Current Issue : July - September Volume : 2020 Issue Number : 3 Articles : 5 Articles
Validity of the approximate equation for predicting compressive stress in the posttensioned anchorage zone presented in the\nAASHTO LRFD Bridge Design Specifications was investigated in this study. Numerical analysis based on the finite element\nmethod (FEM) and theoretical analysis showed that the AASHTO formula gives relatively accurate stress values when the effect of\nduct holes is neglected. However, it was found that the formula can significantly overestimate the stresses in the actual prestressed\nconcrete member with spaces occupied by ducts. Therefore, an improved equation was proposed for the existing AASHTO\nequation to consider the effect of the duct holes on the stress distribution. This resulted in relatively accurate prediction of the\ndistribution and magnitude of the compressive stresses even with the presence of the duct holes. The proposed equation was also\nvalidated by comparing with the stresses measured in the test of a posttensioned full-scale specimen. This study is expected to\ncontribute to the design of the anchorage zone in prestressed concrete structures by suggesting a more reasonable way to assess the\nappropriateness of anchorage devices....
Concrete creep plays a significant role in the long-term performance of the prestressed concrete structure. However, most of the\nexisting prediction models cannot accurately reflect the in-site concrete creep in a bridge construction environment. To improve\nthe prediction accuracy of creep effects in concrete structures, an innovative creep analysis method is developed in this study.\nParameters in the creep model in fib MC 2010 have been calibrated with respect to the long-term loading test results of the\nprestressed concrete beam. The measured strains of concrete and the midspan deflections of the test beam are compared with the\npredicted results using the creep model in fib MC 2010. It indicates that the results predicted by the calibrated creep model are in\ngood agreement with the test results. However, the results predicted by the creep model in fib MC 2010 significantly deviate from\nthe test results. This proposed creep analysis method can provide a new thought to improve the predicted effect of the creep effects\non creep-sensitive structures....
Accidental loads such as explosion and vehicle impact could lead to failure of one or several load-bearing members in the\nstructures, which is likely to trigger disproportionate progressive collapse of overall structures. Prestressed concrete (PC) frame\nstructures are usually at great risk of collapse once load-bearing members fail, because the members in PC frame structures are\nusually subjected to much more load than those in common reinforced concrete (RC) frame structures. To investigate the\nprogressive collapse behaviors of PC frame structures, five one-fourth reduced scaled frame substructures were fabricated and\ncollapse tests were conducted on them. Influence of span-to-depth ratios of frame beams and prestress action modes on the\ncollapse performance of PC frame structures was discussed. Experimental results indicated that PC frame substructures with\ndifferent prestress action modes, including bonded prestress and unbonded prestress, presented different collapse resistance\ncapabilities and deformability. Tensile force increment of the unbonded prestressing strands almost linearly increased with the\nvertical displacement of the failed middle column. Catenary action is one of the most important mechanisms in resisting structural\ncollapse. Prestressing strands and longitudinal reinforcing bars in the frame beams benefited the formation and maintaining of\ncatenary action. The ultimate deformability of the PC frame structures was tightly connected with the fracture of prestressing\nstrand. In addition, a calculation method of dynamic increase factors (DIFs) suitable for PC frame structures was developed,\nwhich can be used to revise the design collapse load when static collapse analysis is conducted by the alternative path method. The\nDIFs of the five substructures were discussed on the basis of the proposed method; it revealed that the DIFs corresponding to the\nfirst peak loads and the ultimate failure loads for the PC frame substructures were less than 1.49 and 1.83, respectively....
As a new low-carbon material, development of preplaced aggregate concrete (PAC) will \nachieve huge economic and social benefits. However, few existing research is focused on applying \nPAC in structural elements. This paper is attempt to apply PAC in concrete filled steel tube (CFST) \nstub columns and the bearing behaviors of PAC filled steel tube (PACFST) stub columns under \naxial compression are also experimentally investigated. The results indicate that the failure modes \nof PACFST stub columns are all drum like failure mode which are analogous to that of CFST stub \ncolumns. ...........................................
In order to address the influence of aging on the performance degradation of SBS-modified asphalt, a composite modification of\nSBS-modified asphalt by nano-zinc oxide (nano-ZnO) and Trinidad Lake asphalt (TLA) was proposed. Several tests were\nconducted after adding nano-ZnO and TLA to SBS-modified asphalt, including a rotary film oven test (RTFOT), ultraviolet aging\n(UV), and the pressure aging vessel test (PAV). The conventional physical index, rheological index, and four-component content\nof SBS-modified asphalt before and after three aging modes were tested, and the characteristic functional groups in SBS-modified\nasphalt were tracked and analyzed by Fourier transform infrared spectroscopy (FTIR)...........................
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