CYPECAD requires users to define the conditions at the base of the supports, whether they are columns, shear walls, walls or starts, when they are entered into the model:
This requirement is due to the internal operation of the program in the analysis process. In CYPECAD, the foundation systems formed by footings, pile caps and tie beams and strap beams are analysed independently, including the loads applied by the rest of the model on their supports. However, other elements such as foundation beams, foundation slabs or any of the elements of the overhead structure, which can also serve as supports, are integrated together with the rest of the model in the same design matrix.
Supports with external fixity
A support resting on a footing or pile cap must be defined with external fixity, as its base is an external support or rotation coercion for the overall model of the structure and the load is delivered to elements external to the model. For the same reason, a support resting on any element independent of the model that is not defined in the program must also be considered with external fixity.
These supports correspond to columns, shear walls and starts defined “With external fixity” and to walls with foundations defined with “Fixity” or on “Strip footing without soil-structure interaction“.
In the analysis, this condition is considered by setting it to 0 and thus preventing the displacement of the support base. However, it is still possible to consider entries in defined supports with external fixity using the options corresponding to the “Soil-structure interaction“.
Supports without external fixity
A support that rests on any element other than a footing or pile cap shall be defined without external fixity, as its base does not provide external support or restriction to the model of the structure, but internal fixity, as it is in contact with other elements belonging to the same model. Among these cases, the following can be mentioned:
- The support starts in a slab beam.
- The support starts in a foundation beam.
- The support starts in a floor slab.
- The support starts in a wall.
- The support starts in a matfoundation.
These supports correspond to columns, shear walls and starts defined as “Without external fixity” and to walls with foundations defined as “Other structural support“, on a “Foundation beam” or on “Strip footing with soil-structure interaction“.
In the program, the base of a support without external fixity may be subject to displacements, as they are not fixed beforehand. The displacement must be evaluated in the design process and depends on the behaviour of the elements under the support.
Associated errors
Some input errors associated with the definition of supports with or without external fixity are shown below:
The columns or shear walls with PX references, have been entered without external fixity to the structure and start from a strip footing with external fixity, from a pad footing, or from a pile cap. To be able to analyse the job, the columns must be entered with external fixity.
The PX columns have been defined with external fixity and coerced rotation, and are in contact with beams. This is probably a data entry error because this way, the rotation of the beam is impeded, and so is its contribution in absorbing the foundation loads. It is possible to eliminate the ‘X’ rotation or ‘Y’ rotation coercion in option ‘Column Definition > Entry > Columns, shear walls and starts > Edit’ or ‘Column Definition > Entry > Columns, shear walls and starts > External fixity’.
Columns or shear walls with PX references have been entered with external fixity to the structure and start on a floor slab. This is incorrect because by doing so, the vertical displacement of their base is hindered and the forces acting on these floor slabs are not calculated adequately. To be able to analyse the job, the columns must be entered without external fixity.
The X beams are in contact with mat foundation %d. A mat foundation can only be in contact with foundation beams, with its own slab limits or with columns and walls that start from it. If the beams indicated are the foundation of a wall, edit the wall and change to a foundation beam or strip footing. This limitation is entered to avoid inadequate structural models such as external fixities in the perimeter or the interior of the slab that may distort the forces on it or the stresses on the soil.
The X walls from the Y group have been entered with external fixity to the structure and are in contact with beams that are neither wall fixities, nor wall supports, nor strap beams for walls. Bear in mind that this way, vertical displacements in the beam are prevented. Usually these walls should be exempt or in contact with wall supports or fixities, or wall strap beams. The job will continue to be analysed, and so it is possible to interrupt the calculation process or upon ending, check the indicated encounter and, if necessary, correct it.
To correct these errors, users should study the support mentioned in the message, the definition of the conditions of its base and the existence of the elements in contact with it, to adapt the situation of the model to the guidelines given in the text of the message and in this space.
Summary
| Supports with external fixity | Supports without external fixity | |
| Description | The support base is linked to an element external to the general model of the structure. | The support base is linked to an element from the same general model of the structure. |
| General behaviour | The displacement of the support base is prevented. | The displacement of the support base must be evaluated during the analysis. |
| Diagram |  |  |
| Use cases (elements in contact with the support base) | The support starts in a footing. The support starts in a pile cap. The support starts in an element that will be designed outside the program. | The support starts in a floor beam. The support starts in a foundation beam. The support starts in a floor slab. The support starts in a wall. The support starts in a mat foundation. |
| Options in the program | Column “With external fixity”. Shear wall “With external fixity”. Start “With external fixity”. Wall defined with “Fixity”. Wall defined on “Strip footing without soil-structure interaction”. | Column “Without external fixity”. Shear wall “Without external fixity”. Start “Without external fixity”. Wall defined with “Other structural support”. Wall defined on “Strip footing with soil-structure interaction”. |
