At present, there are two forms of the main structure of large steel structure billboard: one is t, the main frame of which is made up of an independent steel column and a transverse main beam in the upper part in a T-shape welding. The main structure of the system has clear stress, and a beam is welded on the top of the column to form a T-shaped rigid frame structure system consolidated on the foundation, The panel of advertising light box is connected with T through various hangers and diagonal braces. Its main framework is welded by an independent steel column and several parallel transverse main beams in the upper part. The main beams are connected by horizontal and oblique supports, and the advertising light box is directly attached to the main framework.
Through comparison and selection, firstly, the control design load of the billboard structure is the wind load, which is transmitted from the panel to the skeleton, at this time, the stress concentration at the joint of the main beam and the column can be reduced; the main beam of the parallel truss structure is made of channel steel to make the structure smooth and convenient for the attachment of the advertising panel, so as to reduce the deformation of the panel and ensure the visual effect of the advertising surface, The internal maintenance ladder can be set at the elevation of each main beam, which brings great convenience to the maintenance, repair, hanging and unloading of advertising cloth, and ensures the personal safety of operators; in addition, the form is simple, beautiful, the stress is clear, and the construction is convenient, so as to ensure the construction quality.
The structure layout of the project adopts independent steel structure column, and the diaphragm beam and diagonal support are set between the main beams to form the space truss stress system, and make the panel skeleton node consistent with the main skeleton node, so as to strengthen the connection between the panel and the main skeleton. The framework of the billboard panel is hung and welded on the main structure to form the overall superstructure. The main beam is made of channel steel, and other members are made of angle steel. In addition to considering its strength and stability, structural analysis is carried out
Load and load combination structure bears the following main loads: 1) wind load; 3) maintenance live load; 5) load combination has three types: 1) special combination; 3) stress analysis since the steel column is a compression bending member, the calculation shows that the main beam of the upper structure can be simplified as a rigid or hinged cantilever structure on the steel column, and the space parallel composite truss is formed by the beam and diagonal brace hinge between the main beams. The calculation of internal force is completed by finite element program on computer.
According to the design theory of steel structure, the strength can reach the strength of base metal, so there is no need to check the weld stress, and the weld bears the stress transfer between members. For billboards and other structures, the upper structure members are generally not stressed, and can be welded by girdling, and the welding foot size is HF = 10 mm; however, the welding of the hanging points between the billboard panel frame and the main framework must be calculated one by one.
The height of billboard column is 18m, and the upper structure is cantilever truss. Under the action of wind load and self weight, if these displacements are too large, they will directly affect the use and sensory effect of billboards. These displacements will also cause additional internal forces, increase the internal stress of the structure, and reduce the safety of the structure. In the design of billboards, the displacement should be strictly limited. According to the code for design of steel structures (GBJ17? 88), the horizontal displacement of billboard should be controlled within 10 mm.
Foundation engineering design
As the foundation type and layout of this type of billboard, there are mainly two types of foundation types: one is the balanced gravity type, that is, the upper load is mainly balanced by the gravity of the large volume foundation, and the amount of concrete is more, but the construction is simple, and it is suitable for use when the soil is soft and there is an open construction site. The other is pile foundation type, in which reamed pile is the main one. Its advantage is that the foundation construction site is very small, and the concrete consumption is only about one third of that of the balanced gravity foundation,
As this billboard is built in flower beds on both sides of the square in front of a railway station, if the foundation pit is excavated by slope, the concrete floor and cement concrete pavement on both sides will be destroyed. The repair project cost is considerable. After comprehensive comparison, the manual hole digging and belled pile foundation is selected. The upper 4m surface soil and the second layer of silty clay are not reamed, and the diameter is 1.5m, starting from the 4m third layer of clay), In order to increase the load-bearing area of the foundation, the size is 3 × 3M, and the cross orthogonal tooth wall is set under the foundation to enhance the torsional and shear resistance of the foundation.
In the calculation of pile foundation structure, the calculation results of method and m are consistent. The bending moment of pile body appears at 62mm (m, 4.86mm) from the ground (m method is 4.78mm). Calculation of pile material strength and reinforcement,
Different combinations of axial force, bending moment and torque should be considered in the foundation design to ensure that the strength and stiffness of the foundation, the bearing capacity and shear strength of the foundation meet the requirements of the code.
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