Water accumulation (esas.30)



Esas.30 is a module for the automatic generation of rain water ponding according to NEN 6702. The loads and corresponding deformations as a result of water accumulation are calculated iteratively, taking into account the deformed shape of the structure.

Rain water ponding is potentially dangerous for slender flat roofs; it occurs when the drainage system malfunctions or is not sufficient to take in excessive flow of rain water. Deformations caused by permanent loads and by the rain water load itself additionally increase the water level and amplify the effect.

Calculation of rain water ponding on roofs according to NEN 6702.
Detailed input of roof surface, storage capacity, slopes, drains.
Iterative calculation of water accumulation taking into account deformations caused by permanent loads.

User input and settings

  • Due to initial imperfections and deformations in a real structure, it is not possible to know in advance how rain water will be distributed over the structure's envelope. Therefore, the user has to only indicate which surfaces are exposed to rain and can accumulate water;
  • The locations where ponding might occur are defined as areas through standard GUI methods in the 3D environment of SCIA Engineer - by drawing polygons, entering coordinates, etc.;
  • The water load is derived and applied to the adjacent load-bearing elements. The user determines which beams will be loaded and which not. This allows for certain structural elements to be used for stability only, without these having to bear significant loads;
  • The user defines the initial water depth indirectly, by entering values for the parameters that define the roof surface, slopes, storage capacity, drains;
  • SCIA Engineer calculates the water level and evaluates whether points on the structure are submerged or not. If submerged, locations are loaded with the derived load. The user may specify the density of points to be evaluated in order to speed up the calculation or obtain higher accuracy.
  • The user may simulate ponding at different places on the structure at the same time; also, one ponding location may be set to influence the water accumulation at another place on the structure.

Calculation of loads and deformations

The initial water depth on the undeformed structure is derived in function of the following parameters (per area):

  • a slope or pre-camber of the roof ponding area - defined in the ponding area properties;
  • roof slope, if the insulation requirements explicitly determine the slope of the roof;
  • storage capacity of the roof surface;
  • additional water accumulation due to construction errors/imperfections;
  • drains are defined by location, size, height relative to the roof surface, and area drained by a single pipe; the following drain type is available: a non-deforming square drain along the edge of a façade, with water flow capacity according to NEN 6702, art.;
  • The provided options allow for a roof slope to be taken into account for water accumulation, even if this slope is not present in the FE analysis model.

SCIA Engineer controls if the introduced roof and drain geometry is logical. If not, the calculation is aborted and a message is sent to the user.

The derivation of water accumulation loads is iterative, taking into account deformations in the structure caused by permanent loads and loads from water ponding. The load functions are generated automatically on all loaded beams. If the calculation is performed according to the NEN standard, it is possible to reduce the stiffness of the structure during ponding load analysis, using a model factor to represent the pond load.

Load combinations and analysis

  • After the analysis of water accumulation, the obtained load functions are visualised on the loaded beams as any other type of line load;
  • These line loads are automatically assigned to the variable load case that was used during the ponding load definition.
  • The water ponding loads may be combined with other load functions to form load groups and combinations (envelopes, according to code). Then, structural analysis, member or stability checks may be performed as usual, according to any available national norm.