r7.01.02 Prestress cable modeling#

Summary

To improve the strength of certain civil engineering structures, prestressed concrete is used: for this, the concrete is compressed using prestressed steel cables. In Code_Aster, it is possible to make calculations of such structures: the prestress cables are modeled, either by elements BARRE with two nodes or by elements CABLE_GAINE with 3 nodes, which are then linked kinematically to the volume or plate elements that make up the concrete part of the structure. To perform this calculation, there are three commands specific to these prestress cables, DEFI_CABLE_BP, which makes it possible to define the cable and the tension conditions geometrically, AFFE_CHAR_MECA, operand RELA_CINE_BP, which makes it possible to transform the information calculated by DEFI_CABLE_BP into loading for the structure, and CALC_PRECONT, which allows the application of prestress on the structure.

The main specificities of modeling based on the elements BARRE or CABLE_GAINE in the adherent case are as follows:

  • The tension profile along a cable can be calculated (i) either according to regulation BPEL 91 [bib1] taking into account anchor recoil, rectilinear and curvilinear friction loss, cable relaxation, creep and concrete shrinkage, (ii) or according to regulation 91 [], or according to regulation 91 [] taking into account anchor recoil, friction loss and cable relaxation. ETC In these two cases, the cable/concrete connection is assumed to be perfect, like sheaths injected by a grout.

  • It is possible to define an anchor zone (instead of an anchor point) in order to mitigate the singularities of constraints due to the application of tension on a single node of the cable (effect of modeling).

  • The behavior of cables is elastoplastic, as thermal expansion can be taken into account.

  • Thanks to operator CALC_PRECONT, we can simulate the phasing of the tension of the cables and the tension can be done in several steps of time in the event of the appearance of non-linearities. Finally, the final voltage in the cable is strictly equal to the voltage prescribed by BPEL.

  • Since the cables are modelled by finite elements, their stiffness remains active throughout the analyses.

The main specificities of modeling based on elements CABLE_GAINE, in non-adherent cases are as follows:

  • It is possible to model adherent, slippery or rubbing cable-concrete connections.

  • In the adherent case, it is the tension profile calculated according to BPEL91 that is imposed; in the rubbing and sliding cases, the profile is obtained by simulating the tension of the cable and possibly the anchor recoil. Other types of loss cannot be taken into account.

The operators DEFI_CABLE_BP and CALC_PRECONT are compatible with all types of solid mechanical finite elements and plate elements (DKT, Q4GG) for the description of the concrete medium crossed by the prestressing cables and the tension.