How deep to concrete in a H frame lifting gantry?

CharlieBear62

As a part of my rat rod build I plan to make myself a H frame lifting gantry and concrete the posts into the ground.

I can have a guy come and bore the 2 x 500mm diameter holes and I'm wondering going by the H frame layout how deep would be suitable to concrete in the posts. Before the frame posts go into the ground I'll add steel X supports on the bottoms and after the H frame is upright I'll weld on 2 support poles to each side and concrete them into the ground.

I've had a look on the tape and was thinking 1 meter but that's a deep hole and also a lot of concrete.

MitchellMc

Hi @CharlieBear62 ,

Given this is a lifting gantry that will potentially be supporting significant loads overhead, I'd be very cautious about relying on general rules of thumb for footing depth or post installation.

The required depth, footing size and overall structure will depend on a number of factors, including the weight you intend to lift, the span of the gantry, the post and beam sizes, soil conditions and how the loads will be applied. Because of the safety implications if the structure were to fail, it's not something I'd be comfortable providing specific advice on.

As a very general rule, posts for non-load-rated structures are often embedded around one-third of their above-ground height. For example, a 3.5m-high post might typically have around 1.1-1.2m below ground. However, that rule is commonly applied to structures such as fences, pergolas and shade sail posts, not lifting equipment, so it shouldn't be used as a design guide for a gantry crane.

For a project like this, I'd strongly recommend engaging a structural engineer or qualified fabricator familiar with lifting devices. They can calculate the required footing depth, concrete volume, reinforcement and member sizes to ensure the gantry is safe for the loads you intend to lift.

Given the consequences of a failure, professional design advice is money well spent.

Please let me know if you have any questions.

Mitchell