CABLE-STAYED STRUCTURES
keywords : Cable, Structure, Architecture, Struktur, Kabel, Arsitektur
1. DEFINITION
Cable-stayed structures support horizontal planes (bridge decks, roofs, floors) with inclined cables that are attached to, or run over, tower(s).
2. STRUCTURAL CHARACTERISTICS
The cables of a cable-stayed structure work solely in tension. The cables must not only have sufficient capacity to carry the dead load, but must also have enough reserve capacity to carry the live load. Otherwise, the horizontal surface may suffer serious deformations. The horizontal surface must be sufficiently stiff to transfer and/or resist the lateral and torsional stresses induced by wind, unbalanced live loads, and the normal force created by the upward pull of the stays. The stays are usually attached symmetrically to the column or tower with an equal number of stays on both sides. This is so that the horizontal force component of the inclined cables will cancel each other out and minimalize the moment at the top of the tower or column.
3. CABLE CONFIGURATIONS
There are two primary cable configurations: radial patterns and parallel systems (or harp). In the radial system, the upper end of all of the the stays attach to a single point at the top of the tower. The advantage to this system is that the maximum de gree of inclination of the cables is achieved which creates nearly vertical forces exerted at the top of the tower. This minimizes the bending moment in the tower. In the parallel system of stays, each stay is parallel and thus connects to the tower at a different height. This creates large bending moments in the tower because the forces from the cables have larger horizontal components.
4. CONSTRUCTION CHARACTERISTICS
The horizontal surface (bridge deck, roof, etc.) usually acts as a simple beam, most commonly in the form of a truss or box beam. The box beam is advantageous because resists torsional forces well; however, it provides a greater surface area subject to the lateral forces of the wind.
The towers are the first portion of the structure to be constructed. The section of the horizontal surface supported by the first stay is built next. In a similar fashion, the remaining pieces are connected until the horizontal surface is successfully c ompleted and supported.
5. TYPICAL MATERIALS
A steel deck beam is most common, however, a concrete beam, despite the considerable increase in weight, can be used for some shorter spans. The towers may be of any material, historically stone, concrete or steel. The cables are of high stre ngth steel.
6. RULES OF THUMB DESIGN
The tower height is usually 1/6 or 1/5 of the span length. Longest Spans:
7. CASE STUDY EXAMPLES
8. Author
Matt Rumbaugh, University of Oregon. 1995
9. Adapted from
http://darkwing.uoregon.edu
1. DEFINITION
Cable-stayed structures support horizontal planes (bridge decks, roofs, floors) with inclined cables that are attached to, or run over, tower(s).
2. STRUCTURAL CHARACTERISTICS
The cables of a cable-stayed structure work solely in tension. The cables must not only have sufficient capacity to carry the dead load, but must also have enough reserve capacity to carry the live load. Otherwise, the horizontal surface may suffer serious deformations. The horizontal surface must be sufficiently stiff to transfer and/or resist the lateral and torsional stresses induced by wind, unbalanced live loads, and the normal force created by the upward pull of the stays. The stays are usually attached symmetrically to the column or tower with an equal number of stays on both sides. This is so that the horizontal force component of the inclined cables will cancel each other out and minimalize the moment at the top of the tower or column.
3. CABLE CONFIGURATIONS
There are two primary cable configurations: radial patterns and parallel systems (or harp). In the radial system, the upper end of all of the the stays attach to a single point at the top of the tower. The advantage to this system is that the maximum de gree of inclination of the cables is achieved which creates nearly vertical forces exerted at the top of the tower. This minimizes the bending moment in the tower. In the parallel system of stays, each stay is parallel and thus connects to the tower at a different height. This creates large bending moments in the tower because the forces from the cables have larger horizontal components.
4. CONSTRUCTION CHARACTERISTICS
The horizontal surface (bridge deck, roof, etc.) usually acts as a simple beam, most commonly in the form of a truss or box beam. The box beam is advantageous because resists torsional forces well; however, it provides a greater surface area subject to the lateral forces of the wind.
The towers are the first portion of the structure to be constructed. The section of the horizontal surface supported by the first stay is built next. In a similar fashion, the remaining pieces are connected until the horizontal surface is successfully c ompleted and supported.
5. TYPICAL MATERIALS
A steel deck beam is most common, however, a concrete beam, despite the considerable increase in weight, can be used for some shorter spans. The towers may be of any material, historically stone, concrete or steel. The cables are of high stre ngth steel.
6. RULES OF THUMB DESIGN
The tower height is usually 1/6 or 1/5 of the span length. Longest Spans:
- Alex Fraser Bridge: 1515 feet (British Columbia, Canada)
- Skarnusundet Bridge: 530 meters (Finland)
- Normandy Bridge: 2826 feet = 856 meters (France)
7. CASE STUDY EXAMPLES
- Frampton, Kenneth, Tishchchauser, Webster, Anthony C, Artemis Pub., Zurich, 1993.
- Frampton, Kenneth, Tishchchauser, Anthony and Webster, Anthony C, Calatrava Bridges, Artemis Pub., Zurich, 1993.
8. Author
Matt Rumbaugh, University of Oregon. 1995
9. Adapted from
http://darkwing.uoregon.edu
