IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 04 Special Issue: 13 | ICISE-2015 | Dec-2015, Available @ http://www.ijret.org 463
EXPERIMENTAL AND NUMERICAL STUDY ON THE FLEXURAL
BEHAVIOR OF PRECAST LIGHT-WEIGHT CONCRETE SANDWICH
PANELS
J. Daniel Ronald Joseph
1
, J. Prabakar
2
, P. Alagusundaramoorthy
3
1
Scientist, CSIR Structural Engineering Research Centre, CSIR Madras complex, Chennai, India
2
Senior Principal Scientist, CSIR Structural Engineering Research Centre, CSIR Madras complex, Chennai, India
3
Professor, Structural Engineering Laboratory, IIT Madras, Chennai, India
*
Corresponding author: ronald.dany@gmail.com;
Abstract
Use of light-weight structural elements in buildings is becoming popular in the recent years. This paper presents the experimental
and numerical studies carried out to understand the flexural behavior of prototype precast light-weight concrete sandwich panels
under four-point bending. In the experimental study, two prototype panels were cast and tested. Transverse deflections of the
panels were recorded during testing and the results are presented and discussed. Numerical studies were carried out using the
general purpose finite element software ABAQUS. 8-noded linear brick element and 2-noded linear truss element were used to
model the wythes and mesh reinforcements, respectively. Saenz model is used to model the behavior of concrete in compression. It
is observed from the tests that, the panels behaved as composite elements until failure. Experiments indicate that the thickness of
the panel affect the load carrying capacity of the concrete sandwich panel significantly. The load-deflection curves of the panels
determined using numerical studies are comparable to that of the experimental results.
KEYWORDS Precast, Sandwich Panels, Light-Weight Panels, Expanded Polystyrene, Self Compacting Concrete
----------------------------------------------------------------------***--------------------------------------------------------------------
1. INTRODUCTION
Precast concrete structural elements are manufactured under
controlled factory conditions and therefore concrete
structural elements with good precision in geometry and
finishing can be manufactured. Background information on
precast technology can be found in the literature [1-3].
Precast concrete elements besides being structurally and
economically efficient [4], also have social and
environmental benefits [5]. Precast structural elements if
light-weighted also have advantages such as (i) less
attraction of seismic forces, (ii) ease of handling and
transportation and (iii) cost effective. Light-weight concrete
sandwich panels produced by replacing core concrete using
lesser dense material consist of two skins of concrete called
wythe, one on either side of the core. Welded wire mesh or
conventional steel rebars may be used to reinforce the
wythes. The core is made of material that provides
significant thermal and sound insulation. In this study, EPS
(Expanded PolyStyrene) is used as the core. In order to
achieve composite action of the panel under flexural load
shear transfer between the two wythes is ensured by using
shear connectors that connect the two wythes.
Experimental studies on the behavior of light-weight
concrete sandwich panels under different load conditions
can be found in the literature [6-18] which have proved the
feasibility of using these panels for floors, roofs and walls of
the buildings. Nevertheless, it is noted that in the literature
no studies are found reported on the flexural behavior of
light-weight concrete sandwich panels with wires as shear
connectors. In this paper the results of the experimental
study carried out to determine the flexural behavior of
prototype precast light-weight concrete sandwich panels
with wires as shear connectors under four-point bending are
presented. Two prototype panels are tested in the present
study to study the effect of percentage of reinforcement in
wythes and the total thickness of the panel, both of which
are directly proportional to the moment carrying capacity,
ultimate load carrying capacity and the flexural behavior of
light-weight concrete sandwich panel. The variation in the
thickness of the panel is achieved by using different core
thicknesses. The paper is organized as follows. Section 2
presents the materials used and casting of the panels,
Section 3 presents the test set-up and the instrumentation
details, Section 4 presents the results and discussions and
Section 5 presents summary and conclusions.
2. EXPERIMENTAL STUDY
2.1 MATERIALS USED
Two numbers of prototype precast light-weight concrete
sandwich panels with different thicknesses (100mm and
150mm) are tested to failure. The panel with thickness
150mm is named FA and the one with 100mm is named FB.
