Types of Steel Structures - Tension Members, Compression Members, Trusses Shell etc

Classification of Steel Structures

1. Tension Members
2. Compression Members
3. Truss Systems and Frame Systems
4. Built-up Members and Structures
5. Shell Structures
6. Suspension Structures

Tension Members:

Primarily occur as:

1. Chord Members in trusses
2. In diagonal bracing in bracing systems
3. Cable elements in suspension roofs, main cables of suspension bridges and suspenders.

Compression Members

Primarily Occur as:

• Columns in buildings;
• Chord Members in trusses and diagonal members in end panels of trusses
• Stability is an important consideration in design and behavior of compression members
• Area is generally spread out to maximize Radius of Gyration

Beam Members:

1. Primarily loaded transverse to the longitudinal axis and resist loading by flexure
2. X-sectional area is located as far from the neutral axis as is practical
3. Commonly W shapes are used in most cases
4. For deeper beams I-shaped sections made by welding plates are commonly used
5. For smaller loads and spans open-web joists are commonly used
6. Instability due to lateral Torsional Buckling is an important consideration

Open-Web Steel Joist

1. Economical & popular for Roof & floor framing.
2. Bar joist are supported by bearing walls or steel girders.
3. Floor of thin concrete reinforced in both directions with rebars or welded wire fabric.

Classification Based on Shape

1. Classical Skeleton framing
2. Steel truss
3. Rigid frames
4. Arches
5. Domes
6. Cable supported Roofs
7. Classical system supported by beams, girders and columns.
8. Beams: W or S shapes, Channel shapes for roof purlins
9. Columns: generally W shapes

Steel Trusses

1. Triangular rigid structure
2. Most common double pitched roof trusses
3. Fink & Pratt.
4. Most common flat trusses: Pratt & Warren
5. No span limit
6. Often prefabricated
7. Used with wood or steel purlins to support the roof.
8. Bracing: if resting on masonry walls
   1. Diagonal bracing in alternate bays
   2. Continuous struts(angles, channels

Truss Bridge

Built-up Members

Rigid Frames

1. For large unobstructed floor areas and ceiling heights.
2. Spans generally 40' to 100'
3. Members are connected by bolting and welding
4. Members: W shapes or web plates fillet welded to flange plates
5. Connection to foundation with a base plate(bolted)

Steel Arch Structures

1. Used in field houses, exhibition halls,. with span over 300'
2. Most common type: three hinged arch

• Lateral bracing;
• Diagonal bracing in curved surfaces between arches
• Lateral bracing of ribs with purlins or trussed purlins.

Steel Domes

• Used for large circular areas: Assembly halls, gymnasium, field houses..
• Spans up to 400' in diameter
• Structural members:
• Perimeter (Tension ring)
• Domes and rings are supported by columns braced laterally or by bearing walls
• Purlins supports the roof deck and span between ribs

Cable Supported Roofs

Chicago O'Hare International Airport Restaurant

1. Reinforced concrete compression ring 190'dia
2. Ring is supported on 26 RCC columns 58ft above ground
3. Tension ring W-shape 13' dia
4. Sag of cables 10.5'
5. Ends of cables are anchored to the two rings
6. Roof deck: precast RCC slabs 3.5" thick which fit between cables with projecting ends of reinforcement hooking over the cables.

Examples of Famous Steel Structures

Eiffel Tower, Paris

1. The World's tallest structure at times(990').
2. Was originally built to last 20 years.

James R,Thompson Center, Chicago

1. The building is enclosed by 17 story curtain walls.
2. The diameter of rotunda is 160'
3. The rotunda projects as a cylinder and its top resembles a drum without a dome slanting towards plaza.
4. Office spaces are between rotunda's walls and outer skin

The Geodesic Dome at Walt Disney World

1. Spaceship earth is a huge golf ball, standing 180 ft.
2. The structure is designed to withstand wind speeds of 200 mph
3. Structure: steel framing clad with faceted aluminum panels, and stands on 3 pairs of steel legs.
4. Site was mostly swamp, filled with much, organic material with 95% water content.
5. As a solution, 2.5 million cubic yards of soil was removed and replaced by clean material

Indoor Football Facility,University of Illinois, Urbana

• The roof structure is semi-parabolic dome
• A large single arched box truss spans the length of the field and supports 1/2 of roof load.

1. 110 Stories Tall
2. Total Height = 1725 ft
3. Based on revolutionary Bundled Tube Design
4. Rigid outer walls act as walls of hollow tube
5. There are 9 tubes in all
6. The number of tubes reduces with height
7. Designed by late Fazl-ur-Rehma from Bangladesh
8. Supported by 114 piles