Loss-Prevention Requirements for Vulcraft Steel Deck Systems
Should the project require Factory Mutual insurance underwriting, the Specifying Professional for the project should consult with the FM Regional Engineer to determine any provisions they may require be met as part of the design of the structural system. The Specifying Professional remains responsible for the interpretation of these requirements on the job. The following guidelines outline Vulcraft's understanding of two possible approaches that may be taken concerning additional roof deck design requirements FM may require:
1. FM Wind Rating Specified only: In this situation, the FM Regional Engineer specifies that the roof must have a wind rating such as 1-60, 1-75, or 1-90. This may be all that is specified. In this case, the Specifying Professional may refer to the Vulcraft document “Vulcraft FM Deck Data” (available at www.vulcraft.com) and determine needed information as follows:
- The Specifying Professional will refer to Section 9.1.1 for mechanical support fasteners and 9.1.2 for welds. Definition of the fastener patterns at both the supports and sidelaps is provided in the initial paragraph of each of these sections. This fastener pattern is appropriate for Zone 1, Field, only.
- The fastener pattern in Zone 2, Edge, should be two times the requirement in Zone 1.
- The fastener pattern in Zone 3, Corner, should be two-and-one-half times the requirement in Zone 1.
- Once the appropriate table for the desired deck type is located within the section chosen in Step 1, choose deck gages for the secondary support spacing desired and that match the FM wind rating specified. Values are provided for one, two, and three-span conditions. Please note that these maximum span values include consideration of:
- A construction loading of 200 pounds, including strength and a serviceability limit of L/240.
- Pull-over resistance of the fasteners at the FM wind rating given per AISI S100.
- Flexural strength of the deck loaded at the FM wind rating given, assuming the attached membrane spacing is less than one-half the deck span.
- If the membrane attachment spacing is greater than one-half the deck span, specifier should switch to the method defined in section 2 of this document from FM Data Sheets 1-28 and 1-29.
The approach outlined in the Vulcraft document is sufficient only for wind ratings up to 1-90. In situations where deck profile or gages desired are not listed in the Vulcraft FM documents available on this page or the wind rating required is greater than 1-90, the specifier should contact Vulcraft for assistance in seeking special consideration from the FM Regional Engineer.
Allowable FM deck span charts for windstorm ratings less than 1-105 are based upon numerous limit states defined in FM Class 4451 Approval Standard which include;
- 200 lb construction and maintenance deck stress and deflection,
- Uplift deck stress,
- Fastener tensile capacity and
- Membrane width < 1/2 deck span
Membrane widths > 1/2 deck span require additional calculations beyond the scope of this summary. Minimum connection patterns listed per windstorm rating are within Zone 1 (Field) with prescriptive patterns in Zones 2 and 3;
- Zone 1 (Field) fastener patterns are listed per windstorm rating.
- Zone 2 (Edge) fastener pattern = 2.0 x Zone 1.
- Zone 3 (Corner) fastener pattern = 2.5 x Zone 1.
Listed and prescriptive patterns are minimums and do not supersede structural requirements defined by the Specifying Professional.
Windstorm ratings equal to or greater than 1-105 require panel yield strength of 80 ksi and calculations to satisfy Standard 4451 performance requirements for fastener and deck stress based on field, corner, and edge zone pressures. Negative pressures and zone widths can be calculated from FM data sheet 1-28 or RoofNav. Please refer to data sheets 1-28 and 1-29 for additional above deck securement.
Vulcraft’s 2018 IBC Deck Diaphragm tool can assist in determining tensile capacity of desired fasteners by inputting appropriate uplift pressures and checking fastener strengths in the “Connections” tab.
2. Required to Meet FM Data Sheets 1-28 and 1-29: If the project requires adherence to the full provisions outlined in FM’s Data Sheet 1-28 (Wind Design) and 1-29 (Roof Deck Securement and Above-Deck Roof Components), the following approach may be followed:
- Determine the required FM wind ratings for the field, edge, and corner zones of the roof per requirements in FM 1-28. This is done by:
- Determining a Roof Design Negative Pressure (RDNP) from Tables 3, 4 or 5, as appropriate.
- Determining the RDNP multipliers for each roof zone from Table 6.
- The FM wind rating for each roof zone is the value determined multiplied by the RDNP Multiplier and then by a factor of safety of two and rounded up to the next 15 PSF increment.
- See Section 3.3.2, page 24, for an example.
- Determine the maximum steel deck span from FM 1-29 Tables 1A-1D (for 1.5B-decks) or 1E (for 3N decks) for the roof covering required. Please note also the needed deck gage and yield strength. This will apply for Zone 1.
- Please note that FM 1-29 Section 126.96.36.199.2 recommends that the spans in Tables 1A-1E should be reduced by 10% if Acoustical Deck is required.
- Also, should the Zone 1 wind rating required be greater than 1-90, the yield strength of the deck is required to be 80 ksi and the number of support fasteners can be determined per DS1-29 (2015) as follows;
188.8.131.52 Provide deck securement as required by RoofNav for the needed wind rating using one of the following methods:
A. Performance-based approach: Where RoofNav assemblies are selected to account for the higher wind ratings needed in the perimeter and corner areas, the entry for the RoofNav assembly will address the specific securement requirements.
B. Prescriptive enhancement approach: Where a single RoofNav assembly is selected based on the needed field-of-roof wind rating (assuming deck span is adequate for all areas as noted above), enhance deck securement in the perimeter and corner areas as follows:
Perimeter areas: Double the deck securement required by RoofNav for the needed field-of-roof rating.
For example, if the specific fastening detail is required every 12 in. (300 mm) on center in the field of the roof, use the same securement every 6 in. on center (150 mm) in the perimeter. If a specific fastening detail is required every 6 in. (150 mm) on center in the field of the roof, use two of the same deck welds or fasteners in the same deck rib in the perimeter (FM 1-29 184.108.40.206).
- The Support Fastener Pattern should be determined for the type of fastener desired using the RDNP determined above. This pattern would then be used in the field-of-roof.
- The ‘Connection Tension’ tab of the Vulcraft Online Design Tool called ‘2018 IBC Deck Diaphragm’ can be used to quickly determine needed fastener uplift capacities.
- Please note that FM 1-29 Section 220.127.116.11 suggests that mechanical fasteners are preferred over welding for fire-prevention reasons. If welding is to be used, FM Data Sheets 1-0 and 10-3 must be considered as well.
- Perimeter and corner area support fastening patterns are most-easily determined using the prescriptive approach outlined in FM 1-29 Section 18.104.22.168, which is identified in the prescriptive enhancement approach outlined above. Side-lap fastener patterns can be determined from FM 1-29 Table 4 using the Zone 1 wind rating.