STRENGTH CAPACITY OF ONE-WAY CONTINUOUS REINFORCED CONCRETE SLABS

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World Journal Of Engineering


779

STRENGTH CAPACITY OF ONE
-
WAY CONTINUOUS

REINFORCED CONCRETE SLABS


Domagoj Matešan
, Jure Radnić,
Nikola Grgić

and Vatroslav Čamber


Faculty of Civil Engineering and Architecture, University of Split, 21000 Split, Croatia.


Introduction


Limit strength ca
pacity and deformability of continuous
reinforced concrete slabs are affected by, among other
parameters, length of longitudinal tensile rebars above
the inner supports. A number of experimental studies of
the behavior of reinforced concrete slabs under sh
ort
-
term static load were carried out (the results of some
studies can be found in [
1
-
6
]
, where the authors of this
paper were not familiar with the research of slabs
related to the previously mentioned issue.

The paper first presents the results of experi
mental tests
of the limit strength capacity of a continuous concrete
slab with two spans of 1.4 m, loaded with concentrated
force at the middle of each span. The effect of length of
longitudinal tensile rebars above the inner support on
the limit strength
capacity and slab deformability was
analyzed. Already developed model of the authors for
the numerical analysis of reinforced concrete and
prestressed concrete slabs and shells [
7
,
8
], was
additionally tested on the obtained experimental test
results. Compa
rison between the experimental tests and
the obtained numerical results confirms the reliability of
this numerical model. The limit strength capacity and
deformability of the continuous reinforced slab, with
two 6.0 m spans and different reinforcement
arra
ngements above the inner support, loaded by a
uniformly distributed load, were analyzed by the model.



Experimental tests


The slab is rectangular, 3.0 m × 0.5 m plan size and 0.05
m thick
, made of concrete
. The slab was freely
supported by three line sup
ports, namely, it was a
continuous girder with two spans.

The slab was reinforced by a welded mesh. Three
different lengths of longitudinal tensile reinforcement
A
s2

above the inner support were analyzed:

S1


slab without tensile reinforcement above the i
nner
support;

S2


slab reinforced with welded mesh Q
-
283 (6 mm
diameter rebars at 100 mm axial spacing, A
s2

=
2.83 cm
2
/m = 0.57% A
c
) above the inner support,
of longitudinal rebars length 2×0.3 = 0.6 m;

S3


slab reinforced with mesh Q
-
283 above the inner

support, of longitudinal rebars length 2×0.6 = 1.2
m.

The slab was loaded by concentrated force
P

at each
mid
-
span. The force was gradually increased until
slab
failure.

Figure
1

shows the deflection of the slab mid
-
span
(mean value of measured deflection
s in each span) as a
function of force
P
. The deflections of slab S1 were
significantly greater than of slabs S2 and S3 for the
same force level. Likewise, the limit bearing capacity of
slabs S2 and S3 was greater than the limit bearing
capacity of slab S1
. The
behavior

of slabs S2 and S3
almost overlapped until their collapse. The collapse of
all slabs occurred through the tensile reinforcement at
the slab mid
-
span. Numerical results obtained by the
model [
7
,
8
] are shown in the same Figure. As can be
obser
ved, there is a good correspondence between the
experimentally determined and the obtained numerical
results.



0
3
6
9
12
15
0
5
10
15
20
25
Deflection [mm]
Force P [kN]
S3 experimental
S3 numerical
S2 experimental
S2 numerical
S1 experimental
S1 numerical
S3
S2
S1


Fig
.

1

Deflection of slab at mid
-
span




World Journal Of Engineering


780


Numerical tests


The slab is a continuous girder over two spans, of span
6 m and 0.20 m thick.
T
he
slab was loaded by uniformly
distributed load
q

until failure.

The slab was reinforced by a welded mesh R
-
283 in the
bottom layer (6 mm diameter longitudinal rebars at 100
mm axial spacing, A
s1

= 2.83 cm
2
/m = 0.14% A
c
). Slab
Q1 is without tensile reinforc
ement above the inner
support. Slabs Q2
-

Q6 are reinforced in the upper layer
above the inner support by a welded mesh R
-
503 (8 mm
diameter longitudinal rebars at 100 mm axial spacing,
A
s2

= 5.03 cm
2
/m = 0.25% A
c
). The longitudinal length
of the mesh
abov
e the inner support
was varied

(Q2; 0.5
m, Q3; 1.0 m, Q4; 1.5 m,

Q5; 2.0 m and

Q6; 12.0 m)
.

The deflection at the mid
-
span of the slab, as a function
of load
q
,

is shown in Figure
2
. Until load
q

increased to
a height value, all slabs had almost similar
be
havior
.
The slab without tensile reinforcement above the inner
support (Q1) had the lowest bearing capacity and the
lowest stiffness (the greatest deflection). Even when
short, tensile reinforcement above the inner support
significantly increases the stiff
ness and limit bearing
capacity of slabs. As the result of longer tensile
reinforcement above the inner support, the limit bearing
capacity of the slab increases and the slab deflection
decreases. The length of the tensile reinforcement of
slabs Q2, Q3 and

Q4 above the inner support is short for
the usual practical application
.

T
he fracture of slabs Q1,
Q2, Q3 and Q4 occurred through tensile reinforcement
in the span, while the fracture of slabs Q4 and Q5
occurred through tensile reinforcement above the inn
er
support.


0
2
4
6
8
10
12
14
0
10
20
30
40
50
60
70
Deflection [mm]
Load q [kN/m
2
]
Q6
Q5
Q4
Q3
Q2
Q1
Q6
Q5
Q4
Q3
Q2
Q1

Fig. 2 Deflection at the mid
-
span of the slab as a
function of load
q


Conclusion


The reliability of the already developed model by the
author for the numerical analysis of reinforced concrete
slabs and shells [
7
,
8
] was confirmed by the resu
lts of
experimental tests of a one
-
way continuous reinforced
concrete slab with three different reinforcement
arrangements.

The length of tensile longitudinal reinforcement above
the inner supports of one
-
way continuous slabs a lot
affects the limit streng
th capacity and deformability of
slabs. Longer tensile reinforcement bars above the inner
supports increases the stiffness and limit bearing
capacity of the slabs. Limit bearing capacity and
deflection are much lower on slabs without tensile
reinforcement
above the inner supports. Their
behavior

after occurrence of concrete cracks above the inner
supports is similar with the
behavior

of simply
supported concrete slabs.

We shouldn't skimp on the length of tensile
reinforcement above the inner supports in pra
ctice,
because it can significantly reduce the limit bearing
capacity and increase deflection and concrete cracks
widths of the slabs.

References

1

Taylor
, R.
, Maher,
D.R.H. and
Hayes,
B.
Effect of the
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reinf
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,

187

(
1966
)

85
-
94.

2

Moy, S.S.J.

and

Mayfield, B.

Load
-
deflection
characteristics of rectangular reinforced concrete slabs
.

Mag. Conc. Res.

24

(
1972
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209

218.

3

Regan,
P. E.
Symmetric punching of reinforced concrete
s
labs
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38

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115
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834
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6

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7

Radnić, J., Harapin, A. and Matešan, D. Static and
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Radnić,
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