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Design and calculation of wind load on high pole lamps

time:Nov 15, 2022 Views:

High pole lamp refers to the high pole lighting facilities with the pole height equal to or greater than 20m, which are used as large area lighting facilities for urban roads and highways, squares, stadiums, airports, ports and docks. The high pole lamp belongs to the high-rise structure, so the load design of the high pole lamp must meet the load design requirements of the high-rise structure. Loads on high-rise structures can be divided into the following three categories.

Design and calculation of wind load on high pole lamps(图1)

(1) Permanent load: dead weight of structure, weight of fixed equipment, weight of materials, weight of soil, earth pressure, tension of line, etc.

(2) Variable load: wind load, ice load, common earthquake action, snow load, installation and maintenance load, live load of tower floor or platform, temperature change, foundation settlement, etc.

(3) Accidental load: conductor breakage, cable breakage, impact, explosion, rare earthquake action, etc.

Snow load is the weight of snow on the exposed surface of the building roof or other structures. The snow load value S is multiplied by the snow weight of the ground area, that is, the basic snow pressure S o, and the snow distribution coefficient of the roof area μ R Determine:

S = μ r S o

The basic snow pressure generally refers to the specifications or local meteorological records. The basic snow pressure for 10, 50, and 100 years in some large and medium-sized urban areas in China is specified. For general structures, the basic snow pressure of 50 years is taken. For temporary buildings, warehouses, and unimportant structures, the value can be taken as 10 years or 30 years, or adjusted appropriately.

The main factors that affect the snow load of structures are the local snow weight and the snow distribution on the structural members, which are directly related to the value of snow load and the safety of structures.

Ice load refers to the weight of ice on the surface of tower members, cables and wires. In winter or early spring, under specific climatic conditions, it is formed in some areas by freezing rain, freezing drizzle, fog, cloud or melting snow with the temperature below 0 ℃, and its value can be determined according to the thickness and volume weight of ice coating.

Ice load is often an important load for structures such as transmission towers and lines. Because ice coating increases the cross-section of members and cables, or closes the gaps of some lattices, not only the weight of the structure or components increases, but also the wind load is significantly increased due to the increase of the wind shielding area of the structure, which makes the structure more unfavorable. The damage of earthquake load to high-rise structures is very serious, and the damage often hides potential dangers. The earthquake theory mainly includes the following three parts.

(1) Static theory. This theory does not consider the dynamic characteristics of buildings. It assumes that the structure is absolutely rigid, that the building motion is absolutely consistent with the ground motion during an earthquake, that the maximum acceleration of the building is equal to the maximum acceleration of the ground motion, and that the maximum load on the building is equal to the product of its mass and the maximum acceleration of the ground. This theory is only applicable to low and rigid buildings.

(2) Response spectrum theory. It not only considers the dynamic characteristics of the ground during the earthquake, but also considers the dynamic characteristics of the structure itself. It is one of the most widely used seismic design methods in current engineering design. The response spectrum theory is a method to analyze the structural response based on the response of single particle system under actual earthquake action. In seismic design, only the maximum load value under earthquake action is usually required, and its value is: F=ma max=w() ga max. In the formula, w is the mass of particle, which is called horizontal earthquake influencing factor.

(3) Direct dynamic analysis theory. In the analysis of long-span flexible structures, due to the influence of nonlinear factors, the calculation error of response spectrum method is large. The direct dynamic analysis theory can overcome the shortcomings of the response spectrum theory. The displacement, velocity and acceleration of the structural node at each time during the earthquake can be directly obtained, so as to calculate the vertical seismic action at each time and the seismic internal force of the component. These theories are called direct dynamic analysis theories.

Temperature changes, solar radiation, heat source and other factors shall be considered for temperature effect. The temperature effect on the structure or component shall be expressed by its temperature change. The linear thermal expansion coefficient of materials shall be used when calculating the temperature effect of structures or components. For large or super large structural members composed of different material components, the temperature effect between different component materials and the change of temperature field of the whole structural member shall be considered at the same time.

As one of the variable loads of the structure, the combination of temperature effect and other variable loads shall be considered according to the possible simultaneous situations during the construction and use of the structure.

As it is found in practical application that wind load is the largest and most critical factor affecting the intensity of high pole lamps, we will take the 40m high pole lamp as an example to design and calculate the wind load of high pole lamps.

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