An application of the PEER performance based earthquake engineering framework to structures in fire (original) (raw)

PRELIMINARY PROPOSAL FOR PERFORMANCE-BASED STRUCTURAL ENGINEERING FOR FIRE FOLLOWING EARTHQUAKE

The problem of fire following large earthquake raises significant concerns in earthquake prone areas. The evaluation of the occurrence and consequences of fires following earthquakes are a highly nonlinear and uncertain problem. The purpose of this paper is to report the ground work that the authors have been developing on the topic of performance-based assessment of building structures due to fire following earthquake cascading hazard. The paper presents a probabilistic framework for performance-based structural engineering (PBSE) that is currently under development and which includes earthquake performance assessment and fire performance assessment, namely in the special case of fire following earthquakes. The probabilistic framework presented can be seen as an extension of the performance-based earthquake engineering (PBEE) methodology developed by the Pacific Earthquake Engineering Research (PEER) center in the past decades. PEER's PBEE framework includes four main analytical steps: (i) probabilistic seismic hazard analysis, (ii) probabilistic seismic demand analysis, (iii) probabilistic seismic damage analysis, and (iv) probabilistic loss analysis. In the proposed PBSE approach for fire following earthquake, three additional analytical steps are proposed for linking the probabilistic seismic damage to the probabilistic loss analysis, which are: (a) probabilistic conditional fire hazard analysis, (b) probabilistic fire demand analysis, and (c) probabilistic fire damage analysis. The PBSE approach proposed represents a first step towards a rational methodology for fire following earthquake performance assessment of structures.

Practical case studies in performance-based structural fire engineering design

The specialist field of structural fire engineering is developing rapidly, along with the more general discipline of fire safety engineering. The results of international research and large-scale tests such as those conducted at Cardington in England during the 1990s are now starting to be used in practical fire-resistance design. Performance-based structural fire engineering guidance documents and standards have now been published in the United Kingdom and these are being used to realise more cost effective buildings. Furthermore, sophisticated finite element analysis software programs are being adopted by consulting engineers to predict the actual performance of structural frames in fire scenarios, and thus to enable robust yet cost-effective design solutions which optimise the extent and placement of fire protection. Such techniques are suitable for use as part of an integrated structural design process, treating the fire case as one of a series of limit states which contribute to both the conceptual and detailed design phases, rather than simply as a means of retrospectively calculating thicknesses of fire protection materials. This paper uses the recently completed Leeds Nuffield Hospital in England, as an example of how such structural fire engineering techniques can be used by designers to optimise the inherent fire resistance of structures and the fire protection strategies which have been used to produce safe but economic solutions. It describes the use of Vulcan, a finite element program developed at the University of Sheffield, together with other levels of design calculation, and also outlines the rigorous sensitivity studies and checking procedures that were imposed to ensure flexible, robust solutions.

Performance based investigations of structural systems under fire

Prescriptive measures and procedures developed over the past here are mostly aimed at preventing structural failures of single elements for the time required for the evacuation (Giuliani&Budny, 2010). The response to fire and fire effects of the structural system as a whole remains often unknown and the survival of the construction after this time cannot always be granted. This is even more true in case of unaccounted events like human errors or rare but severe occurrence like a fire after explosion, which cannot be contemplated in the usual design. Even if a structure could be hardly designed to resist fully integer all these kinds of events, the mitigation of possible collapse induced by fire should be achieved. In this respect, a performance-based investigation of the structure aimed at highlight fire effects and fire-induced collapse mechanisms becomes of interest. In the paper collapse mechanisms of some simple structures are presented and discussed, with particular attention to methodological aspects. The effects of different assumptions in the modeling and in the definition of the collapse are highlighted, as critical aspects of a performance-based investigation.

