Effect of confinement on the behaviour of high-strength lightweight concrete columns

Abstract

This paper summarizes an experimental investigation into the behaviour of high strength sandlightweight concrete columns confined with rectangular ties. Fifteen reinforced and three unreinforced specimens were tested under monotonically increasing axial compression. Variables considered in this study were the longitudinal steel distribution and tie configuration, the tie steel spacing, the amount of tie steel, and the amount of longitudinal steel.The results indicated that unconfined high-strength lightweight aggregate concrete is a brittle material. The addition of lateral confining steel significantly improved the behaviour of this material, with a large amount of lateral steel resulting in very ductile behaviour. The tic configuration and resulting distribution of longitudinal steel contributed significantly to the confinement of concrete, with well-distributed steel resulting in improved bchaviour. The ratio of specimen to cylinder concrete strength was observed to be 0.98, which is much higher than the commonly assumed value of 0.85.The test results were compared with results from selected theoretical confinement models. Based on the results of this investigation, existing models for concrete confinement give unconservative results for high-strength lightweight aggregate concrete and overestimate the ductility that can be achieved with this material.Cette communication resume une Ctude expkrimcntale du comportement dc poteaux de bkton lCgcr h haute rksistancc retenus par des agrafes mktalliques. Quinze kchantillons arrnCs et trois non armCs ont fait I'objet d'cssais sous compression axialc progressivement augmentie. Les variables dont on a tenu compte dans cette Ctude sont la rkpartition longitudinale de I'acicr et la configuration des agrafes, I'espacement de I'acicr des agrafes, la quantite d'acier dans les agrafes et la quantiti d'acier longitudinal.Les rCsultats indiquent que le beton d'agrCgats ICgers h haute rksistance sans Ctreinte laterale est un matkriau fragile. L'addition de supports IatCraux en acier a amCliorC de faqon significative le comportement de ce matkriau, I'importante quantitC d'acier lateral entrainant une trks grande ductilite. La forme des agrafes et la repartition de I'acier longitudinal qui en a rdsultec ont contribuk de faqon significative au confinement du Eton, I'acier bien rkparti favorisant un mcillcur comportement. On a observe que le rapport entre I'Cchantillon et la resistance du bCton cylindrc Ctait de 0,98, cc qui cst beaucoup plus ClcvC quc la valeur de 0,85 gtneralement admise.Les rksultats d'essais ont CtC comparks aux rksultats de ccrtains modkles dc confinement thkoriques. En tcnant compte des rksultats de cette Ctude, les modkles actuels de confinement du beton donnent des rksultats excessifs pour le beton d'agrkgats ICgers A haute resistance et surestiment la ductilitk qu'on peut obtenir avec ce matkriau.

Axial compressive behavior of lightweight aggregate concrete columns confined with transverse steel reinforcement

“…Martinez et al 12 tested 27 LWAC columns confined by circular spirals under concentric loading and established relationships between the lateral confined force and the peak stress, peak strain, and ductility ratio. Basset and Uzumeri 13 determined the behavior of confined high-strength LWAC in full-size columns by considering the effects of selected variables, such as longitudinal steel distribution and tie configuration, tie steel spacing, amount of tie steel, and amount of longitudinal steel, on confinement effectiveness. Bjerkeli et al 14 studied strength, ductility, and creep behavior of confined LWAC columns under long-term load and indicated that the behaviors of confined LWAC columns are significantly different from those of unconfined specimens.…”