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August 2020 #12253 Page #116
Webinar Alert: Choosing the Right Connections for Wind-Resistant Design By Bryan Wert
According to the Greek philosopher Heraclitus, “The only constant in life is change.” When the latest Wood Construction Connectors catalog (C-C-2019) was published, my colleague, Paul McEntee, PE authored an excellent blog post to announce some big changes within the catalog. He shared that Simpson Strong-Tie® was 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 was one of those rare times where being first didn’t exactly feel like winning. Let me explain … The 2015 and 2018 International Building Code (IBC) Section 2303.5 specifies that joist hangers shall be tested per ASTM D7147 Testing and Establishing Loads of Joist Hangers. Previous versions of the IBC required testing to comply with ASTM D1761 Test Method for Mechanical Fasteners in Wood. Both standards determine a connector’s allowable load as the lowest of the following: 1. Lowest ultimate of three tests (or average of 6) with a safety factor of 3 2. Average load at 1/8-inch deflection 3. Calculations per American Wood Council National Design Specification for Wood Construction (NDS). The primary changes from ASTM D1761 to ASTM D7147 are requirements to measure properties of the tested materials, such as steel strength, fastener strength, and wood specific gravity. The tested ultimate loads must be reduced when tested material properties exceed the minimum specified properties. But what if the material properties were not recorded in older tests? ICC Evaluation Services (ICC-ES) revised AC13 – Acceptance Criteria for Joist Hangers and Similar Devices in October 2016 to incorporate a methodology to evaluate products originally tested in accordance with ASTM D1761 to the 2015 I-Codes. Annex 1 of AC13 allowed for materials over-strength assumptions and calculated load reductions to existing connector tests. Long story, short: While our code reports and catalog were all updated to meet the latest building codes (yay!), the result was that some connectors with long-established allowable loads now showed lower values (boo!). This change didn’t excite designers, contractors or builders. Paul’s blog post and a new 2015 and 2018 IBC Resources Portal were created to help explain why, but we weren’t stopping at that in our support for our customers. Continued next page
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