Browsing by Author "Bayraktar, Alemdar"

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Assessment of Semi-Rigid Connections in Steel Structures by Modal Testing
(Elsevier Sci Ltd, 2009) Turker, Temel; Kartal, Murat Emre; Bayraktar, Alemdar; Muvafik, Murat
In conventional design and analysis, the common assumption is that connections of steel frames are fully rigid or frictionless pinned. However, today, the accepted notion is that the connections of members of a steel structure exhibit semi-rigid characteristics. Semi-rigid connections as well as damage cause changes in the dynamic characteristics of the structures. This study presents an investigation into the determination of the quality of the semi-rigid connections when considering changes in dynamic characteristics of steel structures. The investigations involve three scaled models: columns with box cross-sections, columns with rectangular cross-sections, and a 21) frame. The investigation algorithm first calculates natural frequencies and mode shapes from theoretical modal analyses by assuming the supports and joint connections are fully rigid. Secondly, experimental measurements on the models are performed to obtain natural frequencies, mode shapes and modal damping ratios. Thirdly, to reduce differences between theoretical and experimental results, linear elastic rotational springs are used on supports and joint connections of the analytical model. Finally, the connection percentages of both support and beam-to-column connections are determined using an approach improved depending on the rotational spring stiffness. (c) 2009 Elsevier Ltd. All rights reserved.
Damages of Minarets During Ercis and Edremit Earthquakes, 2011 in Turkey
(Techno-press, 2014) Bayraktar, Alemdar; Altunisik, Ahmet Can; Muvafik, Murat
This paper illustrates the damages of reinforced concrete and masonry minarets during October 23 (Ercis) and November 9 (Edremit), 2011 Van earthquakes in Turkey. Ercis and Edremit are townships located 90km and 18km from Van city center in Turkey, respectively. Ground accelerations and response spectrums for these earthquakes are given in this paper. A total of 63 reinforced concrete and masonry minarets are heavily damaged or collapsed in the city center and villages nearby after both earthquakes. Because of the fact that there is no Turkish standard and specification directly related to design of minarets, nearly all of the constructions are carried out by workers using only their own technical knowledge. So, all of the non-engineering reinforced concrete and masonry minarets completely collapsed or damaged heavily. From the study, it is seen that the damages are due to several reasons such as site effect, location, and length of the fault, reduction in cross section and formation of the discontinuity, use of plain reinforcement steel, use of concrete with insufficient strength, existence of short lap splices and incorrect end hook angle, larger mass and stiffness concentrations on some region, longitudinal reinforcements discontinuity, cracks at the cylindrical body, and damage of spire and end ornament. In addition to these reasons, the two earthquakes hit the minarets within seventeen days, causing progressive damage. So, the existing design and construction practices should be improved to provide sufficient earthquake performance. Also, it is recommended that there should be a safe distance between the minaret and surrounding structures to reduce the loose of life after earthquake.
Field Investigation of the Performance of Masonry Buildings During the October 23 and November 9, 2011, Van Earthquakes in Turkey
(Asce-amer Soc Civil Engineers, 2016) Bayraktar, Alemdar; Altunisik, Ahmet Can; Muvafik, Murat
This paper addresses field investigations of the performance of masonry buildings during the October 23 (Erci) and November 9 (Edremit), 2011, Van earthquakes in Turkey. Erci and Edremit are villages respectively located 90km and 18km from the city of Van in Turkey. Ground accelerations and response spectra for these earthquakes are discussed. A total of 28,000 buildings were damaged or collapsed in the city center and surrounding villages after the Erci earthquake. This number increased to 35,000 after the Edremit earthquake. Almost all masonry buildings were affected in the region. Most of them in the area were constructed of random or coursed stone walls with no reinforcement to support heavy clay tile roofing over wooden logs. A large number of such buildings were heavily damaged or collapsed. Cracking and failure patterns are examined and interpreted according to current provisions for earthquake resistance of masonry structures. From the field investigations, it is shown that damages had several causes, among them site effect, location and length of the fault, and poor construction quality. In addition, the two earthquakes hit the masonry buildings within 17 days, causing progressive damage. A large number of nonengineered masonry buildings completely collapsed or were heavily damaged. Most of those in the affected area were not designed and constructed in accordance with the Turkish Earthquake Resistant Design Code.
Nonlinear Structural Performance of a Historical Brick Masonry Inverted Dome
(Taylor & Francis inc, 2020) Ozturk, Sehabettin; Bayraktar, Alemdar; Hokelekli, Emin; Ashour, Ashraf
Traditional domes are obtained by double curvature shells, which can be rotationally formed by any curved geometrical plane figure rotating about a central vertical axis. They are self-supported and stabilized by the force of gravity acting on their weight to hold them in compression. However, the behavior of inverted domes is different since the dome is downward and masonry inverted domes and their structural behaviors in the literature received limited attention. This article presents a nonlinear finite element analysis of historical brick masonry inverted domes under static and seismic loads. The brick masonry inverted dome in the tomb of scholar Ahmed-El Cezeri, town of Cizre, Turkey, constructed in 1508 is selected as an application. First, a detailed literature review on the masonry domes is given and the selected inverted dome is described briefly. 3D solid and continuum finite element models of the inverted masonry dome are obtained from the surveys. An isotropic Concrete Damage Plasticity (CDP) material model adjusted to masonry structures with the same tensile strength assumed along the parallel and meridian directions of the inverted dome is considered. The nonlinear static analyses and a parametric study by changing the mechanical properties of the brick unit of the inverted masonry dome are performed under gravity loads. The acceleration records of vertical and horizontal components of May 1, 2003 Bingol earthquake (Mw = 6.4), Turkey, occurred near the region, are chosen for the nonlinear seismic analyses. Nonlinear step by step seismic analyses of the inverted dome are implemented under the vertical and horizontal components of the earthquake, separately. Static modal and seismic responses of the inverted masonry dome are evaluated using mode shapes, minimum and maximum principal strains and stresses, and damage propagations.