Yes.

Unfortunately, without knowing anything about your design, it's difficult to advise you.

Do you understand the difference between the two types of weld?

Near as I can tell, in this case the material of construction doesn't affect the joining process. So, just use the same weld you would use with your steel design.

Good Luck.

A drawing or sketch would help. What are the cross-sections of each member of the structure, and the dimensions of the welds? In what direction is it loaded?

The beam is 1 set of 70mm depth x 25 mm, supports 2 sets of 25mm x 75 mm. Weld size, say 10mm butt.

The test assembly to pull the hook up to 15 tons (150KN)

thank you

rgs

Off the top of my head, I think this structure is too weak; but I haven't analyzed it.

Off the top of my head, I think this structure is too weak; but I haven't analyzed it.

I agree. Why not steel. If its a proven design and weight is not a factor?

Ron

I agree with Tornado. Just guestimating, that looks close to minimal structure for steel. Redesigning it for aluminum may result in little to no weight savings, just more expensive.

The total volume of the material is 0.00375 m3, this will translate into 10.5 kg for aluminium and 29.25 kg for mild steel. Assuming densities of 2800 kg/m3 and 7800/m3, respectively. If the test to be conducted on lifting hook fixed on soffit, lgihter material is preferable as only one man is needed to hold up the reaction frame during setting up.

Yes, the cost of the Aluminium is about 30% more but for such a small usage this is cheaper than the needs of extra manpower to hold up the mild steel frame.

good day mate

The total volume of the material is 0.00375 m3, this will translate into 10.5 kg for aluminium and 29.25 kg for mild steel.

So, you're going to switch materials without changing the structure in any way?

The specified structure is designed using 7075 yield strength of 500N/mm2 and E modulus of 72N/mm2 (for deflection check). The mild steel may not achieve the require capacity since it's yield strength is lower.

Hope this answer your question

tks Mate

Deflection will be your biggest problem if using aluminum.

Deflection will only be a problem until the welds fail.

The delfection is about 0.01mm and the allowable is 2mm. Can you clarify your assumption, please.

Good day mate

That looks like Enerpac gear and the cylinder is the 20 US short ton x 2" thru rod unit.

It's a lump in itself.

What you are not explaining here is 'the span required at the base'.

This has a great impact on the beam strength of the bridge between the columns.

As in; why not just bring the columns together to just clear the dimension of the deflection attachment?

Anyhow;

Welding 7### series Al₃ results in major loss of properties, compared to some 5### , 6### and 2### series alloys.

In some series properties are recoverable through heat treatment - 7### is not generally on that list, unless special composition fillers and techniques are used.

All the above means;

You have a structural design to solve first - starting with why the 'span' has to be whatever it is thought to be.

THEN you figure out what structure will best resolve the forces.

Then you choose the best material for the application.

And in making that choice, bear in mind elasticity in aluminium may just mean you exceed the range of the cylinder. Do not forget the other total deflections, including take up and pre-loads in measuring apparatus.

I wouldn't want to be near that rig in aluminum at 30000 lbs compression. Just a feeling from building aluminum fishing boat structures.

GA for very comprehensive reply!

Will Brazing technique be suitable to weld the 7075?

tks mate

No - you need to look at what "T6" means

Sir,

Thanks for your superb and enriching technical explanation!

by the way, ALL heat treatable aluminum alloys continue to age or form additional precipitates for their entire lifespan, just like how concrete will continue to harden basically forever. All of the alloys will eventually be overaged, but again, it may be decades or more before this occurs, unless the part is in an elevated temperature which will hasten the process. This is why preheating the material before welding is such a very bad idea.

Appreciate your sharing on this topic. And also expertly explained the process in such a great length. Many layman will benefit from here..

I raised the issue because the welder responsed that he is able to join the 7075 pieces (beam and column/leg) using BRAZING method which I have some doubt. Since it is so troublesome to consider welding, perhaps the best solution is using bolts and nuts SS 316 to tied the two identical square u-frame (in one piece) together with spacers in between. Any comment on this?

