They are lighter in weight than a … Opening at Exterior Wall Chapter 4.0 - Evaluation Phase (Tier 2) FEMA 310 Seismic Evaluation Handbook 4 - 73 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. 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. 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. Figure 2. Bravo! Light gauge shear angle clips are typically used to transfer the shear from the truss bottom chord to the top of the shear wall. Collector elements must be capable of transferring the seismic or wind forces originating in other portions of the … A typical truss profile from the truss manufacturer, per Section 2.3.5.5. endstream endobj 175 0 obj <. With no clear directive in the design codes, there have been multiple design rationale techniques developed (e.g., Drag-Strut Analogy, Cantilever Beam, Diekmann), which has caused some dispute between design professionals as to which technique is the most precise. ... 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 STRUCTURE magazine is the premier resource for practicing structural engineers. Several common considerations are summarized below. 23-82). The loading source – whether wind or seismic – also needs to be noted. The design professional must indicate if the specified loads are reduced (i.e., for ASD 0.6W or 0.7E). 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.) Good Engineering judgement should be used when designing collectors or drag struts within shearlines. Special Design Provisions for Wind and Seismic, American Wood Council, Leesburg, VA. Clear explanation, useful details, and a real-world example. The most popular drag race rear suspension is … Comments posted to STRUCTURE website do not constitute endorsement by NCSEA, CASE, SEI, C3 Ink, or the Editorial Board. 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. Its light weight results in less force due to inertia during an earthquake, and less force means less damage. (Central Mass.) Good Engineering judgement should be used when designing collectors or drag struts within shearlines. The DSC2 is a smaller, lighter version that installs with fewer fasteners. Figure 3. (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. Malone, R. T., & Rice, R. W. Diaphragm Basics. The DSC drag-strut connector transfers diaphragm shear forces from a girder truss or beam to shearwalls. 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). Seismic Design of Wood Light-Frame Structural Diaphragms Systems [PDF]. h�bbd```b``��+��M�� "�4��}��(0� ,�̎�U���`�����&3Ad�������@�l�]� ��Dr��g����z����`6�m���K�k�.��e`��� H�� analyzed in example one and their results are compared with experimental data and found to give good ... and axial compression in the struts ... consists not only the force acting on the normal projection of the cofferdam but also on the drag force acting along the sides. Structure over Podium Slab Design Example Design a complete load path. %%EOF For wind applications, uplift and lateral loads can occur simultaneously. From a connection standpoint, adding and locating a drag truss directly above the LFRS element (Figure 1) when the typical spacing does not place a truss above the LFRS is the most direct solution and functions equally well for light and heavy shear loads. A single-ply drag truss top and bottom chord may be adequate to handle the axial tension/compression force demanded but inadequate to accommodate the nailing. Collector (typ.) Commonly used types of lumber web reinforcement include scab bracing and T- and L-bracing. 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. In most common roof truss designs, drag loads are mostly from the wind forces. 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. 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. Where wood structural paneling sheathes and shapes the diaphragm, it also mechanically restrains and braces pitched trusses to provide permanent lateral stability. *�VF@Z�e�"���2�3��,Xu�`��=. 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 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. 229 0 obj <>stream the presence of any drag struts. building professionals to design and construct safe, strong buildings that meet code require-ments while fulfilling lateral design criteria. Shear walls of 10 feet and 8 feet are sectioned to accommodate for architectural features, which yields approximately 445 plf to be t… 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. Collector (typ.) 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. If it is Cobeen, K. E., Dolan, J. D., Thompson, D., & Van de Lindt, J. W. (n.d.). Example Problem 2.1. Boundary members include chords and drag struts at diaphragms and shear wall perimeters, interior openings, discontinuities, and re-entrant corners. The DSC5 has been designed to optimize fastener location. the design of a drag strut truss more accurate. 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 Design Details for The Transfer of Forces in Wood Diaphragms to Vertical Elements. The Diekmann method provided strap force estimates that were approximately two times higher than the drag strut method. 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. Contact publisher for all permission requests. The Analysis of Irregular Shaped Structures: Diaphragms and Shear Walls (pp. However, either way is possible. Web development and content management by C3 Ink™, a division of Copper Creek Companies, Inc. Before linking, please review the STRUCTUREmag.org linking policy. APA Force Transfer Around Openings Calculator. 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.” For the condition presented in Figure 5, additional parameters on the plan include the bearing surface width, the location and extent of the truss, and shear walls below. Shear wall: A wall designed to resist lateral forces parallel to the plane of the wall. When this is the case, the design professional can specify to the truss manufacturer the required number of plies, the species, and the minimum size lumber required. elements are called “drag struts.” Generally, greater lengths of perforated shear walls are needed to resist lateral loads than segmented shear walls. Proper communication with the truss manufacturer is vital. Shear walls that exist under the drag truss, whether partial, sectioned, or full-length, might receive both lateral and gravity forces from the drag truss and can be simultaneously subjected to uplift. Clip location, however, should not coincide with the metal plate, either the primary plate or the shear plate of the truss joint. Trusses adjacent to the shear wall 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). The McGraw Hill Companies. Kolba (2000) performed a detailed experimental study on perforated wood shear walls focusing estimated following the drag strut analogy. The nailing pattern is generally dictated by the number of truss plies required to resist the shear demand along the top chord of the drag truss. 