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Öğe Elasto-plastic buckling analysis for perforated steel plates subject to uniform compression(2011) Kömür, Mehmet AydiınThis study investigates the elasto-plastic buckling behaviour of simply supported square and rectangular thin steel plates having elliptic cut-outs by means of finite element method. Plates with simply supported in the out-of-plane direction are applied uniform compression in long-edge direction. A50 steel was used in the analysis and the focus was on the effect of plate aspect ratio, elliptical hole size, elliptical hole angle, elliptical hole location and slenderness ratio on buckling behaviour. It was found in the study that as the plate slenderness ratio increases, the critical buckling stress decreases for all the perforated plates. © 2011 Elsevier Ltd. All rights reserved.Öğe Cyclic behavior of high density polyethylene (HDPE)(American Institute Physics, 2010) Düşünceli, Necmi; Aydemir, Bülent; Terzi, Niyazi Uğur; DAmore, A; Acierno, D; Grassia, LThis article presents the mechanical behavior of high density polyethylene (HDPE). Samples were prepared by extracting extruded HDPE pipe. Cyclic and strain rate jump behavior of HDPE were studied under uniaxial tensile loading conditions. The strain jump tests indicated that mechanical behavior of HDPE has deformation memory. Further, it was found that increasing cycle number on cyclic loading test increased strain accumulation amount and HDPE exhibited ratcheting behavior at on loading-unloading-reloading at constant stress level.Öğe Evaluation of ınstallation quality on polyethelene pipe performance under surcharge loads(American Institute Physics, 2010) Terzi, Niyazi U.; Düşünceli, Necmi; Yılmaztürk, Ferruh; Yıldırım, Sönmez; DAmore, A; Acierno, D; Grassia, LIn this study, a comprehensive laboratory test on 100 mm diameter HDPE 100 polyethylene flexible pipe buried in quartz sand is described. The laboratory test was performed in a 40 mm thick plexiglass-fronted test tank which replicated a classical trench section in field conditions. The polyethylene flexible pipe was positioned against the glass with its longitudinal axis perpendicular to the glass. This allowed direct observation of the backfill-pipe interactions and pipe performance under surcharge loads. Three high definition photogrammetric cameras were taken photogrammetric images through the glass allowing the discrete measurement and image processing of the deformation patterns of the polyethelene pipe conduit during the pipe installation and incremental surcharge loading. Vertical loads were applied in increments of 10 kPa to 150 kPa using air pressure membranes. According to the test results, it is understood that the installation technique and backfill properties have an important effect on circumferential strains, performance and deformation characteristics of polyethelene HDPE pipe. It was also observed that close-range image processing is a very simple and appropriate method for measuring three dimensional pipe deformations under various conditions.Öğe A numerical evaluation of a cover embankment model on very soft halic dredge material(IOS Press, 2011) Terzi, Niyazi Uğur; Selcuk, M. Ergenekon; Sengul, T.; Chung, CK; Kim, HK; Lee, JS; Jung, YH; Kim, DSThe objective of this study is to evaluate the consolidation process and long-term deformation behavior of an embankment constructed on dredge material from the Halic (know as Golden Horn) in Istanbul. A comprehensive laboratory studies were performed on dredge material and with using the laboratory test results, finite element numerical method was carried out to analyze the embankment construction procedure, and its relationship with the Halic dredge materials. The Soft Soil Creep Model for very soft dredge material and the Mohr-Coulomb Soil Model for embankment material was utilized in the numerical investigations. For the numerical analysis, engineering and consolidation characteristics of the Halic dredge material were determined by using in-situ and laboratory tests. The results proved that the chosen Soft Soil Model and Mohr-Coulomb for the Halic dredge and embankment materials are efficient in assessing the geotechnical behavior and the long term pore water pressure dissipation of the embankment-foundation system model.Öğe Mathematical modeling of bed - Topography changes at bridge abutments(2009) Köse, Ömer; Yanmaz, Ali MelihRiver bridges are very important elements of transportation systems, failures of which may not only lead to loss of several lives and excessive damages but also various deficiencies including socio-economic factors. Several aspects of bridge failures should be investigated jointly to gather information for scour-resistant design practices. This study specifically focuses on the effect of clear water scouring at vertical-wall abutments on bridge stability. Determination of the time-dependent volume and surface area of scour hole around a vertical-wall abutment would yield relevant information to assess the safety level of the bridge foundation. To this end, temporal variation of geometric features of scour holes around vertical abutments under clear water conditions are examined with reference to an experimental study. Findings of this study would yield some information concerning loss of structural resistance, safe design of footing and sizing and placement details of armoring countermeasures against scouring. © 2009 ASCE.Öğe Solution techniques for nonlinear equilibrium equations(2008) Torkamani, Morteza A.M.; Sönmez, MustafaMethodologies for solving nonlinear equilibrium equations are reviewed in this article. Two basic numerical procedures, the pure incremental and the direct iteration methods, are briefly discussed. Then the most frequently used increment-iterative methods are presented and their limitations are discussed. These techniques are the Newton-Raphson and the displacement control method. One of the advanced nonlinear solution procedures, generalized displacement control method, is outlined, and its algorithm is also presented. The generalized displacement method shows that it is a robust numerical technique for solving nonlinear structural problems which may include softening, stiffening behavior and in the bifurcation vicinity of critical points. The elstica problem which is a classic highly geometrically nonlinear problem is presented to show the versatility of the generalized displacement control method for the solution of highly nonlinear problems. © 2008 ASCE.Öğe Strengthening of RC shear walls with CFRP strips(The Hong Kong Polytechnic University, 2016) Altın, Sinan; Anıl, Özgür; Kopraman, Yağmur; Kara, Mehmet EminThe purpose of this study was to investigate the hysteretic behavior of shear deficient reinforced concrete (RC) walls that were strengthened with carbon fiber reinforced polymer (CFRP) strips. Totally, ½ scale five specimens with 1.5 aspect ratio walls were constructed. One of them was tested without any retrofitting as a reference specimen and four of them were retrofitted specimens with CFRP strips. All of the specimens were tested under cyclic lateral loading. CFRP strips with different configurations were tested like X-shaped, horizontal and parallel strips or combinations of them. All of the CFRP configurations were symmetrically bonded to both sides of the shear wall and were anchoraged to the wall. The research focuses on the effect of using CFRP strips for enhancing strength and increasing ductility of the non-seismic detailed shear walls. Test results shows that all of the CFRP strip configurations significantly improves the lateral strength, energy dissipation and deformation capacity of the shear deficient RC walls. The specimen that was strengthened with X-shaped CFRP strips was failed with premature shear failure. The specimen that was strengthened with horizontal strips was showed flexural hysteretic behavior and plastic hinge was developed at the wall base. CFRP strips were controlled shear crack propagation and resulted in improvement of displacement capacity. Copyright © 2016 Department of Civil and Environmental Engineering & Research Institute for Sustainable Urban Development, The Hong Kong Polytechnic University.
