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Setting seismic parameters

LimitState:GEO is able to apply horizontal and/or vertical pseudo static accelerations to any problem. These may be applied as fixed accelerations or it is possible to apply an adequacy factor to one or both of these parameters. Further information on modelling with these parameters may be found in Modelling seismic loads.

To set seismic accelerations, click the next to the Seismic Actions entry in the project level Property Editor. Four new values will appear as shown in seismic parameters. To set a horizontal acceleration of e.g. 0.3 (i.e. 0.3 9.81 m/s), set Horizontal Accel. k (g) to 0.3. To apply this as a fixed acceleration set Adequacy (on k) to False. Positive values are modelled as resulting in a horizontal right to left acceleration on the problem. (This corresponds to an equivalent base acceleration in the opposite i.e. positive x-direction).

Frequently the user may wish to ask the question ‘At what horizontal acceleration will the modelled soil construction collapse?’. In order to get LimitState:GEO to answer this question set Horizontal Accel. k (g) to 1.0, and Adequacy (on k) to True, while ensuring that Adequacy is not set on any other parameter e.g. a load. On solving, LimitState:GEO will return an Adequacy factor equal to the required horizontal acceleration. This procedure will also work with a fixed vertical acceleration.

An exactly equivalent procedure is applicable to the vertical acceleration. Positive values are modelled as resulting in an additional vertical downward acceleration on the problem. (This corresponds to an equivalent base acceleration in the opposite i.e. positive y-direction).

Additionally, if it is required to answer the question ‘At what horizontal acceleration will the modelled soil construction collapse such that the vertical acceleration equals 0.2 times the horizontal acceleration?’ then set Horizontal Accel. k (g) to 1.0, Adequacy (on k) to True, Vertical Accel. k (g) to 0.2, and Adequacy (on k) to True. On solving, LimitState:GEO will return an Adequacy factor equal to the required horizontal acceleration.