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Pasala D.T.R.,Rice University | Sarlis A.A.,State University of New York at Buffalo | Reinhorn A.M.,State University of New York at Buffalo | Nagarajaiah S.,Rice University | And 2 more authors.
Journal of Structural Engineering (United States)

The peak deformation, acceleration, and the base shear experienced by the structures can be reduced by simulating yielding in an elastic system - also referred as apparent weakening. The negative stiffness device (NSD), used in this study, exhibits nonlinear-elastic negative stiffness behavior; by adding NSD to the elastic structure (primary structure), the resulting structure-device assembly behaves like a bilinear-elastic structure. In an elastic structure, the acceleration and base shear experienced by the structure can be reduced by adding the negative stiffness device, and the additional deformations caused from the reduced stiffness can be contained by adding viscous dampers. Previously, the authors have carried out experimental studies to demonstrate the effectiveness of apparent weakening in elastic structures, but little is known about the behavior of these systems when the primary structure itself yields. This paper focuses on the issues that may emanate with the addition of NSD to the systems prone to yielding while highlighting the response reduction achieved by proper design of the NSD. Shake-table studies of a three-story fixed-base structure (3SFS) braced in top two stories, that is acting as a single degree of freedom system (SDOF) are presented in this paper. Two NSDs and a viscous damper are installed in the first story of the SDOF-3SFS. The structure is subjected to strong ground motions, with and without the NSDs, so that the columns of the SDOF-3SFS in the first story yield. Analytical models for all the components, that can capture the observed experimental behavior, are also presented in this paper. To demonstrate the advantages of apparent-weakening in yielding SDOF structures, experimental and analytical responses of four different systems, (1) 3SFS, (2) 3SFS with damper, (3) 3SFS with NSD, and (4) 3SFS with NSD and damper, are compared for a suite of ground motions. Shake-table tests on SDOF-3SFS have confirmed that by adding the NSD and damper, the acceleration and base shear and deformation of the bilinear inelastic structure and NSD assembly will be reduced by more than 20% for moderate ground motions, and the collapse of structure can be prevented for severe ground motions. © 2014 American Society of Civil Engineers. Source

Downey A.,Iowa State University | Cao L.,Iowa State University | Laflamme S.,Iowa State University | Taylor D.,Taylor Devices | Ricles J.,Lehigh University
Engineering Structures

Implementation of high performance controllable damping devices can ameliorate cost-effectiveness of structural systems for mitigation of natural hazards. However, the applications of these damping systems are limited due to a lack of (1) mechanical robustness; (2) electrical reliability; and (3) large resisting force capability. To broaden the implementation of modern damping systems, a novel semi-active damping device is proposed. The device, termed Banded Rotary Friction Device (BRFD), has enhanced applicability compared to other proposed damping systems due to its cost-effectiveness, high damping performance, mechanical robustness, and technological simplicity. Its mechanical principle is based on a band brake, which results in a high amplification of the applied force while enabling a variable control force. The theoretical model of the BRFD is presented and experimentally verified by subjecting a prototype to various harmonic loads. Results show that the prototype BRFD is capable of a maximum force of 45 kN (10 kips) using only a 267 N (60 lb) actuation force, therefore providing a mechanical advantage of 169. A 3-stage dynamic model previously developed by the authors can successfully be used to model the dynamic behavior of the BRFD. © 2016 Elsevier Ltd. Source

Laflamme S.,Massachusetts Institute of Technology | Taylor D.,Taylor Devices | Abdellaoui Maane M.,Massachusetts Institute of Technology | Connor J.J.,Massachusetts Institute of Technology
Structural Control and Health Monitoring

