On This Page. Str uctural Design Criteria 53 Seismic forces: See Sec. Cobeen, K. E., Dolan, J. D., Thompson, D., & Van de Lindt, J. W. (n.d.). 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.” Practical ways to reduce potential failure mechanisms are also discussed. For wind applications, uplift and lateral loads can occur simultaneously. endstream endobj 175 0 obj <. A typical illustration of truss shop drawings showing a drag truss over a shear wall. Proceedings of a Workshop on Design of Horizontal Wood Diaphragms, 199-251. 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. The design professional should also review the truss manufacturer’s nail spacing into the drag truss chord to verify that the allowable on-center spacing is not exceeded. Seismic Design of Wood Light-Frame Structural Diaphragms Systems [PDF]. Shop drawings involving drag trusses should be reviewed and scrutinized by the design professional upon receipt. Figure 2. *�VF@Z�e�"���2�3��,Xu�`��=. 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. Both sequencing and pattern of the nailing must be evaluated. The Advanced Drag Load Dialog Window defaults to “Wind” + “Seismic” and “Include all live loads”. The DSC2 is a smaller, lighter version that installs with fewer fasteners. The Diekmann method provided strap force estimates that were approximately two times higher than the drag strut method. Good Engineering judgement should be used when designing collectors or drag struts within shearlines. It should be noted that the truss designer is not responsible for calculating drag force loads in the structure. The tributary-based unit diaphragm shear of 8 kips is to be transferred along the drag truss and must be called out on the framing plans. 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. Coil-Overs, Struts, Springs, K-Members. 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. It also acts as a drag strut in the lateral load resisting system of the building that it is a part of. SANTHUFF'S Suspension Specialties 12886 County Road 1394 Sinton, Texas 78387 361-364-3169 1.1.4. Contact publisher for all permission requests. 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. FEMA 451B Topic 13 Notes Wood Structures 13 - 2 Instructional Material Complementing FEMA 451, Design Examples Timber Structures 13 - 2 Objectives of Topic Understanding of: • Basic wood behavior • Typical framing methods • Main types of lateral force resisting systems • Expected response under lateral loads • Sources of strength, ductility and energy dissipation The effective strength and stiffness of horizontal wood diaphragms depend primarily on the mechanism of force transfer between adjacent wood structural panels. I rarely work with wood trusses but the next time I do, I’ll know exactly what to do. ... Shear Walls, Drag Struts collector v = 100 lb/ft 8 ft 32 ft 8 ft v = 300 lb/ft v = 300 lb/ft 1,600 lb ... 3 - Diaphragm Design Examples.pptx Author: Richard McLain The preferred truss layout aligns the drag truss above the vertical LFRS. Drag trusses interior to a diaphragm will generally receive unit shears from two separate diaphragm spans. Truss-framed roof systems with high-pitched top chords and horizontal bottom chords have a smaller weak-axis moment of inertia than, say, a flat roof or floor joists, and under shear load will tend to deflect more in weak-axis bending. (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. Clip location, however, should not coincide with the metal plate, either the primary plate or the shear plate of the truss joint. Commonly used types of lumber web reinforcement include scab bracing and T- and L-bracing. Experience STRUCTURE magazine at its best! In the upper example of Figure 3, one might think that the force is transferred through the steel—and with the bottom example, one might think that the forces would transfer through the diaphragm. Diekmann, E. F. (1980). Questions or comments regarding this website are encouraged: Contact the webmaster. Also, the truss manufacturer will provide, within the truss design drawings, the fastening requirements from the reinforcement to the trusses. The drag force, as developed within the plane of the diaphragm sheathing and transferred into the truss, must be called out on the framing plan or in the framing notes for the truss manufacturer. 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). I have been reviewing many example sets of plans from engineers across the country, and it appears that either method #1 or #3 above is being utilized. Collector (typ.) Also, in perforated shear walls, more attention in the detailing and design is needed above doors and windows, where framing functions as drag struts. 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