3　Basic Design Provisions

3.1　Design Principles

3.1.1　The limit state design method based on the probability theory is adopted for the structure design for mobile communication engineering steel tower and mast.Reliable indicators are used to measure the reliability of the structural components，and the partial coefficient design expression is adopted for calculation.

3.1.2　The design reference period of structure for mobile communication engineering steel tower and mast is 50 years.

3.1.3　The design service life of structure for mobile communication engineering steel tower and mast is generally 50 years.

3.1.4　The safety level of structure for mobile communication engineering steel tower and mast is Level Ⅱ.

3.1.5　The structure for mobile communication engineering steel tower and mast shall be designed in accordance with the bearing capacity limit state and normal use limit state.

1　Bearing capacity limit state：this limit state corresponds to a situation where the structure or structural component has reached the maximum bearing capacity or a deformation where the structure or structural component shall not bear loads any more.

2　Normal use limit state：this limit state corresponds to a situation where the structure or structural component has reached relevant specified limit value of its deformation or durability.

3.1.6　The basic combination of load effect is adopted for design of the bearing capacity limit state of the structure for mobile communication engineering steel tower and mast，and the most unfavorable value in the expression is determined according to the following limit state.

1　Combination dominated by variable load effect：

2　Combination dominated by permanent load effect：

Where，γ0——structure importance coefficient，which shall not be less than 1.0；

γG——partial coefficient of permanent load，adopted according to Table 3.1.6：

γQi——the partial coefficient of variable load i.Thereinto，is the partial coefficient of the variable load.Take 1.4 in general conditions，and take 0 in the case that the variable load effect is propitious to the structure；

SGk——effect of the permanent load standard value；

SQik——item i is the effect of the variable load standard value.Thereinto，is the effect of the first variable load standard value，and the load effect may control various variable load effects；

ψCi——the combined value coefficient of the variable load，which shall be adopted in accordance with Article 3.1.7 and based on different load combinations；

n——number of variable loads in the combination；

R——design value of the structure or component resistance.

3.1.7　The following two different basic load combinations shall be considered for design of the limit state of the component bearing capacity of structure for mobile communication steel tower and mast，and the coefficients of the combined value of the variable load shall be adopted in accordance with Table 3.1.7.

3.1.8　For seismic calculation of the structure or component bearing capacity，the following limit state design expression shall be adopted：

Where，γG——partial coefficient of the gravity load，the value is the same as above；

SGE——gravity load representative value effect.The sum of the structure self-weight and the combined value of various vertical variable loads shall be taken as the gravity load representative value，which is specified as follows：-For the structure self-weight（self-weight of the structure components and mating parts，fixed equipment and so on），take 1.0；-For the equivalent uniform load of the platform，take 0.5.or 1.0 as the case may be；-For the snow load of the platform，take 0.5；

γEh，γEV——the partial coefficients of the horizontal and vertical seismic actions respectively，which are adopted according to Table 3.1.8；

SEhk——horizontal seismic action standard value effect；

SEVk——vertical seismic action standard value effect；

γW——partial coefficient of the wind load，take 1.4；

SWk——wind load standard value effect；

ψW——combined value coefficient of the wind load in the anti-seismic basic combination，may take 0.2；

γRE——anti-seismic adjustment coefficient of the bearing capacity，take 0.8 for steel components，0.9 for connection welding seam and 0.85 for the connecting bolt.

3.1.9　The normal use limit state shall be conducted in accordance with the standard combination and quasi-permanent combination of the load effect.Besides，the limit value required in the specification shall be conformed to：

1　The standard combination shall be used to calculate deformation of the structure or components.The expression is：

2　The quasi-permanent combination is used for calculation of foundation deformation.The expression is：

Where，δ——variable limit value of the structure or component；

S——specified limit value of foundation deformation；

ψqi——quasi-permanent value coefficient of any variable load i in case of quasi-permanent effect combination，which is taken according to Table 3.1.9.

3.1.10　The control conditions of the normal use limit state of the structure for mobile communication engineering steel tower and mast shall conform to the following provisions：

1　Under the action of the standard load combination，mainly the wind load，the horizontal displacement of any point in the tower and mast structure shall not be larger than the value specified in Table 3.1.10.

2　Under the action of standard load combination，mainly the wind load，when the microwave antenna is hung on the tower and mast structure，the deflection angle and torsion angle of the tower（pole）at the position of the microwave antenna shall meet the process design requirements and shall not be larger than the half-power angle of 1/2 microwave antenna.

3　The foundation deformation of the steel tower and mast structure shall conform to provisions in Article 7.2.6 of the specifications.