Keywords: composite beam, floor height reduction capability, deflection, limit state, precast concrete, cast-in-place concrete, curvature.

The study described in this paper was carried out to investigate analytical solutions of the deflection of structural encased steel reinforced concrete composite tee beams with storey height reduction capability. This composite beam is divided into precast concrete and cast-in-place concrete beams. The structural tees are embedded in the precast concrete and the web of structural tees is positioned up to the cast-in-place concrete [1]. The slab is cast on the top of the precast concrete, which permits a reduction in floor-to-floor height. To find the analytical solutions of the deflection for this composite beam, an experiment was performed on a simple beam, and the deflection both at the yield limit state and the maximum load limit state was measured. The comparisons were made between the measured deflection and the analytical calculations based on yield curvature and ultimate curvature, which was ultimately intended to accurately study the section of plastic hinge beyond the yield limit state for deflection calculations.

This paper investigates a variety of available deflection calculation methods in order to calculate the deflection values of composite beams consisting of structural tees encased in precast concrete. It also seeks to analyse the reliability of the selected calculation method by applying it experimentally.

Two simple beams were manufactured and tested to evaluate the deflection in the centre of the beam [2]. Loading and unloading protocols were implemented. The simple beam was subjected to its yield limit state using a load control method. It was unloaded at its yield limit state and then loaded once to its maximum load limit state. After reaching its maximum load limit state, the experiment was conducted to about 80% of the maximum load using a displacement control method.

As a result, the envelope calculated using strain compatibility showed similar behaviour to the experimentally measured load-strain curve, indicating that the strain compatibility method is a reliable method for estimating the strain on steel-framed, reinforced concrete composite beams. The deflection in the elastic range calculated using the elastic-beam theory tended to be lower than the measured (experimental) deflection. The maximum deflection at both the yield limit state and maximum load limit state was calculated using stiffness degradation [3]. The results of the analytical study based on stiffness degradation showed less error than that observed in the analytical value calculated using the deflection differential equation. Consequently, high reliability is achieved when analysing the maximum deflection using stiffness degradation.

1

W.K. Hong, S.I. Kim, S.C. Park, J.M, Kim, S.G. Lee, K.J. Yoon, S.K. Kim, "Composite Beam Composed of Steel and Pre-cast Concrete.(Modularized Hybrid System, MHS) Part IV: Application for Multi-Residential Housing", Structural Design of Tall and Special Buildings, 19(7), 707-727, 2010.

2

T.H. Yoon, W.K. Hong, S.C. Park, D.Y. Yune, "Serviceability Evaluation of Green Beam for the application of multi-residential apartments", Earthquake Engineering Society of Korea, 14(1), 163-166, 2010.

3

W.K. Hong, J.M. Kim, S.C. Park, S.I. Kim, S.G. Lee, H.C. Lee, K.J. Yoon, "Composite Beam Composed of Steel and Pre-cast Concrete.(Modularized Hybrid System, MHS) Part II: Analytical Investigation", Structural Design of Tall and Special Buildings, 18(8), 891-905, 2009. doi:10.1002/tal.484

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