Advanced Materials Research Vols. 163-167

Abstract: The structural behavior of a steel reinforced concrete (SRC) transfer beam in high-rise building is studied in the paper. Mechanical properties and deformation characteristics between transfer beam and shear wall are analyzed by an analytic approach and the nonlinear finite element method. The stress analytical solutions for the SRC transfer beam are obtained and agree with finite element calculation data in an actual project. The results show that the beam can be as an eccentric tension member, meanwhile the performance of shear wall must be considered. And it also shows that the shear stress and vertical compressed stress must be considered in end both transfer beam and shear wall and there is interaction between the beam and the shear walls above. The results can be used to describe the behavior of the SRC transfer beam under complicated loads.

Abstract: The constitutive relation of concrete under uniaxial compression is the essential theoretical basis for structural analysis of concrete. Because of lack of sufficient stiffness for ordinarily tester, stable falling branch of stress-strain curve cannot be obtained. The common methods to increase rigidity of loading system include direct and indirect method. The condition of realizing the stress-strain complete curve for concrete uniaxial compression is derived. A set of stiffness experimental equipment is designed by using the indirect method, which has the advantages of simple, dependable and strong adaptability. Experiment shows that stress-strain complete curve of uniaxial compression under different strain rate could be achieved by using this equipment and electro-hydraulic loading system of MTS co. ltd. It will lay foundation for putting forward the stress-strain curve equation of uniaxial tension and compression under considering the effect of strain rate. It can provide theoretical basis for structural analysis of concrete.

Abstract: Two simply supported deep beams were tested, one with draped prestresssing tendons and the other without for reference. Shear behavior and the prestressing effect were focused on. The test results showed that deep beams with the longitudinal reinforcement ratio of a normal amount were inclined to fail in flexural-shear, and the prestressing could greatly increase both the cracking load and the shear strength. Beside, the Modified Strut-and-Tie Model (MSTM) and the sectional design method from China Code (GB02) have also been adopted for predictions. The comparisons indicates that the MSTM can not only well predict the shear strengths of deep beams, but also well account for the prestressing effect, while the sectional design method seems so conservative due to its not properly considering the shear mechanism of deep beams. It can be concluded that the MSTM is capable of predicting the shear strength of PC deep beams with draped tendons and thus can be employed in practical designs.

Abstract: The internal-force distributing of the slab computed according to the existing design methods is different from that of the bidirectional slab supported on beam. The mechanical characteristic of the slab on unbonded prestressing tendons concentrated arranged along the columns is analyzed. The results show that the hidden beams of prestressing tendons couldn’t replace the role of the actual beam. Therefore, the prestressing tendons layout in the beam-less slab should not be disposed according to the internal stress distribution of the two-way slab supported on actual beams. Based on the FEM, a accurate method for calculating the amount of two-way prestressing tendons is put forward according to the bearing counterforce that existe in beam-supported two-way slab. The linear of the prestressing tendons is deduced and reasonable value of the equivalent load of prestressed tendons is suggested.

Abstract: Owing to the outstanding advantages of unbonded prestressed technology, it has been widely used in high-rise building floor. However, with the continuous improvement of the function requirements of the building, the boards with openings become more and more common, not only in new constructions but also in renovation projects. These holes will change the mechanical properties of the original floor, and cause stress concentration around the holes easily. This article carries on the simulation analysis by modeling the experimental model using ANSYS software, focuses on the deflection, crack and ultimate load of unbonded post-tensioned prestressed concrete board with open-hole (under uniform load in tensioning and loading stage). After making the comparative analyses to the mechanical behavior and failure mechanism under the different locations of the holes, the simulation results are compared with experimental results, shows that ANSYS can simulate the whole process of loading better, provides theoretical basis for its application and promotion in practical engineering.

Abstract: Based on the contrast experiments of unbonded prestressed concrete slabs with openings subjected to uniform load strengthened by different methods, this paper investigates and analyzes the appearance and the development of cracks, deflections, bearing capacity of the unbonded prestressed concrete slabs that are with strengthening steel and with hidden beams. According to the experimental failure mode of the slabs, prestressed concrete slabs with openings by yield line theory considering the conditions to enhance the contribution of hidden beam and the strengthening steel. Compared with the experimental data, this paper puts forward some bearing capacity lift-off effect of the slabs under different strengthened methods.

Abstract: The reinforced concrete (RC) beams have three failure modes using large-scale finite element procedure LS-DYNA to simulate dynamic responses and failure modes of RC beams under blast loading. Holmquist-Johnson-Cook material model was used in concrete, the damage and strain rate effects were considered the kinematic hardening plasticity material model was used in reinforcing bars. With different rebar ratios and charges of weight TNT equivalent and stand-off distance were investigated and discussed. The numerical simulation can predict responses and flexure, flexure-shear and direct shear of the RC beams under different blast loading. The influence of the several factors have been identified and provided a theoretical basis for blast resistant design and retrofitting of the RC beam.

Abstract: Over-deflection of beam in continuous rigid frame bridge has become an serious problem in recent years. The reason is complex. Some reseachers think that the bad quality of sectional joints in cantilever construction will cause additional shearing deformation and affect the beam deflection, this idea need to be further studied. In the paper, two three-dimensional models are built up based on a factual bridge, the simulation method of joints is studied, the influence of shearing deformation caused by sectional joints on beam deflection in construction is analysed. The study shows that shearing deformation of sectional joints has influence on deflection in cantilever construction, and it shouldn’t be ignored. This may be important to improve the loading property and renovate the design concept of this kind of bridge.

Abstract: The loads of reinforced concrete buildings are bore by shores and early age concrete members during construction. In order to analysis the distribution of vertical load between concrete members and shores, the approximate method was developed based on the finite element method and simplified method. According to the process of construction, seven primary structures were brought forward in the approximate method. The coefficients of vertical load distribution between concrete members and shores are confirmed through the finite element method. The loads of concrete members and shores could be obtained conveniently through the distribution coefficients. Three shoring systems (2S, 2S1R and 3S) could be calculated by the approximate method, so the suitable shoring systems for reinforced concrete buildings would be confirmed.

Abstract: The purpose of this study is to investigate the influence of specimen size and shape on compressive strength of concrete. Concrete cubes, cylinders and prisms with their size ranging from 150mm to 450mm were tested in unaxial compression. Failure patterns and the effect of specimen shape and size on compressive strength of concrete were investigated. In addition, theoretical size effect models, such as the MSEL and MFSL were used to analyze the size effect of concrete strength. It is shown that for specimens tested in this study, the two models are both applicable to predicting the compressive strength of specimens in various sizes with a reasonably good accuracy.