Vol.38/No.4 (150) (2023)
| Title | Study on analysis of a reinforced concrete portal frame retrofitted with an elliptically hollow steel frame infilled with rubber cylinders |
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| Author | Chia-Chuan Hsu,Chia-Wei Hsu,Hsiao-Hui Hung, Kuang-Wu Chou,Chin-Kuo Su,Yu-Chi Sung |
| Keywords | near-fault ground motion, seismic retrofit, RC frame, steel oval hollow section, rubber, equivalent brace |
| Abstract | This study proposes an analysis procedure for engineers to apply a new method of retrofitting a reinforced concrete frame. This retrofitting method uses an elliptically hollow member, which is created with a steel frame infilled with rubber cylinders. This method enables rapid retrofitting construction and could help the retrofitted structure bear more loadings, resist strong earthquakes, and recenter, without sacrificing too much space for usage. Moreover, applying this method could effectively reduce structural damage caused by near-fault earthquakes. The proposed analysis procedure separates the three-dimensional finite element modeling of such a complex retrofitting member from the frame analysis that engineers need to perform for design. A retrofitting member alone gets detailed finite element modeling and pushover analysis to create a brace that can equivalently represent the retrofitting member in the frame analysis of the retrofitted RC frame. The comparison of the structural analysis result and the experiment result shows the proposed analysis procedure can prudently predict the behavior of a retrofitted RC frame with acceptable bias. |
| Title | Flexural Behavior of Steel Beam-to-Column Connections with Concrete as Fire Protection Material |
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| Author | Cheng-Cheng Chen, Pin-Da Wu and Chen-Wei Fan |
| Keywords | steel structure, steel girder, beam-to-column connection, steel reinforced concrete structure, fire protection layer |
| Abstract | The mechanical properties of steel are greatly affected by high temperature; thus, steel structure buildings need to have appropriate fire protection measures to prevent premature collapse of buildings in the event of fire. In some cases, steel structure buildings use concrete as fireproofing material. Although longitudinal and transverse steel bars are also provided as auxiliary reinforcements, but the strength that can be contributed by these steel bars is not considered in the strength calculation during design process. In engineering practice, this kind of structure is known as SC structure. In this study, five beamcolumn sub-assemblage was tested under cyclic loading to investigate the influence of SC beam structural details on beam strength, ductility, and crack development. The test results show that the use of reduced beam section beamtocolumn connection detailing is necessary since it can significantly increase the flexural ductility of the SC beams. The SC beams can develop the full composite action even though without using any shear stud. The use of isolation layer between beam flange and concrete in plastic hinge region is not necessary since it only slightly increase the plastic rotation capacity of the SC beams but causes larger crack in the concrete at the beam-to-column interface. The auxiliary longitudinal rebar is provided up to the face of box column and the use of 90° hooks are not recommended since it will cause additional cracks. The local buckling of the auxiliary longitudinal rebar can be effectively avoided when the distance between the rebar is less than ten times of its diameter. |
| Title | Study on New Retrofit Methods for an Reinforced Concrete Beam with the Opening |
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| Author | Chien-Kuo Chiu ,Min-Yuan Cheng, Yu-Chen Ou, Sheng-Huei Wang, Jie-Cih Jhou, Yin-Yi He |
| Keywords | Reinforced concrete beam, plastic hinge, opening, retrofitting method, one-piece double-square hoop, inclined U-shape stirrup, strength, deformation capacity |
| Abstract | To prevent a reinforced concrete (RC) beam member from undergoing shear failure instead of flexural failure or flexure-shear failure under earthquakes, it is generally not recommended to make the opening within a region extending twice the beam depth from the face of the support column toward the central position of the span of the beam. However, in recent years, for actual requirements of the pipeline configuration, the problems of arranging the openings in the plastic hinge zone of an RC beam member have been already faced in the design and construction. Therefore, it is necessary to establish a set of design guidelines for the retrofit of the openings in the plastic hinge zone of an RC beam member. A total of nine specimens are tested in this study. The main test variables include: (1) opening location, (2) retrofitting methods of the openings. All specimens are subjected to cyclic lateral load. This work investigates the crack development and mechanical behavior of reinforced concrete beams with the circular openings, and provide the novel retrofitting methods with one-piece double-square hoops and inclined U-shape stirrups for the beams with circular openings. The experimental results are used to to verify the effectiveness of the proposed retrofitting methods. Additionally, based on the experimental results, this work also investigates the application of the design formulas that are recommended from AIJ-1999 and AIJ-2010 for an RC beam with the opening. |
