一、了解电缆桥架的荷载

1、 Understand the load of cable trays

电缆桥架的荷载分为荷载、动荷载和附加荷载。

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

静荷载是指敷设在电缆桥架内的电缆种类、根数、每根的外径重量/单位长度,按电缆敷设的不同路由分别列表统计。

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.

动荷载是指电缆桥架安装和维护过程中施工维修人员的重量。对于轻型电缆桥架,一般不考虑动荷载,即不允许在桥架上站(行)人,如果需要考虑站人,则应将跨距适当缩小。附加荷载仅在室外是指冰雪、风和电磁力所形成的荷载,它与安装场所的地区自然气象条件和带电体的性质有关,设计中应根据各种条件加以计算。

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、选用桥架的步骤

2、 Steps for selecting cable trays

1.确定桥架宽度、层数、支撑点的型式和间距、以及电缆在各层桥架上的分布。

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.计算每层电缆的均布荷载(kN/ m2),初步确定桥架的型号、规格。

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.按的电缆总均布荷载值来验算桥架强度。验算式如下：

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 --电缆的均布荷载（各层的均布荷载中取值）（kN/m2），均布荷载是托盘、梯架或电缆槽的荷载；

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--考虑电缆敷设或检修时,人的重量等效的均布荷载（kN/m2）,q2值的计算，人的重量一般按p=90kg计。

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.

表示集中荷载和均布荷载的弯距如图2

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

按弯距相等的条件折算：

Converted based on the condition of equal maximum bending distance:

令pι/4=q2ι2/8则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人的荷载(kg)

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

ι--1个支撑点间距(若支点间距不等时取值)(m)

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

q2--1 人的等效均布荷载(kg/m)

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

根据上述初步确定的桥架型号、规格及支点间距,查阅生产厂家的样本资料,反复核查间距和桥架型号,直满足负荷要求为止。

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.挠度

4. Deflection

挠度值如何取定,目前尚无明确的规定,在重负区显然应考虑减小绕度,这意味着钢材的用量会相应增加,因此,计算时只要充分利用钢材的允许应力,并保证有足够的系数,一般挠度与跨距(支撑点间距)之比取1/250~1/150为宜。

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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