Keywords: energy dissipation capacity, ductility, cyclically loaded exterior beam-column joints, earthquake resistant design.

The difficulties arising in analysing beam-column joint test results is due to different test procedures and loading histories adapted by different researchers. In order to determine the overall performance of cyclically loaded beam-column joints, the energy dissipation capacity is one of the most important criteria because in cyclically loaded beam-column joints, the main design goal is to prevent the degradation of either the strength or stiffness.

The most comprehensive of the methods for determining the energy dissipation capacity of cyclically loaded reinforced concrete exterior beam-column joints is the index proposed by Ehsani and Wight [1] based on the energy index developed by Hwang and Scribner [2]. This index is more advantageous than the previously suggested indexes as it takes into account the stiffness degradation and energy dissipation at each loading cycle as well as the effect of the displacement ductility ratio. The normalised energy index is defined as follows:

where
is the energy dissipated during the th cycle, each cycle is assumed to start at zero displacement and end at zero displacement.
is the stiffness corresponding to the yield displacement .
is the stiffness in the th cycle corresponding to the maximum displacement .
is the yield load of the specimen.
is the number of cycles for which
is the maximum load attained at maximum displacement during each cycle.

In this study, the authors have used an experimental database to investigate the influence of different parameters on this normalised energy index. The experimental database was consisted of tests without slabs and transverse beams. All the specimens were uniaxially and cyclically loaded exterior beam-column joints. The tests belonged to different researchers such as Scribner [3], Lee [4], Alameddine [5], Scarpas [6] and Uzumeri [7]. Several parametric studies are carried out on the experimental database. The results showed that the normalised energy index was independent of the parameters such as the column axial stress, the joint aspect ratio, and the area ratio of the intermediate column bars. The parametric studies showed that four parameters; concrete cylinder strength, stirrup ratio, column bar ratio, beam bar ratio (tensile) and the ratio of the area of the compressive reinforcement to the area of the tensile reinforcement were most influential on the normalised energy index of the cyclically loaded exterior beam-column joints. It is apparent from the parametric studies that as the concrete cylinder strength, beam longitudinal reinforcement ratio and the column longitudinal reinforcement ratio are increased, the normalised energy index decreases. As the stirrup ratio and the ratio of the area of the compressive reinforcement to the area of the tensile reinforcement increase, the normalised energy index increases.

1

Ehsani M.R., and Wight, J.K., "Confinement steel requirements for connections in ductile frames," Journal of the Structural Division, ASCE, 116, No.ST3, 1990.

2

Hwang, T.H., and Scribner, C.F., "RC Member cyclic response during various loading" Journal of the Structural Division, ASCE, 110, No.3, 477-487,1984.

3

Scribner, C.F., and Wight J.K., "Delaying Shear Strength Decay in Reinforced Concrete Flexural Members Under Large Load Reversals", Report No. UMEE 78R2, The University of Michigan, 221 pp, 1978.

4

Lee, D.L.N., and Wight J.K., and Hanson, R.D., "RC Beam-Column Joints Under Large Load Reversals", Journal of Structural Division, Proceedings of the ASCE, 103, NO. ST12, 2337-2350, 1977.

5

Alameddine, F.F., "Seismic Design Recommendation for High Strength Concrete Beam-to-Column Connections", PhD Thesis, University of Arizona, 257 pp, 1990.

6

Scarpas, A., and Paulay, T., "Behaviour of Exterior Beam-Column Joints", Bulletin of the New Zealand National Society for Earthquake Engineering, 14, No: 3, 131-144,1981.

7

Uzumeri S.M., and Seckin M., "Behaviour of Reinforced Concrete Beam- Column Joints Subjected to Slow Load Reversals", Publication No: 74-05, Department of Civil Engineering, University of Toronto, 1974.

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