Mobile loads (esas.02, esas.35)


esas.02, esas.35

The esas.02 module allows for simulation of loads moving along a specified path on frames.

The esas.35 module is an extension of the esas.02 module and allows for load paths to be introduced also on surfaces.

Influence lines are generated based on selected mobile load paths on the structure.
It is possible to define a system of mobile point and line loads.
The programme will automatically search for the critical positions of the load system on the structure, by analysing the calculated influence lines.
The envelope of the most unfavourable effects in the structure is also calculated automatically.

For the esas.35 module the functionality is extended:

  • instead of a planar moving load group, groups of simultaneously occurring loads may be defined in the lateral direction of movement as well;
  • individual settings for the values and position of the loads in a system are provided per lateral plane.

Load systems

  • Each system is a combination of a distributed load of indefinite length and point loads that move together on a predefined path on the structure;

  • There is no limit to the number and variety of load systems that can be defined;
  • A library of predefined load systems according to various standards is provided.

Traffic lanes

  • The user manually defines the track along which the mobile loads will move;

  • Tracks can be updated and do not need to be redefined after changes in the model geometry - changed node coordinates, cross-sections, etc.;
  • Along the selected tracks, the extreme design components (such as maximum and minimum bending moments, reactions and deformations) are determined per load system.

Analysis (envelope derivation)

SCIA Engineer determines the effect of moving load systems through influence line analysis:

  • Influence lines (esas.02) or surfaces (esas.35) for internal forces and deformations are generated per section on the existing traffic lanes;
  • An automatic searching routine determines the critical position of the load systems.

Some automated decisions are made in function of the sign of influence line ordinates:

  • Uniformly distributed loads only act in unfavourable regions of the influence line function;
  • Concentrated loads can be set to only act in unfavourable regions of the influence line function;
  • The user may specify whether it is allowed to place the load partially outside the structure, if this would result in higher internal forces or deformations;
  • Loads can be set to appear only on a restricted interval of the traffic lane.

Based on the influence line analysis, envelopes (minimum and maximum functions) for internal forces, reactions and deformations are generated.

  • Envelopes are automatically calculated per mobile load system;
  • For this, the user may select to ignore regions with beneficial values in the influence lines (with opposite sign);
  • An additional multiplication factor can be applied according to the VOSB code (NEN code) for internal forces and reactions.

The standard stipulates that this factor is not to be applied on deformations. Therefore, it is possible to obtain larger deformations form a load case linked to envelope internal forces compared to load cases linked to envelope deformations.

Load case generation

Actual or fictitious load cases may be generated based on envelopes.

  • Actual load cases contain the load systems converted to standard loads on the structure, and placed on the critical positions as determined in the influence-line-based analysis;
  • A series of fictitious load cases with the maximum and minimum functions of the components of internal forces and displacements may be generated; these load cases contain no actual loads - rather just the effect of such loads - moment diagrams, deformations, etc.
  • These load cases can be combined with other types of loads in standard combinations and thus be used in section and stability checks.

Fictitious load cases have the limitation of being valid only for the component for which they were derived. Thus, a load case derived for minimum bending moments My will contain valid and meaningful results only for My diagrams, and not for other internal force or deformation components.