Risk and Performance Based Fire Safety Design of Steel and Composite Structures

摘要

For the development of performance based design on a proper scientific basisudthe use of the concept of risk is inevitable. However, the application of thisudconcept to actual structural design is not simple because of the large rangesudof probability and consequences of events which exist. This is compoundedudby a plethora of different actions that can be taken to reduce the probabilitiesudof the events and also the magnitude of the consequences. It is the reductionudin the magnitude of these consequences which is essentially the goal of design.udThis work aims to address the challenges posed by the application of theudconcepts of performance based design for structures in fire. Simple methodologies have been developed for the assessment of the consequences of anudextreme event. These methodologies are based upon fundamental behaviourudof structures in fire.udA methodology has been developed which can be used to assess the capacity/deflection behaviour through the complete thermal deflection of floorudslabs. This takes into account positive effects on the capacity of floor slabs ofudthe membrane stress at the slabs boundaries at low deflections as well as theudfinal capacity provided by the tensile membrane action of the reinforcementudmesh at high deflections.udFor vertical stability of structures in fire, analytical equations to describeudthe behaviour of floor systems at the perimeter of a building are developed.udFrom these equations, the resulting pull-in forces on external columns canudbe calculated as well as the resulting horizontal load applied to the column.udFrom this, a simple stability assessment is proposed which can be used to assess the consequences of multiple floor fires on tall buildings.udThese analytical methodologies are brought together in a risk based frame-udwork for structural design which can be used to identify areas in a buildingudor structural components which pose a high residual risk. These elementsudcan be qualitatively ’ranked’ according to their relative risk and appropriateudmeasures taken to reduce the risk to an acceptable level. The framework isudillustrated via 2 case studies. The first is of a typical small office building,udand the second is of a prestige office development.