Rectangular Hollow Section – Plastic Section Modulus Calculator
The Rectangular Hollow Section (RHS) Plastic Section Modulus Calculator calculates the plastic section modulus (Zₚ) of rectangular hollow steel sections. This value is widely used when determining the ultimate bending capacity of structural steel members.
Section Diagram
What is Plastic Section Modulus?
Plastic Section Modulus describes the capacity of a cross-section once the entire section has reached its yield stress. It represents the maximum bending resistance before plastic collapse occurs and is an important property used in structural steel design.
Unlike elastic section modulus, which only considers elastic behaviour, plastic section modulus assumes the section has fully yielded. This allows engineers to calculate the plastic moment capacity of beams and structural members.
Rectangular hollow sections are commonly specified because they provide excellent bending performance while remaining lightweight and economical. Their closed shape also offers improved torsional stiffness compared with many open sections.
Why calculate the Plastic Section Modulus of a Rectangular Hollow Section?
Plastic section modulus is essential when designing or assessing RHS members subjected to bending.
Engineers use this value to:
- Calculate plastic bending capacity
- Size steel beams efficiently
- Compare alternative section sizes
- Verify structural designs against Eurocode requirements
- Assess modifications to existing buildings and steelwork
Accurate section properties enable safe, economical and compliant structural designs.