It's fast and cheap! Component-type curtain wall de assembly construction

Keywords: component-type curtain wall, assembly, integrated bearing, section construction method, mobile rail crane

1 Introduction

In recent years, building industrialization has become a new development direction, and the Ministry of Housing and Urban-Rural Development has also highlighted the need to vigorously develop prefabricated buildings in the "14th Five-Year Plan" construction industry development plan, and the market share of unitized curtain walls has increased significantly. However, for buildings with a building height of about 100 meters, the advantages brought by the application of unitized curtain wall are not obvious, because the utilization rate of construction hoisting facilities is low and the cost of measures is high. This has brought a stable market space to the continued use of the component curtain wall, but the problems of construction quality and efficiency of the component curtain wall are still unsolved, and in the current downward environment of the construction industry, the troubles brought to the construction party are becoming more and more prominent.

We have been focusing on the technical research of "component-type curtain wall unitization" for a long time. In the early days, it was mainly to solve the construction difficulty and efficiency problems of special components such as "stone lines" and "aluminum plate modeling", and later it was found that the unitization process of component-type curtain wall was not only an improvement at the structural level, but also profoundly affected its production and construction organization, and derived new construction methods and construction machinery. Today, we have iterated from version 1.0 of "modular curtain wall unitization" to version 2.0 of "prefabricated construction technology of modular curtain wall", and have created value for our customers.

2. The assembly idea of component curtain wall

The principle of "component-type curtain wall unitization" is very simple, that is, under the premise of not changing the basic structure of the component-type curtain wall, the parts of the component-type curtain wall are assembled into units on the ground through positioning and constraints, and then installed as a whole. Under the guidance of this line of thought, all kinds of lines and modeling special components can be easily "unitized", such as the aluminum plate eaves in Figure 1 and the aluminum plate modeling in Figure 2.

After the success of the unitization of the component-type curtain wall, we began to expand our vision to the direction of its processing technology, construction methods and construction machinery, and systematically sorted out this technology, and initially formed the assembly idea of the component-type curtain wall: through the division of units, it meets the requirements of on-site assembly and hoisting; By solving the positioning and constraints of the parts of the component curtain wall before the wall, the assembly quality meets the installation requirements; By taking auxiliary measures, it is ensured that the assembly unit can maintain the shape and position accuracy and bear the installation load during the lifting and installation process; By adopting the method of "section construction", the requirements for construction facilities and other conditions are reduced.

2.1 Division of curtain wall units

"Curtain wall unit division" mainly refers to the unit division of the curtain wall in a suitable way to meet the requirements of on-site unit assembly and hoisting. As far as the principle of unit division is concerned, the following methods are generally adopted:

Units are divided by the styling elements of the curtain wall. This type of curtain wall is usually regularly distributed with decorative lines or modeling elements, which can be simply divided by lines or modeling elements to divide the entire curtain wall into suitable units (Figure 3). In this practice, since the structure of the line itself is relatively independent of the structure of the curtain wall, the work of unitization is relatively simple. Generally speaking, line elements and curtain wall units can maintain their own construction practices and form independent units on their own. The focus was on solving the design problem of the integrated support, ensuring that the two different cell plates could maintain an accurate spatial position and that they needed to be connected in such a way that they could be easily lifted.

The unit is divided according to the principle of complex modeling and overall hoisting. This kind of application scenario is mainly aimed at the complex modeling elements on the curtain wall, and solves the problems of complex on-site assembly and difficult construction. In the specific operation, the difficult process on the façade will be put on the ground for implementation, and at the same time, taking into account the hoisting conditions on the site, a complex shape will be decomposed into several units that can be assembled. This type of unitization focuses on breaking down the size of the unit and reducing the number of splices as much as possible (Figure 4).

