Development and Numerical Validation of New Hybrid Multi-core Buckling-restrained Braces for Enhanced Seismic Performance PDF Download
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Author: Pierre Thibault Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Contemporary seismic-resistant design of steel structures relies on the dissipation of earthquake energy through significant inelastic deformations. Buckling-restrained braced frames (BRBFs) are a type of concentrically-braced system characterized by braces that yield both in tension and in compression. Thanks to a restraining mechanism that confines a ductile steel core, buckling-restrained braces (BRBs) can take advantage of the cyclic ductility of the steel material. However, BRBs commonly display a low post-yield stiffness, causing substantial interstory drifts and large residual drifts after seismic events. Moreover, yielding of the core is often tied to only a single performance objective, thus making its response at other levels of seismicity largely unpredictable. Hybrid BRB solutions are explored as an alternative to the traditional BRB system to overcome its limitations. The hybrid concept is hinged on harnessing different characteristics from different materials that are carefully combined into one ductile design to achieve a desirable response. This numerical study has three main objectives. Potential core metals are first evaluated to determine the best combinations of two materials with complementary engineering properties. Analysis of experimental data indicates that the post-yield behavior of hybrid BRBs is improved by employing 350WT carbon steel in conjunction with another metal, which possesses a low-yield and high-strain-hardening capacity (e.g., 304L stainless steel, 5083-O aluminum alloy, A36 carbon steel, or LYP-100 low-yield-point steel). Afterwards, two new hybrid BRB systems are designed to accommodate the complex deformation pattern of three core plates connected in parallel. The first proposed option has a restraining mechanism made from concrete-filled steel tubes, while the second hybrid BRB option is fabricated exclusively from metal plate components. Lastly, multiple finite element simulations are carried out on numerical models to quantitatively validate the performance enhancement. Compared to conventional BRBs, hybrid BRBs exhibit an improved strain hardening response, a slight increase in axial stiffness, and a greater energy dissipation capability for an equivalent brace strength.
Author: Pierre Thibault Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Contemporary seismic-resistant design of steel structures relies on the dissipation of earthquake energy through significant inelastic deformations. Buckling-restrained braced frames (BRBFs) are a type of concentrically-braced system characterized by braces that yield both in tension and in compression. Thanks to a restraining mechanism that confines a ductile steel core, buckling-restrained braces (BRBs) can take advantage of the cyclic ductility of the steel material. However, BRBs commonly display a low post-yield stiffness, causing substantial interstory drifts and large residual drifts after seismic events. Moreover, yielding of the core is often tied to only a single performance objective, thus making its response at other levels of seismicity largely unpredictable. Hybrid BRB solutions are explored as an alternative to the traditional BRB system to overcome its limitations. The hybrid concept is hinged on harnessing different characteristics from different materials that are carefully combined into one ductile design to achieve a desirable response. This numerical study has three main objectives. Potential core metals are first evaluated to determine the best combinations of two materials with complementary engineering properties. Analysis of experimental data indicates that the post-yield behavior of hybrid BRBs is improved by employing 350WT carbon steel in conjunction with another metal, which possesses a low-yield and high-strain-hardening capacity (e.g., 304L stainless steel, 5083-O aluminum alloy, A36 carbon steel, or LYP-100 low-yield-point steel). Afterwards, two new hybrid BRB systems are designed to accommodate the complex deformation pattern of three core plates connected in parallel. The first proposed option has a restraining mechanism made from concrete-filled steel tubes, while the second hybrid BRB option is fabricated exclusively from metal plate components. Lastly, multiple finite element simulations are carried out on numerical models to quantitatively validate the performance enhancement. Compared to conventional BRBs, hybrid BRBs exhibit an improved strain hardening response, a slight increase in axial stiffness, and a greater energy dissipation capability for an equivalent brace strength.
Author: David J. Miller Publisher: ISBN: Category : Languages : en Pages :
Book Description
Although conventional earthquake-resisting structural systems provide adequate life safety when properly designed, they often rely on significant structural damage to dissipate the seismic energy. The structural damage and the residual drift that may result from the inelastic response can make a building difficult, if not financially unreasonable, to repair after an earthquake. As a result, development of systems that return to their initial position (i.e., 0́−self-center0́+) following an earthquake and minimize structural damage is a crucial need. The research presented in this thesis aims to address this need by creating an innovative self-centering brace for advanced seismic performance. In the present study, the seismic behavior and performance of self-centering buckling-restrained braces (SC-BRBs) using shape memory alloys (SMAs) is investigated. The SC-BRBs consist of a typical BRB component, which provides energy dissipation, and pre-tensioned superelastic NiTi shape memory alloy rods, which provide self-centering. The SMA rods are attached to the BRB portion of the brace using a set of concentric tubes and free-floating anchorage plates that cause the SMA rods to elongate when the brace is both in tension and compression. Using a five-story building as context, half-scale SC-BRBs are designed and fabricated for experimental validation. To characterize hysteretic response, the braces are subjected to a cyclic loading protocol adapted from the AISC Seismic Provisions for Structural Steel Buildings. The results of the experiments are used to validate an SC-BRB model in OpenSEES, which is used to conduct further parametric studies of SC-BRB behavior.
Author: American Society of Civil Engineers Publisher: ISBN: 9780784414859 Category : Buildings Languages : en Pages : 550
Book Description
Standard ASCE/SEI 41-17 describes deficiency-based and systematic procedures that use performance-based principles to evaluate and retrofit existing buildings to withstand the effects of earthquakes.
