Compared with the traditional on-site management of precast concrete buildings, there are three key issues and approaches in on-site assembly planning, on-site general layout, and final assembly building quality that must be paid great attention to, and these issues must be systematically resolved before the project is started. You cannot leave it to the scene to make changes as you go.
At present, the national and local governments have many supporting policies for prefabricated buildings. Some economically developed areas also stipulate minimum assembly rates, such as 15%, 20%, 30%, etc. Just imagine, if the assembly rate of the main structural part of a building is so low, how can it be called a prefabricated building? This can only be called a building using a small number of PC components. Therefore, we believe that only buildings with a certain level of PC prefabrication rate can be called prefabricated buildings. In this context, it is more meaningful to discuss the on-site management of prefabricated buildings and provide better solutions for future building construction. Management reference.
Traditional construction site management has many shortcomings. However, in the past ten years, with the continuous improvement of the supervision level of local authorities, the gradual increase in supervision intensity, and the large number of demonstrations by some outstanding companies, the entire site management level has been improved. raised dramatically. But there are still some problems that are difficult to solve. For example, there are problems such as nighttime construction noise that disturbs residents, on-site dust problems, labor shortages, and the resulting common quality problems. These problems seem difficult to solve well by relying solely on management improvement. Prefabricated buildings supported by construction industrialization can better solve the above problems.
In continuous practice, we have found that compared with the traditional on-site management of prefabricated buildings, there are three key issues and approaches that require great attention, and these issues must be systematically solved before the project is started and cannot be left until changes are made on the spot.
1. On-site Assembly Plan
Construction plan management is also important in traditional project management wrong, it's not that difficult if something goes wrong to fix. The traditional construction industry is an industry with highly developed productivity and various resource supply systems are very developed. Theoretically, whatever resources are needed at the construction site can be deployed in a very short time.
The PC prefabricated building is different. It has more PC components than traditional buildings. This is the biggest difference. PC components have two major characteristics. First, a single component is very heavy and difficult to move. Second, it must be prefabricated and maintained in the factory before being transported to the site.
This places high demands on planning work. It is necessary to accurately calculate how many PC components are on each floor, how to classify and number them, and send out requirements to the PC factory in advance for customization. The demand comes early, and the PC factory can't stack it, resulting in inventory. The demand comes late, and the PC factory can't produce it, which affects the construction progress. At the same time, if a PC component is missed or damaged during transportation, other work on site will be stopped, resulting in a wait for work, which is a huge waste. In addition, if the order of the PC components is not correct, the components need to be adjusted on-site, which is very difficult, time-consuming, and labor-intensive.
So how do you plan? PC prefabricated construction project management planning work must grasp one core, that is, "PC component hoisting" is the core of the plan. Everything else must be subject to this plan and allocate various resources with PC components as the core. Only by doing this can all problems be grasped at their roots, and the busy scene will soon become tense and orderly.
The construction management of the traditional construction industry can only work at the project site, but the plan management of prefabricated buildings must go deep into the PC factory. If there is a factory supply error, it cannot be solved in a short time because the guarantee of resources has undergone major changes. In the past, there was an unlimited supply, but now it is a customized supply. Therefore, to plan well, you must adapt to these new changes.
2. General Layout Of The Site
This is an all too familiar problem for traditional construction sites. However, for PC assembly construction sites, new situations have emerged because of the existence of PC components.
The first problem is vertical lifting.
Previously, too precise calculations were not required. If the tower crane cannot cover the area, use manual labor. Because they are all in pieces, they can be taken apart without much difficulty. But now we are faced with several tons or even ten tons of PC components, and the method is very different. When laying out the overall layout, accurate calculations for lifting must be made. What is the longest lifting distance? What is the maximum lifting weight? What tonnage tower crane is the most economical and cost-effective? If the calculation is wrong in advance, as long as one component cannot be hoisted in place, you will be in big trouble. At this time, it cannot be moved manually. It can be said that there is no solution. Therefore, the model selection of vertical lifting equipment is a very critical point. An undersized model will cause the above problems, an oversized model will cause an increase in costs, and any sloppiness will bring immeasurable losses.
The second important issue is the traffic layout problem caused by the transportation of PC components to the site.
Because the load capacity of the PC component transport truck is very large, it must be considered that the truck must be transported at one time and unloaded near the lifting point, but cannot be transported twice. This requires that on-site transportation roads must be carefully planned, taking into account not only the turning requirements of heavy-duty vehicles but also the carrying capacity of the road itself. If there is a problem in either aspect, the project management site will be chaotic and a lot of additional costs will be incurred.
3. Final Assembly Construction Quality
Some common quality problems that are difficult to overcome in traditional buildings, such as water seepage in exterior walls, plaster hollowing, cracking, geometric deviations, and a series of other problems, are theoretically difficult to eradicate by hand. The emergence of prefabricated buildings can solve these common problems.
However, prefabricated buildings solve old problems, and not everything is ok. New quality risks will likely arise. If we do not pay close attention to it, new problems will seriously offset the benefits brought by technological progress, and the problems will even become more serious.
