With the development of multimedia technology, LED electronic display screens are widely used in commercial displays, which produce good advertising effects, and well-designed support structures for display screens can also become beautiful landscapes in urban buildings. Combined with the viewing distance requirements of the display screen and the characteristics of the investment area, the structure type design is usually carried out according to the construction site and building requirements. The LED display is usually set up in the form of an independent floor or an attached building (Figure 1, 2). For the support structures of different display forms, the force characteristics should be accurately analyzed and the corresponding structural forms should be selected. This paper will classify and summarize the support structures of LED electronic display screens, and propose the scope of application of various support structure schemes, design difficulties and corresponding solutions. Optimizing design schemes and construction measures.

Display support structure type

1.1 Floor support structure

Floor-mounted LED electronic displays are mostly set up in city squares or important traffic intersections. The analysis of the force characteristics of the supporting structure of the floor-standing display shows that the supporting structure should adopt a space steel truss structure. On the foundation, 4 steel columns are combined to form a space lattice column. The upper part of the screen body adopts a multi-layer horizontal space truss structure, which can not only meet the structural force requirements, but also meet the setting of maintenance channels.

Binwang Road, Yiwu City transparent led video wall display screen area The effective size of the screen is 13.4m×8.6m, which is a typical floor-standing support structure, and the display support structure system is formed by lattice columns. The 4 main limbs of the steel lattice column are 300mm×300mm×10mm, the horizontal beams are 200mm×100mm×6mm, and the oblique web bars are 100mm×100mm×6mm. Combining with the internal space of the lattice column, the access for maintenance is set; The back and side members of the body adopt a steel truss structure, and the upper chord, lower chord, and web are all 100mm×100mm×6mm in size, and 6mm thick steel plates are laid on the upper part to meet the maintenance access requirements. The foundation is an independent concrete foundation. The support structure is shown in Figure 3.

1.2 Wall-mounted support structure

The density of urban construction is relatively high, and only a few areas can meet the construction conditions of floor-to-ceiling display screens. The LED electronic display screen has the advantages of playing dynamic picture advertisements, etc., and a large number of LED display screens need to be built in the bustling commercial areas of the city. The solution to this contradiction is to build a display screen attached to an existing building. According to the construction conditions, renovation conditions and building height of the building, the led display support structure attached to the building is usually divided into a wall-mounted display support structure and a roof-mounted display support structure.

The support structure of the wall-mounted display screen is mostly fixed to the listening surface of the main structure 1 with a single-layer steel structure, and an inspection channel is set inside. China Telecom Wenzhou Branch South Station Building LED large screen project display 24.0mx13.4m, is a typical wall-mounted display support structure, using square steel pipe 160mm×160mm×6mm to form a node system, and laying 6mm thick embossing on channel steel 14a The steel plate forms the maintenance channel, and each node is anchored to the side of the frame column of the main structure through 6 M16 anchor bolts. The front elevation and side elevation of the project are shown in Figure 4.

1.3 Roof support structure

In actual use, the wall-mounted LED electronic display screen will affect the lighting of the building because it occupies a large building facade, so the wall-mounted electronic display screen is only suitable for large commercial buildings such as shopping malls. The LED electronic display screens installed in office buildings and residential buildings with moderate building heights can only be designed on the top of the building. At this time, the display screen support structure system should be classified as the roof display screen support structure.

China Communications Services Guangxi Company’s display screen support structure is set on the top of the building, making full use of the original main structure shear wall to set up a steel lattice system. The beams and columns are all made of lattice components to form a space truss system with good stress state. The effective size of the display screen is 17.5mx8.0m. The 4 main limbs of the steel lattice column use a mouth of 100mm×100mm×5mm, the horizontal beams use a mouth of 100mm×100mm×5mm, and the diagonal rods use a mouth of 60mm×60mm×5mm, of which Horizontal beams and vertical beams form a truss system to resist lateral wind loads and earthquake loads. The nodes are anchored to the main structure by 10 M12 bolts. The front elevation of the project is shown in Figure 5.

load action

The floor-mounted, wall-mounted or roof-mounted LED electronic displays need to calculate permanent loads, live loads, wind loads, snow loads, ice-wrapped loads, and earthquake loads. Among them, the permanent load needs to be included in the self-weight load of the screen, and the live load needs to consider the maintenance load involved in the maintenance of the screen body. The load combination factor shall meet the specification requirements.