Author: Stefan Wijanto Publisher: ISBN: Category : Earthquake resistant design Languages : en Pages : 406
Book Description
The recent series of damaging earthquakes in Christchurch, New Zealand (NZ) has encouraged greater recognition of the post-earthquake economic impacts on NZ society and higher emphasis on low-damage earthquake resisting systems. Buckling Restrained Braces (BRB) are seen as a significant contender for such a system. They have been developed and used in both North America and Japan and are recognised for their superior seismic performance compared to existing concentrically braced systems due to the suppression of brace buckling in compression, and hence the development of equal strength and stiffness under tension and compression loading. However, the focus of development in those countries has been on establishing a testing regime to which companies produce patented systems. This has limited their application in New Zealand due to small demand and has generated interest in development of a generic solution. This research project focuses on the development of a reliable design procedure and detailing requirements for a generic BRB system. This started with the development of a design procedure based on modifications of the concentrically braced frame (CBF) design procedure contained in HERA Report R4-76 (1995). This has been used to develop a representative design for a 10 storey building, from which a brace size and bay has been chosen for experimental testing. A series of dynamic sub-assemblage tests were performed at the University of Auckland on this BRB frame with two different brace connection configurations to gauge the performance of the designed system. The results are presented and discussed herein. An initial prototype model for analytical modelling of the sub-assemblage frame has also been constructed and subjected to inelastic time history analyses. The experimental tests show stable hysteresis loops which is a principal feature of the BRB system, albeit with the occurrence of slack in the connections. These test results show the reliability of the proposed design procedure and detailing, especially after procedural modifications to prevent slack from occurring in the two different connection systems.
Author: John Andrew Tinker Publisher: ISBN: Category : Aluminum, Structural Languages : en Pages : 212
Book Description
An ultra-lightweight buckling-restrained brace (ULWBRB) is developed using a highly ductile aluminum core and FRP restrainer. Utilization of lightweight materials results in a BRB that is 25% the weight of traditional mortar-filled tube varieties allowing easy installation in small to medium sized buildings requiring seismic retrofit without the need for heavy equipment. Construction utilizes commonly stocked materials able to be customized for required strength, drift, and geometry limitations. Analytical single degree of freedom (SDOF) and Euler buckling models are compared with published equations to determine the required restrainer stiffness (RRS). SDOF models yield RRS values 200% higher than the Euler model. Applied end moments due to frame deformation are incorporated into a modified design method that gives RRS values 50% higher than Euler model without eccentricity. RRS is provided using a bundled and wrapped FRP tube configuration using a developed shear flow method considering composite action. Uniaxial low-cycle fatigue (LCF) testing of a 6061-T6 candidate alloy provides data for a constitutive model using combined kinematic-isotropic hardening. LCF testing of round short gage coupons indicates the candidate alloy is capable of stable cycling to 2%, 3%, and 4% total strain with excellent ductility. Early fracture of specimens at 24, 18, and 11 cycles, respectively, also indicates that other candidate alloys should be examined for improved fatigue life. However, inconsistency is noted between similar tests of 6061-T6 that were able to achieve up to 76 cycles at 2.5% total strain. ULWBRB FEA models loaded monotonically consistently give higher RRS values as compared to the analytical methods. This is due to assignment of initial imperfections, longer more realistic unbraced length, higher axial loads achieved through the post-yield region, and plastic hinging potential. Cyclic simulations of braces with the same RRS values are also able to achieve reliable and stable hysteretic behavior through 21 cycles. If a less stiff restrainer is used, cumulative energy dissipation potential is reduced considerably due to pinched hysteresis loops and strain ratcheting. Applied end moments are found to have a linear effect on the RRS that can be modeled by superposition of the buckling effect plus end moment.
Author: Yue Xiao Publisher: ISBN: Category : Buckling (Mechanics) Languages : en Pages : 213
Book Description
A series of earthquakes occurred in Christchurch that demonstrate the need for developing low damage economic multi-storey structures. Post tensioned timber was proposed to be used on constructing such multi-storey framed structures with additional seismic resisting system to reduce the damage on structure. Buckling Restrained Braces (BRB) as a well-designed, widely used seismic resisting system used on multi-storey steel structures has been modified into a timber steel BRB for artistically fitting into the proposed structure. This research project focuses on designing and testing a feasible Timber Steel BRB that can meet New Zealand design requirements. A detailed design procedure has been developed based on a case study in a 7 story office building located in Christchurch. Based on the case study, the design load and minimum displacement requirement for one full scale BRB is calculated as 668kN and 25mm. After preliminary Finite Element Modelling analysis and required strength calculations on performance of yielding core with different cross-section detail (cruciform, H-section, flat section and I-section). An I-section yielding core with a flange width to web height ratio of 0.42 is selected due to the lower requirement in restraining strength. With further design, the timber outer casing is separated into 4 pieces and glued together to encase the I-section shape. Due to the limitations in the testing machine, three 1:2.5 scale Timber-Steel BRBs are constructed and tested. The experimental tests show stable hysteresis loops which suggest good performance of the proposed Timber-Steel BRB and two test specimens with perpendicular to grain reinforcement are able to deform to the minimum required deformation which indicates this design is feasible to use in New Zealand. The results also indicate the timber reinforcement along the brace in both yielding core axes and the debonding agent for glue bound timber steel BRB are necessary.
Author: Pierre Thibault
Author: Pierre Thibault
Author: David J. Miller
Author: American Society of Civil Engineers
Author: Stefan Wijanto
Author: John Andrew Tinker
Author: Michael G. Gray
Author: Yue Xiao
Author: Toru Takeuchi
Author: Wei Song
Author: Subhash Chandra Goel