Tygra_1983
Student
- Oct 8, 2021
- 125
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
Where:
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.
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
Where:
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.