Divide the units according to the principle of improving the efficiency of curtain wall construction. This kind of application scenario is usually a conventional curtain wall with a relatively fragmented grid and a large amount of on-site work. This type of curtain wall is very flexible when dividing the units, and can adopt "continuous unitization", that is, all panels are grouped into their respective units, but it will cause the curtain wall keel at the unit splicing to adopt the "half-unit frame structure" or a split keel plug structure similar to the unit curtain wall. Another method is to partition unitization, that is, a part of the panel is excluded from the unit, and the related transverse keel is not included in the unit, and the transverse keel and panel at the interval are installed after the adjacent unit is hoisted.

The so-called "half-element framed structure" is actually to use the "framed unit" to solve the problem of mosaic space between two adjacent main units, vacate a compartment between the two main elements, and after the main unit is installed in place, the "framed unit" is fixed on the keel of the left and right main units (Fig. 5). Since the "framed unit" is only responsible for integrating the panel materials together, it is lightweight and easy to install, and when it is fixed to the two main units, it can be carried with the main unit keel. This approach is ideal for curtain wall constructions where the sash is flush with the columns, and its unitization can be easily achieved. In addition, it is also widely used in the curtain wall and ceiling system of slicing and overall hoisting.

The practice of imitating the horizontal and vertical keel insertion of the unit-type curtain wall is generally not recommended, mainly because this practice will lead to an increase in material costs, and once the plug-in structure is adopted, the advantage of free installation of the plate in no order will be lost, which is not conducive to the construction organization. However, the plugging method has a large degree of freedom for unit division, and it is a simple and easy unit transformation scheme. Both approaches have advantages and disadvantages, depending on the needs of the project.

2.2 Technological measures for assembly transformation

The first thing to face in the assembly of component-type curtain wall is the problem of processing and assembly. Since the assembly cells are completed in the factory or on the ground in the field, there is an opportunity to use a variety of auxiliary positioning fixtures to improve assembly accuracy and efficiency. Especially for more complex shapes, the keel and panel can be accurately positioned at one time using a special tool, which greatly improves the assembly accuracy and efficiency (Fig. 6).

Relates to the situation that the unit body and the main structure have a plurality of connection points and part of the connection points are shaded by plates, and an auxiliary positioning and guiding structure need to be arranged, so that the connection points of the hoisting unit in the invisible part can be smoothly connected to the main structure. This is very important, and it is the key to whether the curtain wall unit with multiple compartments can be successfully hoisted.

Another problem that needs to be paid attention to is that, unlike the conventional unitized curtain wall, the transverse keel of the component-type curtain wall generally has a small cross-section, resulting in the low overall in-plane stiffness after the framing. If the cross-section size is not increased, local reinforcement is usually required. The in-plane stiffness of the element is generally increased by placing supports in a non-visible area. In addition, the hoisting scheme must take into account the influence of factors such as the construction sequence, the stress mode and the stress part, and carry out simulation calculations, adopt appropriate lifting points and spreaders, and avoid the deformation of the unit body during hoisting.

2.3 Component curtain wall assembly construction method

The horizontal and vertical directions between the conventional unit-type curtain wall plates are plugged in structure, so the unit plates must be installed in order, and the unit plates on one floor are installed in turn, and the next layer of unit plates is installed after the closed water test of the sink is completed. However, for the curtain wall system that has undergone unit transformation, because the principle of its waterproofing is different from that of the unitized curtain wall, it does not need to be constructed strictly in order, and the conditions of the working surface are not high, and the construction can be carried out at multiple points at the same time, which is of great help to improve the construction speed.

Based on this characteristic, we find that the most suitable way is to "construct in sections", which is based on the principle of flow operation: in a construction section, it is divided into a plurality of flow sections along the transverse direction, and the next flow section operation is carried out after the plate in each flow section is hoisted from bottom to top during construction; The flow section that has completed the hoisting operation can be unfolded for gluing and sealing on the outdoor side and fireproof sealing on the indoor side. In this way, hoisting, gluing, and fireproof plugging operations can form flowing water, and will not be hindered by vertical cross construction.

