Week 11 Challenge

Analysis & Design of Pipe Rack Structure in STAAD.pro

1.Friction load determination

Aim: To calculate the friction load on the axis.

Given: A pipe carrying LNG rests on the shoe having vertical force of 125 kN.

Solution: Friction factor/coefficient and friction load on Piping:

Materials	Friction factor
Steel to Steel	0.3
Teflon to Steel	0.1

(A)  When Steel pipe is resting on steel:

Friction force in longitudinal direction (Ff) = Coefficient of friction x Gravity Load = 0.3 x 125 = 37.5 kN

Friction load in transverse direction = 10% of piping operation load = 0.1 x 125 = 12.5 kN

Steel pipe is resting on Teflon:

Friction force in longitudinal direction (Ff) = Coefficient of friction x Gravity Load = 0.1 x 125 = 12.5 kN

Friction load in transverse direction = 10% of piping operation load = 0.1 x 125 = 12.5 kN

Result:

• Friction load in longitudinal and Transverse direction are 37.5 kN & 12.5 kN respectively when pipe is resting on steel
• Friction forces are 12.5 KN & 12.5 KN respectively when pipe is resting on Teflon.

2.Support Types

Aim: To identify the type of support as Spring, Guyed, Stop or Semi Anchor (Guyed + Rest + Stop ) or Rigid Strut from following images.

Given:

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Solution:

• Fig-1 has Spring Support which permit the pipe to move in vertical direction.
• Fig-2 has Rigid Support which allow small angular displacement and thermal movement.
• Fig-3 has Stop support which restrained the movement of pipe in axial direction but allows the pipe movement in lateral direction.
• Fig-4 has Semi Anchor Support which restrict the pipes to move in axial as well as transverse direction. 
• Fig-5 has Guid support which restrained the lateral movement in two directions therefore also limits the rotational movement of pipe but permit axial movement of pipe.
• Fig-6 has associated with Anchor Support which does not permit the pipe to move in any direction thus movement in all 6 degree of freedom is restricted.

3.Design of a pipe rack

Aim: To Model and Design a typical pipe rack bent in Oil Plant using STAAD Pro.

Given:

Figure 1

Figure 2

Height of Column      =     9 m

Height of First tier     =     6 m

Height of Second tier =      7.5 m

Height of Third tier     =      9 m

Width of Pipe Rack      =      7.5 m (C/C of Column in width of pipe rack)

Span of each Bay        =      6 m

Number of bays          =       7

Top tier of pipe rack has 3 number of cable trays each 150 mm wide

Second tier of pipe rack has 4 pipes, one of 24 " dia and one of 12 " dia, remaining two pipes are of dia 8"

First tier of pipe rack has 6 pipes, one of 18 " dia and remaining 5 pipes are of dia smaller than 8"

Solution: 

Step 1: Following Loads are to be assigned:

1. Structural Dead Load: Load due to weight of Structure excluding weight of pipe
2. Operating Dead Load: Weight of pipe, fluid in it and insulation. UDL of 1.9 kN/m2 is assumed for pipe of dia 8". Point load is considered at appropriate location for pipe larger than 8" dia pipes which will be reported by Piping Engineer.
3. Empty Dead Load:Weight of empty pipe without fluid in it but including insulation, it is assumed as 60% of operating load.
4. Test Dead Load: In case test medium in pipe is not known, water with density of 1000 Kg/m3 is considered as test medium so generally test load is same as operating dead load.
5. Cable Tray Load:UDL of 1 kN/m is considered

Step 2: Load Calculations for Dead load, Operating load and Empty Load.

Dead Load Calculation:

Lets assume Selfweight as 1.1 factor. Where 10% extra for connections.

Longitudinal members are assumed to ISMB 225.

Weight of ISMB 225 is 31.2 kg/m = 0.312 kN/m

Load due to Longitudinal member = 0.312 x 6 = 1.87 kN

Operating Load Calculation:

Weight of Pipe upto 8" = 1.9 kN/m2

Load acting on deck slab = 1.9 x 6 = 11.4 kN/m

Weight of Pipe 12" = 1.49 kN/m2

Load acting on deck slab = 1.49 x 6 = 8.94 kN/m

Weight of Pipe 18" = 2.66kN/m2

Load acting on deck slab = 2.66 x 6 = 15.96 kN/m

Weight of Pipe 24" = 4.06kN/m2

Load acting on deck slab = 4.06 x 6 = 24.36 kN/m

Empty Load Calculation:

Empty Load is taken as 60% of Operating load = 0.6 x 11.4 = 6.84 kN/m

Test Load Calculation:

Test Load is the load of pipe carrying water as Operating load = 11.4 kN/m

Cable Tray Load Calculation:

Cable Tray load = 1 x 6 = 6 kN/m

Step 3: Open Staad Software, create a new file.

In Geometry tab model a Pipe rack structure using Nodes, Beams command as shown below.

Step 4: Select Properties Tab, click Section Database and Choose the sections required. Then assign the sections to the members.

Step 5: Then Create a Fixed support and Fixed but support. Now assign the supports to the model.

Step 6: Now add the Load cases and assign the load cases to the model as shoen below.

Step 7: Now go to Analysis tab and select define commands.Then select Perform analysis and click ok. Then in Design tab, define the parameters required and click Run Anlaysis. Output show 0 Errors and 0 Warnings.

Result: Modelling and Designing of a typical pipe rack bent in oil plant was done successfully.