The analytical modelling of infilled frames is a complex issue because these structures exhibit a highly non- linear inelastic behaviour resulting from the interaction of the masonry infill panel and the surrounding frame. This paper presents a general review of the different procedures used for the analysis of infilled frames, which can be grouped in local or micro-models and simplified or macro-models, depending on the degree of refinement used to represent the structure. The finite element formulation and the equivalent truss mechanism are the typical examples of each group. The advantages and disadvantages of each procedure are pointed out, and practical recommendations for the implementation of the different models are indicated.
The effect of infill panels on the response of RC frames subjected to seismic action is widely recognised and has been subject of numerous experimental investigations, while several attempts to model it analytically have been reported. In this work, the implementation, within a fibre-based Finite Elements program, of a double-strut nonlinear cyclic model for unreinforced masonry panels is carried out. The adequacy of the model in predicting the cyclic/seismic response of multi-storey infilled reinforced concrete frames is then verified through comparisons against experimental results.
Reinforced concrete frames infilled with masonry panels constitute an important part of the high-risk structures in different regions of high seismicity. In some developing countries, they are still used as main structural system for low to medium rise buildings. Consequently, reliable methods to analyse infilled frames are required in order to reduce the loss of life and property associated with a possible structural failure.
The equivalent strut model, proposed in the 1960s, is a simple procedure to represent the effect of the masonry panel. Several improvements of the original model have been proposed, as a result of a better understanding of the behaviour of these structures and the development of computer software. This paper presents a new macro-model for the evaluation of the global response of the structure, which is based on a multi-strut formulation,. The model, implemented as 4-node panel element, accounts separately for the compressive and shear behaviour of masonry using a double truss mechanism and a shear spring in each direction. The principal premises in the development of the model are the rational consideration of the particular characteristics of masonry and the adequate representation of the hysteretic response. Furthermore, the model is able to represent different modes of failure in shear observed for masonry infills. The comparison of analytical results with experimental data showed that the proposed model, with a proper calibration, is able to represent adequately the in-plane response of infilled frames.
This paper describes an experimental programme in which two one-storey single-bay specimens were tested under cyclic lateral loading. The first specimen was designed according to the normal practice for framed masonry structures, whereas new reinforcing details were provided in the second specimen, with the objective of enhancing the structural response. Special precautions were taken for the application of the lateral forces, considering that experimental and analytical results indicated that the loading system could markedly affect the structural response. Consequently, an adequate procedure should be adopted for laboratory tests in order to obtain realistic data. The most important conclusion of the experimental programme was that the response of reinforced concrete frames with masonry infills can be significantly improved by a rational design aimed at reducing the distortion of the masonry panels while the plastic deformations are concentrated in selected regions of the structure.
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