Keywords: cellular concrete, stress-strain curve, wall panels, numerical technique.

This paper presents a study of load-bearing wall panels made of moist-cured aerated cellular concrete, which has not been widely considered as a structural load-bearing material in the building industry. Results from experiments show that a bilinear model for the stress-strain relationship of cellular concrete is adequate to analyse the performance of cellular concrete panels by means of a numerical technique. The prediction of the numerical modeling shows good agreement with experimental data.

The stress-strain relationship of materials is very important in predicting the behaviour or performance of structural elements. That relationship of cellular concrete has, however, not been thoroughly investigated. The literature shows that only elastic modulus characteristic of cellular concrete was reported, not the whole stress-strain curve. In this study, the stress-strain relationship of cellular concrete with three porosity levels was investigated. An elastic modulus measurer was created to obtain the stress-strain data from the test of cellular concrete prism. The apparatus consists of two linear variable differential transformers (LVDT), measuring the displacement, and hence the strain, in the middle third of two opposite longitudinal surfaces of the sample. Samples were tested under displacement control at the rate of around 5 micro-strain per second.

Experimental data shows that the stress-strain curve of cellular concrete is almost linear up to around 80% of the ultimate stress. Although the second part of the curve is somewhat non-linear, an estimated linear approximation shows a good fit; where is in the interval of 95-98%. A bilinear model is then proposed to describe the constitutive stress-strain relation of this material. This stress-strain curve model is used as input for a computer program to predict the ultimate strength of aerated cellular concrete wall panels.

The program called Aerated Cellular Concrete Wall Panel was written in C++ language, with the references of the FRMPHI program developed by Setunge et al [4] and the WASTAB program from reference [3]. The program consists of two main parts: the moment-curvature relationship and the instability analysis. The moment-curvature relationship of the wall panel is derived on the basis of strain compatibility and force equilibrium. Plane sections before bending are assumed to remain plane after bending. In the instability analysis, the height that a cellular concrete wall can sustain with a given loading configuration is predicted, based on the moment-curvature characteristic derived in the first part. The convergence of the program is found to be dependent on the initial values of compressive strain. This issue needs to be taken into account to ensure that meaningful results can be achieved. Results from experiment and proposed model show that Aerated Cellular Concrete Wall Panel program predicts the strength of the cellular concrete panel reasonably well. Formulae suggested in references [1,2] for normal weight concrete structures seem to underestimate the strength of aerated cellular concrete wall panels.

In this study, aerated cellular concrete wall panels with slenderness ratio of 18 did not show any bending failure mode. These results are in agreement with conclusions from references [4,6,7].

1

American Concrete Institute, ACI 318 Building Code Requirements for structural Concrete and Commentary, Detroit, 2005

2

Australian Standards Association, AS 3600 Concrete structure, Homebush, NSW, Australia, 1994

3

Fragomeni, S., Design of normal and high strength reinforced concrete walls, PhD, Civil and Environmental Engineering, The University of Melbourne, 1995.

4

Pillai, S.U., Parthasarathy, C.V., "Ultimate strength and design of concrete walls", Building and Environment, 12, 25-29, 1977. doi:10.1016/0360-1323(77)90003-8

5

RILEM, Autoclaved aerated concrete, Properties, Testing and Design, E & FN Spon, London, 1993

6

Saheb, S.M., Desayi, P., "Ultimate strength of reinforced concrete wall panels in one-way in-plane action", Journal of Structural Engineering ASCE, 115, 2617-2630, 1989. doi:10.1061/(ASCE)0733-9445(1989)115:10(2617)

7

Seddon, A.E., "The strength of concrete walls under axial and eccentric loads", in: "Symposium of strength of concrete structures", Cement and Concrete Association, London, 1956.

8

Setunge, S., Mendis, P.A., Darvall, P.L., "Full range moment curvature behaviour of reinforcement concrete sections", in: "Proceedings of the Australasian Structural Engineering Conference, ASCE94", Sydney, Australia, 507-513, 1994.

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