| Title | Shear Strength Design for Reinforced Concrete Shear Walls of Dual System |
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| Author | Shyh-Jiann Hwang, Shao-Kai Huang, Pu-Wen Weng, Yu-Chen Ou, Ming-Huoy Huang |
| Keywords | Dual system, Reinforced concrete, Shear strength design, Shear wall, Softened strut-and-tie model. |
| Abstract | Past earthquake reconnaissance already demonstrated that the reinforced concrete dual system, which consists of ductile moment resisting frames and shear walls, is one of the most effective earthquake resisting systems. A dual system can provide the 2nd line of defense when shear walls are coupled with frames. In seismic design, the 2nd line of defense is a secure protection against impulsive earthquakes. The shear walls of the dual system provide a continuity over height, which effectively prevent the story sway mechanism and provide uniform and reduced lateral drift resulting in a better damage control. The new building design code of Civil 401-110 requires the shear capacity design of the special shear wall. After the inclusion of the over-strength effect and the dynamic amplification factor, the shear strength demand can be doubled or even tripled, which leads to the shear walls with highly improbable thickness. This strict demand will hamper the application of the dual system in seismic design. This problem should be resolved. A feasible solution to overcome this difficulty is to adopt the dual system with the shear walls designed by the strut-and-tie method. The structural walls of the dual system are equipped with substantial boundary members appearing as both beams and columns, which create a special shear force transferring mechanism within the framed squat walls. The framed squat walls possess very high shear resisting capacities, which can effectively reduce the thickness of shear walls, if well designed by the strut-and-tie method. The objective of this paper is to demonstrate the merits of the dual system and to promote its application in seismic design. The content of this paper includes the requirements of the new building design code, the softened strut-and-tie model, the shear strength design of framed squat walls of the dual system, design verification using Japanese shaking table tests, design suggestions for shear wall and the related case study. |
| Title | Seismic Performance of Reinforced Concrete Buildings with Viscoelastic Damping Wall under Shanchiao Fault Earthquakes |
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| Author | Chung-Che Chou, Jian-Lin Lai, Kuan-Hua Chen, Shu-Hsien Chao |
| Keywords | viscoelastic damping wall, lever viscoelastic damping wall, Shanchiao fault, near-fault effect, nonlinear response time history analysis |
| Abstract | Viscoelastic damping wall (VEW) is a common velocity-dependent energydissipating device, which is used to reduce the lateral deformation of building frames in small earthquake or wind loadings. Its allowable deformation is smaller than the displacement-dependent energy-dissipating device so that VEW is unable to reduce the earthquake response under large earthquakes. The lever viscoelastic damping wall (LVEW) is a new velocity-dependent and displacement-dependent energy dissipating device, which is composed of viscoelastic and frictional damping in one single device. Under small or service level earthquakes, the LVEW could amplify its interstory drift by using a leverage mechanism so it can amplify the shear deformation and energy dissipation of a viscoelastic mechanism to reduce the frame response. Under large earthquakes, the stopper in the LVEW limits the deformation of viscoelastic damper, and activates frictional damping for energy dissipation. In this study, 8-story and 14-story reinforced concrete (RC) buildings with moment-resisting frames and shear walls were designed, representing a fundamental period of 1.0 second and 1.8 seconds. The frames were added with the traditional viscoelastic damping wall (VEW) and the leveraged viscoelastic damping wall (LVEW) for studying their seismic response. The building site was assumed to be located in Taipei Zone 1, close to the Shanchiao fault so the analysis was conducted by using acceleration time histories obtained based on the movement of Shanchiao fault. The work was focused on investigating the seismic response of RC frames with VEWs or LVEWs under Shanchiao fault ground motions. |