It can be noticed that the model with concentrator leads to the robust hysteretic loops of fig 3.9 a while the uncoupled model results do resemble the part of positive forces of the hysteretic loops in fig 3.9 It must be emphasized that in the experimental results with the entire infill, no pinching is observed. Therefore, the conventional models do not represent correctly the experiments in this important case. Of course, in the latter, the pinched curve is not completely formed It is due to the lack of a second diagonal strut. Author Conclude that - The model of uncoupled diagonal bars is based on an unrealistic hypothesis since the real infill is a unique element. Thus, the conventional models need to be improved by the inclusion of some coupling between the bars. A coupling strategy has been proposed. The diagonal strut model is modified through the plastic concentrator concept that is similar in many aspects to the plastic hinge notion. The result is a model as simple as the original one but that represents in a more realistic way the observed behavior. Most of the models already available in the literature can be modified by the inclusion of plastic concentrators. It is important to emphasize that the proposed model is still a very simple one and the real behavior is much more complex. (Fig 3.12) Planar frame with perfect elasto-plasticity (a) Without infill (b) with infill and without plastic concentrator (c) with infill and plastic concentrator, Puglisi, M et al. (2008)
Civil Engineering Department, Thapar University Page 34 Asteris, P.G (2008) proposed a realistic criterion to describe the frame-infill separation, in order to better simulate the complicated behavior of infilled frames under lateral loads. The behavior of the composite frame not only depends on the relative stiffness of the frame and the infill and the frame geometry, but is also critically influenced by the strength properties of the masonry also increase of dissipated energy. Computational complexity: The particulate in fill material and the ever changing contact conditions along its interface to concrete constitute additional sources of analytical burden. The real composite behavior of an infilled frame is a complex statically indeterminate problem. Structural uncertainties: The mechanical properties of masonry, as well as its wedging conditions against the internal surface of the frame, depend strongly on local construction conditions. He has done review on numerical models of infilled frames, A basic characteristic of a macro- (or simplified) model is that they try to encompass the overall (global) behavior of a structural element without modeling all the possible modes of local failure. Micro- (or fundamental) models, on the other hand, model the behavior of a structural element with great detail trying to encompass all the possible modes of failure.
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