Vol.32/No.2 (126) (2017)
| Title | Seismic Design, Tests and Analysis of Steel Panel Dampers for Steel Moment Frames |
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| Author | Chung-Hsiang Hsu, Chao-Hsien Li, Pu-Yuan Chin, Keh-Chyuan Tsai |
| Keywords | steel panel damper, capacity design, seismic design, finite element model analysis, non-linear structural analysis |
| Abstract | A ductile vierendeel frame can be constructed by incorporating the steel panel dampers (SPDs) into the moment resisting frame (SPD-MRF). Thus, the lateral stiffness, strength and energy dissipation capacity of the building can be enhanced.This paper presents the mechanical properties, capacity design procedures and the buckling-delaying stiffeners for the proposed 3-segment SPDs using two specimens subjected to cyclic increasing deformations. This paper also discusses the seismic design procedures of the SPD itself and the boundary beams connected to the SPDs in typical SPD-MRFs. Tests confirm that the proposed SPDs possess excellent ductility and energy dissipation capacities. The cyclic force vs. deformation relationships of the two SPD specimens can be accurately predicted using either the ABAQUS or PISA3D model analyses. This paper also investigates the seismic performance of a 6-story example SPD-MRF by using nonlinear response history analysis procedures and 240 ground accelerations. Results indicate that under the 80 MCE ground accelerations, the mean plus one standard deviation shear deformation of the SPD inelastic core segment is 0.055 radian, substantially less than the 0.11 radian capacity observed from both two SPD specimens. In addition, the cumulative plastic deformation of the proposed SPD is 127 times the yield deformation, capable of sustaining the MCE at least 4 times before failure. This paper concludes the method of using one equivalent element for effective modeling of the 3-segment SPD. The effects of the core segment relative length and stiffness on the overall SPD elastic, post-elastic stiffness, elastic deformation limit and inelastic deformational demand are discussed. |
| Title | Seismic Tests and Nonlinear Time History Analyses of Full-Scale Two-Story Steel Frames with DC-SCBs and SBRBs |
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| Author | Chung-Che Chou, Chia-Hung Hsiao, Ze-Bang Chen, Ping-Ting Chung, Dinh-Hai Pham |
| Keywords | Dual-core self-centering brace (DC-SCB), Sandwiched buckling-restrained brace (SBRB), Tests of two-story steel braced frames |
| Abstract | Traditional seismic resisting systems in a large earthquake can experience significant damage and residual drifts due to energy dissipation of some structural members, which leads to difficult or expensive to repair after earthquakes. A steel dual-core self-centering brace (DC-SCB), which utilizes three steel bracing members, two friction devices, and two sets of tensioning elements that are in a parallel arrangement for doubling its axial deformation, has been proposed and validated to provide both the energy dissipation and self-centering properties to seismic resisting systems. A prototype three-story steel dual-core self-centering braced frame (DC-SCBF) was designed, and its full-scale one-bay DC-SCBF was tested to validate the system response. The DC-SCB was then replaced by the sandwiched buckling-restrained brace (SBRB) in a full-scale two-story frame, so the seismic performance of the DC-SCBF and the special mixed braced frame (SMBF) that has both the DC-SCB and SBRB in a frame could be evaluated. The full-scale two-story DC-SCBF, SMBF and BRBF subassembly specimen performed well up to an interstory drift of 2% after multiple tests. Nonlinear time history analyses were also performed on the prototype braced frames to obtain seismic demands. |
| Title | Curvature effect on seismic responses of pendulum sliding isolators subjected to vertical and horizontal bi-directional ground excitations |
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| Author | Chun-Chung Tsai, Lyan-Ywan Lu, Liang-Wei Wang, Lap-Loi Chung |
| Keywords | base isolation, sliding isolation, pendulum isolator, curvature effect, bi-direction excitation, centrifugal force |
| Abstract | Friction pendulum system (FPS) isolator is one of most widely used sliding isolators, presently. This type of isolators usually has a spherical sliding surface with constant radius, in order to produce a restoring force for the isolation system. The energy dissipation of the isolator is provided by sliding friction force. The common model adopted for an FPS isolator usually contains a constant-stiffness spring and a friction element placed in parallel. This model assumes that the isolator displacement is much smaller than the radius of the sliding surface, therefore the curvature and slope effects of the spherical surface on the restoring and friction forces can be neglected. This simplified model may not be applicable for FPS isolators under earthquakes that produce large isolator displacements or sliding velocities, since in these earthquakes the curvature and slope of the sliding surface may have significant effects on the dynamic response of the isolation system. In order to capture the actual response of a FPS-isolated structural system under an extreme earthquake, in this paper, complete dynamic equations of motion for the isolation system under