The effect of preloading on the strength of jacketed R/C columns

The influence of core preloading on the strength of jacketed reinforced concrete (R/C) columns is analytically investigated. A recently proposed method for arbitrary composite section analysis in biaxial bending and axial load is extended to include preloading actions. A parametric evaluation of the preloading effect using quantitative indices is performed, considering the variability of several parameters such as section geometry, amount of reinforcement, and various axial and moment preloading levels. Results are presented in the form of 3D failure surfaces and moment-curvature curves. Specific cases where the preloading effect is more pronounced are finally highlighted

Tests of reinforced concrete short columns laterally strengthened with wire rope units and steel elements

YesThe current paper presents a simple unbonded-type column strengthening technique with wire rope units and few steel elements. Eleven short columns were strengthened using the proposed procedure and tested under monotonic concentric axial loads. The main variables investigated to evaluate the confinement effectiveness of strengthened concrete columns were the volume ratio, prestress, diameter, spacing and configuration of wire rope units. The strength gain factor and ductility ratio increased with the increase of volume ratio of wire ropes. The prestress applied to wire ropes had little influence on the strength gain factor but the ductility ratio decreased with the increase of prestress in the wire ropes, owing to earlier rupture of wire ropes. At the same volume ratio of wire ropes, the maximum strength of columns was nearly independent on the configuration of the wire ropes, but higher ductility was exhibited by columns strengthened with rectangular spiral-type wire ropes than by columns strengthened with hoop-type wire ropes, until rupture of the wire ropes. The strength gain factor and ductility ratio of strengthened columns were compared with those of tied columns tested in a previous study. The load capacity of strengthened columns was also predicted using the ACI 318-05 equation modified to reflect the load-carrying effect of steel elements. A much higher strength gain factor and ductility ratio were exhibited by strengthened columns than tied columns having the same lateral reinforcement, except for strengthened columns with wire rope spacing above 0.5 times core width. The axial load capacity of strengthened columns was higher than that of unstrengthened columns by 5¿20%, and could be reasonably predicted using the modified ACI 318-05 equation

Boundary Element Implementation of a Rough Crack Constitutive Model

Introduction The boundary element method offers significant advantages over the finite element method due to the fact that only the boundary needs to be discretized for the solution. This feature is becoming increasingly attractive in recent years as witnessed by significant developments. However, due to lack of accurate material models, the boundary element method suffers the same disadvantages as the finite element method. Its accuracy depends to a large extent on the accuracy of the material model used. It has been shown that discontinuities such as cracks and interfaces can also be modeled as constitutive equations so that they can be used in numerical modeling procedures such as the finite element method and the boundary element method (see e.g., This paper presents an application of a micromechanics based constitutive model previously developed by the authors for rough cracks in the boundary element method. The multidomain approach is used to include the effect of the discontinuity using the direct boundary element method

Comparative study of analytical and numerical algorithms for designing reinforced concrete sections under biaxial bending

This paper presents a comparative study of different integration methods of stresses (both analytical and numerical) for concrete sections subjected to axial loads and biaxial bending. Such methods are applied to circular and rectangular sections. The constitutive equation used is a parabola-rectangle from the Eurocode-2. The comparison was performed with regard to the accuracy and the computational speed of each method. The objective of the paper is to determine which of the integration methods compared is more efficient in computing the interaction surfaces for rectangular and circular sections. The analytical method proposed by Barros et al. [Barros MHFM, Barros A, Ferreira C. Closed form solution of optimal design of rectangular reinforced concrete sections. Eng Comput 2004;21(7):761-76] for rectangular sections is compared with the numerical method termed "modified thick layer integration" proposed by Bonet et al. [Bonet JL, Romero ML, Miguel PF, Fernandez MA. A fast stress integration algorithm for reinforced concrete sections with axial loads and biaxial bending. Comput Struct 2004;82(2-3):213-25] and with the well-known fiber method. Furthermore, two new methods are proposed for circular sections: one analytical and one numerical based on the Gauss-Legendre quadrature. The results of both methods are compared with the classical layer decomposition method.http://www.sciencedirect.com/science/article/B6V28-4M6SB97-1/1/1fd1ef570eb4d3e7a25d2df2137bf7f