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TECHNICAL PAPER

ECONOMICAl AND

RATIONAl DESIGN OF

‘ONE-WAY’ RC BEAM-

SlAB SYSTEMS AnuRAg SIngh, BIjILy BALAkRIShnAn,

DEvDAS MEnOn

Abstract L y : Overall effective span of the beam-slab system along
In the conventional design of reinforced concrete (RC) long span
rectangular slabs in beam-slab systems subject to gravity l x : Effective span of single panel unit along short span
loading, it is assumed that the code-specified moment
coefficients (derived based on yield line theory, assuming l y : Effective span of single panel unit along long span
non-deflecting supports at the edges) can be used, provided M x : Positive moment capacity of beam along short span
the beams provided at the edges are adequately stiff. Recent : Positive moment capacity of beam along long span
experimental and theoretical studies have established that M y
such designs turn out to be over-conservative, as the assumed m x : Positive moment capacity (per unit length) of slab
yield line mechanism of the slab does not occur. In general, a along short span
combined beam-slab collapse mechanism occurs at the limit
m y : Positive moment capacity (per unit length) of slab
state of collapse, in which the yield lines in the slab connect along long span
to plastic hinges in the supporting beams. With a proper
understanding of possible collapse mechanisms and estimation q : Total line load (including self-weight) acting on beam
of the lowest collapse load, using yield line theory, a more R : Overall aspect ratio of the beam-slab system (L y/L x)
rational and economical design of the beam-slab system is
possible. Considerable savings in steel can be achieved, while r : Aspect ratio of single panel unit (l y/l x)
fully complying with the strength and serviceability requirements w : Collapse load per unit area
of the code.
w service : Service load per unit area
Keywords: Combined beam-slab failure, Rectangular beam-slab w u : factored uniformly distributed gravity loading per unit
system, Relative beam-slab flexural strength, Slab alone failure, area
Yield line theory.
x u : Depth of neutral axis at ultimate limit state
NOtAtIONs α, α x, α y : Beam-slab relative strength parameter

: Area of tension steel in slab along short span n : Number of beam-slab systems
A st,x
μ : Orthotropic coefficient
: Area of tension steel in slab along long span
A st,y
: Effective depth of slab along short span
d x 1. INtRODUCtION
: Effective depth of slab along long span Consider the two reinforced concrete (RC) rectangular ‘one-way’
d y
floor slab systems shown in Figures 1 and 2, with aspect ratio
: Yield strength of reinforcing bar
f y
exceeding two. The isolated system in Figure 1 comprises a
: Ratio of negative to positive moment capacities of slab, integrally connected to four edge beams, which are simply
i x
slab along short span supported on masonry pillars provided at the four corners.
The example shown in Figure 2 is a textbook problem , used
[1]
: Ratio of negative to positive moment capacities of
i y to demonstrate one-way continuous slab design. Covering
slab along long span
an overall area of 8m × 14.5m, the floor slab in Figure 2 is
L x : Overall effective span of the beam-slab system along simply supported on masonry walls at the four boundaries, and
short span provided with three intermediate RC beams.

12 The IndIan ConCreTe Journal | MarCh 2020