Structural steel design:

This page is under construction, future topics are:

• Design steel joist metal roof

• Design of metal deck concrete floor

• Design of steel beam with W, I shape and Channel (Allowable stress design 1989 edition)

• Design of steel beam with W, I shape and Channel (Load and resistance factor design, 2nd edition)

• Design of steel column (allowable stress design, 1989 Edition)

• Design of steel column (Load and resistance factor design, 2nd edition)

• Connection design: bolt connection, weld connection.

Topics in this page:

• Compact, non-compact, and slender sections

• Determine unsupported length for beams

Compact, non-compact, and slender sections

Steel sections are categorized in three category: compact, non-compact, and slender sections based flange width to thickness ratio, b/t, and web thickness to thickness ratio, h/t_w.

Flange: 

Compact section: when b/t £ l_p. The section is a compact section.

Non compact section: when l_p £ b/t £ l_r. The section is a non-compact section.

Slender section: when b/t > l_r. The section is a slender section.

Web: 

Compact section: when h/t_w £ l_p. The section is a compact section

Non compact section: when l_p £ h/t_w£ l_r. The section is a non-compact section.

Slender section: when h/t_w > l_r The section is a slender section.

Limits of  l_p and l_r AISC 13th edition Table B4.1

Note: 

1. Most steel rolled sections are compact sections.  

2. For other shapes, please see AISC manual. 

Determine unsupported length for beams

Simply supported beams

1. For simply supported beam, the top flange is in compression. If the beam is directly attached to roof deck or floor slab, the compression flange is fully supported.  The unsupported length L_b is 0.

2. When the beam supporting joists or other beams, and its flange is directly attached to the supported joists or other beams, the unsupported length is the spacing of the joists or other beams.

Cantilever beams:

1. For cantilever beam, the compression flange is at the bottom of the beam.  If the bottom flange is unbraced, the unsupported length is the length of the cantilever beam. 

2. If bracing is provided at the bottom flange, the unsupported length is the spacing between bracings.

Continuous beams:

1. For the positive moment portion of the beam, the compression flange is at the top of the beam.  The unsupported length is determined as a simply supported beam.

2. For the negative moment portion of the beam, the compression flange is at the bottom of the beam.  The unsupported length is determined as a cantilever beam.