In structural engineering, a diaphragm is a structural element that transmits lateral loads to the vertical resisting elements of a structure (such as shear walls or frames). Diaphragms are typically horizontal, but can be sloped such as in a gable roof on a wood structure or concrete ramp in a parking garage. The diaphragm forces tend to be transferred to the vertical resisting elements primarily through in-planeshear stress. The most common lateral loads to be resisted are those resulting from wind and earthquake actions, but other lateral loads such as lateral earth pressure or hydrostatic pressure can also be resisted by diaphragm action.
The diaphragm of a structure often does double duty as the floor system or roof system in a building, or the deck of a bridge, which simultaneously supports gravity loads.
Diaphragms are usually constructed of plywood or oriented strand board in timber construction; metal deck or composite metal deck in steel construction; or a concrete slab in concrete construction.
Floor Coating Solutions. Traffic Coating Solutions. Wall Coating Solutions. Technical Spotlight. NEW: Become a NEOGARD Certified Applicator in Roofing. We invite you to be a part of the $1 billion and growing roofing market in North America. Capitalize on the proven performance of our roofing products and systems. Our Spray Polyurethane Foam. Chapter 4, Floor Construction 75 When an interior braced wall also is a bearing wall and joists below the wall are parallel to the wall, a double joist or a beam typically is provided in the floor below the wall. Occasionally this pair of joists may be spaced apart to allow for piping or vents passing vertically from the wall.
The two primary types of diaphragm are flexible and rigid. Flexible diaphragms resist lateral forces depending on the tributary area, irrespective of the flexibility of the members that they are transferring force to. On the other hand, rigid diaphragms transfer load to frames or shear walls depending on their flexibility and their location in the structure. The flexibility of a diaphragm affects the distribution of lateral forces to the vertical components of the lateral force resisting elements in a structure. [1]
Parts of a diaphragm include:
- the membrane, used as a shear panel to carry in-plane shear
- the drag strut member, used to transfer the load to the shear walls or frames
- the chord, used to resist the tension and compression forces that develop in the diaphragm, since the membrane is usually incapable of handling these loads alone.
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Floor and roof framing systems must be an economical choice since the system selection can significantly impact overall project costs. In addition, the system must also meet design requirements for gravity and lateral loads; comply with fire-safety standards; support architectural flexibility; and offer occupancy comfort without cracking, warping, twisting, or expanding.
In response to an open invitation from Structural Engineering & Design , a number of companies provided the following information about their products. Company web addresses are provided for immediate access to additional information. If you are a manufacturer or software developer and wish to participate in the Structural Engineering & Design Specifiers Guides scheduled for 2010, visit www.gostructural.com/specguide to submit your product information.
Aegis Metal Framing, LLC (www.aegismetalframing.com) is a provider of pre-fabricated cold-formed steel truss and panel systems, floor joists and headers, and services for commercial, institutional, and residential construction.
Ainsworth Group of Companies (www.ainsworthengineered.com) offers Durastrand Floorings, an enhanced grade, APA-rated Sturd-I-Floor guaranteed against delamination for 50 years. Durastrand Flooring reduces or eliminates the need for sanding at the jobsite because of an enhanced edge that blocks moisture and reduces swelling.
APA (www.apawood.org) provides engineered wood products that flex with one’s imagination, offering a wide range of options for nearly any building type. APA Performance Rated Panels, glulam, LVL, I-joists, and Rim Board can be used in floor, wall, and roof systems, as well as covered walkways, bridges, and other construction uses.
California Expanded Metal Products Co.’s (CEMCO) (www.cemcosteel.com), Sure-Span Steel Floor Joist System is manufactured from mill-certified prime steel containing high-quality recycled content. According to the company, Sure-Span C-joists and rim-tracks provide the construction industry with a dependable, cost-effective solution for floor framing in today’s competitive environment.
Canam Steel Corporation (www.canam-steeljoists.ws) designs and fabricates structural steel trusses and complex components for commercial and institutional buildings. The product design team provides value added engineering solutions for complex truss and joist design. Visit the company’s website for information.
CENTRIA/HH Robertson Floor Systems (www.hhrobertson.com), a CENTRIA company, manufactures cellular steel deck, trench headers, and electrical outlet boxes that are cast into the floor slab. This provides a proven, cost-effective wire raceway system for handling the rapidly changing wiring and cabling needs of the building industry. Applications of HH Robertson in-floor cable distribution systems include offices, casinos, libraries, schools, and government buildings.
