Research On Seismic Behavior Of Steel Reinforced High Strength Concrete Short-Leg Shear Walls

Short-leg shear walls refer to specific reinforced concrete walls with the ratio of limb length to thickness in between 5-8. The mechanical properties of short-leg shear walls are intervenient between special-shaped columns and common long shear walls. Structure system consisting of short-leg shear walls has been popular in China for about twenty years, as it has few extruding edges or corners that not only ensures the building function tidy and perfect but also helps in architectural layout. Although a large number of buildings have been built using this approach in China, the seismic design methods of the short-leg shear wall are rarely considered in the existing codes.Comparing with ordinary long shear walls, short-leg shear wall is considered to be insufficient in side rigidity, seismic behavior and bearing capacity due to its relative short limb. For this reason, the Chinese seismic codes specify more severe restriction to short-leg shear walls than ordinary shear wall both in the anti-seismic class and the limits of axial force ratio. At present the application of this structure system has been confined to tier dwellings and high-rises of 10-25 stories. Therefore, it is important to break through the limitation of short-leg shear wall structure and expand its scope of application. For this reason, a new type of element named steel reinforced high-strength concrete (SRHC) short-leg shear wall was proposed. SRHC short-leg shear walls are high-strength concrete short-leg shear walls with encased structural steel. The bearing capacity of short-leg shear wall can be considerably improved by using high strength concrete, meanwhile the encased steel profile offers a better seismic behavior to the structure.As a new type of element, further studies are needed to extend the range of test data and to investigate the unknown aspect.In this paper, experimental, theoretical and numerical studies were performed to evaluate the mechanical behavior of SRHC short-leg shear walls. The research reported herein elucidates many new aspects of the mechanic behavior of the SRHC short-leg shear wall, including the failure pattern, strength, ductility, stiffness deterioration, energy dissipation and the local stress and strain distributed on the steel skeleton.The following conclusions can be drawn within the limitation of the current research:1.Based on low-cycle loading experiment for 6"-" shape specimens of steel reinforced high strength concrete (SRHC) short-leg shear walls, the bearing capacity, hysteretic response and failure pattern of the specimens with different types of steel reinforcement and different compression ratios were studied. The results indicate that lattice steel reinforced specimens and solid steel reinforced specimens exhibit similar damage patterns. Cracks on the lattice reinforced specimens were more intensive, and damages of the solid steel reinforced specimens were less severe. The influence of compression ratios to bearing capacity and ductility for both kinds of steel reinforced specimens are the same, namely, with the increase of axial compression ratios, the loading capacity gets higher while the ductility is worse. Compared with common short-leg shear walls, the SRHC short-leg shear walls have higher loading capacity, while ductility is about the same.2. Based on low-cycle loading experiment on SRHC short-leg shear walls, numerical models of SRHC short-leg shear walls and SRHC short-leg shear wall-couple beam joints were developed using the commercially available software ABAQUS, and the results were compared with the corresponding experimental results. The numerical results are generally in good agreement with the experimental data. Comparing the two types of steel reinforced specimens, it can be found a better distribution of stress in the steel plate. Taking into account the crack distribution and ductility behavior, the SRHC short-leg shear walls with embedded steel-plate skeleton is considered to be superior and recommended for engineering practice. In order to assure a higher bearing capacity of SRHC short-leg shear walls a high class of concrete is recommended, whereas a decrease in ductility happens with the increase of the concrete strength due to the inherent brittleness of high-strength concrete. Therefore a range of concrete strength between C50-C60 is recommend for SRHC short-leg shear walls. Numerical analysis to SRHC short-leg shear wall-couple beam joints indicates that specimens with steel couple beam has better ductility but lower loading capacity and stiffness than specimens with steel-concrete couple beam. The influence of compression ratios to bearing capacity and ductility for SRHC short-leg shear wall-couple beam joints is the same with that of RC short-leg shear walls, namely, with the increase of axial compression ratios, the loading capacity gets higher while the ductility is worse.3. Based on experimental research and theoretical calculation on bearing capacity of eccentric compression element, by considering the contribution of shape steel at the edges of the wall, steel plate in middle of the wall and longitudinal bar to bearing capacity, the bending strength formulas for SRHC short-leg shear walls were proposed. The calculation result agrees well with the experimental data.4. By analysis to existing experimental data on steel truss SRHC short-leg shear walls, and modification on shear capacity formula in current codes, shear capacity formula for SRHC short-leg shear walls was proposed. Comparing with test data shows that the formula proposed in this paper is good in precision. By finite element analysis to steel plate SRHC short-leg shear walls, the contribution of shear capacity of steel plate was obtained, and the calculation formula of shear capacity was proposed. The finite element model in this paper can be reference in further experimental research.5. Based on low-cycle loading experiment, a four-linear restoring force model for SRHC short-leg shear walls was established with degradation of stiffness taken into account. Through theoretical analysis and experimental results, characteristic values on skeleton curve, calculation formula for stiffness in each phrase and hysteretic characteristics were proposed. Comparisons of experimental and analytical lateral load-displacement relationships indicate good agreement, which can be conveniently applied to nonlinear dynamic analysis of SRHC shear wall buildings. The restoring force model proposed in this paper can be available for elasto-plastic time history analysis for this type of structure.