Design of tall buildings with friction damper coupled reinforced concrete shear walls

Shear wall systems with coupling energy dissipation devices has recently been investigated for tall buildings. A common structural system for tall buildings is a conventional coupled shear wall system, which provides higher rigidity and overall performance for tall buildings compared to uncoupled walls. Due to the interaction between shear walls, coupling beams, which can be considered as the "fuse elements" of the structural system, primarily exhibit nonlinear behavior and receive damage under major lateral loads before any other structural elements. In this context, coupling beams should provide ductile behavior with high energy dissipation capacity, which is procurable by ensuring proper detailing. Coupling beams, which are one of the most important members of the structural system, can not be designed as intended by the structural engineers due to the architectural and mechanical restrictions. Some researches suggest replacing conventional steel or reinforced concrete coupling beams with damping devices to overcome these limitations. This approach also helps designer to avoid complex design issues and reduces residual damage possibility of conventional coupling beams. However, there is no research available in the literature that addresses design issues associated with damper coupled shear wall structures. Therefore, design of shear walls with coupling dampers is considered as another research subject herein. This study presents seismic performance evaluation of tall buildings with reinforced concrete shear walls coupled by friction dampers based on the nonlinear behavior and analysis of the structure. Evaluation is completed in three steps as summarized below: First, a 43-story tall building that has recently been built in Istanbul, Turkey is considered, where a reinforced concrete core shear wall formed by two C-shaped walls that are coupled by steel beams are the main elements of the seismic force resisting system. Some simplifications are made on actual structural system of tall building for this study. The design of structural system is conducted considering locally and universally accepted design guidelines and specifications. Second, equivalent frame methods are investigated to facilitate the analysis. For tall buildings, using frame elements to represent shell slab elements is commonly preferred to obtain analysis results quicker. In this context, shell-slab elements in the actual structural system of the sample building are represented as equivalent frame elements, which are derived according to the recommended methods in literature. The structural behavior of structure model with shell elements and equivalent frame model are compared by using equivalent lateral load and modal combination procedures. Third, as an alternative to the original structure, steel beams are proposed to be replaced with friction dampers, which are known to experience no damage when properly designed and detailed. Several levels of activation forces for the dampers are considered. Friction dampers are modeled with the nonlinear behavior depicted by the tests provided by the damper manufacturer. Three scenarios are evaluated: In the first scenario, all dampers are considered to have an activation force comparable to the steel beam shear yield force. In the second scenario, different damper configurations in the structural system are investigated. In the third, scenario, damper activation force is reduced to a level where the cost of the dampers are comparable to the sum of initial cost and possible retrofit cost of the steel beams. Performance evaluation of the structure based on the analyses of a nonlinear model reveals that steel coupling beams of the first 20 floors of the structure are expected to get the highest damage level. Details of the nonlinear modeling of the structure, including the shear walls, frame elements, coupling beams and friction dampers are given. Seven pairs of historical ground motion acceleration data that is scaled to a design response spectrum are used for the nonlinear analyses. Effects of the damper options on the nonlinear behavior of the structure, are investigated in detail. Energy dissipation properties, structural displacements, wall forces and several other structural properties of the original system and the proposed system are compared, and results are presented tabularly and graphically. Numerical simulations show that friction dampers can achieve significant energy dissipation capacity, while reducing the rigidity of the structure resulting increased displacements. Friction dampers can be cost-effective alternative to conventional coupling beams when designed and configured considering the damage on the coupling beams and shear walls. However, it is also shown that for a more objective comparison of performance and cost, research is needed to define performance concepts for tall building structures more accurately, such as collapse and damage levels that require retrofit or replacement.