Efficiently Shorten Your Boat Trailer for Winter Storage | 5" Aluminum I-Beams

[pjm]

Ill try to send some more pics shortly but at least we are on the same page now.
Thanx

 

[dacarls]

Ill try to send some more pics shortly but at least we are on the same page now.
Thanx

Yeah- the photo does not include the tongue.

 

[pjm]

Ok Idea is to cut at pencil line, unbolt the u-bolt at the end of the 3x3 tubing, and remove the whole front end of the trailer including winch and wheel jack for the winter. In summer reassemble by sandwiching the i-beams between two pieces of channel on either side of each
beam and bolted through the web of each beam on either side of the splice. Re bolt u bolt supporting 3x3 and trailer is back together and same length as original. Comments

 

[nvn]

pjm: To be able to check this, we need the exact height, width, flange thickness, and web thickness of your I-beam (h1, b1, tf1, tw1). And we need the exact height, width, flange thickness, and web thickness of your channel (h2, b2, tf2, tw2). The flange and web often have different thicknesses, so you would need to give us both. Also, can you give us the exact dimensions of your proposed bolt pattern?

 

[pjm]

Ok: Just walking out the door so I will get this info to you early next week

 

[pjm]

NVN: Measurements are as follows:
I-Beam h1-5.535" Channel h2-trimmed to 4.951" from 5"
b1-3.485" b2-trimmed to 1.642" from 2"
tw1-.20" tw2-.281"
tf1-.292 tf2- trimmed to .256" from .281"

h- total outside height
b- total outside width
tw-web thickness
tf- flange thickness

Total length of splice channels - 30"
Bolt size 1 1/2 x 1/2" Stainless with washers and nylock nuts
Cross section sketch attached.
Any comments appreciated

 

[nvn]

pjm: I would like to see you not reduce the moments of inertia of your I-beam in this modification. Therefore, for your current dimensions given in post 41, that particular channel would need to be 54.2 mm (2.134 inch) wide, not 41.7 mm (1.642 inch) wide. Can you accommodate this?

Secondly, your current bolt pattern does not look good. I envisioned at least two rows of bolts, not one. I will get back with you in several days regarding correct bolt pattern dimensions.

Third, stainless steel bolts are corrosion-resistant, but weak. Are you sure you must use stainless steel fasteners in this application? Check the other major structural connections in your existing trailer framework. Do the other major structural joints use stainless steel bolts? Or are they steel, SAE grade 8 bolts? Or ISO property class 8.8, or 10.9? Or what? What marks or designations are on the existing bolt heads? Steel grade 8 bolts and nuts have six marks on the head and nut.

 

[pjm]

NVN: If I understand you correctly, the moment of inertia would be in regard to the vertical stresses on the I-Beam?? Because this is a tandem axle trailer, the weight at the cut point is only about 150lbs and because the trailer is so well balanced there is very little vertical stress as compared to a single axle unit. The only reason that I wanted to trim the flanges off on the channel was for looks so I could leave them at 2.00" if necessary. Most fasteners on the trailer are stainless except for the U-bolts holding the axles to the frame. I can easily use grade 8 bolts here because this part of the trailer never gets in the salt water so corrosion/electrolosis should not be so much of an issue.
I would appreciate any help you can give me on bolting pattern and dimensions. I thought that the middle was the best place because I felt it was the neutral point in the beam. Any additional comments are greatly appreciated.

 

[dr dodge]

I have to compliment ya'll on this thread, it was great to see the engineering going on. the formulas and explanations made the whole process very understandable.

great job to all

dr

oh, and the OP ought to let us know this spring how well it performs on the hiway

 

[nvn]

I am concerned that grinding the channel might change the aluminum temper or heat treatment. I do not know what effect it would have on the channel properties. And, grinding might create lateral (not longitudinal) scratches, which might introduce additional fracture initiation sites. There is no need to grind off a channel. A typical steel I-beam splice is something like what is shown in the attached diagrams. Not at all to scale! The diagrams show a side view of an I-beam. Method 1 is a four-plate I-beam splice. Method 2 is an eight-plate I-beam splice. It uses only flat plates, not a channel.

