• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.1
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• pp.231-237
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• 2004

Most of the masonry buildings have many structural defects under an earthquake load due to the small tensile force and ductility. In the foreign countries there are many the reinforcing methods of masonry buildings, but the glass fiber sheet reinforcements must be used due to various conditions in Korea. The purpose of this paper is to estimate the seismic capacity of masonry buildings damaged by earthquake and reinforced by Glass Fiber Sheet. On the basis of test results, the maximum base shear force and deformation of the masonry building with GFS were remarkably increased. From the comparison by existing strength equations and test data, the new strength equation of reinforced masonry buildings with GFS was developed.

• Earthquakes and Structures
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• v.7 no.3
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• pp.349-365
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• 2014

The dynamic response of structures under extremely short duration dynamic loads is of great concern nowadays. This paper investigates structures' response as well as the associated structural damage to explosive loads considering and ignoring the supporting soil flexibility effect. In the analysis, buildings are modeled by two alternate approaches namely, (1) building with fixed supports, (2) building with supports accounting for soil-flexibility. A lumped parameter model with spring-dashpot elements is incorporated at the base of the building model to simulate the horizontal and rotational movements of supporting soil. The soil flexibility for various shear wave velocities has been considered in the investigation. In addition, the influence of variation of lateral natural periods of building models on the obtained response and peak response time-histories besides damage indices has also been investigated under blast loads with different peak over static pressures. The Dynamic response is obtained by solving the governing equations of motion of the considered building model using a developed Matlab code based on the finite element toolbox CALFEM. The predicted results expressed in time-domain by the building model incorporating SSI effect are compared with the corresponding model results ignoring soil flexibility effect. The results show that the effect of surrounding soil medium leads to significant changes in the obtained dynamic response of the considered systems and hence cannot be simply ignored in damage assessment and response time-histories of structures where it increases response and amplifies damage of structures subjected to blast loads. Moreover, the numerical results provide an understanding of level of damage of structure through the computed damage indices.

• Corrosion Science and Technology
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• v.18 no.3
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• pp.92-101
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• 2019

This study investigates how rivet head height affects the corrosion performance of carbon fiber reinforced plastic (CFRP) to aluminum alloy self-piercing riveted joints. Specimens with two different head heights were prepared. A rivet head protruding out of the top CFRP laminate forms the proud head height while a rivet head penetrating into the top CFRP generates the flush head height. The salt spray test evaluated corrosion performance. The flush head joints suffered from severe corrosion on the rivet head. Thus, the tensile shear load of flush head joints was substantially reduced. Electrochemical corrosion tests investigated the corrosion mechanisms. The deeper indentation of the flush head height damaged the CFRP around the rivet head. The exposure of damaged fibers from the matrix increased the cathodic potential of local CFRP. The increased potential of damaged CFRP accelerated the galvanic corrosion of the rivet head. After the rivet head coating material corroded, a strong galvanic couple was formed between the rivet head base metal (boron steel) and the damaged CFRP, further accelerating the flush rivet head corrosion. The results of this study suggest that rivet head flushness should be avoided to enhance the corrosion performance of CFRP to aluminum alloy self-piercing riveted joints.

• Journal of the Korean Geotechnical Society
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• v.21 no.2
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• pp.67-84
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• 2005

This research was conducted to evaluate the effectiveness of reinforcement for nearly saturated soft clay compaction. The effectiveness was investigated by roller compaction test using nearly saturated clay specimens. The nearly saturated condition was obtained by submerging clay in the water for 12 hours. High water content specimens were compacted in plane strain condition by a steel roller. A specimen was compacted by four 5 cm horizontal layers. Specimens were prepared fur both reinforced and unreinforced cases to evaluate the effectiveness of reinforcement. Used reinforcement is a composite consisted of both woven and non-woven geotextile. The composite usually provides drainage and tensile reinforcement to hi인 water-contented clay so that it increases bearing capacity. Therefore, large compaction load can be applied to reinforced clay and it achieves higher density effectively. The reinforcement also increases compaction efficiency because it reduces the ratio between shear and vertical forces during compaction process. The maximum vertical stress on the base of specimen usually decreased with higher compaction thickness. The reinforcement increases soil stiffness under the compaction roller and it initiates stress concentration. As a result, it maintains higher vertical stress level on the base of specimen that provides better compaction characteristics. Based on test results, it can be concluded that the reinforcement is essential to achieve effective compaction on soft clay.

• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.2 s.13
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• pp.47-52
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• 2004

Whereas The masonry buildings are safe under gravity loads, most of the masonry buildings in Korea have many structural defects under a lateral load due to an earthquake acceleration. But there is no earthquake resistant design code for the Masonry in Korea. Therefore it may be necessary to be set up an seismic code and be suggested for reinforcing methods for existing masonry buildings. The purpose of this paper is to investigate seismic capacity of reinforced masonry buildings subjected to earthquake load. The typical two models of the masonry building in Korea are selected through a site investigation. On the basis of test results, the fiber reinforcing effect of the two models was considerable. The maximum base shear force and deformation capacity for RM were remarkably increased. It was found that the pier rocking failure was a dominant mode for the RM buildings during a seismic excitation.

• Steel and Composite Structures
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• v.21 no.4
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• pp.863-882
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• 2016

This study aims to introduce a new bracing system by which even super-wide frames with large openings can be braced. The proposed system, hereafter called Cable-Pulley Brace (CPB), is a tension-only bracing system with a rectilinear configuration. In CPB, a wire rope passes through a rectilinear path around the opening(s) and connects the lower corner of the frame to its opposite upper one. CPB is a secondary load resisting system with a nonlinear-elastic hysteretic behavior due to its initial pre-tension load. As a result, the required energy dissipation would be provided by the MRF itself, and the main intention of using CPB is to contribute to the initial and post-yield stiffness of the whole system. Using a stiffness calibration technique, optimum placement of the CPBs is discussed to yield a uniform displacement demand along the height of the structure. A displacement-based design procedure is proposed by which the MRF with CPB can be designed to achieve a uniform distribution of inter-story drifts with predefined values. Obtained results indicated that CPB leads to significant reductions in maximum and residual deformations of the MRF at the expense of minor increase in the maximum base shear and developed axial force demands in the columns. In the case of a typical 5-story residential building, compared to SMRF system, CPB system reduces maximum amounts of inter-story and residual drifts by 35% and 70%, respectively. Moreover, openings of the frame are not interrupted by the CPB. This is the most appealing feature of the proposed bracing system from architectural point of view.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.255-266
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• 1999

The objective of this experiment is to observe the elastic and inelastic behaviors of high-rise reinforced concrete frames having non-seismic details. To do this, a building frame designed according to Korean seismic code and detailed in the Korean conventional practice was selected. A 1:12 scale plane frame model was manufactured according to similitude law. A reversed lateral load test and a monotonic pushover test were performed under the displacement control. To simulate the earthquake effects, the lateral force distribution was maintained to be an inverse triangle by using a whiffle tree. From the tests, base shears, crack pattern, local rotations in the ends of critical members and the relations between interstory drift versus story shear are obtained. Based on test results, conclusions are drawn on the implications of the elastic and inelastic behaviors of a high-rise reinforced concrete frame having non-seismic details.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1C
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• pp.41-51
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• 2008

The load distribution and deformation of single piles which is embedded in Jumunjin sand and Kimhae clay are investigated, based on small scale model tests. Special attention is given to the consideration of flexural rigidity in laterally loaded piles. To consider the flexural rigidity of the pile, tests are performed with the aluminium piles of three different length under different relative densities and undrained shear strength. The test results indicate that the initial slope from the results of tests is proportional to the depth and pile-soil rigidity in both soils. But the increasing rate of the initial slope in the clay is less than in the sand. In addition, the soil resistance is more related to the depth and soil condition than the pile rigidity. Base on the test results, an empirical formula is proposed, which is good agreement with previously published small scale model test and field lateral load test.

