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Frontiers of Structural and Civil Engineering

Front. Struct. Civ. Eng.    2017, Vol. 11 Issue (4) : 412-423
Research Article
Instantaneous deflection of light-weight concrete slabs
Centre for Built Infrastructure Research (CBIR), University of Technology Sydney (UTS), P.O. Box 123, Sydney, Australia
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Construction loading before the age of 28 d can have the most significant effects on the slabs, especially for multi-story structures. The changing properties of the young concrete complicate the prediction of serviceability design requirements also. An experimental investigation is performed on four simply supported Light-Weight Concrete (LWC) one-way slabs subjected to immediate loading at 14 d. Effects of aggregate type, loading levels and cracking moment together with the influences of ultimate moment capacity and service moment on the instantaneous deflection of slabs are studied. Comparison of the obtained results with predictions of existing models in the literature shows considerable differences between the recorded and estimated instantaneous deflection of LWC slabs. Based on sensitivity analysis of the effective parameters, a new equation is proposed and verified to predict the instantaneous deflection of LWC slabs subjected to loading at the age of 14 d.

Keywords instantaneous deflection      light-weight concrete      expanded polystyrene      effective moment of inertia      cracking moment      moment capacity      service moment     
Corresponding Author(s): Behnam VAKHSHOURI   
Online First Date: 16 June 2017    Issue Date: 10 November 2017
 Cite this article:   
Behnam VAKHSHOURI,Shami NEJADI. Instantaneous deflection of light-weight concrete slabs[J]. Front. Struct. Civ. Eng., 2017, 11(4): 412-423.
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Fig.1  Deformation response of idealized reinforced concrete beam at critical section
Fig.2  EPS beads in fresh and hardened LWC
[13]Im=23IcrIe8Icr+15Ie(1)FRP beamIm: average I
Ie from ACI-318-87
[15]Ie=(McrMa)3βdIg+[1(McrMa)3]×Icrγγ=(0.0017ρρb+0.8541)(Ef2Es+1)(2)FRP beamEs : steel
Ef : fiber
ρ: tensile steel ratio
[16]Ie=[1.4215(McrMa)]IcrIg:1McrMa<3(3)FRP beam
[17]Ie=IcrIgIcr+[1β1β2(McrMa)2](IcrIg)Ig(4)CC beamβ1 : 0; 1smooth; ribbed bar
β2 : 0;1sustained; first load
FRP , CCLcr : cracked length
L : member length
ρ: tensile steel ratio
[19]Ie=(McrMa)3Ig7+0.84[1(McrMa)3]IcrIg(7)FRP beam
CC beampower in equation
2 : Initially expected
3 : Average behavior
4 : Section behavior
(11)CC beamβ : 1; 0 for complete and no tension stiffening
[29]Ie=Icr+(IgIcr)(McrMa)30.8ρIg(12)Point loadρ: tensile steel ratio
[3032]Ie=(McrMa)3Ig+(1(McrMa)3)IcrIg(13)CCIe≤0:6Ig in AS-3600(09)
[33]Ie'=Icr1γηβ(McrMa)Ig(14)Equivalent Iesimply supported beam
(15)CCoriginally for axial tension
[14,31]Ie=(McrMa)3βdIg+[1(McrMa)3]×IcrIgβd=ab(Ef/Es+1),ab=0.2ρ/ρb1(16)FRP bar in tensionEf ; Es
elasticity of
FRP bar and steel
[36]Ie=Icr?IgIcr+[10.5(McrMa)2](IcrIg)Ig(17)FRP beam
[37]Ae=PcrP3Ag+[1(PcrP)3]AcrAg(18)Direct tensionanalogous approach
for Ie in ACI-318
Tab.1  Existing models of effective moment of inertia (Ie) in literature
sieve sizepassing (%)
pepper-threewashed Kurnell
4.75 mm100
2.36 mm80
1.18 mm55100
600 µ m3799
300 µ m2358
150 µ m112
≤75 µ m (%)5Nil
uncompacted bulk density (t/m3)1.691.33
compacted bulk density (t/m3)1.861.47
particle dry density (t/m3)2.692.52
particle density (SSD) 1)(t/m3)2.712.55
apparent particle density (t/m3)2.762.59
water absorption (%)0.91.0
pH value of soil8.8
degradation factor of aggregate85
the wash water after using permitted 500 mlClear
method of determining void content (% voids)40.7
silt content (%)3
Tab.2  Properties of fine and coarse sand types
sieve sizepassing (%)
13.2 mm100
9.5 mm88
6.7 mm53
4.75 mm20
2.36 mm4
1.18 mm2
misshapen particles (%)
ratio 2:123
ratio 3:16
uncompacted bulk density (t/m3)1.33
compacted bulk density (t/m3)1.5
moisture of the aggregate (%)3.0
particle dry density (t/m3)2.63
particle density (SSD) 1)(t/m3)2.66
apparent particle density (t/m3)2.76
water absorption (%)1.9
ave. dry strength (kN)366
ave. wet strength (kN)246
strength variation (wet/dry) (%)33
test fraction (mm)–9.5+6.7
amount of significant breakdown (%)<0.2
abrasion resistance (%)15
Tab.3  Properties of crushed Dunmore latite
chemical componentsphysical propertiesmechanical properties
CaO (%)62.6fineness (m2 /kg)395initial setting time (min)105
SiO2 (%)19.26autoclave Expansion (%)27.7final setting time (min)150
Al2O3 (%)5.15residue (45 µm )2.3drying shrinkage-28 d (µε)570
Fe2O3 (%)3.08fc − 3 d (MPa)34
MgO (%)1.14fc − 7 d (MPa)45.6
K2O (%)0.53fc − 28 d (MPa)61.1
Na2O (%)0.08Soundness (mm)1
LOI (%)4.1
SO3 (%)3.1
Tab.4  Properties of SL cement
cement (kg/m3)500
water (liter)180
water to cement ratio0.36
BST aggregate (Liter) (vol. %)300 (23%)
fine aggregate (kg/m3)
coarse sand310
fine sand310
coarse aggregate (kg/m3)800
WRA (liter)2
Tab.5  Mixture proportions of the EPS-LWC (Based on SSD condition)
Fig.3  Bar arrangement, cover details and dimension of slab specimens. cs= 40 mm, cb= 25 mm, s = 106 mm 4N12 bars in the section
Fig.4  Loading blocks and LVDT positioning for flexural test of LWC slabs
Fig.5  Development of compressive strength and modulus of elasticity with age
slabWa (kN/m)Mu (kN/m)Ma(kN/m)Ma/ Mu (%)Δe (mm)
14 d28 d14 d28 d14 d28 d
Tab.6  Loading values, moment ratios and elastic deflection of slabs
Fig.6  Ratio of recorded deflection to estimated elastic deflection at two ages
Fig.7  (Dins/De) 14 under different ratios of service and ultimate moments
Fig.8  Growing rate of Dins−14 due to 10 % increment of Ma/Mu
Fig.9  Effect of moment ratios on (Dins/De) 14
Fig.10  Predictions of existing models for Dins−14 and recorded data
limitEc−14/ Ec−28≥0.005≤3≤0.6Ig
Tab.7  Coefficients and limitations of proposed model for Ie in LWC slabs
Fig.11  Comparison of the recorded and predicted deflection of slabs at 14 d by proposed model
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