Several common considerations are summarized below. Comments posted to STRUCTURE website do not constitute endorsement by NCSEA, CASE, SEI, C3 Ink, or the Editorial Board. The staggered nature of the sheathing generally dictates the sequencing. The effective strength and stiffness of horizontal wood diaphragms depend primarily on the mechanism of force transfer between adjacent wood structural panels. 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.) ... 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 Also, the truss manufacturer will provide, within the truss design drawings, the fastening requirements from the reinforcement to the trusses. (f)(7) of the truss standard and IBC 2303.4.1.1(6), is required to show superimposed drag force loads on the truss shop drawings. 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. Good Engineering judgement should be used when designing collectors or drag struts within shearlines. 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. Questions or comments regarding this website are encouraged: Contact the webmaster. Light gauge shear angle clips are typically used to transfer the shear from the truss bottom chord to the top of the shear wall. Similarly, Section 7.3.3.5 of the truss standard recognizes gypsum board installed directly to the bottom chord of the truss and fastened in accordance with ASTM C840 as an approved continuous lateral restraint and brace mechanism. 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 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. APA Force Transfer Around Openings Calculator. STRUCTURE magazine is the premier resource for practicing structural engineers. 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. Seismic Design of Wood Light-Frame Structural Diaphragms Systems [PDF]. 1.1.4. SANTHUFF'S Suspension Specialties 12886 County Road 1394 Sinton, Texas 78387 361-364-3169 Fastening of the clip into a plate can potentially push the plate “teeth” out of the truss bottom chord. *�VF@Z�e�"���2�3��,Xu�`��=. 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 Collector (typ.) 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. A typical truss profile from the truss manufacturer, per Section 2.3.5.5. The Analysis of Irregular Shaped Structures: Diaphragms and Shear Walls (pp. Practical ways to reduce potential failure mechanisms are also discussed. Chords and Drag Struts. Space frame system: A structural system composed of interconnected members, other than bearing Where wood structural paneling sheathes and shapes the diaphragm, it also mechanically restrains and braces pitched trusses to provide permanent lateral stability. 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 The design professional should also specify any other tolerance-driven limits. 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). 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. For example, a biplane with cabane struts and one set of interplane struts on each side of the aircraft is a single-bay biplane.. For a small type such as a World War I scout like the Fokker D.VII, one bay is usually enough. Often the great majority of the load is derived from the mass ... Strut-and-tie analysis methods; and 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. Design Details for The Transfer of Forces in Wood Diaphragms to Vertical Elements. Special Design Provisions for Wind and Seismic, American Wood Council, Leesburg, VA. Clear explanation, useful details, and a real-world example. Figure 3. Given: The beam shown in Figure 2.4.1.1 supports a floor system and a column. 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. Example Problem 2.1. 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. A typical truss profile by the truss manufacturer, per Section 2.3.5.5. STRUCTURE® magazine is a registered trademark of the National Council of Structural Engineers Associations (NCSEA). Web development and content management by C3 Ink™, a division of Copper Creek Companies, Inc. Before linking, please review the STRUCTUREmag.org linking policy. As with all drag race cars a single A-arm or strut car benefits from narrower tires in the front. Clip location, however, should not coincide with the metal plate, either the primary plate or the shear plate of the truss joint. 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. The load sources are: Source 1: Floor loads (acting as a uniform load over the entire span). 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. The DSC2 is a smaller, lighter version that installs with fewer fasteners. Figure 1. I understand how to apply it, just not particularly to which items. Also, in perforated shear walls, more attention in the detailing and design is needed above doors and windows, where framing functions as drag struts. The preferred truss layout aligns the drag truss above the vertical LFRS. DSC Drag-Strut Connector. The Diekmann method provided strap force estimates that were approximately two times higher than the drag strut method. endstream endobj 175 0 obj <. This discussion raised a question of which design analogy was more correct. 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. estimated following the drag strut analogy. The most popular drag race rear suspension is … A typical illustration of truss shop drawings showing a drag truss over a shear wall. Shop drawings involving drag trusses should be reviewed and scrutinized by the design professional upon receipt. 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. Top and bottom chords in compression can buckle laterally if not braced or appropriately reinforced. Kolba (2000) performed a detailed experimental study on perforated wood shear walls focusing Last Revised: 11/04/2014. 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. Both sequencing and pattern of the nailing must be evaluated. 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. Shear panel: A floor, roof, or wall component sheathed to act as a shear wall or diaphragm. • 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 … If you have a race-only car you may choose to run Moroso front tires (not DOT-approved tires). 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. Nail withdrawal capacity can be increased with properly fastened ring-shank nails and should be considered by the design professional. Components of Shear Wall Design Collector & Drag Design Shear Wall Construction Shear Transfer Detailing Shear Resistance. The Advanced Drag Load Dialog Window defaults to “Wind” + “Seismic” and “Include all live loads”. Collector elements must be capable of transferring the seismic or wind forces originating in other portions of the … 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 Figure 2. 23-82). the design of a drag strut truss more accurate. Its light weight results in less force due to inertia during an earthquake, and less force means less damage. 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). The loading source – whether wind or seismic – also needs to be noted. 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. 