aspects of piperack design
DESCRIPTION
Steel Piperack analysisTRANSCRIPT
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Dipesh H Dahanuwala Date : 25-June-2013
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Agenda
Aim
Key Objectives
Aspects of Pipe racks
Optimization Idea
Summary
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Aim
To present different aspects of pipe rack
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Key Objective
Purpose of Pipe rack
Materials of Construction
Execution Stages
Analysis and Design Concepts
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Purpose of Pipe rack
To support group of parallel pipes running at different elevations with emerging or merging branches
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Materials of Construction
Concrete
Cast-in-situ
Precast
Application : Concrete Pipe racks are
made in case of corrosive environment
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Materials of Construction
Structural Steel
Structural Steel has been used for pipe rack in all projects executed by NPCC
Reason :
FEED requirements
Other advantages are :
Speed of Construction
Better Quality Control
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Execution Stages
Preliminary sizing of Pipe rack based on geometry and loading firmed up by Piping
Raise PR for procurement of items
Detailed Engineering
Construction Engineering
Fabrication / Painting
Erection of Pipe rack at site
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Analysis and Design Concepts
Geometrical Planning
Loading
Structural Design
End Connection
Base Plate and Anchor Bolt Design
Foundation Design
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Analysis and Design Concepts
Geometrical Planning
Grid Location
Tier Elevation
Planning of Beams
Planning of Elevation Bracings
Planning of Plan Bracings
Expansion Joint
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Geometrical Planning
Grid Location : by Piping Discipline
Basis :
Width of pipe rack : No. of pipes to be routed with future allowance.
Grid distance :
Based on Piping Support requirements.
Road crossing horizontal clearance
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Geometrical Planning Grid Location
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Geometrical Planning
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Geometrical Planning
Tier Elevations : by Piping Discipline
Basis :
To maintain the minimum headroom for the pipes crossing the roads
Tie-in elevation
Sloping lines
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Geometrical Planning Tier Elevation
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Geometrical Planning
Planning of Beams : Location of main beam as per Main Grid distances
provided by Piping
Location of secondary beam between Main Grid beams depends on support for small bore pipes provided by Piping
Longitudinal beams to stabilize the Grid Frames, transfer longitudinal forces to vertical braced bay and support secondary beam.
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LARGE BORE PIPES
SMALL BORE PIPES
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Geometrical Planning
Planning of Elevation Bracings In the middle of pipe rack to allow thermal expansion of
pipe rack on either side thus minimizing thermal restraint in longitudinal direction
To transfer longitudinal forces to foundation
To provide stability to pipe rack in longitudinal direction
Avoid multiple braced bay on same pipe rack to avoid thermal forces in longitudinal beams and braces
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Geometrical Planning
Planning of Plan Bracings
Purpose :
To effectively transfer horizontal forces to column
Make better use of structure by introducing truss action instead of bending.
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Geometrical Planning
Expansion Joint
Purpose :
To account for thermal expansion of structure
Basis :
As per Company requirement
Methods :
Provide slotted hole connection in the longitudinal beam at all levels at identified location
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Pipe rack with slotted joint as expansion joint
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Loading
Loads Generated by Civil Discipline
Dead Load (DL)
Live Load (LL)
Temperature Load on Structure (TL)
Earthquake Load (EQ)
Wind Load (WL)
Contingency Load (CL)
Miscellaneous Load (ML)
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Loading
Loads Furnished by Piping Discipline
Pipe Empty Load (PE)
Pipe Operating Load (PO)
Pipe Hydro test Load (PT)
Pipe Anchor / Guide Load (PA)
Pipe Friction Load (PF)
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Loading
Dead Load (DL)
Weight of Structure
Weight of Fireproofing
Weight of Grating and Handrail in case of platforms on pipe rack
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Loading
Live Load (LL)
Applicable in case platform on pipe rack
Normally LL = 5 kPa, but depends on platform use defined by Piping.
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Loading
Temperature (Thermal) Load on structure (TL) Due to difference between highest and lowest mean
temperature and based on Design Basis. Typical value for UAE is taken as 60 deg C.
Thermal loads can be minimized by providing Flexible Structure i.e. reduce structural redundancy.
Note : Length of slotted hole connection is based on deflection due to thermal expansion / contraction of structure.
