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CAESAR II Users Guide

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CAESAR II
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CAESAR II Version
13

With this type of profile, the load unpredictably changes direction or magnitude with time. Even with the unpredictability, some load characteristics can predominate. Loads with random force/time profiles are best solved using a spectrum method or a static equivalent.

The major types of loads with random time profiles are wind and earthquake.

Wind

Wind velocity causes forces due to the decrease of wind momentum as the air strikes the pipe creating an equivalent pressure on the pipe. Wind loadings, even though they can have predominant directions and average velocities over a given time, are subject to gusting, such as sudden changes in direction and velocity. As the time period lengthens, the number of wind changes also increases in an unpredictable manner, eventually encompassing nearly all directions and a wide range of velocities.

Earthquake

Seismic (earthquake) loadings are caused by the introduction of random ground motion, such as accelerations, velocities, and displacements and corresponding inertia loads (the mass of the system times the acceleration) into a structure through the structure-to-ground anchorage. Random ground motion is the sum of an infinite number of individual harmonic (cyclic) ground motions. Two earthquakes can be similar in terms of predominant direction (for example, along a fault), predominant harmonic frequencies (if some underlying cyclic motions tend to dominate), and maximum ground motion, but their exact behavior at any given time can be quite different and unpredictable.