Lateral Load Cases

Lateral load cases can be defined to analyse various pile design scenarios. Load conditions (either forces, moments or displacements and rotations) can be specified at any number of points along the pile for a single load case. For example one situation where multiple applications of pile load might be necessary is to analyse a pile that is subjected to jackup interaction. OPILE allows for pile stickup which means that loads can also be applied above the mudline, this might be necessary in situations such as the design of jetty piles.

Sign Convention

The sign convention for lateral loading in OPILE is shown in the figure below. Applied shear forces and displacements are positive acting to the right and moments and rotations are positive in the anti-clockwise direction. For axial loads applied during lateral load cases a compression load (downwards) is positive.

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Illustration of sign convention

Automatic Load Case Generation

OPILE will automatically generate load cases for some common pile scenarios, or the load cases can be manually entered by users. The parameters which can be varied (as shown in the figure below) within the automatic load case generation include:

  1. Rotation - this can be used to control the fixity of the pile at the point where the load or displacement is to be applied.

  2. Grid point is used to control the point at which the load or displacement is applied.

Note

In the automatic load case generation OPILE always uses displacement and rotation control as these are quicker to solve and there is a high degree of certainty that the full capacity of the pile will be mobilised within displacements of a certain proportion of the piles diameter. Automatically generated load cases can be edited by the user afterwards and automatic generation can be switched off.

Displacements and rotations take precedence over shear forces and moments that are defined. This means, for example, that if a shear force and displacement are defined for the same grid point in the same load case the displacement will override the shear force.

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Illustration of Load Case definition

Type of Load Cases

The types of load cases analysed will obviously vary depending on what the intended purpose of the pile is. A displacement and rotation controlled load case will always solve in fewer iterations than a shear force and moment controlled load case. Some common analysis scenarios are:

  1. Jacket pile (or a pile for a subsea frame) where the pile is often assumed to be loaded in a fixed headed manner. OPILE will automatically generate load cases which can determine the load displacement response of a fixed headed pile.

  2. Anchor pile. An anchor pile is usually a free head pile (i.e. not restrained in rotation) and may be loaded at the pile head or some distance below it.

Additionally for each lateral load case an axial load can be specified to account for the p-delta effect, whereby an axial load induces a bending moment within the pile when some lateral displacement occurs. The axial load is uniform down the length of the pile and must be a number greater than or equal to 0kN.