• Advances in nano research
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• v.16 no.2
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• pp.127-140
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• 2024

Upon direct/indirect exposure to flame or heat, composite structures may burn or thermally buckle. This issue becomes more important in the natural fiber-based composite structures with higher flammability and lower mechanical properties. The main goal of the present study was to obtain an optimal eco-friendly composite system with low flammability and high thermal buckling resistance. The studied composite consisted of polypropylene (PP) and short abaca fiber (AF) with eggshell powder (ESP) and halloysite clay nanotubes (HNTs) additives. An optimal base composite, consisting of 30 wt.% AF and 70 wt.% PP, abbreviated as OAP, was initially introduced based on burning rate (BR) and the Young's modulus determined by horizontal burning test (HBT) and tensile test, respectively. The effects of adding ESP to the base composite were then investigated with the same experimental tests. The results indicated that though the BR significantly decreased with the increase of ESP content up to 6 wt.%, it had a very destructive influence on the stiffness of the composite. To compensate for the damaging effect of ESP, small amount of HNT was used. The performance of OAP composite with 6 wt.% ESP and 3 wt.% HNT (OAPEH) was explored by conducting HBT, cone calorimeter test (CCT) and tensile test. The experimental results indicated a 9~23 % reduction in almost all flammability parameters such as heat release rate (HRR), total heat released (THR), maximum average rate of heat emission (MARHE), total smoke released (TSR), total smoke production (TSP), and mass loss (ML) during combustion. Furthermore, the combination of 6 wt.% ESP and 3 wt.% HNT reduced the stiffness of OAP to an insignificant amount by maximum 3%. Moreover, the char residue analysis revealed the distinct differences in the formation of char between AF/PP and AF/PP/ESP/HNT composites. Afterward, dilatometry test was carried out to examine the coefficient of thermal expansion (CTE) of OAP and OAPEH samples. The obtained results showed that the CTE of OAPEH composite was about 18% less than that of OAP. Finally, a theoretical model was used based on first-order shear deformation theory (FSDT) to predict the critical bucking temperatures of the OAP and OAPEH composite plates. It was shown that in the absence of mechanical load, the critical buckling temperatures of OAPEH composite plates were higher than those of OAP composites, such that the difference between the buckling temperatures increased with the increase of thickness. On the contrary, the positive effect of CTE reduction on the buckling temperature decreased by raising the axial compressive mechanical load on the composite plates which can be assigned to the reduction of stiffness after the incorporation of ESP. The results of present study generally stated that a suitable combination of AF, PP, ESP, and HNT can result in a relatively optimal and environmentally friendly composite with proper flame and thermal buckling resistance with no significant decline in the stiffness.

• Journal of Welding and Joining
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• v.29 no.6
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• pp.56-64
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• 2011

Friction stir spot welding between 5454 aluminum alloy sheets with the different thicknesses of 1.4 and 1.0 mm was performed. In the welding process, the tool for welding was rotated ranging from 500 to 2500, and plunged to the depth of 1.8 mm under a constant tool plunge speed of 100 mm/min. And then, the rotating tool was maintained at the plunge depth during the dwell time ranging from 0 to 7 sec. The pull-out speed of the rotating tool was 100 mm/min. The increase of tool rotation speed resulted in the change of the macrostructure of friction-stir-spot-welded zone, especially the geometry of welding interface. The results of the tensile shear test showed that the total displacement and toughness of the welds were increased with the increase of the tool rotation speed, although the maximum tensile shear load was decreased. However, the change in the dwell time at the plunge depth of the tool did not produce the remarkable variation in the macrostructure and mechanical properties of the welds. In all cases, the average hardness in friction-stir-spot-welded zone was higher than that of the base metal zone. By the friction stir spot welding technique, the welds with the excellent mechanical properties than the mechanically-clinched joints could be obtained.