Steel plate shear wall

In the past two decades the Steel Plate Wall (SPW), also known as the Steel Plate Shear Wall (SPSW), has been used in a number of buildings in Japan and North America as part of the lateral force resisting system. In earlier days, SPWs were treated like vertically-oriented plate girders and design procedures tended to be very conservative. Web buckling was prevented through extensive stiffening or by selecting an appropriately thick web plate, until more information became available on the post-buckling characteristics of web plates. Although the plate girder theory seems appropriate for the design of an SPW structure, a very important difference is the relatively high bending strength and stiffness of the beams and columns that form the boundary elements of the wall. These members are expected to have a significant effect on the overall behaviour of a building incorporating this type of system and several researchers have focused on this aspect of SPWs. The energy dissipating qualities of the web plate under extreme cyclic loading has raised the prospect of using SPWs as a promising alternative to conventional systems in high-risk seismic regions. A further benefit is that the diagonal tension field of the web plate acts like a diagonal brace in a braced frame and thus completes the truss action, which is known to be an efficient means to control wind drift.

From a designer's point of view, steel plate walls have become a very attractive alternative to other steel systems, or to replace reinforced concrete elevator cores and shear walls. In comparative studies it has been shown (Timler et al., 1998 and Agelidis and Mansell, 1982) that the overall costs of a building can be reduced significantly when considering the following advantages:

-An SPW system, when designed and detailed properly, has relatively large energy dissipation capability with stable hysteretic behaviour, thus being very attractive for high risk earthquake zones.

-Because the web tension field acts much like a diagonal brace, an SPW system has relatively high initial stiffness, and is thus very effective in limiting wind drift.

-Compared to reinforced concrete shear walls, SPWs are much lighter, which ultimately reduces the demand on columns and foundations, and reduces the seismic load, which is proportional to the mass of the structure.

-Compared to reinforced concrete construction, the erection process of an all-steel building is significantly faster, thus reducing the construction duration, which is an important factor affecting the overall cost of a project.

-By using shop-welded, field-bolted SPWs, field inspection is improved and a high level of quality control can be achieved.

- For architects, the increased versatility and space savings because of the smaller cross-section of SPWs, compared to reinforced concrete shear walls, is a distinct benefit, especially in high-rise buildings, where reinforced concrete shear walls in lower floors become very thick and occupy a large proportion of the floor plan.

- All-steel construction with SPWs is a practical and efficient solution for cold regions where concrete construction may not be feasible, as very low temperatures complicate construction and freeze-thaw cycles can result in durability problems.

- In seismic retrofit applications, SPWs are typically much easier and faster to install than reinforced concrete shear walls, which is a critical issue when building occupancy needs to be maintained throughout the construction time.

In comparison with conventional bracing systems, steel panels have the advantage of being a redundant, continuous system exhibiting relatively stable and ductile behaviour under severe cyclic loading (Tromposch and Kulak, 1987). This benefit along with the high stiffness of the plates acting like tension braces to maintain stability, strongly qualifies the SPW as an ideal energy dissipation system in high risk seismic regions, while providing an efficient system to reduce lateral drift. Thus, some of the advantages of using SPWs compared with conventional bracing systems are as follows:

-Reduces seismic force demand due to higher SPW ductility characteristics and inherent redundancy and continuity

-Accelerates structural steel erection by using shop-welded and field-bolted steel panels, and thus, less inspection and reduced quality control costs

- Permits efficient design of lateral-resisting systems by distributing large forces evenly.

A steel plate shear element is comprised of steel infill plates bounded by a column-beam system. When these infill plates occupy each level within a framed bay of a structure, they constitute an SPW. Its behaviour is analogous to a vertical plate girder cantilevered from its base. Similar to plate girders, the SPW system optimizes component performance by taking advantage of the post-buckling behaviour of the steel infill panels. An SPW frame can be idealized as a vertical cantilever plate girder, in which the steel plates act as the web, the columns act as the flanges and the cross beams1 represent the transverse stiffeners. The theory that governs the design of plate girders for buildings proposed by Basler in 1960 should not be used in design of SPW structures since the relatively high bending strength and stiffness of the beams and columns is expected to have a significant effect in the post-buckling behaviour. However, Basler’s theory could be used as a basis to derive an analytical model for SPW systems.

Designers pioneering the use of SPWs did not have much experience nor existing data to rely upon. Typically, web plate design failed to consider post-buckling behaviour under shear, thus ignoring the advantage of the tension field and its added benefits for drift control and shear resistance. Furthermore, the inelastic deformation capacity of this highly redundant system had not been utilized, also ignoring the significant energy dissipation capability that is of great importance for buildings in high-risk seismic zones. One of the first researchers to investigate the behaviour of SPWs more closely was Kulak at the University of Alberta. Since the early 1980s, his team conducted both analytical and experimental research focused on developing design procedures suitable for drafting design standards (Driver et al., 1997, Thorburn et al., 1983, Timler and Kulak, 1983, and Tromposch and Kulak, 1987). Recent research in the United States by Astaneh (2001) supports the assertion by Canadian academia that unstiffened plate, post-buckling behaviour acts as a capable shear resisting system.