Parametric Study of Friction-Damped Braced Frames with Buckling-Restrained Columns Using Recommended Frame and BRC Strength Factors PDF Download

Author: Chibuike Anozie
Publisher:
ISBN:
Category : Buildings
Languages : en
Pages : 172

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The friction-damped braced frame system with buckling restrained columns (FDBF-BRC) is being developed to provide significant drift capacity while limiting damage due to residual drift and soft-story mechanisms. BRCs will be on both ends of the frame, where they will experience tension and compression due to conditioned earthquake simulations on OPENSEES. This research is a continuation of previous work by Dr. David A. Roke's previous graduate student, Dr. Felix C. Blebo, for multiple stories, based on the established design recommendations. This study includes buildings with 4, 6, and 8 stories, with application of recommended frame hardening factor and BRC hardening factor. This system consists of beams, columns, braces interlocking at a central column, a pinned support condition, and BRCs at both external columns of first story. Energy dissipation to minimize overall seismic response on each floor level are products of the incorporated BRCs and friction generated at the lateral-load bearings. A suite of 20 DBE, 20 MCE, and 20 FOE-level ground motions is numerically applied to several FDBF-BRCs. Based on dynamic analysis results, the FDBF-BRC still proves to be an effective seismic-resistant system. The system's performance shows a nearly uniform inter-story drift response, high ductility, and high energy dissipation capacity.

Author: Felix C. Blebo
Publisher:
ISBN:
Category : Damping (Mechanics)
Languages : en
Pages : 172

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Book Description
Conventional concentrically braced frame (CBF) systems have limited drift capacity prior to brace buckling, and related damage leads to deterioration in strength and stiffness. CBFs are also susceptible to weak story failure. A pin- supported self-centering friction-damped braced frame system with buckling-restrained columns (FDBF-BRC) is being developed to provide significant drift capacity while limiting damage due to residual drift and soft-story mechanisms. The FDBF-BRC system consists of beams, columns, and braces branching off a central column, with buckling restrained columns (BRCs) incorporated into the system at the first story external column positions. The BRCs and friction generated at lateral-load bearings at each floor level are used to dissipate energy to minimize the overall seismic response of the FDBF-BRC system. Vertically aligned post-tensioning bars provide additional overturning moment resistance and aid in self-centering the system to eliminate residual drift. The pin support condition and the lateral stiffness of the system enable it to exhibit a nearly uniform inter-story drift distribution. In this study, a suite of 44 DBE-level ground motions used in FEMA P695 is numerically applied to several FDBF- BRCs to demonstrate the seismic performance of the system. The results show that the FDBF-BRC system has a nearly uniform inter-story drift response, high ductility, and a high energy dissipation capacity, and is an effective seismic-resistant system.

Author: Felix C. Blebo
Publisher:
ISBN:
Category : Civil engineering
Languages : en
Pages : 135

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Book Description
Conventional braced frame systems have limited drift capacity before brace buckling and related damage leads to deterioration in strength and stiffness. A friction-damped braced frame (FDBF) system is being developed to provide significant drift capacity while limiting damage and residual drift. The FDBF system consists of beams, columns, and braces branching off a central column. Friction at lateral-load bearings that transfer inertia forces from the floor diaphragms to the FDBF is used to dissipate energy, to reduce the overall seismic response of the FDBF system, and to provide overturning moment resistance. Vertically oriented post-tensioning bars provide additional overturning moment resistance and help to reduce residual drift. The thesis introduces a preliminary design approach for FDBF systems. Several FDBF systems are designed, and pushover and dynamic nonlinear analysis results are presented. Dynamic analysis results confirm the expected drift capacity and behavior of the system.

Author: Brandon Jeffers
Publisher:
ISBN:
Category : Civil engineering
Languages : en
Pages : 129

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Conventional concentrically-braced frame (CBF) systems have limited drift capacity before brace buckling and related damage leads to deterioration in strength and stiffness. Self-centering concentrically-braced frame (SC-CBF) systems have been developed with increased drift capacity prior to initiation of damage. SC-CBF systems are intended to minimize structural damage and residual drift under the design basis earthquake. The behavior of SC-CBF system differs from that of a conventional CBF system in that the SC-CBF columns are designed to uplift from the foundation at a specified level of lateral loading, initiating a rigid-body rotation (rocking) of the frame. Vertically-oriented post-tensioning bars resist uplift and provide a restoring force to return the SCCBF columns to the foundation (self-centering the system). This thesis considers an SC-CBF configuration that includes two sets of columns: the SC-CBF columns, which uplift from the foundation, and the adjacent gravity columns, which do not uplift. Lateral-load bearings between the columns at each floor level transfer the inertia forces from the gravity columns (which are connected to the floor diaphragm) to the SC-CBF (which is not directly connected to the floor diaphragm). Friction at the lateral-load bearings increases the overturning moment capacity of the SCCBF and dissipates energy under cyclic loading. A parametric study of SC-CBFs with friction-based energy dissipation elements is presented in this thesis. Nonlinear static and dynamic analyses of SC-CBFs with different coefficients of friction at the lateral-load bearings are presented to illustrate the effect that changing the coefficient of friction has on the design, behavior, and dynamic response of SC-CBF systems.

