Concrete Design - new 1D Solution for EN 1992-1-1

 

15.0

SCIA Engineer 15 brings brand new solution for 1D concrete members. This solution is based on our powerful technology Open Design (integration of Design Forms technology into SCIA Engineer). It allowed us to make complete revision of our solution for concrete structures. Thanks to the integration of the Open Design technology, we have been able to use powerful features of Design Forms platform - creation of transparent outputs of the calculation (formulas with substitutions and units, code references, dynamic images and diagrams, ….).

Somebody can ask what benefit is to do something which was already developed and implemented. The answer is not easy. Checks of concrete members have been based on technology which is 15 years old now. The original old checks did not allow us to present the calculation in a detailed form (which is common in current main civil engineering programs). The Open Design technology brings the possibility to display all steps transparently. Another drawback of the old solution was the missing possibility to process more than one combination of load (combination of biaxial shear and torsion) and the limitation of cross-section shapes (only rectangle and circle for columns). The old technology also did not support modern technologies such as multicore CPU and parallelism. For all these reasons together, we decided to adopt the Open Design technology for the new concrete checks. And what's more, this platform allows the users themselves to create their own calculations and/or checks.

Highlights

Revised and updated generic functions for design & checking of reinforced concrete columns & beams

Compliance with EN 1992-1-1:2004/AC:2010-11 including National Annexes
Support of arbitrary cross-section shapes including openings & arbitrary reinforcement positions

Support of interaction of all internal forces (N, My, Mz, Vy, Vz, T)

High performance

Clear & transparent reporting: assisting in dealing with EN 1992-1-1

Revised global and member settings, including 'quick search' function

New technologies

The revised design and check functions are developed within the Design Forms environment. This platform is linked as a post-processor to SCIA Engineer. The new solution is advantageous especially regarding the presentation of results. Next to text and tabular output, also formulas, code references, dynamic images and diagrams are included to give a deep insight into the calculation.

Presentation of results

Results are displayed numerically as well as graphically, including dynamic images of interaction diagrams and stress - strain distributions.

Level of output detail

The level of output detail can be chosen in the Properties menu (Output).

The brief output lists the unity check values of the selected members, or the required area of reinforcement. It is a simple table. Brief output can be also displayed in Table Results.

The detailed output first gives an overview of the input data, followed by a detailed calculation report. It also includes dynamic images displaying:

  • drawing of cross-section including reinforcement layout,
  • stress and strain distributions in different limit states,
  • 2D prints of 3D interaction diagrams.

New features (compared to SCIA Engineer 14)

All design & check functions are applicable to

  • General cross-section shapes including openings & arbitrary reinforcement positions
  • All member types (columns & beams)

New checks

  • Capacity check for Vy-Vz interaction (ULS)
  • Crack width check for columns (SLS)
  • Stress limitation (SLS)

Improved design acc. to ULS requirements

  • Design of multiple layers of reinforcement
  • Expanded design for columns
  • Design Asw based on Vy-Vz interaction
  • Design Asw including detailing provisions
  • Design additional longitudinal reinforcement caused by shear and torsion
  • Design of longitudinal reinforcement including detailing provisions

Clear & transparent reporting

  • Formulas, dynamic images of stress/strain distributions, interaction diagrams, …
  • Error handling, incl. suggestion for solution

New tree

Development of new service have been focused on user experience. The first improvement have been made in whole workflow of standard user. New service have been rearranged to mirror work-flow of an engineer.

Old concrete tree

Concrete tree in version 15

New setup for concrete data (global settings)

At the beginning there are global settings – setup. There is a brand new setup for concrete members that contains all required settings coming from the code and calculation routines. The global settings located in the setup are, by default, valid for all members in the project, unless they are overwritten by local settings - member data.

A lot of input parameters and calculation settings are collected here in the setup, reflecting the complexity of the Eurocode. The user can choose between a 'standard' or 'advanced' level, which filters the amount of data to be defined. The setup is arranged as a kind of table with 9 columns (description, symbol, value, default, unit, chapter, code, structure and check type). Search and filter functions are available. Furthermore, very useful is the possibility to switch the type of view in the setup - concrete commands view, code chapter view or list view. The user can also create his own view.