Semi-active control of civil structures has shown to be promising at mitigating vibrations. Those systems typically perform significantly better than passive systems, and only necessitate small power to operate. Nevertheless, semi-active control devices are not yet accepted by the construction and structural engineering communities. Among impeding factors, semi-active devices are not perceived as sufficiently reliable or robust. In this paper, a new semi-active damping device based on existing reliable technology is proposed. It is composed of a stiffness element, a viscous damper, and a braking mechanism in parallel. The device, termed the modified friction device (MFD), is essentially a variable friction damper based on vehicular braking technology, equipped with a fail-safe mechanism. The MFD is investigated as a replacement to the actual viscous damping contained in an existing structure in Boston, MA, for mitigation of accelerations caused by wind excitations. Simulations have showed that the MFD of 200 kN is capable of wind mitigation when compared with the performance of a passive viscous strategy of much larger capacity. Also, an MFD of 1350 kN capacity can perform similarly by using only a third of the number of dampers currently contained in the existing structure. Finally, the proposed device shows to be promising at mitigating inter-story displacements in the occurrence of an earthquake. Copyright © 2011 John Wiley & Sons, Ltd. Source

Nagarajaiah S.,Rice University | Pasalas D.T.R.,Rice University | Reinhorn A.,State University of New York at Buffalo | Constantinou M.,State University of New York at Buffalo | And 2 more authors.
Advanced Materials Research

Yielding can be emulated in a structural system by adding an adaptive "negative stiffness device" (NSD) and shifting the "yielding" away from the main structural system-leading to the new idea of "apparent weakening" that occurs ensuring structural stability at all displacement amplitudes. This is achieved through an adaptive negative stiffness system (ANSS), a combination of NSD and a viscous damper. By engaging the NSD at an appropriate displacement (apparent yield displacement that is well below the actual yield displacement of the structural system) the composite structure-device assembly behaves like a yielding structure. The combined NSD-structure system presented in this study has a re-centering mechanism thereby avoids permanent deformation in the composite structure-device assembly unless, the main structure itself yields. Essentially, a yielding-structure is "mimicked" without any, or with minimal permanent deformation or yielding in the main structure. As a result, the main structural system suffers less accelerations, less displacements and less base shear, while the ANSS "absorbs" them. This paper presents comprehensive details on development and study of the ANSS/NSD. Through numerical simulations, the effectiveness and the superior performance of the ANSS/NSD as compared to a structural system with supplemental passive dampers is presented. A companion paper presents the NSD and its mechanics in detail. © (2013) Trans Tech Publications, Switzerland. Source

Cao L.,Iowa State University | Downey A.,Iowa State University | Laflamme S.,Iowa State University | Taylor D.,Taylor Devices | Ricles J.,Lehigh University
Journal of Sound and Vibration

Supplemental damping can be used as a cost-effective method to reduce structural vibrations. In particular, passive systems are now widely accepted and have numerous applications in the field. However, they are typically tuned to specific excitations and their performances are bandwidth-limited. A solution is to use semi-active devices, which have shown to be capable of substantially enhanced mitigation performance. The authors have recently proposed a new type of semi-active device, which consists of a variable friction mechanism based on a vehicle duo-servo drum brake, a mechanically robust and reliable technology. The theoretical performance of the proposed device has been previously demonstrated via numerical simulations. In this paper, we further the understanding of the device, termed Modified Friction Device (MFD) by fabricating a small scale prototype and characterizing its dynamic behavior. While the dynamics of friction is well understood for automotive braking technology, we investigate for the first time the dynamic behavior of this friction mechanism at low displacements and velocities, in both forward and backward directions, under various hydraulic pressures. A modified 3-stage dynamic model is introduced. A LuGre friction model is used to characterize the friction zone (Stage 1), and two pure stiffness regions to characterize the dynamics of the MFD once the rotation is reversed and the braking shoes are sticking to the drum (Stage 2) and the rapid build up of forces once the shoes are held by the anchor pin (Stage 3). The proposed model is identified experimentally by subjecting the prototype to harmonic excitations. It is found that the proposed model can be used to characterize the dynamics of the MFD, and that the largest fitting error arises at low velocity under low pressure input. The model is then verified by subjecting the MFD to two different earthquake excitations under different pressure inputs. The model is capable of tracking the device's response, despite a lower fitting performance under low pressure and small force output, as it was found in the harmonic tests due to the possible nonlinearity in Stage 2 of the model. © 2015 Elsevier Ltd. Source

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