Seismic vulnerability index method for hybrid timber-masonry structures. Numerical calibration and application to the city of Valparaiso, Chile

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.

Performance-based approach for the retrofit of URM wall structures by RC walls

Katrin Beyer, Alessandro Paparo

In several countries of moderated seismicity, with the re-evaluation of the seismic hazard most unreinforced masonry (URM) buildings with reinforced concrete slabs failed to satisfy the seismic design check. A possible seismically retrofit solution consists of adding RC walls to the existing structure or replacing selected critical URM walls with RC ones. Experimental and numerical studies have shown that this retrofit technique can be very effective since it modifies the global deformed shape of the structure, leading to an increase in the system’s displacement capacity. The paper proposes a Displacement-Based Design methodology for the retrofit of URM structures by replacing selected URM walls by RC walls. The methodology follows the Direct Displacement-Based Design (DBD) approach by Priestley et al. (2007) and is based in particular on the DBD procedure for frame-wall buildings (Sullivan et al., 2005 and 2006). The design procedure consists of three main phases: (i) A preliminary design check of the URM building by means of the DBD approach. (ii) If the structure does not fulfil the design check and exhibits at the same time a dominant shear behaviour, replacing the critical URM wall or walls with RC ones leads to an improved system’s behaviour. (iii) In the final phase, the DBD design of the mixed RC-URM wall structure, in which both the URM and the RC walls are taken into account, is carried out. The design methodology is then investigated through non-linear dynamic analyses of one case study.

2014

Le facteur séisme dans l'architecture vernaculaire

Milo Hofmann

A large part of ancient built environments in earthquake prone areas have been accomplished exclusively thanks to the experience that their builders developed over centuries of practice. Several of the resulting techniques have showed a satisfactory performance during earthquakes, attesting sometimes of risk cultures. Nowadays, the seismic phenomenon is not systematically considered as a factor that might have been taken into account by ancient builders. A lack of knowledge about vernacular building cultures and their correlation with these phenomena raises the probability that interventions on ancient built stock and prevention activities do not take advantage of site potentialities, even increasing its vulnerability. These issues have been investigated on the basis of the following research assumption: decoding the link between vernacular architecture and earthquakes considering cultural, structural and cognitive aspects, could contribute to reduce the vulnerability of people and ancient built environments, thanks to an in-depth understanding of mechanisms and dynamics supporting their resilience. Thus, this research aimed at highlighting questions and arguments fostering the appreciation of inventiveness inherent to past building cultures and enhancing their value in contemporary practice. Correlation factors between vernacular built environment and seismic phenomena have been explored through three research axes. The first one considers cultural determinants, namely the aspects that have a marked impact on the society reactions to earthquakes. The second one investigates types of vernacular structures that could be qualified as paraseismic. The third research axe concerns cognitive resources regarding effectiveness of a particular building practice implemented in many seismic regions, based on the integration of horizontal wood elements in masonry walls. The exploration of these axes has been accomplished through literature review and field studies considering vernacular built environment from multiple perspectives. It has been perceived as an environment permeated by resilience strategies referred to measures reducing building vulnerability and to precautionary behaviours adopted by populations (L'Aquila Province, Italy). At the same time, buildings have been examined as testimony of structural solutions adapted to the historical seismicity of the area (territory of North Anatolian Fault, Turkey), and as the expression of knowledge closely related to horizontal forces effects (Ohrid Lake region, Macedonia & Albania). Findings from this research highlight the potential of an approach questioning aspects referred to perception, technique and knowledge. Decoding the link between vernacular architecture and earthquakes as between cultural determinants, types of structures and cognitive resources, thus becomes a source of substantial and contextualized elements from which develop resilience strategies that are multi- and trans-disciplinary.

EPFL2015

Le facteur séisme dans l'architecture vernaculaire

Milo Hofmann

EPFL2015