by According to unreliable information, the Construction Commission of XX city requires that when all projects of XX are submitted for drawing review, the precast buildings shall not use vertical stressed components (i.e.
frame columns and shear walls); For the project under drawing review, it shall be adjusted that there is no vertical stressed component for review; For the projects that have passed the drawing review, it is also recommended to make design changes, cancel the vertical stressed components and adopt the cast form.
The reason is clear to all: at present, the connection of the vertical assembled stress system is immature, which is mainly manifested in the lack of effective detection means for the compactness of the grouting material at the mortar anchor link joint, and the grouting quality is mixed in the market.
After hearing this news, peers in the industry agreed: for the assembled type, I have been worried about the seismic problem.
In fact, each splice is a weak point.
I don’t know how the seismic performance is? Do you have any friends who do research in this field to give you a brief introduction I very much agree with XXX’s opinion that assembly should not be a new topic, nor should there be too strong policy support and strong promotion measures.
We all like good things, and we only want to cheat the government’s money for bad things At present, the on-site control is indeed a problem: the biggest problem of precast concrete structure is the on-site inspection means.
Its quality depends too much on the on-site operation.
If the inspection means can’t keep up, no matter how good the system of the laboratory arrives at the site, we don’t know what it will look like.
China’s construction projects can not test the consciousness and self-discipline of construction personnel Many frameworks in Japan are assembled, and the connection method is basically similar to ours (or we are modified), so it is not a technical problem, but a management problem: The main energy consumption of concrete is cement.
The energy consumption of on-site casting and factory prefabrication is the same! However, the promotion of assembly is under the banner of energy conservation and environmental protection! However, the first problem that the structure should solve is security There are still many differences between laboratory and on-site management and control: Those who went to the construction site should not be optimistic, hehe: The compactness check of grouting may be a problem: I feel like I’m assembling for the sake of assembling now! In fact, the assembly type of infilled wall is more reliable General manager Mao Hongbin said in his wechat < wechat >: precast buildings may be a good thing, but not all good things are feasible.
Any technology should do both feasibility study and non feasibility study.
If only feasibility study is done, we may only see its advantages and ignore its disadvantages.
At present, some local governments are pushing for precast buildings, which requires the assembly rate and prefabrication rate in a few rings to reach how many indicators.
In fact, it is unnecessary.
Only by adjusting measures to local conditions and allowing the market to choose is the most correct path.
If a technology or process does not improve productivity, has no cost advantage, or even significantly increases the cost, and the quality can not be guaranteed, then it has no promotion value.
In order to change the mode of construction and production, transformation and upgrading, the construction industry also needs to have practical feasibility.
Some people think that the labor volume of precast buildings is significantly reduced by 30% ~ 50% compared with traditional cast-in-place buildings, so they come to the conclusion that the labor volume has obvious advantages.
In fact, the total labor force of precast buildings will not be reduced, and may still increase.
It is only that part of the workers required for reinforcement engineering, woodworking formwork and concrete pouring originally constructed on site have been transferred to the precast component processing plant.
In addition, the PC installation personnel on the construction site are new, which was not originally available.
Some people think that precast buildings use less time than traditional cast-in-situ buildings, which is only one thing.
The parts and components of precast buildings can be processed in advance in the factory, but the installation of PC components takes more man hours.
According to the field survey, precast buildings take more man hours than cast-in-situ structures, and the construction period is longer.
If the PC factory has insufficient capacity, the construction site may have to wait in line, thus delaying the construction period.
It was analyzed that compared with the cast-in-place structure, the loss of water, electricity and formwork of precast buildings was reduced by 20% ~ 40%.
Precast buildings have obvious advantages in four sections and one environmental protection.
The only advantage of precast buildings is to reduce on-site wet operation, and water and electricity may not be saved.
After investigation and research, the author found that precast buildings have little advantages over cast-in-place structures.
So why are foreign precast buildings so successful? Because the foreign assembly technology is relatively mature, the parts are standardized.
There are the following factors restricting the development of assembly in China: first, the assembly technology at home and abroad is immature, and there are no skilled operators in this field.
Secondly, domestic building components are not standardized, and various specifications are changeable, which is equal to personalized customization, mass production is not allowed, and the reuse rate is low, so it is impossible to reduce its marginal cost.
Third, due to the lack of craftsmanship, migrant workers have been used to rough manufacturing, so they can not adapt to and meet the accuracy requirements of precast buildings.
Fourth, the assembly building leaves huge quality hidden dangers, such as water seepage from the outer wall.
If the quality of cast-in-situ structure is not good, it will also cause water seepage of the outer wall, but it is integral cast-in-situ after all, while the precast building has a large number of joints due to the assembly of PC components.
If the joints are not handled well or cut corners, although there may be no problem within one or two years after the completion, water seepage is bound to occur after three years, and the cost of future maintenance is quite high.
Moreover, these joints also affect the mechanical properties of the structure.
Fifth, due to the non standardization of parts, PC factory needs many kinds of “molds”, PC needs maintenance period, and PC finished products need to be stacked on site.
How large site does a PC factory need to meet production and needs? Now it is some developed cities that push assembly buildings, and the land in developed cities is very expensive.
Therefore, the cost of building a PC factory is very high.
If the PC factory is built more remote in order to save land cost, it will increase the transportation cost..
