• Earthquakes and Structures
• /
• v.7 no.5
• /
• pp.705-718
• /
• 2014

This paper presents an analytical model for determining the transverse reinforcement required for reinforced concrete exterior beam-column joints subjected to reversed cyclic loading. Although the joint aspect ratio can affect joint shear strength, current design codes do not consider its effects in calculating joint shear strength and the necessary amount of transverse reinforcement. This study re-evaluated previous exterior beam-column joint tests collected from 11 references and showed that the joint shear strength decreases as the joint aspect ratio increases. An analytical model was developed, to quantify the transverse reinforcement required to secure safe load flows in exterior beam-column joints. Comparisons with a database of exterior beam-column joint tests from published literature validated the model. The required sectional ratios of horizontal transverse reinforcement calculated by the proposed model were compared with those specified in ACI 352R-02. More transverse reinforcement is required as the joint aspect ratio increases, or as the ratio of vertical reinforcement decreases; however, ACI 352R-02 specifies a constant transverse reinforcement, regardless of the joint aspect ratio. This reevaluation of test data and the results of the analytical model demonstrate a need for new criteria that take the effects of joint aspect ratio into account in exterior joint design.

• Steel and Composite Structures
• /
• v.28 no.1
• /
• pp.63-71
• /
• 2018

This paper reports an experimental study that was accomplished to assess the seismic behavior of steel tube reinforced concrete bridge columns (SBCs). The motivation of this study was to verify a supposition that the core steel tube may be terminated at a rational position in the column to minimize the material cost while maintaining the seismic behavior of this composite column. Four SBC specimens were tested under combined constant axial load and cyclic reversed lateral loads. The unique variable in the test matrix was the core steel tube embedment length, which ranged from 1/3 to 3/3 of the column effective height. It is observed that SBCs showed two distinctly different failure patterns, namely brittle shear failure and ductile flexural failure. Tests results indicate that the hysteretic responses of SBCs were susceptible to the core steel tube embedment length. With the increase of this structural parameter, the lateral strength of SBC was progressively improved; the deformability and ductility, however, exhibited a tendency of first increase and then decrease. It is also found that in addition to maintained the rate of stiffness degradation and cumulative energy dissipation basically unchanged, both the ductility and deformability of SBC were significantly improved when the core steel tube was terminated at the mid-height of the column, and these were the most unexpected benefits accompanied with material cost reduction.

• Earthquakes and Structures
• /
• v.9 no.2
• /
• pp.281-303
• /
• 2015

The effects of infill panels on the response of r.c. frames subjected to seismic action are widely recognized. Numerous experimental investigations were effected and several analytical models were developed on this subject. This work, which is part of a larger project dealing with specific materials and structures commonly used in Italy, discusses experimental tests on masonry and samples of bare and infilled portals. The experimental activity includes tests on elemental materials, and 12 wall samples. Finally, three one-bay one-story reinforced concrete frames, designed according to the outdated Italian technical code D.M. 1996 without seismic details, were tested (bare and infilled) under constant vertical and cyclic lateral load. The first cracks observed on the framed walls occurred at a drift of about 0.3%, reaching its maximum capacity at a drift of 0.5% while retaining its capacity up to a drift of 0.6%. Infill contributed to both the stiffness and strength of the bare reinforced concrete frame at small drifts thus improving overall system behavior. In addition to the experimental activities, previously mentioned, the recalibration of a model proposed by Comberscue (1996) was evaluated. The accuracy of an OpenSees non linear fiber based model of the prototype tested, including a strut element was verified through a comparison with the final experimental results. This work has been partially supported by research grant DPC-ReLUIS 2014.

• Earthquakes and Structures
• /
• v.20 no.1
• /
• pp.123-132
• /
• 2021

Deficient beam-column joints of reinforced concrete (RC) structures designed to older practices and codes often lead to destructive local or global failures. A strengthening technique for these joints based on the use of the new and innovative Carbon-FRP (C-FRP) ropes is presented and investigated. The C-FRP ropes are diagonally placed in superficial notches on the two sides of the joint. Two full scale external substandard joint subassemblages with the same characteristics, one unstrengthened and one strengthened with diagonally applied C-FRP ropes, are constructed and tested in cyclic loading. Special attention has been given to the elaboration of the acquired test measurements. The extracted conclusions are based on the comparative study of the hysteretic responses of the specimens, the observed maximum load envelopes, the comparisons of the joint body shear deformations as measured using diagonally mounted LVTDs, the calculated nominal principal stresses developed in the joint regions, the assessed joint damage as expressed by the damage index by Park and Ang and finally the calculated values of the equivalent damping ratio. From these comparisons it is concluded that application of diagonally mounted C-FRP ropes on the two sides of the joint body of exterior connections is an efficient easy-to-apply technique for the strengthening of substandard RC joints.

• Journal of the Korea Concrete Institute
• /
• v.22 no.3
• /
• pp.357-366
• /
• 2010

This paper presents experimental results about shear wall with various lateral reinforcement details in boundary elements. The research objective is to study the structural behavior of shear wall with boundary column confined by rectangular spiral hoops and headed cross ties developed to improve workability in the fabrication of boundary columns. These two details can be fabricated in a factory and put together on-site after being delivered so that the construction work may be reduced. Main parameters in the experimental study were the types of hoop and cross tie: rectangular spiral hoop and headed cross tie vs. standard hoop and cross tie with hook. Four half scaled shear wall specimens with babel shape were made and tested by applying horizontal cyclic load under constant axial force, 10% of nominal compressive strength of concrete. Based on the test result, it was shown that the shear wall with rectangular spiral hoop and headed cross tie in boundary columns has structural capacity compatible with conventional shear wall. The specimen SW-Hh which has bigger hoop bar and higher volumetric ratio of transverse reinforcements than other showed improved energy dissipating characteristic but it presented a rapid reduction of strength after peak point. The results indicates that, it is necessary to consider volumetric ratio of transverse reinforcements as well as hoop space in designing of shear wall with boundary columns for improved strength and ductility.