The advantages of this are very many, first of all, the width of the transverse working surface of each flow section is smaller, and the construction area can be arranged more freely; Secondly, the curtain wall plate of each flow section has few varieties and large batches, which is convenient for centralized procurement and processing of materials; Third, the hoisting operation position is concentrated, the horizontal transportation distance is short, and the construction efficiency is high; Finally, the outside of the curtain wall is glued and sealed, and the flow operation method can greatly reduce the number of hanging baskets and the number of turnovers, and effectively reduce the cost of measures.

2.4 A construction machine suitable for prefabricated component curtain wall

Common hoisting facilities for curtain wall unit plate slabs include annular rail cranes, mobile single-arm cranes, truck cranes, etc. Among them, the annular rail crane is the most commonly used construction facility, which can be used for prefabricated curtain wall hoisting. However, due to the fact that rail crane facilities contain more materials and components such as supports, arms and rails, the cost is high, the erection period is relatively long, and the safety risk of installation and removal is also relatively large. This is not very cost-effective for prefabricated component curtain walls with a height of less than 100 meters.

For the prefabricated component curtain wall, because there is no need for transverse and sequential construction, the annular rail crane can be omitted. In fact, we have used mobile single-arm cranes and hanging baskets in many projects to cooperate with the construction, but the mobile single-arm cranes also have small hoisting coverage, even in a small flow section, the crane position needs to be constantly moved, and the construction efficiency is low.

Through the analysis and study of the advantages and disadvantages of various hoisting facilities, we have developed a mobile rail crane. On the basis of the mobile single-arm crane, a horizontal track is added, and an electric hoist is installed under the track, which realizes the function of the rail crane in a sense. The length of the guide rail is about 8 meters, the effective walking distance of the electric hoist is 7.5 meters, the hoisting coverage is large, and 6 rows of curtain wall plates can be hoisted at one time. The overall width of the crane also matches the module of the building column pitch, and the number of movements is an integer to maximize the role of the equipment. In addition to this, it has an integrated winch that can be lifted directly from the ground, and the lifting work is completed by an electric hoist by means of an aerial hook change. Due to the reduction of transshipment links, the construction efficiency is greatly improved.

The main body of the mobile rail crane adopts a modular assembly method, which is divided into four parts: chassis, arm, hoisting system and track (Fig. 7 and Fig. 8). The chassis is welded by steel square pass, and a total of 6 tank wheels are installed in 2 rows to facilitate movement. After the crane moves into place, the supporting feet are lowered and the height is adjusted to transmit the force to the roof. The boom is composed of steel trusses welded into steel, and the hoisting system consists of a winch, a front boom and a tie rod. The front boom is pinned to the front of the body using pins and can be rotated for easy retraction when the crane needs to be transferred to the next station. The track is made of guide rail steel, and 1 electric hoist is installed at the bottom for hoisting the plate.

3 Introduction to implementation cases

3.1 Case of "Component-type Curtain Wall Assembly Version 1.0".

One of the projects we implemented in 2019 adopted a component-type curtain wall unit renovation scheme, with a total construction area of 143,300 square meters, four towers, and a curtain wall height of 106 meters. The project is divided into two lots, each with two towers and a conjoined podium.

The main curtain wall system of the project is a combination of glass curtain wall and stone curtain wall, the horizontal and vertical stone lines are divided into 800mm, and the glass is 1150mm, which naturally forms the glass unit and the stone unit, plus the opening unit hidden behind the stone line, which constitutes all the elements of the system.

In the original design scheme, the stone lines are made of three pieces of stone, and the quality of the splicing is very high. The stone moulding and the glass part are two separate systems, each of which is connected and fixed to the main structure (Fig. 9).

One of the core ideas of assembly transformation is to simplify the difficulty of panel installation. We pre-lay the stone panels on the tire mold and then place the steel frame on the tire mold. Under the action of gravity, the connecting code is automatically attached to the back of the stone panel, and the leveling work is automatically completed without intervention, and then the assembly of the stone panel can be completed by simply locking the relevant adjustment bolts. The whole stone unit is taken out of the tire mold as the finished state, and it can be installed immediately, which greatly improves the installation accuracy and construction efficiency.

