Introduction to the knowledge of the structure of the communication tower
1. The truss tower flat facade form
The most commonly used structure of communication towers is the space truss tower, and most of its plane forms are regular triangles or regular quadrilaterals, as shown in Figure 2-1.
Space truss parts often use angle steel and steel pipe, so there are angle steel towers and steel pipe towers. The domestic angle steel is basically a right angle steel, and rarely has an internal angle of 60° angle steel. Therefore, the angle steel tower basically adopts a regular quadrilateral cross section, which is convenient for the connection of the web members. The steel pipe components are much more flexible, and the steel pipe tower has regular triangle and regular quadrilateral cross-sections.
Because the minimum radius of gyration of the angle steel is very small, it is only about 1/5 of the side width. If a single angle steel member is used, the limit of the slenderness ratio of the member must be considered. Therefore, the web member of the angle steel tower uses the sub-divided type (Figure 2-1a) to reduce the free length of the member. The radius of gyration of the steel pipe is about 1/3 of its diameter, which is much larger than that of the angle steel. Therefore, the internodes of the steel pipe tower can be opened. It is appropriate to use a single inclined rod or a cross web rod system (Figure 2-1b, c).
The most commonly used structural form of communication tower truss tower components can also use round steel as the main limb or web member. Its advantage is that the material price is lower, and the wind resistance of the circular section is small. It is used in the cross web member as the prestressed flexible inclined rod ( It is better to use flower basket bolts. If it is used for the main limb, the material of large diameter round steel is poor and it is not economical.
2. Application of prestressed flexible web
The web members of the steel tower are divided into rigid oblique web bars and prestressed flexible oblique web bars. The latter has a small windward area, and the length of the members is not restricted by the slenderness ratio. Therefore, the use of prestressed flexible oblique web bars requires more steel. The rigid oblique web is less.
The tower is a cantilever structure, and the bending moment and shear force of the tower body increase downward along the height of the tower body. The increase of the bending moment changes in a parabolic form, and the increase of the shear force presents a linear relationship. Therefore, the internal force of the tower column (mainly bearing the bending moment of the tower body) presents a quadratic curve, and the internal force of the inclined rod (mainly bearing the tower body shear force) changes linearly.
The most commonly used structure of communication towers is the truss tower. The lower column of the truss tower bears a lot of force, and the force on the oblique rod is relatively small. When the lower oblique rod is long, it is more economical to use prestressed flexible oblique webs.
It is best to use pre-stressed flexible inclined rods. On the one hand, the flexible inclined rods are prevented from exiting work once they are compressed. On the other hand, non-prestressed flexible inclined rods have slenderness ratio restrictions, while prestressed inclined rods have no slenderness ratio restrictions. In addition, the rigidity of the prestressed flexible oblique web pole tower is greater than that of the non-prestressed oblique web pole tower. Therefore, it is best to apply prestress if flexible oblique web poles are used.
