Chui-Hsin Chen

Bio: Chui-Hsin Chen is an academic researcher from National Chiao Tung University. The author has contributed to research in topics: Braced frame & Frame (networking). The author has an hindex of 8, co-authored 17 publications receiving 305 citations.

Pseudo-dynamic tests of a full-scale CFT/BRB frame-Part I: Specimen design, experiment and analysis

Abstract: A series of pseudo-dynamic tests (PDTs) of a full-scale 3-story 3-bay buckling-restrained braced frame (BRBF) using concrete-filled tube columns was tested in the Taiwan National Center for Research on Earthquake Engineering using networked PDT techniques in October 2003. During the tests, real-time experimental responses and video were webcasted to Internet viewers. The input ground motions adopted for the PDTs were chosen from the 1999 Chi-Chi and the 1989 Loma Prieta earthquakes and scaled to represent three seismic hazard levels. This paper is in two parts, focusing on the investigations of the overall structure and the local members. This paper constitutes Part I and discusses the design, analytical investigations, and key experimental results of the specimen frame, such as the buckling of the brace-to-gusset joints. Part II of the paper, the companion paper, describes the gusset stiffening schemes and detailed experimental behavior of the BRBs and their connections. Experimental peak inter-story drifts of 0.019 and 0.023 radians, prescribed for the design basis and the maximum credible earthquakes, respectively, are within the target design limits of 0.020 and 0.025 radians. These tests confirmed that the PISA3D and OpenSees nonlinear structural analysis computer programs can simulate the experimental peak shears and floor displacements well. Copyright © 2008 John Wiley & Sons, Ltd.

Experimental study on the dynamic response of gravity-designed reinforced concrete connections

Abstract: This paper reports an experimental programme aiming to shed some light on the response of non-seismic RC beam–column joints to excitations of different frequencies. The RC connections tested were designed only for gravity loads, thus rendering the joint cores weaker than the adjoining members when subjected to a lateral load. Altogether, six tests were conducted on full-scale specimens, which were subjected to reversed cyclic displacements applied at different speeds varying from slow quasi-static loading to high-speed dynamic loading as fast as 20 Hz. Although all specimens as expected suffered joint shear failure, the maximum joint shear stresses observed in the tested specimens, despite lacking transverse hoops inside the joint cores, were more than the horizontal shear stresses allowed in ductile RC joints with the same grade of concrete according to the existing seismic design codes. The damage patterns and failures of the specimens showed a better correlation with the residual storey shear stiffness than with the loss of storey shear strength during the repeated cycles. By analysing the test results, this paper also discusses how an inadvertent inertial force develops during high-speed displacement reversals.

Performance-Based Seismic Demand Assessment of Concentrically Braced Steel Frame Buildings