CMC Steel Products (www.cmcsteelproducts.com) is the leading manufacturer of the SmartBeam. With depths ranging from 12 inches to 60 inches and the ability to manufacture asymmetrical sections, the SmartBeam is ideally suited for composite floor construction.
Metal Stud Crete (MSC) Floor System (www.metalcrete.com) from Earl Composite Systems is an engineered concrete and light-gauge steel joist floor system using composite action to connect the thin concrete to the joists.
Ecospan NUCOR-Vulcraft/Verco Group (www.ecospan-usa.com) offers Vulcraft’s Ecospan Composite Floor System. It is comprised of 99 percent recycled material in the steel joists and 70 percent recycled material in the decking. The composite design of the Ecospan System allows for longer span, light-weight, shallow steel joists that offer greater rigidity while remaining economically advantageous.
Hambro Concrete Composite Floor Systems (www.hambro-floors.ws) are ideal for multi-story commercial and single-family homebuilders seeking quality and stability. The Hambro D500 features a steel joist top chord embedded in concrete. The system of top and bottom chords of bent rods connected together reduces the vertical shear common in a standard truss.
iLevel By Weyerhaeuser (www.ilevel.com) offers iLevel Forte single-member sizing software — a specialized structural-frame design tool for sizing wood structural beams and joists. It enables users to evaluate alternatives quickly for joists, flush and drop beams, sloped roof members, and wall headers to optimize materials and reduce construction cycle time, waste, and cost.
Nuconsteel (www.nuconsteel.com) is introducing NUTRUSS, a fully engineered, integrated truss system for floors and roofs that goes from plans through fabrication straight to job site installation. Combined with Truswal design and engineering software, NUTRUSS, according to the company, is second-to-none in the industry and provides superior strength, design flexibility, wider spans, and the added benefits of cold-formed steel framing.
Open Joist – Universal Forest Products (www.openjoist.com) manufactures Open Joist to deliver superior strength, ease of use, and performance, using less embodied energy than products such as steel or aluminum. Using the structural power of a triangle, Open Joist’s through-web engineering creates a stronger, more solid floor and makes installation of mechanical systems easier. Now earn as many as 4.5 points under the LEED for Homes green building certification system.
Simpson Strong-Tie (www.strongtie.com) offers new Strong-Drive SDS screw options in the Simpson Strong-Tie line. Strong-Drive SDS screws now include 316 stainless-steel SDS screws for added corrosion resistance in higher-exposure environments. It also includes a new 8-inch length of its original carbon-steel screw, which the company said is ideal when a longer fastener is needed for wood-to-wood fastening applications, such as floor-to-floor and five-ply truss.
Southern Pine Council (www.southernpine.com) invites engineers to discover the advantages of a raised floor foundation system by reviewing the Raised Wood Foundations publication. Engineers can use this free, comprehensive guide during the design and building phases.
Spancrete (www.spancrete.com) hollowcore plank is used for structural roof and floor applications. The product is plant cast over a bed of prestressed wire strands, producing an incredibly strong product that tolerates high load capacities and covers long spans. Hollowcore contains continuous voids that reduces weight and cost, and may be used for electrical/mechanical runs.
Steel Joist Institute (www.steeljoist.org) is a nonprofit organization open to manufacturers who produce, on a continuing basis, steel joists of the K-, LH-, DLH-, CJ-Series and/or Joist Girders, conforming to the Institute’s Standard Specifications, Load Tables, Weight Tables, and Bridging Tables, as appropriate. These products are suitable for the direct support of floors and roof slabs or decks in buildings or other structures. Additional information regarding the Institute and its membership is available online.
TrusSteel cold-formed steel trusses, offered by TrusSteel, An ITW Company (www.trussteel.com), are easy to specify, design, and inspect (design manual and specs available), according to the company. They are easy to handle and install because of their superior stiffness and high strength-to-weight ratio. Local TrusSteel fabricators across the United States provide engineered designs, standard details, specifications, hardware, estimates, and finished trusses.
Unique Structural Systems/MHS (www.modularhousingsystem.com) offers MHS-Post and Beam Frame Assembly consisting of prefabricated modular extrusions aluminum framing members connected by the MHS connectors for roofs, floors, and walls in-filled with structural insulated panels between framing members at the jobsite. The MHS roof and floor diaphragm framing system is tested according on IBC 2006 and ASTM E455.