• Journal of the Korean Wood Science and Technology
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• v.36 no.4
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• pp.37-43
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• 2008

The research attempted to develop an eco-friendly wood adhesive based on vegetable oil (soybean oil), the renewable and sustainable natural resources, using ozonification technology for the chemical structure modification. The soybean oils (SBO) were reacted with $O_3$ at the rate of 7.13 g/h for different times, 15 minutes, 30 minutes, 60 minutes, and 120 minutes. Modified chemical structure of the ozonized SBOs were examined by Fourier transform Infrared (FT-IR) spectrum. The FT-IR spectrum of SBO had an absorbance peak at $3010cm^{-1}$ that is the characteristic peak of the unsaturated double bonds. As ozone treatment time increased, the peak of the double bond was disappeared and aldehyde or carboxyl peak appeared at $1700cm^{-1}$. The dry, wet, and cyclic boiling bond strengths of the ozonized SBO mixed with polymeric diphenylmethane-4, 4-diisocyanate (pMDI) were also investigated. In the dry shear test, all strengths met constantly the standard requirement of $7.0kgf/cm^2$ (KS F3101 2006). The bond strengths gradually increased with increasing ozone treatment time. The highest strength showed at 60 minutes ozone treatment and decreased values at 120 minutes. In the cyclic boiling shear test, 30, 60 and 120 minutes exceeded the standard requirement.

• Structural Engineering and Mechanics
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• v.30 no.6
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• pp.733-761
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• 2008

The failure of reinforced concrete structures in recent earthquakes caused concern about the performance of beam column joints. Confinement of joint is one of the ways to improve the performance of beam column joints during earthquakes. This paper describes an experimental study of exterior beam-column joints with two non-conventional reinforcement arrangements. One exterior beam-column joint of a six story building in seismic zone III of India was designed for earthquake loading. The transverse reinforcement of the joint assemblages were detailed as per IS 13920:1993 and IS 456:2000 respectively. The proposed nonconventional reinforcement was provided in the form of diagonal reinforcement on the faces of the joint, as a replacement of stirrups in the joint region for joints detailed as per IS 13920 and as additional reinforcement for joints detailed as per IS 456. These newly proposed detailing have the basic advantage of reducing the reinforcement congestion at the joint region. In order to study and compare the performance of joint with different detailing, four types of one-third scale specimens were cast (two numbers in each type). The main objective of the present study is to investigate the effectiveness of the proposed reinforcement detailing. All the specimens were tested under reverse cyclic loading, with appropriate axial load. From the test results, it was found that the beam-column joint having confining reinforcement as per IS: 456 with nonconventional detailing performed well. Test results indicate that the non-conventionally detailed specimens, Type 2 and Type 4 have an improvement in average ductility of 16% and 119% than their conventionally detailed counter parts (Type1 and Type 3). Further, the joint shear capacity of the Type 2 and Type 4 specimens are improved by 8.4% and 15.6% than the corresponding specimens of Type 1 and Type 3 respectively. The present study proposes a closed form expression to compute the yield and ultimate load of the system. This is accomplished using the theory of statics and the failure pattern observed during testing. Good correlation is found between the theoretical and experimental results.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.109-113
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• 2002

Interfacial and electrical properties for the carbon fiber reinforced epoxy-amine terminated (AT) PEI composites were performed using microdroplet test and electrical resistance measurements. As AT PEI content increased, the fracture toughness of epoxy-AT PEI matrix increased, and IFSS was improved due to the improved toughness and energy absorption mechanisms of AT PEI. The microdroplet in the carbon fiber/neat epoxy composite showed brittle microfailure mode. At 15 wt% AT PEI content, ductile microfailure mode appeared because of improved fracture toughness. After curing, the changes of electrical resistance (ΔR) with increasing AT PEI content increased gradually because of thermal shrinkage. The matrix fracture toughness was correlated to IFSS, TEC and electrical resistance. In cyclic strain test, the maximum stress and their slope of the neat epoxy case were higher than those of 15 wt% AT PEI. The results obtained from electrical resistance measurements under curing process and reversible stress and strain were consistent well with matrix toughness properties.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.1
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• pp.55-60
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• 2010

The honeycomb composite joint structure designed for application to a tilting KTX railroad car body is subjected to bending loads of a cantilever type. Honeycomb sandwich composite panel-joint attached in the real tilting car body was fabricated and sectioned as several beam-joint specimens for the bending test. The fracture behaviors of these specimens under static loads were different from those under cyclic loads. Static bending loads caused shear deformation and fracture in the honeycomb core region, while fatigue cyclic bend loading caused delamination along the interface between the composite skin and the honeycomb core, and/or caused a fracture in the welded part jointed with the steel under-frame. These fracture behaviors could occur in other industrial honeycomb composite joints with similar sub-structures, and be used for improving design parameters of a honeycomb composite joint structure.

• Earthquakes and Structures
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• v.12 no.1
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• pp.119-133
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• 2017

Several theoretical and analytical formulations for the prediction of shear strength in reinforced concrete (RC) beam-to-column joints have been recently developed. Some of these predictive models are included in the most recent seismic codes and currently used in practical design. On the other hand, the influence of the stiffness and strength degradations in RC joints on the seismic performance of RC framed buildings has been only marginally studied, and it is generally neglected in practice-oriented seismic analysis. To investigate such influence, this paper proposes a numerical description for representing the cyclic response of RC exterior joints. This is then used in nonlinear numerical simulations of RC frames subjected to earthquake loading. According to the proposed strategy, RC joints are modelled using nonlinear rotational spring elements with strength and stiffness degradations and limited ductility under cyclic loading. The proposed joint model has been firstly calibrated against the results from experimental tests on 12 RC exterior joints. Subsequently, nonlinear static and dynamic analyses have been carried out on two-, three- and four-storey RC frames, which represent realistic existing structures designed according to old standards. The numerical results confirm that the global seismic response of the analysed RC frames is strongly affected by the hysteretic damage in the beam-to-column joints, which determines the failure mode of the frames. This highlights that neglecting the effects of joints damage may potentially lead to non-conservative seismic assessment of existing RC framed structures.