By the way what is O condition ?

tks mate

O condition is the solution annealed state. You COULD POSSIBLY braze 7075 (more than likely it would technically be soldering, not brazing. the difference between the two is that magic 800F number). but the question is, what state would the base metal be in when you are done? You are clearly fixated on 7075 because of that whopping 73 ksi yield strength, but it won't be 73 ksi! If it survives the process at all without cracking (which I doubt.), it will be somewhere much closer to 15ksi. You are seeing stars in your eyes when you look at that strength, but you are failing to grasp that that strength is an illusion if you do anything other than machine it or bolt it together. ANY HEAT will change the properties and not for the better. Aluminum reacts to heat JUST THE OPPOSITE to steel. It doesn't get hard and strong, it gets soft and weak, and 7075 is MUCH more sensitive to it than other alloys. you are much better off using 4130 at 120 ksi yield and twice the rigidity of aluminum which allows you to make the plates half as thick (or half as tall) and much more rigid than 7075, the weight difference will be relatively negligible. maybe 25-30% heavier but also about 25-30% more rigid too.

Frustrating isn't it - you must have covered that 5 times by now + others.

I guess temper and elasticity/rigidity are difficult to grasp

I'm still a bit puzzled why the OP would want to duplicate the 'welded steel/beam' design when it could be two water-cut arch like plates with a joining web, or tie rods (read handles), bolted in place. Seems to me it could be remarkably lighter if designed properly - irrespective of; in steel, or Al alloy, or even titanium.

Agreed, it is getting a bit frustrating having to repeat myself.

The initial thought was to use readily available extruded sections as this is cheaper. In view of the weld issue, your suggestion to produce structural section without welded joints is agreeable. Below is the suggested option.

Tks Mate

I find the views confusing.

The column function does not require much material - but should have a high resistance to "S" bending.

What you need to remember here is elasticity = spring

That top span (beam) is like a 15 ton trampoline, or bow string, if the sample suddenly fails

For a multitude of reasons, I would use a tripod design.

I'd be thinking; say 450 MPa steel tube welded to a 'cup/tube socket' to hold the cylinder, with a thin triangular strap base, (or three rods and foot pads), to resist spreading of the legs.

Wow, something different, thank you. The tunnel is 6.0m in diamater, hope the tripot can take care of the potential curvature of the tunnel lining.

tks mate.

The structure appears to be in bending of the horizontal beam, and compression of the two side columns and the welds. I don't think the columns or welds would fail, but I wonder about the bending of the beam. It isn't clear whether the 70mm dimension is the depth vs. the width of the beam. Real (properly dimensioned) drawings would help. Shortening the horizontal beam would also help.

Thank you for the article.

What would you recommend as replacement to mild steel. The aim is to reduce the weight of the reaction frame. The frame is to support central point load of 150 tons.

A separation of 30mm between the 400mm length parallel beams is required.

How about using bolt connection.

which series is easier to work with in term of welding. how about 2024

tks mate

150 tons? Are we now starting over with new calculations? How will the illustrated cylinder produce 150 tons?

The vertical members would more aptly be described as columns rather than beams.

You might not even need bolts, let alone welds.

In rough numbers, aluminum is about 2/3 the strength and 1/3 the weight of steel; this will enable an aluminum structure to be lighter.

The beam is supporting the hydralic Jack which will provide central tensile load of 150 tons when pulling the hook below.

The beam is supported by two legs or columns (stachion). In view of the current difficulty in welding for 7075, bolt connection presumbly the only viable option.

Alum is 2/3 of steel but the 7075 yield strength 500N/mm2 . This is greater than high yield steel. ?? I am confused. Is this exception?

This project was dubious even at 15 tons, and is completely insane at 150 tons. You should abandon it immediately.

Hi Tornado,

Well spotted, It should have been at 15 TONS (or 150kN) point load. My apology for the error. Base on BS8118:part 1:1991 code, the specified sizes yield the following:

1. Moment Capacity, Mu = 19.53 kNM > 15.75 KNM (applied)

2. Shear Capacity Vps = 362.5 kN > 112.5kN

3. Combined moment & Shear Mrs - not affected (low shear)

4. Lateral Torsional Buckling Shear, Mrs = 19.53 kNM > 15.75 KNM (applied)

5. Compression (resistance to overall buckling) Pr = 1562.5 kN > Pu = 16.88 kN

6. Deflection = 1.58mm < 2.0mm assume E =72E3 N/mm2

Weld connection

Direct shear + Moment shear = 1.05 N/mm2,

adopt 8mm fillet weld round, 1.4 N/mm2 assuming Pw = 250 N/mm2.

The only problem now is WELD connection. Perhaps, bolt connection is the only solution ??

Greatly appreciate the brain storming sessions with all great mind of engineering. Let me know other potential solution when available.

According to this picture, the horizontal member could be reduced to 1/3 of its present length, which would multiply its deflectional strength by 27. I would probably favor square tube, just guessing 3x0.25 SA36 steel, or 3x0.375 6061-T6 aluminum, which is weldable.

