When people are talking "press forces and ratings" it is easy to quote numbers without really appreciating what they mean. And if the frame is distorting then it may be strong enough not to fail, but is certainly not STIFF enough to hold its shape!
A 1.5Tonne jack will lift one end of your family car easily and safely. This force to lift - say the front under the engine/axle - would be on maybe a 2inch piston. But not lifting 1.5 Tonnes, as the load is not the jack's safe (quoted) limit.
My Compact Suzuki is only 1.5 Tonnes when wet! - Roughly 1 Tonne front, 1/2 tonne rear axle.
A Mitsubishi Truck may be able to pull a 3.5 Tonne Horse box - including the horse. It will only weigh maybe 2.5Tonnes itself? - But is rated for braking to be able to stop the gross weight of 5 tonnes... - even though you may drive so you only use maybe 1 tonne of braking force - fully laden? (0.2g decelleration to stop the horse falling over?).
A truck for hauling a 30 Tonne trailer may be 10 Tonnes ?....
The trailer complete with all the goods on board may be up around the 30 tonne region... So a big hydraulic system from and old truck jack is what we are talking about to apply a 30 tonne lift... Just look at how much metal is used on the truck's axle members etc. to get a good idea of the forces required by seeing the metal used to manage these forces. As the 30 tonne trailer will have maybe 3 axles, each axle is managing 10 tonnes... Is the 30 tonne press built like a truck axle or stronger?
Cheap mild steel has a 20 tonne tensile strength, good stuff has a 40 tonne tensile, and "stronger steels" up to 100 tonne.... but that is the Ultimate Tensile strength derived in tons per square inch.
To make a 30 tonne jack, you need everything stressed so you have way less than the tensile strength of the material managing the forces. A 1 inch 80 tonne bolt will strip threads or snap at maybe 30 tonnes, as there isn't enough steel to withstand 80 tonnes: that is just the rating of the steel used to make the bolt. And threads have stress raisers that quadruple the stress in the material, so you can consider a 1/2 inch bolt in "80 tonne steel" to go "ping" at maybe 8 tonnes? - Depending of tensile/bending/shear loading...
The "20 Ton" press where I worked as a lad had a pressure gauge - indicating the hydraulic pressure applied on the 3 1/2" ram.... It had 2 main steel legs at least 6" diameter to take the tensile forces when in use, and retain the STIFFNESS required for any off centre loads. One day my rig slipped because it was not EXACTLY square and true to the alignment of the pressing job, and flew across the workshop and hit the steel cladding with a loud "Bang". - Nowadays we have guards in industry, but the Boss gave me a stern lesson in safety and care when doing any job after that.
Looking at the frames shown, I guess they will likely distort after little more than 1 tonne applied load? I'm OK, watching on the computer, but please be careful if trying to apply such huge loads as you are discussing. When the load is applied the frames distort and then everything is a big spring of stored energy awaiting some point where it goes out of alignment and slips, when it fires small metal bits like a catapult!
I suspect your 2 tonne jack is only applying 1/10th Tonne load to press in a bearing, or it would destroy the bearing and housing?
I have been in a small group where we used a car as a jack to press-in a small job, simply jack the car up (front-end with a screw jack), fit the bits beneath the frame and road (with bricks and wood packing) then lower car gently (easy with a screw jack) and it pushed the shaft into the next bit of the assembly. (may have been a bearing? - I can't remember!).
I removed and fitted crankshaft bearings on motorcycle crankcases using similar methods - in a stair-well between 2 walls at the apartment block where I lived. More than 2 tonnes load would have pushed the walls out!
So be careful with how you describe the strength of these flimsy frames...
Of course, Manufacturers have reputations, safety legislation etc. to consider when they make and rate their goods. We do not always follow those rules (do we even know the rules?) when we make stuff in the workshop, so just be careful.
K2