HomeMy WebLinkAboutCertification Letter for Increased Loads 09.05.2013Microsoft Word - Purlin letter 8-5-13.doc
FORBES ENGINEERING CIVIL & STRUCTURAL ENGINEERING September 5, 2013 Mr. Andy Schwaller Garfield County Building Department 108 8th Street, Suite 401 Glenwood Springs, Colorado 80601
Certification Letter for Increased Loads to Existing Roof Purlins 4J Arena Re-roof 2101 County Road 245 New Castle, Colorado Mr. Schwaller: This letter is in regards to the additional
load produced by the Roof Hugger system to the roof of the above referenced building. The concern is the added dead load produced by the addition of a roof-hugger system. The standing
seam metal roof panel and roof hugger system consists of 24 gauge metal roof panels attached to 16 gauge Roof Hugger zee purlins positioned parallel to and attached through the existing
metal roof panels and into the top flange of the existing metal roof purlins. The existing metal roof purlins have been identified as 16 gauge metal Cee’s spaced at 5’ on center. The
span of the existing purlins is approximately 20’ to 25’ and bears on the main force resisting system. The attachment of an addition structural member (i.e. Roof Hugger purlins) to the
top of existing purlins and when using adequate connections, adds depth to the member and therefore increases the section modulus of the combined purlins which can only strengthen the
original member. A Load Increase Test Report compiled by Force Engineering & Testing has been performed on the Roof Hugger system according to the American Society of Testing Material
(ASTM). The results are an increase of 79% in the moment reduction factor when subjected to AISI Gravity Load Base Testing and a 94% increase in moment reduction factor in the AISI Wind
Uplift Load Base Testing (see attached data sheets). The full report can be sent if requested. The additional dead load produced by the roof hugger system has been estimated at 2 lbs/sf.
This takes in account the 24 gauge roof panels, the roof hugger zee purlins, the attachment clips and fasteners. This amount of additional dead load is less than the amount that requires
an increase of the resistive members of a structure.
As outlined in the 2009 IBC, Section 606.2, Gravity Loads, states; Addition or replacement of roofing or replacement of equipment. Where addition or replacement of roofing or replacement
of equipment results in additional dead loads, structural components supporting such reproofing or equipment shall comply with the gravity load requirements of the International Building
Code. Exceptions: 1. Structural elements where additional dead load from the roofing or equipment is not increased by more than 5 percent. 2. Buildings constructed in accordance with
the International Residential Code or the conventional construction methods of the International Building Code and where the additional dead load from the roofing or equipment is not
increased by more that 5 percent. 3. Addition of a second layer of roof covering weighing 3 pounds per square foot or less over an existing, single layer of roof covering. Conclusion,
the addition of the roof hugger sub-purlins will support the additional dead load and will strengthen the roof structure. Also the amount of additional dead load is less than what would
require additional bracing. Note that the analysis for the 4J Arena Re-roof does not include any analysis of the main force resisting system or the foundation pads or footings. It is
the assumption of this letter that the existing frame & foundation has been built to meet or exceed the local building specifications and therefore is covered by Section 606 of the IBC.
If I can be of further assistance in this matter, or if you have any questions, please call. I can be reached at (970) 295-4874. Sincerely, FORBES ENGINEERING __________________________
Kevin Forbes, Colo. PE #35265 President