M ACdverti$er
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omponent
anufacturing
August 1st, 2016 #09205 Page #60
Adverti$er
Don’t Forget! You Saw it in the
How to Select a Connector – Hurricane Ties
by Keith Cullum, PE, SE, Simpson Strong-Tie When it comes to wood frame construction, hurricane ties are among the most commonly specified connectors. They play a critical role in a structure’s continuous load path and may be used in a variety of applications, like attaching roof framing members to the supporting wall top plate(s), or tying wall top or bottom plates to the studs. They are most commonly used to resist uplift forces, but depending on regional design and construction practices, hurricane ties may also resist lateral loads that act in- or out-of-plane in relation to the wall. Simpson Strong-Tie manufactures approximately 20 different models of hurricane ties, not counting twist straps, other clips, or the new fully-threaded SDWC screws often used in the same applications. This assortment of models raises the question, “How do you select the right one?” This article outlines some of the key elements to consider when selecting a hurricane tie for your project.
Demand Load Let’s start with the obvious one. If your building’s roof trusses have an uplift of 600 lb at each end, don’t select a hurricane tie with a published capacity of less than 600 lb. It’s also important to consider combined loading if you plan to use the tie to resist both uplift and lateral loads. When the connector is resisting lateral loads, its capacity to resist uplift is reduced. I won’t go into too much detail on this topic since it was covered in a recent blog post, but in lieu of the traditional unity equation shown in the table, certain Simpson Strong-Tie connectors (hurricane ties included) are permitted to use the alternative approach outlined in the table. Traditional Linear Interaction Equation When a connector is loaded simultaneously in more than one direction, the allowable load must be evaluated as shown here. For all connectors use the following equation:
Alternative Approach for Simultaneous Loading As an alternate, certain roof-towall connectors (embedded truss anchors, pages 180 and 181, seismic and hurricane ties, pages 178–179, and twist straps, page 168) can be evaluated using the following:
Design Uplift/Allowable Uplift + Design Lateral Parallel to Plate / Allowable Lateral Parallel to Plate + Design Lateral Perpendicular to Plate / Allowable Lateral Perpendicular to Plate < 1.0.
The design load in each direction shall not exceed the published allowable load in that direction multiplied by 0.75.
The three terms in the unity equation are due to the possible directions that exist to generate force on a connector. The number of terms that must be considered for simultaneous loading is at the sole discretion of the Designer and is dependent on their method of calculating wind forces and the utilization of the connector within the structural system. What if the tabulated loads in the catalog for a single connector just aren’t enough? Use multiple connectors! An important note on using multiple connectors, though: Using four hurricane ties doesn’t always mean you’ll get 4x the load. Check out the recently updated F-C-HWRCAG16 High Wind-Resistant Construction Application Guide for allowable loads using multiple connectors and for guidance on the proper placement of connectors so as to avoid potential overlap or fastener interference.
Figure 1. Allowable Load Comparison for Single and Multiple H2.5A Connectors PHONE: 800-289-5627
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