Good Connections Magazine

G O O D CO N N E C T I O N S | S U M M E R 2 0 1 5 7 on the TPI 1-2007 fc-perp calculation. Truss heels fastened to the side of a post or sitting in a slotted post in post-frame construction already satisfy this requirement. TPI 1-2014 sections 7.6.1 through 7.6.3 change the creep factors (KCR) used for deflection calculations. The creep factor was increased from 1.5 to 2.0 for trusses using seasoned (dry) lumber and used in dry service conditions, and from 2.0 to 3.0 for trusses using unseasoned (green) lumber in dry or wet service conditions, or using seasoned lumber in wet service conditions. The creep factors for framing members were not affected and are still 1.5 and 2.0 for dry and wet service conditions, respectively, per NDS. To be consistent with the deflection limits found in the International Building Code as those limits apply to all types of wood framing members, the calculated immediate deflection due to dead load for trusses using seasoned lumber and used in dry service conditions will be based on KCR -1. This will result in the calculated deflections used for comparison with the code-required minimum deflection limits (e.g. – L/360 Live and L/240 Total for floor trusses) to be based on Live Load (rLL) + Dead Load (rDL) with no creep factor included in the calculated Dead Load. The new code requirements for deflection for trusses now match the previous code requirements for framing members, which were already based on the immediate non-creep factored deflection. Truss Design Programs Keep in mind that for truss designs analyzed using IBC/IRC 2015 and TPI 1-2014, truss design programs will report both the immediate deflection (using KCR -1), which is consistent with code-prescribed minimum deflection limits, and the long- term deflection (using full KCR ), which may be specified by building designers on certain projects. Warnings indicating a deflection failure may be related to the long-term deflection rather than the immediate deflection, so it is important to understand the information your truss design program is reporting and what is required for a particular job. TPI 1-2014 section 8.7.1 has added an alter- nate CSI equation for plate steel moment capacity on 2x trusses. The alternate check was already in use for tension forces at a chord-break joint, but now is included for compression forces at those joints as well. TPI 1-2014 section 8.7.1 also added a plate steel moment capacity check for SY42 (4x) trusses at chord splice joint locations. If you have questions regarding changes in the IRC 2015 or IBC 2015 code, TPI 1-2014 standard or anything else discussed in this article, feel free to contact your Alpine engineer. We will be pleased to help you understand and apply these changes to your work. n Alpine's IntelliVIEW versions 15.01.01 and later and TrusPlus 6.5.21 or later offer IBC 2015 and IRC 2015 as available options.

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