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[Dr. N. Subramanian]

DUCTILE COUPLED REINFORCED CONCRETE SHEAR WALLS

Coupled shear wall systems are recognized as distinct from isolated shear wall systems in Canadian and New Zealand codes; they are also accorded higher response modification factors in view of their superior seismic performance. ASCE 7 has so far made no such distinction.

A ductile coupled wall system of reinforced concrete has now been defined in ACI 318-19. Issue Team (IT) 4 of the Provisions Update Committee (PUC) of the Building Seismic Safety Council (BSSC) developed a successful proposal to add four line items to ASCE Table 12.2-1, Design Coefficients and Factors for Seismic Force-Resisting Systems, featuring the ductile coupled wall system of reinforced concrete. The line items are under: A. Bearing Wall Systems, B. Building Frame Systems, and D. Dual Systems with Special Moment Frames.

Based on a FEMA P-695 study, R = 8, Cd = 8, and Ωo = 2.5 have been proposed in all the line items. The height limits are the same as for corresponding uncoupled isolated wall systems. Seven different changes made in ACI 318-19 for the design and detailing of special structural walls were implemented in the design of prototypes for the FEMA P-695 study.

The above changes appear in the 2020 Edition of NEHRP Recommended Seismic Provisions for Buildings and Other Structures. The changes have now also been approved for inclusion in the upcoming 2022 edition of ASCE 7, which will be adopted by the 2024 International Building Code.