The Diekmann method provided strap force estimates that were approximately two times higher than the drag strut method. building professionals to design and construct safe, strong buildings that meet code require-ments while fulfilling lateral design criteria. Wind Loads Above, Figure 1609, Basic Wind Speed (3-second gust), 33 feet above ground, exposure C IBC 2003 Zone V 30 (mph) 1 2 3 70 80 90 (Western Mass.) The adequacy of the walls to span out-of-plane between points of anchorage shall be evaluated and the adequacy of the diaphragm connections to resist wall out-of-plane forces shall be evaluated. Example Problem 2.1. If a Seismic Design Rule is applied to a beam member which is not hot rolled steel (such as a wood drag strut), that member will ignore the design rules except for the Overstrength required flag. Strut chord Strut /chord Strut Strut/chord Strut/chord SW1 SW5 SW2 SW3 SW6 SW4 Strut MRF1 Multiple offset diaphragm Offset strut Support Support Collector Collector Collector (typ.) DSC Drag-Strut Connector. An alternative load path and connection detail (Figure 2) can be used if the drag trusses and shear wall are not aligned vertically but works better for light shear loads and less well for heavy shear loads. Collector (typ.) The DSC2 is a smaller, lighter version that installs with fewer fasteners. • Drag strut (or collector) • Diaphragm • Collector beam (or drag strut) Vertical Plane Horizontal Plane 17 Rigid v. Flexible Diaphragm •Importance •Distribution of load to shear wall •Flexible •Diaphragm load is distributed to shear walls by tributary area •Rigid •Diaphragm load is … Drag trusses interior to a diaphragm will generally receive unit shears from two separate diaphragm spans. Malone, R. T., & Rice, R. W. Diaphragm Basics. They are lighter in weight than a … On This Page. This is the equivalent of the original Drag Load Dialog Window that was described in the example above. A typical truss profile from the truss manufacturer, per Section 2.3.5.5. For wind applications, uplift and lateral loads can occur simultaneously. The design professional, however, is ultimately responsible for the design of the structure and, therefore, needs to confirm that the truss system bracing design has been addressed adequately. Good Engineering judgement should be used when designing collectors or drag struts within shearlines. If it is National Institute of Standards and Technology (NIST). The design professional should provide the magnitude of this force, in units of force per unit length of the sectioned shear wall(s) below (e.g., pounds per linear foot), and note whether it is factored or nominal (unfactored), as stipulated by the applicable code under which the structure is designed. h�b```g``:������ Ā B,@Q���-��Jn[j�g�^���d�Uװ���c�5�yч�;R��/V��)\���}�EGG��d�B@���1H! Collector (typ.) Nail withdrawal capacity can be increased with properly fastened ring-shank nails and should be considered by the design professional. Shear wall: A wall designed to resist lateral forces parallel to the plane of the wall. In-plane unit diaphragm shears are usually limited by the localized load transfer nail capacity in the wood, rather than by the shear capacity of the panels. This article provides a review of additional considerations required from the design professional for specifying common truss design variables to be used by the truss designer. The following example shows a common application typical to the nature of a drag truss. The truss design drawings will indicate, per Section 2.3.5.5(m) and Section 2.3.5.5(o) of the truss standard, which web members require lateral restraint, the maximum axial forces in the truss members, as well as the type and location of the reinforcement. Depending upon the increased diaphragm shear demand and building footprint, interior shear walls may need to be engaged. design of building systems entails controlling the building displacements, typically by providing resistance to the inertial forces generated by the acceleration of the building mass. 23-82). Questions or comments regarding this website are encouraged: Contact the webmaster. This drag strut, drag truss or collector is a single element or component designed to transmit lateral loads to lateral load resisting systems that are parallel to the applied force.” 229 0 obj
