READING PASSAGE 15283s1
You should spend about 20 minutes on Question 1-13, which are based on Reading Passage 1 on the following pages,
The Diagnose of Bridge
MOST road and rail bridges are only inspected visually, if at all. Every few months, engineers have to clamber over the structure in an attempt to find problems before the bridge shows obvious signs of damage. Technologies developed at Los Alamos National Laboratory, New Mexico, and Texas A&M University may replace these surveys with microwave sensors that constantly monitor the condition of bridges.
“The device uses microwaves to measure the distance between the sensor and the bridge, much like radar does,” says Albert Migliori, a Los Alamos physicist. “Any load on the bridge – such as traffic – induces displacements, which change that distance as the bridge moves up and down.” By monitoring these movements over several minutes, the researchers can find out how the bridge resonates. Changes in its behavior can give an early warning of damage.
The Interstate 40 bridge over the Rio Grande river in Albuquerque provided the researchers with a rare opportunity to test their ideas. Chuck Farrar, an engineer at Los Alamos, explains: “The New Mexico authorities decided to raze this bridge and replace it. We were able to mount instruments on it, test it under various load conditions and even inflict damage just before it was demolished.”丨n the 1960s and 1970s, 2500 similar bridges were built in the US. They have two steel girders supporting the load in each section. Highway experts know that this design is “fracture critical” because a failure in either girder would cause the bridge to fail.
After setting up the microwave dish on the ground below the bridge, the Los Alamos team installed conventional accelerometer at several points along the span to measure its motion. They then tested the bridge while traffic roared across it and while subjecting it to pounding from a “shaker,”，which delivered precise punches to a specific point on the road.
“We then created damage that we hoped would simulate fatigue cracks that can occur in steel girders,” says Farrar. They first cut a slot about 60 centimeters long in the middle of one girder. They then extended the cut until it reached the bottom of the girder and finally they cut across the flange – the bottom of the girder’s “I” shape.
The initial, crude analysis of the bridge’s behavior, based on the frequency at which the bridge resonates，did not indicate that anything was wrong until the flange was damaged. But later the data were reanalyzed with algorithms that took into account changes in the mode shapes of the structure – shapes that the structure takes on when excited at a particular frequency. These more sophisticated algorithms, which were developed by Norris Stubbs at Texas A&M University, successfully identified and located the damage caused by the initial cut.
“When any structure vibrates, the energy is distributed throughout with some points not moving, while others vibrate strongly at various frequencies,” says Stubbs. “My algorithms use pattern recognition to detect changes in the distribution of this energy.” NASA already uses Stubbs’ method to check the behaviour of the body flap that slows space shuttles down after they land.
A commercial system based on the Los Alamos hardware is now available, complete with the Stubbs algorithms, from the Quatro Corporation in Albuquerque for about $100 000.
Tim Darling, another Los Alamos physicist working on the microwave interferometer with Migliori, says that as the electronics become cheaper, a microwave inspection system will eventually be applied to most large bridges in the US. “In a decade I would like to see a battery or solar-powered package mounted under each bridge, scanning it every day to detect changes,” he says
The reading Passage has seven paragraphs A-l.
Which paragraph contains the following information?
Write the correct letter A-l, in boxes 1-5 on your answer sheet.
1 The professional team put pressure to test the motion of the bridge.
2 Engineers apply knife to the bridge to excite cracks.
3 A precious chance of experiment to certificate ideas.
4 The popular application of the microwave inspection system within a decade
5 How the microwave works
Choose the correct letter, A, B, C or D.
Write your answers in boxes 6-9 on your answer sheet.
6 What is the responsibility of engineers in order to prevent the damage of the bridge before the invention of the microwave sensors?
A They have to climb over the bridge.
B They have to regularly check the bridge
C They have to inspect the condition of the bridge through monitors.
D They have to employ others to help them check the bridge.
7 What did the device take advantage of the microwaves to do?
A to calculate the distance
B to induce displacements
C to change the distance
D to give an advanced warning
8 Why did highway experts think the design as “fracture critical” ?
A Engineers failed to take several tests according to different conditions.
B Engineers failed to install conventional accelerometers.
C The supporting part would probably make the bridge fall down.
D No cars drove past the bridge.
9 What was the achievement of Norris Stubbs’ s complicated algorithms?
A the identification and location of the damage.
B the movement of some points.
C the renounce of the bridge
D the distribution of the energy
Complete the blanks below. Choose No MORE THAN THREE WORDS from the passage for each answer.
10. The weight of the 2500 bridges is sustained by…………………… in every sector.
11 ……………………were set up by the Los Alamos team in order to test the movement of the bridge.
12. In order to cause break, the Los Alamos team decided to make a …………………… at first step.
13. The …………………… in the bottom of the bridge resembles shape.
The Diagnose of Bridge
10 two steel girders
11 accelerometer/conventional accelerometer