【正文】 ossible to influence the level of live load in a building by conducting audits and placing restrictions on contents. However, in the case of a fire start, there are many factors that can be brought to bear to influence the ultimate size of the fire and its effect within the building. It is known that occupants within a building will often detect a fire and deal with it before it reaches a sig nificant size. It is estimated that less than one fire in five (Favre, 1996) results in a call to the fire brigade and for fires reported to the fire brigade, the majority will be limited to the room of fire origin. In oc cupied spaces, olfactory cues (smell) provide powerful evidence of the presence of even a small fire. The addition of a functional smoke detection system will further improve the likelihood of detection and of action being taken by the occupants. Fire fighting equipment, such as extinguishers and hose reels, is generally provided within buildings for the use of occupants and many organisations provide training for staff in respect of the use of such equipment. The growth of a fire can also be limited by automatic extinguishing systems such as sprinklers, which can be designed to have high levels of can also be limited by the fire brigade depending on the size and location of the fire at the time of arrival. Effects of Fire The structural elements in the vicinity of the fire will experience the effects of heat. The temperatures within the structural elements will increase with time of exposure to the fire, the rate of temperature rise being dictated by the thermal resistance of the structural element and the severity of the fire. The increase in temperatures within a member will result in both thermal expansion and,eventually,a reduction in the structural resistance of the member. Differential thermal expansion will lead to bowing of a member. Significant axial expansion will be acmodated in steel members by either overall or local buckling or yielding of local ised 5 regions. These effects will be detrimental for columns but for beams forming part of a floor system may assist in the development of other load resisting mechanisms (see Section ). With the exception of the development of forces due to restraint of thermal expansion, fire does not impose loads on the structure but rather reduces stiffness and strength. Such effects are not instantaneous but are a function of time and this is different to the effects of loads such as earthquake and wind that are more or less instantaneous. Heating effects associated with a fire will not be significant or the rate of loss of capacity will be slowed if: (a) the fire is extinguished (. an effective sprinkler system) (b) the fire is of insufficient severity – insufficient fuel, and/or (c)the structural elements have sufficient thermal mass and/or insulation to slow the rise in internal temperature Fire protection measures such as providing sufficient axis distance and dimensions for concrete elements, and sufficient insulation thickness for steel elements are examples of (c). These are illustrated in Figure 2. The two situations described in the introduction are now considered. 3 FIRE WITHIN BUILDINGS Fire Safety Considerations The implications of fire within the occupied parts of the office building (Figure 1) (Situation 2) are now considered. Fire statistics for office buildings show that about one fatality is expected in an office building for every 1000 fires reported to the fire brigade. This is an order of magnitude less than the fatality rate associated with apartment buildings. More than two thirds 6 of fires occur during occupied hours and this is due to the greater human activity and the greater use of services within the building. It is twice as likely that a fire that mences out of normal working hours will extend beyond the enclosure of fire origin. A relatively small fire can generate large quantities of smoke within the floor of fire origin. If the floor is of openplan construction with few partitions, the presence of a fire during normal occupied hours is almost certain to be detected through the observation of smoke on the floor. The presence of full height partitions across the floor will slow the spread of smoke and possibly also the speed at which the occupants detect the fire. Any measures aimed at improving housekeeping, fire awareness and fire response will be beneficial in reducing the likelihood of major fires during occupied hours. For multistorey buildings, smoke detection systems and alarms are often provided to give “automatic” detection and warning to the occupants. An alarm signal is also transmitted to the fire brigade. Should the fire not be able to be controlled by the occupants on the fire floor, they will need to leave the floor of fire origin via the stairs. Stair enclosures may be designed to be fireresistant but this may not be sufficient to keep the smoke out of the stairs. Many buildings incorporate stair pressurisation systems whereby positive airflow is introduced into the stairs upon detection of smoke within the building. However, this increases the forces required to open the stair doors and makes it increasingly difficult to access the stairs. It is quite likely that excessive door opening forces will exist(Fazio et al,2020) From a fire perspective, it is mon to consider that a building consists of enclosures formed by the presence of walls and enclosure that has sufficiently fireresistant boundaries (. walls and floors) is considered to constitute a fire partment and to be capable of limiting the spread of fire to an adjacent partment. However, the ability of such boundaries to restrict the spread of fire can be severely limited by the need to provide natural lighting (windows)a