اثر تغییر زاویه‌ی جبهه میدان موج برشی بر کرنش های دیواره‌ی سازه های زیرزمینی مستطیلی شکل

نوع مقاله : Articles

نویسندگان

پژوهشگاه بین‌المللی زلزله‌شناسی و مهندسی زلزله

چکیده

رفتار لرزه‌ای سازه‌های زیرزمینی به‌صورت استاندارد در سه مرحله‌ی متوالی محاسبه‌ی حرکت میدان آزاد، محاسبه‌ی تغییر شکل‌ها در دیواره‌ی ناحیه‌ی حفاری شده و محاسبه‌ی اندرکنش دیواره‌های ناحیه حفاری شده با سازه‌ی درون آن بررسی می‌گردد. در این میان در هر سه مرحله‌ی فوق نقاط مبهمی در ادبیات فنی وجود دارد. از جمله این ابهامات، زاویه‌ی مواجهه‌ی سازه با میدان موج می‌باشد. در روند متداول تحلیل و طراحی سازه‌های زیرزمینی، میدان موج عموماً برشی در نظر گرفته شده و زاویه‌ی مواجهه‌ی میدان موج با سازه برابر صفر لحاظ می‌گردد. فرض زاویه‌ی مواجهه‌ی صفر در مناطق دارای توپوگرافی رو سطحی و زیرسطحی می‌تواند تقریب زیادی وارد محاسبات نماید. در این مقاله اثرات تغییر در زاویه‌ی مواجهه‌ی سازه با میدان موج برشی بر کرنش‌های ایجاد شده در سازه مورد بررسی قرار گرفته است. آنالیز لرزه‌ای به روش اجزاء محدود دو بعدی استاتیکی و برای حالت مشخصی از نسبت سختی خاک به سازه به‌وسیله‌ی نرم­افزار آباکوس انجام پذیرفته است. همچنین سازه‌ها در دو بخش سازه‌های به شکل مستطیل کامل و سازه‌های شبه مستطیلی مورد بررسی قرار گرفته‌اند. نتایج حاکی از آن است که فرض زاویه‌ی مواجهه‌ی صفر در تحلیل‌های لرزه‌ای می‌تواند منجر به محاسبات غیر محافظه‌کارانه‌ی چشمگیری در روند طراحی لرزه‌ای شود.A Study on the Effect of Seismic Wave Incident Angle on Lining Strains Imposed to Underground Rectangular 2D StructuresAmir Hossein Pariz, Hossein Jahankhah, and Morteza Bastami Soil-Structure Interaction (SSI) problems are usually broken down into four fundamental parts. The first step is the estimation of free field motion (FFM). FFM is representative of the field motion in the absence of any activity relating to the building construction procedure. The second step is the calculation of excavated field motion (EFM), which translates the effect of including void on alternation in FFM. This later motion usually is defined in the perimeter of the cavity. The third step accounts for kinematic aspects of SSI. In this part, foundation deformations due to EFM are estimated. In the fourth and final step, the previously calculated deformations are used to impose the acceleration history on structural mass. In current practice, it is known that the third step has the highest influence on underground structures and hence it dictates the design criteria for such systems.To implement the above-mentioned analysis plan, FFM is usually considered as shear waves with upward propagation direction. Such assumption has formed the popular simplified seismic design method for underground structures. Though, this common assumption may not be valid for topographic urban areas were wave fields reach the surface through different incident angles. Such inclination would lead to various states of confrontation between embedded structures and wave fields. The state variety, in turn, causes underground constructions to experience different stress fields and hence dissimilar lining deformations. Therefore, there is a serious need to uncover the role of face-off orientation of wave field and the structure on lining strain demands.Here, the effect of face-off angle between shear wave field and rectangular underground structures, on lining strains is investigated. For this purpose, a 2D isotropic soil model including homogeneity is included under statically simulated seismic shear deformations. The analysis was performed through finite element method regarding different aspect ratios for underground structure and subsequently lining strains were reported. To drive strain demands, in the analyzed model, first, the axial, shear and moment demands are estimated. Then the results are normalized to proper parameters that lead to relative strains. Beside these three types of strain, with a combination of strains resulted from axial and moment forces, the total axial strain is also extracted. This parameter is commonly used in any structural member design. The analysis was repeated for three aspect ratios of 1, 2 and 4. Besides, four face-off angles of 0, -15, -30 and -45 degrees were considered while the flexibility ratio was set to 10. The outcomes were reported in contour format. There in each graph, the variation of strains was illustrated by changing incident angle in one axis against different sections along the target element in the other axis. The first part of this research examines the performance of perfect rectangular structures against different incident angles. The second part deals with samples of semi-rectangular sections. The selected cases, which belong to different metro stations in Kobe metropolitan, possess rectangular sub-parts.With an overview of results for perfect rectangles, it can be figured out that the total axial strain is notably governed by moment induced strain rather than pure axial strain. In that case, the maximum strain at corners belongs to zero incident angle while in the middle part of the element, the confrontation angle of -45 degree takes the highest strain values. For shear strains, zero face-off angle caps all results for both corner and middle parts. For the case of semi-rectangular sections, the effect of variation in incident angle on demands becomes highlighted. From the results, it can be seen that for more than 50 percent of elements, face-off angles other than zero dominate the results. It is worth mentioning that to reach a comprehensive influence map on the critical face-off angle, further investigation is required. Keywords: Seismic Analysis; Underground Structures; Rectangular Cavities; Lining Strains; Shear Deformations 

