# Constraints Files¶

Once the required reinforcement is calculated, the physical reinforcement elements have to be designed in such a way that it satisfies optimally the design constraints, code specifications, and other particular demands. Usually, the engineer has to evaluate all the possibilities based on his own experience and knowledge in order to determinate the most convenient solution.

One approach to access such kind of implicitly given knowledge is Expert System technology. Expert systems are regarded as branch in the area of Artificial Intelligence and are currently used in many fields of application like medical diagnostics or assembly layout of computers. One of the key assumptions in (rule based) expert systems is, that the knowledge of an expert can be expressed in IF … THEN … type rules. The system provides facilities to enter these rules by the expert in a very simple and accessible syntax, often similar to human language, which enables the expert to enter his knowledge without deeper programming skills. These rules are then processed by the expert system within the so-called inference engine in order to generate new conclusions or initiate certain actions.

The automatic generation of the 3D-rebar model in SOFiSTiK Reinforcement Generation follows this approach. Each step in the generation of the rebar model, like the determination of the rebar layout in the cross-section or the calculation of anchorage and laps can be controlled by rules.

For example, in order to control the diameter of the longitudinal bars in a beam, the user may define the following rules:

//$range of allowed parameters for the diameter of longitudinal bars. d_asl = [ 0.006, 0.008, 0.010, 0.012, 0.014, 0.016, 0.020, 0.025, 0.028, 0.032, 0.040 ] //$ restrictions of the range according to the height of the cross-section
Is_Beam {
d_asl <= 0.028
Section_Height <= 0.50 : d_asl <= 0.025
Section_Height <= 0.40 : d_asl <= 0.025
Section_Height >= 0.50 : d_asl >= 0.016
Section_Height >= 0.80 : d_asl >= 0.020
}


According to the different requirements in the design process, there will also be different kind of rule sets for controlling the rebar generation. There will be rules for maintaining the design code regulations or rules which the user can define on a project or company specific basis.