Recommendations for seismic design of hybrid coupled wall systems

Prepared by ASCE Technical Committee on Composite Construction; edited by Sherif El-Tawil [et al.]. — American Society of Civil Engineers, 2010. — 80 p. — ISBN: 978-0-7844-1060-8.After approximately four decades of construction history and about fifteen years of extensive experimental and computational research activity, existing design guidelines for HCW systems are still quite limited. The main design specifications that address this system are prescriptive provisions published within the AISC Seismic Provisions for Structural Steel Buildings (2005). These provisions trace their origin to the 1994 NEHRP provisions (BSSC 1994), which introduced general provisions for composite steel-concrete structures. The 1994 NEHRP provisions for hybrid walls were adopted with some changes into a new section of the 1997 AISC Seismic provisions called: Part II - Composite Structural Steel and Reinforced Concrete Buildings. The same provisions were included by reference in the 1997 NEHRP Recommended Provisions (BSSC 1997) and the International Building Code (ICC 2000). Design provisions for HCW have not been substantially changed in successive editions of the AISC Seismic Provisions, where they still reside. Furthermore, there has been no coordinated effort to develop performance-based design provisions that are specific to HCW and comparable to those proposed for steel systems (e.g. FEMA-350 2000) or other types of systems including reinforced concrete systems, e.g. FEMA 273 (1997) and its successor document FEMA-356 (2000).
Even though HCW systems have documented and well understood structural and economic benefits compared to alternative traditional systems, they continue to be used with reluctance in practice, mostly in situations where designers have little alternative. Part of the reason for this is the lack of well established design guidelines that designers can refer to when considering the system. The objective of this report is to synthesize existing information into practical recommendations that can be utilized by practitioners in the design of HCW systems in regions of moderate to high seismic risk.
The recommendations made in this document are for proportioning HCW systems comprised of two or more reinforced concrete walls connected with steel beams distributed along the height of the walls. Only beam-to-wall connections where moment is transferred by embedment of the steel section into the wall (Figure 4) are considered. The recommendations can be applied to design the lateral load resisting system and its components including structural walls, coupling beams, and the connections between the beams and walls.
The provisions in this document are based largely on research conducted by Deason et al. (2001), El-Tawil et al. (2003, 2002a,b), Fortney et al. 2007a,b, Fortney et al. (2006), Fortney (2005), Gong and Shahrooz (2001a,b,c), Gong et al. (1998), Harries et al. (2000, 1998, 1996, and 1992), Hassan and El-Tawil (2004), Rassati et al. (2006), Shahrooz et al. (2004a,b, 2001, 1993, 1992), and Xuan and Shahrooz (2005). Where applicable, the recommendations also draw upon existing specifications for steel and concrete, as well as other research on composite systems.
The recommendations have been derived from limited test data and computational results. Therefore, they should not be applied to configurations that are substantially different than those considered in the development of these provisions. The provisions apply for proportioning systems with the following characteristics:
Material specifications: normal weight concrete, with concrete strength not exceeding 70 MPa; reinforcing steel bars with specified yield strength not less than 280 MPa and not greater than 410 MPa; and A36, A572 Gr. 50, or A992 structural steel (specified yield strength of 345 MPa). These limits are imposed due to lack of experimental data for connections with light weight or high strength concrete or steels with higher strengths.
Geometric specifications: The core wall thickness in the connection region must be equal to or wider than the width of the steel coupling beam (i.e., the steel beam must fit inside curtains of wall steel and/concentrated reinforcement in the wall end boundary element).
System layout: The provisions are suitable for horizontally and vertically regular systems comprised of two or more wall piers coupled in series.
Beam-Wall connection types: The provisions are suitable for embedded connections where steel beams are embedded into the wall piers as described in Chapter 5 and shown in Figures 4 and 14.
Application: the provisions can be applied to buildings in regions of moderate to high seismicity.