Over the past decade, the development of industrial construction has been very rapid, not only in the continuous expansion of industrial construction planning but also in the breakthrough of the traditional single-type factory building framework and roof panels. This has led to the application of various types of roof layouts in industrial construction, resulting in a more diverse range of industrial building styles. The double-T panel system industrial factory is a new type of industrial factory layout that differs from the traditional system. Compared to the commonly used system factory, it offers advantages such as simplicity and beauty, good seismic performance, simplified design, strong general layout capabilities, shorter construction time, and material savings.

The double-T slab produced using the reinforced pre-tensioned wire mesh method was developed in the early 1950s in the United States as a long-span building component. The initial cross-section width of the double-T slab was only 1.22 meters, with a rib height of 0.46 meters. With the advancement of production techniques and concrete strength, the cross-section gradually widened and increased in height to enhance economic efficiency. By the 1990s, the large cross-section had widened to 3.66 meters, and the rib height increased to 0.80 meters. When a 3.05-meter-wide panel replaced a 2.44-meter-wide panel, due to savings in labor, materials, transportation, and installation costs, the cost per panel could be reduced by 17%. These two components can not only replace traditional long-span building components but also fully utilize the potential advantages of precast prestressed concrete, thus maintaining strong vitality and enduring popularity in the United States, Canada, Western Europe, and Northern Europe.

In 1958, our country began to introduce and utilize prestressed prefabricated slabs. In 1978, the Wuhan Metallurgical Construction Research Institute collaborated with the Wuhan Air Force Logistics Department Repair Factory to complete the research and design of the "Double T-Beam Layout System Industrial Plant." This resulted in the construction of the first industrial plant in China with a Double T-Beam system (see Figure 1). Compared to commonly used system plants, this system has advantages such as simplicity and beauty, good seismic performance, simplified design, strong versatility in layout, short construction period, and material savings.

Due to the limited span of the factory building, the advantages of steel structures are not fully utilized. Moreover, steel structures have poor corrosion and fire resistance, and the processing procedures are relatively complicated. The roof protection system and the high requirements for water drainage and insulation further increase the cost. In comparison, prestressed concrete double-T beams (compared to steel structures) offer many advantages, such as light weight, low cost, and easy construction. Practical comparisons show that prestressed concrete double-T beams, compared to steel frames of the same span, reduce the weight of the structure and save steel by over 50%. Additionally, they significantly decrease the building's structural height, resulting in considerable overall benefits.

The commonly used concrete roof layout in industrial construction is the prefabricated roof panel system with trusses (roof beams). Such factory buildings are characterized by poor overall structural integrity in the layout space, requiring many horizontal supporting members. They feature high layout space heights, long equipment pipelines, increased investment, and high heating energy consumption. The trusses are pre-fabricated on-site, demanding high technical and quality standards, with significant template consumption and long production and maintenance cycles. Due to the separate beam and slab system of this layout, repeated hoisting is necessary during construction, thereby extending the construction period. It is difficult to optimize this type of factory building in terms of technical advancement, construction efficiency, and cost-effectiveness. In single-story, multi-story, and high-rise buildings, double-T slabs can be directly placed on the structure, beams, or load-bearing walls as floor or roof layouts. In single-story industrial factories, double-T slabs can be used as roof panels, placed horizontally on the supporting beams or load-bearing walls, or vertically on the truss beams. Because double-T slabs are suitable for wider spans, factories can choose larger spans or column grids to achieve better technical and economic effects. The key feature of double-T slabs is their factory prefabrication, large modular forms, steam curing, flat surface finish, and guaranteed quality. Since they require minimal on-site time, they greatly save on construction duration. Materials: The concrete design grade for double-T slabs is C40, with a concrete slump of 5 cm to 7 cm; the stone particle size is 5mm to 20mm, and the sand is medium grain. Prestressed steel strands are used in 12.7mm and 15.2mm diameters.

The production process of the double-T slab involves the use of long-line beds ranging from 60m to 150m in the factory for prestressed double-T slabs, typically employing the pre-tensioning method. The molds can be made of steel or concrete, with adjustable rib widths, heights, and overhangs at the ends of the slabs. This allows for the production of prestressed or non-prestressed double-T slabs of different spans and sizes using the same bed and mold, offering great flexibility and convenience. Currently, the most widely used production method is steel mold production. Common steel mold production methods for double-T slabs include the portable mold, fixed pipe hot mold, and fixed directional circulation heat-protected steel mold. The portable mold has the advantage of mobility but consumes more steel, resulting in higher costs due to the increased number of crane operations and higher energy consumption in the maintenance pit. The fixed pipe hot mold uses less steel than the portable mold, with the feature of installing pipes inside the mold cavity to directly heat the steel mold with steam during heating, which has a longer maintenance cycle due to the limitations of heat conduction. The directional circulation heat-protected steel mold consumes even less steel than the previous two methods, particularly when using steam in the nozzle to create a high-speed circulation field for direct heating of the steel mold without additional equipment or energy consumption. This method is faster, more economical, and more energy-efficient, making it a more time and cost-saving production approach.

The Double-T slab is a precast reinforced concrete load-bearing member, composed of a large panel and two narrow yet massive ribs. Its slab surface serves both as a horizontal load-bearing layout and as the compression zone for the longitudinal load-bearing ribs. The compression zone has a larger cross-section, with the neutral axis close to or within the panel, and the tensile main reinforcement has a significant moment arm. Therefore, the Double-T slab boasts excellent layout mechanical properties, clear force transmission layers, and concise lines, making it an economically viable load-bearing member capable of spanning large distances and covering extensive areas.

The double-T slab can be vertically mounted on a strip foundation to serve as a wall panel. At this point, the ribs act as columns, while the panels and the insulating layer attached to them form the protective structure. If double-T slabs are used simultaneously for the wall, roof, and floor components, the slabs should have the same width and rib spacing to facilitate interlocking and support. Buildings entirely constructed with double-T slabs can reduce the types and quantities of precast components, lighten the building's weight, shorten the construction period, and achieve better technical and economic benefits. The double-T slab cross-sections include both isosceles and two-slope variable sections, with the former also suitable for use as wall panels.

The use of double-T roof panels in conjunction with a roof layout plan that separates beams from panels reduces the concrete equivalent thickness by 20%, saves 40% in steel consumption, and cuts the roof load per square meter by 20%, thereby reducing the amount of concrete and steel used in columns and their foundations. Double-T roof panels do not require plastering; the joints only need to be sealed with cement mortar. The 12-meter span double-T panels have a rib height of only 480mm, which not only saves wall materials but also reduces the vertical load, effectively controlling the cost of the foundation. In the construction phase, the double-T roof panels are large-scale roof structure components, where installing one panel can complete nearly 29 meters of roofing work. In contrast, to cover the same area with thin-walled beam hollow panels would require lifting 0-3 thin-walled beams and at least 8 hollow panels. This significantly reduces the number of crane shifts, shortens the construction period, and offers better economic benefits.