Unfortunately, the calculations are nontrivial, and I do not have time to investigate. I only have time to say, bolt spacing is usually something like 4*D (for steel), where D = bolt nominal diameter. Bolt edge distance does not need to be less than 3*D (?). There is often one row of bolts along the centerline of each half of each flange, and two or more rows of bolts in the web plate.

However, the dilemma is that you can never get back, even close, to 100 % of the I-beam capacity, because the flanges are drilled. And aluminum is less forgiving than steel. It has a lower fatigue strength. The first bolt holes are highly stressed, and have high stress concentrations. This I-beam splice needs to be carefully calculated, to see if it would be OK. But unfortunately, I do not have time to investigate (nor comment further) for probably at least a couple of months.

 

[pjm]

NVN: Thanks for the help, I've learned more from you than anyone else. Appreciate it.
PJM

 

[turbo]

Because this is a tandem axle trailer, the weight at the cut point is only about 150lbs and because the trailer is so well balanced there is very little vertical stress as compared to a single axle unit.

You're talking about a static load, which bears very little resemblance to the changing forces that will be exerted on the trailer under load. You have a pretty big boat there, and as you hit bumps, potholes, etc the trailer will have to offset the tendency of the boat to travel in a straight line (momentum).

 

[pjm]

<< quoted text deleted by berkeman at nvn's request -- please see subsequent post for corrected data >>

NVN- Thanks this looks simple enough -I appreciate your taking the time to look into this for me. PJM

 

[nvn]

pjm: I envisioned something like the following, using eight aluminum 6061-T6 plates. See attached file.

D = bolt nominal diameter = 9.525 mm
a1 = a3 = 31 mm
a2 = a4 = 35 mm
s1 = 42 mm
s2 = 57 mm
a5 = 22 mm
s3 = 44.5 mm
a6 = 25 mm
s4 = 60 mm
Plate thickness, t1 = t2 = 6 mm, t3 = 5 mm.

0.3750-16 UNC, SAE grade 8 bolts, grade 8 nuts, and grade 8 flat washers; installation torque, T = 50 N*m (37 ft*lbf) above running torque of locking device, if unlubricated. If lubricated, let me know.

 

[pjm]

NVN: I thought I had replyed back this morning, but something must have happened. This is what I was looking for and I thank you very much. The only thing I might think about changing would be to replace the top plates with one triangular shaped plate covering both i-beams and the area between (about 2'x3' made out of 1/4" aluminum checker plate and bolted through both sides of flanges on both beams as you show. Thanks again for your time and patience. PJM

 

[dacarls]

Now you are getting somewhere. Trimming edge of girders to 4.91 inches from 5 inches, while adding 1/4 inch Al plate - A problem? not to me, the "amateur but practical engineer". Just put another small piece of Al plate for a spacer on top of the (removable) tongue when it is replaced and before the tower bolts are retightened. This keeps it from collapsing 1/4 inch down onto the tongue.

 

[nvn]

pjm: Checker plate is too weak. It cannot be used as a replacement for the I-beam splice top plate. I-beam splice components are primary structural components, whereas checker plate is not. Furthermore, the rough surface of checker plate would cause uneven seating of the I-beam splice washers; the washers need to be perfectly level on a flat, smooth surface, to prevent prying on the bolt head.

 

[pjm]

pjm: Checker plate is too weak. It cannot be used as a replacement for the I-beam splice top plate. I-beam splice components are primary structural components, whereas checker plate is not. Furthermore, the rough surface of checker plate would cause uneven seating of the I-beam splice washers; the washers need to be perfectly level on a flat, smooth surface, to prevent prying on the bolt head.

NVN: OK I get the picture. Incidently, what was the reason for reducing the bolt size in your last message. Thanks again
PJM

 

[nvn]

pjm: The smaller the bolt size, the better (if adequate), because you want to remove as little of the I-beam flange material as possible. Even 0.3125-18 UNC, grade 8 bolts, torqued to 28 N*m (unlubricated), might work, and might be better, because they would remove less flange material. Or, if you use 0.3750-16 UNC bolts, intuition tells me you could probably omit one column of the bolts shown in post 49, which would still be twelve bolts holding each I-beam, instead of eighteen. And t1 = t2 = t3 = 5 mm might work.