structural beam calculation?

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have and existing garage, 24'x24' with straight gable roof. pitch is 6.  I want to remove the existing ceiling joist/ties that keep the rafters from spreading the walls in order to get a cathedral open area so I can use my car lift to it's full height.   In short I need to size a beam that will be set under the existing ridge board and create a structural ridge so the cross ties and collar ties can be removed. North East snow load, I come up with approx. a total load of around 12,000 lbs,  this reflects 1/2 the load on the outer bearing walls, half supported by the ridge. This would task the ridge beam with supporting about 500 lbs per linear foot.  Beam will be supported at both ends, clear spanning 24 Ft.   local lumber yard sent out for calculations, came back with (3) 1 3/4 x 20 " deep LVL microlams.  That is one huge beam for a small garage, and will cost over 750.   anybody want to size a steel beam , figure 40-50lbs load per sq. ft on the roof for dead and live load, and again, 24X24 6 pitch asphalt shingles. Rafters are 2x8   24" O.C."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:Time to have a professional engineer do some calculations for you.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:Scissor truss. Use unpunched 16 or 14 gauge metal studs where you plan to cut the chords and ceiling but in a scissor truss. You dont have to use unpunched (electrical punches). Criss cross the metal and tie in to the opposing wood outer shell/roof (term?).  Look up scissor truss.BTW, dont cut out the cieling until your completelty tied in. LOL
Reply:What you are proposing is really non-trivial, from an engineering perspective.  Yeah, I have a professional engineering license.The lower part of the truss is what keeps the weight of the roof from pushing out the side walls.I think that it might make more sense to jack up the entire roof, trusses and all, and then add a couple of feet onto the side walls of the garage.  That way you don't alter the structural integrity of the truss.  You get more storage space also, although you might need a rolling ladder to really make good use of it.Another approach would be to buy replacement roof trusses, cathedral style, and install all the new trusses before cutting the old ones.  This would give you more headroom in the center of the garage, but not at the side.What really makes more sense is to do your lifting outside, and leave the roof alone.  Buy some equipment moving gear, roll the equipment out of the garage, do what you need to do, and roll it back into the garage.  Of course, if your driveway has a severe slope, this might not be a good plan. You have seen the tire dollies that they sell, you put one under each tire, and then you can move the car in any direction that you want.Scrap this plan and rethink.RichardLast edited by raferguson; 07-30-2013 at 01:01 AM.Reason: Add note about cathedral trussesSculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge
Reply:On my shop, I converted a 26' x 32' milking barn into my steel/mechanic shop.The ceiling was 6 feet.  I raised the cross-tie up 2 feet and made each truss into an "A" truss.I did it one truss at a time so the building could stay together.What made this work was the 2" x 12" rough cut rafters.  They had the strength to carry the weight in this different configuration.Good luck on your conversion - heed the warnings above and hire the calculations done.If no calculations will be done - I vote for raising the entire roof structure as suggested above.  It's done around here often.Also common here is to raise the whole building and add rows of cinder block under it.Dave J.Last edited by MinnesotaDave; 07-30-2013 at 01:10 AM.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:There are beam calculators on the internetI am just a little perfuzed about your design.  You wanna pull the collar ties, but you are aware that they keep the building from falling down  under roof loading so you wanna do something to reinforce the walls holding them together without collar ties. I am not a fan of the sissors truss.  They take a fair bit of engineering to get right unless you are planning on overbuilding everything by a factor of 3 or 4. What you might  do is consider that you don't need to remove all the collar ties, but rather just those where you plan to place and use the hoist.Then you can construct reinforced rafters and build a sissors truss system to occupy that area. Maybe you'll need to remove  9 collar ties or  maybe a lot less.  If you were able to make the sissors truss from steel 2x4x5/16" wall thickness box beams with reinforcing at the joints you might really have something.   It'd be expensive to replace all the collar ties with steel, but it'd be quite strong. If this were me  I think I'd contemplate building a lower profile hoist before I modified the building.Last edited by Raul; 07-30-2013 at 08:46 PM.Hey~!! It's a hobby. It's not supposed to make sense~!!
Reply:Originally Posted by RaulThere are beam calculators on the internetI am just a little perfuzed about your design.  You wanna pull the collar ties, but you are aware that they keep the building from falling down  under roof loading so you wanna do something to reinforce the walls holding them together without collar ties.
Reply:If your unsure about what your doing and to avoid loss of life / property then, seek advice from a professional engineer. Where I live, theres only 2 or 3 truss builders. New construction requires trusses to be made only by a truss manufacturer.  A cut and stack (ridge beam with jack studs) can be built by any competint bulder.My advice is either buy the $750 micro lams; you could make your own by laminating 2x12's sandwiched with plywood or; go to a truss builder with your current design and see if they can modify for you. Truss builders here have PE's on staff and quotes are free.
