Dipesh H Dahanuwala Date : 25-June-2013
Agenda Aim Key Objectives Aspects of Pipe racks
Optimization Idea Summary
Aim To present different aspects of pipe rack
Key Objective Purpose of Pipe rack Materials of Construction Execution Stages
Analysis and Design Concepts
Purpose of Pipe rack To support group of parallel pipes running at different elevations with emerging or merging branches
Materials of Construction Concrete Cast-in-situ Precast
Application : • Concrete Pipe racks are made in case of corrosive environment
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
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
Analysis and Design Concepts Geometrical Planning Loading Structural Design End Connection Base Plate and Anchor Bolt Design
Foundation Design
Analysis and Design Concepts Geometrical Planning Grid Location Tier Elevation
Planning of Beams Planning of Elevation Bracings Planning of Plan Bracings Expansion Joint
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
Geometrical Planning Grid Location
Geometrical Planning
Geometrical Planning Tier Elevations : by Piping Discipline Basis :
To maintain the minimum headroom for the pipes crossing the roads
Tie-in elevation
Sloping lines
Geometrical Planning Tier Elevation
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.
LARGE BORE PIPES SMALL BORE PIPES
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
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.
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
Pipe rack with slotted joint as expansion joint
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)
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)
Loading Dead Load (DL) Weight of Structure Weight of Fireproofing
Weight of Grating and Handrail in case of
platforms on pipe rack
Loading Live Load (LL) Applicable in case platform on pipe rack Normally LL = 5 kPa, but depends on platform
use defined by Piping.
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.
Loading Thermal Load
Good Design
Release of thermal stresses (free to move in both directions)
Loading Thermal Load
Bad Design
Thermal stresses are arrested (restrained by bracings at ends)
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
Loading Pipe Operating Load (PO) < 12” Pipes : ~ 2 kPa >=12” Pipes : concentrated load (as per Pipe
Stress Analysis) Operating Equipment Load, if any
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)
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
Anchor Lug
Only Top flange effective
Both Flanges effective
Loading Pipe Friction Load (PF) Cause : Hot lines sliding across beam
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
Loading Pipe Friction Load 0.1 0.3 0.2 PP
For Local beam check 0.1 P 1 5
7 3 8 4 6 2 P = Piping Operating Load
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 <= 3) Note : Most critical load from above combination shall be considered for design In
Transverse direction :
10%
of the operating weight
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
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.
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
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
Pipe Dia = D1+D2+D3+D4 for pipe rack width > 4m
D1, D2, D3 and D4 are largest pipe dia in descending order.
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
Loading Miscellaneous Load, if applicable (ML) Crane Load Dynamic Load (considered as equivalent static load) Blast Load
Structural Design Member end releases Support Condition at base plate level Load Combinations
Design Parameters Support reactions
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
Structural Design Member end release
Fixed Pinned Truss
Structural Design Member end release Pinned Connection
Fixed Connection
Truss Connection
Structural Design Support Condition at base plate level
Fixed Base
Pinned Base
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
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
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
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
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)
Structural Design Support Reaction Obtained from STAAD-Pro For base plate and anchor bolt sizing For pedestal and foundation design
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
End Connection Shop Weld :
Used for gusset plate, base plate welding
Field Weld :
Limited to few location •
FEED requirement
•
Expensive and poor quality control
End Connection Bolted Type FEED requirement Easy to install and remove Easy to transport at site in small assembly
Base Plate and Anchor Bolt Design
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
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
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)
Foundation Design Stability Checks
Bearing capacity for individual footing design
Overturning and Sliding for overall pipe rack structure with foundation.
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.
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
Acknowledgement Mr. Rachid Younis (EM-Civil)
Thank You
