A New Reinforcing Configuration for Achieving High-Ductility and High-Strength Rectangular Squat Structural Walls
Ghassan Almasabha and Shih-Ho Chao
Appears on pages(s):
confinement; diagonal compression failure; ductility; post-earthquake functionality; squat walls; strut-and-tie model
Reinforced concrete squat structural walls (SSWs) are a popular seismic force-resisting system used in low-rise buildings due to their high strength and stiffness. However, extensive studies have shown that rectangular SSWs have limited shear strength and drift ductility, primarily because their deterioration initiates from brittle compression failure of the diagonal concrete struts across the wall’s web. This research investigated a new reinforcing detail for SSWs
to achieve substantially improved ductility and strength. While the current ACI Code requires a mesh of steel reinforcing bars to reinforce the SSW web, the new detail presented in this paper fortifies the SSW by multiple steel cages which contain vertical reinforcing bars enclosed by transverse hoops. These steel cages can be easily prefabricated at a shop to minimize on-site assembly work and time. Each steel cage is similar to that in well-confined columns, which increases concrete’s strength and ductility, therefore allowing a higher amount of vertical reinforcement for greater shear strength.
Five specimens with an aspect ratio of 0.5 and reinforced according to either the ACI requirements or by the proposed details, and one specimen with an aspect ratio of 0.33 using the proposed details were tested. Similar to prior research results, SSWs using conventional details exhibited a fast strength deterioration at low drift ratios due to severe damage of the diagonal concrete struts under cyclic loading. Conversely, the proposed SSWs provide an increase of approximately 100% in the drift and ductility ratios, as well as a very gradual strength degradation and concrete damage progression. The proposed design allows SSWs to develop a ductile seismic behavior which is essential to safety against collapse, post-earthquake
functionality and repairability, and seismic response predictability of structures. The enhanced ductility warrants a higher shear strength reduction factor, ϕ, of greater than 0.6 for SSWs as well as the diaphragms and foundations connected to them. In addition, a seismic response modification coefficient, R, of greater than 6 can be justified, which translates into a smaller seismic design base shear. These adjustments can ultimately lead to a more economical
design of structures with SSWs.