Advanced Materials Research Vols. 250-253

Abstract: The focuses are to analyze the complicated damage process, and to determine the deformation field of the localized deformation and damage of the double notched concrete beam. Basic principle of the digital-speckle-correlate method (DSCM) was introduced. The displacement field of the beam under four-point- shear loading has been investigated with white-light speckle method, which can determined the speckle field of the surface of the deformation body rapidly and can be used to calculate the phase of deformation. Furthermore, the localized band of the deformation of the concrete can be recorded accurately. This method has shown that the procedure of experiment is convention, and can be used to determine various kind of deformation situation, including finite deformation and small deformation. Numerical calculation has been done to simulation the damage field and the whole damage field. The conclusion indicate that: compared with the localized band of the damage field and the damage process region of the experiment, damage field of the double of the notched beam from the numerical calculation can match it very well

Abstract: The experiments of 26 unbonded prestressed concrete flat beams under fire with elevating the temperature according to the ISO time-temperature standard curve were accomplished in the large structures electrical heating furnace that was manufactured independently. The macroscopical phenomena of water penetration, the lube flowing, the spalling of concrete and the corlor change of aspect were observed. The laws of behaviors such as temperature distribution on section,the deformation characteristic and stress varieties of prestressed tendons were investigated through the tests. The experiments indicated that temperature distribution was not uniform, the dynamic continuous deformation and the complicated varieties of prestressed stress occurred at high temperature. Based on the increment temperature-stress coupling constitutive models and chief deformation compatibility of the unboded prestressed tendons, the nonlinear finite element calculation formula took the unknown nodes displacements and the tensile forces in the unbonded tendons as unsolved column matrix simultaneously. The Increment format of nonlinear finite element method and calculation model for whole process analysis of unbonded prestressed concrete flexural members at high temperature were presented. The solution of nonlinear equilibrium equations for unboded prestressed concrete flexural members at high tempure was proposed, and a FORTRAN program named NAUPCLF was developed also and the results were in good agreement. The conclusions can supply the way and basis for further fire-resistant design and analysis of prestressed concrete structures.

Abstract: For engineering practice purpose, the macroscopic model capable of simulating the main characteristics of nonlinear behavior is desirable to reduce computational efforts in nonlinear structural analysis. Several different types of macroscopic models for shear walls have been developed. The shear wall element used in the commercial program PERFORM-3D is one types of macroscopic models for reinforced concrete shear walls. The application of PERFORM-3D in the nonlinear static analysis of reinforced concrete shear walls is introduced in this study. The selection of constitutive models and the determination of related parameters of the constituent material are presented in detail. The applicability of the shear wall element is verified by numerical simulation on three reinforced concrete shear wall specimens under cyclic loading. The comparison between the numerical analysis and test results leads to the conclusion that the shear wall element with appropriate constitutive models can capture the nonlinear behavior of reinforced concrete shear wall well and be conveniently applied in engineering practice.

Abstract: In this paper, the different sizes of enlarged weld access hole (EWAH) in steel beam-column connection are presented. Based on the commercial nonlinear finite element code ABAQUS, firstly, the sequential welding process is simulated, and the non-linear pseudo-static is performed. Through the comparison of results between the FEA and finished pseudo-static experiment when EWAH size is adopted by x=115mm and y=35mm, it is demonstrated that this analysis method is rational and effective, moreover, the stress concentration effects and cracks are discovered. And then the FEA method still obtains, the EWAH size y=35mm is changeless, the nine structural models are made up for only considering the value range from x=70mm to x=110mm. Furthermore, the impacts of the EWAH size on mechanical behaviour are discussed, and the reasonable geometric range is proposed.

