Let me tell you a story: a person buys flea medicine, and the sign says: selling high-quality flea medicine.
Question: How to use it?
Answer: Catch the flea, apply the medicine to its mouth, and it will die.
(Comment: This is good medicine! Included in health insurance! Subsidized! Promoted vigorously.)
I oppose prefabricated PC! But I do not oppose the technology of prefabricated PC. I oppose the application of prefabricatedPCtechnology in high-rise residential concrete shear wall structures. Why do I oppose it? The approach is wrong; it’s all nonsense!
The construction industry is sick; this is a consensus among everyone. Where is the illness? It is that the construction industry cannot be industrialized.
So the question arises, what is industrialized construction? Industrialized construction is an abbreviation; the full term should be: the modern industrial production organization method of the construction industry. So does doing prefabricated buildings count as industrialized construction? The automotive industry has always been prefabricated, but before Henry Ford, the automotive industry was just prefabricated and not modern industrialized production.
Got it? Industrialized construction is not equivalent to prefabricated buildings! Prefabricated buildings are also not equivalent to prefabricated PC!
Anyone who has received training in structural engineering and has practical experience in the construction industry should know: there is no structural system that is universal; each has its applicable range.
The development history of the Chinese construction industry clearly shows: from the 1980s to now, it has gone through: brick-concrete structures, concrete frame structures, concrete tube structures, high-rise reinforced concrete shear wall structures, and high-rise steel structures. Each of these has become the mainstream technology in urban construction at different times.
Why do these structural forms become the market mainstream in phases? Because urban buildings are getting taller. At different times, the mainstream building heights in the market will have different load characteristics, leading to corresponding optimal structural system solutions. This is determined by market demand and engineering technology levels.
What is the current period? The current mainstream height in the urban residential market is within 180m, and the corresponding mainstream structure is the concrete high-rise shear wall structure.
Thus, it is clear why prefabricated PC factories rush to develop high-rise concrete shear wall prefabrication. The residential real estate market is huge!
So, is the concrete high-rise shear wall system suitable for prefabrication? For building heights between 150m and 180m, under horizontal forces (wind load, earthquake) and vertical forces, the requirements for the structural component integrity and connectivity of the shear wall system, including the reliability of nodes, are of utmost importance (nodes must be rigidly connected, and the components must be continuous in all directions). Concrete structures are a dual-material system; concrete is under compression, while steel bars are under tension. The better the continuity of the steel bars and the concrete, the safer and more reliable the structure will be. Due to the limitations of existing material and construction technology, we cannot make all the steel bars in a building seamlessly continuous, nor can we pour the entire building’s concrete in one go (if someone can do this, they would probably become an academician). Therefore, the industry has developed various reliable steel bar connection technologies and concrete segmented pouring techniques through long-term engineering practice, but the common feature of these technologies is: the fewer the steel bar joints, the easier the connection method to construct, the more reliable the node’s stress; the fewer the concrete construction joints, the more reliable the structure.
Now let’s look at high-rise shear wall prefabricated PC and compare the nodes: has the difficulty and defect rate of steel bar connections increased or decreased? How many times have the vertical and horizontal joints that require secondary pouring and connection increased?
To disassemble a well-designed and well-stressed structural system into fragments.
Some experts keep emphasizing the strength and reliability of prefabricated connections: our steel bar joints are amazing, our secondary grouting materials are advanced. Let me ask a few questions: do you understand stress concentration? Do you understand equal-strength connections? Do you understand constructability? Do you understand failure probability?
If you break your leg and have it connected with titanium alloy, how would you feel?
Don’t blame migrant workers when there are quality issues with the house!
Therefore, the most suitable method for high-rise residential concrete shear wall structures is to use continuous pouring. Whether in the past, present, or future, using segmented prefabrication and assembly technology on high-rise concrete shear wall structures is a wrong direction.
Currently, the most mature, safest, and cost-effective structural system; representing the future in-depth research direction of this system: is the full pouring technology commonly used by mainstream real estate developers represented by Vanke, which employs aluminum formwork and continuous lifting scaffolding.
The current fact is: the current prefabricated PC practitioners have evolved from developing fully prefabricated components to developing double-skin walls to researching high-precision non-removable formwork systems (some are being developed in Shenyang), essentially continuously increasing the pouring rate, returning to full pouring. Within the category of high-rise residential concrete shear wall structures, these technologies have no vitality.
Conclusion: The application of prefabricated PC in high-rise residential concrete shear wall structures is a dead end. The market is not foolish; homebuyers are not foolish. Those who refuse to repent will perish, and they do not deserve sympathy.
However, is prefabricated PC technology a dead end? The answer is no; it is not a dead end, but a broad and bright avenue.
At the end of my next article, I will provide: after in-depth research and thought, three directions regarding the development of prefabricated PC technology and the market.
Follow-up article: “BIM Technology is the Meng Po Soup of Industrialized Construction”
This article only represents the author’s personal views