Precast Raker Beams-Analysis
Precast Raker Beams-Analysis
(OP)
Does anyone have any guidance on the analysis of precast raker beams for stadiums / arenas?
My two concerns are:
1. Vibration analysis
2. Accounting for the in-place geometry of the raker beam (the incline of the member, versus a beam that is level and flat) on the statics of the member.
My two concerns are:
1. Vibration analysis
2. Accounting for the in-place geometry of the raker beam (the incline of the member, versus a beam that is level and flat) on the statics of the member.






RE: Precast Raker Beams-Analysis
If you have more specific questions, I will try to address them. I'll keep an eye on the thread.
Regards,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
RE: Precast Raker Beams-Analysis
For vibrations, I am going to keep the natural frequency of the beams above a certain minimum, and will follow the PCI Design Handbook (and CPCI Design Handbook in Canada).
With the geometry, I wonder if the inclined beam is designed for the vertical loads on the horizontal span, or do you put all the loads into components along the inclined member axis, and perpendicular to the member axis and then design for the diagonal span length?
For the latter case, I guess one would have axial load to contend with and may have axial tension in the beam from the incline? Maybe tomorrow, I'll try to post a sketch - kinda crazy here today!
Working in Winnipeg, under my snow covered home, thinking of New Zealand.....
RE: Precast Raker Beams-Analysis
If axial loads are small then they can be ignored, if large then the whole thing needs to be designed as a column.
Regards
csd
Working in UK, missing the snow already!
RE: Precast Raker Beams-Analysis
And keep in mind that if this is a large stadium, you're likely going to need prestress or post-tensioning to make the rakers work. Some pretty serious moment redistribution can help a great deal to get the supporting frames to be economical.
As for your vibrations, I'm not actually familiar with either of the texts you're employing, but definitely respect the publishers. I would caution you to make sure you are using recent texts (newer than roughly the middle 1990s) as you don't want to be analyzing a structure like this with foot-fall methodologies (which were created empirically against structures with significant inherent damping during the 1970s).
If you get stuck or would like an authoritative external reviewer, I would strongly recommend David E. Allen, PhD, who is retired, but previously of the NRC and is possibly Canada's foremost vibration expert. He's excellent value and very helpful... Also makes good dinner conversation for business meetings. *smiles*
Keep asking questions as needed! Hope to help as much as I can.
Cheers,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
RE: Precast Raker Beams-Analysis
Not necessarily - there are many stadiums out there that don't use prestressed rakers. It depends upon the available depth but usually mildly reinforced raker beams can be adequate.
The attached drawing shows a raker beam - non-prestressed, used in Texas. With the deep depth, the natural frequency is quite high and thus doesn't resonate with bouncing fans.
RE: Precast Raker Beams-Analysis
Added cost, complexity and stress to the job... But kept the rakers small.
Cheers,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...