How many jacks does it take to raise a tank? Well, that depends on many factors – with the most important being the tank’s weight. It took 24 jacks to raise a two-million-gallon above ground storage tank in Northern Kentucky.
With a tank jacking, the tank is assembled from the top on down rather than from the bottom up. Installation of the wall’s top portion is completed once the foundation is in place. Sections of the shell are then welded into place from the top down until the project is complete.
When to jack a tank
There are several factors to consider when deciding on a tank erection method: owner requirements, access to the tank site and surrounding areas, time of construction, tank style, height, and diameter, and what other construction is ongoing at a nearby location. Even the type of foundation can impact the decision.
Safety generally plays a role in the decision. Tanks are, of course, erected according to safety regulations. However, some owners require tethering all tools and equipment above 6’. At best, this is difficult and time-consuming. Tanks built using the jacking method keep workers at a work level for most of the work activity, thus reducing exposure to fall and dropped tools.
A jacking system is most beneficial on tall tanks that are large in diameter. It can be a challenge attempting to maneuver a crane or manlift in tight quarters. Using a jacking system allows the limited access to the tank to remain unobstructed.
Engineers consider weight and other aspects when offering recommendations on how to space the jacks. For example, the Northern Kentucky tank is 80-feet tall and 70-feet in diameter. The wind girder, if applicable, and roof type should also be factored in.
The jacks can be spaced, at most, 11 feet apart on any given project. The jacks for the Northern Kentucky project were spaced closer. The jacks were spread out at 8 feet due to the outside scaffolding system used.
Jacking every storage tank isn’t worth it. At some point, if the tank isn’t very tall or wide in diameter, it doesn’t justify the upfront time of setting up the system and taking it down.
For larger tanks, using a jacking system means a more economical use of everyone’s time. Since it’s faster to construct and requires less scaffolding equipment, it’s cheaper.
Putting it together
Set up requires building elevators and putting the jacks in place. The elevators come equipped with rollers. Each section is hung on the load-bearing elevators, keeping them immobile as the crew works.
Crews weld clips on the rail and hang the girth welder on the tank’s exterior. Hand welding is done on the interior, while girths are welded on the exterior. A weld buggy goes on the outside.
For the Northern Kentucky project, crews put the top ring up and then the wind girder and the top angle. A wind girder’s function is to prevent the tank wall from buckling from a wind load. Top angles are stiffening rings that help stabilize the tank against strong winds. Due to their location at the top of the tank, the wind girder and the top angle are usually installed at the end of the project.
Once a ring is complete, the crews jack it up. The scaffolding remains until each ring is welded in place.
Nozzles are installed as the crew members work. It’s a lot easier to place the nozzles from a few feet above the ground rather than 70 or 80-feet in the air.
One of the last steps is setting the tub – or first – ring in place. The elevators are removed, the tub ring is placed on the ground, and then the scaffolding, boards, and cables come down. The jacking system remains in place the entire time. It doesn’t have to be taken down or put back up.
Using jacks to raise a tank has several advantages. Safety is a strong selling point.
Tank jacking projects use scaffolding. However, it’s never more than six feet above the ground. Six feet is the point where OSHA requires 100 percent tie-off for fall protection. Some owners use 4’ as the limit, exceeding OSHA requirements.
In the usual process, scaffolding would go up and around the circumference of the storage tank. Each ring of the tank would then be welded on from the bottom up. Scaffold systems used to erect tanks are heavy and hard to move from ring to ring. A jacking system eliminates this difficult task.
Crews suffer less back strain with the jacking system. That’s because they don’t lift boards every time they raise a ring.
With the traditional method, usually, you would hang the 3 o’clock welder. Crew members would be hanging on the top ring of the tank and riding the welder, progressively in 8’ increments as the tank goes up. Using the jacking system, crew members are still welding at an eight-foot level, but their feet are less than six feet off the ground.
Using the jack system can be quicker with tall tanks. The taller the tank, the more scaffolding is needed to complete construction. Crews not having to jump scaffolding is a time saver.
Even taking bathroom breaks or water breaks is much more convenient since workers are on the ground level instead of scaffolding. Crews that use jacks are less than six feet from the ground so getting down is less time-consuming.
The jacking system can be a win-win for storage tank owners. Since people are working closer to the ground, there is less risk of falls and grave injuries. Less safety equipment is also required, so all this adds up to savings on the overall cost. The jacking system eliminates the need for man lifts to complete the project.
Any construction project is at the mercy of Mother Nature. Using a jacking system can help offset weather issues.
With as tall as the Northern Kentucky tank is, crews would have typically fretted any potential storms. The jacking system allayed those fears.
Since the wind gird and top angle are installed early during a jacking, the tank stiffens immediately, making it more resistant to wind.
The wind girder and top angle are not in place until the end when the tank is constructed from the bottom up. Therefore, the structure isn’t as stable. To solve this, the tanks are tied down or braced overnight to keep them secure.