7.11
Cable Subjected to Concentrated Loads
Flexible cables are commonly used in various applications for support and load transmission. Consider a cable fixed at two points and subjected to mul…
Flexible cables are used for support and load transmission in various applications.
Consider a cable AB fixed at two points, experiencing multiple vertical concentrated loads.
Determine the shape of the cable and the tension in each portion of the cable, knowing the horizontal distances between the loads and support.
For analysis, the cable is assumed to be flexible, inextensible, and have negligible weight.
The cable consists of several straight-line segments, each subjected to constant tensile force.
Draw a free-body diagram of the cable to determine the reaction forces at supports. Here, the number of unknown reaction components exceeds the equilibrium equations.
Consider point D on the cable at a known distance and draw a free-body diagram of segment AD. By using the moment equilibrium equation at point D, an additional equation is obtained.
By recalling the equilibrium equations and using the reaction forces, the vertical distance between support A to each concentrated load is obtained.
Similarly, the tension in each segment can be obtained, which is maximum when the segment has the largest inclination angle.
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Q1: What assumptions are made when analyzing a cable subjected to concentrated loads?
Cables are assumed to be flexible, allowing them to change shape under applied loads, and inextensible, meaning their length does not change under tension. Additionally, the cable's weight is assumed negligible, so it does not significantly impact the cable's behavior during analysis of concentrated loads.
Q2: Why is a free-body diagram of a cable segment necessary for solving concentrated load problems?
A free-body diagram of the entire cable often yields more unknown reaction components than available equilibrium equations. By isolating a segment at a known distance and applying the moment equilibrium equation at that point, an additional equation is obtained, allowing the system to be solved for reaction forces and tensions.
Q3: How does the shape of a cable change when subjected to multiple concentrated loads?
A cable subjected to concentrated loads forms several straight-line segments between load points and supports. Each segment maintains constant tensile force and connects at the load application points, creating a polygonal shape that reflects the distribution and magnitude of the applied vertical loads.
Q4: What is the relationship between cable segment inclination and tension magnitude?
Tension in a cable segment is maximum when the segment has the largest inclination angle relative to the horizontal. Segments with steeper angles experience greater tensile forces because they must support larger vertical load components while maintaining static equilibrium across the cable system.
Q5: How are vertical distances from support to load points determined in cable analysis?
Once reaction forces are known from equilibrium equations, vertical distances from support A to each concentrated load are determined by recalling the equilibrium equation that states the sum of vertical forces acting on the cable must equal zero. This allows calculation of the cable's vertical geometry.
Q6: What information is needed to determine tension in each cable segment?
To calculate tension in each cable segment, you need the reaction forces at supports, the horizontal distances between loads, and the vertical distances from support to each load point. With these values, the tension in each segment can be computed, with maximum tension occurring in segments with the largest inclination angle.
Q7: How does the moment equilibrium equation help solve indeterminate cable systems?
When the number of unknown reaction components exceeds available equilibrium equations, applying the moment equilibrium equation at a point on the cable segment provides an additional independent equation. This transforms the indeterminate system into a determinate one, enabling complete solution for all reaction forces and segment tensions.