ASD/LRFD Manual - American Wood Council

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ASD/LRFD MANUAL FOR ENGINEERED Wood Construction 49 Figure M7.4-8 Lateral Support Requirements for Joists in Hangers When top flange style hangers are used to support one I-joist from another, especially the wider flange I-joists, web stiffeners need to be installed tight to the bottom side of the support joist’s top flanges. This prevents cross grain bending and rotation of the top flange (see Figure M7.4-9). When face-nail hangers are used for joist to joist connections, nails into the support joist should extend through and beyond the web element (Figure M7.4-10). Figure M7.4-9 Top Flange Hanger Support Filler blocks should also be attached sufficiently to provide support for the hanger. Again, nail diameter should be considered to avoid splitting the filler block material. Multiple I-joists need to be adequately connected together to achieve desired performance. This requires proper selection of a nailing or bolting pattern and attention to web stiffener and blocking needs. Connections should be made through the webs of the I-joists and never through the flanges. 7 M7: PREFABRICATED WOOD I-JOISTS American Forest & paper association
50 M7: PREFABRICATED WOOD I-JOISTS For a double I-joist member loaded from one side only, the minimum connection between members should be capable of transferring at least 50% of the applied load. Likewise, for a triple member loaded from one side only, the minimum connection between members must be capable of transferring at least 2/3 of the applied load. The actual connection design should consider the potential slip and differential member stiffness. Many manufacturers recommend limiting multiple members to three joists. Multiple I-joists with 3½" wide flanges may be further limited to two members. The low torsional resistance of most wood I-joists is also a design consideration for joist to joist connections. Eccentrically applied side loads, such as a top flange hanger hung from the side of a double joist, create the potential for joist rotation. Bottom flange restraining straps, blocking, or directly applied ceiling systems may be needed on heavily loaded eccentric connections to resist rotation. Figure M7.4-10 shows additional I-joist connection considerations for use with face nail hangers. Figure M7.4-10 Connection Requirements for Face Nail Hangers Vertical Load Transfer Bearing loads originating above the joists at the bearing location require blocking to transfer these loads around the wood I-joist to the supporting wall or foundation. This is typically the case in a multi-story structure where bearing walls stack and platform framing is used. Usually, the available bearing capacity of the joist is needed to support its reaction, leaving little if any excess capacity to support additional bearing wall loads from above. The most common type of blocking uses short pieces of wood I-joist, often referred to as blocking panels, positioned directly over the lower bearing and cut to fit in between the joists. These panels also provide lateral support for the joists and an easy means to transfer lateral diaphragm shears. The ability to transfer lateral loads (due to wind, seismic, construction loads, etc.) to shear walls or foundations below is important to the integrity of the building design. Compared with dimension lumber blocking, which usually is toe-nailed to the bearing below, wood I-joist blocking can develop higher diaphragm transfer values because of a wider member width and better nail values. Specialty products designed specifically for rim boards are pre-cut in strips equal to the joist depth and provide support for the loads from above. This solution may also provide diaphragm boundary nailing for lateral loads. American Wood Council
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2005 EDITION ASD/LRFD MANUAL MANUAL
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Updates and Errata While every prec
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100 M15: SPECIAL LOADING CONDITIONS
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102 M16: FIRE DESIGN M16.1 General
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104 M16: FIRE DESIGN Table M16.1-4
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106 M16: FIRE DESIGN Figure M16.1-2
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American Forest & Paper Association
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