Journal of Earthquake and Tsunami

In this work, seismic performance of conventional X-braced frames is enhanced by using Drawer Bracing Systems (DBS). DBS is an innovative structure, which increases ductility and energy absorption capacity of the X-braces through elimination of the harmful effects of local and global buckling and by converting the induced axial forces inside diagonal arms to flexural moments. Two half-scale specimens are tested under cyclic loading and the seismic performance of an X-shaped DBS is compared to that of an X-braced frame. Both braced frames are designed for equal nominal base shears and have similar frame sizes and dimensions. Test results confirm that converting the axial force to flexural moments in rational dissipative elements inside braces helps prevent the global and local buckling of braces in X-shaped DBS. Consequently, ductility and energy absorption capacity of the Concentrically Braced Frames (CBFs) is increased remarkably.

The seismic design of slopes, dams, or embankments is usually based on limit-equilibrium calculations, which include the seismic action by means of an equivalent static force acting on the failure mechanism. This approach is limited, especially in situations in which existing over-inclined structures or steep natural slopes have to be analyzed. An alternative approach which overcomes the limitations of the classical limit-equilibrium calculations is available with displacement-based methods. The displacement-based analysis offers the possibility of evaluating the seismic behavior in terms of displacements, in contrast to the limit-equilibrium calculations, which only provide information about the ratio between the stabilizing and destabilizing forces acting on the structure. The displacement-based approach allows the analysis of the seismic behavior and, based on the resulting deformations, the corresponding risk evaluation. In addition to that, the optimized seismic design of new geotechnical structures is possible by ensuring the compliance of the seismic behavior with given requirements. This paper presents a displacement-based procedure to be incorporated in the Swiss design codes for the seismic analysis of slopes, dams, and embankments.

Due to the inherent complexity, the common approach in analyzing nonlinear response of structures with soil–structure interaction (SSI) in current seismic provisions is based on equivalent Single Degree-of-Freedom systems (E-SDOF). This paper aims to study the influence of higher modes on the seismic response of SSI systems by performing intensive parametric analyses on more than 6400 linear and non-linear Multi Degree-of-Freedom (MDOF) and E-SDOF systems subjected to 21 earthquake records. An established soil-shallow foundation-structure model with equivalent linear soil behavior and nonlinear superstructure has been utilized using the concept of cone models. The lateral strength and ductility demands of MDOF soil–structure systems with different number of stories, structure-to-soil stiffness ratio, aspect ratio and level of inelasticity are compared to those of E-SDOF systems. The results indicate that using the common E-SDOF soil–structure systems for estimating the strength and ductility demands of medium and slender MDOF structures can lead to very un-conservative results when SSI effect is significant. This implies the significance of higher mode effects for soil–structure systems in comparison with fixed-based structures, which is more pronounced for the cases of elastic and low level of inelasticity.

In seismic design, excitations are usually considered separately in two perpendicular directions of structures. In fact, the two components of ground motions occur simultaneously. This paper clarifies the effects of bi-directional excitations on structures and proposes the response spectra called “bi-directional pseudo-acceleration response spectra”. A simplified analytical model of a two-degree-of-freedom system was employed. The effect of directivity of ground motions was taken into account by applying strong motion records in all directions. The analytical results were presented in the form of the acceleration ratio response spectrum defined as the bi-directional pseudo-acceleration response spectrum normalized by a pseudo-acceleration response spectrum.

Debris produced by coastal forest destruction due to the tsunami after the Great East Japan Earthquake caused secondary damage to buildings by collision. To limit such destruction, the trapping action of a finite-length forest was examined in a flume considering the effects of ‘forest density’, ‘debris length to forest width ratio’, and ‘forest width-length ratio (aspect ratio)’ because the trapping height greatly affects the rate of damage to the forest itself. Higher forest density and a higher aspect ratio decrease the velocity in front of the forest. Debris having a specific gravity up to 0.80 floated after collision but oscillated vertically as forest density was increased. With debris of a higher specific gravity (0.90–1.05), increased forest density resulted in debris attachment closer to the ground, which reached a plateau beyond a forest density of 0.48 cylinders/cm². In sparse forest, when debris was longer than the forest width; most debris fell at the foot of trees, while it was caught in the upper half of water depth in dense forest. The flow structure in front of and around a forest greatly affected the debris trapping capacity. It was deducted that the inland forest with a density of 0.48 cylinders/cm² and an aspect ratio of 1.7 trapped most of the debris of all lengths at the foot of trees.

In this study, liquefaction and earthquake response analysis of Panipat pond ash embankment in India has been carried out considering saturated and natural water table conditions. Laboratory and field studies have been carried out to obtain the material properties required for the nonlinear response analysis of the Panipat pond ash embankment. Nonlinear finite element analysis has been carried out by using open system for earthquake engineering simulation (OpenSees). Three earthquakes namely Chamba, Chamoli and Uttarkashi earthquakes have been considered for liquefaction and earthquake response analysis. The standard penetration test (SPT)-$N$ value indicates that the ash deposit in Panipat pond ash embankment is in loose to medium dense state. The excess pore pressure ratio obtained from the analysis is found to be one or more than one below upstream and downstream locations of the pond ash embankment for both saturated and natural water table conditions. The horizontal and vertical displacement is found to be maximum near the toe and first rise slope of pond ash embankment. Hence, ash embankment in Panipat is prone to liquefaction under the excitation of moderate to high earthquake loading.