Ahmad Yamin Rasa

This study presents a robust Lagrangian infinite fluid element (LIFE) for seismic analysis of dams. The proposed LIFE effectively replaces the conventional [ ]-fixed, [ ]-roller boundary conditions (BC) at the far end of the reservoir in Lagrangian fluid modeling, allowing for realistic simulation of unbounded water domains by absorbing outgoing seismic waves and preventing artificial reflections. The developed finite element (FE) model was implemented in FORTRAN 90 programming language and validated against benchmark solutions from the literature. A parametric study is conducted on the Koyna dam, subjected to horizontal (H) and horizontal [ ] vertical [ ] Koyna earthquake ground motions, considering three different near-field reservoir lengths (RL) of 1D, 2D, and 3D, where D is the reservoir water depth. The results revealed that the LIFE maintains accuracy and stability even for short RL domains [ ], whereas the traditional model required a minimum of [ ] to radiate wave reflections, thus decreasing computational cost without much loss of accuracy. Results also indicate that the displacement-decay parameter (DDP) in the LIFE strongly influences performance, with [ ] producing physically consistent crest responses and hydrodynamic pressure distributions.

Hillside buildings are particularly vulnerable to earthquakes owing to their structural configuration; however, research addressing this issue remains limited. This study investigates the effectiveness of high-damping rubber bearings (HDRBs) in enhancing the seismic resilience of hillside structures. Five numerical models were analyzed using non-linear time-history (NTH) analysis, including two flat-plane structures (one isolated and one with a fixed base) and three dropped-layer structures on hillside terrain (one with base isolation, one with inter-story isolation, and one with a fixed base). Deformation history integral (DHI) modeling was employed to simulate the HDRBs. Six earthquake ground motions from the PEER database and one scaled from 0.2–0.8 g were used to assess the seismic responses of the buildings. The results indicate that HDRBs significantly improved the seismic performance. The flat-plane isolated system (FIS) model achieved a nearly 90% reduction in peak roof acceleration compared to fixed-base structures. The dropped-layer isolated system (DIS) and dropped-layer inter-story isolated system (DIIS) models exhibited reductions of approximately 80% in the peak roof acceleration. Furthermore, the isolated structures demonstrated up to 78% reduction in the maximum inter-story drift, along with significant decreases in the story shear forces and overturning moments. Compared with non-isolated dropped-layer structures, the DIS and DIIS models showed reductions of 70% and 55% in the base shear force, respectively. The results highlight the efficacy of HDRBs in energy dissipation and their significant role in enhancing the seismic resilience of mountain structures.

The effective numerical model that examines the seismic behavior of concrete gravity dams in the Laplace domain-Finite Element (FE) approach is presented. Further research on the potential damage levels and seismic performance of the dam body is done considering the simultaneous effect of horizontal (H) and vertical (V) components of six different earthquake loads. The time durations of the selected earthquakes vary from 10 sec to 80 sec with the magnitude range from 6.5 to 7.62 Mw. The Lagrangian fluid finite elements are utilized to model the near-field water domain. On the other hand, the fluid infinite elements are utilized to model the far-field water domain considering the rigid base rock foundation condition. The two-dimensional (2D) model is developed in FORTRAN 90 and MATLAB programming languages. The findings of this study suggest that the seismic behavior of concrete gravity dam affects not only with the seismic severity; the length and significant time duration of the earthquake are also important factor. The evaluation of the obtained results revealed that the longer length of significant earthquake duration leads to the high deformations, the high stress excursions and high probability of damages in the dam. 20.9% and 18.8% of the selected dam cross section experiences overstress condition under the H and H + V components of the Chi-Chi earthquake loads, respectively; which result the dam failure.

A comparative research has been carried out for obtaining the time-consuming exact solution (state-space) and approximate solution (mode superposition) of transient and steady-state vibrations of linearly damped linear frame buildings. In the mode superposition method, the proportional damping matrix has been constructed by different approaches such as modal combination of mass and stiffness matrixes (Rayleigh) and disregarding the off-diagonal elements of the non-classical damping matrix, while in the state-space method the non-proportional damping matrix is constructed in exact situation. These observations are individually investigated, which the most suitable parameter to render the approximate results as close as possible to the exact results. Harmonic forces are applied on the different storeys of three and five storey frame buildings, and the responses are displayed in comparative tables and figures. The maximum responses are calculated by square root of sum of the squares (SRSS) method. A MATLAB code is generated and the equations of exact and approximate methods are solved.