Analytical model for steel fiber concrete composite short-coupling beam

Abstract

Lateral stiffness of a high-rise building is significantly influenced by the design of coupling beams to spread plasticity over the system height. Design and reinforcement detailing should be performed to retain strength and a significant percentage of stiffness during large deformations into a plastic range. The cracking and low toughness problems of high-strength concrete can be overcome by the addition of short randomly distributed steel fibers. These steel fibers provide a crack bridging the interference plan between shear walls and coupling beam. An alternative design is proposed in this paper, using an analytical model for high-strength fiber reinforced concrete (HFC). This is to reduce the reinforcement congestion and construction difficulties. In this study, the fiber composite enables the use of straight bars as partial or total replacement of diagonal bars. An analytical relationship is proposed, herein, to generate the complete stress–strain curve of HFC subjected to uniaxial compression. The fiber generates a passive confinement inside the composite that prevents the concrete from spilling-out during cycles of seismic load. Based on nonlinear fracture mechanics, a continuum approach is developed, as a linear elastic-strain softening material, for modeling the tensile behavior of HFC. The model accounts for composite inelasticity and ductility. It also slows down crack growth, fiber debonding and pullout mechanisms, and also attenuates fracture energy and element size effect. There is a wide variation in the code limit for predicting maximum shear stress. For this reason, based on experimental results, a proposed strut-and-tie model is developed to determine the contribution of fiber composite in the shear resistance of short-coupling beams. Comparing the analytical results with experimental results, the adopted analytical model shows a good agreement. A non-linear finite element model is proposed to examine the effect of using HFC on forty stories high-rise building.