The length and breadth of a panel is 1200x3000mm. The
schematic sketch of the components of panels considered is
shown in Fig. 1. Welded wire mesh of grid size 50x50mm
was used for reinforcing concrete wythes. The two meshes
were connected at equal intervals using shear connectors
inclined at an angle of 45°. The wires of the mesh and the
IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 04 Special Issue: 13 | ICISE-2015 | Dec-2015, Available @ http://www.ijret.org 464
shear connectors were nearly 2.2mm in dia. The average
tensile strength of the steel wire as supplied by the
manufactures is 651.64MPa. Self Compacting Concrete
(SCC) was used for making the wythes. The mix proportion
for SCC was arrived based on the guidelines of ACI
19
and it
is 1:1.89:2.34:0.3:0.41:0.6% in the order of Cement, Coarse
aggregate, Fine aggregate, Ground Granulated Blast Furnace
Slag (GGBFS), Water and Superplasticizer (by weight of
binder content). It was ensured that the SCC mixture
considered satisfies the recommended
6
minimum
requirements. Coarse aggregates passing 10 mm sieve were
used in SCC. Same mix proportion was used for casting
both panels. The average compressive and flexural tensile
strengths of SCC were found to be 45.97MPa and 4.34MPa,
respectively. Table 1 gives the details of the prototype
precast light-weight concrete sandwich panels considered
for the present experimental study.
2.2 CASTING OF PANELS
The sequence of casting the panel is shown in Fig. 2. A steel
mould of size 1200x3000mm was placed on a level surface
and SCC was poured to a depth of 25mm to form bottom
wythe. EPS with wire mesh was placed over the concrete.
SCC was then poured on the EPS to form top wythe of
25mm thickness. Stiffening concrete beams were provided
along the supporting edges to avoid failure due to local
crushing of concrete. The panels manufactured were cured
for 28 days. The manufacturing methods reported in the
literature [6-18] involved either plastering on the EPS panel
using cement mortar or placing normal concrete on the EPS
panel and vibrating for achieving better compaction of
concrete. These methods require skilled labor and sufficient
time for casting and finishing the panel. The method of
manufacturing adopted in this paper does not require highly
skilled labor. Time taken for casting a panel is 30 minutes.
This method of manufacturing light-weight concrete
sandwich panel using ready-made EPS panel and SCC is
expected to suit mass production of the panels.
2.3 TEST SET-UP AND INSTRUMENTATION
The panels manufactured were tested under four-point
bending. This type of loading was chosen because of
constant bending moment being developed between the
loading points. Displacement controlled loading was applied
until the panels failed. One edge of the panel was supported
by a hinge and the other was supported by a roller. It was
ensured that the supports were provided on the stiffening
beams. Linear Voltage Displacement Transducers (LVDTs)
with 50mm range were used to measure the deflections of
the panels. Strain gauges with gauge length of 2mm and
30mm were used to measure the strains on the wires and
concrete surface, respectively. Schematic sketch of the test
set-up and the locations of the LVDTs are shown in Fig. 3.
Photograph of a panel ready for testing is shown in Fig. 4.
3. NUMERICAL STUDY
Numerical studies were carried out in the general purpose
finite element software ABAQUS to model the nonlinear
behavior of the concrete sandwich panels. In ABAQUS, the
behavior of concrete was modeled using the material model
concrete damaged plasticity. In this model, concrete is
assumed to be isotropic in elastic and inelastic regime both
in compression and tension. To describe the behavior of
concrete under compression, stress-strain curve for concrete
under uni-axial compression is constructed by using the
model proposed by Saenz [24]. The Young’s modulus of
concrete was determined using the empirical relation given
in IS 456:2000 [25].
E = 5000√f
ck
= 5000√45 = 33541 MPa.
Under tension, the concrete is assumed to behave linearly
elastic until tensile strength of the concrete. The tensile
strength of concrete is chosen by inverse analysis so as to
predict the load-deflection curves comparable to that of
experimental results. The post-peak behavior of concrete
under tension is specified using fracture energy method. The
fracture energy of the concrete was determined using the
relation given in CEB-FIB Model Code [26], which is a
function of concrete cylinder strength (f
cm
). The cube
strength is converted to equivalent cylinder strength by
multiplying a factor of 0.8.
Fracture energy, G
f
= 73f
cm
0.18
= 73x(0.8x45)
0.18
= 139 J/m
2
8-noded linear brick and 2-noded linear truss elements were
used to model the wythes and mesh reinforcements,
respectively. It is assumed that there is no slip between the
mesh reinforcements and the concrete and hence the
bonding is assumed to be perfect. The shear connectors were
modeled as springs. The slope of the load-deflection curve
of the wires under uni-axial tension within elastic limit is
specified as the stiffness of the spring. Considering the
symmetry of the panel, one quarter of the sandwich panel is
modeled. The support condition specified for the model is
shown in the Fig. 5. The FE model developed in ABAQUS
is shown in Fig. 6.
