Cable tray load and selection

The load on the cable tray is divided into loads, dynamic loads and additional loads.

Static load refers to the type of cable, the number of cables, the weight of each outer diameter per unit length laid in the cable tray, and the different routes according to the cable are listed separately.

Dynamic load refers to the weight of construction and maintenance personnel during cable bridge installation and maintenance. For light cable trays, dynamic loads are generally not considered, that is, they are not allowed to stand on the bridge. If it is necessary to consider the station, the span should be appropriately reduced.

The additional load is only the load formed by ice, snow, wind and electromagnetic force. It is related to the natural meteorological conditions of the installation site and the nature of the charged body. The design should be calculated according to various conditions.

Steps to select the bridge:

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

(2) Calculate the uniform load (kN/m2) of each layer of cable, and initially determine the type and specifications of the bridge.

(3) Check the bridge strength according to the maximum cable total uniform load value. The test formula is as follows:

Q uses =q1+q2

In the formula:

Q1 -- the uniform load of the cable (maximum of the uniform load of each layer) (kN / m2), the uniform load is the load of the pallet, ladder or cable trough;

Q2--When considering cable laying or overhaul, the human weight equivalent uniform load (kN/m2), q2 value calculation, the human weight is generally p=90kg.

Converted according to the condition that the maximum bending distance is equal:

Let pι/4=q2ι2/8 then q2=2p/ι

∵P=90kg

∴q2=180/ι

In the formula:

P--1 person's load (kg)

Ι--1 support point spacing (maximum if the fulcrum spacing is not equal) (m)

Equivalent uniform load of q2--1 person (kg/m)

According to the pre-determined bridge model, specifications and fulcrum spacing, consult the manufacturer's sample data, and check the spacing and bridge model repeatedly until the load requirements are met.

(4) Deflection

How to determine the deflection value, there is no clear regulation at present. In the heavy-weight zone, it is obvious that the reduction of the winding should be considered. This means that the amount of steel will increase accordingly. Therefore, the maximum allowable stress of the steel should be fully utilized in the calculation, and it is guaranteed Sufficient safety factor, generally the ratio of the maximum deflection to the span (support point spacing) is preferably 1/250~1/150.