Seismic Response Prediction of Self-centering Concentrically Braced Frames Using Genetic Programming PDF Download

Author: AmirHossein Gandomi
Publisher:
ISBN:
Category : Earthquake engineering
Languages : en
Pages : 115

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Book Description
One of the commonly used earthquake-resistant structural systems is the conventional concentrically braced frame (CBF) system, which is widely used in the US. However, CBFs have limited drift capacity prior to a brace buckling occurrence. Self-centering concentrically braced frame (SC-CBF) systems have been recently developed to increase drift capacity prior to initiation of damage and to minimize residual drift. SC-CBF systems have more complex behaviors than conventional CBFs: the seismic response of SC-CBF systems depends on many new parameters such as rocking behavior, post-tensioning bars, and energy dissipation elements. Additionally, uncertainty of earthquake properties affects the system response. An accurate prediction of roof drift is essential to the design of SC-CBF systems. In this study, a robust modeling tool, genetic programming, is used to predict the peak roof drift response under seismic loading. At first, the design and analysis procedure of the SC-CBF is automated in this study, as is not available in current design software. Three levels of complexity are considered for the numerical models: i.Linear materials and geometry ii.Nonlinear materials and linear geometry iii.Nonlinear materials and nonlinear geometry where nonlinear materials capture yielding of the structural members and nonlinear geometry is considered by modeling buckling in the braces. Using these three levels of nonlinearity, the effect of nonlinearity on SC-CBF response is also investigated in this study.Several SC-CBF systems are designed based on the design basis earthquake using a variety of mechanical and geometrical parameters. Then, the peak roof drift is predicted and formulated in two ways. First, the statistical parameters of peak roof drift (mean and standard deviation) are formulated based on the design variables (mechanical and geometrical parameters) in three different nonlinearity levels. Second, the peak roof drift response of each earthquake is formulated based on the design variables and selected ground motion intensity measures. To select the prediction parameters, particularly the ground motion intensity measures, evolutionary correlation coefficients are introduced in this study. There are many parameters involved in the formulation of the peak roof drift response of an individual earthquake. Therefore, a multi-objective strategy is also used in this study to maximize the accuracy and minimize the complexity of the model. The results of this study can then be used in future designs to implement more efficient SC-CBF systems with a more accurate roof drift prediction.

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: Nathan Brent Chancellor
Publisher:
ISBN: 9781321222487
Category :
Languages : en
Pages : 828

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Book Description
The SC-CBF lateral force resisting system has been studied and a first generation design procedure for SC-CBFs has been developed. A laboratory testing program at Lehigh University tested a 4-story, 0.6-scale SC-CBF using hybrid simulation. The 4-story SC-CBF was subjected to 31 intense earthquakes at both the design basis earthquake (DBE) intensity level as well as the maximum considered earthquake (MCE) level. The SC-CBF performed very well.

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: Jiun-Wei Lai
Publisher:
ISBN:
Category :
Languages : en
Pages : 1023

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Book Description
This dissertation summarizes both experimental and analytical studies on the seismic response of conventional steel concentrically braced frame systems of the type widely used in North America, and preliminary studies of an innovative hybrid braced frame system: the Strong-Back System. The research work is part of NEES small group project entitled "International Hybrid Simulation of Tomorrow's Braced Frames." In the experimental phase, a total of four full-scale, one-bay, two-story conventional braced frame specimens with different bracing member section shapes and gusset plate-to-beam connection details were designed and tested at the NEES@Berkeley Laboratory. Three braced frame specimens were tested quasi-statically using the same predefined loading protocol to investigate the inelastic cyclic behavior of code-compliant braced frames at both the global and local level. The last braced frame specimen was nearly identical to one of those tested quasi-statically. However, it was tested using hybrid simulation techniques to examine the sensitivity of inelastic behavior on loading sequence and to relate the behavior observed to different levels of seismic hazard. Computer models of the test specimens were developed using two different computer software programs. In the software framework OpenSees fiber-based line elements were used to simulate global buckling of members and yielding and low-cycle fatigue failure at sections. The LS-DYNA analysis program was also used to model individual struts and the test specimens using shell elements with adaptive meshing and element erosion features. This program provided enhanced ability to simulate section local buckling, strain concentrations and crack development. The numerical results were compared with test results to assess and refine and the ability of the models to predict braced frame behavior. A series of OpenSees numerical cyclic component simulations were then conducted using the validated modeling approach. Two hundred and forty pin-ended struts with square hollow structural section shape were simulated under cyclic loading to examine the effect of width-to-thickness ratios and member slenderness ratios on the deformation capacity and energy dissipation characteristics of brace members. The concept of a hybrid system, consisting of a vertical elastic truss or strong-back, and a braced frame that responds inelastically, is proposed herein to mitigate the tendency of weak-story mechanisms to form in conventional steel braced frames. A simple design strategy about member sizing of the proposed Strong-Back System is provided in this study. To assess the ability of the new Strong-Back System to perform well under seismic loading, a series of inelastic analyses were performed considering three six-story hybrid braced frames having different bracing elements, and three six-story conventional brace frames having different brace configurations. Monotonic and cyclic quasi-static inelastic analyses and inelastic time history analyses were carried out. The braced frame system behavior, bracing member force-displacement hysteresis loops, and system residual drifts were the primary response quantities examined. These indicated that the new hybrid system was able to achieve its design goals. Experimental results show for the same loading history that the braced frame specimen using round hollow structural sections as brace members has the largest deformation capacity among the three types of bracing elements studied. Beams connected to gusset plates at the column formed plastic hinges adjacent to the gusset plate. The gusset plates tend to amplify the rotation demands at these locations and stress concentrations tended to result in early fractures of the plastic hinges that form. To remedy this problem, pinned connection details used in the last two specimens; these proved to prevent failures at these locations under both quasi-static and pseudo-dynamic tests. Failure modes observed near the column to base plate connections in all of the specimens suggest the need for further study. Both OpenSees and LS-DYNA models developed in this study predict the global braced frame behavior with acceptable accuracy. In both models, low-cycle fatigue damage models were needed to achieve an acceptable level of fidelity. Shell element models were able to predict local behavior and the mode of failures with greater but not perfect confidence. OpenSees analysis results show that the proposed hybrid braced frames would perform better than conventional braced frames and that the story deformations are more uniform. Finally, future research targets are briefly discussed at the end of this dissertation.