• Earthquakes and Structures
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• v.18 no.2
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• pp.215-222
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• 2020

In this paper, slit steel rubber bearing is presented as an innovative seismic isolator device. In this type of isolator, slit steel damper is an energy dissipation device. Its advantages in comparison with that of the lead rubber bearing are its simplicity in manufacturing process and replacement of its yielding parts. Also, slit steel rubber bearing has the same ability to dissipate energy with smaller value of displacement. Using finite element method in ABAQUS software, a parametric study is done on the performance of this bearing. Three different kinds of isolator with three different values of strut width, 9, 12 and 15 mm, three values of thickness, 4, 6 and 8 mm and two steel types with different yield stress are assessed. Effects of these parameters on the performance characteristics of slit steel rubber bearing are studied. It is shown that by decreasing the thickness and strut width and by selecting the material with lower yield stress, values of effective stiffness, energy dissipation capacity and lateral force in the isolator reduce but equivalent viscous damping is not affected significantly. Thus, by choosing appropriate values for thickness, strut width and slit steel damper yield stress, an isolator with the desired behavior can be achieved. Finally, the performance of an 8-storey frame with the proposed isolator is compared with the same frame equipped with LRB. Results show that SSRB is successful in base shear reduction of structure in a different way from LRB.

• Journal of the Korean GEO-environmental Society
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• v.8 no.5
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• pp.23-29
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• 2007

The performance of the improved soil against liquefaction depends upon the chemical density, and it has been decided on the basis of the unconfined compressive strength of the improved soil up to date. On the other hand, several authors have proposed that the stiffness degradation could be treated as the clue for the judgment of the possibility of liquefaction. In this study, therefore, the stiffness degradation of the improved soil was estimated as the resistance against liquefaction by using the strain controlled cyclic triaxial test equipment. Based on the test results, it is concluded that the chemically treated sand can resist against the liquefaction in aspect of the reduction in effective stress and in the stiffness. Furthermore, even in the case of low chemical density, such as 2% in this study, has enough liquefaction resistance when compared with the 5~6% which often used in practical design. Considering this fact, the design of chemical density based on the unconfined strength can lead the overestimation in chemical density, and chemical density can be reduced when considering the stiffness reduction shown in this study.

• Steel and Composite Structures
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• v.22 no.1
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• pp.141-159
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• 2016

Commonly in steel frames, steel beam and concrete slab are connected together by shear keys to work as a unit member which is called composite beam. When a composite beam is subjected to positive bending, flexural strength and stiffness of the beam can be increased due to "composite action". At the same time despite these advantages, composite action increases the strain at the beam bottom flange and it might affect beam plastic rotation capacity. This paper presents results of study on the rotation capacity of composite beam connected to Rectangular Hollow Section (RHS) column in the steel moment resisting frame buildings. Due to out-of-plane deformation of column flange, moment transfer efficiency of web connection is reduced and this results in reduction of beam plastic rotation capacity. In order to investigate the effects of width-to-thickness ratio (B/t) of RHS column on the rotation capacity of composite beam, cyclic loading tests were conducted on three full scale beam-to-column subassemblies. Detailed study on the different steel beam damages and concrete slab damages are presented. Experimental data showed the importance of this parameter of RHS column on the seismic behavior of composite beams. It is found that occurrence of severe concrete bearing crush at the face of RHS column of specimen with smaller width-to-thickness ratio resulted in considerable reduction on the rate of strain increase in the bottom flange. This behavior resulted in considerable improvement of rotation capacity of this specimen compared with composite and even bare steel beam connected to the RHS column with larger width-to-thickness ratio.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.25-32
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• 2016

The pile-cap connection part which transfers foundation loads through pile body is critical element regarding flexural and shear force because the change of area, stress, and stiffness occurs in the this region suddenly. The purpose of this study is to investigate the structural behavior of pile-cap connection dependent on fabrication methods using conventional PHC pile and composite PHC pile. A series of test under cyclic lateral load was performed and the connection behavior was discussed. From the test results, it was found that the initial rotational stiffness of pile-cap connection was affected by the length of pile-head inserted in footing and the location of longitudinal reinforcing bars. The types of pile and location of longitudinal reinforcing bars governed the behavior of pile-cap connection regarding load-carrying capacity, ductility, and energy dissipation.

• Journal of the Korea Concrete Institute
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• v.18 no.4 s.94
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• pp.497-506
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• 2006

The precast concrete beam-column connectors for the high-rise office buildings were investigated experimentally in this study. The specimens of general precast beam-column connector which is used in a domestic site, specimen of DDC(dywidag ductile connectors) of Germany, and specimen of DDC with post-tensioning and modified DDC with post-tensioning were constructed and tested to verify the safety. The DDC with and without post-tensioning showed reliable joint strength and ductility but failed in critical inclined shear crackings at the column. The modified one showed better behaviors in tests because they did not show critical column crackings at failure. The use of prestressing did not helpful significantly to increase the strength and ductility of connectors but helpful only to develop self-centering behavior for stability.