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The newly proposed Precast Segmental Method (PSM), which makes use of precast elements for election, is relatively new, efficient and fast method for the construction of prestressed box girder bridges. A precast segment of 25 m long pretensioned in the fabrication yard is transported by a special trailer and a launching truss to its final position. The segments are then connected in the site by post-tensioning to make a continuous prestressed concrete box girder bridges. The purpose of this paper is to analyze and evaluate the design of precast prestressed concrete box girder bridges. The detailed analyses including time-dependent behavior of PSM bridges are conducted. The major results and findings, which have been obtained from finite element analysis of PSM bridge, are discussed in this paper and these results will be a good base for the design and analysis of a new precast bridges.
The shear design provisions of the current design codes and various models consist of many empirical equations. Because those were derived from the different types of members and loading conditions, there has been dissatisfaction with the empirical equations in the shear strength calculations for various types of concrete member. This study focuses on the development of the analytical model based on the truss action theory. It allows sectional analysis of shear behavior for the prestressed concrete member according to concrete strength and shear reinforcement.
An effective live load model for analyzing probable maximum live load effects such as moment and shear in transverse direction was developed. The main procedure of this live load model is composed of four parts, i.e., firstly, determination of the appropriate influence lines in longitudinal direction, secondly, application of the characteristics of vehicles and traffic patterns in longitudinal direction, thirdly, determination of the appropriate influence lines in transverse direction, and fourthly, application of the characteristics of vehicles and traffic patterns in transverse direction. Through this procedure, the probabilistic distributions of maximum probable load effects are deduced in the form of probability density function (PDF) and/or cumulative density function (CDF). This live load model is able to consider local or global deterioration of bridges in the structural analysis.
The test results on the deterioration process of concrete under single and combined action of chloride penetration have been obtained. Within the test period of 15 weeks, it is seen that the internally pemetrated chloride ion contents are slightly less in the combined action of NaCl and Na<sub>2</sub>SO<sub>4</sub> than the single action of NaCl. Also the theoretical prediction of chloride penetration based on measured diffusion coefficient ingress well with the test data of single deterioration process but disagrees with that of combined process. Therefore it should be needed that improved chloride diffusion model for the combined deterioration process
The prestress force can be introduced prestress force continuously through the construction joints of PSC bridge superstructure using tendon couplers. This method is easier and more economical to use in practice. However, the stress distributions in the direct vicinity of tendon-coupled construction joints of PSC bridge members are very complicated and the evaluation method of stress distribution in the construction joints of PSC bridge members is not established yet. The main objective of this study is to evaluate the structural behavior around coupling joint in PSC girder bridge members. To this end, a comprehensive experimental program has been set up and a series of full-scale tests have been performed to identify the effects of tendon coupling. The comprehensive finite element analyses, which simulate the segmental construction of PSC girder bridges, have been also performed to compare with test data and to figure out more detailed structural behavior around tendon coupling joint in PSC bridge girders. It is expected that the proposed method of determining the concrete stress distribution in the vicinity of tendon coupled joints provides a good basis for realistic design guidelines and thus contributes to advanced bridge construction technologies.
The non-destructive tests are widely used to predict the strength of existing structures. However, the current prediction equations give no satisfactory results when the aggregate, water to cement ratio, ages of concrete are different. The purpose of the present study is to propose the prediction equations for strength evaluation of concrete with limestone aggregate focusing on the rebound method and ultrasonic pulse velocity method. The major test variables include water to cement ratio and curing methods. The water to cement ratios are 0.3, 0.4, 0.5, 0.6, 0.7 respectively and the curing methods cover air-dry condition and standard curing condition. The present study indicates that the test data and the proposed equations agree well with each other.
The mass concrete structures are generally constructed in an incremental manner by deviding the whole structures by a series of many blocks. The temperature and stress distributions of any specific block are continuously affected by the blocks placed before and after the specific block. For an accurate analysis of mass concrete structures, the sequence of all the blocks must be accordingly considered including the change of material properties with time for those blocks considered. The purpose of this study is to propose a realistic and efficient analysis method which can take into account not only the influence of the sequence, time interval and size of concrete block placement on the temperatures and stresses, but also the change of material properties with time by the minimum number of blocks.
In this study, an analytical model is presented to predict the increase in cyclic creep strain and long-term deflection. Creep strain of the compression zone of concrete beams subjected to cyclic loading should be a significant factor in increasing strain and deflections. The effect of concrete-creep is accounted by the term E<sub>N</sub> and I<sub>cr,N</sub> whereas the effect of the progressive reduction in the tensile-stiffening contribution of concrete is included in the term M<sub>cr,N</sub>. According to the results of this study, it is concluded that cyclic creep exponents 'n' which means the velocity of the damage process, based on controlled variables such as strength and stress-range have various properties and values.
최근 다양한 침해환경에 건설되는 구조물이 증가함에 따라 철근 및 강재의 부식위험성이 높아지면서, 철근 콘크리트 구조물의 내구성 저하문제가 큰 관심으로 떠오르고 있다. 특히 해양 환경하에 건설된 철근 콘크리트 구조물의 경우 구조물 외부로부터 침투되는 염분의 영향으로 인한 철근부식이 발생 및 진행되어 콘크리트 구조물에 균열, 박리 등의 손상을 받게된다. 그러므로 해양콘크리트 구조물은 염해에 대해 내구성 및 신뢰성 확보가 중요시되고 있다. 따라서, 본 연구에서는 철근의 부착강도를 크게 감소시키지 않게 하는 방법으로서 시멘트 계통의 방청시멘트를 철근에 도막한 후 내부식성능과 부착강도특성을 실험적으로 연구하였다. 본 연구결과, 방청시멘트 도막철근은 소요의 내부식성능을 갖고 있으면서도 부착강도특성도 일반철근과 유사하였으며, 앞으로 실구조물의 내구성증진을 위해 효율적으로 사용될 수 있는 토대가 될 것으로 사료된다. Recently, large scale concrete structures exposed to severe environments are increasingly built in various locations, The corrosion may severely affect the durability and service life of such a concrete structure. It is, therefore, necessary to develop a method to enhance the corrosion resistance of a concrete, The purpose of this paper is, therefore, to investigate the corrosion resistance and bond strength characteristics of anti-corrosive cement coated reinforcements. To this end, a comprehensive experimental study has been done to explore the corrosion and bond behavior of those coated reinforcements. The test results indicate that the anti-corrosive cement coated reinforcements do not exhibit any corrosion after corrosion tests and the bond strengths are very good as much as plain bar. It is seen that the anti-corrosive cement coated reinforcements can be efficiently used to enhance the durability of reinforced concrete structures.