Shearwall Design

Aspect Ratios

The International Building Code (IBC) and the Uniform Building Code (UBC) place limits on the dimensions of wood-frame shear walls. These restrictions are based on the poor performance of tall, narrow wood-frame shear wall segments observed in previous earthquakes. The limits are in the form of maximum height-to-width ratios (h:b). The maximum allowable ratios are a function of the type of shear wall construction and the location (seismic zone) of the structure. Much of the information in UBC Table 23-II-G is presented below.

Be sure to pay special attention to the footnotes as they may dictate your design.

Material	Horizontal Diaphragms maximum. Span :Width	Shearwalls maximum Height :Width
1. Diagonal Sheathing, conventional	3:1	1:1¹
2. Diagonal Sheathing, special	4:1	2:1²
3. Wood Structural panels... nailed all edges	4:1	2:1^2,3
4. Wood Structural panels... no blocking	4:1	not permitted

¹ .In Seismic Zones 0, 1, 2, 3, the maximum ratio may be 2:1
² In Seismic Zones 0, 1, 2, 3, the maximum ratio may be 3½:1
³ In Seismic Zones 4, the maximum ratio may be 3½:1 for walls not exceeding 10 feet in height on one side of the door to a one-story
Group U Occupancy

Topics of this module include:

Introduction, Load Path, Segmented Design Method, UBC Design Table, Wall Shear, Chord Design,
Anchorage, Deflection, Perforated Design Method, Method Comparison, Shearwall Failures

In order to design lateral force-resisting elements such as shear walls and diaphragms, it is important to understand how lateral loads are applied to a structure and the path that the loads travel through a structure. The following is a demonstration of the path taken by an applied wind load through a single story flat roof structure. It may be helpful to refer back to this demonstration as you work through the rest of the shear wall and diaphragm modules.

Click on the number to view the event.

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last updated: July 08, 2004

Segmented Shear Wall Design

There are two design methodologies used for shear walls: Segmented Design and Perforated Design. The majority of this tutorial concentrates on the traditional segmented shear wall (SSW) design approach. An introduction to the perforated design approach and its benefits will be presented later in this tutorial.

Segmented Shear Wall Design (SSW) is the traditional design method that has been used for many years. In the SSW method, walls are divided into segments of full-height sheathing. These segments are typically separated by openings in the wall such as doors and windows. The lengths of each full-height sheathing segment (b_i) are summed together, resulting in a conservative estimate of the length of the wall that will resist shear forces. The full-height segments are then designed to resist the applied loads. Hold-down connectors (HD) are required at the bottom corners of each segment to prevent each segment from overturning.

The following illustrations depict a typical shear wall. Figure 1 shows that the wall is made up of six sheathing panels, typically plywood or oriented strand board (OSB), that have been mounted vertically to the framing members. Holes have been framed into the wall to accommodate a window and a door. This wall geometry will be used several times throughout this tutorial.

Figure 1 - Wood-frame wall with openings

Figure 2 - Segmented shear wall model

Figure 2 illustrates the shear wall divided into full-height sheathing segments, shown in green. Only the full-height sheathing segments are assumed to provide resistance to lateral loads. The sheathing grade and thickness and the nail size and spacing determine the shear capacity per foot of length of the full-height segments. IBC Table 2306.4.1 and UBC Table 23-II-I-1 relate these variables so that designers can determine the shear capacity (v) in units of lb/ft (plf) of the full-height segments. The design shear capacity, V, is found using the following equation:

V = v Sb_i

Where:
	V =	total allowable shear capacity of wall (lb)
	v =	allowable shear capacity per unit length (lb/ft)
	Sb_i =	sum of lengths of full-height sheathing segments

Topics of this module include:

Introduction, Load Path, UBC Design Table, Wall Shear, Dimension Ratios, Chord Design,
Anchorage, Deflection, Perforated Design Method, Method Comparison, Shearwall Failures