Using NiTi SMA tendons for vibration control of coastal structures

Abstract

Hurricane damage inflicted upon coastal structures, particularly residential structures, results in millions of dollars in financial damage and loss of life each year. A major cause of this damage usually begins with roof uplifts of coastal structures; prevention of roof uplift helps mitigate damage to coastal structures by hurricanes. Development of more effective fastening mechanisms for the connections between the walls and the roofs of these structures will aid in damage reduction to coastal structures. Recent developments in the new field of auto-adaptive materials offer promising opportunities for developing radically new fastening mechanisms. One of the classes of materials in this category is shape memory alloys (SMAs). SMAs are very attractive for structural application because of their major constitutive behaviors such as pseudoelastic characteristics. The pseudoelastic behavior of NiTi SMAs is a unique hysteretic energy dissipation behavior which, combined with a very long fatigue life, makes NiTi a viable candidate for developing new fasteners. However, as a first step it is important to develop an in-depth understanding of NiTi behavior under dynamic loads. Research carried out in this area has been very limited in scope. Therefore, in this paper, eight different configurations of bracing systems, divided into two categories, are explored on a single degree of freedom (SDOF) structure to investigate the feasibility of developing devices for the mitigation of hurricane damage. These bracing devices basically utilize the hysteretic energy dissipation of NiTi resulting from its pseudoelastic characteristic. Since the main goal of this ongoing research is to develop a thorough understanding of the pseudoelastic and hysteretic behavior of SMAs under severe dynamic loading/excitation, a series of earthquake data has been considered as the source of excitation. Through this analysis both the damping and stiffening characteristics of NiTi wires and the effect of these dynamic characteristics on changing the dynamic response of the structure are studied. In the first category the NiTi wires are not pre-strained, while in the second category they are pre-strained. In each category, four different combinations of wire length and modeling of pseudoelastic behavior of NiTi wire are considered. A bilinear stress-strain model is used for representing the pseudoelastic behavior of NiTi tendons, capable of representing internal yield, internal recovery and trigger line concepts. This study establishes that hybrid tendons have the highest damping and stiffening effects on the structure. It is also concluded that, when the amplitude of excitation is small, tendons act as stiffening devices. Once the amplitude of the excitation is large enough to initiate stress-induced phase transformations, tendons act as energy absorption devices. These findings provide very useful information for the development of more effective fastening devices that can withstand severe dynamic loads, such as hurricane loadings.

Semi-Active Control of Concrete Building Frames using Smart Cables of Shape Memory Alloys

“…The comparison of peak values of the dynamic response and control parameters for the eight story frame model with SMA based semi-active tendons installed at alternate floors (1,3,5,7), consecutive floors (1,2,3,4) versus the corresponding uncontrolled frame are summarized in Table 1. For purposes of comparison, the table also includes the peak displacement response and control force for the originally reported multi-story frame model with an active mass driver (AMD) installed at the roof.…”

“…Previously reported applications of SMAs in structural base isolation include implementation of SMA bars for base-isolation of highway bridges [3], and SMA wire re-centering devices for buildings [4]. The SMAs have been implemented as passive energy dissipation devices in braces for framed structures [5,6,7], in dampers for cable-stayed bridges [8] and in connection elements for columns [9]. Most of the reported research focuses on application of SMAs for passive vibration control of structures, which takes advantage of only the damping property of super-elastic SMAs.…”

A homogenized free energy model for hysteresis in thin-film shape memory alloys

“…Additionally, SMAs exhibit a damping capacity much larger than that of a number of conventional materials. In this case, SMA hysteresis is being utilized to design earthquake and hurricane-resistant civil structures [21,92,105,113]. Most of these macroscopic applications are limited in bandwidth because of heating and cooling restrictions inherent to bulk SMAs.…”

Pseudo-elastic hysteresis damping characteristics of SMA hybrid composite lamina

“…The mechanism of using pseudo-elastic SMA for passive vibration control is based on the stress-induced martensite transformation of the austenite phase, which produces high pseudo-elastic hysteresis damping. In the application of passive vibration control, the pseudo-elastic SMA are often seen to be fi xed or hung outside of structures in the form of wires, especially used for energy dissipation devices or dissipaters [2][3][4][5] . As we all know, a single SMA wire can only be used in tension, otherwise buckling will occur, which limits the application of pseudo-elastic SMA.…”