Improvements in Brazilian concrete

 

15.0

SCIA Engineer 15 presents improved design and check functionalities for reinforced concrete according to the Brazilian code (NBR 6118:2014). The solution is based on a powerful Open Design technology. Brazilian customers have already been able to use the open material library with concrete and steel grades and automatic generation of load combinations according to NBR. This made it possible to easily perform analysis of the internal forces . The following paragraphs present more about the novelties related to NBR implementation with respect to concrete design in SCIA Engineer 15.

HIGHLIGHTS
Calculation of design values of internal forces for columns, taking geometrical imperfections and 2nd order effects into account.
Design of reinforcement for 1D members, consisting of a predefined or arbitrarily shaped cross-section:
  • Design of longitudinal reinforcement (As,req) according to ULS.
  • Design of shear reinforcement (Asw,req) according to ULS.
Design of longitudinal reinforcement for 2D member according to ULS.
Input of practical reinforcement in the form of longitudinal bars, stirrups and/or free reinforcement bars. Import and export also via IFC format.

Response check for 1D member (based on check of the limit values of concrete and steel stresses and strains).

Graphical and numerical display of all results, with level of detail chosen the by user.
Preparation of a bill of reinforcement.
Generation of simple reinforcement schemes.
All outputs available for presentation in Engineering Report.

The new Concrete service offers an overview of the available functions for the design and checking of reinforced concrete columns and beams according to the NBR

General data

The Concrete setup stores several general values like partial safety factors and creep coefficient that are used in design and check calculations. By default, the values defined in NBR are taken into account, but manual modifications are allowed.

‘Member buckling data’ can be assigned to each 1D member separately, to influence the buckling length used for the calculation of additional bending moment(s) for columns.

Internal forces

The calculation of design values of internal forces, Mdy and Mdz, is available for columns. The additional moments due to geometrical imperfections are automatically taken into account. The ones due to 2nd order effects are only taken into account if required by the user.

These design values of internal forces are the basis for the design and checks described further on.

For beams, the characteristic values of internal forces are currently being used for the design and checks.

The currently implemented methods for calculation of additional moments are valid for short columns (ll1) and columns of middle-range slenderness (l1l≤90).

Geometrical imperfections

Currently a minimum bending moment (M1d,min) is taken into account to replace the effect of local imperfections in columns in 3D frames (NBR 6118 §11.3.3.4.3).

2nd order effects

For short columns the 2nd order effects do not need to be taken into account.

For columns of middle-range slenderness this is required, and two approximate methods are available. By default, the standard method based on an approximate curvature (NBR 6118 §15.8.3.3.2) is used. Only in case the option ‘Use k approx. method’ is activated by the user, the standard method based on approximate rigidity k (NBR 6118 §15.8.3.3.3 of) is used. This method is similar to the previous one based on approximate curvature, but can be applied only for rectangular columns.

Design

1D members

Reinforcement design according to NBR is supported for 1D members (columns and beams) with predefined or arbitrarily shaped cross-sections. The design is performed according to the ultimate limit state requirements.

The design of longitudinal reinforcement (As,req) is based on several input properties, like e.g. concrete cover. Next to the ‘required value’ also a ‘designed value’ is shown, based on the reinforcement diameter chosen by the user.

For the design of shear reinforcement (Asw,req), the user can choose values for the reinforcement diameter, number of legs and angle of the stirrups.

2D members

SCIA Engineer 15 brings also the possibility to design longitudinal reinforcement for 2D members according to NBR code. The user can select two directions for the design of reinforcement - independently for the upper and lower surface of the 2D member. Design forces in these directions are recalculated from the internal forces using the Baumann’s transformation formulas. The direction angle of the concrete strut is optimised according to the condition of the smallest force in that direction. A substitude (1 metre wide) cross-section is generated in each of the user-specified directions. The longitudinal reinforcement is designed for this generated 1D cross-section and corresponding dimensional forces. The designed reinforcement is checked according to the detailing provisions defined in the NBR code.

The following list of detailing provision is checked

  • Minimum ratio of reinforcement in tension
  • Minimum ratio of reinforcement in compression
  • Maximum ratio of reinforcement
  • Minimum transverse reinforcement
  • Maximum spacing of main reinforcement

The check of concrete strut is performed after the check of detailing provisions to find out whether the strength of the concrete can transfer the forces in the direction of the concrete strut.

Input of reinforcement

As a basis for the checks, the user can define practical reinforcement to any concrete columns and beam. This is possible in the form of longitudinal bars, stirrups and/or free reinforcement bars (= bars with little restriction to their form, so even complicated bends can be obtained).

There are innumerable possibilities with regard to the reinforcement layout, but to facilitate the input, open libraries of reinforcement templates for stirrups and longitudinal bars have been created.

By using the 3D representation of practical reinforcement bars, it is easy to display their actual geometry and position within the concrete member. There are also multiple visualisation options to be found in the ‘View parameters settings’.

Moreover, it is possible to import and export the configuration of practical reinforcement via IFC format, allowing for exchange of the properties of the structural model between SCIA Engineer and other (CAD) software, in which one may for example create bending schedules and production drawings.

Check of 1D members

Based on a user-defined practical reinforcement layout, two checks of concrete members are supported according to NBR. The columns and beams to be checked may be of a predefined or arbitrarily shaped cross-section.

A check of the limit values of the concrete and steel stresses and strains is by default available. It is called a ‘Response check’ and takes into account the interaction of the design values of internal forces N+My+Mz. Calculated values include stresses and strains in the concrete fibres in compression and in reinforcement bars in tension and compression as well as the values of unity checks.

Results output

The results of the design and checks can be displayed graphically as well as numerically, and the level of detail can be chosen by the user.

The ‘Brief’ output shows a default SCIA Engineer table. The ‘Full’ output shows directly the detailed output from the calculation and can contain tables as well as pictures.

All result outputs can be presented in Engineering Report.

Presentation of reinforcement layout

For the presentation of the final reinforcement layout, the wizard for the automatic generation of simple reinforcement schemes may be used. The generated pictures can be added to Engineering report, put together in the Paperspace gallery to be plotted, or exported to *dwg/*dxf format for further editing in CAD software.

Also a ‘Bill of reinforcement’ can be created, giving an overview of the number of used bars per diameter, the total length and total weight of the reinforcement bars per steel grade.

 

References
  1. Baumann, Th. : "Zur Frage der Netzbewehrung von Flächentragwerken". In : Der Bauingenieur 47 (1972), Berlin 1975
  2. Brazilian standard ABNT NBR 6118-2014: Design of structural concrete – procedure.

12/04/2015