The structural behaviour of Precast Lightweight Foamed Concrete Panel (PLFP) under flexural load is investigated by using ABAQUS 6.13. The PLFP is made up of two Whyte’s with a polystyrene insulator placed in between them using a double shear truss connector of diameter 6mm placed at an angle 45 °. The panel is reinforced with both vertical and horizontal steel reinforcement of 9 mm diameter. Four panels with varying dimensions are simulated to investigate their Ultimate Strength and Load-deflection profile. The results show that the length to thickness ratio of the panel is the major contributing factor to the ultimate strength of the PLFP. From the load deflection curve, the panel with the least deflection has the highest thickness which also results in a high ultimate strength recorded at 34.43 KN.
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Flores-Johnson & Li [
Three (3) dimensional finite element models were developed to study the structural behaviour of the PLFP using four points bending test. The finite element results were validated by comparing the values obtained with the experimental results and theoretical calculation. ABAQUS 6.13 [
The foamed concrete is composed of inner and outer wythe with different concrete densities. The concrete damage plasticity, available in ABAQUS 6.13 [
There were both horizontal and vertical reinforcements at top and bottom with diameter bar 9 mm of yield strength 559 MPa and tied to each other at 300 mm centre to centre. The material properties summarised in
Three 6 mm mild steel double shear truss connector bent to an angle 45˚ were used for each panel to transfer the load from one wythe to the other. The double shear truss connectors were joined to the vertical reinforcement in the steel mesh. This shear connector had yield stress of 518 MPa, tensile strength of 544.28 MPa and young modulus of 197.8 GPa. The shear connectors where arranged in such a way that they were evenly spaced across the width of the PLFP slab (
Dilatation angle | Eccentricity | Initial/biaxial/uniaxial ratio, σc0/σb0 | K | Viscosity | |
---|---|---|---|---|---|
27˚ | 0.1 | 1.16 | 1 | 0 | |
Compressive behaviour from experiment | Tensile behaviour from experiment | ||||
Yield stress (MPa) | Inelastic strain | Damage parameter, D | Yield stress (MPa) | Cracking strain | Damage parameter, D |
8.751 | 0 | 0 | 0.861 | 0 | 0.000 |
9.850 | 0.0017 | 0 | 0.776 | 0.00159 | 0.204 |
10.356 | 0.0033 | 0 | 0.605 | 0.00409 | 0.476 |
10.032 | 0.0041 | 0.215 | 0.518 | 0.00526 | 0.582 |
9.714 | 0.0047 | 0.337 | 0.431 | 0.00638 | 0.673 |
9.357 | 0.0055 | 0.456 | 0.345 | 0.00746 | 0.752 |
8.734 | 0.0066 | 0.577 | 0.259 | 0.00854 | 0.824 |
7.725 | 0.0078 | 0.682 | 0.173 | 0.00966 | 0.889 |
5.450 | 0.0127 | 0.862 | 0.086 | 0.01082 | 0.947 |
3.962 | 0.0194 | 0.934 | 0 | 0.01202 | 1.000 |
Steel | Yield stress σy (MPa) | Tensile strength σt (MPa) | Strain at failure | Young modulus ES (MPa) |
---|---|---|---|---|
6 mm bars | 518 | 544.28 | 0.0478 | 197,800 |
9 mm bars | 559 | 626.5 | 0.1934 | 203,680 |
The model was in such a way that there was capping at both ends so that the applied load would be evenly distributed. Therefore, a 100 mm length normal concrete capping at both ends were added to the model so as to prevent it from premature cracking around the loading and supports areas. CDP was also used for modelling the normal concrete as proposed Tomasz [
Polystyrene was used as an insulation material in the core layer. The polystyrene sheet was inserted in between the steel mesh. It had a mass density of 16 kg/m3, a Young’s Modulus of 0.896 MPa and poison ratio of 0.4
The load, boundary condition, and field managers are used to view and manipulate the step wise history of prescribed conditions. The PLFP is simply supported along two lines parallel with the x-axis; the distance is 1800 mm for panel 1, 2 and 4 while it is 2300 mm for panel 3. The PLFP has been extended with a capping of 100 mm from the support in order to increase the area over which the reaction stresses can be distributed. There were two (2) concentrated loads exerted on two different points of the PLFP slab since this is a four points bending setup. The ultimate load is however computed by adding the two concentrated loads.
For this study models with different mesh sizes were analysed to determine the best mesh density that would give a result which is closer to the experimental work and theoretical work.
The four panels are treated as separate models because they all have different dimensions. The ultimate strength achieved by the PLFP panels depended on various factors and not just the materials that are used for the analysis of various panels. The values for the ultimate strength of the panels were recorded by summing the values of P. (p/2 + p/2). Factors that had very significant effects on the ultimate strength include the panel’s aspect ratio and the number of shear connectors used. Panel 4 had the highest ultimate load of 34.43 kN while panel 3 had the lowest ultimate load of 16.21 kN and this was as a result of their length to thickness ratio as Panel 4 had the highest and panel 3 the lowest.
