NON-LINEAR ANALYSIS OF INFILLED FRAMES

Abstract

This thesis is concerned with the analysis of\rbuilding frames acting compositely with infilling wall\rpanels. The significance of the composite action is\remphasized and previous work on infilled frames is reviewed.\rThe existing methods of analysis are categorized and their\ranalytical assumptions are highlighted. It is concluded\rthat more accurate results may be obtained from the\rdevelopment of a non-linear finite element analysis. The\rfinite element method is reviewed and new elements for\rrepresenting beams, interfaces and loading are developed.\rFailure criteria for concrete under multiaxial stress and\ralso failure criteria for masonry under uniaxial compression\rare developed. The non-linear elastoplastic behaviour of\rconcrete is modelled using the concept of equivalent\runiaxial strain and the model is extended for cracked\rmaterials. Elastoplastic models are also developed for\rductile materials(steel) for secant and incremental changes\rof stresses and strains. These models and the newly\rdeveloped elements are incorporated into the finite element\ranalysis which is numerically implemented by a new computer\rprogram, NEPAL. A number of steel frames with concrete\rinf ills covering the practical range of beam, column and\rinfill strengths and also wall panel aspect ratios, are\ranalysed using this program. The finite element results are\rcompared with the predictions of a range of existing methods\rof analysis and their limitations are discussed in detail.\rA new method of hand analysis is developed, based on a\rrational elastic and plastic analysis allowing for limited\rductility of the infill and also limited deflection of the\rframe at the peak load. The new method is shown to be\rcapable of providing the necessary information for design\rpurposes with reasonable accuracy, taking into account the\reffects of strength and stiffness of the beams and columns,\rthe aspect ratio for the infill, the semi-rigid joints and\rthe condition of the frame-infill interfaces (co-efficient\rof friction and lack of fit). It is concluded that simple\rand economical design approaches can be established for\rframes with infilling walls.