28-06-2012, 05:56 PM
STRUCTURAL APPLICATION OF SMART MATERIALS
STRUCTURAL APPLICATION OF SMART MATERIALS,1.docx (Size: 90.33 KB / Downloads: 55)
Introduction
The development of durable and cost effective high performance construction materials and systems is important for the economic well being of a country mainly because the cost of civil infrastructure constitutes a major portion of the national wealth. To address the problems of deteriorating civil infrastructure, research is very essential on smart materials. This paper highlights the use of smart materials for the optimal performance and safe design of buildings and other infrastructures particularly those under the threat of earthquake and other natural hazards. The peculiar properties of the shape memory alloys for smart structures render a promising area of research in this field.
Materials and Application
Shape Memory Alloys(SMA)
The term shape memory refers to the ability of certain alloys (Ni – Ti, Cu – Al – Zn etc.) to undergo large strains, while recovering their initial configuration at the end of the deformation process spontaneously or by heating without any residual deformation .The particular properties of SMA’s are strictly associated to a solid-solid phase transformation which can be thermal or stress induced. Currently, SMAs are mainly applied in medical sciences, electrical, aerospace and mechanical engineering and also can open new applications in civil engineering specifically in seismic protection of buildings.
Its properties which enable them for civil engineering application are
1. Repeated absorption of large amounts of strain energy under loading without permanent deformation. Possibility to obtain a wide range of cyclic behaviour –from supplemental and fully recentering to highly dissipating-by simply varying the number and/or the characteristics of SMA components.
2. Usable strain range of 70%
3. Extraordinary fatigue resistance under large strain cycles
4. Their great durability and reliability in the long run.
Structural Uses
1. Active control of structures
The concept of adaptive behavior has been an underlying theme of active control of structures which are subjected to earthquake and other environmental type of loads. The structure adapts its dynamic characteristics to meet the performance objectives at any instant. A futuristic smart bridge system (An artist rendition) is shown below :Fig.1 (3)
(Courtesy: USA Today dt. 03.03.97). Sun and Sun (6) used a thermo mechanical approach to develop a constitutive relation for bending of a composite beam with continuous SMA fibers embedded eccentric to neutral axis. The authors concluded that SMA’s can be successfully used for the active structural vibration control. Thompson et al (3) also conducted an analytical investigation on the use of SMA wires to dampen the dynamic response of a cantilever beam constrained by SMA wires.
2) Passive control of structures
Two families of passive seismic control devices exploiting the peculiar properties of SMA kernel components have been implemented and tested within the MANSIDE project (Memory Alloys for New Seismic Isolation and Energy Dissipation Devices). They are
Special braces for framed structures and isolation devices for buildings and bridges. Fig.2.shows the arrangement of SMA brace in the scaled frame model and the reduced scale isolation system.
3) Smart Material Tag
These smart material tag can be used in composite structures. These tags can be monitored externally through out the life of the structure to relate the internal material condition . Such measurements as stress, moisture, voids, cracks and discontinuities may be interpreted via a remote sensor(6)