Comportement plastique de structures en portiques remplis.

Abstract

Masonry infills inside steel or reinforced concrete frames are generally considered as nonstructural elements and are neglected in design by different codes. In fact, the presence of these infills should have an important influence on structural properties such as the lateral stiffness and the overall strength. In the present work, a new macro-model is proposed to model the masonry infill by two equivalent diagonal struts passing across each other pined in both extremities and linking respectively the beams and the columns. The model has been validated by theoretical predictions (Wood 1978) and experimental results (Samai 1984). In order to show the effect of infill concerning the collapse loads and collapse mechanisms, the plastic hinges theory is adopted as an appropriate approach. Using plastic analysis principles, this approach succeeded to give the appropriate collapse loads and mechanisms with the exact position of the hinges and the order of their appearance. It must be said that the collapse mechanisms associating infill panels have been presented for the first time. Moreover, interaction diagrams for infilled structures are realized where the values of λV and λH of plastification of diagonal struts are precisely detected. The influence of the main parameters (infill thickness and the ratio, α =λV/λH) is highlighted. The different ranges of values of, α, in relation to the nature of the collapse mechanisms observed are given with precision and more particularly for values of over collapse (two mechanisms taking place simultaneously). Comparing the collapse loads for the infilled frames to corresponding open frames, it has been shown that the lateral collapse load has been considerably enhanced (524 % for IFS). However, the vertical collapse load has slightly increased (26 % for IFM). It may be concluded that the proposed model can give the totality of potential collapse mechanisms of infilled frames. Finally, important conclusions are drawn up concerning the collapse loads and mechanisms of infilled frames.