vertical-and-horizontal bi-directional ground excitations were derived by using Lagrange’s equation. It is shown that the derived governing equations in both horizontal and vertical directions contain high-order nonlinear terms related to the slope and curvature of the sliding surface. These terms that are functions of horizontal sliding velocity and acceleration cause the coupling effect between horizontal and vertical motions and result in extra vertical acceleration and isolator axial load. The existence of the coupling effect was further verified by the shaking table test conducted in this study. In addition, by using the derived complete dynamic equations, the time responses of a FPS-isolated rigid structure under 168 ground motions with different intensities and characteristics were simulated. The simulation result demonstrates that the high-order terms have less effect on the horizontal response (acceleration and isolator drift) of the isolated system, but are more influential on the vertical responses (acceleration and isolator axial load). Neglecting the high-order terms may underestimate the vertical response by about 20-40% in a sever earthquake. |
| Title | Investigation on Safety Problems of SRC Structures used in Construction |
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| Author | Jui-Lin Peng, Chung-Ming Ho, Wen-Jinn Lee, Liang-Jenq Leu |
| Keywords | critical load, direct analysis method, second-order analysis, steel reinforced concrete structure |
| Abstract | The steel reinforced concrete structures (SRC) integrate into the merits of steel structures (SS) and reinforced concrete structures (RC). The steel reinforced concrete structures, combined by reinforced concrete and steel structures, have a good ductility, earthquake resistantce and fire resistance. In recent years, some construction projects with high safety and seismic requirements have considered the design of steel reinforced concrete. However, in the construction of SRC structures, an unexpected construction load may cause the collapse of SRC structures if the correct construction procedures is not considered. This study investigates the construction safety of SRC structure based on the collapse of a SRC structure using a second-order analysis and a simplified model of composite columns. The study result of the second-order analysis shows that designers might fail to consider the overall steel self-weight of the SRC construction structure to exceed the critical load of this structure. This caused that the SRC construction structure buckled and then immediately collapsed after a slight disturbance. The analysis result of the simplified model of the composite column shows that the self-weight of SRC may exceed the critical load of the SRC construction structure and then the structure fails finally. The analysis result implies that the SRC construction structure collapses if the construction procedure of SRC only follows that of SS regardless of the setup progress of reinforced concrete beams and columns at the bottom. In order to avoid the collapse of SRC construction structure, this study proposes that, in terms of construction, the government authorities should develop a safety assembly procedure of SRC structures so that the hoisting of steel beams and columns can combine reinforced concrete operations perfectly. In terms of design, the government authorities should add the direct analysis method or the second-order analysis into the domestic design specifications of steel structures based on those used in advanced countries. |
| Title | Numerical simulation of shaking table tests on dynamic response of a bridge model with scoured piled foundation |
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| Author | Kuang-Yen Liu, Zheng-Hong Chen, Chia-Han Chen, Kuo-Chun Chang |
| Keywords | Shaking table test, Pile foundation, Scouring effect, Soil springs |
| Abstract | The simplified analysis process of soil-structure interaction is proposed in this research to study the response of the bridge with scoured piled foundation under earthquake. The simplified analysis applies soil spring to simulate soil-structure interaction behavior. Both soil shear wave velocity and dynamic shear modulus are used to estimate initial value of linear soil spring. Given two assumptions: (1) the shear strain of the soil near the pile is consistent to the strain of the pile, and (2) modification of dynamic shear modulus of soil follows the relationship of effective shear strain and maximum shear modulus, proposed by Seed and Idriss, the parameters of soil springs can be determined iteratively. Furthermore, a simplified approach to identify the soil layers subjected to seismic loading was also introduced by the predominant frequencies of soil layers by the transfer function analysis. Based on the proposed method, the SDOF bridge model with equivalent linear soil springs was built to simulate behavior of soil-pile-structure interaction in the shaking table test. The acceleration and relative displacement of superstructure, the strain of pile top, and the maximum strain of pile can be effectively predicted by the proposed method, either in the condition of exposed or no exposed pile foundation. In addition, the analyzed result of the model considering the double layers of soil can obtain better accuracy than that of the model with single layer of soil. |