Another important point is the structural design of the "composite steel corbel" (Fig. 10), which ensures that the glass unit and the stone unit can be accurately seated at one time, so that the component-type curtain wall unit without a plug-in relationship has the same hooking characteristics as the unit curtain wall. This technical feature has laid the main technical route for the iteration of our component-type curtain wall assembly technology to version 2.0.

When this project was implemented, we entered the site 3 months later than the construction unit of the other bid section, but finally completed the construction task 1 month ahead of schedule. More importantly, the installation accuracy and appearance of the curtain wall are much better than those of conventional component curtain walls, which has been highly praised by the owner. The project won the National Excellence Award.

3.2 Case of "Component-type Curtain Wall Assembly Version 2.0".

After the unitization technology of component-type curtain wall matures, we find that because in the unitization technology route of component-type curtain wall, if there is no plugging relationship between the unit plates, it is not necessary to construct strictly in the horizontal sequence. This technical feature led to the emergence of the "section construction" construction method, which greatly increased the construction speed of the curtain wall. On this basis, we have further improved the existing curtain wall construction machinery and developed a "mobile rail crane" that is compatible with this construction method. After summarizing and sorting out these innovative points, the "component-type curtain wall assembly construction technology" was formed, and the component-type curtain wall assembly was upgraded to version 2.0.

In 2024, we will apply version 2.0 of the "Component-type Curtain Wall Assembly Construction Technology" to a new project, in which the facades of buildings 1 and 2 are mainly composed of glass curtain walls and stone curtain walls, of which the width of glass is 1100mm and the width of stone is 900mm. The original design was a component-type curtain wall, with an aluminum alloy keel for the glass curtain wall and a steel keel for the stone curtain wall (Fig. 11).

After undertaking the project, we proposed a detailed design plan for assembly to the owner, and won the favor of the owner with the promise of saving 3 months of construction period. According to the characteristics of the façade, the curtain wall is divided into glass units and stone sheets, which are completely independent and have no plugging relationship, and are positioned and fixed on the main structure of the building through integrated supports. The glue sealing method is still used between the unit plates, and the glue injection and sealing operation is completed by using the hanging basket after the plate is hoisted (Fig. 12).

The two buildings of the project have a total of about 3,200 plates, all of which are produced in the processing plant. The construction method of "section construction" is adopted on site, and the "mobile rail crane" is used to complete all the work from vertical transportation of plates, horizontal positioning to hoisting completion. Because the installation process of the component-type curtain wall assembly unit is less than that of the unit-type curtain wall, the hoisting speed is much faster than that of the unit-type curtain wall. The displacement of the "mobile rail crane" does not delay the effective construction time, and the anchorage point of the wind cable for vertical transportation is done in advance, and it only takes half an hour for each shift. The original plan was to complete the hoisting of all the plates within 60 days, but in fact, it only took 30 days to complete the hoisting work of all the plates except for the construction elevator entrance, which exceeded our own expectations.

4 Conclusion

From the perspective of the development trend of the curtain wall industry, prefabricated will be the mainstream direction. However, due to the impact of cost, buildings below 100 meters will still be dominated by component-type curtain walls for a long time. Component-type curtain wall assembly is a beneficial innovation in response to building industrialization in this application scenario. In fact, the unitization of component curtain walls has been started for a long time, and there are many successful cases. We believe that the development of component-type curtain wall assembly should not copy the existing model of unit-type curtain wall, and it is still necessary to develop this technology according to the characteristics of component-type curtain wall, so that it will not deviate from the characteristics of simple structure, low material cost and flexible construction of component-type curtain wall. We have done some exploration for this purpose, and after actual engineering testing, it has been proved that this technical route is not only successful, but also has great potential to be tapped. Limited by ability and vision, our existing technical achievements are still very imperfect, and these experiences are displayed in the hope of providing a little help for the development of curtain wall assembly and industrialization.