The Effects Of Construction Errors And Local Small Size Design On The Structure Performance Of Prestressed Concrete Beams

The paper relies on the project of "the disease diagnose and maintenancemethod aiming at early deterioration in small size member of bridge". Strain,displacement and failure state of small size prestressed concrete I-girders underconcentrated loads are mainly studied in this paper. And the result is comparedwith that from using finite element method. In addition, the paper describes thereason of the longitudinal cracks in beam web and early crack in local small sizemember and introduces the corresponding measure for improving the durability.The paper consists of five chapters totally. The emphasis parts are chapter threeand chapter four. The chapter four is the most important part.Chapter one mainly talks about the study background, significance andcontend. In the recent 20~30 years, with the rapid development of prestressedconcrete bridge, large numbers of prestressed concrete bridge have been built atpresent. Especially in the built of super highway and super bridge, prestressedconcrete bridge has been adopted widely. Due to the different degree crackexisting in construction phase and initial operating period the maintenance cost hasincreased. Besides the deficiency of concrete and steel in quality, the reason ofcrack is still related to the exterior factor, for example, design process,construction process and environment. Also, the influence factors have greatrandomicity. Test and practice have proved that construction deviation and designof local small size are main reasons leading to early crack.Chapter two refers to the design and construction of prestressed concreteI-girders. Using the civil building materials in local place and construction method,test beams of small size are making in test condition. During this process, a lot ofpreternatural phenomenon and construction deviation appear: large quantity ofhoneycomb, spot surface and hole inside, particularly concrete in vicinity ofprestress channel;horizontal eccentricity of longitudinal steel in web;thepremature phenomenon leading to the insufficiency of stretching force because ofthe improper maintenance of instrument during stretching process and so on. Allkinds of deviation are not allowed to neglect. Therefore, they will bring seriousproblem before using the structure. Nevertheless, these problems will influence themechanical behavior of the structure in different degree.Chapter three introduces the test beam L14 and L16 under the static loads. Ittakes about one year for the author to carry out the model experiment ofprestressed concrete I-girders in laboratory. Loading equipment iselectro-hydraulic servo system controlled by computer (WAW-1000). Thisequipment can keep the load at any time with error not more than 0.1KN, whichcan meet the precision requirement. Strain of testing point is measured with thestatic data collection system of 3816. This system has sixty test points eachmodule. The precise measurement of force, compressive stress, displacement andetc. are conducted with the corporation of all kinds of sensors and this system. Thevertical deflection is measured by displacement gauge with the dynamic and staticdata collection system of 3817 and the precision is 0.01mm. The results show thatthe crack distributes uniformly, densely and the width is small when the web isthicker and has distinct evidence before failing. However, as for the thinner webbeam, the phenomenon is opposite. Therefore, in the design of prestressed bridge,it should increase the thickness of the web and reduce the influence of constructiondeviation to improve the mechanical behavior.Chapter four is the most important component of the paper. The reasonablenumerical simulated model is put forward. The test process is simulated with themodel. By comparing the test result with that of simulated, the two agree with eachother well. Also, the finite element model is used to analyze the longitudinal crackin the web. The test results are compared with that of ideal in which the deviationis taken into consideration, the conclusion is as follows: (1) construction deviationhas little influence in the mechanical behavior of the whole structure, but great inlocal behavior. The smaller is the local size, the more prone is to come into beingcrack. (2) Tension is the largest around the curve point (650mm from the middlespan) of the prestressed reinforce, the crack is prone to appear. (3) The deficiencyinside really exists for any size beam, and the thinner of the web, the worse of theconstruction of local concrete. Accordingly, the more serious is constructiondeviation. (4) In construction condition, it is different to ensure the critical size.Therefore, when meeting the construction critical size, accordingly the mechanicalcritical size also meets.Chapter five is summary of the paper in which the content and direction arealso pointed out for further study.