Seismic Performance Evaluation and Retrofit of Existing School Buildings (CROCS-System) in Switzerland

Martina Paronesso
2017
Projet étudiant

Résumé

Existing school buildings in Switzerland that have been designed from the early 1970s typically utilized a modular architectural layout and structural system commonly known as CROCS (Centre de rationalization de d’organisation des constructions scolaires). Such buildings were designed without any seismic design requirements. However, Switzerland is a moderate seismic zone and the seismic safety and lateral stability of such buildings should be carefully examined. There is also a similar concern because of hazards due to induced seismicity. In particular, such buildings could develop a soft story collapse mechanism because capacity design principles were not employed. The aim of this Master thesis is to investigate the non-linear static and dynamic behaviour of a CROCS school located in Switzerland in a moderate seismic zone. Its performance is examined based on nonlinear response-history analysis in the context of Performance-Based Earthquake Engineering. A numerical model is developed using the concentrated plasticity modelling approach to identify its most critical seismic deﬁciencies. Based on the ﬁndings, an optimal seismic retroﬁt strategy is proposed and evaluated.

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https://infoscience.epfl.ch/record/232956?ln=fr

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This paper presents a procedure for the extension of the Vulnerability Index Method (VIM) to the seismic assessment of hybrid timber-masonry buildings. The research is based on the execution of a detailed numerical study of this peculiar structural typology to identify the classes and calibrate the scores assigned to influential vulnerability parameters, namely the irregularities of the structural system, the type of floor, and the state of conservation of the building. A sensitivity analysis of the seismic capacity is developed by performing pushover analyses with several models corresponding to realistic variations of each structural or material parameter. The seismic performance of the buildings is analysed by the N2 Method. This methodology leads to the proposal of a new calibrated vulnerability index form that, together with those existing in literature for masonry and reinforced concrete structures, can be used for the seismic assessment of heterogeneous urban environments. The proposed VIM is applied to the assessment of 111 buildings located in the historical centre of the city of Valparaiso, Chile. The computation of the vulnerability index allows a fast evaluation of the seismic vulnerability of the urban buildings. The results plotted on vulnerability maps built within a GIS environment allows the assessment of the impact of potential collapses on the serviceability of two emergency evacuation routes included in the civil protection plans of the city.

ELSEVIER2021

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The Role of the Composite Floor System and Framing Action in the Seismic Performance of Composite Steel Moment-Resisting Frames

Hammad El Jisr

With the advent of performance-based earthquake engineering (PBEE), the need for reliable prediction of earthquake-induced collapse of structures is essential. Despite the significant progress that has been made towards this goal, there are several hurdles that still need to be overcome. Deterioration models, which are currently used for simulating structural collapse, are largely based on available test data that featured subassemblies with overly simplified boundary conditions. These experiments did not ac-count for the force redistribution occurring within structural systems after the onset of nonlinear geo-metric instabilities under cyclic loading. For the case of composite steel moment resisting frames (MRFs), which is the primary focus of this thesis, the influence of the axial restraint provided by the slab continuity and framing action on the seismic behavior of composite steel MRFs has been recognized in prior work. Nevertheless, these effects have neither been thoroughly investigated nor quantified at lateral drift demands associated with dynamic instability of composite steel MRFs under seismic loading.In this doctoral thesis, a unique experimental program of a two-bay composite steel MRF subsystem was conducted at full-scale. The experimental program, which was corroborated by continuum finite element analyses, aimed at comprehending the role of the underlying physical mechanisms, associated with the slab continuity and framing action, on the hysteretic behavior of composite steel MRFs with a particular emphasis at large deformations associated with collapse. The research findings suggest that the slab continuity limits the extent of local buckling and beam shortening within the dissipative zones of composite steel MRFs. While nonlinear geometric instabilities attributable to local buckling and concrete crushing are pronounced in composite steel beams at large inelastic deformations, the framing action and slab continuity preserve the overall stability of the structural system even in cases that ductile cracks form within a dissipative zone. The test results suggest that the presence of the transverse beams within the floor system should be factored in capacity design principles of composite steel MRFs. The experimental findings also suggest that methods for computing the effective slab width in composite steel MRFs should be reassessed. The available data along with information from prior experiments informed the development of practice-oriented engineering models for the seismic assessment of composite steel MRFs. Moreover, a macro-model was proposed for simulating the hysteretic behavior of composite steel beams under cyclic loading. The model, which was validated thoroughly with available experimental data, simulates explicitly the cyclic deterioration in strength and stiffness of composite steel beams and their respective beam-slab connections. The proposed macro-model was employed to benchmark the seismic col-lapse risk of prototype buildings with composite steel MRFs, as well as the repairability of beam-slab connections within the framework of PBEE.

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The emergence of new high-performance materials and equipment, as well as advancements in numerical calculation techniques, have allowed base isolation to take its place among the strategies used by engineers in earthquake resistant design. Despite the enormous advantages of implementing seismic isolation, its applications have so far been limited to critical infrastructures (hospitals, re stations, etc.) located in earthquake-prone areas. The relatively high costs associated with the installation of an isolation system constitute a major constraint when choosing the structural system of a building. In this Master's project, a 4 storey composite-steel administrative building located in Sion (Switzerland) is designed, according to several importance classes, in order to study the relevance of the installation of a base isolation system. Two dierent design methodologies are adopted to determine the dimensions of the foundations and the main load-bearing elements of two buildings, one with a xed-base and the second with a seismic isolation system. The results of the various design procedures clearly indicate that the choice of installing isolating supports is not obvious. Indeed, when the building under study is considered as a critical infrastructure, signicant savings, up to more than 20% in terms of building materials, can be achieved for an isolated structure. On the other hand, for an ordinary structure, the additional costs associated with the installation of isolated supports cannot be oset by savings in construction materials. These results reinforce the perspective that, in the presence of an ordinary building, the traditional xed-base solution remains the most ecient. However, despite its relatively high cost, a base isolated building performs better during a seismic event, with structural demands and damages signicantly mitigated compared to a xed-base building. To compare the responses of the two structural systems, two non-linear models are created on OpenSEES. Two dynamic analyses are then conducted for two groups of 40 seismic records, calibrated according to two characteristic intensities. Based on the results obtained, it is clear that the xed building undergoes higher demands (in deformations and accelerations in particular) than its isolated counterpart. These demands are then used and transformed into a decision variable (in this case, repair costs) through loss analyses conducted on the EarL software. These analyses show that after the occurrence of an earthquake, the repair costs of a conventional building can reach 25 % of the initial construction costs, almost 10 times the value obtained in the case of a base isolated building. This Master's project demonstrates that despite the high initial cost of base isolation technologies, their implementation can not only be amortized through possible material savings, but also, through the reduction of repair costs due to a better performance of the building over its lifecycle.

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