Considering thermal and rheological effects

CYPECAD does not automatically consider thermal and rheological effects in the analysis of the structure. This issue can be addressed in two ways:

  1. Introducing expansion joints in the structure to eliminate the need to consider these effects in the analysis.
  2. Introducing loads on the structure to simulate these effects.

Expansion joints

In buildings, different expansion joints are used for the structure, envelopes, terrace floors and other construction systems.

For Eurocodes, Eurocode 1 – Actions on Structures, Part 1-5: General actions – Thermal actions, point 3 – Design situations, paragraph 2, states: “The elements of loadbearing structures shall be checked to ensure that thermal movement will not cause overstressing of the structure, either by the provision of movement joints or by including the effects in the design”.

In Eurocode 2 – Design of concrete structures, Part 1-1 General rules and rules for buildings, point 2.3.3 – Deformations of concrete, paragraph 3, refers to: “In building structures, temperature and shrinkage effects may be omitted in global analysis provided joints are incorporated at every distance djoint to accommodate resulting deformations. Note: The value of djoint is subject to a National Annex. The recommended value is 30 m. …”

The specialised technical documentation gives less restrictive joint spacing values. In the “Expansion Joints in Buildings” technical report by the National Academy of Sciences in Washington, DC, it is stated that expansion joints for reinforced concrete structures can be placed at a maximum distance of 60 to 90 m apart. The information is completed by stating that the joints in exterior brick masonry walls in façades should be spaced between 12 and 18 m apart, and in the case of flat roofs, between 5 and 8 m apart. These data in turn are based on measurements performed on nine real buildings and on numerous theoretical structural analyses.

These data are also cited by José Calavera in the book for the design and analysis of concrete structures “Proyecto y Cálculo de Estructuras de Hormigón“, Volume 1, published by INTEMAC, in table T-24.1 (page 474). Previously, in chapter 24 (page 473), he states that the placing of joints every 30 metres is very conservative.

Introducing loads to simulate thermal and rheological effects 

To carry out an analysis of thermal and rheological effects in CYPECAD, a copy of the file can be made and modified considering the following:

1. Slabs should not be introduced into the model since, should they exist, the program will apply the load from a rigid diaphragm. This consideration means that no two points on the same floor cannot be either separated or close together in the horizontal plane, making the set behave like a non-deformable tray. Therefore, work would only be carried out with a structural skeleton of columns and beams.

2. From the “Beams” menu, the rigid diaphragm beams must be disconnected from the “Rigid diaphragm in unconnected beams“, “Disconnect“. This is an additional precaution and allows the beams to have more degrees of freedom than those they have by default. If this operation is not carried out, the beams themselves will again constitute a rigid diaphragm.

3. The loads for thermal or rheological effects must be estimated and entered manually. To do this, if loads on the columns are to be applied, the “Column definition” tab and the “Horizontal Loads” or “Head Loads” options can be used for the desired load.

Once the analysis has been completed, users must check the model to check the compliance of the sections and the reinforcement values of the elements.