一、了解電纜橋架的荷載

1、 Understand the load of cable trays

電纜橋架的荷載分為荷載、動荷載和附加荷載。

The load of cable tray is divided into load, dynamic load, and additional load.

靜荷載是指敷設(shè)在電纜橋架內(nèi)的電纜種類、根數(shù)、每根的外徑重量/單位長度,按電纜敷設(shè)的不同路由分別列表統(tǒng)計。

Static load refers to the type, number, and outer diameter weight/unit length of cables laid in cable trays, which are listed and counted according to different routes of cable laying.

動荷載是指電纜橋架安裝和維護過程中施工維修人員的重量。對于輕型電纜橋架,一般不考慮動荷載,即不允許在橋架上站(行)人,如果需要考慮站人,則應(yīng)將跨距適當(dāng)縮小。附加荷載僅在室外是指冰雪、風(fēng)和電磁力所形成的荷載,它與安裝場所的地區(qū)自然氣象條件和帶電體的性質(zhì)有關(guān),設(shè)計中應(yīng)根據(jù)各種條件加以計算。

Dynamic load refers to the weight of construction and maintenance personnel during the installation and maintenance of cable trays. For lightweight cable trays, dynamic loads are generally not considered, which means that people are not allowed to stand (walk) on the tray. If people need to be considered, the span should be appropriately reduced. The additional load only refers to the load formed by ice, snow, wind, and electromagnetic force outdoors, which is related to the natural meteorological conditions of the installation site and the properties of the charged body. It should be calculated according to various conditions in the design.

二、選用橋架的步驟

2、 Steps for selecting cable trays

1.確定橋架寬度、層數(shù)、支撐點的型式和間距、以及電纜在各層橋架上的分布。

1. Determine the width, number of layers, type and spacing of support points, as well as the distribution of cables on each layer of the bridge.

2.計算每層電纜的均布荷載(kN/ m2),初步確定橋架的型號、規(guī)格。

2. Calculate the uniformly distributed load (kN/m2) of each layer of cable and preliminarily determine the model and specifications of the cable tray.

3.按非常大的電纜總均布荷載值來驗算橋架強度。驗算式如下：

3. Verify the strength of the cable tray based on the maximum total uniformly distributed load value of the cable. The verification formula is as follows:

Q使用=q1+q2式中：q1 --電纜的均布荷載（各層的均布荷載中取非常大值）（kN/m2），均布荷載是托盤、梯架或電纜槽的荷載；

In the formula q1+q2, q1 represents the uniformly distributed load of the cable (taking the maximum value among the uniformly distributed loads of each layer) (kN/m2), which is the load on the tray, ladder, or cable tray;

q2--考慮電纜敷設(shè)或檢修時,人的重量等效的均布荷載（kN/m2）,q2值的計算，人的重量一般按p=90kg計。

Q2- When considering cable laying or maintenance, the uniformly distributed load equivalent to the weight of a person (kN/m2), the calculation of q2 value, the weight of a person is generally calculated as p=90kg.

表示集中荷載和均布荷載的彎距如圖2

The bending moment representing concentrated load and uniformly distributed load is shown in Figure 2

按非常大彎距相等的條件折算：

Converted based on the condition of equal maximum bending distance:

令pι/4=q2ι2/8則q2=2p/ι

If p iota/4=q2 iota 2/8, then q2=2p/iota

∵P=90kg

∵P=90kg

∴q2=180/ι

∴q2=180/ι

式中：P--1人的荷載(kg)

In the formula: Load of P-1 person (kg)

ι--1個支撐點間距(若支點間距不等時取非常大值)(m)

The distance between one support point (taking the maximum value if the distance between the support points is not equal) (m)

q2--1 人的等效均布荷載(kg/m)

Q2-- Equivalent uniformly distributed load of 1 person (kg/m)

根據(jù)上述初步確定的橋架型號、規(guī)格及支點間距,查閱生產(chǎn)廠家的樣本資料,反復(fù)核查間距和橋架型號,直至滿足負(fù)荷要求為止。

Based on the preliminary determination of the bridge model, specifications, and support spacing mentioned above, consult the manufacturer's sample data, repeatedly check the spacing and bridge model until the load requirements are met.

4.撓度

4. Deflection

撓度值如何取定,目前尚無明確的規(guī)定,在重負(fù)區(qū)顯然應(yīng)考慮減小繞度,這意味著鋼材的用量會相應(yīng)增加,因此,計算時只要充分利用鋼材的非常大允許應(yīng)力,并保證有足夠的安全系數(shù),一般非常大撓度與跨距(支撐點間距)之比取1/250~1/150為宜。

There is currently no clear regulation on how to determine the deflection value. In heavy load areas, it is obvious to consider reducing the deflection, which means that the amount of steel used will increase accordingly. Therefore, when calculating, as long as the maximum allowable stress of steel is fully utilized and sufficient safety factors are ensured, the ratio of maximum deflection to span (support point spacing) is generally 1/250~1/150.

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