In recent years, China’s photovoltaic industry has developed rapidly, but recently under the siege of developed countries in Europe and America, it has been struggling and can only turn to the domestic market. At present, only by adopting new ideas, new designs and new materials to provide domestic users with safe, economical, reliable and multi-functional steel structure brackets, can we provide a broader application space for the comprehensive promotion and development of PV power generation in China.
Introduction: With the rapid development of China’s green economy, monocrystalline silicon/polysilicon photovoltaic power generation and thin film BIPV technology are becoming more and more mature. Compared with other structures, steel structures have great advantages in terms of usage function, design, construction and comprehensive cost. Therefore, it is important to actively develop and produce new steel PV bracket system to replace the existing angle steel bracket system.
1, solar steel bracket with steel type
At present, in view of the solar photovoltaic bracket structure is simple, small size characteristics, in the selection of steel mostly to light structural steel and small cross-section of ordinary steel structural steel.
Light structural steel: light structural steel mainly refers to round steel, small angle steel and thin-walled section steel. Among them, angle steel used as a support member, can make good use of the strength of steel, and facilitate the installation of the overall bracket, but used as a bending and compression members, the deformation produced relatively large. At present, the national standard angle steel relative to the solar bracket, there are not many models available, so more small angle steel models are needed to adapt to the current rapid development of the solar market. The purlin members of thin-walled section steel are generally made of thin steel plates with wall thickness of 1.5-5mm, which are cold-formed or cold-rolled into various thin-walled section steel products with different cross-sectional forms and sizes. Compared with hot-rolled sections, the radius of gyration of thin-walled sections can be increased by 50-60% and the moment of inertia and moment of resistance of the section can be increased by 0.5-3 times in the same cross-sectional area, thus the strength of the material can be used more reasonably, but since the processing of thin-walled sections is mostly in the factory, high-precision drilling is required to match the screw holes after the PV panels. The factory processing drilling buckle, in order to hot dip galvanizing anti-rust; transported to the site installation, due to the steel cross-section is small, tools are difficult to operate, the construction is more difficult. Most of the current domestic panels can not be installed directly and thin-walled steel connection, are required to other auxiliary fixed structures (such as pressure blocks, etc.).
Common structural steel: Common structural steel is often smelted easily, low-cost carbon structural steel or low-alloy steel, cross-section has many types, PV commonly used mainly include I-beam, H-beam, L-beam and a variety of design requirements of shaped cross-section. There are various processing methods, among which welded sections are made of steel plates of different thicknesses, which are welded and processed in the factory to form steel according to the design requirements, and this forming method can take different thicknesses of steel plates in different parts according to the force calculation of different structural parts of PV projects, which is more reasonable than hot-rolled once-formed products, more suitable for on-site installation and can save steel.
2, solar bracket on the steel performance requirements of solar steel structure steel should have the following properties.
(1) tensile strength and yield point. High yield point can reduce the section of steel sections, reduce the weight of the structure, save steel and reduce the overall project cost. High tensile strength can increase the overall safety reserve of the structure and improve the reliability of the structure.
2) Plasticity, toughness and fatigue resistance. Better plasticity can make the structure produce larger deformation before damage, which can enable people to find and take remedial measures in time. Better plasticity can also adjust the local peak stress, itself solar panel installation often in order to adjust the angle, using forced installation, and plasticity can make the structure produce internal force redistribution, so that the structure or members of some of the original stress concentration part of the stress tends to uniform, improve the overall load bearing capacity of the structure. Better toughness can make the structure in the external impact load is destroyed when absorbing more energy, especially windy desert power station and roof power station, wind vibration effect is obvious, the toughness of steel can effectively reduce the degree of danger. Better fatigue resistance can also make the structure has a strong resistance to alternating repeated wind loads.
(3) processing performance. Good processing properties include cold working performance, hot working performance and weldability. Photovoltaic steel structures used in the steel should not only be easy to process into various forms of structures and components, but also need these structures and components do not cause excessive adverse effects on the strength, plasticity, toughness and fatigue resistance due to processing.
