• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.168-179
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• 2006

This paper summarizes full-scale test results on CFT column-to-flat plate connections subjected to gravity loading. CFT construction has gained wide acceptance in a relatively short time in domestic building construction practice due to its various structural and construction advantages. However, efficient details for CFT column to flat plate connections have not been proposed yet. Based on the strategies that maximize economical field construction, several connecting schemes were proposed and tested. Test results showed that the proposed connections can exhibit punching shear strength and connection stiffness exceeding those of R/C flat plate counterparts. A semi-analytical procedure is presented to model the behavior of CFT column-to-flat plate connections. The five parameters to model elastic to post-punching catenary action range are calibrated based on the limited test data of this study. The application of the proposed modeling procedure to progressive collapse prevention design is also illustrated.

• Advances in concrete construction
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• v.8 no.2
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• pp.91-100
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• 2019

In this paper three damaged exterior RC beam-column joints made of recycled aggregate concrete (RAC) were repaired. The aim of the study was to restore back the lost capacity of the beam-column joint to the original state or more. A relatively cheap material locally available galvanized steel welded wire mesh (GSWWM) of grid size 25 mm was used to confine the damaged region and then jacketed with cement mortar. Repaired specimens were also subjected to similar cyclic displacement as those of unrepaired specimens. Seismic parameters such as load carrying capacity, ductility, energy dissipation, stiffness degradation etc. were analyzed. Results show that repaired specimens exhibited better seismic performance and hence the adopted repairing strategies could be considered as satisfactory. These findings would be helpful to the field engineers to adopt a suitable rapid and cost efficient repairing technique for restoring the damaged frame structural joints for post earthquake usage.

• Earthquakes and Structures
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• v.12 no.1
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• pp.109-118
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• 2017

A novel post-tensioned self-centering (SC) concrete beam-column connection with web friction devices has been proposed for concrete moment-resisting frames. This paper presents a probabilistic performance evaluation procedure to evaluate the performance of the self-centering concrete frame with the proposed post-tensioned beam-column connections. Two performance limit states, i.e., immediate occupancy (IO) and repairable (RE) limit states, are defined based on peak and residual story drift ratios. Statistical analyses of seismic demands revealed that the dispersion of residual drifts is larger than that of peak drifts. Due to self-centering feature of post-tensioning connections, the SC frame was found to have high probabilities to be recentered under the design basis earthquake (DBE) and maximum considered earthquake (MCE) ground motions. Seismic risk analysis was performed to determine the annual (50-year) probability of exceedance for IO and RE performance limit states, and the results revealed that the design objectives of the SC frame would be met under the proposed performance-based design approach.

• Steel and Composite Structures
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• v.15 no.6
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• pp.585-603
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• 2013

Generally the required strength and stiffness of an I-shaped beam to the box-shaped column connection is achieved if continuity plates are welded to the column flanges from all sides. However, welding the forth edge of a continuity plate to the column flange may not be easily done and is normally accompanied by remarkable difficulties. This study was aimed to propose an alternative for box columns with continuity plates to diminish such problems. For this purpose a double-web I-shaped column was proposed. In this case the strength and rotational stiffness of the connection was provided by nearing the column webs to each other. Finite element studies on about 120 beam-column connections showed that the optimum proportion of the distance between two column webs and the width of the column flange (parameter ${\beta}$) was a function of the ratio of the beam flange width to the column flange width (parameter ${\alpha}$). Hence, based on the finite element results, an equation was proposed to estimate the optimum value of parameter ${\beta}$ in terms of parameter ${\alpha}$ to achieve the highest connection performance. Results also showed that the strength and ductility of post-Northridge connections of such columns are in average 12.5 % and 54% respectively higher than those of box-shaped columns with ordinary continuity plates. Therefore, a double-web I-shaped column of optimum arrangement might be a proper replacement for a box column with continuity plates when beams are rigidly attached to it.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.5
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• pp.291-298
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• 2018

Existing reinforced concrete building structures have seismic vulnerabilities under successive earthquakes (or mainshock-aftershock sequences) due to their inadequate column detailing, which leads to shear failure in the columns. To improve the shear capacity and ductility of the shear-critical columns, a fiber-reinforced polymer jacketing system has been widely used for seismic retrofit and repair. This study proposed a numerical modeling technique for damaged reinforced concrete columns repaired using the fiber-reinforced polymer jacketing system and validated the numerical responses with past experimental results. The column model well captured the experimental results in terms of lateral forces, stiffness, energy dissipation and failure modes. The proposed column modeling method enables to predict post-repair effects on structures initially damaged by mainshock.