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. 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. Most wood light-frame construction in low-rise single- or multi-family dwellings have sloped roofs. Reprinting or other use of these materials without express permission of NCSEA is prohibited. Figure 4-33. Premanufactured, metal plate-connected, wood drag trusses can provide a pathed load-delivery mechanism designed to assist and engage the lateral force-resisting system (LFRS) elements during high-wind or seismic events. I was hoping I … On This Page. The following example shows a common application typical to the nature of a drag truss. Product Details. It should be noted that the truss designer is not responsible for calculating drag force loads in the structure. Fastening of the clip into a plate can potentially push the plate “teeth” out of the truss bottom chord. Experience STRUCTURE magazine at its best! Seismic Use Group: See Sec. The design professional should also specify any other tolerance-driven limits. The effective strength and stiffness of horizontal wood diaphragms depend primarily on the mechanism of force transfer between adjacent wood structural panels. %PDF-1.5 %���� As a result, the delegated truss manufacturer requires clear and well-documented plan callouts and details from the design professional. Figure 1. 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). Shear walls of 10 feet and 8 feet are sectioned to accommodate for architectural features, which yields approximately 445 plf to be transferred into each shear wall below (Figure 5). SECTION 2305 GENERAL DESIGN REQUIREMENTS FOR LATERAL FORCE-RESISTING SYSTEMS 2305.1 General. The load sources are: Source 1: Floor loads (acting as a uniform load over the entire span). Drag loads are due to lateral (horizontal) loads generated in high-wind or seismic events. The staggered nature of the sheathing generally dictates the sequencing. 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. Drag Strut Analogy Forces are collected and concentrated into the areas above and below openings Strap forces are a function of opening and pier widths 22 ho/2 F1 V1 L1 h1 F ho/2 2 V2 L2 hU 1 2 History of FTAO Research at APA Prominent FTAO Techniques Cantilever Beam Analogy Forces are treated as moment couples Segmented panels are piers at • 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 … 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. National Institute of Standards and Technology (NIST). 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). Intricate building layouts or complex building geometries result in diaphragm irregularities that can result in significant stress concentrations and increased demands at localized boundary element disruptions. 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 Advanced Drag Load Dialog Window defaults to “Wind” + “Seismic” and “Include all live loads”. If drag It is the responsibility of the design professional to specify and detail the design intent and requirements in a clear and unambiguous manner on the construction documents. A typical illustration of truss shop drawings showing a drag truss over a shear wall. This is the equivalent of the original Drag Load Dialog Window that was described in the example above. Proceedings of a Workshop on Design of Horizontal Wood Diaphragms, 199-251. framing members (drag struts) if the diaphragm has insufficient strength. 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 … Reforming Structural Engineering Education. Practical ways to reduce potential failure mechanisms are also discussed. Diekmann, E. F. (1980). endstream endobj startxref All materials contained in this website fall under U.S. copyright laws. For more information regarding the design and criteria of metal plate connected wood trusses, the reader is encouraged to read a free, read-only download of the standard ANSI/TPI 1-2014 on the Truss Plate Institute website, www.tpinst.org.■. Both sequencing and pattern of the nailing must be evaluated. The following example shows a common application typical to the nature of a drag truss. Components of Shear Wall Design Collector & Drag Design Shear Wall Construction Shear Transfer Detailing Shear Resistance. This discussion raised a question of which design analogy was more correct. Q -����^ݺY�q�����eA�W� F�3,yh6@ݧ��j�H3200�i5V��>�^ �����Hk2��1B�� ��=� 1.1.4. Coil-Overs, Struts, Springs, K-Members. 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. SANTHUFF'S Suspension Specialties 12886 County Road 1394 Sinton, Texas 78387 361-364-3169 Often the great majority of the load is derived from the mass ... Strut-and-tie analysis methods; and Also, the truss manufacturer will provide, within the truss design drawings, the fastening requirements from the reinforcement to the trusses. Questions or comments regarding this website are encouraged: Contact the webmaster. STRUCTURE® magazine is a registered trademark of the National Council of Structural Engineers Associations (NCSEA). If this is selected, then the non-steel member's capacity will be checked against the forces derived from the overstrength seismic load combinations. Nail withdrawal capacity can be increased with properly fastened ring-shank nails and should be considered by the design professional. I understand how to apply it, just not particularly to which items. It engages, enlightens, and empowers structural engineers through interesting, informative, and inspirational content. This analogy assumes that the shear loads in the full-height segments are collected and concentrated into the sheathed segments above and below the openings. Shop drawings involving drag trusses should be reviewed and scrutinized by the design professional upon receipt. 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. 1.1.4. 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. h�b```g``:������ Ā B,@Q���-��Jn[j�g�^���d�Uװ���c�5�yч�;R��/V��)\���}�EGG��d�B@���1H! 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