A framework methodology for performance-based earthquake engineering

2004

The Pacific Earthquake Engineering Research Center (PEER) aims to develop a robust methodology for performance-based earthquake engineering. To accomplish this objective, the performance assessment and design process has been broken into logical elements that can be studied and resolved in a rigorous and consistent manner. Elements of the process include description, definition, and quantification of earthquake intensity measures, engineering demand parameters, damage measures, and decision variables. A consistent probabilistic framework underpins the methodology so that the inherent uncertainties in earthquake performance assessment can be represented. The methodology can be implemented directly for performance assessment, or can be used as the basis for establishing simpler performance metrics and criteria for performance-based design.

“Performance-based fire design of complex structures”, International Journal of Lifecycle Performance Engineering, 1(2), 185-208

The problem of structural fire safety in the recent years has gained a predominant position within the engineering design, with the affirmation of performance-based structural codes and standards, replacing more and more the traditional prescriptive ones. This is because nowadays, structures always bigger and more complex are designed and built. In modelling such complex structures, there are important aspects and relevant uncertainties that need to be taken into account. This paper focuses on the application of the performance-based fire design to this kind of structures; the systemic approach is identified as the proper tool to manage all the aspect related with the problem. A general framework is presented for this purpose and it is applied to a facility made of steel for the storage of helicopters, with a relatively complex geometry subject to fire. The structure is of interest since, due to its occupancy, it is prone to elevate fire risk. The modelling of the problem proposes the use of non-linear analysis that includes thermo-plastic material, geometric non-linearity and the representation of fire action are done according to a standard parametric curve.

Severity Measures and Stripe Analysis for Probabilistic Structural Fire Engineering

Fire Technology, 2018

This paper presents modifications to the adoption of a Performance-Based Earthquake Engineering (PBEE) framework in Probabilistic Structural Fire Engineering. Potential Fire Severity Measures, which capture significant characteristics of fire scenarios, are investigated. A suitable Fire Severity Measure (FSM), which best relates fire hazard intensity with structural response, is identified by satisfying efficiency and sufficiency criteria as described by the PBEE framework. The study also implements a new analysis method called Fire Stripe Analysis (FSA) to obtain the relationship between FSM and the structural response. In order to obtain the annual rate of exceedance of damage and repair cost/time for an office building, an occurrence model and an attenuation model for office structure fires are generated for both Christchurch city and New Zealand. The process is demonstrated with the help of a case study performed for a steel-concrete composite beam. Structural response is recorded for the beam exposed to several fire profiles which are generated by varying fuel loads from 200 MJ/m 2 to 1000 MJ/m 2 and ventilation factors from 0.02 m 1/2 to 0.08 m 1/2. FSA and dispersion curves of structural response are plotted for every fire severity measure. Cumulative incident radiation is found to be the most efficient and sufficient FSM. The mean annual rate of exceedance of given levels of fire severity and structural response are evaluated for both New Zealand and Christchurch city. It is found that Christchurch city has a 15% less probability of exceedance of the given fire severity level in comparison to the whole of New Zealand. The extension of this work would facilitate designers/insurers to evaluate the probability of damage or failure of a structure due to a probable fire hazard.

Methodology and Applications for Integrating Earthquake Aftershock Risk into Performance-Based Seismic Design

Aftershocks have the potential to cause severe damage to buildings and contribute to threaten life safety following a major earthquake. However, their effect on seismic hazard is not explicitly accounted for in modern building design codes, nor in emerging methodologies such as performance-based seismic design. In this dissertation a methodology was developed to systematically integrate aftershock seismic hazard into performance-based earthquake engineering (PBEE). This is achieved through a combination of analytical studies with structural degradation models derived from existing publicly available Network for Earthquake Engineering Simulation (NEES) data as well as numerical models. The design adjustments due to aftershock seismic hazard were calculated for the Direct Displacement Design (DDD) approach for a building portfolio. A comprehensive sensitivity analysis was performed to investigate the effect of different factors such as the location and number of stories of the buildin...

Risk-based structural fire design

2014

To date, structural fire design has been largely based on extreme fire scenarios. Now, the University of Canterbury is investigating the use of probabilistic assessment to improve building performance during fires.