The influence of the degree of elongation to the displacements of seismic walls with maximum code-prescribed reinforcement ratio

Abstract

It is expected that walls which were designed either with increased ductility requirements according to the Greek Concrete Code 2000 or were designed to be in a high ductility category according to EC8: 2004, NZS 3101: 2006 and other modern international codes, present extensive tensile deformations, especially in the plastic hinge region of their base. Depending on the geometric characteristics and the level of ductility design of walls, large tensile deformations are expected. These tensile deformations can cause their lateral instability depending on their size. Large width cracks, which are created as result of deep entry in the plastic region, are required to close, so that the in-plane flexural mode of wall can be completely developed at the reversal of loading sign. It is obvious that there should be a sufficient wall thickness, so that it is ensured that the compressive force can be developed in the compression zone of the wall cross-section without the event of out-of-plane buckling. A critical situation arises when at the reversal of the sign of moment, the cracks that emanate from tension (at the previous semi-cycle of loading) cannot close and thus, traverse buckling takes place, which leads the wall end section to lateral instability. The current work investigates one of the most basic parameters affecting the stability of structural walls, which is (apart from the wall thickness) the degree of tensile strain of the longitudinal reinforcement of the boundary edges of load-bearing walls. The present work is experimental. It has to be noted that in order to examine experimentally the influence of tensile strain, 5 test specimens of scale 1:3 simulating the boundary edges of structural walls were used. These specimens were reinforced with the maximum code-prescribed longitudinal reinforcement ratio (4.02%) and they all had the same reinforcement ratio. The degree of elongation which was applied was different for each specimen and it took values equal to 0‰, 10‰, 20‰, 30‰ and 50‰. The present article tries to investigate the influence of the degree of tensile strain to the displacements and the modes of failure of test specimens.