Abstract: Author(s): Chen, Chui-Hsin | Advisor(s): Mahin, Stephen A | Abstract: The special concentrically steel braced frame (SCBF) system is one of the most effective struc-tural systems to resist lateral forces. Because of its effectiveness and straightforward design, many SCBFs are incorporated in structures throughout the world. However, the highly nonlin-ear behavior associated with buckling and non-ductile fracture of braces reduces the ability of the system to dissipate energy resulting in undesirable modes of behavior. While many studies have investigated the cyclic behavior of individual braces or the behavior of subassemblies, the dynamic demands on the structural system under various seismic hazard levels needs additional study for performance-based earthquake engineering. Archetype buildings of SCBFs and buckling restrained braced frames (BRBFs) were analyzed using the computer program OpenSees (the Open System for Earthquake Engineering Simulation) to improve the understanding of the seismic behavior of braced frame systems, and to assess seismic demands for performance-based design. Numerical models were calibrated using test data determined from testing of conventional buckling braces, buckling restrained braces, and the braced frame specimens. In addition, fiber-based OpenSees models were constructed and compared with results of a sophisticated finite-element model that realistically captured local buckling and local fracture of structural elements. Because the OpenSees models are reasona-bly accurate and efficient, they were chosen to perform set of parametric computer simulations. The seismic demands of the system and structural elements were computed and interpreted for 3-, 6-, and 16-story SCBFs and BRBFs under various hazard levels. The analysis results show large seismic demands for the 3-story SCBF, which may result in unexpected damage of struc-tural and non-structural elements. The median expected probability of a brace buckling at one or more levels in a 3-story SCBF is more than 50% for an earthquake having a 50% probability of exceedance in 50 years (the service-level event). The possible need to replace braces fol-lowing such frequent events due to brace buckling should be considered in performance-based earthquake engineering assessments. In addition, brace fracture in SCBFs is likely for an earthquake having a 2% probability of exceedance in 50 years (the MCE-level event). Analy-ses show that in general, BRBF models had larger drift demands and residual drifts compared to SCBF systems, because of the BRBF's longer fundamental period. However, the tendency to form a weak story in BRBFs is less than that in SCBFs. Evaluation of seismic demand parameters were performed for 2-, 3-, 6-, 12-, and 16-story SCBFs and BRBFs, which demonstrated that short-period braced frame systems, especially SCBFs, had higher probability of collapse than longer-period braced frame systems. Substantially improved response was observed by lowering the response reduction factor of the 2-story SCBF building; this reduced the collapse risk at the hazard level of 2% probability of exceedance in 50 years. For long-period (taller) structures, although the collapse probability was lower compared to the short-period structures, weak story behavior was commonly observed in conventionally designed SCBF. A design parameter related to the ratios of story shear demand and capacity under a pushover analysis is proposed to modify member sizes to reduce weak story behavior efficiently. This is demonstrated for a 16-story SCBF building. Regarding local deformation and force demands, simple methods to estimate out-of-plane buck-ling deformation of braces and column axial force demands are proposed. The investigation of system performance and member behavior provides seismic demands to more accurately assess the socio-economic losses of SCBFs and BRBFs for performance-based earthquake engineering.

Pseudo Dynamic Tests of a Full Scale CFT/BRB Composite Frame

Abstract: A full scale 3-story 3-bay concrete filled steel tube (CFT) column and buckling restrained braced (BRB) composite frame was tested using pseudo dynamic testing procedures and four earthquake accelerations. The key features of the structural system include using three different types of beam-to-CFT column moment connections as well as three different types of BRB . The CFT/BRB frame was designed using the displacement based seismic design procedure with a target inter-story drift limits of 0.02 and 0.025 radians for two hazard levels, 10% and 2% chances of exceedance in 50 years, respecti vely. The pseudo dynamic and analytical predicted responses of the specimen observed during the application of the earthquake load effects are in good agreement. This experimental program illustrates that the experimental response data and the video images of the specimen can be effectively disseminated through the Internet during and after the test s.

Pseudo-dynamic test of full-scale rcs frame: Part I - Design, construction, testing

Abstract: A full-scale three-story, three-bay composite steel-concrete frame was pseudodynamically tested under ground motions representing four earthquakes of varying hazard levels, with imposed story drift ratios up to about 5.5%. The frame was then subjected to a quasi-static pushover, which imposed story drifts up to 10%. Overall, the test demonstrates that the composite frame performs as implied by building provisions, exhibiting very little damage under frequent earthquakes, controlled and repairable damage under the design earthquake, and collapse prevention under the maximum considered earthquake. This paper summarizes the planning, design, construction, and execution of the frame test, including a summary of the test results. Comparisons with analytical simulations and design implications are discussed in a second companion paper.

Subassemblage tests and finite element analyses of sandwiched buckling-restrained braces

