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Yayın Improvement of seismic performance of precast frames with cladding panels fastened by energy dissipative steel cushions(Springer, 2021-09) Özkaynak, Hasan; Khajehdehi, Arastoo; Yüksel, Ercan; Karadoğan, Hüseyin FarukPrecast reinforced concrete panels are commonly used as wall claddings in precast buildings. The cladding panels are generally evaluated as non-structural members and are joined to structural systems via mechanical, welding, and bolted dry connections. Several failures were observed in the last seismic events in Southern Europe, which demonstrate the deficiencies of the cladding connections in terms of strength and ductility. A comprehensive research activity named SAFECLADDING was conducted in Europe to provide knowledge for proper seismic design of precast structures with cladding panels. In this context, energy dissipative steel cushions were developed and evaluated through the extensive experimental and numerical studies. Steel cushions can provide robust interaction of the structural system with the cladding panels. This paper numerically evaluates the effects of cladding panels with steel cushions on the global seismic behaviour of the buildings. An existing representative industrial building is selected to perform intensive nonlinear dynamic analyses. Analyses performed on the bare and hybrid systems showed that the hybrid system has high performance in terms of story drifts, internal forces, and deformations with respect to the bare system. The overall drifts in longitudinal and transversal directions of the building are reduced by about 78 and 54%, respectively. Average residual drifts of cladding panels and steel cushions indicated that the applied steel cushion placement scheme has a promising re-centring capability during seismic action.Yayın Pros and cons of using building information modeling in the AEC industry(ASCE-AMER Soc Civil Engineers, 2019-08-01) Seyis Kazazoğlu, SenemAlthough a plethora of studies on building information modeling (BIM) have been conducted in the last decade, none of the previous studies collate and/or prioritize the benefits, risks, and challenges of BIM based on the data collected from a comprehensive literature review and subject matter experts (SMEs). In order to allow architecture, engineering, and construction (AEC) professionals and academics see the true potential of BIM in a wider context and help them understand its multiorganizational and multidisciplinary functions, there is an obvious necessity for identifying, classifying, and prioritizing the pros and cons of BIM; however, such a study is still currently absent in the AEC literature. The aim of this study is to identify, classify, and rank the pros and cons of BIM that address the benefits, challenges, and risks of BIM in the transition from computer-aided design (CAD). A literature review was performed and face-to-face semistructured interviews with SMEs on BIM were conducted for identification and classification purposes. A total of 41 types of benefits, 11 types of risks, and 13 types of challenges of BIM were identified via triangulation of literature review and face-to-face semistructured interviews with SMEs. The Delphi method was performed for prioritizing the benefits of BIM in terms of time, cost, and sustainability as well as the risks and challenges of BIM encountered in the transition process from CAD to BIM. The interrater agreement and significance-level statistics were performed to analyze and validate the consensus reached by the Delphi panel experts. This paper contributes to the existing body of knowledge on BIM by providing comprehensive identification and classification of the benefits, challenges, and risks of BIM, and prioritization of the benefits for BIM in terms of time, cost, and sustainability as well as the risks and challenges of BIM. The priority rankings of benefits, risks, and challenges of BIM ensure successful completion of projects and create additional value by allowing professionals to make well-informed decisions that support decreasing time and cost-related waste in the transition process from CAD to BIM.Yayın Coupled influence of content, gradation and shape characteristics of silts on static liquefaction of loose silty sands(Elsevier Sci Ltd, 2017-10) Monkul, Mehmet Murat; Etminan, Ehsan; Şenol, AykutStatic liquefaction is a challenging problem of geotechnical engineering as its consequences are generally catastrophic when they occur on site. Previous laboratory studies focused on various factors that could influence the static liquefaction potential of silty sands. Most popular of those investigated factors are stress conditions, deposition method and fines content. The purpose of the present study is to investigate the other possible factors, of which very little is known, mainly focusing on the silt characteristics including grain size distribution, relative size, and shape effects of the silt grain matrix within the sand. Undrained monotonic triaxial compression tests were conducted on thirty sands with varying fmes contents, which were prepared by mixing three base sands (Sile Sands 20/30, 50/55, 80/100) with same geologic origin but with different gradations and three different non-plastic silts (IZ, SI and TI' silts) with different gradations and shape characteristics. The experimental results revealed that each of the mentioned factors had their own influence on static liquefaction behavior of sands. The static liquefaction potential of all the three sands in this study was observed to increase with decreasing coefficient of uniformities of the silt grain matrix (CUsiit) in sands. For a particular base sand, static liquefaction potential was observed to increase with decreasing mean grain diameter ratio (D-50.sand/d(50.silt)) due