Composite design for structural steel in Indianapolis, IN and Cleveland, OH

Composite design marries some of steel and concrete’s best attributes together for an efficient structural system. Let’s start by thinking about a structural system that isn’t composite design. Structural steel beams placed at 4′ on center with a steel deck spanning perpendicular which will have 4″ of concrete placed on top of the steel deck is not a composite system. That means the steel beams will carry their own weight, the weight of the steel deck and concrete above and whatever live load gets applied. The steel deck and the concrete must carry their own weight and the live load spanning from steel beam to steel beam. Another way to state the proposition: the steel beam acts on its own structurally and the steel deck and concrete act on their own structurally.

A composite system ties together that steel beam and concrete floor and forces them to act as a single structural unit. Some connector on top of the steel beam makes the steel and concrete act as one unit. The steel beam can’t slide independently of the concrete slab, the two are bonded together. Since the concrete is strong in compression, the composite system can be quite efficient structurally. The figure below illustrates the concept.

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Various types of steel structures


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.

Steel Tension And Compression Members

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

Steel Beam Members

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.

Open Web Trussed Joist

Classification Based on Shape

Shape based Classification of Steel Structures

  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

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

Types of roof Trusses

Truss Bridge

Truss Bridge

Built up members

Built-up Members

Top & Bottom Chord Bracing

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)

Rigid Steel Frame

Braced Frame

Steel Arch Structures

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

Three Hinged Truss

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

Three Hinged Arches

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

Steel Domes

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.

Cable Supported Roof Domes

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.

Eiffel Tower - Famous Steel Structure

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

James Thompson Center, Chicago

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

Geodesic Dome, Disney Land

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.

Indoor Football Facility, Illinois

  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

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