4. RESULTS AND DISCUSSIONS
The picture of a panel tested is shown in Fig. 7. No
separation of wythes was observed for both panels tested
and hence, it can be concluded that both panels behaved as
composite elements until failure. For both panels first crack
appeared in the tensile region of the panel between one of
the loading points and the nearest support.
Very few flexural cracks were seen in the maximum
bending moment region of panel FB. Panel FA deformed
extensively which resulted in relatively more numbers of
flexural cracks in the maximum bending moment region. It
is noted that, for both panels first crack occurred in the
region between one of the loading points and the nearest
support (and not in the maximum bending moment region).
The formation and propagation of first crack in all the
panels is thus attributed to mixed-mode fracture, i.e.,
combined effect of tensile stress (due to flexure) and shear
stress. The load-deflection curves obtained from the
experiments and numerical studies are shown in the Fig. 8.
From Fig.8 it is observed that, the panels FA and FB behave
IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 04 Special Issue: 13 | ICISE-2015 | Dec-2015, Available @ http://www.ijret.org 465
linearly upto loads 9.71kN and 5.48 kN, respectively. The
ultimate failure load of the panel FA is almost 200% greater
than that of the panel FB. This is due to the higher thickness
of the panel (and hence larger lever arm). It is observed that,
the load-deflection curves obtained using the numerical
models are in close agreement with the experimental results.
The distribution of inelastic strain (along the span) of the
panel is shown in the Figs. 9 and 10.
From Figs. 9 and 10, it can be observed that, as expected,
for both panels strains are higher in the maximum bending
moment region. For the panel FB the strain in the bottom
wythe under (almost) the loading point is observed to be
larger comparative to any other location. For both the
panels, the inelastic strain is seen to be larger between the
points at which the springs are connected to the bottom
wythe.
5. SUMMARY AND CONCLUSIONS
The results of the experiments carried out to study the
flexural behaviour of precast light-weight concrete sandwich
panel are presented in this paper. It is found from the
experiments that the thickness of the panel have profound
effect on the load carrying capacity of the panel. Numerical
study indicates that, the model developed is capable of
predicting the load-deflection curves comparable to that
determined experimentally. Carrying out further
experimental and numerical study with different mesh sizes,
with additional conventional steel rebars and thickness of
the panel may form future area of the research towards
developing design guidelines.
ACKNOWLEDGEMENT
This paper is published with the permission of the Director,
CSIR-SERC.
REFERENCES
[1]. Alfred Yee A. Prestressed concrete for buildings. PCI
J 1976;24(5):112-157.
[2]. Alfred Yee A, Kim Chang Nai. One hundred
Washington square: Structural Design and
Construction. PCI J 1984;29(1):24-48.
[3]. Alfred Yee A. Design considerations for precast
prestressed concrete building structures in seismic
areas. PCI J 1991;36(3):40-55.
[4]. Alfred Yee A. Social and environmental benefits of
precast/prestressed concrete construction. PCI J
2001;46(3):14-19.
[5]. Alfred Yee A. Structural and economic benefits of
precast/prestressed concrete construction”. PCI J
2001;46(4):34-42.
[6]. Benayoune, A., Samad, A.A.A., Trikha, D.N., Abang
Ali, A.A., Ellinna, S.H.M. (2008). “Flexural behavior
of pre-cast concrete sandwich composite panel -
Experimental and theoretical investigations”. J
Constr Build Mater 2008;22:580-592.
[7]. Bush, T.D., Stine, G.L. Flexural behaviour of
composite precast concrete sandwich panels with
continuous truss connectors. PCI J 1994;39(2):112-
21.
[8]. Bush, T.D., Wu, Z. Flexural analysis of prestressed
concrete sandwich panels with truss connectors. PCI
J 1998;43(5):76-86.
[9]. Carbonari, G., Cansario, S.H.P., Cavalaro, M.M.,
Aguado, A. Flexural behaviour of light-weight
sandwich panels composed by concrete and EPS. J
Constr Build Mater 2012;35:792-799.
[10]. Einea, A., Salmon, D.C., Tadros, M.K., Culp, T. A
new structurally and thermally efficient precast
sandwich panel system. PCI J 1994; 39(4): 90-101.
