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Over the past 10 years there has been a growing need to introduce closed-loop control technology for vibration suppression of buildings subject to wind or earthquake disturbances. This paper deals with the investigation of the effectiveness of a fuzzy logic based time variable damping tuned mass damper (TMD) on a building structure undergoing free and forced vibrations. The uniqueness of this approach is the application of a robust, nonlinear fuzzy based controller to emulate a time-optimal control strategy. Fuzzy logic based time variable damping is introduced into a semi-active TMD in order to enhance its performance in the vibration suppression of buildings. First, a single story structure for three different vibration suppression approaches is studied. The fuzzy logic based time variable damping TMD (fuzzy TMD) is compared to the baseline passive TMD as well as a conventional proportional-derivative (PD) controller. Forced vibration is introduced using a resonant harmonic sinusoidal excitation (i.e. same frequency as the fundamental frequency of the structure). Finally, the fuzzy TMD is compared to the baseline for the free vibration of a 15 story structure. For both structures studied, MATLAB® based simulation results show that the passive TMD and the PD, both constant gain approaches, provide similar results whereas the fuzzy TMD yields half the settling time. This effort clearly demonstrates the potential of a variable gain (damping) strategy for the vibration suppression of buildings. [ABSTRACT FROM AUTHOR]

Abstract: The results of the finite element simulations are used to develop a modified stiffness model to predict the behavior of thick-flange in built-up T-stub connections with Complete Joint Penetration (CJP) and fillet welds. Using ABAQUS, three-dimensional finite element (FE) models are developed for the selected cases. The performance of the FE model results is compared to experimental results for validation. The FE model results are used to develop the modified stiffness model that characterizes the behavior of thick-flange in built-up T-stub connections. The model is based on a combination of finite element and a stiffness modeling approach that incorporates the overall flange deformations of key component elements, and it includes nonlinear material behavior of both tension bolts and base material, accounts for pretension of fasteners, and contact interactions. The modified stiffness model consists of linear and nonlinear springs which model deformations from tension bolt elongation, T-stub flange, and prying force. The model predicts the force-deformation curve of the whole T-stub flange taking into account flange-partial-yielding and accounting for the contact force encountered. A new failure limit state is highlighted, which is partial-yielding at the K-zone followed by bolt fracture, with or without prying. The behavioral characteristics of the flange in T-stub connections are examined including strength, stiffness, and deformation capacity. Comparisons of model predictions with FE and experimental data show that the modified stiffness model accurately predicts the response of thick-flange built-up T-stub connections with CJP or fillet welds and accounts for flange-partial-yielding followed by tension-bolt-fracture, with and without prying. [Copyright &y& Elsevier]

Abstract: This study investigates the prying behavior in thick-flange built-up T-stub/column systems that should be addressed in designing full-strength double tee connections for use in moment resisting frames which satisfy prequalification requirements. In particular, this study focuses on the phenomenon herein indicated as secondary prying, which is related to the additional forces that are introduced into the tension bolts due to significant bending of the column flange. Three-dimensional finite element models that incorporate pretension of fasteners, full contact interactions, and nonlinear material characteristics are used to investigate secondary prying effect in thick-flange T-stub/column system with and without continuity plates. This study provides insight as to whether continuity plates are necessary in columns when designing and detailing full-scale T-stub connections for prequalification. The effect of secondary prying is incorporated into an existing prying strength model for thick T-stubs to quantify the amount of total prying encountered in thick built-up T-stub connections with and without continuity plates. Parameters that impact the secondary prying in thick flange T-stub/column systems were identified based on the geometric configuration that results from the design of full-strength double tee connections with deep girders. The results show that decreasing the effect of secondary prying is achieved through either increasing the column size, or adding continuity plates to the column. This study provides information for detailing columns without continuity plates as well as quantifying the amount of prying so engineers can design for the additional load by increasing the bolt diameter. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to quantify the impact of semi-rigid connection properties on steel frame behavior. A finite element model and computer program is developed to investigate the moment–rotation behavior of eight-bolt stiffened endplate connections. The model includes both the beam side and the column side of a connection. A mesh generator is developed to generate a three-dimensional mesh with desired fineness. The numerical results are verified by comparison with experimental results. Parametric studies are conducted to develop prediction equations for the parameters in a power model representing the connection behavior. Frame analyses are conducted incorporating this connection model. A formula to classify fully and partially restrained endplate connections is proposed based on frame analysis results. [Copyright &y& Elsevier]

Features an approach toward formulating analytical models to predict the moment-rotation hysteresis behavior of top and seat angle steel frame connections. Experimental program; Test results; Analytical models in moment-rotation hysteresis; Conclusions.

The results of a series of finite-element (FE) simulations and experimental studies are used to develop two prying models that predict the failure strength of thick-flange built-up T-stub connections with complete joint penetration (CJP) and fillet welds. A parametric study based on identifying the major geometric and force-related parameters that vary within current acceptable steel fabrication and design practices is used to select the cases for analysis. The strength prying models predict the capacity of thick-flange built-up T-stub connections with CJP and fillet welds for the failure limit state of the partial yielding tension flange followed by bolt fracture. The accuracy of the developed strength models are verified with FE results of built-up T-stubs designed for full strength compared with existing models reported in the literature. Based on the results of this study, a refined design procedure that takes into account the partial yielding in thick-flange T-stubs is proposed. [ABSTRACT FROM AUTHOR]

Abstract: As a result of the SAC project, rolled T-stub connections have been demonstrated to be a viable alternative to welded connections for steel frames in seismic areas. One difficulty with these connections is that oftentimes the rolled profiles needed to fabricate the T-stub needed for deep beams are not immediately available to fabricators and so built-up sections are the only alternative. The goal of this investigation is to demonstrate through experimental and finite element studies that built-up T-stub connections can be successfully detailed for use in special and intermediate moment frames in seismic areas. The results of a series of component tests on built-up T-stubs, obtained by means of complete joint penetration welding (CJP) and fillet welding are presented and discussed, providing supporting evidence for the best fabrication choice. Component tests investigating hole fabrication practices are also presented, studying their effect on ductility under monotonic and cyclic loads. Furthermore, finite element models of thick flange T-stub connections is presented and finite element simulation results are compared to experimental results to demonstrate the applicability of built-up T-stub connections for use in special and intermediate moment frames. The finite element results show an acceptable agreement with the experimental results and describe the behavior. A partial yielding of the T-stub flange followed by bolt fracture is highlighted as a failure mode based on the finite element and the experimental results. It is anticipated that the data collected from a forthcoming series of full-scale tests will lead to the prequalification of this connection typology. [Copyright &y& Elsevier]