بررسی تاثیرات متقابل گسلش سطحی و فونداسیون صلب بر یکدیگر در طراحی لرزه ای ساختمان های نزدیک گسل (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
وقوع زمین لرزه های بزرگ در نزدیکی شهرهایی که در حوزه نزدیک قرار دارند غیر قابل انکار است. زمین لرزه ها در حوزه نزدیک اثرات و ویژگی های بسیار متفاوتی، نسبت به زمین لرزه ها در حوزه دور دارند. با توجه به این که گسلش سطحی اثرات مخرب و غیر قابل جبرانی را برای سازه های نزدیک گسل به وجود می آورند و در آیین نامه ها کمتر به آن توجه شده است به این منظور نحوه طراحی سازه برای رسیدن به عملکرد مناسب در برابر این پدیده از اهمیت بالایی برخوردار است. در این پژوهش سعی شده است به بررسی و ارزیابی پارامترهایی نظیر مکانیزم گسل، پهنه گسلی، گسلش سطحی و نیز تعداد طبقات و موقعیت فونداسیون در طراحی لرزه ای ساختمان های نزدیک گسل پرداخته شود. برای این عمل ابتدا به نحوه انتشار گسلش در خاک زیر سازه و اثرات آن بر روی سازه با توجه به تعداد طبقات مختلف دیده شده است. در پایان مشاهده گردید با افزایش تعداد طبقات در خاک های ماسه ای مورد مطالعه گسلش به بیرون فونداسیون منحرف شده و در نتیجه آن، میزان دوران پی با توجه به خاک زیر آن کاهش می یابد. همچنین مشاهده می شود افزایش جابه جایی گسل در میزان دوران تأثیر بسزایی داشته به طوری که با افزایش جابه جایی قائم از 5/0 به 5/1 متر، دوران فونداسیون تا 4 برابر افزایش داشته است.Investigating the mutual effects of surface faulting and rigid foundation on each other on in the seismic design of buildings near fault
The occurrence of great earthquakes in the vicinity of the cities which are in near field is undeniable. Near-field earthquakes have very different effects and characteristics than far-field earthquakes. Considering that the surface faulting causes destructive and irreparable effects for structures near the fault and less attention is paid to it in the regulations, for this purpose, how to design the structure to achieve proper performance against this phenomenon is of great importance. in this study it has been tried to study and evaluate the parameters such as fault mechanism, fault zone, surface faulting, story numbers and the position of the foundation in the seismic design of buildings near the fault. For this purpose, the fault propagation in the substructure soil and its effects on the structure have been investigated according to the number of different story. In the end, it has been observed that with increasing the number of story in the studied sandy soils, the fault deviates out of the foundation and as a result, the amount of foundation rotation decreases with respect to the soil beneath it. It is also observed that the increase in fault displacement has a significant effect on the rotation so that with the increase in vertical displacement from 0.5 to 1.5 meters, the foundation rotation has increased up to 4 times.IntroductionEarthquakes primarily cause ground shaking and ruptures, both of which are pivotal elements contributing to a number of minimal or extensive damages to buildings, or other structures such as bridges and so on and so forth. Apart from seismic shaking, ground ruptures, and visible displacements on the surface along the fault line, earthquakes can impact structures in their path. This can potentially lead to the collapse of these structures. Ground ruptures pose a significant and potential risk to various structures, including bridges, dams, nuclear power plants, and residential buildings. Surface faulting poses a significant risk that necessitates careful consideration during the design or evaluation of structures situated in areas with shallow active faults. In areas where innovative construction methods are not employed, the extent of damage and, consequently, the mortality rate tends to be higher compared to areas where strict building regulations are followed. This underscores the need for more rigorous enforcement of construction standards. Therefore, efforts have been made to set regulatory guidelines by studying the detrimental impacts of surface faulting phenomena.MethodologyIn this study, ABAQUS software which is a suite for finite element analysis has been used for simulation. Previous studies indicate that this software has proven effective in simulating the surface faulting distribution within the soil. In the current study, Abaqus software has been used to conduct a static analysis, examining the impact of various factors on the seismic design of buildings. These factors include surface faulting, the number of floors, fault mechanism, and the width of the fault zone. Moreover, in order to estimate fault propagation path, Mohr-Coulomb theory has been employed for soil modeling. To identify the location of the fault rupture and the foundation’s position relative to the fault, the parameter S/B is defined. Here, ‘S’ represents the distance from the fault rupture to its endpoint on the ground surface in the absence of a foundation. For the model analysis, we have considered three scenarios for this parameter: 0, 0.5, and 1.Results and discussionIn this study, a rigid foundation is considered for the analysis. Also, Abaqus software was used to simulate the foundation and two types of soil (dense and loose sand). The goal was to examine the impacts of surface faulting with various vertical shifts (0.5 and 1.5 meters) on the degree of foundation rotation. This was done by considering the foundation’s location in relation to the surface faulting when the foundation was absent. The slope faulting considered in this study was 45 degrees. Moreover, A dip-slip fault mechanism has been considered, and its impacts on the foundation were observed.ConclusionThe key findings of this study are as follows:As the number of floors increases, the degree of rotation diminishes. The greatest rotation is observed when the S/B parameter equals 0. However, even when S/B equals 1, there is a non-zero rotation and a minimum value, the opposite is also true.The condition associated with S/B=1 is the most critical. Nevertheless, as the density of the sandy soil increases, a reduction in the degree of foundation rotation is observed, irrespective of the number of floors. Put differently, as the slope of the fault increases, the degree of foundation rotation diminishes in the critical condition.Due to the stiffness of the soil, it is prevented from rupturing beneath the foundation when surface faulting occurs, therefore, the foundation subsides minimally or not at all.
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