Abstract: Strengthening using prestressed CFRP plate is a new developed technology in recent years, which can significantly improve the flexural behavior of reinforced concrete (RC) beams. In this paper, an experimental study including four RC beams stengthened with CFRP plates using self-developed anchorage system was carried out. The nonlinear finite element models of the strengthened beams were constructed to simulate the influence of flexural behavior on RC beams strengthened with CFRP plates under different damage degrees. The experimental results indicated that initial damage degrees have greatly influence on the crack distribution and ductility, deflection and the ultimate flexural strength of the strengthened beams, as well as steel reinforcement strain and CFRP plate strain. Meanwhile, the finite element model can predict accurately performances of strengthened RC beams before CFRP debonding. In addition, the numerical analysis indicated that the sustained loading while strengthening RC beam using prestressed CFRP plates would induce adverse effect, so the live loading should be removed before starting the strengthening works.

Abstract: Vertical static load test is widely used in the determination of pile bearing capacity, the mathematical model used to fit test pile data in determining the bearing capacity is essential. From the perspective of analytic geometry, the paper analyzes the traditional method of hyperbola, of which the asymptotic line of equilateral hyperbola was used to determine the ultimate bearing capacity. By extending the equal-axed conditions, a more general form of hyperbolic equation is derived and feasibility of such method is also analyzed, which indicates that the maximum point of curvature in such hyperbolic curve can determine the ultimate bearing capacity and such method is proved to be reasonable in practical projects.

Abstract: It is common to have a foundation pit accident, when failing to deal with the effect of confined water. In order to avoid such accidents, the Jiangnan launching shaft of Qingchun Road River-Crossing Tunnel in Hangzhou was investigated. According to the analysis of on-site monitoring data of wall deflection, settlement, and strut load, some conclusion can be drawn. Firstly, the wall deflection is closely related to the plane size of the foundation pit, and through strengthening the stiffness of the central support, the wall deflection can be greatly controlled. Secondly, the maximum settlement point is 0.5 times depth of the excavation away from retaining wall. Finally, load in the first level strut gradually decreased during the construction, and even can turn to be tensile force.

Abstract: A nonlinear force method model is proposed to study the dynamic behavior of cable trusses. In the paper, travelling wave method is employed to solve the governing equation of motion. After support reaction forces are considered as excitations, cable trusses are extended to infinitude, and D’Alembert solution to the partial differential equation (PDE) is achieved. Substituting the solution into compatibility condition and boundary conditions, the governing equation expressed by dynamic tension is derived, which is named force method dynamic equation (FMDE). Hence the dynamic system of infinite-degree-of-freedom is simplified as a system with only one unknown without any loss of precision. Nonlinear governing equations are developed through considering the effect of quadratic terms of displacements. At last, an example is given to verify the force method model presented in the paper.

Abstract: In current seismic design procedure, structural base shear is calculated according to the linear elastic response spectra divided by response modification factor R. The response modification factor is important to the reliability and economy of building seismic design. In this paper, the response modification factors of Twelve Y-eccentric braced steel frames with various stories and spans lengths were evaluated by capacity spectrum method based on the global capacity envelops obtained from an improved pushover analysis and incremental dynamic analysis. According to the results, an appropriate formula of the response modification factor for the Y-eccentric braced steel frames was suggested.

Abstract: The rise of groundwater level can reduce soil’s effective stress and destroy it’s structure. As a result, the dynamic characteristics of pile-soil-structure system will be changed remarkably. In this paper, a structural dynamic model was used for saturated loess, and the finite-infinite element model of pile-soil-structure system was established to study the groundwater level’s influence on the system’s dynamic characteristics, which included the distributions of pile section’s shearing stress, horizontal displacement and acceleration. The results indicated that, the height of groundwater level did not change the distribution shapes of shearing stress, horizontal acceleration, but had effect on their values. To the top section’s shearing stress and horizontal displacement, there almost had a same dividing groundwater level. When groundwater level was higher than that one, the shearing stress and horizontal displacement were increasing with the rising of groundwater level, but the regulations were just opposite when groundwater level under that height. The study also shown that, to a determinate geological condition and pile foundation, there has a dividing groundwater level, and which is also the most secure level to the pile-soil-structure system. The conclusion can give theoretic instruction for the safety evaluation of pile-soil-structure system around water area.