Code dependent deflections (CDD)

 

17.0

Long-term deflections, especially in cracked and slender R/C flexural members, may cause delayed damage in non-structural elements, so they must be accurately estimated at the design stage.

The CDD calculation has been designed exclusively for concrete beams and plates, as it is based on the wording of technical standards for design and checking of concrete structures. The aim is to calculate the long-term deflections according to the rules described in the national code.

A big improvement has been added to give the designer very fast and sophisticated tool to calculate the long-term deflection in according with Eurocode and the national annexes.

Highlights
Fast and reliable calculation of CDD calculation
Automatic calculation of the creep coefficient
Automatic load combination for CDD calculation
Possibility to calculate the deflection of 1D & 2D members at the same time
Taking into account the required or provided (user) reinforcement
Stiffness calculation with respect to the non-linear stress-strain relationships in concrete and its reinforcement.
Graphical and numerical presentation of the results

Principle of the CDD calculation in SCIA Engineer

This calculation of deflections depends on (is based) on standards. Therefore, it represents a standard-related calculation that is performed in two steps. First, a normal linear calculation is carried out and the computed internal forces are used to input the reinforcement (required, provided or user). The procedure continues with the calculation of cracks and their effect on the stiffness of individual elements. This weakening is then inputted into the solver. Finally, the calculation (linear one) is run once more with these reduced stiffnesses taken into account. Which is exactly what the technical standards require.

Limits of deflection

There are two limits defined for the calculation of the long-term deflection. The first one is the limit for the deflection of 1D members which is calculated automatically by the software depending on the boundary condition of each member or it can be defined directly by the user through the global or the local concrete setting.

The second limit is for 2D elements like slab and walls and this should be manually imputed by the user as absolute value .

Supported reinforcement types for the calculation of CDD

Three different types of reinforcement can be used to perform the long-term deflection. To give the designer a smooth workflow, SCIA Engineer calculates the required reinforcement for 1D and 2D element before the calculation of CDD automatically in case that the user has not calculated them before. In addition, it is very important to mention that SCIA Engineer will skip this step when the designer has already calculated the reinforcement in advanced to save the time of the calculation.

Advantages of this version regarding the long-term deflection

  • Possibility to calculate the long-term deflection for 1D and 2D members at the same time
  • The necessary load combination will be generated automatically
  • Three different types of reinforcement are supported (required, provided and user reinforcement)
  • Clear and easy way to see the unity check after the calculation
  • Step by step calculation of deflection (immediate, short, total deflection)
  • Automatic calculation of the creep coefficient

Results and presentation of results

The results of the calculation of the long-term deflection can be presented graphically or numerically. In addition, the designer can see the results of 1D and 2D in the same graphical screen.

This version of SCIA Engineer supports only brief output. This output includes all the deflection results in each step of the calculation.

The CDD calculation is available within v17 environment, which can be activated from the Project data dialogue under the Post-processing section.

22/03/2017