Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Author: search.filters.author.Eğilmez, Oğuz Özgür

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Now showing 1 - 6 of 6
  • Master Thesis
    Stiffnes Requirements of Shear Diaphragms Used To Brace Steel I-Beams
    (Izmir Institute of Technology, 2017) Akbaba, Andaç; Dönmez, Cemalettin; Eğilmez, Oğuz Özgür
    The buckling capacity of steel I-beams can be increased by providing lateral bracing along the length of the beams by either cross-frames or diaphragms. Metal sheeting that is often used in steel building and bridge constructions to support the fresh concrete, acts like a shear diaphragm and provides continuous bracing to steel beams. In building industry, metal deck forms are considered as a lateral support to the beams. However, due to their flexible connection detail between the girder and shear diaphragm, metal deck forms are not considered as a brace source for bridge construction industry. But with the recent studies, by improvements of the flexible connection details, metal decking can be used as a bracing system. An adequate bracing system must possess sufficient stiffness and strength. A computational study was conducted to investigate stiffness requirements of shear diaphragms used to brace stocky and slender steel I-beams. Both doubly and singly symmetric sections were studied. The computational study consists of eigenvalue buckling analyses on perfectly straight twin-girder system braced by shear diaphragms and large deformation analyses with imperfect girders with different configurations of girder sections and spans. A three dimensional computer programme was utilized to perform analytical studies. Analytical model is verified by a full-scale twin-girder system laboratory test that is carried out on a previous study. Stiffness requirements have been proposed for shear diaphragms used to brace stocky and slender steel I-beams.
  • Master Thesis
    Strength Requirements of Shear Diaphragms Used To Brace Steel I-Beams
    (Izmir Institute of Technology, 2014) Vardaroğlu, Mustafa; Eğilmez, Oğuz Özgür; Dönmez, Cemalettin; Dönmez, Cemalettin; Eğilmez, Oğuz Özgür
    Lateral torsional buckling, also known as flexural torsional buckling is a failure mode that often controls the design of I-shaped steel beams during construction. In order to increase the lateral torsional buckling capacity of the girders in this stage, discrete or continuous bracing systems are often utilized in building and bridge constructions. Light gauge metal decking acts like a shear diaphragm and provides continuous lateral bracing to the beams. The building industry has long relied on metal decking to laterally support the beam top flanges. Bridge construction industry does not consider metal decking as a brace source due to the flexible connection between the girder and the diaphragm. However, recent studies have shown that metal sheeting can also be used in the bridge industry as construction bracing as long as the flexibility of the connections can be controlled by modifications. An adequate bracing system must possess sufficient strength and stiffness to control deformations and brace forces. A parametrical study was conducted to investigate the stiffness and strength of shear diaphragms used to brace stocky and slender steel I-beams. This thesis focuses on the strength requirements. The parametrical study consists of eigenvalue buckling analyses and large displacement analyses on a twin girder shear diaphragm system with various girder and metal deck configurations. A three-dimensional finite element analysis program was selected for the analyses. In the model metal deck-girder connections and the connection between adjacent decks are modeled respectively. Finite element model is verified by a full-scale twin-girder buckling test as the part of a previous study. According to the numerical study an equation is proposed for the estimation of the brace forces in the deck connections. The equation is shifted for possible deck and girder configurations.
  • Master Thesis
    Experimental Study on Improving Local Buckling Behavior of Steel Plates Strengthened With Glass Fiber Reinforced Polymers
    (Izmir Institute of Technology, 2009) Güven, Can Ali; Eğilmez, Oğuz Özgür
    Glass Fiber Reinforced Polymer (GFRP) applications becoming one of the most efficient strengthening methods to improve mechanical properties of previously built steel structures. In strengthening applications FRP materials generally used in web or flange sections of steel members to provide a bracing against local buckling. By the help of their easy application and their tailorable mechanical properties, FRPs provide various options for selecting the most suitable FRP material for applications. This study focuses on using GFRP to enhance the buckling behavior of GFRPstrengthened steel plates under axial loading. For that purpose, a detailed experimental study program has been followed revealing mechanical properties of GFRP material, steel and interaction between steel-GFRP. Previous studies showed that the surface bond between GFRP and steel section as the weakest link of the structure. As a result of this, various epoxies, surface preparation primers, surface treatments are used to produce Lap-Shear specimens to provide most efficient surface interaction between GFRP and steel. Results of these experiments provided us data to decide most suitable surface treatment, surface primer and epoxy combination in the GFRP Strengthened Steel Plate Tests with the ability to in-situ application. 350x200x20 mm steel plates are strengthened with various thickness (2, 4 and 16 layers) and surface areas (80mm x 300mm, 160 x 300mm) of GFRP to compare the stabilization in buckling values with bare steel plates. Plates are strengthened with GFRP on both sides and they are tested in compression testing equipment. LVDTs are used to collect axial and lateral buckling while strain-gauges attached to both composite used to collect axial and lateral buckling while strain-gauges attached to both composite plates strengthened with GFRP material showed that application of GFRP provides enhancement to the plastic buckling of steel plates.
