Interaction curves, diagrams and stability graphics

Display detailed graphical results for performed checks


The Reinforced Concrete BIM Designers provide graphical results for the performed verifications giving a better overview of the status of the designed element. The Stability section of the Reinforced Concrete BIM Designers for footings is divided into four sections or viewports, which display the results for a certain verification: compressed surface verification, sliding, overturning and eccentricity check.

The user can instantly distinguish the main results and is able to choose both the soil condition (drained or undrained), and the combination to be analyzed.

Compressed surface verification

This verification is related to the Eccentric load effects section in the Design Assumptions dialog.

The ability of a spread foundation to carry forces is significantly reduced when they are applied eccentrically to the foundation. To avoid the footing's edges losing contact to the ground, the value of the compressed footing area (effective area) should be set over a minimum percentage.

In this section, user can define the percentage value to be considered for the minimum footing area in compression:

  • Verify: check this option to verify the percentage of compressed footing area at the Serviceability and Ultimate Limit States
  • ULS (FUN/ACC/SEI): enter a percentage for the footing area in compression for the ultimate limit states (fundamental, accidental, seismic)
  • SLS (QPR/FRQ): enter a percentage for the footing area in compression for the serviceability limit states (quasi-permanent, frequent)
  • SLS (CHR): enter a percentage for the footing area in compression for serviceability limit state (characteristic)



Sliding verification

The assumptions for this verification are defined in the section 'Sliding' from the Design Assumptions dialog.

Note: Where the loading is not normal to the foundation base, foundations shall be checked against failure by sliding on the base. [EN 1997-1 §6.5.3(1)]

  • Cast-in-situ concrete: if this option is checked, the friction angle d is assumed to be equal to the design critical state angle of shearing resistance f 'crit. According to EN 1997-1 §6.5.3(10), "The design friction angle dd may be assumed equal to the design value of the effective critical state angle of shearing resistance f'cv;d, for cast-in-situ concrete foundations [...]."
  • Imposed value: if this option is checked, a value can be entered for the friction angle between the footing and the foundation soil.



Overturning verification

This verification is related to the Overturning EQU section from the Design Assumptions dialog.

  • Verify: check this option to verify the footing's stability for overturning
  • Safety factor: enter the value of the factor of safety against overturning



Eccentricity check

The eccentricity verification is performed according to the article §6.5.4 from EN 1997-1: "Special precautions shall be taken where the eccentricity of loading exceeds 1/3 of the width of a rectangular footing [...]."

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The verification refers to whether the design load is within a critical ellipse; for the situation of a bidirectional eccentricity, the limit is set by an ellipse equation:
(ex/A)2 + (ey/B)2 = (1/3)2

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For columns the Reinforced Concrete BIM Designers comes with an Interaction Curves feature which allows engineers to visually check stresses in an interactive and real-time manner.

The sample below shows how to verify a reinforced concrete column section using the interaction curves. A simple, 4 m high column with an 80x80 cm cross section will be subjected to combined bending and compression from axial forces.

After calculation, the software generates the interaction curve resulted for the provided reinforcement area. The corresponding values for each resistant torsor are displayed on the interaction curves page.

Three viewports are available for the interaction curves: one displaying the 3D curve N-Mx-My and two planar views, N-My and Mx-My. With this graphic representation, the user can easily control the effects of his reinforcement changes on the column resistance. For example, if the bar diameter is reduced from 12 mm to 10 mm, the interaction curve is updated and the resistant efforts are reduced accordingly.

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If the design efforts are outside the interaction curve, it means that the section is not verified. The following error message is displayed :

The example below ilustrates such a situation:

For beams the Reinforced Concrete BIM Designers have four sections containing graphical results also known as diagrams.




This section contains the main internal forces diagrams: bending moment, shear force, axial force, torsional moment and resisting moment.

The user can choose the combination to display the results and/or hide some of the diagrams for a clearer view.

By using the ruler included in this section, diagram values can be displayed at any point along the element.



The Stresses section also contains graphical results, displaying the main stresses diagrams: concrete compressive stress, reinforcement compressive stress, reinforcement tensile stress, as well as the diagram for the neutral axis position on a top fiber basis and crack width.

The effective values for the stresses/neutral axis position/crack width are displayed in green while the limit values for these parameters, in red, helping the user to easily notice if any of the limits are exceeded.




For both the longitudinal and the transverse reinforcement, the required reinforcement areas are displayed in blue, while the provided reinforcement areas are represented in red, helping the user to easily analyse if the calculated reinforcement is sufficient while simultaneously contributing to the optimisation process.




A simple, yet very effective representation is the deflection diagram. This section is related to the Deflection dialog, where the user can set the main assumptions that must be considered, chose the deflection method and set the deflection limit.

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