Am I correct to say that you have suggested 3nos. 375mm length (one beam + 2 legs or column) ? Would it be better to suggest rectangular tube, a greater depth is needed for beam to carry moment and deflection? Below is the current set up of u-frame and its lifing hook attachement and jack. The whole set up is 35kg and the u-frame itself is 20kg. To hold up the u-frame against the slab soffit during setting up is stressful. I am trying to find a lighter frame to ease my colleague task.

thank you for your feedback, mate

That is a different picture and proportions from the one in your post 22. We still don't have detailed dimensions, but at least now the 375mm lengths allow for some estimating. The idea of square tube allows for the crossbeam to be drilled for passing the cylinder rod through. The crossbeam could also still be reduced to about 200-250mm long.

Unless this assembly is fastened to the table, if the test specimen breaks, the whole assembly will jump up.

Yes, they are different pictures, the earlier set up is to test 20mm dia lifting hooks and the later is to test 32mm dia lifting hook. The beam is 400mm length supported by columns (75mm wide). This gives a clear span of 250mm (400mm - 2x75mm).

What cross beam are you refering to ?

If test fail the whole set up will drop to the ground as the lifting hook is protroded from the slab soffit (underside of the RC structure), or upside down. The hook is designed to take much higher load than the max test load of 15tons.

Tks Mate

Have you asked for help from the engineer that designed the original test rigs?

There is only one possible element here that could be referred to as a crossbeam, namely the same beam you mentioned in paragraph 1.

If you want to ease the "Fatigue" of your tester, why don't you consider using a tool to lift this heavy beast and not waste our time with silly questions like using Aluminum where Steel is the best suited material for the task (It is only obvious to us regarding the number of responses to the contrary). I would recommend an electric chain hoist from Harbor Frieght or Grainger. Man should be not performing repetitive lifting, which leads to injuries.

Respectfully submitted.

You could make a 4130 Beam (weldable) at maybe near the same weight as the aluminum and your deflection will decrease by more than half. This is a wise suggestion.

Can you advise what is the density of 4130? I think it is around 7800 kg/m3), about 3 times of alumi (2800kg/m3).

Sure the density is 3 times, but the amount of material volume is radically decreased due to the strength of the material. Your cross sectional areas can go down.

The density of 4130 is essentially the same as any other steel, roughly .289 lbs/cubic inch. The strength however can be as high as 160kpsi if heat treated after welding depending on the thickness of the section (100-130kpsi is more typical though.) and the hardness can approach 50 HrC. (heat to 1575 F, water quench, then temper at 900F).. Do not attempt to weld on heat treated steel, it will most likely crack. Instead, weld it in the normalized condition and heat treat after welding. You can get away with it on A36 and similar mild steels because their hardenability is essentially nil.

Also the strength and rigidity of a beam is driven more by the height of the beam in the direction of loading, not the thickness so much. a tall skinny rectangle section is stronger in the axis of loading here than a shorter fatter one. the fatter one will be better for buckling and off axis loading however.

If you absolutely MUST save a LOT of weight and have the money to spend, then there is always Titanium. many of the alloys are weldable. but many of the same issues apply to titanium as they do for Aluminum. The resultant welds are not aged and the HAZ are overaged, leading to a loss of strength. Welding in the O condition and then PWHT to the T6 condition (or whatever, depending on the alloy chosen) after welding will result in the optimum strength. If the welds can be designed so that they are in compression then the loss of strength might not be as much of an issue. That will be entirely up to your design skills however.

Consider making it out of two half moon shaped plates with a flat on top for your hydraulic cylinder with bolted spacers separating them every couple of inches. this avoids welding completely AND an arch is the strongest shape possible, particularly if you could design a base plate that would tie the two ends of the arch together to keep them from spreading apart. Also an arch eliminates some of the extraneous structure and eliminates two points of singularity that will be stress concentrators.

Thank you for your suggestion. Perhaps, I just cut out two u-shape and ties them together using bolts with spacer in btw.

If I switch to 6061 T6/T651, welding should be of lesser problem ? of course, I need to increase the size of the structure.

tks mate

Thank you for sharing such a fine know-how, much appreciated.

Hopefully, the reduction in tensile strength is not too much. Any idea what is the typical reduction ? I suppose the reduction in strength will not affect the reaction frame which is in compression at all time.

tks mate

The reduction will depend on the weld process control. Excessive heating will be deleterious. Any case if you have based loads on T6/T651 mechanical properties it will not be a safe structure After all a chain cannot be stronger than its weakest link!