Compared with traditional construction methods, the most typical quality problems of prefabricated buildings mainly fall into three categories:
Pc Component Installation Accuracy Issues.
PC components mainly include exterior wall components, interior wall components, floor components, and other components. Moreover, these components are all heavy, and their movement must rely on a large number of tower crane equipment, which is beyond the capabilities of manual labor. The accuracy of these components during the installation process directly determines the geometric accuracy of the building structure. Generally speaking, we install peripheral components first. Because this is the component that requires the highest accuracy, if there are deviations in the installation of peripheral components, it will lead to two serious consequences. First, the exterior walls on the same floor are uneven, and second, the verticality of adjacent floors cannot be guaranteed. The existence of these two major problems will cause difficult-to-repair problems for the look and feel of the exterior wall. What's more, if the cumulative error is too large, it will seriously affect structural safety. Of course, the installation of internal PC components is relatively easier to control. But it must also be strictly controlled within the allowable error. To control the installation accuracy error, each construction company must formulate strict construction methods and operate according to the construction methods to ensure accurate placement at one time. Only in this way can the fundamental advantages of prefabricated buildings be reflected.
Vertical Connection Reliability Issues Of Pc Components.
If PC buildings want to improve the assembly rate, they must make breakthroughs in vertical structural assembly. If internal pouring and external plug-ins are used to build PC buildings, it will be difficult to reflect the comprehensive advantages of prefabricated buildings. When using prefabricated components instead of cast-in-place methods for vertical components, the biggest problem encountered is the safety and reliability of vertical connections. The connection method of sleeve grouting is also a very mature technology in Germany and Japan, and our country's specifications also have corresponding construction and acceptance standards. Therefore, we do not have to worry about safety and reliability from a subjective perspective.
The most important issue at the moment is that each construction unit must strictly follow the grouting sleeve technology and operate without any compromise. Ensure that the sleeve is a qualified product, ensure that the grouting material is a qualified product and that the fullness of the on-site grouting meets the specification requirements. These materials are all qualified and operated in strict accordance with the process, so the quality must be guaranteed. All construction units must avoid opportunism, otherwise it will lead to big mistakes. There are currently some products on the market that have not undergone strict inspection and certification and do not have patents. They are counterfeit products made by some small businesses, but the prices are low, so they are very marketable. Enterprises must not take risks, otherwise, once structural safety problems occur, the losses will be unbearable.
The Problem Of Seam Waterproofing
The quality advantage of PC buildings is that factory manufacturing replaces on-site manual construction, but a factory cannot build a complete house. The house can only be broken down into components. These components are produced in factories, and their quality is guaranteed, both safe and beautiful. However, when these components are assembled on site, a large number of joints are created in the connection of each component. Relatively speaking, the joints of interior walls are relatively easy to deal with. Even if there is a problem, the consequences are not serious and it is easy to repair. If there is a problem with the joints of the exterior wall, serious problems will occur. First, the appearance will be greatly compromised and the house cannot be delivered. Second, the joints will leak, which will seriously affect the use function, thus turning into an unqualified project.
To solve the problem of joint leakage, it is not enough to rely on the construction process alone. It must first be solved from the structural design. Reliable waterproofing must first rely on the structure. Therefore, when reviewing the drawings, the structural waterproofing design must be carefully reviewed. Whether it is a horizontal joint or a vertical joint, the structural waterproofing design must be done well. Secondly, when entering the final assembly stage, horizontal joints must be seated and grouted. Under the action of gravity, it is entirely possible to prevent leakage. Vertical joints, as there is no squeezing by gravity and expansion and contraction caused by temperature stress, must be treated with caution. At least two layers of waterproofing must be done, one layer of expansion mortar and one layer of waterproof and weather-resistant glue. Of course, it will be safer if rubber water-stop strips are added to the seams. If these processes are carried out carefully and in a standardized manner, it can be guaranteed that vertical joints will not leak.
The on-site management of prefabricated buildings has many similarities with traditional projects but also has many more advanced differences. In the specific management process, we need to look at it dialectically, which means that we can fully draw on traditional experience and practices, but at the same time we need to be firm and unwavering in the direction of the future. Prefabricated construction is the only way forward for the industry. The most important issue at present is to take seriously the three major problems that arise, strengthen research on construction site management under new technologies, and form a standardized and replicable management and control model. As long as the in-process control work is done well in advance, most problems of prefabricated buildings can be solved. Of course, there may be other problems encountered on site, but as long as the main contradiction is resolved, it is generally not too difficult to solve other minor problems.
In short, on-site management of prefabricated buildings is a management upgrade of traditional project management. It requires us to go deep into the site, perform standardized operations on each node, form accurate and feasible operation instructions, and form a more scientific and effective management model. And this kind of management must be the best quality and lowest cost method. Once used maturely, the productivity it releases will be immeasurable.
Based on continuous upgrading of on-site management, the quality of products is more guaranteed. Coupled with the advantages of energy saving, environmental protection, and no pollution brought by prefabricated buildings, the development of prefabricated buildings will have great value to the whole society and the entire industry.