Author: Mojtaba Dyanati Badabi
Publisher:
ISBN:
Category : Earthquake engineering
Languages : en
Pages : 180

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Book Description
Self-centering concentrically braced frame (SC-CBF) systems have been developed to increase the drift capacity of braced frame systems prior to damage to reduce post-earthquake damages in braced frames. However, due to special details required by the SC-CBF system, the construction cost of an SC-CBF is expected to be higher than that of a conventional CBF. While recent experimental research has shown better seismic performance of SC-CBF system subjected to design basis earthquakes, superior seismic performance of this system needs to be demonstrated for both structural and nonstructural components in all ground motion levels and more building configurations. Moreover, Stakeholders would be attracted to utilize SC-CBF if higher construction cost of this system can be paid back by lower earthquake induced losses during life time of the building. In this study, the seismic performance and economic effectiveness of SC-CBFs are assessed and compared with CBF system in three building configurations. First, probabilistic demand formulations are developed for engineering demand parameters (inter-story drift, residual drift and peak floor acceleration) using results of nonlinear time history analysis of the buildings under suites of ground motions. Then, Seismic fragility curves, engineering demand (inter-story drift, peak floor acceleration and residual drift) hazard curve and annual probabilities of exceeding damage states are used to evaluate and compare seismic performance of two systems. Finally, expected annual loss and life cycle cost of buildings are evaluated for prototype buildings considering both direct and indirect losses and prevailing uncertainties in all levels of loss analysis. These values are used evaluate economic benefit of using SC-CBF system instead of CBF system and pay-off time (time when the higher construction cost of SC-CBF system is paid back by the lower losses in earthquakes) for building configurations. Additionally, parametric study is performed to find acceptable increase in cost of SC-CBFs comparing to CBFs and impact of economic discount factor, ground motion suite and building occupancies on economic effectiveness of the SC-CBF system in three configurations. Results of this study indicates that, SC-CBF system generally shows better seismic performance due to damages to structural and non-structural drift sensitive components but worse performance due to damages to acceleration sensitive components. Therefore, loss mitigation in structural and non-structural damages are major source of economic benefit in SC-CBFs. SC-CBF system is not feasible for high rise buildings and low seismic active locations. If the cost of SC-CBFs are twice as CBF frames, the higher cost is paid back in a reasonable time during the life time of the buildings. SC-CBFs are more feasible for banks/financial institutions than general office buildings.

Author: 范廷海
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: David Alan Roke
Publisher:
ISBN: 9781124195391
Category :
Languages : en
Pages : 733

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Book Description
The scope of this study includes the development of a design procedure for SC-CBF systems, a parametric study of different SC-CBF configurations, analytical and experimental studies of a large-scale SC-CBF test structure, and evaluation of the performance of the SC-CBF test structure.

Author: Lucie M. Blin-Bellomi
Publisher:
ISBN:
Category : Civil engineering
Languages : en
Pages : 94

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Book Description
This paper focuses on the finite element simulation of a self-centering concentrically-braced frame (SC-CBF) using the LS-DYNA 971 solver. SC-CBFs have been developed as a damage-free alternative to conventional concentrically braced frame (CBF) systems. Previous experimental pseudo-dynamic hybrid simulation results for SC-CBF systems indicated that the system works as intended; however, these pseudo-dynamic tests were unable to measure the effect of the mass of the SC-CBF structure on the dynamic response. This thesis analyzes the dynamic effect of the mass on a SC-CBF using the LS-DYNA software. A finite element model (FEM) of a buckling restrained braced frame (BRBF) was built to calibrate an LS-DYNA model to experimental results. This study parallels published experimental and finite element analysis results, and validates the finite element analysis method chosen to conduct the SC-CBF impact study. The objective of the thesis is to determine the effect of the mass of the SC-CBF on dynamic response. A comparative study is undertaken with two different FEMs of the SC-CBF system: one including the mass of the steel, and one treating the steel as massless.

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

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Book Description
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.