Document Type : Research Note
Authors
Dept. of Civil Engineering Urmia University of Technology
Abstract
Progress in our knowledge of seismic systems due to modern research and observations about recent earthquakes, makes it necessary to review building regulations and refine former versions from time to time. Analysis software also needs to be updated according to these changes, to cope with new requirements. In standard AISC341-10, it is mentioned that beams and columns should be braced in special concentrically braced frames. After structure analysis and design, according to design regulations, first, the braces should be eliminated, and the floors restrained against side movement in order to avoid structural instability. Then, after applying the highest expected tensional and compressional forces along the eliminated braces, structures with gravity loads should be analyzed. Using this new regulation, emergence of plastic hinges in bars and pillars will be avoided as long as possible, and the braces can be used for energy amortization.Due to the inability of current software, like ETABS, SAP2000, to apply loads along brace elements, these forces should be decomposed to horizontal and vertical elements. This method, specifically in high-rise structures containing many braced bays, is too complex, time consuming and prone to error. Also, considering the reciprocal effects of earthquakes, this control should be applied twice in order to design the structure for worst case scenarios.In this paper, the new temperature variation loading method is proposed. This method is more efficient than current force loading methods, and it can be used to analyze and design building frames with concentrically braced. The temperature variation loading method has resulted from the concept of thermal strains and stresses, and is performable by the mentioned analytic software. Actually, instead of force loading, the corresponding temperature variation is assigned to brace members in the appropriate analytic software, and finally, it becomes easy to control the mentioned provisions in the above regulations. The elasticity module of the braces is altered in order to eliminate thermal strains. Without this change, utilizing temperature variation loading is impossible. Another advantage of the temperature variation method is that the corresponding themorature change of tension elements is the same for every stage of the structure, and is independent of section type. This method is more applicable for high-rise structures containing many braced bays, because it needs less accuracy in comparison to the force loading method and also reduces the time of analysis and design of the structure.
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