Moment Arm

What is Moment Arm?

Definition of Moment Arm in Construction
The length or distance ,between the force or load, and the supportive connection.

The moment arm is an extremely important factor in structural design of beams, columns and especially connections. The moment force ( turning force ), on a connection, can be tremendously enhanced if the length of the moment arm is increased. Failure to properly determine the operating length of a structure, or a piece of equipment can result in a devastating failure. Crane collapses are in many cases the result of a shift or lengthening of the moment arm of the boom. The angle of the boom on a crane in association with the horizontal, is a measuring point for the ability of the crane to sustain a load. If the boom is dropped too low and becomes too horizontal, the moment arm is extended, and the forces are exponentially multiplied. The moment arm is one of the most important structural elements of a system, due to its importance to the resultant loading of a connection. The understanding of a moment arm is intrinsic to the basic construction ability. The uses of an increase moment arm with the same forces available can assist in most construction activities. Tools such as hammers, wrenches, pry bars all use the moment arm concept.