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2025-05-17 07:25 本頁面
【正文】 n of any construction loads. Even under the weight of an erector, the joists may exhibit some degree of lateral instability until the bridging is installed. The bridging also serves the purpose of holding the steel joists in position as shown on the plans. The minimum number of rows of bridging is a function of the joist chord size and span length. A table is furnished in the standard specifications that establishes the required number of rows of bridging. Spacing of bridging rows should be approximately equal. Two permissible types of bridging may be observed in Figure 92. Horizontal bridging (Figure 92a) consists of two continuous horizontal steel members, one attached to the top chord and the other attached to the bottom chord by means of welding or mechanical fasteners. The attachment must be capable of resisting a horizontal force of not less than 700 lb. If the bridging member is a round bar, the diameter must be at least 2 in. The maximum slenderness ratia4V/rj~ofthe bridging member cannot exceed 300, where k is the distance between bridging attachments and r is the least radius of gyration of the bridging member. The bridging member shall be designed for a pressive force of times the area of the top chord. Diagonal bridging (Figure 92b) consists of crossbracing with a maximum B/r of 200, with Z and r as defined previously. Where the crossbracing members connect at their intersection, E is the distance between the intersection attachment and chord attachment. The ends of all bridging lines terminating at walls or beams must be properly anchored. A typical detail may be observed in Figure 92b. FIGURE 92 Typical bridging. Joist extensions are frequently used with KSeries joists to support a variety of overhang conditions. Two types are shown in F
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