Causes and treatment methods for cracks in the bottom plate and bottom ring plate of storage tanks
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The problem arose on-site with a friend; the tank is used for storing wastewater. It has a diameter of 16 meters and a height of 24 meters. Cracking occurred right after the tank was manufactured, during the application of shrinkage-free cement grouting to the foundation. The foundation was not constructed in a proper manner at the time; it was a reinforced concrete structure without any asphalt sand layer applied. After the tank was completed, the base of the cone shape was filled with high-strength, non-shrinking grout; the cone’s base was thus filled. Upon completion of the filling process, a thudding sound was heard, and it was later found that the bottom plate together with the lowest ring of wall panels had cracked. My analysis shows that shrinkage-free grouting materials will expand, causing the bottom of the tank to rise and leading to stress concentration. Since only the base of the cone was filled, stress concentrated in the form of bending moment at the bottom plate of the tank wall section, resulting in cracking. Since I have never worked on large storage tanks and have not encountered similar problems, I am seeking everyone’s help to analyze the reasons and discuss possible solutions.
Our storage tank has a fixed roof and a capacity of 2,000 cubic meters; it was constructed according to the dimensions specified in the standard catalog. The foundation consists of a ring beam; Gobi soil is filled in the middle, soaked thoroughly, compacted using a vibrator along with a small roller, and then 5CM–8CM of asphalt sand is laid on top
To eliminate stress, when welding the tank floor, welding is carried out starting from the center and radiating outward. The welders are all from Jining, Shandong, and are quite experienced
I haven’t heard of cracks like this occurring.
This post was last edited by wanlirn on 2021-4-6 at 16:17. Our company has produced hundreds of these small jars; it’s the first time I’ve seen jars with this kind of bottom. I really have no idea what happened
It has a conical bottom; when making tar sand, no one can guarantee that its shape will be the same as that of the bottom. That’s why grouting is used – it’s definitely something done by amateurs, based on guesswork
It is very important that the basic traffic safety checks are passed. Excluding factors related to inadequate foundations, the fact that such high stresses occur in the bottom welding area is still surprising. A fairly typical defect; it’s been collected
The key is that this isn’t weld cracking. But on the steel plate.
If the access opening in the second diagram is a panel that was cut after the bottom plate of the wall panel had been welded, stress concentration resulting from that cutting might be the cause (there is no reinforcement ring before cutting in the diagram), and grouting could be a factor that contributed to the disruption of balance. Perhaps the base material has defects, or there is damage on the outside of the bottom plate; or its strength has decreased as a result of heat treatment (flame cutting), and the friction between the two sides or uneven expansion (settlement) has torn apart the bottom plate, along with the wall panels.
I’ve been looking at the design drawings for several large tanks recently, and I’m quite confused about the foundation aspect; collection studies*.
Speaking from a practical perspective, it can be said that there are definitely issues with the foundation. On the other hand, there may also be problems with the alignment and welding of the conical bottom plates (as it’s unclear whether the arrangement of the plates at the bottom of the tank is in a fan shape or a linear pattern, and the welding sequence is also uncertain). With a diameter of 16 meters, this tank is not small at all; its foundation and tank structure should be designed and constructed in accordance with relevant standards. Analysis of the cracking mechanism: The cracking area already had high stress due to improper alignment and welding. If sand were poured into the opening, cracking would not occur; however, when grouting material is poured, the expansion of this grouting material creates additional external frictional forces in that area. The combined effect of stress and friction exceeds the tensile strength of the base plate, leading to cracking. The cracking of the base plate in turn causes cracking in the lower wall panels. But then again, even if cracking does not occur after pouring the grouting material, cracking can still happen once materials are loaded in. Suggestion: The foundation should be designed and constructed in accordance with the specifications, and the tank as well should be built per those standards; if only simple measures are taken, the tank will not be suitable for use.