In a seismic design, a structural demand by an earthquake load is determined by design response spectra. The ground motion is a three-dimensional movement; therefore, the design response spectra in each direction need to be assigned. However, in most design codes, an identical design response spectrum is used in two horizontal directions. Unlike these design criteria, a realistic seismic input motion should be applied for a seismic evaluation of structures. In this study, the definition of horizontal spectral acceleration representing the two-horizontal spectral acceleration is reviewed. Based on these methodologies, the horizontal responses of observed ground motions are calculated. The data used in the analysis are recorded accelerograms at the stations near the epicenters of recent earthquakes which are the 2007 Odeasan earthquake, 2016 Gyeongju earthquake, and 2017 Pohang earthquake. Geometric mean-based horizontal response spectra and maximum directional response spectrum are evaluated and their differences are compared over the period range. Statistical representation of the relations between geometric mean and maximum directional spectral acceleration for horizontal direction and spectral acceleration for vertical direction are also evaluated. Finally, discussions and suggestions to consider these different two horizontal directional spectral accelerations in the seismic performance evaluation are presented.

This study is concerned with properties of a thermal convection in a stably stratified Boussinesq fluid caused by partial heating at the lower boundary. For this purpose, two-dimensional, nonrotating system was employed. If the heating is very strong, convection takes the form of a turbulent plume. Otherwise, remains laminar. If the partial heating at the bottom boundary is symmetric, the convection takes the form of axisymmetric with respect to the z-axis. but heating form is not so significant as to alter the main features of the horizontal convection. The convective motion consists of two-cell with the convergence in the lower layer at the center of the partial heating area. The temperature perturbation is characterized by the temperature `Cross-Over` over the partial heating area. These features are cleared according to the increase of temperature difference between the center and side part of the bottom boundary.