• Steel and Composite Structures
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• v.21 no.5
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• pp.1157-1182
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• 2016

A newly puzzle shape of crestbond rib shear connector is a type of ductile perfobond rib shear connector. This shear connector has some advantages, including relatively easy rebar installation and cutting, as well as the higher shear resistance strength. Thus, this study proposed a newly puzzle shape of crestbond rib with a "${\mho}$" shape, and its shear resistance behaviors and shear strengths were examined using push-out tests. Five main parameters were considered in the push-out specimens to evaluate the effects of shear resistance parameters such as the dimensions of the crestbond rib, transverse rebars in the crestbond dowel, concrete strength, rebar strength, and dowel action on the shear strength. The shear loading test results were used to compare the changes in the shear behaviors, failure modes, and shear strengths. It was found that the concrete strength and number of transverse rebars in the crestbond rib were significantly related to its shear resistance. After the initial bearing resistance behavior of the concrete dowel, a relative slip occurred in all the specimens. However, its rigid behavior to shear loading decreased the ductility of the shear connection. The cross-sectional area of the crestbond rib was also shown to have a minor effect on the shear resistance of the crestbond rib shear connector. The failure mechanism of the crestbond rib shear connector was complex, and included compression, shear, and tension. As a failure mode, a crack was initiated in the middle of the concrete slab in a vertical direction, and propagated with increasing shear load. Then, horizontal cracks occurred and propagated to the front and rear faces of the specimens. Based on the results of this study, a design shear strength equation was proposed and compared with previously suggested equations.

• Steel and Composite Structures
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• v.21 no.5
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• pp.1017-1029
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• 2016

When a welded circular hollow section (CHS) tubular joint is subjected to brace axial loading, failure position is located usually at the weld toe on the chord surface due to the weak flexural stiffness of the thin-walled chord. The failure mode is local yielding or buckling in most cases for a tubular joint subjected to axial load at the brace end. Especially when a cyclic axial load is applied, fracture failure at the weld toe may occur because both high stress concentration and welding residual stress along the brace/chord intersection cause the material in this region to become brittle. To improve the ductility as well as to increase the static strength, a tubular joint can be reinforced by increasing the chord thickness locally near the brace/chord intersection. Both experimental investigation and finite element analysis have been carried out to study the hysteretic behaviour of the reinforced tubular joint. In the experimental study, the hysteretic performance of two full-scale circular tubular T-joints subjected to cyclic load in the axial direction of the brace was investigated. The two specimens include a reinforced specimen by increasing the wall thickness of the chord locally at the brace/chord intersection and a corresponding un-reinforced specimen. The hysteretic loops are obtained from the measured load-displacement curves. Based on the hysteretic curves, it is found that the reinforced specimen is more ductile than the un-reinforced one because no fracture failure is observed after experiencing similar loading cycles. The area enclosed by the hysteretic curves of the reinforced specimen is much bigger, which shows that more energy can be dissipated by the reinforced specimen to indicate the advantage of the reinforcing method in resisting seismic action. Additionally, finite element analysis is carried out to study the effect of the thickness and the length of the reinforced chord segment on the hysteretic behaviour of CHS tubular T-joints. The optimized reinforcing method is recommended for design purposes.

• Steel and Composite Structures
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• v.36 no.2
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• pp.163-177
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• 2020

Concentrically Braced Frames (CBFs) are commonly used in the construction of steel structures because of their ease of implementation, rigidity, low lateral displacement, and cost-effectiveness. However, the principal disadvantage of this kind of braced frame is the inability to provide deformation capacity (ductility) and buckling of bracing elements before yielding. This paper aims to present a novel Composite Buckling Restrained Fuse (CBRF) to be utilized as a bracing segment in concentrically braced frames that allows higher ductility and removes premature buckling. The proposed CBRF with relatively small dimensions is an enhancement on the Reduced Length Buckling Restrained Braces (RL-BRBs), consists of steel core and additional tensile elements embedded in a concrete encasement. Employing tensile elements in this composite fuse with a new configuration enhances the energy dissipation efficiency and removes the tensile strength limitations that exist in bracing elements that contain RL-BRBs. Here, the optimal length of the CBRF is computed by considering the anticipated strain demand and the low-cyclic fatigue life of the core under standard loading protocol. An experimental program is conducted to explore the seismic behavior of the suggested CBRF compare with an RL-BRB specimen under gradually increased cyclic loading. Moreover, Hysteretic responses of the specimens are evaluated to calculate the design parameters such as energy dissipation potential, strength adjustment factors, and equivalent viscous damping. The findings show that the suggested fuse possess a ductile behavior with high energy absorption and sufficient resistance and a reasonably stable hysteresis response under compression and tension.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.12
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• pp.109-116
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• 2005

Elastic-plastic structural analysis for regenerative cooling chamber of liquid rocket thrust chamber is performed. Uniaxial tension test is also conducted for the copper alloy in order to get material data necessary for the structure analysis. The results of uniaxial tension test reveal that copper alloy become ductile after brazing process and flow stress becomes lower as temperature becomes higher. As a result of structural analysis using the material data, the deformation of cooling channel is more increased by thermal load than by internal pressure of cooling fluid. Therefore, the results of analysis show that structural stability and cooling performance of combustion thrust chamber which is designed to endure mechanical load and minimized a channel thickness are improved by decreased thermal load as possible.

