Seismic Response of Steel-Concrete Composite Shear Walls
Steel-plate concrete (SC) composite walls consisting of steel faceplates, infill concrete, and connectors used to anchor the steel faceplates together and to the infill concrete, have potential advantages over conventional reinforced concrete and steel plate shear walls in terms of constructability and seismic performance.
SC panels enable modular construction leading to potential time and cost savings over conventional reinforced concrete walls. Double skin SC wall shells can be fabricated offsite, assembled on site, and filled on-site with concrete to create monolithic structure. The use of steel faceplates eliminates the need for on-site formwork, and the faceplates serve as primary reinforcement.
There are limited research studies comparing SC and RC walls. This research focuses to compare the seismic behavior of RC and SC walls with identical geometry and material properties. The major design variables, considered is this study, are aspect ratio, axial load ratio, and presence of boundary elements.
Macro modeling of SC shear walls
The seismic performance of Steel-plate composite (SC) shear walls is assessed for application to high-rise buildings. These walls are attractive for use in seismic regions, but limited knowledge exists on their in-plane cycling inelastic flexural behavior. Prediction of the inelastic SC wall response requires accurate, effective, and robust analytical models that incorporate important material characteristics for steel and concrete which are the two major components of an SC wall and also behavioral response features such as neutral axis migration, concrete tension-stiffening, progressive crack closure, nonlinear shear behavior, flexure-shear interaction and the effect of fluctuating axial force on strength, stiffness, and deformation capacity. Analytical modeling of the inelastic response of SC wall systems can be accomplished either by using microscopic finite element models based on a detailed interpretation of the local behavior, or by using phenomenological macroscopic models based on capturing overall behavior with reasonable accuracy. Although microscopic finite element models can provide a refined and detailed definition of the local response, their efficiency, practicality and reliability are questionable due to complexities involved in developing the model and interpreting the results. Macroscopic models, on the other hand, are practical and efficient, although their application is restricted based on the simplifying assumptions upon which the model is based.
The nonlinear analysis of SC wall systems can be efficiently carried out by using analytical models based on a macroscopic approach rather than by using detailed microscopic models. However, a reliable model for practical nonlinear analysis of SC walls is not available in an engineering computational platform so it is needed to develop a robust analytical tool which is able to simulate the monotonic and cyclic nonlinear response of SC walls.
Since the lack of any macro model for SC walls, it is needed to evaluate all proposed macro models for RC walls due to their similarities with SC walls, however some changes should be imposed to these models in an attempt to use them as SC macro models.
Quantification of seismic performance factors for steel-plate composite shear walls
Advances in performance-based seismic design tools have allowed the use of nonlinear collapse simulation techniques to assess building system performances. Using these collapse simulation techniques in a probabilistic procedure, the FEMA P695 methodology links the seismic performance factors [response modification coefficient (R), system overstrength factor (Ω0), and deflection amplification factor (Cd)] to the building system performance by directly accounting for potential variations in structural configuration, ground motion, as well as available experimental data on structural components.
The FEMA P695 methodology can be used to evaluate collapse performance of archetypes in order to investigate the validity of building system performance and response parameters (R, Cd, and Ω0) used in current building codes for linear design methods. Then the FEMA P695 methodology would be used to determine the performance and response parameters of the newly proposed structural systems which are yet to be included in building codes.
Seismic performance factors determined using the methodology are intended to ensure equivalent safety against collapse for buildings with different seismic lateral force resisting systems. Safety against collapse is determined, for a seismic lateral force resisting system, by 1) developing a series of building designs that comply with proposed seismic design guidelines and reasonably represent all salient features of the system being considered, 2) performing nonlinear response history simulations of the designed buildings using simulation tools capable of identifying system collapse and, 3) ensuring that an acceptably low probability of collapse is achieved when the system is subjected to Maximum Considered Earthquake (MCE) ground motions.
Macro Modeling of RC shear walls
Reinforced Concrete (RC) shear wall is one of the widely used lateral resisting systems in building structures. The behavior of this structural element during earthquake depends on different parameters such as loading condition, aspect ratio (height to length ratio), reinforcement ratio, and cross-section shape. Accurate performance assessment of RC shear walls requires analysis methods that can properly consider the effect of these parameters. During the past three decades, a significant amount of effort has been made to develop various modelling and analysis methods for RC shear walls subjected to cyclic loading. The existing modelling methods can be classified in two general groups: micro models and macro models. Micro models (i.e. finite element methods) are able to capture local damage mechanisms and therefore are typically more accurate than macro models. However, because they are computationally expensive their practical application in engineering offices is questionable. Macro models, on the other hand, are computationally fast and can calculate global response of shear walls with a reasonable accuracy, making them a better analysis tool for engineering offices.
Although a wide range of macro models has been developed in the literature, there are limited verification studies for these models. The existing verification studies have major restrictions in terms of the number of test specimens and parameters considered for validation of macro models. This study presents an overview of available macro-models for RC shear walls in the literature. The accuracy of models in predicting the cyclic response of RC shear walls with a wide range of design variables are investigated using a comprehensive test database. The design variables considered in the study include the cross-section shape (rectangular-, H-, and barbell shapes), level of axial force, wall aspect ratio, and reinforcement ratio. Based on the analysis results, the discrepancies between different macro models as well as their accuracy to simulate the cyclic response of RC walls and capture the failure mode are compared and discussed. The analysis results provide a useful guideline to help researchers and engineers in selecting the most suitable modelling approaches based on their design parameters to get the most accurate result with less computational effort.