The natural vibration period of wall-mounted or roof-mounted display screens should be analyzed in conjunction with the main structure. Usually, the natural vibration period of the main structure can be used for calculation, and the impact of high vibration modes on the roof-type support structure can be analyzed. The calculation of wind load should be carried out according to the design and analysis of the envelope structure, and the large-scale support structure should be analyzed in depth according to the specific structural form. The calculation of earthquake load should comprehensively consider the two-way horizontal earthquake and vertical earthquake action, and especially pay attention to the analysis of the influence of vertical earthquake action under rare earthquakes for wall-mounted support structures.

In addition, the electronic display screen is equipped with an electronic display unit. Long-term lighting and other equipment operations will bring too much heat, and internal heat dissipation problems are prone to occur. There are a large number of power lines inside the support structure, and problems such as line aging are also Easy to cause fire. The support structure of the display screen should have sufficient resistance when such accidents occur, so as not to cause continuous collapse and damage. It is necessary to strengthen the design of key component support nodes to improve safety reserves.

Structure selection

3.1 Floor support structure

The support structure of the floor-standing electronic display screen bears the load of the upper screen body structure through the column connected to the foundation, and can be analyzed and calculated according to the cantilever beam structure. The floor-standing support structure usually adopts a single-column or double-column plus beam structure, and other types can be combined with architectural modeling to select a suitable support structure system. Concrete structure, steel pipe structure and lattice steel column can be used for column design, and steel structure types such as lattice beam can be used for beam. The foundation type selection should be determined according to the geological conditions of the site, and the compression, pull, bending and overturning resistance calculations should be carried out. Combined with the force characteristics of the cantilever structure, the key component of the floor support structure is a vertical column design, and a safe and reasonable section form that meets the technological requirements is selected.

Combined with the characteristics of the construction period of the display screen support structure, the circular steel column and lattice steel column section are selected for analysis, and the amount of steel used under the same stress and strain conditions is studied. The finite element analysis software is used to establish the model, the round steel column adopts ?1000×15, the four main limbs of the lattice steel column adopt the opening of 300mm×300mm×10mm, the horizontal beam adopts the opening of 200mm×100mm×6mm, and the oblique web rod is 100mm ×100mm×6mm, according to the force characteristics of the cantilever structure, the load on the upper screen is simplified to the top of the column, and the finite element analysis is carried out on the two columns according to the simplified model. The analysis results show that for the floor support structure, the cylindrical section and the lattice section are good section forms. Due to the need to maintain the electronic display components of the outdoor electronic display screen, it is necessary to set up a passageway for people. The lattice column can make full use of the lattice space to set up the passageway for people. weak point. When a circular cross-section is required due to the landscape, local reinforcement treatment should be carried out for the superior part. When both cross-section types can meet the practical and appearance requirements, lattice columns should be used first.

3.2 Wall-mounted support structure

The wall-mounted support structure is anchored to the side of the main structure through steel nodes. Usually, frame columns can be used to fix the nodes. When the node spacing cannot meet the requirements, frame beams can be used as auxiliary fulcrum design positions. The beam members are fixed on the support points to form a horizontal sheet structure system. This system bears the wind load transmitted from the display screen and serves as the maintenance channel to bear the maintenance load. It belongs to the main stress system of the wall-mounted support structure. The keels of the screen body are all arranged on the horizontal sheet structure system. Usually, horizontal trusses can be used for this system. For systems with small node distances, section steel can be used directly as beams, and continuous beam schemes can be used for calculation models. The horizontal sheet structural system is the key component of the wall-mounted support structure. Figures 6 and 7 study the stress-strain characteristics of two horizontal sheet-like structural systems. The axis spacing of the main structure is 7500 mm, and no support point can be set in the middle of the maintenance platform set in the middle of the floor. Therefore, the maximum deformation point of this project occurs in the middle of the floor. According to the deformation characteristics, two structural forms are used for analysis. The joint members all adopt the opening of 160mm×160mm×6mm, the single steel horizontal support structure adopts the opening of 100mm×100mm×5mm, the chord of the composite truss horizontal support structure adopts 50mm×50mm×4mm, and the oblique web bar adopts the opening of 30mm×30mm×3mm.

