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March 2019 #11236 Page #90
Code Report: Understanding Allowable Load Changes By Paul McEntee, Manager of Engineering, R&D
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he Simpson Strong-Tie® 2019–2020 Wood Construction Connectors catalog is the first in the industry with updated connector allowable load tables to meet the new ASTM test standards required by the 2015 and 2018 International Building Code® (IBC). It is designed to assist engineers, architects, Designers, and contractors in selecting the right products for improved performance, efficiency, and productivity. This article provides in-depth background about how we re-evaluated our connectors to meet the new standards. I attended ICC-ES Evaluation Committee meetings, where we had the opportunity to provide input on proposed changes in acceptance criteria used to evaluate a variety of building products. Simpson Strong-Tie engineers are active in the development of codes and standards, which allows us to advocate for building safety. It also keeps us up to date on upcoming changes that will affect the building industry. One change from the 2012 to 2015 IBC was a reference to the joist hanger test standard. The 2015 IBC Section 2303.5 specifies testing and evaluation per ASTM D7147, Standard Specification for Testing and Establishing Loads of Joist Hangers. Previous versions of the IBC required testing to comply with ASTM D1761, Test Methods for Mechanical Fasteners in Wood. Both standards determine a connector’s allowable load as the lowest of the following: 1. Lowest ultimate load of three tests (or average of six) with a safety factor of three 2. Average load at ⅛” deflection 3. Calculations per American Wood Council National Design Specification for Wood Construction® (NDS). The primary changes in ASTM D7147 are requirements for measuring properties of the tested materials, such as steel strength, fastener strength, and wood specific gravity. When tested material properties exceed the specified properties, report holders are required to adjust the tested ultimate loads to account for the material over-strength. I discussed some of these reduction factors in a previous blog post covering How We Test Wood Connectors. Over the last several years, Simpson Strong-Tie has worked to update all of our connector evaluation reports to the 2015 IBC. This required a thorough re-evaluation of original test data to account for material strength reductions and, in many cases, new testing. We are the first manufacturer to update all of our connector evaluation reports — 15 ICC-ES ESRs and three IAPMO-UES ERs. Although we updated our code reports over the last couple of years, engineers are likely just seeing these load changes now in the new 2019–2020 Wood Construction Connectors catalog, C-C-2019. To help identify significant load changes, we show loads that changed more than 5% in red. With that overly long introduction out of the way, I’d like to discuss, in general, how these changes affected loads across a handful of product lines. Continued next page
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