14 posts in this topic

For those of us who used the British standards to design in the past, we have a notional load applied to the building which is equivalent to 1.5% of the characteristic dead weight of the building (for concrete structures).

From what I have gathered so far, in Eurocodes we do not have this, instead we have the equivalent horizontal loads and we also need to consider global and local imperfections as well as doing p-delta analysis.

However in our Singapore NA, we have the following clause:

post-1374-14570089612596_thumb.jpg

I want to know what are your opinions out there and if any other EU country adopted something similar.

Thanks!

Share this post


Link to post
Share on other sites

In Eurocode 3 (EN 1993-1-1), the initial imperfections (global initial sway imperfections and relative initial local bow imperfections of members for flexural buckling) are replaced by equivalent horizontal forces. The values of the horizontal forces depend on the vertical loads. For example the global initial sway imperfections (φ) are replaced by a horizontal force HEd=φ*NEd, where NEd is the design value of the axial force. I am not familiar to British Standards but the procedure followed by Eurocodes seems reasonable to me. As for the Singapore's NA method, it looks similar to BS. Am I right?

Share this post


Link to post
Share on other sites

According to Eurocode 2 (reinforced concrete design) and 3 (structural steel design), we can represent initial sway imperfections by using Equivalent Horizontal Forces (EHFs) which are based on 1/200 of the factored vertical load, with reduction factors.

Share this post


Link to post
Share on other sites
In Eurocode 3 (EN 1993-1-1), the initial imperfections (global initial sway imperfections and relative initial local bow imperfections of members for flexural buckling) are replaced by equivalent horizontal forces. The values of the horizontal forces depend on the vertical loads. For example the global initial sway imperfections (φ) are replaced by a horizontal force HEd=φ*NEd, where NEd is the design value of the axial force. I am not familiar to British Standards but the procedure followed by Eurocodes seems reasonable to me. As for the Singapore's NA method, it looks similar to BS. Am I right?

Yes, that is right. In Singapore NA which is similar to BS, the notional forces are to account for these imperfections. So to me, to include them on top of the EHF required by EC is double counting.

To summarise (ignoring Singapore NA):

There are 2 conditions that need to be considered (for a standard column member not contributing to the bracing system of the building):

1. EHF Effect on floor diaphragm (or roof diaphragm) [GLOBAL]

2. EHF Effect on isolated members [LOCAL]

For bracing systems members an additional EHF is needed. [GLOBAL]

All these EHF add on to each other to contribute to the final design. Is that correct?

Share this post


Link to post
Share on other sites

To summarise (ignoring Singapore NA):

There are 2 conditions that need to be considered (for a standard column member not contributing to the bracing system of the building):

1. EHF Effect on floor diaphragm (or roof diaphragm) [GLOBAL]

2. EHF Effect on isolated members [LOCAL]

For bracing systems members an additional EHF is needed. [GLOBAL]

All these EHF add on to each other to contribute to the final design. Is that correct?

I think you are right!

Global and local imperfections as well as their Equivalent Horizontal Forces, should be added together.

Share this post


Link to post
Share on other sites

Thanks for the information friends! I need know how to include the notional load in load combinations.

Can notional load be combined with wind load, dead load and live load....?

Please guide me how to include notional load in load combinations and why...?

Are there any Eurocode references...?

I am looking forward for your reply!

Thank you,

Arun S

Share this post


Link to post
Share on other sites

LOAD 1 : DEAD

JOINT LOAD

13 TO 16 29 TO 32 45 TO 48 61 TO 64 FY -100

LOAD 2: DEAD NOTIONAL LOAD

NOTIONAL LOAD

1 X 0.002

…

LOAD 10: IMPOSED

JOINT LOAD

13 TO 16 29 TO 32 45 TO 48 61 TO 64 FY -50

LOAD 11:IMPOSED NOTIONAL LOAD

NOTIONAL LOAD

10 X 0.002

If we want to combine the load cases in the example shown above, the correct syntax would be:

LOAD 3 : LOAD 1 + LOAD 2 + Notional Loads

REPEAT LOAD

1 1.0 2 1.0

NOTIONAL LOAD

1 X 0.002 2 X 0.002

(Load case number - Direction - factor) is the way it is usually applied..

Hope this was useful to you..

Regards,

Vaidyanathan S

Share this post


Link to post
Share on other sites

Yes, the forces generated by imperfections etc, i.e. the NHL or EHF (call them what you will), should be combined with other 'real' loads, such as wind. For example, your building may have a column that is bent or out of plumb and that will create a horizontal force - the wind may also blow on the imperfect building - the two conditions are not mutually exclusive.

Share this post


Link to post
Share on other sites

Thanks for your valuable information friend.

Share this post


Link to post
Share on other sites

Hi guys, I am also trying to understand how to deal with EHF's.

What you appear to be saying is that EHF's are treated as a 'variable action'.

If that's the case then what combination factor (Ψ0, Ψ1 & Ψ2) should you use for them? Table NA.A1.1 doesnt seem to have an obvious category for them.

Thanks

Chris

Share this post


Link to post
Share on other sites

I could be wrong here and therefore welcome other views but...

The EHF's are due principally to imperfections (bow, out of plumb etc). Those things will be in the structure for all time (a simplification) and will not vary as do imposed variable loads. They are mobilised through a product with the vertical loads though. Therefore, the combination factors do not apply, in my view, for the part generated by permanent loads but could apply for anything that is generated by a product with imposed loads. That would complicate design a little and, given that permanent load for buildings is usually dominant, it may be a conservative simplification to not apply the combination factors to the EHF's. Alternatively you could apply the combination factors to the variable loads before input into you EHF computation.

Share this post


Link to post
Share on other sites

I think due to lack of clear guidance I will take the conservative approach of not applying combination factors to the EHF's.

Should I do two loadcases with the EHF's, one with them applied to the principle axis of my frame and the other with them applied to the secondary axis, or do I only need to apply them to the principle axis?

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By Stelios89
      Hello everyone,
       
      I am not familiar with the use of forums so I am not sure how we can help each other but for starters I'd like some assistance with the design of a steel tee beam.
       
      The section is just shy of 0.5m, and on one side it is bearing onto masonry (100mm blockwork) and the other is bolted onto the web of a steel I-beam. It is also loaded on both its sides by approximately 5.5kN/m (total). 
       
      Please, if possible, provide some guidance as to how this section is classified and which parts of the eurocode would allow me to design it. I've already done some parts of it, where I basically assume that the section is in tension but I am not sure if I am missing anything. 
    • By user277418
      Good afternoon, friends.
      I am analysing car park with long span composite beams and have very large displacements of columns top in plane of frame because of EHF.
      Is it necessary to take into account EHF in SLS combinations?
      Best regards, Ievgen
    • By tekjhe
      I'm right now doing a structural analysis of a shed for bicycles. A bicycle shed normally is uninhabited as people are parking their bicycles there and stay there for about 30 sec before leaving the shed. A building or a house normally is inhabited as people live or staying there during day or night time. A shed however must be able to carry some snow etc. and it is set up permanently. I find of course everything on the topic of roofs etc. in the Eurocode, but wonder if Eurocode differ in the way to analyze uninhibited structures vs. inhibited structures e.g. if the structure has to be analyzed differently whether people just passes through the structure for 30 seconds or live in it, permanently?
    • By saruncivil
      Dear Engineers,
      Please find the attached file for my query.
      In Fin plate calculation. LTB of fin plate to be calculated and in which confusion in slenderness of fin plate calculation.
      Please clarify and give suggestion to my query.
      thanking you,
      Arun S
      Extracted from SCI-P358.pdf