• International Journal of Concrete Structures and Materials
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• v.11 no.2
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• pp.229-245
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• 2017

Post-earthquake observations revealed that seismic performance of beam-column connections in precast concrete structures affect the overall response extensively. Seismic design of precast reinforced concrete structures requires improved beam-column connections to transfer reversed load effects between structural elements. In Turkey, hybrid beam-column connections with welded components have been applied extensively in precast concrete industry for decades. Beam bottom longitudinal rebars are welded to beam end plates while top longitudinal rebars are placed to designated gaps in joint panels before casting of topping concrete in this type of connections. The paper presents the major findings of an experimental test programme including one monolithic and five precast hybrid half scale specimens representing interior beam-column connections of a moment frame of high ductility level. The required welding area between beam bottom longitudinal rebars and beam-end plates were calculated based on welding coefficients considered as a test parameter. It is observed that the maximum strain developed in the beam bottom flexural reinforcement plays an important role in the overall behavior of the connections. Two additional specimens which include unbonded lengths on the longitudinal rebars to reduce that strain demands were also tested. Strength, stiffness and energy dissipation characteristics of test specimens were investigated with respect to test variables. Seismic performances of test specimens were evaluated by obtaining damage indices.

• Computers and Concrete
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• v.24 no.3
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• pp.223-236
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• 2019

Experience of previous earthquakes shows that a considerable portion of concrete precast buildings sustain relatively large damages especially at the beam-column joints where the damages are mostly caused by bar slippage. Precast concrete buildings have a kind of discontinuity in their beam-column joints, so reinforcement details in this area is too important and have a significant effect on the seismic behavior of these structures. In this study, a relatively simple and efficient nonlinear model is proposed to simulate pre- and post-elastic behavior of the joints in usual practice of precast concrete building. In this model, beam and column components are represented by linear elastic elements, dimensions of the joint panel are defined by rigid elements, and effect of slip is taken into account by a nonlinear rotational spring at the end of the beam. The proposed method is validated by experimental results for both internal and external joints. In addition, the seismic behavior of the precast building damaged during Bojnord earthquake 13 May 2017, is investigated by using the proposed model for the beam-column joints. Damage unexpectedly inducing the precast building in the moderate Bojnord earthquake may confirm that bearing capacity of the precast building was underestimated without consideration of joint behavior effect.

• Fisheries and Aquatic Sciences
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• v.16 no.3
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• pp.159-164
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• 2013

The mouse bioassay and high performance liquid chromatography (HPLC) post-column oxidation method are different methods of quantifying paralytic shellfish poisoning toxins. In this study, we compared their ability to accurately quantify the toxicity levels in two types of field sample (oysters and mussels) with different toxin profiles for routine regulatory monitoring. A total of 72 samples were analyzed by both methods, 44 of which gave negative results, with readings under the limit of detection of the mouse bioassay ($40{\mu}g/100g$ saxitoxin [STX] eq). In 14 oysters, the major toxin components were gonyautoxin (GTX) 1, -2, -3, -4, -5, decarbamoylgonyautoxin-2 (dcGTX2), and decarbamoylsaxitoxin (dcSTX), while 14 mussels tested positive for dcSTX, GTX2, -3, -4, -5, dcGTX2, neosaxitoxin (NEO), STX, and dcSTX. When the results obtained by both methods were compared in two matrices, a better correlation ($r^2=0.9478$) was obtained for mussels than for oysters ($r^2=0.8244$). Additional studies are therefore needed in oysters to investigate the differences in the results obtained by both methods. Importantly, some samples with toxin levels around the legal limit gave inconsistent results using HPLC-based techniques, which could have a strong economic impact due to enforced harvest area closure. It should therefore be determined if all paralytic shellfish poisoning toxins can be quantified accurately by HPLC, and if the uncertainties of the method lead to doubts regarding regulatory limits.

• Steel and Composite Structures
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• v.34 no.1
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• pp.107-122
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• 2020

Moment resisting stub columns (MRSCs) have increasingly adopted in special moment-resisting frame (SMF) systems in steel building structures, especially in Asian countries. The MRSCs typically provide a lower deformation capacity compared to shear-panel stub columns, a limited post-yield stiffness, and severe strength degradation as adopting slender webs. A new MRSC design with cored configuration, consisting of a core-segment and two side-segments using different steel grades, has been proposed in the study to improve the demerits mentioned above. Several full-scale components of the cored MRSC were experimentally investigated focusing on the hysteretic performance of plastic hinges at the ends. The effects of the depths of the core-segment and the adopted reduced column section details on the hysteretic behavior of the components were examined. The measured hysteretic responses verified that the cored MRSC enabled to provide early yielding, great ductility and energy dissipation, enhanced post-yield stiffness and limited strength degradation due to local buckling of flanges. A parametric study upon the dimensions of the cored MRSC was then conducted using numerical discrete model validated by the measured responses. Finally, a set of model equations were established based on the results of the parametric analysis to accurately estimate strength backbone curves of the cored MRSCs under increasing-amplitude cyclic loadings.

• Plant Journal
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• v.13 no.2
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• pp.34-38
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• 2017

To reduce global warming, there are so many studies, investments and efforts. The Post Combustion $CO_2$ Capture technology is one of these efforts. But the technologies are having trouble with reducing operating prices. And CCS technology which is using amine solvent uses high price amine solvent. There is solvent losses naturally when operating plant. The solvent loss makes operating and maintenance price higher. In this study, how the washing column of treated flue gas affects the losses of amine solvent and operating was studied.