• Journal of Korean Society of Steel Construction
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• v.15 no.2
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• pp.167-174
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• 2003

This paper presented the results of cyclic loading tests of 7 full-scale beams to column subassemblages with improved connection detail i.e., fillets of the stiffening plates at the column corners and ends of the stiffener-to-beam flange weld. Major findings from the test results were: (1) Fillets reduced the stress concentrations that may cause early brittle fractures and considerably improved the cyclic performance compared to the detail without fillets. (2) As the width of the stiffening plate increased, the stiffness and peak strength increased and energy dissipation capacity decreased. (3) While all specimens failed by a fracture, they could develop a total rotation of 0.04 radian required for special moment resisting frames.

• Computers and Concrete
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• v.22 no.3
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• pp.305-317
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• 2018

Steel reinforced Engineered Cementitious Composite (ECC) components have been proposed for seismic structural applications, for example in coupling beams, infill panels, joints, columns, and flexural members. The development of strain in the steel reinforcement of cementitious components has been shown to vary based on both the steel reinforcement ratio and the applied deformation history. Strain in the steel reinforcement of reinforced ECC components is an important structural response metric because ultimate failure is often by fracture of the steel reinforcement. A recently proposed bond-slip model has been successfully calibrated to cyclically tested reinforced ECC beams wherein the deformation history contained monotonically increasing cycles. This paper reports simulations of two-dimensional finite element models of reinforced ECC beams to determine the appropriateness and significance of altering a phenomenological bond-slip model based on the applied deformation history. The numerical simulations with various values of post-peak bond-slip softening stiffness are compared to experimental results. Varying the post-peak bond-slip softening stiffness had little effect on the cracking patterns and hysteretic response of the reinforced ECC flexural models tested, which consisted of two different steel reinforcement ratios subjected to two different deformation histories. Varying the post-peak bond-slip softening stiffness did, however, affect the magnitude of strain and the length of reinforcing bar that strain-hardened. Overall, a numerical model with a constant bond-slip model represented well various responses in reinforced ECC beams with multiple steel reinforcement ratios subjected to different deformation histories.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.205-208
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• 2008

Steel-embedded composite piers can enhance the resistance of core concrete by confinement of the steel elements and also can strengthen the stability of the embedded steel elements by concrete parts, so that the resistance of the composite members and seismic requirements can be provided without increasing section dimensions and self-weight. While modular composite piers with single segment do not need prestressing, precast segment composite piers with multiple segments need to have prestressing to prevent excessive cracking at the joints. Initial stresses and deformation by the introduced prestress are changed by long-term properties of concrete and need to be considered in the design. This paper deals with the prestress losses by the measurement of load cells, strains of reinforcements, concrete and embedded steel tubes.

• International Journal of Concrete Structures and Materials
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• v.9 no.4
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• pp.401-413
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• 2015

In this study the progressive collapse resisting capacity of a RC beam-column subassemblage with and without strengthening was investigated. Total of five specimens were tested; two unreinforced specimens, the one designed as gravity load-resisting system and the other as seismic load-resisting system, and three specimens reinforced with: (i) bonded strand, (ii) unbonded strand, and (iii) side steel plates with stud bolts. The two-span subassemblages were designed as part of an eight-story RC building. Monotonically increasing load was applied at the middle column of the specimens and the force-displacement relationships were plotted. It was observed that the gravity load-resisting specimen failed by fractures of re-bars in the beams. In the other specimens no failure was observed until the maximum displacement capacity of the actuator was reached. Highest strength was observed in the structure with unbonded strand. The test result of the specimen with side steel plates in beam-column joints showed that the force-displacement curve increased without fracture of re-bars. Based on the test results it was concluded that the progressive collapse resisting capacity of a RC frame could be significantly enhanced using unbonded strands or side plates with stud bolts.

• Structural Engineering and Mechanics
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• v.59 no.2
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• pp.209-226
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• 2016

Integral bridges are typically designed with flexible foundations that include one row of piles. The construction of integral bridges solves difficulties due to the maintenance of expansion joints and bearings during serviceability. It causes integral bridges to become more economic comparing with conventional bridges. Research has been focused not only to enhance the seismic performance of newly designed bridges, but also to develop retrofit strategies for existing ones. The local performance of the pile to abutment connection will have a major effect on the performance of the structure and the embedment length of pile inside the abutment has a key role to provide shear and flexural resistance of pile-abutment connections. In this paper, a simple method was developed to estimate the initial value of embedment length of the pile for retrofitting of specimens. Four specimens of pile-abutment connections were constructed with different embedment lengths of pile inside the abutment to evaluate their performances. The results of the experimentation in conjunction with numerical and analytical studies showed that retrofitting pile-abutment connections with CFRP wraps increased the strength of the connection up to 86%. Also, designed connections with the proposed method had sufficient resistance against lateral load.