  • Master Thesis
    Numerical Study of Enhancement of Plastic Rotation Capacity of Seismic Steel Moment Connections by Fiber Reinforced Polymer Materials
    (Izmir Institute of Technology, 2008) Alkan, Deniz; Eğilmez, Oğuz Özgür
    Flange and web local buckling in beam plastic hinge regions of welded Steel Moment Frames (SMF) can prevent the beam-column connections to achieve adequate plastic rotations under earthquake induced forces. Reducing the web-flange slenderness ratios is the most effective way in preventing local member buckling as stipulated in the latest earthquake specifications. However, older steel beam-column connections that lack the adequate slenderness ratios stipulated for new SMFs are vulnerable to local plastic buckling. This study investigates postponing the formation of local buckles in beam flanges and webs at the plastic hinge region of modified SMF connections (welded haunch) by the use of externally bonded Glass Fiber Reinforced Polymers (GFRP). The research includes finite element (FE) modeling. The energy dissipation capacity of existing SMF connections is anticipated to increase with GFRP laminates bonded to flanges of beams in plastic hinge locations. Cantilever beams with and without GFRP were analyzed under quasi-static cyclic loading and the effects to the plastic local buckling of the GFRP laminates added to the steel beams were observed.Both geometric and material nonlinearities are considered. The mechanical properties of the GFRP material were obtained through standard ASTM tests and were utilized directly in the FE model. Steel beams with flange slenderness ratios of 8 to 12 and web slenderness ratios of 40-60-80 were analyzed. Results indicate that GFRP strips can effectively delay the formation of local plastic buckling in the plastic hinge region.
  • Master Thesis
    Seismic Behavior of Steel I-Beams Modified by a Welded Haunch and Reinforced With Glass Fiber Reinforced Polymers
    (Izmir Institute of Technology, 2009) Özdemir, Timur; Eğilmez, Oğuz Özgür
    Flange and web local buckling in beam plastic hinge regions of welded steel moment frames (SMF) can prevent beam-column connections to achieve adequate plastic rotations under earthquake-induced forces. As the use of fiber reinforced polymers (FRP) have increased in strengthening and repair of steel members in recent years, using FRPs in stabilizing local instabilities have also attracted attention. Generally, high modulus carbon FRP (CFRP) laminates, with elastic modulus similar to that of steel, are preferred in strengthening applications. On the other hand, glass FRP (GFRP) has a much smaller modulus than that of steel, typically one order of magnitude less, which limits its use in strengthening applications. However, this modulus mismatch is an asset when the primary goal is to stabilize inelastic local buckling with the least possible strength increase in the section. In a steel-GFRP hybrid system, while the low modulus of GFRP will not allow a significant strength increase in the beam, the flexural strength of GFRP can provide bracing to the underlying steel, which is flowing plastically. In this research study, the cyclic behavior of steel beams modified by a triangular haunch welded to the beam bottom flange only and reinforced with GFRP laminates at beam flanges have been investigated by finite element analysis (FEA). Cantilever I-sections with flange-web slenderness ratios higher then those stipulated in current seismic design specifications are analyzed under reversed cyclic loading. Both bare beam sections and sections reinforced with GFRP are investigated. The effects of GFRP thickness, width, and length on stabilizing local buckling are investigated. The flexural resistance of the beams at column face, interlaminar shear stresses in GFRP strips, and shear stresses at beam-GFRP binding surface are examined. The results reveal that the plastic rotation capacity of steel beams can be enhanced by the use of GFRP strips.
  • Master Thesis
    Seismic Behavior of Steel I-Beams Reinfor Ced With Glass Fiber Reinforced Polymer: an Experimental Study
    (Izmir Institute of Technology, 2010) Yormaz, Doruk; Eğilmez, Oğuz Özgür
    Design guidelines, which are put into effect in the aftermath of the 1994 Northridge earthquake, require intermediate and special moment frames (IMF and SMF) be capable of maintaining 0.02 and 0.04 radians interstory drift, respectively without significant strength degradation and development of instability. However, local buckles in the plastic hinge region are major hindrances for the ductility capability and stability of the structural system. Thus, the research program aims to mitigate such inelastic instabilities by using glass fiber reinforced polymer (GFRP), which possesses elastic modulus roughly one order of magnitude less than that of steel. On the other hand, this elastic modulus discrepancy between GFRP and steel can be useful for stabilizing local buckles by means of the bracing effect of GFRP during plastic hinge formations. This thesis describes large-scale experimental study of the research program that investigates the seismic behavior of steel I-beams reinforced with GFRP. In this experimental study, four HE400AA beams with welded haunch (WH) modification and three HE500AA beams with no modification were tested under cyclic loading. The results of experimental study indicate that it does not seem possible to rely on GFRP reinforcement to increase the flexural resistance of connections at a rotation of 0.04 radians because the adhesive layer between steel and GFRP fails in rotations much lower than 0.04 radians. However, the seismic performance of the structure can be moderately improved with the bottom flange WH and GFRP reinforcement in order to maintain rotations without local buckles in accordance with the rotation demand of IMFs, which is 0.02 radians.