Bridge steel trusses — support condition and purpose Most steel bridge trusses are supported with a hinge (pin) at one end and a roller at the other end. The main advantage of this hinge–roller arrangement is that the truss remains stable under loads and thermal movement.

Introduction / Context:
Bridge trusses are typically supported by a hinge (pin) at one end and a roller at the other. This classical arrangement appears in steel, concrete, and composite bridges because it guarantees stability while accommodating temperature changes, shrinkage, and support settlements.

Given Data / Assumptions:

• One bearing provides a pin (hinge) that restrains translation in two directions but allows rotation.
• The other bearing provides a roller that restrains one direction and allows longitudinal movement.
• Loads include dead load, live load, wind, and thermal effects.

Concept / Approach:
For a determinate and stable support system, the structure needs just enough reactions to prevent rigid-body motion without over-restraining it. The hinge–roller pair supplies three reaction components in total (two at the hinge, one at the roller). This prevents sway and uplift while permitting expansion/contraction.

Step-by-Step Solution:

Verification / Alternative check:
If both ends were fixed against longitudinal movement, temperature rise would induce large axial forces. Conversely, two rollers would not prevent lateral instability. The hinge–roller combination is the balanced solution.

Why Other Options Are Wrong:

• False: Ignores the stabilizing and movement-accommodating role of the supports.
• Both ends fixed: Over-restraint, leading to thermal stresses and indeterminacy.
• Only for wooden trusses / only short spans: The principle is material-agnostic and applies to a wide range of spans.

Common Pitfalls:
Confusing “stability” with “full fixity.” Stability means no rigid-body motion; it does not require restraining all degrees of freedom.

Final Answer:
True