Enter the total mass supported by the bridge (at maximum capacity) and the total mass of the bridge itself into the calculator to determine the bridge efficiency ratio.
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Bridge Efficiency Formula
The following equation is used to calculate the bridge efficiency ratio (a unitless load-to-self-mass metric). If you want to express it as a percentage, multiply the ratio by 100%.
BE = MS / MB
- Where BE is the bridge efficiency ratio (dimensionless)
- MS is the mass supported by the bridge at maximum capacity
- MB is the mass of the bridge
To calculate the bridge efficiency ratio, divide the mass supported by the bridge at maximum capacity by the mass of the bridge itself. (You can also use weight/force instead of mass, as long as you use consistent units in the numerator and denominator.)
What is a Bridge Efficiency?
Definition:
Bridge efficiency (as defined on this page) is a measure of how much load a bridge can support relative to its own mass. It is closely related to a structure’s strength-to-weight (or load-to-weight) concept: for a given required load capacity, reducing a structure’s self-weight generally increases this efficiency ratio.
This metric can be used for comparing designs (commonly in model bridge testing) because it shows how much supported mass is achieved per unit of bridge mass. In real-world bridge engineering, overall performance is evaluated using many additional factors beyond this simple ratio (for example, allowable stresses, safety factors, fatigue, serviceability/deflection, and durability).
If a bridge is properly designed, it can serve its intended purpose for many years. Achieving the right balance between self-weight and load-carrying capacity is one part of reaching that longevity.
