Performance of Perforated Shear Walls with Narrow Wall Segments, Reduced Base Restraint, and Alternative Framing Methods

Authors: NAHB Research Center Inc.    

Between one and two million new homes are built in the United States each year, predominantly with wood framing. For this reason, efficient utilization of our lumber supply is important. Ideally, the residential construction industry wants to build stronger, safer buildings that can withstand hurricane and earthquake loads while at the same time using material and labor resources more efficiently. In order to accomplish this goal, the actual load capacity and ductility of structures must be better understood from an engineering standpoint.

Shear walls are a primary lateral load resisting assembly in conventionally wood-framed construction. Traditional shear wall design requires fully sheathed wall sections restrained against overturning. Design of exterior shear walls containing openings, for windows and doors, involves the use of multiple shear wall segments and is required to be fully sheathed and have overturning restraint supplied by mechanical anchors. The design capacity of shear walls is assumed to be equal to the sum of the capacities for each full height shear wall segment. Sheathing above and below openings is typically not considered to contribute to the overall performance of the wall.

The traditional method of design described above is significantly different than wall bracing methods used historically in conventional construction. It is also more expensive than conventional construction while providing greater strength. However, there are significant opportunities to optimize this design process so that both safety and economy are achieved through more accurate design approaches. This report is a continuation of an effort to develop, confirm, and enhance such an approach. The ultimate goal is to provide both safety and economy to housing construction an all wind and seismic areas in the United States.

An alternate empirical-based approach to the design of shear walls with openings is the perforated shear wall method which appears in the Standard Building Code [1] and the Wood Frame Construction Manual for One and Two Family Dwellings [2]. The perforated shear wall method consists of a series of simple empirical equations used for the design of shear walls containing openings. When designing for a given load, shear walls resulting from this method will generally have a reduced number of overturning restraints than a similar shear wall constructed with multiple traditional shear wall segments. The inferred performance will be achieved due to the accuracy of the method. Only when strength demands exceed the capabilities of the perforated shear wall method will the more traditional engineering approach be more cost effective.

A significant number of monotonic and cyclic tests have provided verification of the perforated shear wall method [3][4][5][6][7][8]. These studies include one-third scale model tests and full scale monotonic tests with 4 ft.(1.22 m) wall segments [3][4][5][6][7]. Another series of tests investigated the use of corners as end restraints instead of mechanical hold-down devices [8]. The following study provides additional information about the performance of full scale tests with 2 ft. (0.61 m) wall segments, reduced base restraint, and the use of alternative framing practices.

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