Home Made Load Frame 1

[Terratek]

Does anyone have experience building a load frame from scratch? After looking at Gilson and Humboldt prices ($3500+/-) for their basic load frames, I am wondering how hard it might be to make one.

I am a bit of a dunce with mechanical/electrical stuff. Where is a good place to get started to figure out how to build such a machine?

 

[oldestguy]

What are you testing? Concrete cylinders? soil samples for unconfined compression? Consolidation? It makes a difference.

 

[Terratek]

Soil

 

[oldestguy]

OK it's soil, presumably from split spoon or Shelby tubes? For unconfined compression you can use a Remac valve spring tester. Or you can get a used lever arm scale and make up a frame of 1/2' vertical threaded rods vertical and 1" or larger square tubing horizontal. Drill holes in the platform to allow the rods to go. For tests requiring vertical load, such as Qu or consolidation, place the sample or the device on the scale under the square tubing and if necessary a ball bearing to equalize loading pressure. Down under the affair sit an adjustable device, such as a light gauge screw jack or other adjustable device capable of taking vertical load. Measure your vertical strain with magnetic base dial gauges as used on a metal lathe. Springs between the lower square tubing and the platform base keeps the "H" from dropping when no load. With this general scheme you could use other forms of measuring loads. Make sure the loading capability is what you need. Old platform scales can be loaded a lot higher than the weights allow by just using heavier weights out on the hook. Old time testing labs all used this form of gear for a variety of tests.

I've even used this sort of thing for "consolidation" testing of Shelby tubes with peat maybe 12" high to estimate settlements in peat bogs or to estimate time for surcharging needed.

For this idea of doing it yourself for gear you probably need a well equipped shop, including a MIG welder. A metal lathe comes in handy also. Of course a drill press capable of 1" diameter holes in steel. Bench grinder, power hack saw, etc. are a few also very handy.

 

[Terratek]

OG,

The manual load frames are a little cheaper to purchase than the motorized versions. Regarding manual crank and Remac testers; how do you know what your strain rate is? I believe ASTM D2166 states it should be 0.02 inches per minute for soil. If applying a faster rate of strain, you will get a higher compression strength value. Obviously hand crankers and Remacs are used, and Remacs and even sanctioned by certain DOTs for field testing of split spoon samples. Nobody uses Remac testers in my area. I would be afraid of being accused of deviating from standard practice, thus rendering the Remac results useful information but more closer to a pocket pen than to a true UC test regarding the accepted reliablity of the information. Basically, I could supplement UC testing with a Remac, but not replace the load frame. What are your thoughts in this?

 

[oldestguy]

In all my many years of working in this field, no one has ever questioned methods, gear or the results of my testing or that of those under me. If you want to require a known rate of strain for the crude Qu test of squashing a sample that has undergone all sorts of prior disturbance and the variation of test results among several samples from the same formation and then roughly use that info for a rounded off bearing capacity, shear strength, etc. go ahead. Of course the cost of testing will go way up and the results will be no more useful than using the pocket penetrometer in many cases. Common sense in testing and the use of the data should prevail. Having a fancy lab and pretty looking presentation of data, along with a higher cost for the client than the lesser equipped lab using common sense may be ideal, but the results probably will be no different or even less useful and economical than the competitor. Your professional reputation level hinges more on how you analyze and present your recommendations than any laboratory testing details. This also brings up the way you present your report. I'd be willing to bet your clients only want a simple answer, such as "what is the bearing capacity" and that's it. I learned this lesson once when a steady client couldn't find that number in one of my long winded reports. You can bet that was darned embarrassing and I really changed.

 

[Terratek]

OG - I understand what you are saying and was not questioning the viability of how you do your work. I don't disagree that you can get a range of values from UC tests performed in accordance with ASTM D2166 (which really isn't that expensive to run once you have the machine). I also agree that it is not commonplace for a client to question your methods. You can just squeeze a sample of soil in your hand and know if there will be a bearing capacity of 2 to 4 ksf most of the time, so why even use a rimac or a pocket pen for that matter?