Old concrete setup

Concrete setup in version 15 - concrete commands view

Code chapter view

User filter view

New member data - local settings

The second step in a common work-flow is the definition of local settings. These settings overwrite the global settings for a specific member. Member data can easily be copy-pasted to similar members. There is differentiation based on type of member (beam, column, beam as slab). Similarly to setup, also member data have been restyled. The local settings contain the same input parameters and calculation settings as the global settings in setup. Moreover, the user can set his/her own value of limit width of crack, define more environmental classes than just one as in previous version.

Old concrete tree

Concrete tree in version 15

Useful tools for design and checks

Recalculation of internal forces

Internal forces which are used for design or for checks can differ from forces obtained from finite element analysis. The reason is that the design and check forces take into account shear and torsion, second order effects and imperfection of column.

Recalculation of internal forces takes into account the additional forces due to shear and torsion - shift of bending lines - in the case of the beam. This shift is possible both in the z and in the y direction. For columns, the recalculation of internal forces takes into account the second order effects and imperfections. The calculation of second order effects for asymmetrical cross-sections have been revised in the new version. The user has also an option to take into account the internal forces from imperfections for the serviceability limit state. The recalculation of internal forces is included in the design of reinforcement (where user-defined ratio of reinforcement is taken into account) as well as in checks (user defined reinforcement is taken into account).

Calculation of slenderness

Calculation of slenderness ratio is possible for columns. It can be done independently for design and check. The old calculation was performed for user defined reinforcement. The ratio of reinforcement can be defined by the user for each member in the local data.

Calculation of stiffness

Calculation of stiffness is performed for linear as well as short and long term acting load. User has to have defined appropriate combinations for service limit state (characteristic and quasi-permanent). Taking account of these effects is based on different modulus of elasticity and formulas from EN1992 are used for calculation of effective elasticity modulus. Creep coefficient have to be known for this calculation. This coefficient can be defined by user in local data or automatically calculated based on needed times, humidity and cement class. Calculation of curvatures is also done and results are presented.

Design of reinforcement

Improvements have been also made in the design of shear and longitudinal reinforcement according to the ultimate limit state. First, you get an overview of input data for the design:

  • Internal forces, displaying the characteristic and design values.
    For member type 'column', the design values of the bending moments include the 2nd order bending moments (if required) and the moments due to geometric imperfections.
    For member type 'beam', the design values of the bending moments include the shifting of the moment line - to take the additional tensile force due to shear into account.
  • Slenderness calculation (for member type 'column'), determining whether the 2nd order effects need be taken into account.

Longitudinal reinforcement

Algorithm for design of longitudinal reinforcement is based on the Concrete Toolbox and takes into account the influence of normal force and both bending moments. The method of design depends on the type of the member (column or beam) and on the type of load. Design of reinforcement can be used for arbitrary shape of cross-section.

In case the required area of reinforcement exceeds the available space on one layer, more layers (with adapted lever arm) are automatically generated. The designed reinforcement is automatically recalculated to real bars afterwards.

Design of reinforcement for beam contains

  • Taking into account the bending moment with respect to the z-axis (the previous solution respected just one moment – around the y-axis)
  • Design to more than one layer
  • Possibility to recalculate the statically required reinforcement to real bars
  • Calculation of reinforcement with respect to shear and torsion – additional tensile force
  • Display of reinforcement for each axis y+, y-, z+, z-
  • Note: Possible previously user defined reinforcement bars are not taken into account in this calculation.

Design of reinforcement for column contains

  • Old solution supported the design of reinforcement just for rectangular and circular cross-sections. Now, the design for an arbitrary shape of the cross-section is possible.
  • Calculation of reinforcement with respect to shear and torsion – additional tensile force
  • Display of reinforcement for each axis y+, y-, z+, z-
  • Note: Possible previously user defined reinforcement bars are not taken into account in this calculation.

Shear reinforcement

Design of shear reinforcement is done together with the design of longitudinal reinforcement. Shear forces, torsion and interaction of shear and torsion are taken into account.

