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Standards

What each program references

Standard Title SPO · SPX · SPX AI PCO · PCX
NBR 6122 Design and construction of foundations ●
NBR 6118 Design of concrete structures ● ●
NBR 8681 Actions and safety of structures ●
NBR 6120 Loads for the design of building structures ●

In addition to the Brazilian standards, the programs use established formulations from other sources — the semi-empirical bearing capacity methods (Aoki-Velloso, Décourt-Quaresma, Teixeira), the Cintra & Aoki settlement estimate and, for pile caps, the IBRACON Commentaries on NBR 6118 and CEB/FIP recommendations. Each one is identified on the formulation page that uses it.

Where the standards come in

NBR 6122 — Foundations

It enters the calculation of the allowable load. The standard's general criterion is applied to the ultimate resistance:

\[ P_a = \frac{R_{total}}{2} \]

with a global safety factor of 2. Some methods impose additional, more restrictive checks — Décourt-Quaresma separates the toe and shaft factors, and bored piles have their own limit. The program applies the smallest of the applicable criteria. See Bearing capacity.

NBR 6118 — Concrete

It comes in on two fronts:

  • Durability — the environmental exposure class defines the nominal cover:

    Class Exposure Cover
    CAA I Mild 3.0 cm
    CAA II Moderate 3.0 cm
    CAA III Severe 4.0 cm
    CAA IV Very severe 5.0 cm

  • Design — biaxial bending with axial force of the circular section, shear and reinforcement detailing.

NBR 8681 — Actions and safety

Used in the pile cap programs for load combinations and partial factors.

What remains the designer's responsibility

This section is as important as the previous one. The programs do not decide:

  • The choice of bearing capacity method. Aoki-Velloso, Décourt-Quaresma and Teixeira give different results for the same borehole; which one best represents the site is a matter of engineering judgement, supported by regional experience and, when available, load tests.
  • The quality of the site investigation. Shallow boreholes, excessive spacing between them or a doubtful tactile-visual classification produce equally doubtful results, without the program being able to notice.
  • The allowable settlement. The program estimates settlement; how much the structure can tolerate depends on the structure, not on the foundation.
  • Load test verification, when the standard requires it.
  • Group behaviour beyond the simplified estimate provided.
  • Special conditions — collapsible or expansive soils, landfills, negative skin friction, nearby excavations, varying water table.

Technical responsibility

The project is signed by the responsible engineer, not by the program. The formulation documentation exists precisely so that this signature is an informed one: it states which calculation was done, with which coefficients and within which range of validity.