Cutting Out the Bottom Flange of a Beam 2

[cap4000]

I have a 25 foot long M14 x 17.2 built in 1965 which interferes with a door and headroom clearance. The owner would like to cut a 4 foot section out for a new door installation. The 3/4 inch thick top cover plated beam is nominally 14 inches deep and with a 7 inch cut from the bottom it would only have a T top section of 7 inches left. Even if I add 2 new tube steel supports and stiffen the remaining thin web with 2 small channels at the the cut portion in the center of the span Ram Advanse calculates large axial forces thruout the entire beam / truss like section. AISC indicates the max bending stress of only 15ksi as this beam is very thin with a high h/t of 65. The uniform load on the beam is 1.5 kip foot from 40 feet of brick work above. Has anyone ever done something, this scary before?? Appreciate any feedback.

 

[jike]

Why do you have high axial force? Is it a collector or drag strut?

I would be very concerned about deflection since it supports brick. A 7" beam does not sound sufficient to span 25 feet with a deflection limit of L/600 nor 5/16". Is it possible to install a new beam above and hang and brace the lower remaining beam from above?

 

[IFRs]

Best to put uprights on either side of the door, or make the door frame structural.

 

[cap4000]

Great Responses. The axial force is simply from the bending moment internal forces and the fact of a cut beam and nothing else per Ram Advanse. If I do this, I would absoluetly put tube columns next to the door frame. The structural door frame concept is also an excellent idea.

 

[IFRs]

My guess is the axial forces are due to the vertical loading being transferred to the top and bottom chords of the truss. This is what a truss is supposed to do. If you consider the truss split at the door, now it is two separate trusses, each to be analyzed separately. However, the assumptions used for the analysis shoule be closely approximated by real life.

 

[cap4000]

IFRs

Ram Advanse with the support restraints marked as all "PINNED" creates this axial force. I removed all the horizontal restraints except for one support and got exactly what I was looking for. Thanks Again.

 

[archeng59]

I like IFRs' suggestion. If you can add a column on each side of the door and shorten the spans, that will help the beams. The next thing would be to determine how to support the column loads at the foundation.

 

[Redfish205]

cap4000
How long have you used Ram Advance and how do you like it? I have been looking at it and hadn't talked to anyone who had used it. Please give +'s and -'s if you dont mind.

Thanks