Reply:ix-nay on trying to 'build your own' laminated beam from a bunch of 2x12's sandwiched with plywood.  The "design values" for the LVL will most likely be 'better' than you can get with #2 lumber.  (translation:  You'd have to go even bigger with your 'homemade' beam than the LVL version).Next, unless you just 'happen' into a big steel I-beam for cheap, I think you'll end up spending more for the steel and the shipping and the installation (just can't pick up a 24 ft long big-a$$ I-beam by hand, even with a couple of 'buddies' helping) than that ~$750 for the LVL's.And the 'next' next, tying in the roof rafters into a ridge beam and eliminating the ceiling joists or cross-ties/collar-ties changes the entire load structure on the roof rafters (roof rafters would probably have to be beefed up as well.  As well as you now have to have a way to structurally attach the roof rafters to the proposed structural ridge beam and also have structural support posts at the ends to support the structural ridge beam all the way to the foundation.It's all 'doable', but as mentioned by Rafe/Richard above it is not trivial to change your roof support structure around.Jacking the entire roof up off the existing walls and raising it higher is one approach, as well as jacking the entire building up higher and putting in new/additional wall pieces (have to tie everything in structurally, and thier may be overall and/or wall height limitations both structurally as well as zoning resitrictions you have to check into before even attempting something like this).Quick table look-up for 24'x24' ridge beam application does indeed call out for a 5.25 x 20" LVL ridge (50 psf LL and 15 psf DL).  The best laid schemes ... Gang oft agley ...
Reply:Originally Posted by rafergusonWhat you are proposing is really non-trivial, from an engineering perspective.  Yeah, I have a professional engineering license.The lower part of the truss is what keeps the weight of the roof from pushing out the side walls.I think that it might make more sense to jack up the entire roof, trusses and all, and then add a couple of feet onto the side walls of the garage.  That way you don't alter the structural integrity of the truss.  You get more storage space also, although you might need a rolling ladder to really make good use of it.Another approach would be to buy replacement roof trusses, cathedral style, and install all the new trusses before cutting the old ones.  This would give you more headroom in the center of the garage, but not at the side.What really makes more sense is to do your lifting outside, and leave the roof alone.  Buy some equipment moving gear, roll the equipment out of the garage, do what you need to do, and roll it back into the garage.  Of course, if your driveway has a severe slope, this might not be a good plan. You have seen the tire dollies that they sell, you put one under each tire, and then you can move the car in any direction that you want.Scrap this plan and rethink.Richard
Reply:Originally Posted by MinnesotaDaveI think what he is proposing is the way my parents cabin is built. (and my grandfather's machine shop)The ridge beam carries all the load to the two end walls, they carry the load to the ground.The rafters just span from wall top to ridge beam.Since his shop was not built this way, he is proposing "piggy backing" the original ridge beam with a new one.No collar ties needed with this approach.Dave J.
Reply:OK boys and girls, let's start again, first off I was a union Carpenter for 16 years, and happened to be one of the best welders in said union, and worked many permit jobs right next to Iron workers when they were short handed. Now that does't mean I was a premodonna like some and if their was no welding to be done I went home, no I learned my wood trade very well also , That might have a direct correlation to the fact that in 16 years in the trade I was neve laid off or without a job. OK I beat my chest enough on that  As for the weight of the beam don't worry about me, I am superman and can pick the heaviest of beams with 1 hand, maybe 1 finger , of course it will be pulling the lever on my machine(s).  Next item, this is the "Welding Web" remember , and what material do we use mainly on this forum, I know , Steel.  I have been to the local lumber yards and have submitted my little sketches and got my data back from the engineers that do wood, not all that happy with what they suggest and price is just under a grand all said and done.   Now if you want to see and interesting look on someones face ask those same guys about steel, " Uh. what? Steel? UH, UH?  get my point.  Now I am pretty resourcefull and if I had an approx. W beam size I could find 1 or 2 used beams, and if I have to , I better not say this , but what the hell, Weld 2 together, OH my god, I said it , weld beams together the univers will cease.   Don't give me the liabilty talk, or the safety talk, give me the size beam that will support a tributary area of 12 width, 24 ft. length at 40 lbs per Sq. Ft for a total beam load of 11,520 lets call it 12,000lbs or 500 lbs per linear Ft. I am not and engineer but I'm not a door know either, " Sam" help me with these guys will you.LOL.Last edited by kolot; 08-01-2013 at 05:19 PM."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:Originally Posted by rafergusonWhat you are proposing is really non-trivial, from an engineering perspective.  Yeah, I have a professional engineering license.The lower part of the truss is what keeps the weight of the roof from pushing out the side walls.I think that it might make more sense to jack up the entire roof, trusses and all, and then add a couple of feet onto the side walls of the garage.  That way you don't alter the structural integrity of the truss.  You get more storage space also, although you might need a rolling ladder to really make good use of it.Another approach would be to buy replacement roof trusses, cathedral style, and install all the new trusses before cutting the old ones.  This would give you more headroom in the center of the garage, but not at the side.What really makes more sense is to do your lifting outside, and leave the roof alone.  Buy some equipment moving gear, roll the equipment out of the garage, do what you need to do, and roll it back into the garage.  Of course, if your driveway has a severe slope, this might not be a good plan. You have seen the tire dollies that they sell, you put one under each tire, and then you can move the car in any direction that you want.Scrap this plan and rethink.Richard
Reply:Originally Posted by kolot....  Don't give me the liabilty talk, or the safety talk, give me the size beam that will support a tributary area of 12 width, 24 ft. length at 40 lbs per Sq. Ft for a total beam load of 11,520 lets call it 12,000lbs or 500 lbs per linear Ft. I am not and engineer but I'm not a door know either, " Sam" help me with these guys will you.LOL.
