Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

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Forms for Concrete Bridge Decks 441
FIGURE 16-7 Deck forms supported by steel joists.
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As illustrated in Figure 16-7, horizontal and diagonal bridging must
be installed between adjacent joists to prevent transverse movements of
the bottom chords of the joists, following the recommendations of the
Steel Joist Institute. Horizontal bridging consists of two continuous horizontal
steel members, one attached to the top chord and the other to the
bottom chord. Diagonal bridging consists of cross-bracing. The number
of rows of bridging depends on the joist designation and span length in
accordance with standards of the Steel Joist Institute.
Because the joists will be reused several times on a given project,
the bottom chords and possibly the top chords of several rows of
joists should be interconnected by welding ¾-in. steel rods diagonally
across and between adjacent joists. This will permit the interconnected
joists to be lowered onto a truck-mounted traveler as a single
assembly and moved to a new location. The diagonal rods will prevent
racking during the handling and moving of the joists.
Also, if ground conditions under a bridge permit the operation of
a truck equipped with a variable-height traveler, it is possible that an
assembly of several interconnected steel joists, wood joists, and decking
can be lowered intact onto the traveler and moved to a new location,
which can produce considerable economy in formwork. If this
procedure is to be followed, the wood joists should be cut to lengths
that conform to the width of an assembly unit unless the forms for an
entire bay will be moved as a unit.
Table 16-1 provides allowable total safe loads for K-series steel
joists with allowable tensile stress of 30,000 lb per sq in. Dead loads,
including joists, must be deducted to determine the load-carrying
capacity of joists. The values in the tables are pounds per linear foot
along the joist. The component parts of the formwork should be
designed as illustrated in the following example.
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