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Seismic Evaluation and Rehabilitation of Existing Buildings
Published in Bungale S. Taranath, Tall Building Design, 2016
Historic buildings may require special consideration when developing a rehabilitation strategy. For example, the removal of an irregularity by adding a braced frame to balance the strength and/or stiffness of a structure may not be acceptable for a building that has historic features. Seismic isolation may be appropriate alternative to added bracing for limiting the interstory drifts or floor accelerations.
Cyclic Behavior and Modeling
Published in Wai-Fah Chen, Shouji Toma, ANALYSIS and SOFTWARE of CYLINDRICAL MEMBERS, 2020
The main element required to maintain the overall integrity of a braced frame subjected to lateral forces is the brace. The principal objective of this chapter is to develop an analytical model that defines the nonlinear behavior of such braces alternatively subjected to compressive loads, causing inelastic buckling, followed by tensile loads.
Bracing Systems
Published in Suhasini Madhekar, Vasant Matsagar, Passive Vibration Control of Structures, 2022
Suhasini Madhekar, Vasant Matsagar
Dynamic loads can impart a significantly greater effect toward the response of a structure compared to static loading. As such, the properties of the structure, such as lateral stiffness and damping, play a pivotal role in achieving efficient structural performance against dynamic loads, such as typhoons, earthquakes, blasts, and many others. To avoid structural failure and minimize the excessive lateral movement of the structure, part of the energy exerted by the dynamic loading needs to be dissipated. One of the most efficient methods to achieve this objective is providing structural bracings, which work by providing lateral stiffness and stability to the structure, especially for the multistory and high-rise buildings. Bracing systems subsequently increase the lateral load resistance of the structure and reduce the internal forces in the primary structural system through an appropriate arrangement of members. By incorporating bracings, a stiffer and more economical structure can be achieved. In such systems, the beams and columns forming the primary structural system could typically be designed to resist vertical loads, whereas the bracing systems resist lateral loads. In high-rise structures, bracing frames are provided by arranging the beams and columns in an orthogonal form. Braced frames may be considered cantilevered vertical trusses resisting lateral loads, primarily through the axial stiffness of columns and braces. Since the lateral loads are reversible, braces are subjected to alternate cycles of compression and tension. Hence, they are most often designed for the more severe case, i.e., compression. The diagonal bracing members work as web members resisting the horizontal shear in axial compression or tension, depending on their orientation and direction of inclination. The beams act axially when the system is an entirely triangular truss. They undergo bending only when the braces are eccentrically connected to them. Common types of bracings include the buckling-restrained brace (BRB), concentrically braced frame (CBF), and eccentrically braced frame (EBF). Figure 3.1 presents different structural vibration control approaches, including bracing systems.
Compact Hybrid Simulation System: Validation and Applications for Braced Frames Seismic Testing
Published in Journal of Earthquake Engineering, 2022
Elif Ecem Bas, Mohamed A. Moustafa, Gokhan Pekcan
Investigating CBFs under earthquake loading is an attractive topic for researchers, due to the need to quantify ductility for understanding response in seismic areas. The performance of the braced frame structure is susceptible to the performance of its braces. The complete range of the behavior of the braces would include yielding, lateral buckling, and rupture due to low-cycle fatigue (Uriz and Mahin 2008). Various types of computer analysis and numerical approaches are used to model the brace geometry and material to capture such range of behavior. However, most of the approaches use simplified finite element analyses with models that are approximate and calibrated mostly using cyclic-loading experimental data. The unknown performance of the braces would lead to an approximation in the computed performance of the full structure under earthquake excitations. The analytical models developed for steel braces can be divided into three categories: (i) phenomenological; (ii) finite element; and (iii) the physical theory brace models (Ikeda and Mahin 1986). Recently, there have been very successful inelastic brace modeling algorithms developed which includes low-cycle fatigue behavior with the phenomenological models (Uriz, Filippou, and Mahin 2008). However, one of the most commonly used approaches to model the low-cycle fatigue behavior of steel braces using the finite element method is what was developed by Uriz and Mahin (2008) and implemented in OpenSEES (McKenna, Fenves, and Scott 2000). This fatigue material is used with a parent material, where the stress–strain relationship is defined, and is responsible for counting the strain cycles and calculating the damage accumulation until fracture. This model uses Miner’s rule based on the Coffin–Manson relationship for low-cycle fatigue failure. The strain counting algorithm that is used is “rainflow” cycle counting method since earthquake loading does not include the constant number of cycles and strain ranges (ASTM 2017). Moreover, the input parameters should be calibrated with experimental data to obtain accurate constants for the Coffin–Manson relationship. Historically most of the experimental testing used to characterize the fracture life of steel braces considered uniaxial constant amplitude or unifrom cyclic loading. Irregularities in the load paths and loading patterns during earthquake loading could be unrealistically accounted for while calculating damage accumulation. This motivated some research studies, e.g. Mander, Pekcan, and Chen (1995), to develop an alternative damage modeling by using incremental energy-based approach in order to avoid cycle counting but also accounts for the memory effects. Therefore, using only simplified empirical values for the Coffin–Manson constants as suggested by several research studies (e.g. Uriz and Mahin 2008) might not properly capture the fatigue life under different earthquake loading, which is explained in more details in this paper.