• Journal of the Korea Concrete Institute
• /
• v.22 no.3
• /
• pp.325-333
• /
• 2010

In this study, new moment-resisting precast concrete beam-column joint made up of hybrid steel concrete was developed and tested. This beam-column joint is proposed for use in moderate seismic regions. It has square hollow tubular section in concrete column and connecting plate in precast U-beam. The steel elements in column and beam members were connected using bolt. Furthermore, in order to prevent the premature failure of concrete in hybrid steel-concrete connection, ECC(engineered cementitious composite) was used. An experimental study was carried out investigating the joint behavior subjected to reversed cyclic loading and constant axial compressive load. Two precast beam-column joint specimens and monolithic reinforced concrete joint specimen were tested. The variables for interior joints were cast-in-situ concrete area and transverse reinforcement within the joint. Tests were carried out under displacement controlled reverse cyclic load with a constant axial load. Joint performance is evaluated on the basis of connection strength, stiffness, energy dissipation, and displacement capacity. The test results showed that significant differences in structural behavior between the two types of connection because of different bonding characteristics between steel and concrete; steel and ECC. The proposed joint detail can induce to move the plastic hinge out of the ECC and steel plate. And proposed precast connection showed better performance than the monolithic connection by providing sufficient moment-resisting behavior suitable for applications in moderate seismic regions.

• Journal of the Korea Concrete Institute
• /
• v.19 no.3
• /
• pp.265-273
• /
• 2007

The most common structural system for apartment buildings in Korea is adopted to combine structural systems: for example, a moment-resisting frame will be used for lower stories and bearing wall system for the upper stories. This type of buildings have soft and/or weak stories in lower stories, and it may lead to collapse of those buildings during the large earthquake. Reversed cyclic load tests were conducted to estimate the performance and behavioral characteristics of deep beam and exterior column Joints. Experimental parameter is the amount of transverse reinforcement (designed by ACI code and Sheikh's procedure). The results of this study are as follows: (1) The required transverse reinforcement of column designed by Sheikh's procedure requires 2.9 times larger than that designed by ACI procedure. Large amount of transverse reinforcement increase the ductility of the column. (2) Most of the lateral drift in the column is due to the flexural deformation in the joint and plastic hinge region and up-lift rotation. (3) Transverse reinforcement in the exterior column shall be required not only in the hinge region but also in the joint.

• International Journal of Concrete Structures and Materials
• /
• v.11 no.2
• /
• pp.229-245
• /
• 2017

Post-earthquake observations revealed that seismic performance of beam-column connections in precast concrete structures affect the overall response extensively. Seismic design of precast reinforced concrete structures requires improved beam-column connections to transfer reversed load effects between structural elements. In Turkey, hybrid beam-column connections with welded components have been applied extensively in precast concrete industry for decades. Beam bottom longitudinal rebars are welded to beam end plates while top longitudinal rebars are placed to designated gaps in joint panels before casting of topping concrete in this type of connections. The paper presents the major findings of an experimental test programme including one monolithic and five precast hybrid half scale specimens representing interior beam-column connections of a moment frame of high ductility level. The required welding area between beam bottom longitudinal rebars and beam-end plates were calculated based on welding coefficients considered as a test parameter. It is observed that the maximum strain developed in the beam bottom flexural reinforcement plays an important role in the overall behavior of the connections. Two additional specimens which include unbonded lengths on the longitudinal rebars to reduce that strain demands were also tested. Strength, stiffness and energy dissipation characteristics of test specimens were investigated with respect to test variables. Seismic performances of test specimens were evaluated by obtaining damage indices.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.2
• /
• pp.35-42
• /
• 2021

In this study, a steel frame that realized the second floor of a structure was fabricated in referring to NFPA 13. In addition, a riser pipe system with groove joints was installed, and a seismic simulation test was performed using static cyclic loading. Cyclic loading tests on the maximum allowable side sway of seismic design standards for buildings in Korea were conducted using actuators to analyze the seismic behavior of the riser pipe system and major piping elements due to the deformation of the steel frame structure or the displacement-dominant behavior caused by the relative displacement between the structural members in the event of a seismic load. Moreover, the deformation angle of the riser pipe system was measured using an image measurement system because it is difficult to measure using the conventional sensors.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.64 no.3
• /
• pp.45-52
• /
• 2022

Prediction of soil behavior should be interpreted based on the level of axial strain in the actual ground. Recently numerical methods have been carried out focus on the state of soil failure. However considered the deformation of soil the prior to failure, mostly the small strain occurring in the elastic range is considered. As a result of calculating the deformation modulus to 50% of the maximum unconfined compression strength, Deformation modulus (E50) showed a tendency to increase according to the degree of compaction by region. The Poisson's ratio during loading-unloading was 0.63, which was higher than the literature value of 0.5. For the unconfined compression test under cyclic loading for the measurement of permanent strain, the maximum compression strength was divided into four step and the test was performed by load step. Changes in permanent strain and deformation modulus were checked by the loading-unloading test for each stage. At 90% compaction, the permanent deformation of the SM sample was 0.21 mm, 0.37 mm, 0.6 mm, and 1.35 mm. The SC samples were 0.1 mm, 0.17 mm, 0.42 mm, and 1.66 mm, and the ML samples were 0.48 mm, 0.95 mm, 1.30 mm, and 1.68 mm.