Prolyte Campus blog: New calculations and loading tables for Prolyte truss explained

Differences between the old and new calculation principles:
Before the Eurocodes were implemented, calculations for truss and truss structures were made according to the ASD (Allowable Stress Design) calculation method. The principles of these calculations were written in the DIN standard. This standard provided all the figures for the maximum allowable stress for different Aluminium alloys in non-welded and welded positions.

The new calculations of truss and truss constructions are according to the Eurocodes and these calculations are based on the LRFD (Load Resistance Factor Design) calculation method. This is a semi probabilistic safety concept and is based on the theory of probability and partial safety factors.

The difference between these two design methods is the position of the safety factors in the calculations. In the ASD method we put all the required safety factors on the material side of the calculation.
In the LRFD method we put a small safety factor on the material side and a bigger safety factor on the load side of the calculation.

This makes it possible to have different safety factors for different types of loading.

To make it more visible:


ASD Truss calculations
 


How does this affect practical use?
For the practical use of truss spans supported on two suspension points there will be no difference, apart from a slight change in the loading table figures. The loading data as given in the loading tables indicate the maximum loading, which can be supported from the truss, used a single span.
For the calculation of different truss structures, being any other structure than a single span, a structural engineer needs to make separate calculations, according to Euro Code 1 and 9.

As a general rule, all structures need static calculations. This is not a change, this was already obligatory before the implementation of the Euro Code, but is often easily forgotten.

Calculations for structures
In calculations for structures we find significant changes between the old principle of Allowable Stress Design (ASD) and the new principle of Load Resistance Factor Design (LRFD).

The calculation will become more complex and the structural engineer needs to have more information about loading and loading types before he can proceed making the calculation.

If you have further questions: Contact Prolyte Sales 

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Thank you for your knowledge and huge experience

Gleb Kharchenko MF Group, Russia