Renda Zhao

A general and versatile nonlinear analysis program for concrete bridge structure

To meet the application of nonlinear FEM analysis to the real bridge structure, a general and versatile nonlinear analysis program for concrete bridge structures is presented in this paper. The structural effects such as material nonlinear behavior, prestress effect, construction process, temperature, creep of concrete and so on, which are concerned in practical engineering, are covered. To simulate the nonlinear behaviors, an efficient 3D degenerated beam element is adopted. The step-by-step analysis method allows one to comprehend the structural behaviors of the bridges during the construction, service, and failure periods, respectively. Finally, two examples are studied to verify the accuracy of the program and demonstrate its application in practical bridge engineering.

Analysis of thermal behavior on concrete box-girder arch bridges under convection and solar radiation:

The two-dimensional finite element method can be used to calculate the thermal field distribution of prestressed concrete bridge girders. However, this method is not appropriate for the concrete box-girder arch bridges, because they have different azimuth and dip angles at the top and bottom flanges along arch axis. Thus, an experimental and analytical study was conducted on a concrete box-girder arch bridge located in Guizhou, China, to investigate the thermal behavior under convection and the solar radiations. To determine the vertical temperature gradients, a two-dimensional plane finite element model was used to calculate the thermal field based on meteorological parameter methods. In addition, the three-dimensional beam finite element model was proposed to study the thermal stress and displacement of arch bridges using the vertical temperature gradients. Finally, the thermal behavior of the concrete box-girder arch bridges determined by the two-dimensional plane and three-dimensional beam finite element model was verified by three-dimensional solid finite element model.

Interface Behavior between Steel and Concrete Connected by Bonding

AbstractIn this study, push-out tests were conducted to evaluate the interface behavior between steel and concrete connected by bonding. Twelve sets of specimens with different adhesive thicknesses, modulus of elasticity, and interface roughness were investigated. Failure modes, ultimate loads, and load–slip relationships are reported and analyzed in the paper. The experimental results show that factors such as modulus of elasticity of adhesive materials, adhesive thickness, and interface roughness affect the interface behavior. An analytical model is proposed to predict the ultimate load value and the load–slip relationship. The comparison between test results and analytical predictions shows good agreement.

Reliability analysis of circular concrete-filled steel tube with material and geometrical nonlinearity

Most of the previous research on concrete-filled steel tube is restricted to a deterministic approach. To gain clear insight into the random properties of circular concrete-filled steel tube, reliability analysis is carried out in the present study. To obtain the structural nonlinear response and ultimate resistance capacity, material and geometrical nonlinear analysis of circular concrete-filled steel tube is performed with a three-dimensional degenerated beam element. Then we investigate the reliability of concrete-filled steel tube using the first-order reliability method combined with nonlinear finite element analysis. The influences of such parameters as material strength, slenderness, initial geometrical imperfection, etc. on the reliability of circular concrete-filled steel tube column are studied. It can be concluded that inevitable random fluctuation of those parameters has significant influence on structural reliability, and that stochastic or reliability methods can provide a more rational and subjective evaluation on the safety of CFT structures than a deterministic approach.

Influence of steel–concrete bond damage on the dynamic stiffness of cracked reinforced concrete beams

In this article, experiments focusing at the influence of steel–concrete bond damage on the dynamic stiffness of cracked reinforced concrete beams are reported. In these experiments, the bond between concrete and reinforcing bar was damaged using appreciate flexural loads. The static stiffness of cracked reinforced concrete beam was assessed using the measured load–deflection response under cycles of loading and unloading, and the dynamic stiffness was analyzed using the measured natural frequencies with and without sustained loading. Average moment of inertia model (Castel et al. model) for cracked reinforced beams by taking into account the respective effect of bending cracks (primary cracks) and the steel–concrete bond damage (interfacial microcracks) was adopted to calculate the static load–deflection response and the natural frequencies of the tested beams. The experimental results and the comparison between measured and calculated natural frequencies show that localized steel–concrete bond damage does not influence remarkably the dynamic stiffness and the natural frequencies both with and without sustained loading applied. Castel et al. model can be used to calculate the dynamic stiffness of cracked reinforced concrete beam by neglecting the effect of interfacial microcracks.

Experimental study on mix proportion of fiber reinforced cementitious composites

To study the mechanical property of fiber reinforced cementations composites influenced by the fiber length, quartz sand diameter, matrix of water cement ratio, volume fraction of fiber and magnesium acrylate solution. Several 40×40×160u2005mm standard test specimens, “8” specimens and long “8” specimens and 21 groups of fiber concrete specimens were fabricated. The flexural, compressive and uniaxial tensile strength were tested by using the bending resistance, compression resistance and electronic universal testing machine. The results show that flexural and compressive strength of fiber reinforced cementations composites increases along with the increase of quartz sand diameter, with the growth of the PVA fiber length increases; When the water-binder ratio is 0.25 and powder-binder ratio is 0.3, the PVA fiber content is 1.5% of the mass of cementations materials, there is a phenomenon of strain hardening; The addition of magnesium acrylate solution reduces the tensile strength of PVA fiber reinforced cement...

Calculation methods study on hot spot stress of new girder structure detail

To study modeling calculation methods of new girder structure detail’s hot spot stress, based on surface extrapolation method among hot spot stress method, a few finite element analysis models of this welded detail were established by finite element software ANSYS. The influence of element type, mesh density, different local modeling methods of the weld toe and extrapolation methods was analyzed on hot spot stress calculation results at the toe of welds. The results show that the difference of the normal stress in the thickness direction and the surface direction among different models is larger when the distance from the weld toe is smaller. When the distance from the toe is greater than 0.5t, the normal stress of solid models, shell models with welds and non-weld shell models tends to be consistent along the surface direction. Therefore, it is recommended that the extrapolated point should be selected outside the 0.5t for new girder welded detail. According to the results of the calculation and analysis...

Numerical analysis of recycled aggregate concrete-filled steel tube stub columns

This article presents a numerical analysis on the behavior of square recycled aggregate concrete-filled steel tube stub columns with the cold-formed hollow structural steel tube being used. A nonlinear finite element model for the square recycled aggregate concrete-filled steel tube stub column under axial compression has been developed using the general-purpose finite element program. An equivalent stress-strain model is proposed to simulate the behavior of the recycled aggregate concrete confined by a steel tube. The results obtained from the finite element model are compared with the experimental data. The comparison indicates that the finite element model is capable of predicting the mechanical behavior of the square recycled aggregate concrete-filled steel tube stub columns. After the validation of the numerical model, the effects of the recycled aggregate replacement ratio on the behavior of the square recycled aggregate concrete-filled steel tube stub columns are investigated. Furthermore, the applicability of the current design specifications and the proposed empirical formulas by various researchers to predict the ultimate compressive strengths of the recycled aggregate concrete-filled steel tube stub columns are examined. The comparative study shows that the specification Eurocode 4 gives closer prediction of the ultimate compressive strength than the other methods.