Author: Luciano Martin
Publisher:
ISBN:
Category : Damping (Mechanics)
Languages : en
Pages : 0

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Addresses the question of plan-wise slip load and stiffness distribution of friction damper equipped braces in an effort to refine the procedure currently employed in design.

Author: M. R. Hasan
Publisher:
ISBN:
Category : Civil engineering
Languages : en
Pages : 139

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Book Description
Conventional concentrically braced frame (CBF) systems have limited drift capacity prior to structural damage, often leading to brace buckling under moderate earthquake input, which results in residual drift. Self-centering CBF (SC-CBF) systems have been developed to maintain the economy and stiffness of the conventional CBFs while increasing the ductility and drift capacity. SC-CBF systems are designed such that the columns uplift from the foundation at a specified level of lateral loading, initiating a rocking (rigid body rotation) of the frame. Vertically aligned post tensioning bars resist column uplift and provide a restoring force to return the structure to its initial state (i.e., self-centering the system). Friction elements are used at the lateral-load bearings (where lateral load is transferred from the floor diaphragm to the SC-CBF) to dissipate energy and reduce the peak structural response. Previous research has identified that the frame geometry is a key design parameter for SC-CBFs, as frame geometry relates directly to the energy dissipation capacity of the system. This thesis therefore considered three prototype SC-CBFs with differing frame geometries for carrying out a comparative study. The prototypes were designed using previously developed performance based design criteria and modeled in OpenSees to carry out nonlinear static and dynamic analyses. The design and analysis results were then thoroughly investigated to study the effect of changing frame geometry on the behavior of SC-CBF systems. The rocking response in SC systems introduces large higher mode effects in the dynamic responses of structure, which, if not properly addressed during design, can result in seismic demands significantly exceeding the design values and may ultimately lead to a structural failure. To compare higher mode effects on different frames, proper quantification of the modal responses by standard measures is therefore essential. This thesis proposes three normalized quantification measures based on an intensity-based approach, considering the intensity of the modal responses throughout the ground motion duration rather than focusing only on the peak responses. The effectiveness of the three proposed measures and the conventionally used peak-based measure is studied by applying them on dynamic analysis results from several SC-CBFs. These measures are then used to compare higher mode effects on frames with varying geometric and friction properties.

Author: Parvaneh Baktash
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Peter C. Talley
Publisher:
ISBN:
Category :
Languages : en
Pages : 115

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When subjected to strong earthquake ground motions, conventional steel braced frames are vulnerable to soft-story mechanisms, whereby the weakest story accumulates more damage relative to the rest of the structure. This reduces the overall strength of the structure, increases the cost of repairs, and can cause issues during the design process due to the reduced redundancy of the system. One method for mitigating this behavior is the use of an elastic spine frame. These frames combine a stiff vertical "spine", such as a truss or shear wall, with a more ductile, energy-dissipating system. The spine typically spans the height of the structure and is designed to remain elastic, distributing earthquake demands across the height of the structure and bridging weak stories. One proposed elastic spine frame is the "strongback" braced frame, which merges a steel buckling-restrained braced frame and an elastic truss, using the buckling-restrained braces for energy dissipation and the truss for force distribution. However, strongback braced frames do not have well-established design criteria. Specifically, there is no generally accepted method for ensuring that the strongback remains elastic, and seismic performance factors have not been developed. Additionally, conventional capacity design underestimates the demands on the spine. It is desirous to have a method for design of these frames that hews closely to existing methods utilizing the equivalent lateral force method. This thesis presents the first phase of a study to address these gaps in the design provisions and to better understand the behavior of this system. A suite of building frames which employ the strongback system were designed with the intent of using them as the basis for parametric analytical studies in the second phase. The suite of frames was selected using the requirements of FEMA P695, the state-of-the-art method for determining seismic performance factors. Three alternative capacity design methods were developed and compared to basic capacity design to identify which is best suited to efficiently achieve the performance objectives. The methods were evaluated for efficiency in the design process, and for feasibility of the resulting designs. However, evaluation of performance objectives is the goal of future study.

Author: Brandon W. Fuqua
Publisher:
ISBN:
Category :
Languages : en
Pages :

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The hazards of seismic activity on building structures require that engineers continually look for new and better methods of resisting seismic forces. Buckling restrained braced frames (BRBF) are a relatively new lateral force resisting system developed to resist highly unpredictable seismic forces in a very predictable way. Generally, structures with a more ductile lateral force resisting system perform better in resisting high seismic forces than systems with more rigid, brittle elements. The BRBF is a more ductile frame choice than special concentrically braced frames (SCBF). The ductility is gained through brace yielding in both compression and tension. The balanced hysteretic curve this produces provides consistent brace behavior under extreme seismic loads. However regular use of the BRB is largely limited to Japan where the brace type was first designed. The wide acceptance of buckling restrained braced frames requires the system to become easily designable, perform predictably, and common to engineers. This report explains the design process to help increase knowledge of the design and background. This report also details a comparison of a BRBF to a SCBF to give familiarity and promote confidence in the system. The design process of the BRBF is described in detail with design calculations of an example frame. The design process is from the AISC Seismic Provisions with the seismic loads calculated according to ASCE 7 equivalent lateral force procedure. The final members sizes of the BRBF and SCBF are compared based on forces and members selected. The results of the parametric study are discussed in detail.

Author: André Filiatrault
Publisher:
ISBN:
Category : Buildings
Languages : en
Pages : 486

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