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TECHNICAL PAPER

Elevation Bottom
(a) Combined beam-slab failure (1way BSF-long)

Bottom Top
(b) Slab-alone failure (SAF)

Figure 6: Experimental observations of collapse mechanisms of beam-slab systems .
[3]
with heavy reinforcement in the long span beams, failed by the where
conventional SAF mechanism (Figure 3a), as shown in Figure 6b. 2
2 2

Y 2 X X

3
The present study extends the conclusions drawn from the r Y r Y
earlier study [3, 4, 5] to the two ‘one-way’ slab systems shown in
Figures 1 and 2. Yield line analysis is carried out for various m y l y
possible collapse mechanisms for the isolated system (Figures m x , r = l x
3a, 4 and 7) and for the continuous beam-slab system (Figures
3b and 5). The most likely collapse mechanism is identified as X 1 i y1 1 i y2
the one in which the collapse load estimate is the least, for each
of the two systems.
Y 1 i 1 i
x1 x2
2. YIeLD LINe ANALYsIs FOR sLAB-ALONe m x and m y are the positive (sagging) mid-span moment
FAILURe (SAF) capacities along short span and long span respectively, i x1m x and
i x2m x are the negative edge moment capacities along the short
The yield line analysis for a uniformly loaded rectangular slab
with discontinuous or continuous (fixed) edges, shown in Figure span (x) direction (at the long edges 1 and 2 respectively), and
3, is well known . This provides a conservative estimate of the i y1m y and i y2m y are negative edge moment capacities along the
[1]
collapse load, as SAF test results show that the collapse load long span (y) direction (at the short edges 1 and 2 respectively).
For an isolated rectangular beam-slab system, i x1 = i x2 = i x; i y1 =
can get enhanced in such slabs under large deflections owing i y2 = i y. The value of i should be taken as zero when the negative
to tensile membrane action [3, 6] . The expression for the collapse yield line cannot be developed at the slab edges.
load per unit area, w for the generic case, with possible negative
yield lines near all the edges, is given below, in terms of the As per IS 456 , the expressions for m x and m y are obtainable as
[2]
aspect ratio r, ultimate moment capacities (per unit width), and follows, including the material safety factors :
[1]
orthotropy coefficient μ [3, 4, 7] : x
.
.
st x
x
x
y
u
,
w 6 m (1) m 087 f A ( d 0 416 ) (1a)
x
l x 2 m 087 f A ( d 0 416 )
x
.
.
y
st y
u
y
y
,
16 The IndIan ConCreTe Journal | MarCh 2020