When the total mass of the supporting structure system is the same, the deformation of the composite truss structure with diagonal web members is smaller than that of the composite truss structure with straight web members. The results show that the composite truss structure of the horizontal sheet structure system can effectively reduce the deformation of the support structure, especially when the distance between the frame axes is large and the fulcrum cannot be continuously set in the middle area, increasing the density of the diagonal members can effectively reduce the deformation of the support structure.

3.3 Roof support structure

The roof-type support structure needs to be designed in combination with the original structural layout of the roof. It is very important to make full use of the original main structure system to bear the load to optimize the roof-type support structure system. Usually, various structural forms such as plane truss, space truss or grid structure can be used in combination with the building shape. The structural scheme is flexible and changeable, and finite element analysis software can be used for modeling analysis and calculation. In view of the characteristics of light steel on the roof, attention should be paid to the particularity of the natural vibration period and the whiplash effect. It is advisable to conduct finite element analysis on the roof support structure and the overall model of the building to study the stress-strain characteristics of the support structure.

The roof-type support structure belongs to the space structure system, and there are many types of connections between it and the main structure, which need to be determined according to the actual situation at the top of the main structure. The mechanical performance of different structural types is very different. Only by using the finite element method to analyze the mechanical state of the overall space structure can a practical design plan be obtained. Figure 8 is a grid structure formed by combining the shear wall with the protruding page of the main structure of the actual project and the support points arranged at the top of the lower column. Steel girders use combined double angle steel 2xL40x4, and diagonal web bars use combined double angle steel 2xL30x3.
The total mass of the steel used is 13900kg, the stress at the root of the column member is the largest, and its value is 133N/mm2, and the stress of the rest of the members is not greater than 50N/mm2, and the maximum deformation in the plane is 3.08mm, which meets the deformation requirements. Figure 9 adopts the space truss structure system, and the members are all made of square steel pipes. Among them, the openings of the columns and transverse steel beams are 100mm×100mm×5mm, the openings of the secondary steel beams are 80mm×80mm×5mm, and the openings of the oblique webs are 60mm×60mm×4mm. The stress value is 135N/mm2, the maximum deformation value is 3.08mm, and the total steel mass is 14100kg.

Comparing the two structure types, it can be seen that the stress and strain of the space truss structure system and the space truss structure system with the same weight are similar, and the effects of the two structure systems are similar. Considering factors such as construction difficulty and maintenance convenience, the form of space truss should be selected for the roof support structure.

Node analysis

There are a large number of connection nodes in the display support structure that uses steel components as the main component, and the accurate design of the nodes is crucial to the safety performance of the overall structure. Expansion bolts. The number of anchor bolts set at the foundation nodes should meet the bearing capacity requirements and be arranged at equal intervals according to the principle of symmetry. The floor support structure belongs to the cantilever structure system, and the stress at the root of the column is relatively large; the wall-mounted support structure also belongs to the cantilever structure system, and the stress at the root of the node is relatively large. According to the stress distribution characteristics of the joints connected with the foundation and the main structure, the optimized design of the joints at the root can effectively improve the stress of the joints and reduce the amount of steel. Figure 10 shows the optimized two types of root nodes.

conclusion

(1) The supporting structure of the floor-standing display screen belongs to the cantilever structure, and its column is the key component. According to the stress-strain analysis results and the maintenance characteristics of the electronic display screen, the lattice cross section is preferred.

(2) The horizontal sheet structure system of the wall-mounted display screen support structure adopts the composite truss structure of diagonal webs, which is better than the composite truss structure of straight webs. When the axis of the main structure is large and the nodes cannot be set in the middle area, the density of diagonal webs should be increased.

(3) The support structure of the roof-mounted display screen can adopt the grid structure and the space truss structure system. The stress and strain of the two structural systems are balanced. Considering the construction difficulty and other aspects, the space truss system is preferred.

(4) The accurate design of the support structure nodes of the display screen is very important to the safety of the overall structure. The structural measures such as shear keys or cross stiffeners can effectively improve the bearing capacity of the nodes according to the characteristics of the large force at the root of the nodes.