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Loading Thermal Load
Good Design
Release of thermal stresses (free to move in both directions)
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Loading Thermal Load
Bad Design
Thermal stresses are arrested (restrained by bracings at ends)
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Loading
Pipe Empty & Cable Tray Load (PE)
< 12 Pipes : ~ 1.2 kPa
>=12 Pipes : concentrated load (as per Pipe Stress Analysis)
Empty Equipment Load, if any
Cable Tray Load : 1 kPa for each level of cable tray
Critical for checking uplift on foundation
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Loading
Pipe Operating Load (PO)
< 12 Pipes : ~ 2 kPa
>=12 Pipes : concentrated load (as per Pipe Stress Analysis)
Operating Equipment Load, if any
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Loading
Pipe Hydro Test Load (PT)
To account for pressure testing of pipes
As per Pipe Stress Analysis
Hydro-test weight of equipment
For larger dia pipes (>12) only one pipe hydro tested and other pipes empty (To be confirmed by Piping Discipline and reflected in piping isometric and hydro-test specification)
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Loading
Pipe Anchor / Guide Load (PA)
Load to be defined by Piping Discipline
Anchoring lug configuration to be confirmed by Civil in case of high anchor loads
Only Top flange effective Both Flanges effective
Anchor Lug
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Loading
Pipe Friction Load (PF)
Cause : Hot lines sliding across beam
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Loading Pipe Friction (PF)
For Global Check Longitudinal direction = 5% of Pipe operating Load
Transverse direction = 5% of Pipe operating Load
0.05 P
0.05 P
P = Piping Operating Load
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Loading Pipe Friction Load
For Local beam check
1
2
3
4
5
6
8
7
0.3 P
0.1 P
0.2 P 0.1 P
P = Piping Operating Load
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Loading Pipe Friction Load
For Local beam check
In Longitudinal direction :
10% of the operating weight (no of pipes >= 7)
20% of the operating weight (no of pipes = 4 to 6)
30% of the operating weight (no of pipes
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Loading
Earthquake Load (EQ)
As per project geotechnical investigation and design basis
Earthquake load to be generated for following conditions
a) Erection : DL + PE
b) Operating Case : DL + PO + LL
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Loading Earthquake Load (EQ)
As per IBC 2009 & ASCE-7-10, typical parameters for ZADCO site is as follows : Site Class = D
Ss (Short period Spectral Acceleration) = 0.32
S1 (1 sec Spectral Acceleration) = 1.32
I (Importance Factor) = 1 (depends on occupancy category)
R (Response Reduction Factor)
= 3.5 (for ordinary moment resisting frames)
= 7.0 (for special truss frames)
Earthquake Load is generated in STAAD-Pro as per parameters defined in Design Basis.
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Loading
Wind Load (WL) As per project design basis
As per ASCE-7-10, typical parameters for ADCO site is as follows :
Basic wind speed (V) = 44.7 m/sec
Importance factor (I) = 1.15
Exposure Category = C
Wind Directionality Factor (Kd) = 0.85
Topographic factor (Kzt) = 1.0
Velocity Pressure Coefficient (Kz) = depends on height of structure
Velocity Pressure (qz) = 0.613 x Kz x Kzt xKd x V2 x I
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Loading Wind Load
Gust effect factor (G) = 0.85
Force coefficient Cf = 2 for flat surface members
Cf = 0.8 for tubular members
Wind Force on members = qz x G x Cf x size of member
Wind Load on Pipes = qz x G x Cf x (Pipe Dia)
Pipe Dia = D1+D2+D3 for pipe rack width 4m
D1, D2, D3 and D4 are largest pipe dia in descending order.
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Loading
Contingency Load (CL) To account for accidental load on members (e.g.