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Both sequencing and pattern of the nailing must be evaluated. (Central Mass.) In most common roof truss designs, drag loads are mostly from the wind forces. It engages, enlightens, and empowers structural engineers through interesting, informative, and inspirational content. Experience STRUCTURE magazine at its best! At the request of the design professional or local building official, the truss manufacturer must submit a preliminary truss submittal package to the design professional for review and approval before the manufacturing of the trusses. the presence of any drag struts. The following example shows a common application typical to the nature of a drag truss. Bravo! Proper communication with the truss manufacturer is vital. Components of Shear Wall Design Collector & Drag Design Shear Wall Construction Shear Transfer Detailing Shear Resistance. The design professional should also specify any other tolerance-driven limits. Shop drawings involving drag trusses should be reviewed and scrutinized by the design professional upon receipt. Section 2.3.2.4 of ANSI/TPI 1-2014 sub-sections (a), (b), (c), and (d) require the design professional to provide distinct criteria on construction documents as they relate to drag trusses. Collector (typ.) Also, the truss manufacturer will provide, within the truss design drawings, the fastening requirements from the reinforcement to the trusses. A drag truss acting as diaphragm support and boundary chord requires boundary nailing stipulation. The reactions are generally expressed as “RL,” “R,” and “U.” RL is the maximum horizontal reaction in pounds per linear foot from non-gravity loading or drag force loading, R is the maximum vertical reaction from a gravity load case, and U is the maximum uplift reaction from a wind load case (Figure 3). Special Design Provisions for Wind and Seismic, American Wood Council, Leesburg, VA. Clear explanation, useful details, and a real-world example. Several common considerations are summarized below. Ive been searching the web for a sort of comprehensive list of what elements get designed for the Overstrength Factor, Ωo, of ASCE 7-10 and have been unsuccessful. The DSC5 has been designed to optimize fastener location. All materials contained in this website fall under U.S. copyright laws. However, either way is possible. In order to ensure a uniform force transfer, the design professional is required, by sub-sections 2.3.2.4 (a), (b), (c) of the truss standard, to furnish and denote the location, orientation, and extent of each drag truss and the connected shear wall(s) below (Figure 3). Its light weight results in less force due to inertia during an earthquake, and less force means less damage. Common design practice for trussed roof and floor diaphragms in light-frame construction relies on drag trusses to serve as boundary elements (boundary members and their connections) and provide the primary and/or auxiliary load-transfer mechanism configured to carry in-plane axial tension and/or compression forces to the shear walls below. (f)(7) of the truss standard and IBC 2303.4.1.1(6), is required to show bearing and span conditions on the truss shop drawings. However, it is the responsibility of the truss designer to understand, review, and incorporate all applicable framing requirements and framing specifications into the design of the truss system. Shear walls of 10 feet and 8 feet are sectioned to accommodate for architectural features, which yields approximately 445 plf to be t… Commonly used types of lumber web reinforcement include scab bracing and T- and L-bracing. It should be noted that the truss designer is not responsible for calculating drag force loads in the structure. Product Details. This article reviews common force transfer considerations in drag trusses and provides suggestions to design professionals for complying with ANSI/TPI 1-2014, National Design Standard for Metal Plate Connected Wood Truss Construction, the truss standard as referenced by the 2015 International Building Code (IBC) which addresses the design criteria for pre-engineered wood trusses. Space frame system: A structural system composed of interconnected members, other than bearing APA Force Transfer Around Openings Calculator. The span of a wing between two sets of interplane or cabane struts is called a bay.Wings are described by the number of bays on each side. This calculator is an Excel-based tool for professional designers that uses FTAO methodology to calculate maximum hold-down force for uplift resistance, the required horizontal strap force for the tension straps above and below openings, the maximum shear force to determine sheathing attachment and the maximum deflection of the wall system. Coil-Overs, Struts, Springs, K-Members. Kolba (2000) performed a detailed experimental study on perforated wood shear walls focusing Most wood light-frame construction in low-rise single- or multi-family dwellings have sloped roofs. Reforming Structural Engineering Education. The delegated truss manufacturer is responsible for the bracing that resists in-plane buckling of the individual components of the truss while subjected to compression forces. 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