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. Opening at Exterior Wall Chapter 4.0 - Evaluation Phase (Tier 2) FEMA 310 Seismic Evaluation Handbook 4 - 73 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. building professionals to design and construct safe, strong buildings that meet code require-ments while fulfilling lateral design criteria. 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. For wind applications, uplift and lateral loads can occur simultaneously. 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). 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. The design professional must indicate if the specified loads are reduced (i.e., for ASD 0.6W or 0.7E). 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. 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.■. 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. Popular examples of this rear suspension can be found in cars such as the '64 to '72 GM A-bodies and the '79 to '93 Ford Fox Mustangs. Collector (typ.) Boundary members include chords and drag struts at diaphragms and shear wall perimeters, interior openings, discontinuities, and re-entrant corners. %PDF-1.5 %���� 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. Contact publisher for all permission requests. Collector (typ.) It should be noted that the truss designer is not responsible for calculating drag force loads in the structure. Drag truss parallel to the shear wall below. They are lighter in weight than a … Drag trusses interior to a diaphragm will generally receive unit shears from two separate diaphragm spans. The following example shows a common application typical to the nature of a drag truss. 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. Wood’s inherent characteristics make it an ideal material for shear wall and diaphragm design. elements are called “drag struts.” Generally, greater lengths of perforated shear walls are needed to resist lateral loads than segmented shear walls. Details should include proper specification of nail sizes (pennyweight, type, diameter, and length), nail spacing, nail-to-panel edge tolerance, and account for the density-dependent capacity of the framing member. National Institute of Standards and Technology (NIST). To avoid receiving varying edge and field nailing, special uniform nailing along the full extent of the truss top chord should be shown on both the framing notes and section cut detail. 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. I rarely work with wood trusses but the next time I do, I’ll know exactly what to do. Figure 4-33. 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 … If this is selected, then the non-steel member's capacity will be checked against the forces derived from the overstrength seismic load combinations. As a result, the delegated truss manufacturer requires clear and well-documented plan callouts and details from the design professional. 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.” If it is The DSC5 has been designed to optimize fastener location. Str uctural Design Criteria 53 Seismic forces: See Sec. Thanks for this! h�b```g``:������ Ā B,@Q���-��Jn[j�g�^���d�Uװ���c�5�yч�;R��/V��)\���}�EGG��d�B@���1H! Coil-Overs, Struts, Springs, K-Members. Good Engineering judgement should be used when designing collectors or drag struts within shearlines. Shear walls of 10 feet and 8 feet are sectioned to accommodate for architectural features, which yields approximately 445 plf to be t… This is the equivalent of the original Drag Load Dialog Window that was described in the example above. framing members (drag struts) if the diaphragm has insufficient strength. It engages, enlightens, and empowers structural engineers through interesting, informative, and inspirational content. 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. 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. Seismic Use Group: See Sec. Cobeen, K. E., Dolan, J. D., Thompson, D., & Van de Lindt, J. W. (n.d.). The following example shows a common application typical to the nature of a drag truss. In most common roof truss designs, drag loads are mostly from the wind forces. Trusses adjacent to the shear wall below. (Central Mass.) 229 0 obj <>stream Commonly used types of lumber web reinforcement include scab bracing and T- and L-bracing. 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.) Reforming Structural Engineering Education. 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. Most wood light-frame construction in low-rise single- or multi-family dwellings have sloped roofs. 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. 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. Proper communication with the truss manufacturer is vital. The McGraw Hill Companies. The DSC drag-strut connector transfers diaphragm shear forces from a girder truss or beam to shearwalls. The drag strut technique is a relatively simple rational analysis that treats segments above and below the openings as drag struts. All materials contained in this website fall under U.S. copyright laws. 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. 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. endstream endobj startxref Both uplift and lateral load connection capacities must be evaluated under combined loading and need to consider both loading directions. 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. It also acts as a drag strut in the lateral load resisting system of the building that it is a part of. Product Details. Experience STRUCTURE magazine at its best! Bravo! Reprinting or other use of these materials without express permission of NCSEA is prohibited. I was hoping I … 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. (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. Proceedings of a Workshop on Design of Horizontal Wood Diaphragms, 199-251. SECTION 2305 GENERAL DESIGN REQUIREMENTS FOR LATERAL FORCE-RESISTING SYSTEMS 2305.1 General. Q -����^ݺY�q�����eA�W� F�3,yh6@ݧ��j�H3200�i5V��>�^ �����Hk2��1B�� ��=� 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. On This Page. 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). 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. 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). Depending upon the increased diaphragm shear demand and building footprint, interior shear walls may need to be engaged. 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. However, either way is possible. Malone, R. T., & Rice, R. W. Diaphragm Basics. 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. 174 0 obj <> endobj h�bbd```b``��+��M�� "�4��}��(0� ,�̎�U���`�����&3Ad�������@�l�]� ��Dr��g����z����`6�m���K�k�.��e`��� H�� 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. 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. 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. Shear wall: A wall designed to resist lateral forces parallel to the plane of the wall. A drag truss acting as diaphragm support and boundary chord requires boundary nailing stipulation. 0 Example 1: residential roof diaphragm trussed roof (2x lumber) unblocked ... • Chord design – tension and compression • Collector design – tension and comp. Diekmann, E. F. (1980). 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. 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