50 FOOT BEAM SPAN QUESTIONS 1

[DEMACAULAY]

I am looking at a project and have some questions that I am hoping someone might be able to answer for me. The building is 50' by 130' with a 11' ceiling height between the beams.
There are 7"x26"X50' glulam beams every 13'. The exterior walls are cinder block with a cinder block column which the beams sit on. There are 2x10 rafters between the beams making a flat roof. I need more interior height. I dont want to raise the walls. What I want to do is remove the rafters, install double trusses on the sides of the beam and then finish the roof as if it was a pole building. The Truss company is telling me that they can build trusses that sit on top of the beam or bolt to the sides of the beams. I am curious as to peoples opinions on which way is better and why. the snow load is 25lbs and wind is 85.

 

[msquared48]

For a project this size, with the stiffness interactions you describe, you really need to hire a structural engineer.

When was the building constructed? The loads have changed some, but not that much, and the beam size apparently is an older one, maybe only 2000 psi. depending on the date of erection.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[hokie66]

Maybe what you want to do is clear to you, but it is not to me. Any chance of a sketch?

 

[msquared48]

If you do not remove the glulams, how are you going to be able to increase the ceiling height as the underside of the beams is a little less than 9 feet.

Are you removing the roofing to include the 2X10's and installing new 4:12 pitch trusses to either side of the glulams to get a sloped roof?

As Hokie suggested, a sketch and/or further explanation would help here immensely.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[woodman88]

Are you planning to place the trusses parallel to the beams but supported by the beam? If so, than the beams will be laterally unsupported along the top (compression) face and will fail. Have the trusses designed to span bearing to bearing and place them above or to the side of the beams so that there is no contact with the beams. Make sure you have the bearing connection and capacity checked by an engineer.

Garth Dreger PE
AZ Phoenix area

 

[DEMACAULAY]

Ok I will try and get a sketch to you but to answer some questions. I will only gain interior height. Between the beams/trusses. This is for an auto shop and there are garage doors on the long side of the building and allowing hoists to be placed between the beams and the cars will be able to go above the top of the beams. The trusses will be a 5-12 pitch. I have three options for trusses. Either way will be engineered. Just trying to look at all options before making up my mi d as to which way to go
option 1
trusses supported only at the ends and carting all the load. This requires a triple truss
option 2
trusses sit on top of trusses and transfer weightto gbe beam. This requires a double truss
option3
trusses are next to beam and beam is attached to bottom cord of truss at each diagonal. This two would be a double truss
from what I have found out all three options are possible. I am ttying to figure out which one makes the most sense
thanks for the input

 

[hokie66]

You need to get a local structural engineer involved. This is not just a matter of designing trusses. The entire building design, especially lateral load capacity, will need to be evaluated by a structural engineer. If the walls are not built strong enough, you may have to start over.

 

[efsinc]

A. am i right in the following assumptions?
1. the top of 2x10 rafter is flush with top of glulam beam?
2. the 2x10 rafter is perpendicular to glulam beam?
B. how much height are you trying to gain?
C. is the height gain desired along the entire length of the glulam or just a portion?

 

[DEMACAULAY]

Sorry for lack of drawings to answer your questions the rafters are at right angle to the beam and the tops are even. I don't need more clearance for the whole fifty feet but want about three additional feet of head room for most of the span of the beam which a 4/12 or 5/12 pitch will give me. I do agree and have already made arrangements for a structual engineer to help me on this.

 

[RVSWA]

Stranger than fiction I tell you... This project was 8 blocks from my office, he called me upon your recommendations to hire an engineer. As a follow-up, Hokie66 was on the right track. The walls and columns are un-reinforced CMU, seismic accelerations being Ss=1.25 and S1=0.41, I recommended he didn't buy the building. Each corner has diagonal cracking radiating through the grout lines from floor to ceiling.

 

[hokie66]

The world is getting smaller every day. Good result, RVSWA. Glad you were able to lead this fellow in the right direction. Hope he took your advice.

 

[dik]

Off the top, you're beam depth is too shallow for a 50' span.

 

[RVSWA]

It was built in 1960.

 

[msquared48]

Seen too many of those still in use. Scary. As far as I am concerned, at the least in high seismic areas, it should be a public safety mandate that they either be brought to a relatively safe level of structural stability, or torn down.

Yea, like that's going to happen...

But, hey, we all need the work, don't we?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask