The Interstate 40 bridge over the Rio Grande river in Albuquerque provided the researchers with a rare opportunity to text 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.” In 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 accelerometers 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 centimetres 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.
AI explanationShows the answer. Tap to open.
Question Focus: The diagram shows instruments fixed along the bridge to measure movement. We need to identify what these instruments are.
Correct Answer: D
Why this is correct: The diagram shows small devices attached to the bridge to record movement. The passage says the team installed conventional accelerometers along the span to measure its motion, which matches exactly. So the answer is accelerometers.
Passage Reference: After setting up the microwave dish on the ground below the bridge, the Los Alamos team installed conventional accelerometers at several points along the span to measure its motion.
Common Mistake: Some students choose microwave dish because it is also equipment. But the microwave dish was placed on the ground, not attached along the bridge. This is a context shift trap.
Paraphrasing: Passage: 'installed conventional accelerometers to measure its motion' = Diagram: 'devices measuring movement on the bridge'
Tips: If the diagram shows small sensors attached to a structure, look for words like measure, record, or monitor in the passage.
Key Vocabulary:
- installed = put in place
- motion = movement
Question Focus: The diagram labels the main structural beams that support the bridge.
Correct Answer: B
Passage Reference: 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.
Why this is correct: The diagram points to the long beams holding the bridge up. The passage clearly says these bridges have two steel girders supporting the load. That is exactly what the diagram shows. So the answer is steel girders.
Common Mistake: Students sometimes choose bridge, but that labels the whole structure, not one specific part. This is a partial truth trap.
Paraphrasing: Passage: 'two steel girders supporting the load' = Diagram: 'main supporting beams'
Tips: If the diagram arrow points to one part, not the whole object, avoid general words like bridge.
Key Vocabulary:
- girder = large support beam
- load = weight
Question Focus: The diagram shows a piece of equipment placed on the ground below the bridge.
Correct Answer: F
Passage Reference: After setting up the microwave dish on the ground below the bridge,
Why this is correct: The diagram shows a round device on the ground under the bridge. The passage says they set up the microwave dish on the ground below the bridge, which matches perfectly. So the answer is microwave dish.
Common Mistake: Some students pick accelerometers because they remember equipment being used. But accelerometers were installed on the bridge, not on the ground. This is a wrong section trap.
Paraphrasing: Passage: 'microwave dish on the ground below the bridge' = Diagram: 'equipment under the bridge'
Tips: Always check location words like on, under, or along. They are very important for diagram questions.
Key Vocabulary:
- below = under
- dish = round antenna
Question Focus: The diagram labels a specific part at the bottom of the steel girder.
Correct Answer: A
Passage Reference: finally they cut across the flange - the bottom of the girder's 'I' shape.
Why this is correct: The diagram highlights the bottom edge of the girder. The passage explains they cut across the flange, which is the bottom of the girder's I shape. That directly matches the diagram. So the answer is flange.
Common Mistake: Students may choose steel girders, but that names the whole beam, not the bottom part only. This is a partial truth trap.
Paraphrasing: Passage: 'flange - the bottom of the girder's I shape' = Diagram: 'bottom part of the beam'
Tips: When a diagram labels a small section of a larger object, look for technical part names in the passage.
Key Vocabulary:
- flange = bottom edge of a beam
- extended = made longer
General Tips:
- Diagram labels usually follow the passage order, so move through the text step by step.
- Pay close attention to location words like on, below, along, or in the middle.
- Do not choose a general word if the diagram clearly points to one specific part.
- Cross out options as you use them so you do not reuse the same word.
The rest of this explanation is for members. Sign in free to read why the other options are wrong, key words and tips.
Sign in to read the full explanation