  • Beams
    • Support of biaxial shear and torsion
    • Automatic calculation of the angle of compressive strut to satisfy the condition of minimal amount of designed reinforcement
    • Improved generation of the effective thin-walled cross-section
  • Columns
    • Formerly, statically required area of reinforcement could not be designed. The design was based just on detailing provisions.
    • The new solutions is able to design statically required reinforcement with respect to the acting load - biaxial shear, torsion and their interaction

Input of practical reinforcement

As in the past, a practical reinforcement layout can be defined for each 1D concrete member. Longitudinal bars, stirrups and free bars are available for manual input. Additionally, also anchorage types may be chosen and their properties manipulated by the user.

This practical reinforcement layout forms the basis for several ultimate and service limit state checks of reinforced concrete members.

Checks

First, the user gets an overview of the input data for the checks. He can review the recalculation of internal forces and calculation of slenderness. For columns, the recalculation of internal forces takes into account bending moments caused by the second order effects and bending moments caused by imperfections. For beams, shifting of bending moment line (additional tensile forces) is taken into account. The user can also review the calculation of stiffness for selected members.

Available checks for the ultimate limit state:

  • Capacity check for N-My-Mz interaction - based on the resistance calculated from the interaction diagram
  • Response check - based on the check of ultimate stresses and strains for N-My-Mz interaction
  • Check of shear and torsion

Available checks for the serviceability limit state:

  • Stress limitation (for concrete as well as reinforcing steel) - check of strain and stress under short and long term load
  • Crack width limitation - optional user-defined value of limit crack width
  • Simple check for deflection - based on the calculation of stiffness ratio, without the necessity to calculate code dependent deflections

Check of capacity

The new check allows for the calculation of interaction diagram also for plain concrete (coefficient acc is used in EN 1992-1-1 chapter 12). It is also possible to see three vertical sections of the interaction diagram:

  • vertical section for bending moment My - constant value of bending moment Mz
  • vertical section for bending moment Mz- constant value of bending moment Mz
  • vertical section for bending moment Mres - calculated as resultant using equation

The user can also display the horizontal section across the interaction diagram.

Check of response

The check of response contains the check of stress in a cross-section with respect to the code limit value (in old version, it contained just the check of strain). The new solution brings also the possibility to display results of calculation of the compression zone height, lever arm and effective height not only for a section but also along the length of a member.

Check of shear and torsion

Biaxial shear, torsion and interaction of torsion and shear can be checked. Stirrups are taken into account just in the distance perpendicular to the projection of a shear crack. Furthermore, the automatic calculation of the angle of compression strut was added and the generation of the effective thin-walled cross-section was improved (automatic or user selection from four types - from torsional stirrup, from input cross-section, from effective rectangular cross-section, user input values).

Effective thin-walled cross-section created from torsional stirrup

Effective thin-walled cross-section created from original cross-section

Effective thin-walled cross-section created from effective rectangular cross-section

Check of stress limitation

The check of stress limitation has been launched also for a non-prestressed cross-section. It is a brand new check based on the check of limit stress/strain under serviceability limit state load. Multiple settings of environmental classes. Cracking moments are calculated. Further, stress and strain for each phase of the cross-section (cracked, uncracked) are also calculated. This calculation is performed for each component of the cross-section - fibres of cross-section and reinforcement bars.

Check of crack width

Another calculation for the serviceability limit states is the check based on the direct calculation of crack width. In contrast to the old solution, bending moments in both directions are taken into account and the cracks can be calculated also for columns. Next improvement connected to the check is the possibility to select either an automatic calculation of the limit crack width with the respect to the environmental class or user input of the limit crack width, which can be defined in local settings for each member independently.

Check of deflections

The check of deflections is based on a simplified calculation in which the linear deflection is multiplied by a ratio of resultant and linear stiffness. First, the stiffness and curvature are calculated. The corresponding coefficient as calculated afterwards. Finally, the deflections due to short- and long-term load (including creep) are calculated. The check can be performed for envelope combinations and there is no need to create what is called concrete combinations, which was needed in the old solution. A limitation is that the calculation can be performed just for the user defined reinforcement. The advantage is that the check gives an overview of a long-term behaviour of the structure without running the code dependent deflections.

The calculation of deflection depends on the internal forces used for the reduced stiffness. Therefore the check of deflection doesn’t work for case where the internal forces are equal to zero but deflection are not zero. Typically for cantilever structure of member with free overhang. Here the results cannot be considered.

12/04/2015