Notional Loads according to SANS

[Stoppie]

Calling on structural engineers from South Africa.

Please give me your interpretations on notional loads according to the SANS codes regarding ULS partial factors, whether or not it may be omitted in a secondary analysis, and whether it should alternate with other lateral load cases, such as wind, or be applied in conjunction with them?

Two notes as a possible starting points for discussion.

* SANS 10162 states that "notional lateral loads are applied in all lateral load combinations and not as a minimum"​

* Apologies for the absence of a reference, but I once read that BS codes allow for alternation between notional and wind loads in load combinations. Whereas according to the Eurocode they are to act simultaneously​

 

[HTURKAK]

My points ;

- I do not have any idea regarding the SANS codes ,

- Eurocodes ; The Notional horizontal loads shall be considered in addition to lateral loads. ( The notional loads are defined at material specs EC-2 to EC- 6)

- BS 8110 ; AFAIK , Considered only if greater than imposed lateral loads..







Not to know is bad;
not to wish to know is worse.

NIGERIAN PROVERB

 

[canwesteng]

As I understand, SA codes were originally developed from CSA codes (also very close to AISC). Notional loads are included with every load case for every gravity load, and are a percentage of the factored gravity load, and required in secondary analysis (you mean second order I assume).

 

[KootK]

...whether or not it may be omitted in a secondary analysis...

It may not be omitted in a second order analysis. In fact, the only time that the notional loads will do their intended jobs is when they are used in a second order analysis.

...and whether it should alternate with other lateral load cases, such as wind, or be applied in conjunction with them?

The job of a notional load is to act as a "perturbation". A perturbation is just some source of instability that gets things moving laterally in the second order analysis. Without perturbations, it may be the case that nothing happens from a stability perspective when only gravity loads are considered.

Environmental loads such as wind and earthquake can also serve as perturbations. In fact, such loads will usually dominate as perturbations relative to any notional loads acting concurrently. Because of that, including notional loads along with wind and seismic probably doesn't accomplish a whole heck of a lot. So one might be forgiven for not bothering with them.

Still, I would include notional loads concurrently with the environmental lateral loads because:

1) That's what the codes usually say to do.

2) The design penalty for doing so is usually nil.

3) The notional loads usually reflect real loads that result from member out of plumbness, misalignment etc. It is somewhat unconservative to ignore these things.

4) Once notional loads are set up within an FEM package, it's usually dirt simple to just include them in all load cases as the code directs us to do.