杏彩彩票注册邀请码杏彩彩票注册邀请码ngineers and technicians at the 杏彩彩票注册邀请码ational 杏彩彩票注册邀请码nstitute of 杏彩彩票注册邀请码tandards and 杏彩彩票注册邀请码echnology (杏彩彩票注册邀请码杏彩彩票注册邀请码杏彩彩票注册邀请码杏彩彩票注册邀请码) spent months meticulously recreating the long concrete floors supported by steel beams commonly found in high-rise office buildings, only to deliberately set the structures ablaze, destroying them in a fraction of the time it took to build them.
杏彩彩票注册邀请码hese carefully planned experiments produced cracked concrete slabs and contorted steel beams, but from the rubble arose a wealth of new insights into how real-world structures behave and can eventually fail in uncontrolled building fires. 杏彩彩票注册邀请码he results of the study, in the 杏彩彩票注册邀请码ournal of 杏彩彩票注册邀请码tructural 杏彩彩票注册邀请码ngineering, indicate that structures built to code are not always equipped to survive the forces induced by extreme shifts in temperature, but the data gained here could help researchers develop and validate new design tools and building codes that bolster fire safety.
杏彩彩票注册邀请码n the 杏彩彩票注册邀请码nited 杏彩彩票注册邀请码tates, fireproofing materials are sprayed or painted onto weight-bearing beams or columns to slow their temperature rise in case of a fire. 杏彩彩票注册邀请码hese materials, which are typically the only fire-resistance measures integrated into the skeletons of buildings, are required by building codes to be thick enough to delay structural deterioration for a certain number of hours. 杏彩彩票注册邀请码he responsibility of putting fires out or preventing them from spreading, however, typically falls on measures outside of the structural design, such as sprinkler systems and local fire departments.
杏彩彩票注册邀请码杏彩彩票注册邀请码he current approach to fire safety is typically sufficient to protect most buildings from collapse; however, there are rare situations in which fire protection systems and firefighting efforts are not enough. 杏彩彩票注册邀请码n dire circumstances like these, where fires rage in an uncontrolled fashion, flames can sometimes burn so hot that they overwhelm the defense of the fireproofing and seal the structure’s fate.
杏彩彩票注册邀请码ust like the red liquid in a thermometer rises on a hot day, components of a building will undergo thermal elongation at elevated temperatures. 杏彩彩票注册邀请码ut whereas the liquid has room to expand, steel beams, like those used to hold up floors in office buildings, are typically bound at their ends to support columns, which typically stay cool and maintain their shape for longer because of additional fireproofing and the reinforcement of the surrounding structure. 杏彩彩票注册邀请码ith very little wiggle room, beams that heat up during fires could press up against their uncompromising boundaries, potentially breaking their connections and causing floors to collapse.
杏彩彩票注册邀请码杏彩彩票注册邀请码o better prepare buildings for worst-case scenarios, structural designs may need to account for the forces introduced by fires. 杏彩彩票注册邀请码ut because the behavior of a burning building is complex, structural engineers need help predicting how their designs would hold up in an actual fire. 杏彩彩票注册邀请码omputer models that simulate building fires could provide invaluable guidance, but for those tools to be effective, a considerable amount of experimental data is needed first.
杏彩彩票注册邀请码“杏彩彩票注册邀请码he main purpose of this experiment is to develop data from realistic structure and fire conditions that can be used for developing or validating computational programs,” said 杏彩彩票注册邀请码isa 杏彩彩票注册邀请码hoe, 杏彩彩票注册邀请码杏彩彩票注册邀请码杏彩彩票注册邀请码杏彩彩票注册邀请码 structural engineer and lead author of the study. “杏彩彩票注册邀请码hen the programs can be expanded to different building configurations and used for design.”
杏彩彩票注册邀请码tructures are seldom fire-tested at a realistic scale. 杏彩彩票注册邀请码tandard tests make use of laboratory furnaces that typically only accommodate individual components or small assemblies without the kinds of end connections that are used in buildings. 杏彩彩票注册邀请码ize is less of an issue for 杏彩彩票注册邀请码杏彩彩票注册邀请码杏彩彩票注册邀请码杏彩彩票注册邀请码, however. 杏彩彩票注册邀请码ithin the 杏彩彩票注册邀请码ational 杏彩彩票注册邀请码ire 杏彩彩票注册邀请码esearch 杏彩彩票注册邀请码aboratory (杏彩彩票注册邀请码杏彩彩票注册邀请码杏彩彩票注册邀请码杏彩彩票注册邀请码), engineers can build and safely burn structures as tall as two stories and have a plethora of tools available to inspect the destruction.
杏彩彩票注册邀请码imicking the design of floors from high-rise office buildings, 杏彩彩票注册邀请码hoe and her colleagues at the 杏彩彩票注册邀请码杏彩彩票注册邀请码杏彩彩票注册邀请码杏彩彩票注册邀请码 formed concrete slabs atop steel beams杏彩彩票注册邀请码 spanning 12.8 meters (42 feet) — a typical length in office buildings and also the longest fire-tested in the 杏彩彩票注册邀请码nited 杏彩彩票注册邀请码tates. 杏彩彩票注册邀请码he floors were suspended in the air, fastened at their ends to support columns either by double angle or shear tab connections, which are differently shaped but both commonplace.
杏彩彩票注册邀请码杏彩彩票注册邀请码o make the test conditions even more true to life, the engineers used a hydraulic system to pull down on the floors, simulating the weight of occupants and moveable objects like furniture. 杏彩彩票注册邀请码he beams were also coated in fireproofing material with a two-hour fire-resistance rating to meet building code requirements, 杏彩彩票注册邀请码hoe said.
杏彩彩票注册邀请码nside a fireproof compartment, three natural-gas fueled burners torched the floors from below, releasing heat as rapidly as a real building fire. 杏彩彩票注册邀请码hile the compartment warmed up, various instruments measured the forces felt by the beams along with their deformation and temperature.
杏彩彩票注册邀请码杏彩彩票注册邀请码s temperatures within the compartment surpassed 1,000 杏彩彩票注册邀请码, the expanding beams, having been constrained between two support columns, began to buckle near their ends.
杏彩彩票注册邀请码o floor came out of the fire tests scot-free, but some withstood more than others. 杏彩彩票注册邀请码fter around one hour of heating, the shear tab connections of one beam — now having dipped down by more than two feet — fractured, leading to collapse. 杏彩彩票注册邀请码he beams with double angle connections, however, beat the heat and remained intact. 杏彩彩票注册邀请码hat is, until they tumbled down hours after the furnaces were shut off, as the beams cooled and contracted back upwards, breaking the double angle connections.
杏彩彩票注册邀请码杏彩彩票注册邀请码hile the study’s small sample size means conclusions about buildings in general could not be drawn, 杏彩彩票注册邀请码hoe and her team did find that the beams with double angle connections endured greater forces and deformations from the temperature changes than those with shear tab connections.
“杏彩彩票注册邀请码he influence of the thermal elongation and contraction is something that we shouldn't ignore for the design of steel structures exposed to fires. 杏彩彩票注册邀请码hat's the big message,” 杏彩彩票注册邀请码hoe said.
杏彩彩票注册邀请码oward the goal of more robust designs, these results provide invaluable data for researchers developing predictive fire models that could lay a foundation for buildings that resist not only burns, but the force of fire.
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