The second-generation Eurocodes are incoming and will be the biggest regulatory change for a long time. Learning a new standard requires time and effort, but this article series is here to ease the process!
In this article, we will cover the main differences (as of the current working version of the second-generation Eurocodes) regarding Load Combinations. We will discuss combination factors, consequence classes, and changes to the load combination tables.
Combination factors
The first-generation Eurocode table of ψ-factors is on the left, and the second-generation Eurocode is on the right.
The new Eurocode brings a more nuanced table that clarifies that the same factors can be used for road vehicles above 160 kN, as well as more detailed factors for roofs, stairs, terraces, balconies, and construction actions. This will lead to a greater number of Load Combinations and a more complex load handling because of the need to split up loads into multiple categories. Also, a stronger emphasis on SLS checks for terraces and balconies can be seen where the factors are all set to 0.7.
Whether this change will increase or decrease material usage will depend on how your structure is loaded. In general, we believe this will lead to a slight increase in the load effects compared to the current Eurocode. However, this depends on whether you are currently separating the loadings into different categories and considering one load action at a time as the main load. Simplifications where loads are clumped together to save time are the biggest contributors to a higher load effect on the structure and, thus, an overuse of material.
Consequence classes
The current Eurocode presents three types of consequence classes: CC1, CC2, and CC3.
Second-generation Eurocode:
The second-generation Eurocode presents the same three consequence classes but with two special additions at the top and bottom of the spectrum, introducing CC4 and CC0 consequence classes as alternatives to the existing classes. However, CC4 and CC0 are not fully covered in the second-generation Eurocode. Additional provisions may be needed, placing more responsibility on the engineer to find and motivate alternative solutions.
From what we can tell, in these early stages, the CC4 and CC0 consequence classes will be very rare to come across. Most engineers will do what they can to stay within the regulated consequence classes, giving a similar workflow and identical consequence factors to the current Eurocode.
Second-generation Eurocode load combinations
A new logic is introduced for the load combinations where you first look at the overall load combination table A.1.3. Here, you can find an overview of the four different load combinations: persistent and transient (fundamental), accidental, seismic, and fatigue.
The persistent and transient (fundamental) group is then broken down further in the following table with four verification cases:
- VC1 – Used for structural resistance design
- VC2(a) – Static equilibrium and uplift design where “a” constitutes a situation where permanent action is unfavourable.
- VC2(b) – Static equilibrium and uplift design where “b” constitutes a situation where permanent action is favourable.
- VC3 – Used for geotechnical design. Design of slopes and embankments, spread foundations, and gravity retaining structures.
- VC4 – Used for geotechnical design. Design of transversally loaded piles and embedded retaining walls and (in some countries) gravity retaining structures.
The main difference between the first and second-generation Eurocode for these ULS combinations is the non-reduced variable load when permanent action is the main load.
First-generation Eurocode (current):
6.10a: 1.35 Gk + 1.5 y0 Qk,1 + 1.5 y0 Qk,2 + 1.5 y0 Qk,3 = 1.35 Gk + 1.5 y0 (Qk,1 + Qk,2 + Qk,3)
Second-generation Eurocode:
1.35 kF Gk + 1.5 kF Qk,1 + 1.5 kF y0 Qk,2 + 1.5 kF y0 Qk,3= 1.35 kF Gk + 1.5 kF (Qk,1 + y0 Qk,2 + y0 Qk,3)
Note that kF is the factor related to the consequence class.
This will, in most cases, be the designing load combination and will give a higher load effect.
A new table explaining the SLS combinations is also included. However, the present code and the second-generation Eurocode do not change except for the possible action from prestressing.
Conclusion
Of course, this is only based on the recommended values from the Eurocode—national changes may apply. But if we compare the first—and second-generation Eurocodes, the overall impression is that the new Eurocode will slightly increase the load effect and require more work for the structural engineer.
Rest assured, we are on top of the changes and will ensure that our software can deliver up-to-date automatic load combinations quickly and easily for our clients.
If you want to safeguard your business for the next-generation Eurocode, why not try FEM-Design with a free trial?
