Advanced Materials Research Vols. 446-449

Abstract: In moving towards an engineered performance-based approach to structural fire safety, a sound knowledge of the elevated-temperature properties of structural steel is crucial. Of all mechanical properties of structural steel at elevated temperatures, material creep is particularly important. Under fire conditions, behavior of steel members and structures can be highly time-dependent. As a result, understanding the time-dependent mechanical properties of structural steel at high temperatures becomes essential. This paper presents preliminary results of a comprehensive on-going research project aimed at characterizing the material creep behavior of ASTM A992 steel at elevated temperatures. Such creep properties are presented in the form of strain-time curves for materials from the web and the flanges of a W4×13 wide flange section and from the web of a W30×99 section. The test results are then compared against material creep models for structural steel developed by Harmathy, and by Fields and Fields to evaluate the predictions of these models. The preliminary results clearly indicate that material creep is significant within the time, temperature, and stress regimes expected in a builing fire. The results also demonstrate the need for a more reliable creep model for steel for strcutural-fire engineering analysis.

Abstract: In this paper, co-rotational total Lagrangian finite element formulation is derived, and the corresponding numerical model is developed to study creeping behavior of plane steel frames in fire. Geometrical nonlinearity, material nonlinearity, high temperature creeping, and temperature rising rate are taken into account. To verify accuracy and efficiency of the numerical model, four prototypical numerical examples are analyzed using this model. Results are in a great agreement with solutions in literatures. Then the numerical model is used to analyze creeping behavior of the plane steel frames when temperature is lowering. The numerical results have significant contribution to resistance and protection for steel structures against disastrous fires.

Abstract: Due to the use of mathematical cover system and physical cover system, the numerical manifold method (NMM) is very suitable for discontinuity problems, especially for multiple crack problems. In the NMM, the mathematical cover system is independent of the physical boundary, and in this case, fully regular mathematical elements can be used. In the present paper, the NMM, combined with the rectangular mathematical elements, is applied to solve crack interaction problems in the linear elastic fracture mechanics (LEFM). To verify the present method, a typical numerical example is investigated and the results agree well with the reference solutions.

Abstract: Three series compressive tests of concrete columns, CFRP constraint concrete columns and CFRP constraint concrete columns under compression are carried out to study the influence of initial stresses on strengthening effect. Through comparing the data of experiments, initial stresses’ influence on stress peak of 2 times compressive specimens is analyzed and the calculating formula of peak stress is proposed considering the pre-compression ratio, aiming at providing experimental dependences for strengthening design.

Abstract: Based on the numerically iterative technique, we introduce the shear modulus pattern used for accelerating convergence and rebuild the iterative program. Using this program, we analyze the bending problem of a bimodular deep beam under the action of uniformly distributed loads, in which the different ratios of span length to height of the beam, and of elastic modulus in compression to that in tension, are considered. The results show that the bimodularity have great influences on the bending stress and the deflection of deep beam.

Abstract: In order to research on seismic performance of full-scale beam-column joints of RC frames under low cyclic loading, finite element software ABAQUS is used to nonlinear analysis. Analysis results show that: the process of load carrying and fracture development of beam-column joints are simulated using concrete damage plasticity model; nonlinear finite element method is easy to obtain stress-strain relationship; and can effective analyses the complex mechanical behavior of core areas of joints.

Abstract: A new energy approach is proposed by coupling the virtual crack extension with the extended finite element method (X-FEM) to extract the Strain Energy Release Rates and then convert it to stress intensity factors. By means of meshes independence of the location and geometry of the crack, the proposed approach avoids the mesh perturbation around the crack tip to compute the stiffness derivatives with respect to a virtual extension of the crack. In comparison to the interaction integral, this combined method is implemented more easily without the post-processing of the numerical results. The effect of different enriched region around the crack tip on the accuracy of results is discussed. Numerical results presented are in excellent agreement with the available analytical and those obtained using the interaction integral.

Abstract: A structure with steel staggered-truss (SST) system is numerically investigated in this paper, utilizing the finite element 3D simulation analytial soft ware ETABS. Two different 3D models considering or ignoring the stiffness of infilled walls (SIW) are analyzed with Dynamic Time History method including storey drift and equivalent base shear force under frequent earth quake and rare earth quake. Results indicate that the effect of the SIW is prominent and should be considered.

Abstract: Transverse vibration of an Euler-Bernoulli beam with initial axial force is investigated based on nonlocal continuum mechanics. The size effect is considered and a small intrinsic length scale is adopted into the problem model. The linear partial differential equation governing transverse motion is derived. The model is solved for a doubly clamped beam. Expression of natural frequency is obtained. The correlations between the first two order natural frequencies and the small size parameter are also presented and discussed. The bending stiffness and small size effect are proved to play significant roles in dynamic behaviors of nonlocal beams.

Abstract: Dynamic analysis models of two adjacent transmission towers, two adjacent corner towers and the correspond single-tower are established, its dynamic characteristics are analyzed and compared. The results showed that: Dynamic characteristics of two adjacent transmission towers are close, but the towers connected with the corner tower changes much. Compared with the single-tower, its dynamic characteristics have changed regardless of corner tower or straight line transmission towers. It is also shown that suspended cables not only have mass effects, but have coupled stiffness effects applied to towers on transverse direction and longitudinal direction.