• Steel and Composite Structures
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• v.30 no.3
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• pp.271-280
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• 2019

In this paper, numerical and experimental assessments have been conducted in order to investigate the capability of using CFRP for the seismic capacity improvement and relocation of plastic hinge in reinforced concrete connections. Two scaled down exterior reinforced concrete beam to column connections have been used. These two connections from a strengthened moment frame have been tested under uniformly distributed load before and after optimization. The results of experimental tests have been used to verify the accuracy of numerical modeling using computational ABAQUS software. Application of FRP plate on the web of the beam in connections to improve its capacity is of interest in this paper. Several parametric studies were carried out for CFRP reinforced samples, with different lengths and thicknesses in order to relocate the plastic hinge away from the face of the column.

• Journal of Korean Association for Spatial Structures
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• v.22 no.4
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• pp.99-107
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• 2022

Existing reinforced concrete building structures constructed before 1988 have seismically-deficient reinforcing details, which can lead to the premature failure of the columns and beam-column joints. The premature failure was resulted from the inadequate bonding performance between the reinforcing bars and surrounding concrete on the main structural elements. This paper aims to quantify the bond-slip effect on the dynamic responses of reinforced concrete frame models using finite element analyses. The bond-slip behavior was modeled using an one-dimensional slide line model in LS-DYNA. The bond-slip models were varied with the bonding conditions and failure modes, and implemented to the well-validated finite element models. The dynamic responses of the frame models with the several bonding conditions were compared to the validated models reproducing the actual behavior. It verifies that the bond-slip effects significantly affected the dynamic responses of the reinforced concrete building structures.

• Earthquakes and Structures
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• v.26 no.5
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• pp.363-382
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• 2024

In India's north-eastern region, low-strength autoclaved aerated concrete (AAC) blocks are widely used for constructing masonry structures, making them susceptible to lateral forces due to their low tensile and shear strengths and brittleness nature. The absence of earthquake-resistant attributes further compromises their resilience during seismic events. An economically viable solution to enhance the structural integrity of these masonry structures involves integrating steel wire mesh within the masonry mortar joints. This study investigates the in-plane shear behaviour of AAC masonry by employing two approaches: incorporating steel wire mesh within the masonry bed joint "BJ" and the masonry bed and head joint "BHJ". These approaches aim to augment strength and ductility, potentially serving as earthquake-resistant attributes in masonry structures. Three distinct variations of steel wire mesh and three reinforcing arrangements, i.e. (-), (L) and (Z) arrangement were employed to reinforce the two approaches. The test result reveals a significant enhancement in structural performance upon inclusion of steel wire mesh in both reinforcing approaches, with the "BHJ" approach outperforming the "BJ" approach and the unreinforced masonry, along with increase in capacity as the wire mesh size increases. Furthermore, the effectiveness of the reinforcing arrangement is ranked with the (Z) arrangement showing the largest performance, followed by the (L) and (-) arrangement.

• Structural Engineering and Mechanics
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• v.89 no.1
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• pp.77-91
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• 2024

During strong seismic events, inelastic shear deformation occurs in beam-column joints. To capture inelastic shear deformation, an analytical model for beam-column joint in reinforced concrete (RC) frame structures has been proposed in this study. The proposed model has been developed using a rotational spring and rigid links. The stiffness properties of the rotational spring element have been assigned in terms of a moment rotation curve developed from the shear stress-strain backbone curve. The inelastic rotation behavior of joint has been categorized in three stages viz. cracking, yielding and ultimate. The joint shear stress and strain values at these stages have been estimated using analytical models and experimental database respectively. The stiffness properties of joint rotational spring have been modified by incorporating a geometry factor based on dimensions of adjoining beam and column members. The hysteretic response of the joint rotational spring has been defined by a pivot hysteresis model. The response of the proposed analytical model has been verified initially at the component level and later at the structural level with the two actually tested RC frame structures. The proposed joint model effectively emulates the inelastic behavior precisely with the experimental results at component as well as at structural levels.

• Journal of the Korea Institute of Building Construction
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• v.24 no.4
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• pp.413-424
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• 2024

To expedite construction of small precast concrete buildings using dry joints, this study developed and evaluated a connector system for solid slabs. The research included a comprehensive literature review on seismic design requirements for precast concrete floors, followed by an analytical evaluation of the connector's bearing capacity in 3-story buildings. Experimental assessments were conducted to determine the in-plane and out-of-plane capacities of the newly designed semi-circular connector. Finally, the constructability of both the semi-circular and flat connector configurations was compared through tests on single-story precast concrete frames.