Wind resistance engineering programs

In addition, the equation is complex relative to the ability to predict drift accurately. It also requires adjustment factors, such as a nail-slip factor, that can only be determined by testing. Empirical, Nonlinear Load-Drift Equation Drift in a wood structural panel shear wall segment may be approximated in accordance with the following equation:.

Portal Frames In situations with little space to include sufficient shear walls to meet required loading conditions, the designer must turn to alternatives. An example is a garage opening supporting a two-story home on a narrow lot such that other wall openings for windows and an entrance door leaves little room for shear walls. One option is to consider torsion and the distribution of lateral loads in accordance with the relative stiffness method. Another possibility is the use of a portal frame.

Portal frames may be simple, specialized framing details that can be assembled on site. They use fastening details, metal connector hardware, and sheathing to form a wooden moment frame and, in many cases, perform adequately. The ultimate shear capacity of portal frames ranges from 2, to more than 6, pounds depending on the complexity and strength of the construction details.

A simple detail involves extending a garage header so that it is end-nailed to a full-height corner stud, strapping the header to the jamb studs at the portal opening, attaching sheathing with a standard nailing schedule, and anchoring the portal frame with typical perforated shear wall requirements. The system has an ultimate shear capacity of about 3, pounds that, with a safety factor of 2 to 2. Several manufacturers offer pre-engineered portal frame and shear wall elements that can be ordered to custom requirements or standard conditions.

Diaphragm Design Diaphragm Design Values Depending on the location and number of supporting shear wall lines, the shear and moments on a diaphragm are determined by using the analogy of a simply supported or continuous span beam.

The designer uses the shear load on the diaphragm per unit width of the diaphragm i. Similar to those for shear walls, unit shear values for diaphragms vary according to sheathing thickness and nailing schedules, among other factors. Table 8 presents several of the more common floor and roof constructions used in residential construction as well as their allowable diaphragm resistance values.

The values include a safety factor for ASD and therefore require no additional factoring. In addition, the sheathing attachment in floor diaphragms is often supplemented with glue or construction adhesive.

A similar increase to the unit shear capacity of floor diaphragms can be expected, not to mention increased stiffness when the floor sheathing is glued and nailed. TABLE 8. To determine the shear load on a simply supported diaphragm i. The calculations to determine the unit shear in the diaphragm and the tension and compression in the chords are also similar to those given above. It should be noted that the maximum chord forces occur at the location of the maximum moment. For a simply supported diaphragm, the maximum chord forces occur at mid-span between the perimeter shear walls.

Thus, chord requirements may vary depending on location and magnitude of the bending moment on the diaphragm. Similarly, shear forces on a simply supported diaphragm are highest near the perimeter shear walls i.

Therefore, nailing requirements for diaphragms may be adjusted depending on the variation of the shear force in interior regions of the diaphragm. Generally, these variations are not critical in small residential structures such that fastening schedules can remain constant throughout the entire diaphragm.

If there are openings in the horizontal diaphragm, the width of the opening dimension is usually discounted from the width d of the diaphragm when determining the unit shear load on the diaphragm. Shear Transfer Sliding The shear forces in the diaphragm must be adequately transferred to the supporting shear walls.

For typical residential roof diaphragms, conventional roof framing connections are often sufficient to transfer the small sliding shear forces to the shear walls unless heavy roof coverings are used in high-hazard seismic areas or steep roof slopes are used in high-hazard wind regions.

The transfer of shear forces from floor diaphragms to shear walls may also be handled by conventional nailed connections between the floor boundary member i. In heavily loaded conditions, metal shear plates may supplement the connections.

The simple rule to follow for these connections is that the shear force in from the diaphragm must equal the shear force out to the supporting wall. Diaphragm Stiffness Diaphragm stiffness may be calculated by using semi-empirical methods based on principles of mechanics.

For typical residential construction, however, the calculation of diaphragm deflection is almost never necessary and rarely performed. Therefore, the equations and their empirical adjustment factors are not repeated here. Nonetheless, the designer who attempts diaphragm deflection or stiffness calculations is cautioned regarding the same accuracy concerns mentioned for shear wall drift calculations.

The stiffness of floor and roof diaphragms is highly dependent on the final construction, including interior finishes. More articles like these. Terms of Use. Close Menu. Access nearly all our benefits with All-Access Membership and work towards certification at your own pace at no additional cost. House of Horrors The world's 1 training facility. Membership Benefits Everything you need, in one place.

Find a Certified Home Inspector. Members get access to world-class resources to grow their business to the next level. Home Maintenance Book. Steps you can take now to strengthen your home can greatly minimize the cost of repairs afterhigh-wind events. Once your roof is gone, your house is gone. Reinforcing roof-to-wall connections with metal hurricane ties and fasteners is the first step to keeping your roof, and your home, safe.

Nearly all parts of the country are subject to high winds. Know whether your house is storm ready. Select One of Our Sites. High Wind-Resistant Construction for Homeowners. Information shall be provided on the TWIA designated catastrophe zones from the engineering and construction perspective.

Differences between construction in non TDI jurisdiction areas and the designated catastrophe zones will also be discussed. The core concern of coastal areas is the requirement of wind resistant structural design, so Wind resistant design of residential structures will be discussed along with a brief introduction to wind resistance requirements for commercial structures. The essential use of Building codes while designing wind resistant structures and applicability of jurisdiction, permitting issues will also be under focus.

The construction methods which comply as per TDI rules shall also be investigated. This is a good occasion for construction professionals to make GHBA aware of the practical issues they face on the field.