SMART STRUCTURES AND MATERIALS
- A structure which can adapt to the changing environmental conditions is called SMART.
- This smartness can be achieved by using smart materials like Shape-memory alloys (SMA), piezoelectric crystal, magneto-rheological fluids etc.
- Smart structures can take care of their own health and resist natural calamities.
MAIN FACTORS AFFECTING STRUCTURAL HEALTH:
- Differential settlement
- Earth quakes and vibrations
- Structural distress
- Corrosion of reinforcement
- Temperature stresses
Structures constructed on clayey soil prone to differential settlement mainly for two reasons:
- Consolidation in clay is very slow
- Clay has high swell-shrink nature.
The conventional methods adopted to overcome this problem are:
- Under reamed pile foundation
- Providing water proof apron
- Replacing a layer of clay with CNS.
The smart way of preventing settlement
- The volume of clay remains unchanged if optimal moisture content is maintained.
- This can be achieved by adopting the principle of electro-osmosis as shown below.
EARTH QUAKES AND VIBRATIONS
- The seismic waves or other shock waves can be disastrous for a structure if it is at resonant frequency.
- It is characterized by suddenness of onset and violence of attack.
- The conventional design methods of earth quake resistant structures have not proved very effective so far.
Smart Way of Resisting Earth Quake
- Magneto-rheological fluid is a smart material which changes from liquid to solid when exposed to magnetic field.
- When this fluid is filled in a cylinder and exposed to alternate magnetic it can act as a damper for shock waves.
- An ultrasonic device is used to detect the seismic waves. It is converted into AC current and passed to dampers.
- The solid-liquid transformation takes place at a frequency corresponding to that of seismic wave.
- The seismic wave is destructively interfered and the building is prevented from shock.
- It is estimated that a damper of 200kg can resist a force of 20000N of force.
- Many such dampers are fitted to the building as shown in fig.
The structural distress is caused mainly due to:
- Improper analysis and design
- unexpected loading conditions
Serious distress can even cause structural collapse. The conventional way overcoming this problem is by providing a factor of safety.
Dynamic Solution for Structural Distress
- A piezoelectric sheet of polyvinylidene fluoride (PVDF) polymer is placed under the structure.
- When a load causes deflection in beam it the PVDF develops electrical charges.
- These charges are amplified and converted into heat energy.
- This heat energy is supplied to a SMA at the sides of the structure.
- The down ward deflection caused by load is counteracted by the lateral force exerted by the SMA.
- This arrangement can be used to monitor the extent of deflection of the material and thus determine the point of distress before the actual failure.
HEALTH MONITORING OF BRIDGES
CORROSION OF REINFORCEMENT
The reinforcement bars undergo electrochemical reaction mainly due to
· Use of salty water in preparation of mortar.
· Due to seepage of water into the structure.
In both the cases localized electroplating occurs causing stress on concrete member.
The conventional solution for this problem is not economical
Smart Way to Check Corrosion
- A thin metal foil of non corrodible material is provided surrounding the reinforcement bar.
- The metal sheet is given with positive potential and the rod is given negative potential.
- When the reinforcement increases in diameter it comes in contact with the foil.
- Now electroplating takes place in reverse direction.
ADVANTAGES OF THE SMART STRUCTURES
The smart structure has the following advantages:
- This structure cut downs a lot of material cost incurred in using under reamed pile and factor of safety.
- India has 25% of area prone to earth quake. This smart technology will help in saving a lot of men and material.
- The health monitoring of structures will help in forecasting failure and will provide time for rehabitation.
- 35% of deccan pleateau has black cotton soil, the use of this technology can ensure safe and economical construction over there.
- As the structure is constantly maintained the service life increases and the need for repair decreases.