to change of silt gradation. However, shape characteristics of the silt grains are also found to be another important factor, in certain cases observed to have a greater influence than mean grain diameter ratio criterion. As an example, it was shown that at the same FC, base sand, depositional energy and consolidation stress, angular nature of TT silt potentially caused more meta-stable contacts (weaker grain contacts that promote excess pore pressure generation during shearing) within the specimens than sub-rounded SI silt, which caused specimens with TT silt to be more liquefiable than their counterparts with SI silt. Moreover, it was found that there is a coupled relationship between the fines content and investigated silt characteristics (gradation, mean size, shape effects) on the static liquefaction behavior of sands. The unexpected trend regarding the last finding is that the mentioned influence of silt characteristics (i.e. gradation, size and shape) on static liquefaction of sands becomes more considerable with decreasing fines content at loose states.Yayın Pedestrian crossing behavior at midblock crosswalks(Elsevier Ltd, 2019-12) Tezcan, Hüseyin Onur; Elmorssy, Mahmoud; Aksoy, GökerIntroduction: This study investigated the pedestrian crossing behavior at midblock crosswalks, in Istanbul. Method: Data were compiled from field studies at four selected crosswalks that were on one-way streets. Three of the crosswalks were located on three-lane streets while the other one was on a two-lane street. By using two-hour video recordings at each crosswalk, information was collected about pedestrian crossing preferences, pedestrian platoons both at curbside and during the crossing, traffic characteristics including volume, crosswalk occupancy and illegal parking, and pedestrian characteristics comprising age, gender and distraction status. These data were stratified with respect to the number of lanes and two multinomial logit models for platooning and individual crossing behavior was estimated for each stratum. Results: The results showed that the likelihood of platooning increases as the traffic volume and platoon size increase. Moreover, pedestrians who waited for little or no at the curbside and started to cross when one or more lanes were occupied generally lost time during the crossing. In terms of policy, the formation of platoons should be prevented by enforcement or demand-responsive traffic signals with push-to-walk buttons, etc. Overall, the study revealed that the presence of midblock crosswalks is questionable.Yayın Precursors of instability in a natural slope due to rainfall: a full-scale experiment(Springer Heidelberg, 2018-09) Askarinejad, Amin; Akça, Mehmet Devrim; Springman, Sarah MarcellaA full-scale landslide-triggering experiment was conducted on a natural sandy slope subjected to an artificial rainfall event, which resulted in mobilisation of 130m(3) of soil mass. Novel slope deformation sensors (SDSs) were applied to monitor the subsurface pre-failure movements and the precursors of the artificially triggered landslide. These fully automated sensors are more flexible than the conventional inclinometers by several orders of magnitude and therefore are able to detect fine movements (<1mm) of the soil mass reliably. Data from high-frequency measurements of the external bending work, indicating the transmitted energy from the surrounding soil to these sensors, pore water pressure at various depths, horizontal soil pressure and advanced surface monitoring techniques, contributed to an integrated analysis of the processes that led to triggering of the landslide. Precursors of movements were detected before the failure using the horizontal earth pressure measurements, as well as surface and subsurface movement records. The measurements showed accelerating increases of the horizontal earth pressure in the compression zone of the unstable area and external bending work applied to the slope deformation sensors. These data are compared to the pore water pressure and volumetric water content changes leading to failure.Yayın Cyclic behavior of reinforced concrete cladding panels connected with energy dissipative steel cushions(Elsevier Ltd, 2019-06-15) Karadoğan, Hüseyin Faruk; Yüksel, Ercan; Khajehdehi, Arastoo; Özkaynak, Hasan; Güllü, Ahmet; Şenol, ErkanPrecast concrete structures show damage after the destructive earthquakes and indicate that the connections of reinforced concrete (RC) cladding panels might be inadequate. RC cladding panels greatly increase the lateral stiffness and strength of the building when they are rigidly connected to the structural system. However, this also increases the seismic requirements. Consequently, a robust mechanical connection device with energy-dissipating capability was produced for RC cladding panels. Extensive experimental and numerical studies on an energy-dissipative steel cushion (SC) connection device were carried out in the framework of the SAFECLADDING project. Cladding panel tests were conducted with various connection configurations. The fundamental variables are the location, quantity, and thickness of SCs used in the cladding systems. The test results demonstrate that the SCs used in panel-to-panel and panel-to-support connections made large contributions to the total energy dissipation capacity. The parameters of a numerical model were also evaluated to reproduce the experimental results.Yayın Rogue waves of the Kundu-Eckhaus equation in a chaotic wave field(American Physical Society, 2016-03-01) Bayındır, CihanIn this paper we study the properties of the chaotic wave fields generated in the frame of the Kundu-Eckhaus equation (KEE). Modulation instability results in a chaotic wave field which exhibits small-scale filaments with a free propagation constant, k. The average velocity of