Structural Concrete - Hassoun

CHAPTER16
CONTINUOUS
BEAMS AND
FRAMES
Reinforced concrete parking structure, Minneapolis, Minnesota.
16.1 INTRODUCTION
Reinforced concrete buildings consist of different types of structural members, such as slabs,
beams, columns, and footings. These structural members may be cast in separate units as precast
concrete slabs, beams, and columns or with the steel bars extending from one member to the
other, forming a monolithic structure. Precast units are designed as structural members on
simple supports unless some type of continuity is provided at their ends. In monolithic members,
continuity in the different elements is provided, and the structural members are analyzed as
statically indeterminate structures.
The analysis and design of continuous one-way slabs were discussed in Chapter 9, and the
design coefficients and reinforcement details were shown in Figs. 9.8 and. 9.9. In one-way floor
systems, the loads from slabs are transferred to the supporting beams, as shown in Fig. 16.1a. If
the factored load on the slab is w u psf, the uniform load on beams AB and BC per unit length is
w u s plus the self-weight of the beam. The uniform load on beams DE and EF is w u s/2 plus the
self-weight of the beam. The load on column B equals W u LS, whereas the loads on columns E, A,
and D are W u LS/2, W u SL/2, and W u LS/4, respectively.
In two-way rectangular slabs supported by adequate beams on four sides, the floor loads are
transferred to the beam from tributary areas bounded by 45 ∘ lines, as shown in Fig. 16.1b.Partofthe
floor loads are transferred to the long beams AB, BC, DE,andEF from trapezoidal areas, whereas
the rest of the floor loads are transferred to the short beams AD, BE,andCF from triangular areas.
In square slabs, loads are transferred to all surrounding beams from triangular floor areas. Interior
beams carry loads from both sides, whereas end beams carry loads from one side only. Beams in
both directions are usually cast monolithically with the slabs; therefore, they should be analyzed as
statically indeterminate continuous beams. The beams transfer their loads in turn to the supporting
columns. The load on column B equals W u LS, while the loads on columns E, A,andD are W u LS/2,
W u SL/2, and W u LS/4, respectively. The tributary area for each column extends from the centerlines
of adjacent spans in each direction.
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