maintenance load)
Shall be considered for the design of local member
For Beam Design = 10 kN at midspan
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Loading
Miscellaneous Load, if applicable (ML) Crane Load
Dynamic Load (considered as equivalent static load)
Blast Load
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Structural Design
Member end releases
Support Condition at base plate level
Load Combinations
Design Parameters
Support reactions
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Structural Design
Member end releases Main Grid members transverse direction : fixed
Main Grid members longitudinal direction : pinned
Vertical bracings : pinned (to account for local bending due to fireproofing load)
Secondary beams : pinned
Plan Bracings : Truss
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Structural Design Member end release
Fixed
Pinned
Truss
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Structural Design Member end release
Pinned Connection Fixed Connection Truss Connection
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Structural Design
Support Condition at base plate level
Fixed Base Pinned Base
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Structural Design Support Condition at base plate level
Fixed in transverse and pinned in longitudinal
Reduce main frame column and beam size
Reduce lateral deflection
Increase base plate size, anchor bolt, pedestal and footing size
Reduction in structural steel Increase in foundation concrete
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Structural Design Support Condition at base plate level
Pinned in both direction
Increase main frame column and beam size
Increase lateral deflection
Decrease base plate size, anchor bolt, pedestal and footing size
Reduction in foundation concrete Increase in structural steel
Choose support condition to maintain balance between structural and foundation system
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Structural Design
Load Combinations
Erection Case :
0.6 (DL+PE) + WL (or 0.7EQ)
Operating Case :
DL+TL+LL+PO+PA+PF+CL
DL+TL+PO+PA+PF+0.75(LL+WL)
DL+TL+PO+PA+PF+0.75(LL+0.7EQ)
DL+TL+PO+PA+PF+WL
DL+TL+PO+PA+PF+0.7EQ
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Structural Design Load Combinations
Test Case :
DL+TL+PT+LL
DL+TL+PT+0.75(LL+0.5WL)
DL+TL+PT+0.5WL
Maintenance Case :
DL+TL+PO+PA+PF+ML
DL+TL+PO+PA+PF+0.75(LL+ML)
Local member Case :
DL+TL+PO+PA+PF (Full)+CL
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Structural Design
Design Parameters Design code and method of analysis
Yield strength of steel
Slenderness ratio limit
Unsupported length of member in major and minor axis (Ly & Lz)
Unsupported length of compression flange (UNB, UNT)
Deflection limit (DFF)
Deflection parameters (DJ1, DJ2)
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Structural Design
Support Reaction Obtained from STAAD-Pro
For base plate and anchor bolt sizing
For pedestal and foundation design
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End Connection
Welded Type
For onshore projects, complete welded pipe rack modules is not feasible due to :
Size restrictions imposed by Local Transport Authority
Hindrances at site due to existing facilities
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End Connection
Shop Weld :
Used for gusset plate, base plate welding
Field Weld :
Limited to few location
FEED requirement
Expensive and poor quality control
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End Connection
Bolted Type FEED requirement
Easy to install and remove
Easy to transport at site in small assembly
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Base Plate and Anchor Bolt Design
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Base Plate and Anchor Bolt Design
Base Plate Design based on support reaction from STAAD-Pro
Size depends on
Allowable bearing stress on grout due to Compression + Bending from superstructure
Anchor bolt spacing on base plate
Thickness depends on bending stress caused due to
Bearing stress in grout
Tensile force in anchor bolt
Thickness can be reduced by providing stiffeners
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Base Plate and Anchor Bolt Design
Anchor Bolt Design is based on support reactions from STAAD-Pro
Size and arrangement depends on Tension + Bending from superstructure
Designed to carry on tension force
Shear from superstructure to be carried by shear key
Minimum spacing >= 7 x dia of bolt
Minimum edge distance from concrete >= 4 x dia of bolt
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Foundation Design
Type of foundation Depends on bearing capacity and settlement criteria
Generally shallow isolated foundation
Deep foundations (pile) in case of unusual foundation loads
For isolated footing, foundation depth preferred 1.5 m below grade to allow space for utilities (e.g. cable trenches, UG pipes etc)
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Foundation Design
Stability Checks Bearing capacity for individual footing design
Overturning and Sliding for overall pipe rack structure with foundation.
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Optimization Idea
Reduce the piping load on pipe rack by using loads from Stress analysis output
Place heavy Loads on lower tier and near support
Reduce thermal load on pipe rack (long stretches) by introduction of loops
Use of high yield strength steel to reduce usage of structural steel --> reduction in foundation --> Ultimately reduction in overall cost.
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Summary
Planning of beams & bracings : It plays a key role in the overall economy of pipe rack structure and foundation
Understanding of loading application
Various design aspects such as member releases, support at base plate level, load combinations, design parameters, end connection type, base plate and foundation design
Optimization Idea
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Acknowledgement Mr. Rachid Younis (EM-Civil)
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Thank You