B.7 Organization of the calculation

This is an essential step to be carried out at the beginning of the study.

Preliminary reflection on modeling

A preliminary step is essential for the modeler: the analysis of the overall behavior of the structure. Indeed, it would be foolish to start modeling a structure before understanding its overall behavior. A first sketch of the structure reveals a good understanding of the behavior and will be used as a framework for the creation of the model.

Mainly, this analysis of the overall structure allows distinguishing the main elements that reflect the behavior of the structure. Among these main elements, one will distinguish for example :

for civil engineering structures: the load-bearing structure of the deck, the structure of the supports, the bracings,

for reinforced and prestressed concrete buildings: columns, walls, and slabs,

for building structures: columns, beams, bracing elements.

The model must be based on input data, with at least:

a general assumption, which contains a description of the object, the standards applied and the loads applied,

sketches or general drawings of the object to be modeled,

a general construction principle,

an outline of the static and possibly dynamic behavior.

Modeling does not replace these elements of preliminary reflection.

BIM and modeling: The designer may be tempted to use the input data in an automated way to build his model. This is a frequent argument of software publishers. In this case, he will have to be particularly vigilant about the quality of the inputs provided (it is indeed not uncommon to find 3D models with geometric nonsense) and the level of detail of the input data (quantity of hoppers for example).

In the case of automated processing, special focus should be given to the geometry construction process, especially at the connections. Thus, the analysis phase of the overall functioning mentioned earlier is a way of preventing any anomaly.

Input data validation / Input synthesis

All documents defining the geometrical assumptions, materials, loads must be referenced with their origin, index, and date of issue.

It is necessary to validate the coherence of these different documents. For example, are the architectural plans and the structural plans consistent with each other? Are there any geometric discrepancies between the different plan files? Are the data exhaustive? Are infeasibilities already observed (e.g. complex load path, lack of bracing...)?

This synthesis work allows us to highlight the missing input data and/or likely to be modified and to define the conservative measures taken to compensate for the missing data.

Based on this preliminary analysis, certain decisions will be immediately imposed on the designer: exchanges with the client, revision of the geometry of the structure (design revision), input of parameterizable data...

This synthesis phase will ideally take the form of a "Modeling Note" that will evolve as the model progresses. The aim is to have the hypotheses validated by all the participants in the study very quickly to avoid modifications, which are often long and complex.

Specifics of the study

All the specifics of the study must be listed at the beginning of the study:

the physical constraints of the project (important heaving, urban area, construction phasing, ...),

the study constraints (tight schedule, numerous interfaces, missing data, ...),

the particularities of the model (size of the model, non-linear, earthquake, ...),

the requirements and sensitive aspects of the project (slender structure, asymmetrical, heavy wind, etc.).

It is necessary to show that the modeling will consider all these points.

Planning of the study

It must clearly show:

the deadlines of the main modeling phases (geometry, materials, loads, interface or soil-structure interaction, combinations, etc.),

the deadlines for receiving missing or modifiable input data,

the deadlines to send the deliverables used as input data to other study stakeholders (interface) and for other deliverables,

the consistency of the study with respect to the dates of the phases.

Modelling Principles

The goal is to explain the calculation methods, making sure to:

clarify the principles of the structural model, the methods to consider loads, combinations, ...,

justify all approximation assumptions,

if necessary, present small test models validating the hypotheses,

present the sequence of calculations.