Reply:Which way does the roof ridge run, parallel to the garage door or perpendicular to it when viewed from above?Don't forget you have to hold up the ends of this new beam...  Generally builders don't want to put a load on the wall that has a large garage door.  I'm guessing your ridgeline is perpendicular to the garage door in plan view.  So now you have to resize the garage door header to hold the post that supports the new ridge beam...and that would be $$$  Hint.. A photo of the existing condition goes a long way to describing what you want to do accurately and quickly.Last edited by zipzit; 08-02-2013 at 10:33 AM.
Reply:As a licensed professional engineer I will tell you I don't think you will find a building inspector that will approve what you want to do. It would work on a small shed type structure but not a 24x24 garage. First for your situation collar ties are not required. They serve little purpose. When you start to remove ceiling joists that's a different story. You would need a beam that provided zero deflection under heavy snow loads or the walls will start to bow out. I am going to guess that that you have a two car garage door on the front. You would need a bigger beam over the garage door to support the ridge beam. On that side you have little lateral stability. Have you ever seen older garages where they are twisted or not square? Your design would work under ideal conditions but under a heavy wind load it could very well blow over.Yes they build a lot of steel beam buildings this way but that have a lot of moment resistance designed in at the connection from the top of the side wall to the beginning of the rafter. In your wood structure that would be almost none (left to only a few 16 Penney nails). Attached ImagesLast edited by Fab54; 08-02-2013 at 10:50 AM.Millermatic 211Lincoln Precision TIG 225Century 250 MIGLincoln 225 AC Box (sold)I support my local welding store (Amazon, McMasterCarr, Cyberweld, EBay).
Reply:Fab 54 thanks for the input. I did found a standard Steel beam span chart for residential construction on the Web, put out by Pittsburg I believe. I did not find ridge charts but did find one for a 15lb DL and 40lb LL for a total of 50lb per Sq. Ft , On a tributary area of 12 feet I can span 24FT with a W12x22. over the weekend I located and purchased (2) W14x38 beams for $400. You are correct on your sketch w/ dbl door and your point on the racking of the gable end is a good one, But in my experience the garages I have seen racked were old, sheathed with boarding. mine has exterior 1/2 plywood. By adding 3/4 plywood skin to the interior it should make the gable much more rigid. if needed the entire gable could be skinned in the upper portion with say 1/2" to save some green. Understood the existing header will not cut it with a point load, @center of about 6,000lbs. As I said, I ended up with 2 beams, might set the 2nd. beam on steel column bolted to my concrete floor up above the existing header to carry the end of the ridge beam. As far as the connections at the ridge, I think I have a plan to stiffen them up quite a bit. By your signature I see you are in CT. garage has survived the last 3 NE winters and you know what that means , we lost quite a few structures around here. existing ties are 2x6 toe nailed into the plates and a couple into the rafter ends. I removed 1 already, wasn't impressed on how well they were fastened. I did not build the garage. Aslo they are 4 FT O.C.  If I get this going I will post some pictures."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:What about the rafter - ridge connection.  When the ceiling joists/collar ties were in place and the lower ends of the rafters were restrained from moving outwards, the connection of the rafter at the ridge is effectively in compression.  If you remove this restraint now the connection of the rafter at the ridge is now in tension.  If this garage is not recent construction which I suspect it is since trusses were not used, you are probably depending on three nails  for the end of each rafter, two of which are toe nailed, into the side of the ridge board to resist pulling out.I agree with those who recommend an engineer look at this, which would probably be required to satisfy the insurance company and the building inspector anyway, since you are building outside of standard building practices.My preference would be to jack the whole structure and put a row or two of concrete block under it.  I have done this with my own shop to gain some more headroom.  This would also eliminate the expensive laminated wood or I beam.Last edited by norite; 08-05-2013 at 05:31 AM."The reason we are here is that we are not all there"SA 200Idealarc TM 300 300MM 200MM 25130a SpoolgunPrecision Tig 375Invertec V350 ProSC-32 CS 12 Wire FeederOxweld/Purox O/AArcAirHypertherm Powermax 85LN25
Reply:.In the late 70's I remodeled and rebuilt all the girder trusses for a train station that had been long closed and laid to waste, 46 ft. Spans. It has since been taken over buy a restaurant. I visited it last week, spoke with the owner and he agreed to let me into the jupper floor to take a look at those trusses I reconstructed. They are 16 ft on center. That gave me some ideas. And this 200 yr old building hasn't settled or moved since the 70's. The only guidance I had on those trusses were what the original craftsmen built and my gut.  Thanks for the input, I'll go it alone from here. ."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400