Building Design and Construction Handbook - Merritt - Ventech!

7.26 COMPOSITE CONSTRUCTION
STRUCTURAL STEEL CONSTRUCTION 7.83
In composite construction, rolled or built-up steel shapes are combined with reinforced
concrete to form a structural member. Examples of this type of construction
include: (a) concrete-encased steel beams (Fig. 7.37c), (b) concrete decks interactive
with steel beams (Fig. 7.37a and b), (c) concrete encased steel columns, and (d)
concrete filled steel columns. The most common use of this type of construction is
for composite beams, where the steel beam supports and works with the concrete
slab to form an economical building element.
Design procedures require that a decision be made regarding the use of shoring
for the deck pour. (Procedures for ASD and LRFD differ in this regard.) If shoring
is not used, the steel beam must carry all dead loads applied until the concrete
hardens, even if full plastic capacity is permitted for the composite section afterward.
The assumed composite cross section is the same for ASD and LRFD procedures.
The effective width of the slab is governed by beam span and beam spacing
or edge distance (Fig. 7.37a and b).
Slab compressive stresses are seldom critical for interior beams but should be
investigated, especially for edge beams. Thickening the slab key and minimum
requirements for strength of concrete can be economical.
FIGURE 7.37 Steel-concrete composite-beam construction: (a) and (b) with welded-stud
shear connectors; (c) with encasement in concrete.