Design requirements for wire and cable tray

bridge structure

cable tray is divided into a trough, tray and ladder-type structure, bracket, corbel and installation accessories. (See Figure 1), the selection should pay attention to the bridge all parts whether serialization, universal, standardized sets of requirements. Buildings bridge independence assumption, can also be attached in a variety of construction (structures) and the bracket on the pipe rack, should reflect the structure is simple, beautiful shape, configuration flexibility and easy maintenance, all parts required to galvanized installed in the open air outside the building of the bridge, if it is in the neighboring beach or belonging to corrosion District, the material must have anti-corrosion, resistance to moisture, good adhesion, impact resistance, high strength physical characteristics.

also can be used in order to reduce the weight of aluminum cable and FRP bridge, its dimensions, load characteristics are basically similar to the steel bridge, the proportion of aluminum, steel (A1 = 2.7, Fe = 7.86, by weight, aluminum steel ratio of about 1:3, translated in accordance with the market price of the two materials, aluminum tray cost costs 2.0 times higher price compared with similar galvanized steel bridge, aluminum tray with a beautiful, light weight, easy to install advantages, in recent years, aluminum tray in some engineering to apply them.

, bridge load and load characteristics

1, cable tray load

cable tray loading divided into load, dynamic load and additional load.

static load refers to the kind of laying cable in the cable tray, root number, root diameter Weight / unit length, different cabling routing list statistics.

dynamic load refers to the weight of maintenance personnel in the construction of the cable tray installation and maintenance process. For light duty cable tray, generally do not consider dynamic load (rows) to allow the station bridge, if you need to consider the station, the span should be appropriately reduced. The additional load only in the outdoor means snow, wind and the electromagnetic force is formed by the load, which is related to the nature of the installation site region natural weather conditions and charged body, the design should be calculated according to various conditions.

steps, optional trays

(1) determine the bridge width, number of layers, type and spacing of the support points, as well as cable distribution in the layers of the bridge.

(2) on each floor cable uniformly distributed load (kN / m2), initially identified the bridge models, specifications.

(3) the largest cable total uniform load value to checking bridge strength. Checking formula is as follows:

Q uses = q1 + q2

where: q1 - cable uniformly distributed load (layers uniformly distributed load in maximum) (kN /

m2), are uniformly distributed load tray, ladder or cable slot load;

q2 - cable laying or repair, the weight of the human equivalent uniformly distributed load (kN /

m2), the q2 value calculated weight generally p = 90kg.

concentrated load and uniform load bending moment shown in Figure 2

equal conditions of maximum bending moment translation:

make pι / 4 = q2ι2 / 8 Ze q2 = 2p / ι

∵ P = 90kg

∴ q2 = 180 / ι

the

formula: P - 1 load (kg)

ι - 1 support point spacing (if the fulcrum of a maximum spacing ranging) (m)

q2 - 1 equivalent uniform load

consult the manufacturer of the sample data

initially identified above the bridge models, specifications and fulcrum spacing, and repeated verification spacing and bridge models, up to meet the load requirements.

(4) deflection

how to take the set

deflection value, no clear provisions in burden should obviously consider reduce wound degrees, which means that the amount of steel will be a corresponding increase, calculated as long as the full use of the maximum allowable stress of steel and ensure that there are sufficient safety factor the general maximum deflection to span ratio (strong point spacing) take 1/250 to 1/150 is appropriate.

Third, the expansion and contraction of the bridge

due to changes in ambient temperature, steel cable tray will appear the phenomenon of thermal expansion and contraction. Outdoor bridge affected by temperature, such as environmental temperature of 40 ° C maximum, minimum temperature of -20 ° C, the maximum amount of shrinkage of the cable tray following formula is obtained:

Δt = 11.2 × 10-6 × 60deg (degrees) x 1000mm

conclude:

the

temperature difference of 60 ° C, Δι = 0.672mm / m

the

temperature difference is 50 ° C, Δι = 0.560mm / m

the

temperature difference of 40 ° C, Δι = 0.448mm / m

engineering cable tray line segment should consider the spacing of expansion joints, expansion joints is recommended according to the following take given:

when the temperature difference of 40 ° C for 50m;

when the temperature difference of 50 ° C for 40m;

when the temperature difference of 60 ° C for 40m;

, grounding

according to the relevant provisions of the specification, galvanized cable tray good ground.

(1) galvanized cable tray directly plate of each mounting bolts contact resistance

should be less than 0.005Ω, cable tray as the ground trunk (dusting cable trays are not suitable for grounding trunk), the resistance value of each cable tray can be calculated as follows:

r = P.L / S

formula: P = 15 × 10Ω-6/cm (20 ° C);

L = length calculated by 100mm;

S = cross-sectional area cm2.

