Clip location, however, should not coincide with the metal plate, either the primary plate or the shear plate of the truss joint. Chords and Drag Struts. the design of a drag strut truss more accurate. Diekmann, E. F. (1980). Shop drawings involving drag trusses should be reviewed and scrutinized by the design professional upon receipt. Framing a drag truss over an interior shear wall can help alleviate stress concentrations at diaphragm openings, re-entrant corners, offsets, or reduce the aspect ratio of the diaphragm. Special Design Provisions for Wind and Seismic, American Wood Council, Leesburg, VA. Clear explanation, useful details, and a real-world example. 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. Most wood light-frame construction in low-rise single- or multi-family dwellings have sloped roofs. A typical truss profile by the truss manufacturer, per Section 2.3.5.5. Collector elements must be capable of transferring the seismic or wind forces originating in other portions of the … A plan call-out can be phrased as follows: delegated truss engineer to design drag truss for the bottom chord transfer load (ultimate) due to wind: W = 445 plf. 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. Consider a wood-framed, rectangular, single-story family dwelling with a wind-driven uniform distributed loading of 200 plf acting along the diaphragm (Figure 4). It should be noted that excessive drift can occur if the aspect ratio of the shear walls underneath the drag truss is not fully evaluated per AWC’s SDPWS. Fastening of the clip into a plate can potentially push the plate “teeth” out of the truss bottom chord. %PDF-1.5 %���� 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. Good Engineering judgement should be used when designing collectors or drag struts within shearlines. In most common roof truss designs, drag loads are mostly from the wind forces. If it is Depending upon the increased diaphragm shear demand and building footprint, interior shear walls may need to be engaged. Nailing patterns based on species, structural sheathing thickness, and other specified requirements for diaphragms have also been tabulated and are included in the American Wood Council’s (AWC) Special Design Provisions for Wind and Seismic (SDPWS). The staggered nature of the sheathing generally dictates the sequencing. Wood’s inherent characteristics make it an ideal material for shear wall and diaphragm design. Seismic Use Group: See Sec. Shear panel: A floor, roof, or wall component sheathed to act as a shear wall or diaphragm. endstream endobj 175 0 obj <. On This Page. Also, the truss manufacturer will provide, within the truss design drawings, the fastening requirements from the reinforcement to the trusses. Structure over Podium Slab Design Example Design a complete load path. 174 0 obj <> endobj 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. 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.) Connections Tutorial 4 - Design Collectors or Drag Strut ( U.S.) In this tutorial, it will be demonstrated how the results from a WoodWorks shearwalls model can be interpreted to complete connection design of a collector or drag strut. A drag truss, sometimes referred to as a “collector” truss, is a single- or multi-ply pre-engineered truss designed to “drag,” distribute, and transfer shear loads generated within the plane of the diaphragm to the vertical LFRS elements. 1.1.4. 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.) The loading source – whether wind or seismic – also needs to be noted. 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. The design professional must indicate if the specified loads are reduced (i.e., for ASD 0.6W or 0.7E). It engages, enlightens, and empowers structural engineers through interesting, informative, and inspirational content. Connections Tutorial 4 - Design Collectors or Drag Strut (Canadian) In this tutorial, it will be demonstrated how the results from a WoodWorks shearwalls model can be interpreted to complete connection design of a Collector or drag strut. 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. Shear walls of 10 feet and 8 feet are sectioned to accommodate for architectural features, which yields approximately 445 plf to be t… 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. 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. The structural concept of drag struts and brace frames is for the drag strut to “drag” (collect) the forces of lateral seismic motion and bring them to a brace frame (or other rigid bracing element like a shear wall) and channel those horizontal forces into a vertical … 1.1.4. Product Details. The load sources are: Source 1: Floor loads (acting as a uniform load over the entire span). These loads are generated within the structure and transferred into load carrying elements (like drag strut trusses, shear walls or roof diaphragms) which then transfer the loads to the foundation and then safely into the ground. 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.” Opening at Exterior Wall Chapter 4.0 - Evaluation Phase (Tier 2) FEMA 310 Seismic Evaluation Handbook 4 - 73 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). If you have a race-only car you may choose to run Moroso front tires (not DOT-approved tires). 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. 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). 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. Ideally, the drag truss will span the length of and “sit” on the LFRS to develop the lateral and tension/compression overturning forces into the shear wall(s) below. 204 0 obj <>/Filter/FlateDecode/ID[<4C194E5BDA482344B5D704BF300D3BFD>]/Index[174 56]/Info 173 0 R/Length 130/Prev 350325/Root 175 0 R/Size 230/Type/XRef/W[1 3 1]>>stream Design Details for The Transfer of Forces in Wood Diaphragms to Vertical Elements. 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