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Help with Deterrmining to Use Sway or Non Sway for Tall Buildings

Help with Deterrmining to Use Sway or Non Sway for Tall Buildings

Help with Deterrmining to Use Sway or Non Sway for Tall Buildings

Hi there,

I am working on my dissertation which is subjected on the efficiency of structural systems for tall buildings; particularly The Steel Rigid Frame, Core + Outriggers and The Braced Tubular System. I am attempting to design the buildings to relevant Eurocodes but I am a little stuck on whether to class them as sway frames or non-sway frames - this so I can use the correct value for the effective length 'K'.

For sway frames 'K' is always greater than 1. For non-sway 'K' is always less than 1. Therefore, it makes a huge difference when designing my columns, because of the value of the critrical buckling load Ncr = ((pi^2)*E*I)/(KL)^2

Firstly, I used the stability index formula, which is Q = P*delta/V*h


P = the total factored load acting on the columns in the storey
delta = the relative displacement between each storey
V = the shear acting on the storey
h = storey height.

For a frame to be classed as a non-sway frame the value of Q must be less than 0.04.

Now, intially, I designed the Core + Outrigger Structure and Braced Tubular System to be non-sway, because they have bracing, but when used the stability index formula, every storey gave a result of greater than 0.04. Thus, I reasoned that they must be sway frames.

I have therefore designed my columns using the sway formula for calculating 'K'. This meant the column sizes increased dramatically. However, I have just computed the stability index again for The Braced Tubular System (with the new column sizes) and every storey falls under 0.04 for the stability index.

Thus, I am stuck on what to use for my effective length 'K'.

Could anyone please help me?

Many Thanks in advance.

EDIT: Please note, there are two different formulas for calculating 'K' for sway frames and non-sway frames. I am using the french standards for that.

RE: Help with Deterrmining to Use Sway or Non Sway for Tall Buildings


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