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  1. #1
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    Equivalent horizontal forces and notional loading

    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:

    Click image for larger version. 

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

    Thanks!

  2. #2
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    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?

  3. #3
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    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.

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    Quote Originally Posted by Ion View Post
    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?

  5. #5
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    Quote Originally Posted by seighart8888 View Post
    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.

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    Click image for larger version. 

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    Does the above answer your question?

  7. #7
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    Forgot to upload diagram...

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  8. #8
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    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

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    Νotional load can be applied in load combination

    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

  10. #10
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    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.

 

 

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