Vibration Suppression Through Variable Stiffness and Damping Structural Joints

Abstract

This paper introduces a new semi-active strategy for vibration control of truss and frame structures equipped with variable stiffness and damping joints which consist of a shape memory polymer (SMP) core reinforced by an SMP-aramid composite skin. When the joints are actuated to the transition temperature through thermal actuation, the SMP core transitions from a glassy to a rubbery state through a viscoelastic region, which causes a stiffness reduction and an increase of damping. The mechanic behavior of the joint can be thought of as transitioning from a moment to a pin connection. This way, it is possible to cause a shift of the structure natural frequencies and to increase damping, which is employed to obtain a significant reduction of the dynamic response. This paper comprises two parts: (1) characterization of a variable stiffness and damping material model through experimental testing; (2) numerical simulations of a truss bridge and a four-story frame, which are equipped with variable stiffness and damping joints. The truss bridge (case A) is subjected to a resonance and a moving load while the four-story frame (case B) is subjected to El Centro earthquake loading. For case A under resonance loading, the dynamic response can be reduced exclusively through a frequency shift and ignoring viscoelastic effects. For case A under moving load and case B under earthquake loading, vibration suppression is mostly caused by the increase of damping due to viscoelastic effects. Control time delays due to joint heating have been included in the analysis. When the joints are actuated to the transition range 55 • C-65 • C, which is specific to the SMP adopted in this study, the acceleration peak amplitude reduces by up to 95% and 87%, for case A and case B, respectively. For both cases, damping increases by up to 2.2% from undamped conditions (25 • C). This work has shown that the adoption of variable stiffness and damping structural joints has great potential to enable a new and effective semi-active control strategy to significantly reduce the structure response under a wide range of dynamic loading conditions.

Seismic control performance of a three‐story frame prototype equipped with semi‐active variable stiffness and damping structural joints

“…This paper builds on and expands the work carried out in (Wang et al 2020a; Wang et al 2020b) 28,29 , which focused on material characterization and numerical simulations, by providing an experimental assessment of semi-active seismic response control through thermal actuation of variable stiffness and damping structural joints. More specifically, this work offers the following new contributions:…”

“…This paper builds on and expands the work carried out in (Wang et al 2020a; Wang et al 2020b) 28,29 , which focused on material characterization and numerical simulations, by providing an experimental assessment of semi‐active seismic response control through thermal actuation of variable stiffness and damping structural joints. More specifically, this work offers the following new contributions: Detailed design of a 1/10‐scale prototype equipped with 12 adaptive joints, which includes element sizing, joint detailing, thermal actuation system, motion control system (shake table), and data acquisition system. Frequency shift and damping increase caused by thermal actuation of the adaptive joints are measured through free vibration tests. Semi‐active response control through shake‐table tests under four different seismic excitations.…”

“…For structures that are equipped with adaptive joints, the change of material properties that occur in the transition phase triggered by thermal actuation induces a shift of natural frequencies and an increase of damping ratio. Numerical simulations have shown that such frequency shift and damping increment can be effectively employed to mitigate the structure response under dynamic excitations 29 . Under excitations that have several high‐energy frequency components (e.g., earthquakes), although a temporary resonance condition may occur in some cases due to the structure frequency shift, the effect of damping increment is dominant when the joints are actuated to the transition temperature.…”

“…28 Dynamic mechanical analysis (DMA) tests have shown that the joint core material features a significant stiffness reduction through thermal actuation and a parallel increase of damping caused by viscoelastic effects. This property change has been employed in (Wang et al 2020b) 29 to investigate a new semi-active control strategy for truss and frame structures equipped with variable stiffness and damping joints. Vibration control simulations of a truss bridge and a four-story frame subjected to resonance, moving, and earthquake loading have shown that through thermal actuation of the adaptive joints, it is possible to cause a shift of the structure natural frequencies and to increase the damping ratio, which results in a significant reduction by up to 95% of the acceleration peak amplitude.…”

“…(B) joint connected to four aluminum tubes; (C) SMP-aramid skin 29 actuation, and (b) to strengthen the connection of the joint with structural elements. The reinforcement skin is the part of the joint that takes most of the stress, which is the highest when the joint is thermally actuated owing to the core stiffness reduction.…”