|Dr. N. Subramanian
Joined: 21 Feb 2008
Location: Gaithersburg, MD, U.S.A.
|Posted: Thu Nov 12, 2009 5:39 pm Post subject: New Earthquake-Proof Alloy Allows Bridges to Bend but Not Br
|New Earthquake-Proof Alloy Allows Bridges to Bend but Not Break
One of the most tragic story of 2008 was the 7.9 magnitude earthquake that struck on May 12 in the central Sichaun province, China. The quake triggered landslides that sent debris piling into lakes and rivers. News agencies stated that an estimated 14 million homes
collapsed during the quake, leaving more than 60,000 dead. In earthquake-riddled California and Nevada, bridges are some of the structures most vulnerable to intense vibrations, and whose destruction is most worrisome for disaster assistance.
Nature has its own furies but man has consistently fought back to survive. Here is a small discovery to defeat the fury of Earthquakes.
New reinforcing materials, such as a nickel-titanium alloy recently developed and currently being tested by the University of Nevada, could make bridges elastic—allowing them to move slightly with vibrations and then revert back to their original shape.
The University of Nevada's Seismic Performance Testing Center
The ground shook at the University of Nevada last week, registering at a magnitude that topped the Richter scale, but, thankfully, it wasn't due to a devastating earthquake—it was a lab-made rehearsal. Engineers at the University of Nevada
in the US have tested a new design for a flexible bridge that can bounce back after an earthquake. According to a report in New Scientist, the engineers used three large shake tables to test a 33.5-m long, 181-tonne bridge sporting an exotic new design.
The bridge, a quarter-scale replica of its projected real-life size, was subjected to 10 seconds of shaking like that created by an earthquake. The test simulated the intensity of a magnitude 8 quake, and though the concrete bridge suffered a little surface damage, it remained structurally intact.
Saiidi's new alloy, which he calls nitinol, is made to reinforce concrete bridges and try to prevent disasters caused by failing infrastructure, as occurred in a magnitude 6.9 quake in Northridge, Calif. The 1994 quake caused an estimated $20 billion damage to freeways and buildings.
The concrete used in the bridge was reinforced with "smart" nickel titanium - Nitinol - a "shape-memory" alloy commonly used in bendable spectacle frames. The alloy retains a memory of the shape it was cast into and, after deformation, springs back to its intended form. "The nickel-titanium rods replace steel bars in critical segments of bridge columns," said Saiid Saiidi, a member of the research team. Concrete with "dumb" steel inside is designed to yield to a quake''s shocks, flexing to reduce the force it experiences, according to Colin Taylor, an earthquake engineering specialist at the University of Bristol in the UK.
Using shape-memory alloys should mean that, after the quake, a bridge support attempts to return to its former shape instead, and can remain usable.
Advances in materials science are a key component of future bridge design—to hold bridges up longer and take less damage during disasters. But there are many ways to allow bridges to move during earthquakes while remaining intact. The new San Francisco-Oakland Bay Bridge, for example, will be a single-tower span that makes use of collapsible beams that connect the roadway, piles that are placed deep in the ground and beams that shear under excess load.
The UNR research team is taking advantage of unique features of materials such as nickel/titanium alloys, polyvinyl fibers mixed with cement, and rubber materials to potentially revolutionize seismic design of future bridges to help protect lives, prevent damage and avoid bridge closure even when there’s a strong earthquake.
See the Video of this unique Expt:
The experiment is part of a larger multi-university project funded by the National Science Foundation (NSF) under the George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES) research program. Other UNR faculty involved in the $2.4 million project are Dr. I. Buckle and Dr. G. Pekcan. Researchers from U.C. Berkeley, U.C. San Diego, Florida International University, Georgia Tech, Stanford University, Kansas University and University of Illinois, Chicago, Tokyo Institute of Technology, and the University of Ljubljana have been involved in other aspects of the project.
This test is the largest of its kind in the United States. The test was part of a series of three tests of materials and design to make bridges safer. The first test in Feb. 2007 used a standard design bridge of the same size and the third bridge test will continue the look at new innovative designs and materials.
“There is no other facility in the country as big and with the equipment we have to conduct these types of tests,” Saiidi said.
Three 50-ton capacity shake tables acted in unison to shake the 200 tons of concrete and steel that swayed, buckled and cracked as twice the acceleration intensity of the 1994 Northridge, Calif. earthquake tore at the structure. The bridge model was shaken with bidirectional forces to realistically simulate an earthquake. During the 10-second quake simulation, 400 movement sensors mounted at various critical points along the bridge measured the structure''s response. "Our results show that not only (did) the Nitinol/concrete combination reduce the residual tilt (after the earthquake) to near zero, the damage was negligible and repairable," said Saiidi.
Note: The term Nitinol is derived from its composition and its place of discovery: (Nickel Titanium Naval Ordnance Laboratory). William Buehler along with Frederick Wang, discovered its properties during research at the Naval Ordnance Laboratory in 1962. A shape memory alloy (SMA, smart metal, memory alloy, muscle wire, smart alloy) is an alloy that "remembers" its original, cold, forged shape, and which returns to that shape after being deformed by applying heat. This material is a lightweight, solid-state alternative to conventional actuators such as hydraulic, pneumatic, and motor-based systems. Shape memory alloys have applications in industries including medical and aerospace.SMAs are used for Eyeglass frames(under the trademarks Flexon and TITANflex), in Orthopaedic surgery and in dental braces.
In 1989 a survey was conducted in the United States and Canada that involved seven organizations. The survey focused on predicting the future technology, market, and applications of SMA's. The companies predicted the following uses of Nitinol in a decreasing order of importance: (1) Couplings, (2) Biomedical and medical, (3) Toys, demonstration, novelty items, (4) Actuators, (5) Heat Engines, (6) Sensors, (7) Cryogenically activated die and bubble memory sockets, and finally ( lifting devices.
3. "The Alloy That Remembers", Time, 1968-09-13, http://www.time.com/time/magazine/article/0,9171,838687,00.html .