Static analysis - An analysis where the structure is considered in equilibrium under the external loads (temperature, hydrostatic pressure), the self weight and the internal stresses and strains. Internal stresses and strains are evaluated according to the different methods adopted for structural analysis.

Pseudo-static analysis - A seismic analysis carried out as a static analysis where inertia forces are regarded as external static loads. The forces are assumed proportional to the mass of the body and to a suitable distribution of the acceleration.

Dynamic analysis - An analysis where the dam (whose physical properties, mass, damping and stiffness are supposed known) is considered in equilibrium, at every time step, under a system of forces variable in time, taking into account the inertia and damping effects. Solving the system of equations, through a dynamic analysis method, the structural response (in terms of displacements, velocities, ac­celeration, stresses and strains) can be determined.

Finite element method - Numerical method for solving partial differential equations based on the subdivision of the domain, and on the elemental continuity of the numerical solution. The spatial variation of the numerical solution inside the element may be constant, linear or of parabolic order.

Finite difference method - A method closely related to the general theory of the approximation of functions. This method is used to approximate the solution of differential equations. The procedure is approximate in the sense that the derivatives at a point are approximated by difference quotients over a small interval. The smaller the interval, the more accurate is the solution.

Mass matrix -
Lumped-mass matrix - The matrix obtained by concentrating the mass of each element in the discretization nodes. The mass matrix estimated in this manner is a diagonal matrix. In this procedure, the interaction of the nodal inertia forces is disregarded.
Consistent-mass matrix - A matrix including nondiagonal terms that take into consideration the effects of interaction of the nodal inertia forces. This matrix can be easily estimated by means of the finite element method.

Stiffness matrix - A matrix whose generic term k (ij) represents the associated force upon the direction of the degree of freedom (i), induced by a unit displacement upon the direction of the degree of freedom (j). the remaining degrees of freedom being constrained.

Eigenvalue or Natural frequency - The frequency of the harmonic excitations under which the structure shows the maximum tendency to accumulate energy.

Eigenvector or Modal shape - Snapshot of the deformed shape of the dam while it is vibrating at a natural or resonance frequency.

Damping - Property which allows to reduce or oppose vibrations by energy absorption. There are different types of damping, such as material (viscous, Coulomb) and geometric (radiation) damping.

Free-field motion - Ground motion which is not influenced by man-made structures. Also applicable to a medium which contains no structure, or to an area where boundary effects do not influence significantly the behaviour of the medium.

Near-field motion - Ground motion recorded in the vicinity of a fault.

Response spectrum - A plot of the maximum values of displacement, velocity and/or acceleration of a single-degree-of-freedom oscillator as a function of its natural frequency, for a given equivalent damping ratio, when subjected to a time-dependent dynamic excitation such as a ground motion. In a modal analysis of the seismic behaviour of a dam, the response spectrum is used for determining the input values to be adopted for each “mode”.

Computer aided design (CAD) or Computer aided design and drafting (CADD) - The procedure of designing (and drafting) an engineering project with the assistance of a computer.