Vulnerability assessment and feasibility analysis of seismic strengthening of school buildings

The majority of structures in seismic-prone areas worldwide are structures that have been designed either without seismic design considerations, or using codes of practice that are seriously inadequate in the light of current seismic design principles. In Cyprus, after a series of earthquakes that occurred between 1995 and 1999, it was decided to carry out an unprecedented internationally seismic retrofitting of all school buildings, taking into account the sensitivity of the society towards these structures. In this paper representative school buildings are analysed in both their pristine condition and after applying retrofitting schemes typical of those implemented in the aforementioned large-scale strengthening programme. Non-linear analysis is conducted on calibrated analytical models of the selected buildings and fragility curves are derived for typical reinforced concrete and unreinforced masonry structures. These curves are then used to carry out a feasibility study, including both benefit-cost and life-cycle analysis, and evaluate the effectiveness of the strengthening programme

Masonry compressive strength prediction using artificial neural networks

The masonry is not only included among the oldest building materials, but it is also the most widely used material due to its simple construction and low cost compared to the other modern building materials. Nevertheless, there is not yet a robust quantitative method, available in the literature, which can reliably predict its strength, based on the geometrical and mechanical characteristics of its components. This limitation is due to the highly nonlinear relation between the compressive strength of masonry and the geometrical and mechanical properties of the components of the masonry. In this paper, the application of artificial neural networks for predicting the compressive strength of masonry has been investigated. Specifically, back-propagation neural network models have been used for predicting the compressive strength of masonry prism based on experimental data available in the literature. The comparison of the derived results with the experimental findings demonstrates the ability of artificial neural networks to approximate the compressive strength of masonry walls in a reliable and robust manner.- (undefined

Masonry infilled reinforced concrete frames with openings

This work presents an assessment of the behavior of infilled frames. The feasibility of possible immediate implementation of some recent developments both in analysis and design of infilled frames for practical design is investigated. It is now widely recognised that masonry infill panels, used in reinforced concrete (R/C) frame structures, significantly enhance both the stiffness and the strength of the surrounding frame. However, their contribution is often not taken into account because of the lack of knowledge of the composite behaviour of the surrounding frame and the infill panel. Currently, Seismic Design Guidelines (EC8 - Part 3, FEMA - 440, ASCE 41-06) contain provisions for the calculation of the stiffness of solid infilled frames mainly by modeling infill walls as "diagonal struts." However, such provisions are not provided for infilled frames with openings. The present study, based on available finite element results, proposes analytical equations for obtaining the reduction factor, which is the ratio of the effective width of a diagonal strut representing a wall with an opening over that of the solid RC infilled frame. That will allow the calculation of the initial lateral stiffness of infills when an opening is present. The validity of the proposed equations is demonstrated by comparing our results, against work done by various researchers

Evaluation of infilled frames: an updated in-plane-stiffness macro-model considering the effects of vertical loads

The influence of masonry infills on the in-plane behaviour of RC framed structures is a central topic in the seismic evaluation and retrofitting of existing buildings. Many models in the literature use an equivalent strut member in order to represent the infill but, among the parameters influencing the equivalent strut behaviour, the effect of vertical loads acting on the frames is recognized but not quantified. Nevertheless a vertical load causes a non-negligible variation in the in-plane behaviour of infilled frames by influencing the effective volume of the infill. This results in a change in the stiffness and strength of the system. This paper presents an equivalent diagonal pin-jointed strut model taking into account the stiffening effect of vertical loads on the infill in the initial state. The in-plane stiffness of a range of infilled frames was evaluated using a finite element model of the frame-infill system and the cross-section of the strut equivalent to the infill was obtained for different levels of vertical loading by imposing the equivalence between the frame containing the infill and the frame containing the diagonal strut. In this way a law for identifying the equivalent strut width depending on the geometrical and mechanical characteristics of the infilled frame was generalized to consider the influence of vertical loads for use in the practical applications. The strategy presented, limited to the initial stiffness of infilled frames, is preparatory to the definition of complete non-linear cyclic laws for the equivalent strut

Influence of the Modelling Approach on the Failure Modes of RC Infilled Frames Under Seismic Actions

The influence of the masonry infills on the seismic performances of Reinforced Concrete (RC) frames is generally evaluated in analytical and numerical studies by adopting the equivalent strut model; it is based on experimental observations showing that at the onset of damage, stresses migrate to the diagonal of the panel and are transferred to the surrounding frame through the contact zones at the corners. Above the different equivalent strut models available in literature, single-strut models are generally used to evaluate the global behaviour, while multi-strut approaches are preferred to investigate on local interaction phenomena between panel and frame. In case of existing buildings, with poor transversal reinforcement of the columns, the presence of the infills can lead to pre-emptive brittle failure. The present study is aimed at evaluating the influence of the modelling approach on the evaluation of the seismic performance both in terms of global and local behaviour. Nonlinear dynamic analyses have been performed on an 8-storey infilled RC frame, following the Incremental Dynamic Analysis procedure, in order to evaluate structural performances depending on the model adopted to simulate the infills