• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.5
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• pp.281-289
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• 2018

Existing reinforced concrete building structures have seismic vulnerabilities due to their seismically-deficient details resulting in non-ductile behavior. The seismic vulnerabilities can be mitigated by retrofitting the buildings using a fiber-reinforced polymer column jacketing system, which can provide additional confining pressures to existing columns to improve their lateral resisting capacities. This study presents dynamic responses of a full-scale non-ductile reinforced concrete frame retrofitted using a fiber-reinforced polymer column jacketing system. A series of forced-vibration testing was performed to measure the dynamic responses (e.g. natural frequencies, story drifts and column/beam rotations). Additionally, the dynamic responses of the retrofitted frame were compared to those of the non-retrofitted frame to investigate effectiveness of the retrofit system. The experimental results demonstrate that the retrofit system installed on the first story columns contributed to reducing story drifts and column rotations. Additionally, the retrofit scheme helped mitigate damage concentration on the first story columns as compared to the non-retrofitted frame.

• Structural Engineering and Mechanics
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• v.67 no.3
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• pp.233-244
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• 2018

This study aims at evaluating the performance of repairing technique with CFRPs in recovering cyclic performance of damaged columns in flexure in terms of structural response parameters such as strength, dissipated energy, stiffness degradation. A 2/3 scaled substandard reinforced concrete frame was constructed to represent the substandard RC buildings especially in developing countries. These substandard buildings have several structural deficiencies such as strong beam-weak column phenomenon, improper reinforcement detailing and poor material properties. Flexural plastic hinges occurred at the columns ends after testing the substandard specimen under both constant axial load and reversed cyclic lateral loading. Afterwards, the damaged columns were externally wrapped with CFRP sheets both in transverse and longitudinal directions and then retested under the same loading protocol. In addition, ambient vibration measurements were taken from the undamaged, damaged and the repaired specimens at each structural repair steps to identify the effectiveness of each repairing step by monitoring the change in the natural frequencies of the tested specimen. The ambient vibration test results showed that the applied repairing technique with external CFRP wrapping was proved to recover stiffness of the pre-damaged specimen. Moreover, the lateral load capacity of the pre-damaged substandard RC frame was restored with externally bonded CFRP sheets.

• Structural Engineering and Mechanics
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• v.19 no.6
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• pp.679-705
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• 2005

This paper presents a practical method to evaluate the effective length factors for columns in multi-storey unbraced frames based on the concept of storey-based elastic buckling by means of decomposing a multi-storey frame into a series of single-storey partially-restrained (PR) frames. The lateral stiffness of the multi-storey unbraced frame is derived and expressed as the product of the lateral stiffness of each storey. Thus, the stability analysis for the multi-storey frame is conducted by investigating the lateral stability of each individual storey, which is facilitated through decomposing the multi-storey frame into a series of single-storey PR frames and applying the storey-based stability analysis proposed by the authors (Xu and Liu 2002) for each single-storey PR frame. Prior to introducing decomposition approaches, the end rotational stiffness of an axially load column is derived and rotational stiffness interaction between the upper and lower columns is investigated. Three decomposition approaches, characterized by means of distributing beam-to-column rotational-restraining stiffness between the upper and lower columns, are proposed. The procedure of calculating storey-based column effective length factors is presented. Numerical examples are then given to illustrate the effectiveness of the proposed procedure.

• Steel and Composite Structures
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• v.3 no.1
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• pp.47-64
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• 2003

In a nonlinear finite element study on the mechanical behavior of simple beam connections to continuous concrete-filled steel tube columns, two principally different connection types were analyzed: one with plates attached to the outside of the tube wall, relying on shear transfer, and one with an extended plate inserted through the steel section to ensure bearing on the concrete core. The load was applied partly at the connection within the column length and partly at the top, representing the load from upper stories of a multistory building. The primary focus was on the increased demand for load transfer to ensure composite action when concrete with higher compressive strength is used. The results obtained from the analyses showed that the design bond strength derived from push tests is very conservative, mainly due to the high frictional shear resistance offered by pinching and contraction effects caused by connection rotation. However, with higher concrete strength the demand for load transfer increases, and is hard to fulfill for higher loads when connections are attached only to the steel section. Instead, the connection should penetrate into the concrete core to distribute load to the concrete by direct bearing.

• Earthquakes and Structures
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• v.13 no.1
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• pp.89-101
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• 2017

The focus of this paper is the study on the seismic performance of RC buildings with two different connections at the base level under near-fault earthquakes. It is well-known that the impulsive nature of the near-fault ground motions causes severe damages to framed buildings especially at base connections. In the scope of this study, two types of 3-dimensional RC Moment Frames with Fixed Support (MFFS) and Hinged Support (MFHS) containing 5 and 10 stories are assessed under an ensemble of 11 strong ground motions by implementing nonlinear response history analysis. The most vulnerable locations of MFFS, are the connections of corner columns to foundation especially under strong earthquakes. On the other hand, using beams at the base level as well as hinged base connections in MFHS buildings, prevents damages of corner columns and achieves more ductile behavior. Results denote that the MFHS including Base Level Beams (BLB) significantly shows better behavior compared with MFFS, particularly under pulse-type records. Additionally, the first story beams and also interior components undergo more actions. Role of the BLBs are similar to fuses decreasing the flexural moments of the corner columns. The BLBs can be constructed as replaceable members which provide the reparability of structures.