Have you ever been in a lawsuit where a lawyer called in to question any of your methods that were not performed in accordance with a locally accepted practice or an ASTM procedure. If so, what happened?

 

[oldestguy]

Terratek: As to lawsuits I have been an expert witness several times for disputes related to my field of engineering and for some of those times there have been experts also on the other side. The cases have been in court as well as handled by less formal means. Even then, with that expert help on the other side, never have I been questioned as to what methods I might have used regarding the dispute. I should add that of the many jobs I did only one involved me being sued and that was because the client (contractor) did not follow my report recommendations on a very important step. It cost me nothing other than time.

 

[Ron]

Well....Terratek and OG....you're both right!!

OG is correct that the test is not one of critical accuracy, so why worry about the method so much. Well, even though the accuracy of the test doesn't mean a great deal in respect to the overall geotechnical recommendation, there is a reason the procedural aspects of the standard must be followed......

Terratek is right that we have to be concerned about adherence to published/accepted standards. In particular, D2166 is a standard that is referenced in the IBC and in various state codes, thus making it a mandatory standard and must be followed as if included in its entirety within the code. To deviate from the standard can constitute non-compliance with the building code, thus making you violate our standard of care, which in turn, puts you in a liability position.

Construction litigators have gotten a lot more sophisticated over the years. When I first started, almost any lawyer would take a client's construction claim and deal with it as any other litigation. Not so anymore. Construction litigation is a legal specialty and has a lot of legislation and case law to back it up. Even a seasoned attorney who is not a construction specialist will typically shy away from taking on a construction case. As a veteran of over 70 depositions and over 15 trials, a few arbitrations and a bunch of mediations, I can assure you the expert's methods are questioned in every way possible!!

 

[Terratek]

Ron,

I was hoping you would chime in, since you inspired my post in the first place. You made a comment in a past post once about load frames being easy to make and how load cells are ever cheaper online. Do you have an electric powered load frame plan/schematic?

 

[Ron]

Terratek....
It has been a while since I built one, so don't have schematics available. The first one I built was hydraulic and manual. The second was strain controlled using a screw actuator (electric). The software control and the relays we needed for load reversal were a bit of a challenge (it was not for soils....it was for loading tree stands for testing). Same concept applies to soils. That was about 20 years ago. The software and controllers are much better now, so shouldn't be much of an issue. You can probably get by with less than $1500 if you do it yourself. Hopefully you can weld as that makes the frame construction much easier. I built the hydraulic one out of steel channel and it would easily do 10 tons.

 

[mikeofBelAir]

My first lab had EVERYTHING homemade. We had 6 or 7 Triax cells--all schematically the same, but slightly different in detail. For instance, all Triax cells had double linear bearings.
Every now and then we'd have a visitor to the lab who would find "his" piece of equipment and look lovingly at it. Seems as if everything was fabricated as part of the course requirements for Soils Engineering and the prof used all the equipment in his own (private) engineering firm. Some of that eventually came to the satellite office where I worked.
I tried to track down whatever happened to it all, but it seems to have disappeared in a series of office closings and consolidations. Too bad--it was great stuff.

 

[Ron]

mikeofBelAir....been there. In the late 70's, I managed a geotechnical lab for a large branch office of one of the major geotech firms in the country. Because of funds limitations, I ended up building much of my lab equipment. This included a sample extractor made from a hydraulic lift gate purchased for $100 from a junk yard, a back-pressure saturation board built from scratch and a variety of other triaxial cell modifications to older, existing triax cells (including polishing the rams, adding bearings, adding electronics for measurements, etc). All had to meet our internal QA criteria and traceability to what is now NIST. Fun stuff for a tinkerer such as me!

The experience was phenomenal!

 

[mikeofBelAir]

Ron,
Same here--it was a lot of what made the job exciting and fun.