The maximum deflection of all four panels occurred at mid-span and from the load-deflection curves for Panel 1 to Panel 4, it was observed that Panel 3 had the highest deflection of 20.21 mm and Panel 4 achieved the lowest deflection of 8.51 mm. This occurred due to the different length to thickness ratio which is a very important factor that helps in determining the value of the deflection. The length to thickness ratio of panel 1 was larger
Panel | L × W × T (mm) | L/t | Density (Kg/m3) | Fcu (MPa) | Young modulus (Concrete) (MPa) |
---|---|---|---|---|---|
P1 | 2000 × 750 × 100 | 20 | 1650 | 10.6 | 12,000 |
P2 | 2000 × 750 × 110 | 18.18 | 1900 | 20.1 | 16,700 |
P3 | 2500 × 750 × 100 | 25 | 1800 | 15.0 | 13,400 |
P4 | 2000 × 750 × 150 | 13.3 | 1800 | 15.0 | 13,400 |
Model type | Total element | Total nodes | Ultimate load (KN) | % Difference from experiment | % Difference from Theory | Average difference |
---|---|---|---|---|---|---|
Experiment | - | - | 25.63 | 0 | 2.3% | 2.3% |
Theoretical data | - | - | 26.23 | −2.2% | 0 | -2.2% |
C3D8R-1 | 2382 | 3361 | 29.35 | −12.6% | −10.6% | −11.6% |
C3D8R-2 | 12184 | 17816 | 29.12 | −11.98% | −9.9% | −10.94% |
C3D8R-3 | 18954 | 20472 | 28.96 | −11.49% | −9.4% | −10.46% |
C3D8R-4 | 33624 | 43615 | 23.44 | 9.3% | 11.90% | 10.6% |
C3D8R-5 | 62307 | 83392 | 23.62 | 8.5% | 11.04% | 9.77% |
C3D8R-6 | 153824 | 185995 | 23.3 | 9.8% | 12.5% | 11.15% |
Panel | Ultimate load, (kN) | Deflection, (mm) | Thickness (mm) | Compressive strength (MPa) |
---|---|---|---|---|
1 | 21.31 | 14.45 | 100 | 10.6 |
2 | 23.62 | 15.08 | 110 | 20.1 |
3 | 16.21 | 20.21 | 100 | 15 |
4 | 34.43 | 8.51 | 150 | 15 |
than panel 2 but still achieved a lower deflection; this shows not only the length to thickness ratio of the PLFP affects the deflection but the value of their compressive strength. Figures 4-6 show the thickness, compressive strength and deflection of all panels.
The ultimate strength of the PLFP recorded from the finite element analysis is of an acceptable range except for Panel 1 which had a very high ultimate strength when compared to the experimental result.
Panel | Pu FEA (kN) | Deflection, ( d) FEA (mm) | Pu experiment (kN) | Deflection, (d) experiment (mm) | Pu Theory (mm) | Deflection, (d) theory (mm) |
---|---|---|---|---|---|---|
Panel 1 | 21.31 | 14.45 | 8.23 | 13.94 | 26.27 | 17.22 |
Panel 2 | 23.62 | 15.08 | 25.63 | 22.07 | 30.93 | 18.33 |
Panel 3 | 16.21 | 20.21 | - | - | 21.03 | 29.74 |
Panel 4 | 34.43 | 8.51 | - | - | 44.77 | 11.24 |
The purpose of this research was to study the numerical simulation for the structural behaviour of Precast Lightweight Foam Concrete Sandwich Panel slab under flexural loading. The four panels used for this study had different length to thickness ratio which was used to determine the effectiveness of the length and thickness of a slab when determining its ultimate flexural strength. The result obtained from this study was used to show the accuracy level of computer aided simulation software when compared with an experimental and theoretical study to determine the ultimate flexural load of PLFP. The following conclusions were made after the study.
1) The material properties for concrete damage plasticity were obtained from previous research work on concrete. They were carefully factorised to get the appropriate value for each of the panels.
2) The length to thickness ratio for each panel affected the value of the ultimate strength attained. Panel 3 and panel 4 had the highest and lowest length to thickness ratio respectively. Panel 3 had an ultimate strength of 16.21 kN and a length to thickness ratio of 25 mm while panel 4 had an ultimate strength of 34.43 kN and a length to thickness ratio of 13.33 mm.
3) Although panel 1 and 3 had similar thickness but different comprehensive strength, it can be concluded that the compressive strength did not affect the value of the ultimate strength as much as its length to thickness ratio.
4) The ultimate strength increased as a result of an increase in thickness. Panel 3 had the least ultimate strength of 16.21 kN while panel 4 had the highest recorded ultimate strength of 34.43 kN. Their thicknesses were 100 mm and 150 mm respectively.
5) The deflection of all 4 panels occurred at mid span.
6) The deflection value of all the panels was affected by their respective dimensions. Panel 3 with the highest length to thickness ratio had the highest value of deflection 20.21 mm while panel 4 had the lowest value of 8.51 mm.