کلیدواژه‌ها


Kuesel, T.R. (1969) Earthquake design criteria for subways. Journal of the Structural Division, ASCE, ST6, 1213-1231.
Hendron, A.J. and Fernandez, G. (1983) ‘Dynamic and static design considerations for underground chambers’. In: Seismic Design of Embankments and Caverns, Howard, T.R. (Ed.), 157-197, New York.
Merritt, J.L., Monsees, J.E., and Hendron, A.J., Jr. (1985) Seismic design of underground structures. Rapid Excavation Tunneling Conference, 1, 104-131.
St. John, C.M. and Zahrah, T.F. (1987) Aseismic design of underground structures. Tunneling Underground Space Technology, 2(2), 165-197.
Wang, J.N. (1993) Seismic Design of Tunnels: A Simple State-of-the-Art Design Approach. Parsons Brinckerhoff, Monograph No. 7, New York.
Nishiyama, S., Kawama, I., Muroya, K., Haya, H., and Nishimura, A. (2000) Experimental study of seismic behavior of box type tunnel constructed by open cutting method. Proceedings 12th World Conference on Earthquake Engineering, Auckland.
Penzien, J. and Wu, C.L. (1998) Stresses in linings of bored tunnels. Earthquake Engineering and Structural Dynamics, 27(3), 283-300.
Penzien, J. (2000) Seismically induced racking of tunnel linings. Earthquake Engineering and Structural Dynamics, 29(5), 683-691.
Hashash, Y.M., Hook, J.J., Schmidt, B., John, I., and Yao, C. (2001) Seismic design and analysis of underground structures. Tunnelling and Under-ground Space Technology, 16(4), 247-293.
Wood, J.H. (2004) Earthquake design procedures for rectangular underground structures. Earthquake Commission Research Foundation, EQC No 01/470.
Wood, J.H. (2007) Earthquake design of rectangular underground structures. Bulletin of the New Zealand Society for Earthquake Engineering, 40(1), 1-6.
Hashash, Y.M., Park, D., John, I., and Yao, C. (2005) Ovaling deformations of circular tunnels under seismic loading, an update on seismic design and analysis of underground structures. Tunnelling and Underground Space Technology, 20(5), 435-441.
Huo, H., Bobet, A., Fernandez, G., and Ramirez, J. (2006) Analytical solution for deep rectangular structures subjected to far-field shear stresses. Tunnelling and Underground Space Technology, 21(6), 613-625.
Ozcebe, Ali Guney (2009) A Comparative Assessment of Available Methods for Seismic Performance Evaluation of Buried Structures. Master Thesis, Middle East Technical University.
Debiasi, E., Gajo, A., and Zonta, D. (2013) On the seismic response of shallow-buried rectangular structures. Tunnelling and Underground Space Technology, 38, 99-113.
Panji, M., Kamalian, M., Asgari Marnani, J., and Jafari, M.K. (2013) Transient analysis of wave propagations problems by half-plane BEM. Geophysical Journal International, 194, 1849-1865.
Panji, M., Kamalian, M., Asgari Marnani, J., and Jafari, M.K. (2014) Analyzing seismic convex topographies by a half-plane time-domain BEM. Geophysical Journal International, 197(1), 591-607.
Fuentes, R. (2015) Internal forces of underground structures from observed displacements. Tunnelling and Underground Space Technology, 49, 50-66.
Jahankhah, H., Pariz, A.H., and Bastami, M. (2016) An investigation on seismically induced local distortions to underground rectangular 2d cavities: the case of shear wave field of motion with different incident angles. Bulletin of Earthquake Science and Engineering, 3(1), 41-53‏ (in Persian).