Lattice Girder (Pin joint trusses)

[Kurtisreeve]

Hi, I would appreciate any help on my 2 questions about a lattice warren roof truss and the column supporting it. My first time with a large steel structure, and I have some doubts. Picture attached

The Scenario; I have a series of 12 steel warren trusses at 7m bays, the largest spanning 40m. the truss is supported by steel columns. There are no intermediate floors i.e. high roof, however 15m are above ground, and 5m are basement. and separated with one floor.

Q1. The Frame; would you splice a column using the same section size from top to bottom (20m)? or it makes more sense to build the basement in concrete and have 15m columns with a fixed base plate connection on the 5m high basement concrete walls?

Q2. Would having a top PINNED connection by having the truss resting on the column (similar to how space frames are seated on columns), and a FIXED moment base plate be enough to resist the lateral sway?

Q3. Lets assume the best option for the column is to have it 20m high. would the mentioned floor 5m above base of column, and two tie beams (tying along the 7m bays) at 10m and 15m above base of column, mean that the effective length of column is reduced by 4? i.e 5m - 5m - 5m - 5m, therefore smaller column I section


Thank you , for your help.

Kurtis

 

[CELinOttawa]

Location?

Q1: Use the basement.
Q2: Either/Yes/Both - Calculate and Design for the case you want; One is efficient, the other is not.
Q3: It is nearly impossible to reduce your effective length in the manner you show, and I know of no designer to CORRECTLY include this through calculations they know.

Frankly, this appears to be the makings of a disaster. Do you have a real-world mentor to help you with this?

 

[Kurtisreeve]

Thank you for the reply CELinOttowa.

Location of structure is Sicily. wind 23m/s

I forgot to mention that I also have two shear cores and bracing to stabilize the structure in the other direction. I was just trying to avoid having bracing in the 50m direction as it is a glazed facade. Hence the fixed base. However, having vertical bracing at both ends of 50m is also an option.

I was worried that 20m steel column would end up huge to prevent buckling, so I was thinking of a way to reduce the Leff.

Thankyou

PLEASE SEE PIC ATTACHED