Research On The Transverse Forced Crack Of One-way Flexural RC Members

As the strength of longitudinal reinforcement in the construction engineering in China is lower than advanced countries' about 100 Mpa, it has been started for china academy of architectural engineering to extend the use of high strength reinforced bar since 2006.During this period, the crack width control provisions became a bottleneck in the present concrete standard, when uses HRB500 level reinforcement, the reinforcement of most components are controlled by no longer the bearing capacity but the crack width. In this situation, we have to pay more attention on the controlling crack width theory which we have been used more than 20 years.Take analyzed the above contradiction as the research goal, the paper has mainly completed the following 4 aspect work:(1) Contrasting with the crack width control provisions and related provisions offered by ACI318-95/05/08 Code,Eurocode2,CSA A23.3Code,NZS3101 Code and GB50010 -2002.Considering reliability influences, there are three quantitative methods to calculate the crack width of one-way flexural member according to the codes mentioned above.(2)Continuous loading cracking tests of four full sized beams are conducted with screw jack loading, pressure sensor and strain gauge detecting load value for one year.(3)Further integration of relevant tests and the theory proposed by important scholars, three cracking theory models are analyzed according to the ACI, Eurocde2 and Chinese code.(4)This paper traces the latest test on steel corrosion from the perspective of electrochemical and discusses the rationality of experimental results.Based on the analysis of test results, the following conclusions can be reached:(1)Even considering the impact on the reliability factor, the width of the cracks in Chinese formula still has to strict than other countries. The result calculated by many countries' accounts for only 30%-50% of ours.(2)From the record of the test continuous loaded for one year, we found that the crack width is far from 66% which is specified by our standard, only 20%.After the preliminary demonstration, the reason for this is the impact on the compression reinforcement and section height.(3)The paper proposed three kinds of relations for the first time (1.the relationship between the tensile effect and flexural effect 2.the relationship between the reinforcement non-influence area and reinforcement influence area 3.In reinforcement influence area, the relationship between the concrete cover thickness and bond.)From the perspective of a more general sense to explain the one-way bending members of the crack problem, the universal significant theory of the new model crack is established. It is also pointed out that the three cracking theory models of ACI, Eurocode2 and Chinese code put emphasis on different aspects. Meanwhile, a new crack width suggestion is proposed by taking into account for the concrete creep, concrete shrinkage and relaxation of steel according to relevant tests and provisions. (4)The conclusion that the concrete around reinforcement have impact of steel corrosion is much greater than component surface on crack width should be concerned. It is provided a brand-new idea for the concretes component crack control. Whether does the traditional crack control method achieve the goal to prevent the steel bar corrosion effectively needs more comprehensive experimental study as soon as possible.