Advanced Materials Research Vols. 163-167

Abstract: This paper presents a new model for uniaxial stress-strain relationship of concrete confined by rectangular steel tubes. The difference between concrete confinement effect provided by broad faces and that provided by narrow faces of steel tube is considered in the proposed model. The failure criteria for concrete subjected to triaxial compression is applied to estimate the ultimate strength of concrete core. The parameters of the model are determined based on the test results and the calculation of complete load-stress relationship curves is conducted for axially loaded rectangular CFT specimens using the model proposed in the paper. The concrete core strength and stress-strain behavior of rectangular CFT columns is found to exhibit good agreement with test results.

Abstract: New type composite wall is the main bearing member in Multi-ribbed Slab Structure (MRSS), whose cracking load is an important parameter to determine the restoring force model and damage index of the wall. Based on the twin shear unified strength theory, when the influence of intermediate principal stress σ₂ and SD effect of materials are considered, the study on low-frequency cyclic lateral loading experiment of wall is proceed and the practical formula for the wall’s initial cracking load is deduced. The practical computing formulas for the wall’s initial cracking load based on twin shear unified strength theory and maximum tensile stress theory are contrastingly analyzed. The results show that, comparing the calculated values based on the twin shear unified strength theory and the values based on maximum tensile stress theory, the former are more closed to the experimental values, and it can provide more accurate, economic and applicable results for practical engineering.

Abstract: Due to the invasion of chloride ion, the reinforcement in coastal concrete structure is corroded, which causes damage to the concrete structure and becomes the major factor affecting the structure’s service life. Aiming at the existing concrete structure under the coastal environment of Shenzhen City, the durability experimental study has been implemented, discussing the main reason for the insufficient durability of the existing structure. The experiment result shows that the higher chloride ion diffusion coefficient (76.1×10^-12 m²/s) in the concrete structure leads that the chloride ion concentration of the structure in the depth of 30mm surpasses one percent upon using it for two decades. The half-cell potential value also reflects the relatively high possibility of the reinforcement corrosion of the structure. Combining with the experiment result, the service life of this concrete structure has been analyzed, which is hard to be guaranteed to use for five decades under the current concrete parameters and resistance.

Abstract: A total of 10 high-strength concrete columns confined by high-strength complex stirrups were tested under cyclic lateral force and a higher constant axial loading. The results indicate that the hysteresis loop of this type of columns still shows plump spindle-shaped at higher axial compression ratio, with better ductility, energy dissipation capability and stronger anti-collapse ability; so setting closed high-strength stirrups is an effective measure to ensure the HSC columns good ductility and enhance its axial compression ratio limits. Additionally based on the experimental research and theoretical analysis, the limits of axial compression ratio of HSC columns at different levels of seismic are present in this paper.

Abstract: The finite element analysis of high-strength concrete columns confined by high-strength spiral lateral ties under concentric compression is introduced in this paper. The variables of tie strength, tie spacing and tie configuration influencing the characteristics of confined concrete are discussed; and the stress distributions of lateral ties and concrete at cross-section are analyzed. Compared with the test results, this finite element analysis can predict well the behavior of axially loaded concrete confined by lateral ties. It’s indicated that after peak load, normal stirrups loss the effective constraint on concrete due to yielding early, while the high-strength stirrups can continue to provide larger constraint which can improve significantly the ductility of confined concrete.

Abstract: Concrete filled steel tubular (CFST) column-beam joint with the column tube discontinuous in joint zone is a new type of joint. In this paper, the compressive tests on this joint were carried out after the cyclic reversed loading. First the cyclic loading experiment results were introduced briefly, then the compressive tests were presented. The bearing capacity, crack patterns, deformation, strain of the reinforcements of the specimens were studied. These specimens were also compared with the other specimens only under compressive test. The results show that the specimens have good ductility. The concrete of the reinforced concrete (RC) ring beam cracked before the yield of the steel ring bars or the buckling of the steel tube. Although the cyclic loading caused some damage on the ring beam, it had few effects on the axial bearing capacity. The RC ring beam can still confine the joint zone and ensure the capacity of the joint zone was not lower than the CFST column.

Abstract: Concrete dam safety is one of the hot issues in dam study with the increasing of dam’s scale and height. Sliding failure along foundation surface is a potential failure mode of concrete gravity dam, and this mode is relatively rare in practical engineering. Strength reduction method is used to analyze the progressive failure along foundation surface of concrete gravity dam, and the strength parameters of weak layer in the foundation surface are reduced to analyze the occurrence and development regularity of plastic zone. If the plastic zone of foundation surface is totally coalescent, the dam will slide along the foundation surface. To track this process, the failure path and the safety reserve coefficient would be determined. This result will provide certain scientific basis for anti-sliding stability analysis of concrete gravity dam.

Abstract: Both the increasingly-thin walls of box girder cross-sections and the super-loads from trains or track vehicles make the behavior research on diaphragms and side walls become particularly important. According to the deformation of single cell box girder cross-section, the displacement parameters were designed, and the displacement modes of cross-section distortion angles were deduced. The schematic plans of diaphragms and side walls were simulated by rigid frames or plates. Both the shearing strain energy and the shearing stiffness of diaphragms and side walls were deduced on the basis of the principles of mechanics and finite element. The results show that the shearing strain energy increases with the displacement by a power function. And the method calculation results are close to the commercial FE software calculation results, which show that the calculation method of single cell box girder presented in this paper is correct and reliable. The calculation method is simpler than the commercial FE software calculation method. In the calculation method, whether diaphragms and side walls are calculated separately or calculated as some parts of the box girder or the vehicle - bridge system, the calculation precision of diaphragms and side walls remains unchanged.

Abstract: In order to study the meso-structure of concrete deeply, this paper proposes a new approach—intersection method, which is much simpler and more applicable to check the interference for wide varieties of shape aggregate by using the VBA language built-in AUTOCAD. Results show that the procedure to establish the model of concrete aggregate is user-friendly, simple, intuitive and precise. It can be analyzed through introducing into finite element software for the further numerical study of macro and micro mechanical properties of concrete by using the mutual files SAT which is used to exchange the CAD data between AUTOCAD and other software.

Abstract: Through experiment and theoretical analysis, this paper researched the influence of steel bar corrosion of hollow slab hinge joints on the structural mechanical behavior. The results showed that when load was little corrosion of hinge joints steel bar would do little to affect the joint between hollow slabs and hinge joints would work together with hollow slabs as a whole. When load was large, corrosion of hinge joints steel bar would decrease the joint between hollow slabs.