Description |
TNMN is an auxiliary program for seismic analyses of slopes or retaining walls which computes the displacement of a potential sliding mass by double-integrating the difference between the applied acceleration history and the yield acceleration, that is, the horizontal acceleration which reduces the conventional static factor of safety to unity (also called the critical seismic coefficient), in accordance with the suggestion of Newmark (1965). The overall calculation will normally involve a number of assumptions - that the potential sliding mass is rigid, that there is a well-defined potential slip surface, that the yield acceleration is constant (or can at least be represented by several segments each of which is constant) - and the engineer must make his or her own judgement as to the reasonableness of these assumptions. The computed displacements will also be very sensitive to the character of the acceleration histories which are assumed to act on the potential sliding mass. Motions with longer durations and larger numbers of broad peaks will clearly generate larger computed displacements and these parameters can vary substantially even among recorded motions that have been generated by earthquakes with the same local magnitudes. Indeed, there can be a surprisingly large difference between the displacements which are obtained by applying the same acceleration history in the "normal" and "reversed" directions (equivalent to flipping the acceleration history about the time axis), something that the program does automatically. The only printed output that is produced consists of the final displacements for the normal and reversed motions since the results of the calculation are best shown graphically as plots of the acceleration history, the relative velocity history, and the relative displacement history, for each of the normal and reversed motions. Allows the user to read in continuously varying yield accelerations so that simultaneously applied horizontal and vertical acceleration histories can be simulated by adjusting the yield acceleration for horizontal loading to account for the vertical inertia forces. |