the filaments is approximately given by the average group velocity calculated from the dispersion relation for the plane-wave solution; however, direction of propagation is controlled by the beta parameter, the constant in front of the Raman-effect term. We have also calculated the probabilities of the rogue wave occurrence for various values of propagation constant k and showed that the probability of rogue wave occurrence depends on k. Additionally, we have showed that the probability of rogue wave occurrence significantly depends on the quintic and the Raman-effect nonlinear terms of the KEE. Statistical comparisons between the KEE and the cubic nonlinear Schrodinger equation have also been presented.Yayın Assessment and enhancement of SAR noncoherent change detection of sea-surface oil spills(IEEE, 2018-01) Bayındır, Cihan; Frost, J. David; Barnes, Christopher F.Oil spills are one of the most dangerous catastrophes that threaten the oceans. Therefore, detecting and monitoring oil spills by means of remote sensing techniques that provide large-scale assessments is of critical importance to predict, prevent, and clean oil contamination. In this study, the detection of an oil spill using synthetic aperture radar (SAR) imagery is considered. Detection of the oil spill is performed using change detection algorithms between imagery acquired at different times. The specific algorithms used are the correlation coefficient change statistic and the intensity ratio change statistic algorithms. These algorithms and the probabilistic selection of threshold criteria are reviewed and discussed. A recently offered change detection method that depends on generating change maps of two images in a temporal sequence is used. An initial change map is obtained by cumulatively adding sequences in such a manner that common change areas are excluded and uncommon change areas are included. A final change map is obtained by comparing the first and the last images in the temporal sequence. This method requires at least three images to be employed and can be generalized to longer temporal image sequences. The purpose of this approach is to provide a double-check mechanism to the conventional approach and, thus, reduce the probability of false alarm while enhancing change detection. The algorithms are tested on 2010 Gulf of Mexico oil spill imagery. It is shown that the intensity ratio change statistic is a better tool for identification of the changes due to the oil spill compared to the correlation coefficient change statistic. It is also shown that the proposed method can reduce the probability of false alarm.Yayın Uni-axial behavior of energy dissipative steel cushions(Techno Press, 2018-06-25) Özkaynak, Hasan; Khajehdehi, Arastoo; Güllü, Ahmet; Azizisales, Faraz; Yüksel, Ercan; Karadoğan, Hüseyin FarukSeismic excitations may impart a significant amount of energy into structures. Modern structural design attitudes tend to absorb some part of this energy through special dissipaters instead of heavy plastic deformations on the structural members. Different types of dissipater have been generated and utilized in various types of structures in last few decades. The expected earthquake damage is mainly concentrated on these devices and they may be replaced after earthquakes. In this study, a low-cost device called energy dissipative steel cushion (EDSC) made of flat mild steel was developed and tested in the Structural and Earthquake Engineering Laboratory (STEELab) of Istanbul Technical University (ITU). The monotonic and cyclic tests of EDSC were performed in transversal and longitudinal directions discretely. Very large deformation capability and stable hysteretic behavior are some response properties observed from the tests. Load vs. displacement relations, hysteretic energy dissipation properties as well as the closed form equations to predict the behavior parameters are presented in this paper.Yayın A decision making support tool for selecting green building certification credits based on project delivery attributes(Pergamon-Elsevier Science Ltd, 2017-12) Seyis Kazazoğlu, Senem; Ergen Pehlevan, EsinThe Green Building (GB) certification process embodies detailed requirements and specifications that lead to additional tasks for project teams, which increases complexity levels of the entire project delivery process. Previous studies show that if the GB certification credits to be fulfilled are selected without considering project team attributes, then elevated levels of time, money, and labor could get wasted while attempting to meet the additional requirements of GB certification. The aim of this study is to develop a multi-attribute decision making (MADM) support tool to be used by GB experts to select the appropriate GB certification credits based on the project team attributes. The developed framework with relative weights assigned via the Delphi method was used to perform the MADM analysis, which employs the hybrid use of the Multi Attribute Utility Technique (MAUT) and the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). This paper presents the developed MADM tool (i.e., GB-CS tool) and the relative weights of the attributes that were determined following expert opinions. To validate the tool, a case study was conducted at a LEED-registered residential project. The results show that the GB-CS Tool was successful in ranking the GB certification credits to be selected. This hybrid MADM tool can be used for preventing disruptions and bottlenecks in GB project delivery processes by assisting the owners/GB consultants in effectively selecting suitable GB certification credits based on the project team attributes. Thus, with the assistance of the GB-CS tool, root causes of waste can be mitigated in the GB project delivery process, decreasing associated hidden costs.
