What is the main idea of the passage?

Bridge joints and bearings provide controlled space for thermal expansion and contraction, protecting the structure from harmful forces. (The passage connects temperature-driven size changes with designed movement, inspection, and structural safety.)

Why can a small size change matter on a long bridge?

Small changes across many parts add up over the structure's length. (The opening explains that a small change in one beam accumulates across a long span.)

What does “rigidly” mean in the second paragraph?

without allowing movement or bending (The contrast is with joints that let bridge sections shift in a controlled way.)

What can limit a joint's movement?

dirt (The final paragraph lists dirt among conditions that can interfere with movement.)

Why a Bridge Needs a Gap: Level 3 Reading Comprehension Questions

A long bridge changes size as its materials warm and cool. Heat makes many solids expand slightly. Cooling lets them contract. The movement may be tiny in one short beam, but it adds up across a long structure.

If every part were locked rigidly in place, changing length could create large forces. Engineers therefore design bearings and expansion joints that allow controlled movement. A joint may look like a narrow gap or a set of interlocking metal teeth. Vehicles can cross it while sections of the bridge shift by small amounts.

The gap is not evidence that builders ran out of material. It is space reserved for predictable motion over time. Its required size depends on the structure, materials, local temperatures, and design.

Joints need inspection because water, dirt, corrosion, or wear can limit movement. Some newer bridge designs reduce the number of joints, but they still must manage expansion elsewhere. Good engineering does not demand perfect stillness. It decides where motion may occur safely.

Comprehension questions