(4) service life. As the design life of solar photovoltaic systems are more than 20 years, so a good anti-corrosion performance is also an important indicator to measure the bracket system is good or bad. If the bracket life is short, is bound to affect the stability of the entire structure, resulting in an extended payback period and reduce the economic benefits of the entire project.
(5) in line with the above conditions, photovoltaic steel structure with steel should also be easy to buy, production, and also inexpensive.
3, the new solar steel structure bracket technical analysis
At present, the use of angle steel solar bracket is increasingly restricted by the conditions, the main reason is that the current steel quality varies, installation requires a large number of on-site drilling, but after drilling steel and easy to rust, so the need to use new bracket to replace these angle steel bracket to slow corrosion and extend the service life of the purpose.
New solar bracket main structure form.
(1) shaped cold-formed thin-walled steel type bracket structure system. Shaped cold-formed thin-walled steel is a batch production and manufacturing, can be quickly assembled, completely dry operation of the assembly of light steel structure system, with a small amount of steel, construction time, labor and other characteristics. The main manufacturers in China are Hilux, Haimai, etc. The steel structure bracket of shaped cold-formed thin-walled steel structure system is made of factory prefabricated cold-formed thin-walled steel sections that are bolted together at the construction site to form a structural skeleton, and then the panels are installed to form an overall PV array.
2) Factory prefabricated monolithic steel bracket system. Factory prefabricated steel structure with purlins, at the construction site only need to put together the bracket module to fix, and then install the panel to form the whole PV array, the construction speed is fast, suitable for large-scale power station. This kind of steel structure bracket installation requirements are extremely high, generally using the best quality of steel, surface treatment process is extremely excellent, and need and photovoltaic module manufacturers to fully communicate in advance, in order to achieve perfect assembly with.
(3) beam-column frame curtain wall photovoltaic bracket structure system. Photovoltaic curtain wall suitable for the use of beam-column frame steel bracket system. The structure is light weight, reliable structure, due to its small lateral stiffness, when the structure height is high or floor height, lateral support needs to be set to form a support frame structure. High-rise photovoltaic curtain wall design, commonly used steel structure and cast-in-place pre-built components to form a hybrid structure to enhance the overall structural resistance to lateral movement, reduce the amount of steel used, thereby reducing the total cost.
4, new cold-formed thin-walled solar bracket parts installation.
(1) the connection of the steel structure components of the new cold-formed thin-walled solar bracket is assembled from a variety of steel and plastic prefabricated mixed connections from the factory, these steel and plastic mixed connections of various types, can be suitable for different installation conditions, the correct choice of mixed components connected to the form and manner is an important part of the overall structural design.
(2) bracket and foundation connection of the new cold-formed thin-walled solar bracket is lighter in weight, more installation holes. Generally independent foundation is the main, if necessary, need to add reinforced concrete connecting beam. For geological conditions are poor, can use strip foundation or cross foundation, as far as possible not to use raft foundation. All the upper column footings are hinged form, while the pre-built parts can choose to insert the footings, or pre-built bolts outside the waterproof concrete. These two types of column footing form are simple processing, convenient construction, even good performance.
(3) bracket purlin connection installation node connection has three forms: rigid connection, articulation and semi-rigid connection, these three connection methods have ready-made supporting node modular production method. Articulated connection is simple, the most convenient manufacturing and installation, but windy areas need to set up horizontal support or diagonal bracing so that the daughter wall to withstand the horizontal load and provide additional stiffness, do not set up support when the beam and column connection nodes should be made rigid connection. Semi-rigid connection is simpler than rigid connection construction, better than hinged performance, because its force is difficult to control, need to combine experience before the actual use, is basically not used. The field connection is generally hinged with bolts first and then welded on site at both ends.
5, concluding remarks
Relatively speaking, the new cold-formed thin-walled steel type bracket structure system can make the project duration significantly reduced to meet the needs of solar photovoltaic building, especially its superior corrosion resistance, recyclability, reflecting the comprehensive cost advantages of steel structure; new cold-formed thin-walled structure solar bracket system direct economic benefits mainly from the advantages of shortening the construction period and reducing maintenance costs, and with the use of the number of years With the extension of the use of years, the more obvious the increase in benefits. Small Rong Rong that the vigorous development of new cold-formed thin-walled steel type bracket structure system is an inevitable trend.