Studies On The Characteristic Of Smoke Movement And Smoke Control In Shaft Of Ultra-high-rise Buildings

With the rapid development of global economy, science and technology, many high-rise and even ultra high-rise buildings are built or to be built in dense urban areas in large cities or city groups over the world. Ultra high-rise buildings have already become one of the important symbols of urban modernization. There are stairwells, pipe and cable ducts, and other vertical channels in those ultra high-rise buildings. These shafts will facilitate the spread of fire and smoke in a fire by combining natural driving forces with stack effect, smoke buoyancy and wind action. However, there is still not yet a workable fire safety system for ultra high-rise buildings in the world. In China, only "Fire Protection Design Standard for High-Rise Civil Constructions" is formulated particularly for high-rise constructions. It does not include a list of specific fire safety provisions for protecting against ultra high-rise building fires. There are no complete systematic research on the mechanism of fire and smoke movement in the world, and very little research on vertical shafts in ultra high-rise buildings. Therefore, carrying out the study of smoke driving forces and the mechanism of smoke spread in the shafts of ultra high-rise buildings is very important.With the support of the Croucher Foundation in Hong Kong, the State Key Laboratory of Fire Science in the University of Science and Technology of China, The Hong Kong Polytechnic University and the Southwest Jiaotong University, experiments were carried out to study smoke movement and the associated driving forces in this thesis. Efforts were made on reviewing previous studies first. Scale model experiments on a 2.7 m tall vertical shaft were carried out. The natural smoke driving forces, the movement mechanism of smoke under the conditions of different fire positions and lateral openings in the shaft of an ultra high-rise building were investigated by combining scale model experiments and numerical models. Similarity theory and numerical analysis method were applied with reference to the literature.By using a small-scale shaft model, the effect of simple hot smoke buoyancy, outdoor air, their integrated effect and others were studied. From this part of study, it is found that the simple stack effect increases as the temperature difference between the inside and outside of the shaft becomes higher. Without the external heat source maintaining the temperature difference, stack effect will disappear quickly. When the temperature difference is not obvious, the gas flow under the reverse stack effect is faster than under the stack effect. The simple hot smoke buoyancy plays a leading role in the early stage of smoke spreading. As the temperature increases, there is a temperature difference between inside and outside of the shaft. Therefore, stack effect plays a leading role. The near-ground vent influences the smoke spreading inside the shaft significantly, but in the integrated condition of ventilating position and wind direction, the effect on smoke spreading is very different. The order of the impact of wind direction is as follows: wind surface > side surface > lee side. Under the integrated effect of various driving forces, it will facilitate smoke spreading greatly inside the shaft, increase the volume of gas inside the shaft, and change the spreading pattern of smoke. Throughout the course of the experiments, all of the three effects influence fire and smoke spreading significantly.In studying the movement of gas inside the shaft and from numerical simulations of gas under different heights of fire, the relationship between the fire location factor and the highest temperature was derived. A correlation relation of the maximum temperature with the location of fire was derived. From this part of study, it can be concluded that the height of the neutral plane increases with the location of the fire. The location of the fire affects smoke spreading significantly. Most of the smoke flows to the upper region of stack, and the bottom of the region is smoke-free. The maximum temperature in the stack is in inverse proportion to the fire location factor (h/H). The higher the position of the fire, the larger the fire location factor, and the lower the maximum temperature.By studying the movement of gas inside the shaft and from numerical simulations of gas under different opening conditions, other conclusions can be drawn. The movement of gas varies with the structure of the shaft, which mainly depends on the inlet vent and the opening. When only the vents below the neutral plane are open, the number of vents below the neutral plane have direct ratio with the effect of mixing with smoke. When only the vents above the neutral plane are open or some vents both above and below the neutral plane are open, the lower smoke extends in the form of a wall plume along the wall which has vents. Floors under the neutral plane are smoke-free until smoke produced is more than the smoke flowing out. When all the vents are closed, smoke moves slowly and the upper temperature increase slowly. When all the vents are open, there is large air entrainment through the vents below the neutral plane, the velocity of gas is fast. The temperature at the bottom of the stack is low with the same temperature gradient, in steady-state condition it is a constant.The results deduced from this thesis are practical and useful to the industry. Concepts are helpful to the government in drafting standards for fire protection in ultra high-rise buildings.