Current design and assessment guidelines define several seismic performance levels, aiming to ensure that structures exhibit adequate behaviour at different seismic intensity levels. Typically, the acceptance criteria at different performance levels are met by ensuring that local deformation demands are lower than pre-defined capacities. Despite the proven effectiveness of such an approach, it provides an ambiguous measure of the performance of the building, which, in most cases, is neither meaningful nor appropriate for building owners, stakeholders or decision-makers. The main objective of the research presented in this paper is to evaluate the expected direct economic seismic losses of steel moment-resisting frame structures designed according to Eurocode 8 (EC8). A set of 120 archetype buildings, representative of the current building stock in Portugal, were designed according to Part 1 of EC8 using three different behaviour factors, q: a) code-prescribed upper bound limits for medium and high ductility classes; b) behaviour factor defined according to an Improved ForceBased Design (IFBD) procedure. The PEER-PBEE methodology with the improvements proposed by Ramirez and Miranda [1] was employed for the estimation of expected seismic losses evaluated for the seismic intensity levels considered in Part 3 of EC8. The results obtained indicate that the buildings designed in accordance with EC8 comply with the non-collapse criteria. However, the level of damage could imply significant repair costs. Importantly, the results also highlight that a rational selection of the behaviour factor can result in a reduction of steel weight but still ensuring acceptable levels of expected annual losses.

Introduction

Current seismic design guidelines allow for the inelastic behaviour of the structure to be explored during the design earthquake intensity level and, therefore, some degree of damage is therefore expected to occur. Although this is acceptable from an engineering point of view, given the ductile nature of structures designed according to modern provisions, stakeholders and building owners generally perceive that seismic design ensures both the safety and the development of minor damage levels for any seismic intensity level. It is therefore crucial to provide meaningful metrics of seismic performance (e.g. expected levels of earthquake-induced economic losses, fatalities, business interruption time, etc.) to support the decision making process of these agents in order to help stakeholders and building owners to take an informed selection of design options. Seismic design according to current practices and standards aims, primarily, at the protection of life-safety, with a heavy focus on strength control, incorporating comparatively minor provisions for deformation and damage control [1,2]. However, even though code design procedures seek to ensure that buildings meet certain levels of seismic performance, the actual performance is not normally assessed throughout the design process [3]. The concept of performance-based design was firstly introduced in Vision 2000 [4] after the 1994 Northridge and 1995 Kobe earthquakes. In these earthquakes, even though most structures exhibited acceptable non-collapse performances, there were high financial losses due to downtime, damage on non-structural components and losses/damage in building contents.