Compressive behavior of short high-strength concrete columns

The focus of the present paper is the compressive response of short high strength reinforced concrete members. Members have square transverse cross-sections and they are reinforced with longitudinal steel bars and transverse stirrups. A preliminary analysis to check the stability condition of longitudinal bars was made to verify that buckling occurs after yielding in compression. Prescriptions on required diameter and spacing of stirrups are given. In the following, a model is presented which allows us to evaluate the confinement pressures exercised by transverse steel and by longitudinal bars during the loading process taking into account the interaction of the stirrups with the inner core both in the stirrup plane and in the space between two successive stirrups. Confinement induced by corner and side bars is also estimated. The lateral pressure distributions within the stirrup section and along longitudinal bars are obtained by a simple model of an elastic beam on an elastic medium simulating the interaction with the concrete core. Yielding of steel stirrups and longitudinal bars including buckling phenomena and damage of concrete core by means of the variation in the elastic modulus and in the Poisson’s coefficient are taken into account. Finally, with the proposed mechanical model, the load-shortening curves of compressed confined members, including the strength contribution of longitudinal bars with second order effects, are generated. Results obtained are in good agreement with some of the data available in the literature and with analytical results obtained by using recent models given in the literature too.