A crank beam in a staircase is a structural element primarily used in steel stairs to support steps and transfer heavy loads without significant bending or deflection.
Crank beams are introduced specifically when staircases are expected to bear heavy loads. According to the provided reference, this application is mostly in the case of steel stairs. In contrast, RCC (Reinforced Cement Concrete) stairs utilize the slab itself to act as a beam, effectively supporting loads without needing separate crank beams to manage bending.
Function and Purpose
The main function of a crank beam in steel stairs is to ensure that the loads placed on the steps are effectively transferred to the supporting structure without deflection. This prevents unwanted movement or sagging in the staircase, maintaining its structural integrity and stability under stress.
Here's a breakdown of why they are used and where:
- Load Bearing: Designed to handle significant weight, unlike simpler stringers which might suffice for lighter loads.
- Steel Stair Focus: Primarily a component found in steel stair construction, where individual steps need a robust underlying support system.
- Deflection Prevention: Crucial for maintaining a rigid and stable staircase structure, especially under frequent or heavy use.
- Contrast with RCC: Highlights a key difference in structural design between steel and concrete staircases, where RCC slabs inherently provide this beam-like function.
| Stair Type | Primary Load Support Method | Crank Beam Usage |
|---|---|---|
| Steel | Crank beams (under heavy loads) or stringers | Common (for heavy loads) |
| RCC | Stair slab itself acting as a beam | Not typical |
In essence, when designing a steel staircase subjected to considerable weight, integrating crank beams is a critical step to ensure the staircase remains safe, stable, and free from excessive movement.
