What is sag in suspension bridge?
Sag controls the length and stability of the suspension bridge, and is generally taken between 1/8 and 1/12 (a generally accepted optimum is a 1/10). If the main cables have a flat curve or a low sag ratio, the bridge has more vertical stability but the cable stress is high and strong anchorages are required.
How is cable sag calculated?
So for a 10 foot span between level supports, and 30 pounds tension at a given temperature, the sag at the low point (mid point of the span) is d=wl^2/8T = 0.0003 feet, or about 3/1000 of an inch. For a 100 foot span with that same tension, d = wl^2/8T = 0.03 feet (about 3/8 of an inch).
What causes the bridge to sag?
For example, consider the compression and tension stresses on a beam bridge, such as the bridge shown in the photo. Sagging involves compression and tension acting together. The top layer of the beam is squeezed, so it is under compression. The bottom layer is stretched, so it is under tension.
What is cable sag?
Cable sag (h) is value of cable form equation for point l/2 (formula 12), where l is the straightline distance between the position transducer and the application (Figure 1). The length of the cable is the catenary length from point -l/2 to point l/2 (formula 14).
What are the parts of a suspension bridge?
A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. The basic structural components of a suspension bridge system include stiffening girders/trusses, the main suspension cables, main towers, and the anchorages for the cables at each end of the bridge.
What are the four types of stresses that affect a bridge?
Forces that Act on Bridges
- Compression. Tension: Tension is a pulling force. Wood has the ability to resist a lot of tension.
- Tension. Torsion: Torsion is a twisting force. When you wring out a cloth, you are applying torsion to the cloth.
- Torsion. Shear: Shear is an interesting force.
What do the towers do in a suspension bridge?
These towers support the majority of the weight as compression pushes down on the suspension bridge’s deck and then travels up the cables, ropes or chains to transfer compression to the towers.
What is SAG formula?
The maximum dip (sag) is represented by the value of y at either of the supports A and B.At support A, x = l/2 and y = S. (ii) When supports are at unequal levels: In hilly areas, we generally come across conductors suspended between supports at unequal levels.
What is span and sag?
Span – Sag is directly proportional to the square of the span length. Longer span gives more sag. Tension -The sag is inversely proportional to the tension in the conductor. Higher tension increases the stress in the insulators and supporting structures.
What should the SAG ratio be on a suspension bridge?
For suspension bridges the sag ratio of the main suspension cables is normally between 1/11 to 1/9. The higher the denominator the stiffer the bridge. For stay cable bridges (cable stayed), angle of inclination of stays do not generally goes below 22 degrees to the horizontal.
Where are the main cables on a suspension bridge?
An earth-anchored suspension bridge is a type of bridge in which the main cables are anchored on large concrete blocks, or on the ground, located at the ends of the bridge. External loads applied to suspension bridges are transferred to the suspenders main cables anchorages & pylons and finally to the ground.
When is the SAG / height of a bridge determined?
Also known as underdetermined. But the sag/height of the bridge is usually known/set during the design process. Then the tension is calculated, and the appropriate length of cable is spun with cross-sectional dimensions that are suitable to bear the calculated tension.
What kind of Anchorage does a suspension bridge use?
Many suspension bridges use gravity-type anchorages. Tunnel-type anchorage is a method of resisting the loads of the cables by using the shear forces of the outer circumference of the steel frame and the pressure of the plug body.