## FLAC

FLAC, which stands for fast Lagrangian analysis of continua, is a two-dimensional explicit finite difference geo-mechanical numerical modelling program. The program simulates the behaviour of structures built of materials such as soil and rock that undergo plastic flow when their yield limits are reached. Materials are represented by elements, or zones, which form a grid that is adjusted to fit the shape of the object to be modelled. Each element behaves according to a prescribed linear or nonlinear stress/strain (Newtonian) law in response to the applied forces or boundary conditions. Any local disturbance of equilibrium is propagated at a materially dependant rate consistent with Newton's Laws of Motion. Thus the modelling follows a sequence of locally determined dynamic equilibrium states. FLAC also has the ability to model groundwater flow. This can be coupled or uncoupled to the mechanical analysis of deformations.

The material can yield and flow and the applied grids can deform and move with the material it is representing. The explicit Lagrangian calculation scheme allows for distortion of the grid so that the end state at each node is the beginning state of the next cycle. This allows the program to accurately model plastic flow and collapse. In order for the equilibrium to be accessed explicitly or locally the incremental time step between each successive set of calculations must be small enough to prevent propagation of information beyond neighbouring calculation points. Hence problems of numerical instability are overcome and the scheme is conditionally stable and convergent. It is the ability to perform all calculations at a local level which renders the scheme explicit. In other words, at a local level for each time step unknown quantities, such as displacements, can be calculated by establishing simple equations which relate the unknown quantity to currently known variables at, or immediately surrounding, the local point.

## PFC^{2D}

PFC is a two-dimensional particle flow code (timestepping, explicit scheme) to model the movement and interaction of circular particles, such as granular material. The animation below is of a steel bolt being pulled through an element of clayey SAND.

## In House Fire Resistance Model On Clay Masonry Walling

Specialist software to model the fire resistance of clay brick masonry walling has been developed and validated against actual fire tests. The software predicts the variation in temperature across the wall with time for any given fire loading, including standard and parametric curves. These data are then used to predict the structural response of loaded and unloaded clay masonry walls in fire. This performance-based approach should have economic benefits as the need for expensive fire tests is reduced or even eliminated.## Infoworks Drainage

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