• Journal of Korean Society of Steel Construction
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• v.20 no.3
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• pp.445-454
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• 2008

Based on previous research on steel moment connections, experimental and analytical results showed that the deformation capacity was poor in specimens using RHS columns and with conventional weld access holes and strain concentration at the end of beam is influenced by the efficiency in transmitting the moment in the web of beam through the beam-to-column joint. This paper is focused on the retrofitting of pre-Kobe steel moment frame connections using a stiffened RBS and a welded horizontal stiffener. These retrofitting methods were considered only in beam bottom flange. A parametric study was performed using nonlinear finite element analysis to elucidate and improve the retrofit methods of connections.

• Steel and Composite Structures
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• v.22 no.1
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• pp.45-61
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• 2016

The domestic and foreign scholars conducted many studies on mechanical properties of wave web steel beam and high-strength spiral stirrups confined concrete columns. Based on the previous research work, studies were conducted on the anti-seismic property of the end plate bolt connected wave web steel beam and high-strength spiral stirrups confined concrete column nodes applied with pre-tightening force. Four full-size node test models in two groups were designed for low-cycle repeated loading quasi-static test. Through observation of the stress, distortion, failure process and failure mode of node models, analysis was made on its load-carrying capacity, deformation performance and energy dissipation capacity, and the reliability of the new node was verified. The results showed that: under action of the beam-end stiffener, the plastic hinges on the end of wave web steel beam are displaced outward and played its role of energy dissipation capacity. The study results provided reliable theoretical basis for the engineering application of the new types of nodes.

• Advances in Computational Design
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• v.7 no.3
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• pp.173-188
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• 2022

In modern buildings, glass is considered a structurally unsafe material due to its brittleness and unpredictable failure behavior. The possible use of structural glass elements (i.e., floors, beams and columns) is generally prevented by its poor tensile strength and a frequent occurrence of brittle failures. In this study an innovative modelling based on an equivalent thickness concept of laminated glass beam reinforced with FRP (Fiber Reinforced Polymer) composite material and of glass plates punched is presented. In particular, the novel numerical modelling applied to an embedding Carbon FRP-rod in the interlayer of a laminated structural glass beam is considered in order to increase both its failure strength, together with its post-failure strength and ductility. The proposed equivalent modelling of different specimens enables us to carefully evaluate the effects of this reinforcement. Both the responses of the reinforced beam and un-reinforced one are evaluated, and the corresponding results are compared and discussed. A novel equivalent modelling for reinforced glass beams using FRP composites is presented for FEM analyses in modern material components and proved estimations of the expected performance are provided. Moreover, the new suggested numerical analysis is also applied to laminated glass plates with wide holes at both ends for the technological reasons necessary to connect a glass beam to a structure. Obtained results are compared with an integer specimen. Experimental considerations are reported.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.4
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• pp.29-36
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• 2010

To investigate the cyclic characteristics of exterior joints in RC frame buildings which are typically used after 1988, 70% scaled T-shaped beam-column subassemblies were designed and tested with a displacement control that is composed of 9 steps, until 3.5% story drift was reached. Axial forces are applied to columns during the experiment to simulate a real situation. The results show that the non-seismic detailed specimens failed before reaching 0.85% story drift, and their strengths are less than 0.85 times the nominal flexural strength which beam or columns should reach. The relationship of principal stress and story drift of exterior joints is similar to the one that Priestly proposed.

• Steel and Composite Structures
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• v.26 no.6
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• pp.793-808
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• 2018

In this study, the seismic performance of the connections between L-shaped columns composed of concrete-filled steel tubes (L-CFST columns) and H-beams used in high-rise steel frame structures was investigated. Seven full-scale specimens were tested under quasi-static cyclic loading. The variables studied in the tests included the joint type, the axial compression ratio, the presence of concrete, the width-to-thickness ratio and the internal extension length of the side plates. The hysteretic response, strength degradation, stiffness degradation, ductility, plastic rotation capacity, energy dissipation capacity and the strain distribution were evaluated at different load cycles. The test results indicated that both the corner and exterior joint specimens failed due to local buckling and crack within the beam flange adjacent to the end of the side plates. However, the failure modes of the interior joint specimens primarily included local buckling and crack at the end plates and curved corners of the beam flange. A design method was proposed for the flexural capacity of the end plate connection in the interior joint. Good agreement was observed between the theoretical and test results of both the yield and ultimate flexural capacity of the end plate connection.