Generally for 6061 the strength of the weld itself will be about half of the base material, the strength of the HAZ will be a gradient between half to a third less than the base material. Remember too that Aluminum's heat and electrical conduction is 5 times that of steel and you have to use AC instead of DC for GTAW/GMAW welding on Aluminum, so the welding equipment used must be of higher power and capable of AC instead of DC. DO NOT USE PRE_HEAT to attempt to overcome the limitations of your equipment. the Aging temp for Aluminum is only about 400 degrees F, preheating the weldment will overage the base material and you will lose significant strength from the entire structure. Use Zirconiated Tungsten instead of Thoriated Tungsten TIG electrodes with a blunt tip instead of a sharp tip as is used for Steel. And the size of the electrode has to be much larger since the amount of current required is much higher. Start with a 1/8" electrode and move upwards as needed. too much heat will just make your HAZ and weld larger, leading to a even larger weak zone. You should really read the link to the PDF file I linked to earlier. There is a lot of good data there.

Your welds in the squared U shape frame design would not only be in compression, but in shear as well. Shear will be the thing that kills them, not compression.

Thanks for the excellent tutorial!

Well thought out weld fixture to over come weld distortions is also essential.

Very true, since Aluminum expands by about four times that of steel. weld distortion in Aluminum and induced stresses can be a serious problem.

"Perhaps, I just cut out two u-shape and ties them together using bolts with spacer in btw."

Can you share your thought on the above. I heard that it is no good to using steel bolt on aluminium alloy, is this true?

Yes! You are correct.

An assembly of steel with aluminum will result in galvanic corrosion.

Galvanic corrosion is due to an electrical contact with a more noble metal or a non-metallic conductor in a conductive environment. The galvanic corrosion is very dependent of the cathode reaction and which metals are in contact which each other.
The most common examples of galvanic corrosion of aluminium alloys are when they are joined to steel or copper and exposed to a wet saline environment.

Contact between copper, bronze, brass and different kinds of steel alloys (passive and active) and aluminum can cause severe corrosion

The problem can be overcome by insulating contact surface between the two metals with non conducting washer.

Perhaps, ones can use Alumn Pin or bolt, have you come across these product?

tks mate.

It depends on you design load factors. Of course there are aluminum alloy fasteners available.

I will go with steel bolts with nonconducting washers like one turned from fiber laminated phenolic rod.

Unless this is going to be used in the rain or underwater, I doubt it will be a serious problem, but I would use 316 SS fasteners just to be sure. We used to use bolted together 6061-T651 assemblies using 316 SS bolts all the time on Subsea ROV's and junction plates. Some of those things spent their entire lives subsea.

I too agree!

Galvanic corrosion is a problem with aluminum and stainless steel. (The steel will be fine, but the aluminum will suffer.)

It's recommended to use zinc plated, or galvanized fasteners.

http://www.ssina.com/corrosion/galvanic.html

The two beams are link together with a plate (10mm thk weld round) on top at both ends of the beams. Similarly, the columns are linked at the bottoms.

Beam is 75mm depth by 25mm wide. As the column wide is 75mm wide, the clear span is (400-150)mm

tks mate.

Neither of the welding process is advisable for 7075 Aluminum Zinc alloy. These alloys cannot be fusion-welded without experiencing a large amount of cracking in the weld. The cracking can be macroscopic or microscopic. These insidious, cracks are often not detected and f a i l s as soon as it is stressed.

Unfortunately, this alloy appears to be unweldable.

http://archive.metalformingmagazine.com/2000/06/Alum.pdf

Here's a June, 2007 article from AWS about experimental welding procedures on 7075 with a Ytterbium-doped fiber laser.

http://www.aws.org/wj/supplement/wj0607-179.pdf

No doubt there is more research available online. There's always hope that these difficulties will be overcome, but maybe not yet...

We still have not been told which direction the imposed force is, even though the question has been asked.

Is the cylinder pushing downward, thereby putting the frame columns in tension; or is the cylinder pulling upward, thereby putting the frame columns in compression?

The absence of an answer (and properly dimensioned drawing), plus the presence of irrelevant considerations such as unweldable alloys, gives the impression that the OP knows nothing whatsoever about even simple structures.

One hopes this unfavorable impression is soon corrected.

Hi Tornado,

The frame is in compression when the Jack provides tensile force through pulling. Just imagine that you are pulling something from the ground while your body is acting as an reaction frame with your two legs pressing on the ground.

tks mate