On the use of fixed point theory to design coupled core walls
The use of Fixed Point Theory (FPT) to optimize the design of coupling beams in coupled core wall (CCW) systems is demonstrated. The basis for optimization is minimizing the transmissibility of horizontal ground motion by appropriately linking two coupled wall piers having different dynamic properties with beams having appropriate stiffness and damping characteristics. Using 21 example CCW structures illustrating a range of pier properties, it was shown that the resulting optimization of coupling stiffness is quite small and other design considerations will require stiffer, non-optimal coupling beams. Nonetheless, the potential to leverage the small amount of coupling available in a ‘slab-coupled’ series of wall piers in order to reduce transmissibility is suggested by the findings of this study.
Parametric Study of Coupled Wall Behavior—Implications for the Design of Coupling Beams
Coupled walls are known to be efficient lateral load resisting systems; however, the relationship between their global and local behavior is not well understood and has been shown to result in structural systems having excessive internal deformation or strength demands on their component substructures. In order to investigate appropriate parameters for identifying efficient coupled wall geometries, an initial parametric study of over 2000 coupled wall geometries is reported. These analyses permitted the evaluation of the sensitivity of the structural response to various geometric parameters. The objective of this study is to investigate the elastic response parameters of coupled wall structures and to identify parameters that will permit an accurate initial estimate of the global behavior of a coupled system, the local behavior of the coupling beams and the interaction between the global and local behaviors. Using elastic analysis and gross section properties, the role of representative geometric parameters in the response of coupled structures is illustrated. The effect of using various code-prescribed reduced section properties is also discussed. The critical role of the coupling beam design is also illustrated.
Cyclic Response of Composite Coupling Beams
Adequate performance of coupled walls depends on sufficient stiffness, strength, and energy dissipation of coupling beams. To meet these goals, reinforced concrete coupling beams are often deep. On the other hand, shallower steel beams ca be used instead, and steel/composite coupling beams may be designed as shear-yielding members which have a more desirable energy dissipation characteristics. Such an option is not feasible for reinforced concrete beams. Well-established guidelines for links in eccentrically braced frames can be extrapolated to steel coupling beams. However, these provisions ignore the effects of concrete encasement which often surround the steel coupling beam. The reported research was conducted in an effort to fill this void. Four one-third scale subassemblages of a wall segment and a coupling beam were extracted from a prototype structure, and were tested. The main test variables were the presence or lack of concrete encasement, and the number of web stiffeners. The experimental data suggest that nominal encasement is an effective means for preventing web buckling, and stiffeners are not needed. Current design codes need to be reevaluated for the cases where the steel coupling beam is encased.