(2) the ladder the tray unit resistance value are shown in Table 2.

ladder on the tray unit resistance value in Table 2

cable slot of

(3) unit resistance values ​​are shown in Table 3

(4) When the cable tray installation connection process overall, per root the ladder side (or the cable slot) resistance:

R = L (r +1 / 3r ')

formula:

R - ladder side, that is, the full length of the (cable slot) total resistance (mΩ);

r - resistance per unit length of the ladder side (mΩ / m)

r'- direct plate fixing bolt contact resistance.

five bridge design and installation requirements

cable tray as a wiring project supporting the project, currently no specific regulatory guidance, lack of versatility manufacturers specifications of the program, therefore, the design selection process should be based on the weak individual system cables seem the type, quantity, selected reasonably applicable bridge.

(1) determine the direction: easy maintenance, as well as cable routing density according to building floor plan, combined with air-conditioning piping and electrical lines set to determine the best route of the cable tray. Indoors as much as possible along the wall of the building, columns, beams and floor slabs erected, such as the promise should be in the pipeline or on the side of the Pipe Gallery erection

(2) load calculation: calculate the weight of unit length of the cable in the cable tray vertical section on the main trunk.

(3) to determine the width of the bridge: laying the cable number, cable diameter and spacing of the cable length to determine the length of the cable bridge models, specifications, corbel, pillars, spacing, bridge width and the number of layers .

(4) to determine the installation: fixed bridge, determined according to the set conditions of the workplace Choose suspended, vertical, the sidewall or mixed, connectors and fasteners are generally supporting supply, in addition to folding cover, selected according to the bridge structure.

(5) Draw cable tray level, cross-sectional view of the local sites should also draw a table space map, sets out the material.

2, when combined with the power cable tray each straight side of the power cables and weak cable should be the middle partition separated.

3, when the combination of weak cable and other low voltage cable bridge should strictly enforce choose weak cable outer shield of weak systems, to avoid mutual interference.

other installation

cable tray from

(1) outdoor entering the building, the the bridge outward slope shall not be less than 1/100.

(2) crossover cable tray and electrical equipment, during the clear distance of not less than 0.5m.

(3) two sets of cable tray laying of the same highly parallel, during clear distance of not less than 0.6m.

(4) is plotted in parallel graph routing of the bridge, to indicate the bridge starting point, end point, turning point, branch point and lift point coordinates or location size, elevation, can draw bridge laying isometric view, of material statistics will be more accurate.

line segments: indicate the total length of the bridge layers, elevation, models and specifications.

the

turning point and the branch point: models and specifications indicate the turn with the board.

lifting segment: marked elevation change, also available said local big drawing or cross-sectional view.

(5) bridge support points, such as column, corbel or non-standard support, the spacing of the architecture, installation, model specifications, elevation can be agreed that the description of the plane on the list, can also be segmented marked with different profiles chart, line diagram or graph bulk sample.

the

(6) cable cited under point position and cited, in general, a large number of available cable cited under the vertical bend the adapter plate and vertical cited shelves, a small amount of cable cited guides are available, or lead pipe acknowledgment is under way that can.

cable tray should

(7) is more than 2.2 meters above the ground, the bridge at the top from the ceiling or other obstacles should not be less than 0.3 meters, the bridge should not be less than 0.1 meters in width, the bridge cross-section of the fill rate should not exceed 50 %.

vertical laying of cable tray cable

(8), at the upper end of the cable, and at intervals of 1.5 meters should be fixed in the bracket on the bridge level laying the cable first, tail, turn and each interval 3 to 5 meters fixed.

(9) set in the ceiling, the slot cover open surface (80 mm vertical clearance should be maintained, trough-section should not exceed 50% utilization.

(10) cloth on the trunking cable can not lashing tank cable should be straight, tank cable should be straight, and try not to cross, the cable should not overflow trunking cable inlet and outlet slot location, the corner should lashing. Vertical

(11) in a horizontal, vertical, bridge and vertical trunking in laying line, deal with cable lashing. Four pairs of cable 24 to the beam 25 pairs or more main trunk cable, fiber optic cable and other signal cable should be based on the type of cable, cable diameter, cable core number splitting lashing. Banding spacing should not be greater than 1.5 m, buckle spacing should be uniform, moderately elastic.

laying

(12) bridge level, support spacing is usually 1.5-3m, vertical laying fixed buildings isomers spacing should be less than 2m.

(13) laying the metal trough, in the following cases consists of until the rack or hanger: trunking joints; spacing of 3m; leave trunking of two ports 0.5m at; corner.

5, material Statistics

(3) bridge: the statistics of the various the Model Specifications bridge the full-length, in addition to the standard length of the bridge, draw bridge number, an increase of 1% to 2% margin.

(4) column: column, such as the use of a unified specifications can be used The the bridge full length divided by the average column spacing, the draw column number, and then an increase of 2% to 4% margin. Different specifications of Column need respectively statistics.

(1) corbel: bridge full-length divided by a corbel average distance, and then an increase of 1% to 2% margin, extremely total demand.

(2) other components: by multiplying the number of its body by a certain percentage (depending Plant) to obtain the total number.

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