摘要：
A long-term deflection test is performed for 470 days on two simply supported prestressed concrete box beams under sustained uniform load. The deflection growth rules of the box beams under both cracked and uncracked states are studied. The measured longterm deflection of the cracked beam is 18.4% larger than that of the uncracked beam, whereas the deflection growth coefficient of the cracked beam is 65.3% that of the uncracked beam. The larger long-term deflection of the cracked beam is mainly attributed to the huge value of the instantaneous deflection caused by the crack. Then, the cracks lead to the release of concrete stress, thereby reducing the creep effect. For the uncracked beam, the influences of concrete shrinkage, creep, and prestress loss on the long-term mechanical behavior of components are considered, and then deflection is predicted using the blended method based on the age-adjusted modulus method, the prestressed equivalent load method, and the calculation method for prestress loss. Results show that the theoretical and measured values are in good agreement. For the cracked beam, the crack influence coefficient is introduced to revise its effective elastic modulus by considering the influence of cracks on the long-term deflection of the cracked beam. Then, a formula for calculating the long-term deflection of cracked beams that considers stiffness reduction for instantaneous deflection correction is proposed. The formula exhibits high precision in calculating and analyzing the long-term deflection of the cracked beam. The deviation between the calculated and measured values is within 10%.
作者：
Cao, Guohui*;Zhang, Wang;Hu, Jiaxing;Zhang, Kai
期刊：
International Journal of Civil Engineering,2018年16(8):887-895 ISSN：1735-0522
通讯作者：
Cao, Guohui
作者机构：
[Cao, Guohui; Zhang, Kai] Hunan City Univ, Coll Civil Engn, 518 Yingbin East RD, Yiyang 413000, Hunan, Peoples R China.;[Zhang, Wang] Changsha Univ Sci & Technol, Coll Civil Engn & Architecture, 960,2nd Sect,Wanjiali South RD, Changsha 410114, Hunan, Peoples R China.;[Hu, Jiaxing] Hunan Univ, Coll Civil Engn, Lushan South RD, Changsha 410082, Hunan, Peoples R China.
通讯机构：
[Cao, Guohui] H;Hunan City Univ, Coll Civil Engn, 518 Yingbin East RD, Yiyang 413000, Hunan, Peoples R China.
关键词：
Retard-bonded;Prestressed concrete;Beams and girders;Deflection;Creep
摘要：
This study compares the mechanical properties of the retard-bonded and conventionally bonded prestressed concrete (RBPC and BPC, respectively) under uniform loads. Results show that the prestressed strands and concrete of the RBPC T-beams are firmly bonded with harden of retard-bonded materials, thereby exhibiting the same mechanical properties as that of the BPC beams. The growth rate of the long-term deflections of the RBPC T-beam is slightly lower than that of the BPC T-beam. Given the effect of concrete shrinkage, creep and time variation of prestress loss, the regular patterns of deflection growth of the RBPC T-beam mid-spans are analysed based on the age-adjusted effective modulus method, method of equivalent prestress load and calculation model of prestress loss. Accordingly, the long-term deflection development curves of the RBPC T-beam mid-spans under self-weight, prestressing force and external loads are obtained. Calculation results are in good agreement with the test results. This method has immense applicability for the computation of the RBPC T-beams, and can be used to estimate the long-term deflection growth of regular patterns of the RBPC components.
作者机构：
[彭细荣; 张锴; 曹国辉] College of Civil Engineering, Hunan City University, Yiyang, 413000, China;[阳亮] College of Civil Engineering, Hunan University, Changsha, 410082, China
通讯机构：
College of Civil Engineering, Hunan City University, Yiyang, China
通讯机构：
[Cao Guo-hui] H;Hunan City Univ, Coll Civil Engn, Yiyang 413000, Peoples R China.
关键词：
PC box girders;long-term load experiment;flexural behaviors;cracks;static performance
摘要：
Long-term load and flexural failure experiments are carried out on two prestressed concrete (PC) simply supported box girders. In the long-term load experiment, girder-1 (G1) is in an elastic state, while girder-2 (G2) is in a cracking state. To investigate the influence of cracking on the flexural behaviors of PC simply supported box beams, the experiment results are analyzed from many aspects, such as load–deflection, load–strain, and failure mode. Experiment results show the following: 1) the shrinkage and creep of concrete have considerable influences on the long-term deflection and strain of the two girders; 2) in the flexural failure experiment, the cracks and ultimate loads of the two girders are close. The rigidity degeneration of G2 is significantly faster than that of G1, and thus G2 shows nonlinear characteristics earlier; 3) to prove the validity and rationality of the current code, the cracking load and ultimate load of the two girders are calculated according to the current code.
作者机构：
[Cao Guo-hui; Zhang Kai] Hunan City Univ, Coll Civil Engn, Yiyang 413000, Peoples R China.;[Hu Jia-xing] Hunan Univ, Coll Civil Engn, Changsha 410082, Peoples R China.
通讯机构：
[Cao Guo-hui] H;Hunan City Univ, Coll Civil Engn, Yiyang 413000, Peoples R China.
关键词：
prestress;relaxation loss;shrinkage and creep;theoretical analysis;calculation model
摘要：
The calculation model for the relaxation loss of concrete mentioned in the Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts (JTG D62—2004) was modified according to experimental data. Time-varying relaxation loss was considered in the new model. Moreover, prestressed reinforcement with varying lengths (caused by the shrinkage and creep of concrete) might influence the final values and the time-varying function of the forecast relaxation loss. Hence, the effects of concrete shrinkage and creep were considered when calculating prestress loss, which reflected the coupling relation between these effects and relaxation loss in concrete. Hence, the forecast relaxation loss of prestressed reinforcement under the effects of different initial stress levels at any time point can be calculated using the modified model. To simplify the calculation, the integral expression of the model can be changed into an algebraic equation. The accuracy of the result is related to the division of the periods within the ending time of deriving the final value of the relaxation loss of prestressed reinforcement. When the time division is reasonable, result accuracy is high. The modified model works excellently according to the comparison of the test results. The calculation result of the modified model mainly reflects the prestress loss values of prestressed reinforcement at each time point, which confirms that adopting the finding in practical applications is reasonable.
作者机构：
[张锴; 曹国辉] School of Civil Engineering, Hunan City University, Yiyang, China;[胡佳星] School of Civil Engineering, Hunan University, Changsha, China;[张胜; 张旺] School of Civil Engineering and Architecture, Changsha University of Science &, Technology, Changsha, China
通讯机构：
School of Civil Engineering, Hunan City University, Yiyang, China
作者机构：
[曹国辉; 蒋建清] School of Civil Engineering, Hunan City University, Yiyang, Hunan, China;[刘热强] Guangdong Provincial Architectural Engineering Machinery Construction Co., Ltd., Guangzhou, Guangdong, China
作者机构：
[张锴; 曹国辉; 何敏] College of Civil Engineering, Hunan City University, Yiyang, China;[胡佳星] College of Civil Engineering, Hunan University, Changsha, China
通讯机构：
College of Civil Engineering, Hunan City University, Yiyang, China
作者机构：
[张锴; 曹国辉; 何敏] College of Civil Engineering, Hunan City University, Yiyang, China;[胡佳星] College of Civil Engineering, Hunan University, Changsha, China
作者机构：
[张锴; 刘超; 曹国辉] College of Civil Engineering, Hunan City University, Yiyang 413000, China;[胡佳星] College of Civil Engineering, Hunan University of Science and Technology, Xiangtan 411105, China
通讯机构：
College of Civil Engineering, Hunan City University, China
