Applies To
	Product(s):	STAAD.Pro
	Version(s):	ALL
	Environment:	ALL
	Area:	Modeling Solutions
	Subarea:	Geometry
	Original Author:	Modestas Turulis, Bentley Technical Support Group

The following are some of the limitations or features not supported with curved members

• Tapered section properties
• Composite decks
• PRIS ROUND sections
• Beta angle
• Member releases, global or tangent
• Member Springs
• Member offsets
• Member end springs
• Physical members
• Member Tension/compression
• Any span loads except "Uniform load throughout the length in global directions", such as:
  • Member Loads - UMOM, CON, CMOM, LIN, TRAP
  • Area Load, One Way, Floor Load
  • Wind Load, Prestress, Poststress
  • Temperature load, Strain
  • Fixed End Load
  • Snow Load
  • Moving load
• Imperfections
• Geometric stiffness, Pdelta, buckling, Pdelta KG with/without dynamics
• Mass for dynamics will not include the effect of the member cg being off the chord line
• Intermediate section displacements, and hence the deflection diagram
• Intermediate section forces, and hence the bending moment and other forces diagram
• Steel or concrete design at any location other than nodes
• Member selection
• Weld design

Limitations faced with curved beams in designing

It is not advisable to perform steel design on curved members using STAAD. The reasons are:

1. The design codes are written for straight members, not curved ones. The rules in most standard design codes do not adequately address the peculiarities of curved members. LY and LZ for example in the KL/r checks are the straight line distances between the bracing points of a straight member. To use those rules on curved members without adjusting for the curvedness may not be correct. An out of plane load on a curved member causes major torsional moments, but most codes only discuss axial forces, bending and shear, not torsion.
2. STAAD can calculate the member forces only at the nodes of curved members. It cannot calculate them at intermediate span locations. Consequently, during steel design, these members will be designed for the forces at their ends only. Intermediate section points within the span cannot be designed.
3. STAAD can calculate the displacements at the nodes of curved members. It cannot calculate them at intermediate span locations. Consequently, deflection check cannot be performed for curved members.
4. STAAD does not plot beam stresses on curved members. 

Due to all  these limitations, modeling the curved beams using a series of straight segments might be a better option.