Is Newmark Method Conservative?

Newmark method is a commonly accepted practice in geotechnical earthquake engineering to estimate seismically induced displacement of earth structures. The method currently requires performing a series of analyses using multiple computer programs to 1) identify a potential sliding mass, 2) compute a factor of safety, 3) calculate a yield acceleration, and 4) perform a double integration of that portion of a given horizontal acceleration history that exceeds the yield acceleration. The Newmark method provides satisfactory results for a horizontal sliding surface. However, for an inclined sliding surface the result is unconservative and for a nonplanar one is not clear. To avoid the problems and to facilitate the Newmark method a numerical technique was developed and a computer program was written to carry out the analysis. A single analysis determines a two-dimensional pattern of seismically induced displacement due to given earthquake motions. Results of analyses for three examples are given to demonstrate the comparison between the new method and the Newmark method.