection Of The Prestress Small Box Girder By Using Boring-releasing Stress Method

The existing stress is one of the most important indexes reflecting the actual bridgesstructural condition, therefore, the exact prediction of the existing stress becomes crucial. Inthe stress test of bridges structural behavior,the existing stress test of bridges is still a difficulttechnical problem at present. This paper takes pre-stressed concrete small box girder as thestudy subject, which is widely used in bridge engineering. It presents that the existing stressof the pre-stressed concrete small box girder is measured in boring-releasing stress-methodafter looking through a large number of references and information. Basing on the principle oflittle hole method, boring-releasing stress method is proposed to test the existing stress ofpre-stressed concrete small box girder.The existing stress can be calculated through measuringstrain change before and after drilling the hole, determining the compressive strength andelastic modulus of concrete through the drilled sample and combining the calculating resultsof the finite element method.In this paper, the accurate numerical model of the simple supported pre-stressedconcrete small box girder is made by the ANSYS software. The hole in the pre-stressedconcrete small box girder bottom of the cross is drilled, and the stress distribution along theedges of the hole is analyzed. What's more, the article mainly analyzes different sizes anddepthes of boring–holes. The stress distribution and stress concentration factors at the edgesof the hole with different aperture in the columns are studied. Moreover, the relationshipbetween the stress concentration factors and the depth of the hole are investigated. The resultsindicated that the stress concentration factors have great difference. The maximum stressalong the edges of the hole increases with the magnification of the aperture, but the stressconcentration factors does not do. The stress concentration factors are greatly affected by thedepth of the hole.It increases with the depth,but gently when the ratio of depth to diameter ofthe hole reaches1.4,and at the moment the surface release strain of the test columns can betested completely. In addition,when the ratio of depth to diameter of the hole more than1.4,the influence of the small box girder common section size and parameters to stress ratiocoefficient is analyzed.Meanwhile, the stress ratio coefficient has also no influence in the sizeof common section size and span and pre-stressed and elastic modulus. Furthermore,the original strain is calculated by using the release ration form finiteelement analysis, and by the physics equation of the space problem. an approximatecalculation formula is proposed to calculate the existing stress of pre-stressed concrete smallbox girder measured by boring-releasing stress method. And at the same time,throughregressive analysis, the approximate calculation formula is put forwarded to calculate existingstress of pre-stressed concrete small box girder by using the side of hole stress concentrationfactor, based on the finite element calculation and analysis. In the end of the paper,the key testpoints to test the release strain in pre-stressed concrete small box girder by boring-releasingstress method are summarized. And the possible reasons of error analysis in the finite elementcalculation are analyzed.The contribution of this thesis is that we simulate and analyze the stress detection ofpre-stressed concrete small box girder,which gives a simple and practical and reliabledetection method. An effective detection method of engineering quality control is given forthe pre-stressed concrete small box girder. Furthermore, it provides the reference for thepost-test analysis of similar bridges.