[11]. Einea, A., Salmon, D.C., Tadros, M.K., Culp, T.
Partially composite sandwich panel deflection”. J
Struct Eng ASCE 1995;121(4):778-83.
[12]. Gara, F., Ragni, L., Roia, D., Dezi, L. Experimental
tests and numerical analysis of floor sandwich
panels. Eng Struct 2012;36:258–260.
[13]. Henin, E., Marcous, G., Tadros, M.K.
Precast/Prestressed concrete sandwich panels for
thermally efficient floor/roof applications. Pract
Period Struct Des Constr 2014:1-12.
[14]. Salmon, D.C., Einea, A., Tadros, M.K., Culp, T.D.
Full scale testing of precast concrete sandwich
panels”. J Struct ACI 1997;354-362.
[15]. Yardim, Y., Waleed, A.M.T., Jaafar, M.S., Laseima,
S. AAC-concrete light weight precast composite
floor slab. J Constr Build Mater 2013;40:405–410.
[16]. Benayoune, A., Samad, A.A.A., Trikha, D.N., Abang
Ali, A.A., Ashrabov, A.A. Structural behaviour of
eccentrically loaded precast sandwich panels. J
Constr Build Mater 2006;20(9):713-724.
[17]. Benayoune, A., Samad, A.A.A., Abang Ali, A.A.,
Trikha, D.N. Response of pre-cast reinforced
composite sandwich panels to axial loading. J Constr
Build Mater 2007;21(3):677-685.
[18]. Gara, F., Ragni, L., Roia, D., Dezi, L. Experimental
tests and numerical modelling of wall sandwich
panels. Eng Struct 2012;37:193–204.
[19]. ACI commitee 237. Self Consolidating Concrete.
ACI 2007.
[20]. Allen, H.G. Analysis and Design of Structural
Sandwich Panels. Pergamon Press 1968, Oxford.
[21]. Indian Standard IS 516:1959. Methods of tests for
strength of concrete, Bureau of Indian Standards
2002.
[22]. Park, R., Paulay, T. Reinforced Concrete Structures,
John Wiley & Sons Inc., 1975.
[23]. Carmona, J.R., Ruiz, G., Viso, J.R. Mixed-mode
crack propagation through reinforced concrete. Eng
Frac Mech 2007;74:2788–2809.
[24]. Saenz, L.P. Discussion of “Equation for stress-strain
curve of concrete” by Desayi P, Krishnan S. ACI
Journal 1964;61:1229-35.
[25]. Indian Standard IS 456:2000. Plain and Reinforced
Concrete – Code of Practice, Bureau of Indian
Standards 2005.
[26]. The Fib Model Code for concrete structures, Ernst &
Sohn, 2010.
IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 04 Special Issue: 13 | ICISE-2015 | Dec-2015, Available @ http://www.ijret.org 466
Table 1 Details of the sandwich panels considered
Specimen
Mesh size (mm)
Thickness (mm)
Wythe
EPS
Total
FA
50 x 50
25
100
150
FB
50 x 50
25
50
100
Fig. 1 Schematic sketch of sandwich panel
Fig. 2 Sequence of casting a panel
Y
Y
SECTION X-X
SECTION Y-YELEVATION
WIRE MESH EMBEDDED
IN CONCRETE WYTHE
125
25
STIFFENING BEAM
CONCRETE WYTHE
SHEAR CONNECTORS
1200
3000
TOTAL THICKNESS
ALL DIMENSIONS ARE IN MM
XX
5
6
4
2
3
1
IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 04 Special Issue: 13 | ICISE-2015 | Dec-2015, Available @ http://www.ijret.org 467
Fig. 3 Schematic test set-up and locations of LVDTs
Fig. 4 Photograph of a panel ready for testing
Fig. 5 Support condition assumed in FE model
Fig. 6 FE model developed in ABAQUS
Fig. 7 Photograph of tested panel FB
0.0
5.0
10.0
15.0
20.0
25.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0
Load, kN
Deflection, mm
FA - Exp.(L2)
FA - FEM
FB - Exp.(L2)
FB - FEM
Fig. 8 Experimental and FE load-deflection curves
Fig. 9 Inelastic strain distribution along the span of panel
FA
Fig. 10 Inelastic strain distribution along the span of panel
FB
P/2
P
HINGE ROLLER
P/2
100
100
75 75
10001000
270 460
270
ALL DIMENSIONS ARE IN MM
L1 L2
3000
1500
ROLLER
100