47.5 MB - The Whole Building Design Guide

The following design parameters are recommended for structuralsystems (see Section 3.4.2 for critical facilities located in hurricane-proneregions):m If a pre-engineered metal building is being contemplated,special steps should be taken to ensure the structure has moreredundancy than is typically the case with pre-engineered buildings.7 Steps should be taken to ensure the structure is not vulnerableto progressive collapse in the event a primary bent (steelmoment frame) is compromised or bracing components fail.m Exterior load-bearing walls of masonry or precast concreteshould be designed to have sufficient strength to resist externaland internal loading when analyzed as C&C. CMU walls shouldhave vertical and horizontal reinforcing and grout to resist windloads. The connections of precast concrete wall panels shouldbe designed to have sufficient strength to resist wind loads.m For roof decks, concrete, steel, plywood, or oriented strandboard (OSB) is recommended.m For steel roof decks, it is recommended that a screwattachment be specified, rather than puddle welds orpowder-driven pins. Screws are more reliable and much lesssusceptible to workmanship problems. Figure 3-23 showsdecking that was attached with puddle welds. At most of thewelds, there was only superficial bonding of the metal deck tothe joist, as illustrated by this example. Only a small portion ofthe deck near the center of the weld area (as delineated by thecircle) was well fused to the joist. Figures 3-24 and 3-25 showproblems with acoustical decking attached with powder-drivenpins. The pin shown on the left of Figure 3-25 is properlyseated. However, the pin at the right did not penetrate farenough into the steel joist below.m For attaching wood sheathed roof decks, screws, ring-shank,or screw-shank nails are recommended in the corner regionsof the roof. Where the basic wind speed is greater than 90mph, these types of fasteners are also recommended for theperimeter regions of the roof.7. The structural system of pre-engineered metal buildings is composed of rigid steel frames, secondary members (including roof purlins and wallgirts made of Z- or C-shaped members) and bracing.3-44 MAKING CRITICAL FACILITIES SAFE FROM High Wind