Abstract: This study presents the experimental and finite element analysis results of a proposed steel buckling-restrained brace (BRB) The proposed BRB has two components: (1) a steel core plate that carries all axial forces during tension and compression, and (2) two identical restraining members that sandwich the core plate with fully tensioned high-strength A490 bolts to prevent core buckling Instead of using unbonded material, a small air gap is provided between the core plate and the restraining members to allow for lateral expansion of the core plate under compression Since two restraining members can be disassembled easily by removing the bolts, a damaged steel core can be replaced after a large earthquake Thus, manufacturing new restraining members is not required Four BRB subassemblages were tested to investigate the inelastic deformation capabilities and verify the stability predictions for the braces Test results indicate that three BRBs with sufficient flexural rigidity of the restraining member develop (1) stable hysteretic responses up to core axial strains of 21%–26%, (2) maximum compressive loads of 1724–1951 kN (14–16 times the actual yield load), and (3) a cumulative plastic ductility that is much higher than that specified in AISC seismic provisions (2005) One BRB, intentionally designed with inadequate flexural rigidity of the restraining member, experienced global buckling as predicted Nonlinear finite element analysis was conducted for each BRB for a correlation study The objective of the analysis was to conduct a parametric study for different BRBs to further verify the effects of restraining member size, number of bolts, core plate length and cross-sectional area on buckling load evaluation The design procedure for the sandwiched BRB was provided based on test and finite element analysis results

Design Concepts for Controlled Rocking of Self-Centering Steel-Braced Frames

Abstract: The self-centering rocking steel-braced frame is a high-performance system that can prevent major structural damage and minimize residual drifts during large earthquakes. It consists of braced steel frames that are designed to remain elastic and allowed to rock off their foundation. Overturning resistance is provided by elastic post-tensioning, which provides a reliable self-centering restoring force, and replaceable structural fuses that dissipate energy. The design concepts of this system are examined and contrasted with other conventional and self-centering seismic force resisting systems. Equations to predict the load-deformation behavior of the rocking system are developed. Key limit states are investigated including desired sequence of limit states and methods to help ensure reliable performance. Generalized design methods for controlling the limit states are developed. The design concepts are then applied to a six-story prototype structure to illustrate application of the rocking steel fram...

BRBF response modification factor

Abstract: In this paper, overstrength, ductility and response modification factor of Buckling Restrained Braced frames were evaluated. To do so, buildings with various stories and different bracing configuration including diagonal, split X , chevron ( V and Inverted V ) bracings were considered. Static pushover analysis, nonlinear incremental dynamic analysis and linear dynamic analysis have been performed using Opensees software. The effects of some parameters influencing response modification factor, including the height of the building and the type of bracing system, were investigated. In this article seismic response modification factor for each of bracing systems has been determined separately and tentative values of 8.35 and 12 has been suggested for ultimate limit state and allowable stress design methods.

Local buckling restraint condition for core plates in buckling restrained braces

Abstract: Buckling Restrained Braces (BRBs) are commonly used as bracing elements in seismic zones. A key limit state governing BRB design is to prevent flexural buckling. However, when the wall thickness of the steel tube restrainer is relatively small compared to the cross-section of the core plate, the restraint conditions against the local buckling of the core plate can be critical for the stability and strength of the BRB. In this study, cyclic loading tests and numerical analyses of BRBs were carried out using various tube restrainer configurations to investigate the influence of local buckling of the restrainer on BRB strength and ductility.

Pseudo‐dynamic test of a full‐scale CFT/BRB frame—Part II: Seismic performance of buckling‐restrained braces and connections

Abstract: This paper is Part II of a two-part paper describing a full-scale 3-story 3-bay concrete-filled tube (CFT)/buckling-restrained braced frame (BRBF) specimen tested using psuedo-dynamic testing procedures. The first paper described the specimen design, experiment, and simulation, whereas this paper focuses on the experimental responses of BRBs and BRB-to-gusset connections. This paper first evaluates the design of the gusset connections and the effects of the added edge stiffeners in improving the seismic performance of gusset connections. Test results suggest that an effective length factor of 2.0 should be considered for the design of the gusset plate without edge stiffeners. Tests also confirm that the cumulative plastic deformation (CPD) capacity of the BRBs adopted in the CFT/BRBF was lower than that found in typical component tests. The tests performed suggest that the reduction in the BRB CPD capacities observed in this full-scale frame specimen could be due to the significant rotational demands imposed on the BRB-to-gusset joints. A simple method of computing such rotational demands from the frame inter-story drift response demand is proposed. This paper also discusses other key experimental responses of the BRBs, such as effective stiffness, energy dissipation, and ductility demands. Copyright © 2008 John Wiley & Sons, Ltd.