Pattern liveloading for serviceability limit states 2

[Datpt]

Hi everyone.

I am writing to seek your opinions on the application of pattern live loading for serviceability checks of floor systems. I am using Eurocode and ACI for designing floor systems.

According to EC2 Section 5.1.3, pattern live loading is required for the design of slabs and beams. However, the load combinations given in the Notes seem to be similar to those for the ultimate limit state, without the factor Ψ. I wonder if this implies that pattern live loading is not necessary for checking serviceability criteria, such as deflections and cracks, which are reversible.

Similarly, ACI 318-19 Section 6.4 requires the calculation of Mu based on pattern live loading for the strength design of slabs and beams. However, there is no mention of pattern live loading for the calculation of Ma for serviceability design. Does this mean that pattern live loading can be ignored when checking deflections and stresses?

I would appreciate it if anyone could share any reference or guidance on this issue, as it has been a controversial topic in my company for a while and no one has been able to answer it satisfactorily.

Thank you for your attention and input.

 

[Lomarandil]

Without any basis, I've historically applied pattern loading throughout my design when it is appropriate. I'll be curious to hear if there is justification to not do so.

 

[JAE]

We have higher load factors for live loads due to the higher variability. In addition, the codes require the pattern loading to further account for the randomness of live loads.

For continuous beams and slabs, it is quite possible that one span would be more heavily loaded than its adjacent spans. For public safety and welfare it is appropriate to consider this.

For serviceability, the code's requirements are quite rough and approximate in my view - an attempt to control bending, damage to brittle finishes, minimize vibrations, etc.

My practice has been to include pattern loading for serviceability checks.
With continuous spans, you have a similar possibility (probability?) of one span loaded while adjacent spans less so.

The only thing I might consider would be to alternate only 50-75% of the live load when doing serviceability checks as it isn't a public safety issue.

 

[mronlinetutor]

L for live load and the pattern probably directs towards half loads or alternating loads pattern in whatever case has the highest resultant loads.

P.S. I retired this year at 65 and I only have limited experience in structural engineering. I have no jobs so I spend my time reading for 40 yrs.

disclaimer: all calculations and comments must be checked by senior engineers before they are taken to be acceptable.

 

[Datpt]

Without any basis, I've historically applied pattern loading throughout my design when it is appropriate. I'll be curious to hear if there is justification to not do so.
=> thank you so much for sharing, however, the problem is when it is appropriate to design with pattern loading for service states.

 

[Datpt]

My practice has been to include pattern loading for serviceability checks.
With continuous spans, you have a similar possibility (probability?) of one span loaded while adjacent spans less so.

The only thing I might consider would be to alternate only 50-75% of the live load when doing serviceability checks as it isn't a public safety issue.

=> Thank you for sharing your experience. I also think that we don't have to use full magnitues of live loads when consider pattern live loading.
However, I haven't found any instruction to do so in the codes or design manual.

 

[lexpatrie]

Isn't servicability (deflection) not even required to be checked when the concrete member is sufficently deep versus the span? I appreciate everyone wanting to save material, but the thinner elements are, the more critical shear becomes. Just saying. Being frank, I associate "slab too thin, deflection check required and not performed" with collapses, some during construction, some after. Harbour Cay, Champlain Towers South, probably 2000 Commonwealth avenue, probably L'ambiance Plaza..... at least Ronan point was a gas explosion.

Regards,
Brian

 

[Lomarandil]

Datpt, I mean to say that when the structural arrangement is such that pattern live loading is appropriate or required for strength limit state checks, I also use pattern live loading for my service level checks.

 

[Datpt]

Lomarandil, the checking of pattern live loading is a must for strength checking in most cases. Both EC and ACI have very clear requirements for this.
However, the requirement for pattern live loading at service check is quite vague.