Force basis and calculation method of LED lamp pole with high height


LED lamp pole is relatively high, and the pressure afte […]

LED lamp pole is relatively high, and the pressure after installation is relatively large. Before design, the specific data should be fully calculated with the calculation method in the industry. Die casting man selects 20 m pole as a case study for high pole.

(1) basic data: the height of lamp panel is about 20m from the ground, the plane size of square foundation is 3M × 3M, the buried depth of foundation is 2.5m, the cross section of lamp pole is regular dodecagonal, which is simplified as a circle, the top diameter D is 200 mm, the root diameter is D400 mm, and the thickness is divided into two sections from the top to the bottom. δ = 6 mm, length 10.9 m, δ = 6 mm, length 10.9 M. The material is low alloy steel, Q / bqb303ss400. The yield strength is f = 245n / mm2, the design strength is f = 225N / mm2, FV = 125N / mm2, the diameter of lamp panel is 2200mm, the thickness is simplified to 200 mm, and the total weight of high pole lamp is about FK = 40kN.
(2) natural conditions: the local basic wind pressure Wo = 0.75kn/m2, the foundation soil is mucky clay soil, the characteristic value of ground bearing capacity FAK = 60kn / m2, the ground roughness is considered as class B, the buried depth of groundwater level is greater than 2.5m, and the bulk density of foundation soil is γ M = 18kn / m3.

(3) design calculation basis:
① Load code for the design of building structures (GB 5009-2001)
② Code for design of building foundation (GB 5007-2002)
③ Code for design of steel structures (GB 50017-2003)
④ Code for design of tall structures (gbj135-90)
2、 Calculation of standard value of wind load
The basic formula: wk = β Z · μ s · μ Z · ur · wo
Where: wk is the standard value of wind load (KN / m2);
β Z - wind vibration coefficient at height Z;
μ s - shape coefficient of wind load;
μ Z - variation coefficient of wind pressure height;
μ R · - adjustment coefficient of return period for high-rise structures, 1.2 for important high-rise structures. (1) lamp panel: the height is 0.2m, μ z = 1.42, μ s = 0.5, μ r = 1.2
Where ξ is the coefficient of pulsation increase;
ν - fluctuation influence coefficient;
φ Z - mode coefficient;
(2) lamp pole: simplified as uniform load, the height is 10.9m,
3、 Internal force calculation
(1) bottom (δ = 6 mm)
Bending moment design value: M = m lamp panel + m lamp pole
Shear design value: v = V lamp panel + V lamp pole
(2) δ = 6 mm and δ = 6 mm
Design value of bending moment:
Shear design value:
4、 Strength review under wind load (without considering the self weight of high pole lamp)
(1) bottom (δ = 6 mm)
The moment of inertia of cross section I = × (D-D) = (6504-6344) = 8.31 × 108mm4. The maximum tensile stress б max = · y = 426 × 106 × 325 / (8.31 × 108) = 167n / mm2
Maximum shear stress τ max = 2 · V / a = 2 × 27 × 103 / [× (6502-6342)] = 3.3n/mm2max
(2) δ = 6 mm and δ = 6 mm
The moment of inertia of cross section I = × (D-D) = (4004-3884) = 1.44 × 108mm4. The maximum tensile stress б max = · y = 51 × 106 × 200 / (1.44 × 108) = 70.8n/mm2; the maximum shear stress τ max = 2.v / a = 2 × 9 × 103 / [× (4002-3882)] = 2.4n/mm2ax
5、 Checking calculation of foundation bearing capacity
(1) foundation plane size: B × H = 3 × 3M,
The bending modulus of foundation bottom surface w = BH2 = 10.67m3,
The characteristic value of foundation bearing capacity FAK = 60kn / m2,
(2) weight of foundation and soil on the foundation
(3) according to the load effect standard combination, the bending moment acting on the bottom of foundation is: 1
(4) the modified characteristic value of foundation bearing capacity is as follows
(5) the maximum and minimum pressure acting on the bottom edge of foundation corresponding to the standard load effect combination: pkmax=+
==53 + 33 = 86kn / m2 < 1.2fa = 115KN / m2 can meet the requirements.
Pkmax = + = = 53-33 = 20KN / m2 > 0 can meet the requirements.

6、 Calculation description
(1) according to the load code for building structures, when the basic wind pressure Wo of most cities in China is less than or equal to 0.75kn/m2 according to the 50 year return period, if the basic wind pressure Wo of mountainous areas, remote areas, coastal seas and islands is greater than or equal to 0.75kn/m2, the above calculation is multiplied by the adjustment coefficient.
(2) the safety level of high pole lamp shall be grade 1 according to the code for design of high-rise structure.
(3) the basic data required for foundation design are: characteristic value of foundation bearing capacity, physical parameters of foundation soil, and standard combination value of upper load, including bending moment, shear force and axial force.
(4) the foundation selection shall be determined according to the soil conditions and structural requirements of the construction site. Generally, it is a square concrete independent foundation. The bottom area size and reinforcement shall be determined by calculation or drawings provided by the manufacturer.