• Earthquakes and Structures
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• v.8 no.5
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• pp.1039-1054
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• 2015

The purpose of this study was to evaluate the seismic performance of weak-axis column-tree type connections used in steel moment frames. These connections are composed of a shop-welded and fieldbolted steel structure and can improve welding quality. On this basis, column-tree type connections are widely used in steel moment resisting frames in Korea and Japan. In this study, splices designed with a semirigid concept regarding the seismic performance of column-tree connections were experimentally evaluated. The structures can absorb energy in an inelastic state rather than the elastic state of the structures by the capacity design method. For this reason, the plastic hinge might be located at the splice connection at the weak-axis column-tree connection by reducing the splice plate thickness. The main variable was the distance from the edge of the column flange to the beam splice. CTY series specimens having column-tree connections with splice length of 600 mm and 900 mm were designed, respectively. For comparison with two specimens with the main variable, a base specimen with a weak-axis column-tree connection was fabricated and tested. The test results of three full-scale test specimens showed that the CTY series specimens successfully developed ductile behavior without brittle fracture until 5% story drift ratio. Although the base specimen reached a 5% story drift ratio, brittle fracture was detected at the backing bar near the beam-to-column connection. Comparing the energy dissipation capacity for each specimen, the CTY series specimens dissipated more energy than the base specimen.

• Journal of Korean Society of Steel Construction
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• v.27 no.1
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• pp.1-12
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• 2015

Well-designed bolted connections can exhibit excellent ductile behavior through bearing mechanism until the occurrence of bolt shear rupture. The ultimate strength analysis of eccentric bolted connections is an economical and mechanistic approach which uses such ductility. However, the bolt load-deformation relationship, which forms basis of the current practice, is based on very limited combinations of bolt and steel materials. The primary objective of this study was to establish the general bolt force-deformation relationship based on systematic single-bolt bearing connection tests. The test results showed that the projected area of the bolt hole and the strength and thickness of the plate to be connected are the main factors affecting the force-deformation relationship. The results of this study can be used for the instantaneous center of rotation method (ICRM) to achieve more accurate analysis and economical design of a variety of group-bolted connections subjected to eccentric shear.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.10-17
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• 2004

Shear tests were performed on four ends of full scale U-type beams which were designed by optimum process for the depth with a live load of 4903Pa. The ratio of width to depth of full scale 10.5 m-span, composite U-type beams with topping concrete was greater than 2. Following conclusions were obtained from the evaluation on the shear performance of these precast prestressed beams. 1) Those composite U-type beams performed homogeneously up to the failure load, and conformed to ACI Strength design methods in shear and flexural behaviors. 2) The anchorage requirements on development length of strand In the ACI Provisions preyed to be a standard to determine a failure pattern within the limited test results of the shallow U-type beams. 3) Those all shear crackings developed from the end of the beams did not lead to anchorage failure. However, initiated strand slip may leads the bond failure by increasing the size of diagonal shear crackings. 4) The flexural mild reinforcement around the vertical center of beam section was effective for developments of a ductile failure.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.156-163
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• 2002

Hollow core slabs generally have not been used for a bridge or a parking slab in Korea. In this study, high performance hollow core slabs, which have been the most thick one in domestic are re-designed and examined for practical use. Flexural tests were performed on four 315mm deep hollow core slabs to investigate adaptability for high vehicle live loadings and composite action with topping concrete. The precast slabs were pre-tensioned with ten strands of 1/2 inch diameter at the lower of slab and four strands of 1/2 inch diameter at the upper of slab, and cast with 80 mm deep topping concrete. Tested hollow core slabs showed ductile failure behaviors which were conformed to the current Ultimate Strength Design Method for a span of 10m up to the live load of 1,000 kgf/㎡. The rectangular md round shear cotters which were used for the composite action between precast and topping concrete, developed sufficient strengths because cracking, even micro had not been developed at the end of slabs up to the pure flexural tensile failure.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.5
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• pp.469-485
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• 2016

The failure of rock mass around deep tunnel, different from shallow tunnel largely affected by discontinuities, is dominated by magnitudes and directions of stresses, and the failures dominated by stresses can be divided into ductile and brittle features according to the conditions of stresses and the characteristics of rock mass. It is important to know the range and the depth of the V-shaped notch type failure resulted from the brittle failure, such as spalling, slabbing and rock burst, because they are the main factors for the design of excavation and support of deep tunnels. The main features of brittle failure are that it consists of cohesion loss and friction mobilization according to the stress condition, and is progressive. In this paper, a three-dimensional numerical model has been developed in order to simulate the brittle behavior of rock mass around deep tunnel by introducing the bi-linear failure envelope cut off, elastic-elastoplastic coupling and gradual spread of elastoplastic regions. By performing a series of numerical analyses, it is shown that the depths of failure estimated by this model coincide with an empirical relation from a case study.

• Steel and Composite Structures
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• v.36 no.3
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• pp.261-272
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• 2020

A novel precast concrete-encased steel composite beam, which can be abbreviated as PCES beam, is introduced in this paper. In order to investigate the shear behavior of this PCES beam, a test of eight full-scale PCES beam specimens was carried out, in which the specimens were subjected to positive bending moment or negative bending moment, respectively. The factors which affected the shear behavior, such as the shear span-to-depth aspect ratio and the existence of concrete flange, were taken into account. During the test, the load-deflection curves of the test specimens were recorded, while the crack propagation patterns together with the failure patterns were observed as well. From the test results, it could be concluded that the tested PCES beams could all exhibit ductile shear behavior, and the innovative shear connectors between the precast concrete and cast-in-place concrete, namely the precast concrete transverse diaphragms, were verified to be effective. Then, based on the shear deformation compatibility, a theoretical model for predicting the shear capacity of the proposed PCES beams was put forward and verified to be valid with the good agreement of the shear capacities calculated using the proposed method and those from the experiments. Finally, in order to facilitate the preliminary design in practical applications, a simplified calculation method for predicting the shear capacity of the proposed PCES beams was also put forward and validated using available test results.