58
n this page I will talk about Vertical vessel/Tower equipment foundation load calculation. Following are some pictures of Vertical vessel /Tower:
n this page I will talk about Vertical vessel/Tower equipment foundation load calculation. Following are some pictures of Vertical vessel /Tower:
Picture-1 (Left) - A tall tower vessel resting on skirt and on Foundation.
Picture-2 (Right) - A small vertical vessel resting on legs and on fpundation.
Now you will follow the following steps to start the foundation load calculation and design:
Step-1 : Review of vessel drawing (Vendor Equipment Drawing)
You need to review Vessel drawings from foundation design point of view and check whether you have all the following information:
Vessel Erection weight (De1): Vessel Empty weight (De2): Vessel Operating weight (Do): Vessel Hydrotest weight (Dt): Wind Shear and Moment Seismic Shear and Moment (if the Project site is at Seismic zone) Total Height of vessel Vessel Center of Gravity location for Seismic load calculation and application Anchor bolt location (Bolt circle Dia) with respect to center of vessel and also bolt offset with
respect to Plant North line.
Anchor bolt supporting detail ( Anchor bolt size and detail of anchor chair) Base plate detail
Step-2 : Verification of foundation location, elevation and external fittings loads
You need to review Plot plan, Equipment location drawings and 3 -D Models and check whether you have all the following information:
Verify the area available for foundation. Verify Foundation location and Elevation Pipe supports and Nozzle loads on Equipment (Dp) Location and size of Platforms around the vessel Locations of underground pipes Electrical and Instrument duct banks Locations and extent of adjacent foundations Verify the location and extent of new/existing foundations not shown in 3D model or plot
plan.
Step-3 : Description of Foundation Loads:
Please follow this section to understand the different loads on foundation:
Vessel Erection weight (De1): The erection weight is the fabricated weight of the vessel, plus internals, platforms, etc., that are actually erected with the vessel. Data from Equipment drawing.
Vessel Empty weight (De2): The empty weight is the in-place weight of the completed vessel, including the fabricated weight of the vessel, plus the weight of internals, piping, insulation, and platforms, but excluding the weight of fluids or products which will be contained in the vessel during operation. Data from Equipment drawings.
Vessel Operating weight (Do): Vessel Empty weight (De2) + Weight of Fluid inside the vessel. Data from Equipment drawings.
Vessel Hydrotest weight (Dt): Vessel Empty weight (De2) + Weight of test water
Pipe supports and Nozzle loads on Equipment (Dp): Please Coordinate with the Pipe Stress Group for determination of nozzle loads and loads due to pipe supports attached to the vessel.
Wind Shear and Moment: You will find this load data in vendor drawings. However, you have to calculate this load based on project design basis. During wind load calculation, you need to consider the pipes and platforms attached with the vessel. Compare both the data (vendor load data and your calculated data) and apply the critical one for foundation design.
Seismic Shear and Moment (if the Project site is at Seismic zone): You will find this load data in vendor drawings. However, you have to calculate this load based on project design basis. During seismic load calculation, you need to consider the pipes and platforms attached with the vessel. Compare both the data (vendor load data and your calculated data) and apply critical one for foundation design.
Step-4 : Pedestal Sizing Criteria:
Concrete pedestals supporting vertical vessels shall be sized according to the following criteria:
Face-to-face pedestal size shall be the larger of the following:
(a) Bolt circle + 175mm
(b) Bolt circle + 8 x bolt diameters
(c) Bolt circle + sleeve diameter + 150mm
(d) Diameter of baseplate + 100mm
(e) Bolt circle + 2 x (minimum bolt edge distance)
Pedestals having a diameter or least dimension across sides that is equal to or greater than 1.5m shall be octagonal in shape. All other pedestals shall be square in shape. For ease of forming, use multiples of 25mm for each octagonal side or side of square.
It is desirable to make the pedestal deep enough to contain the anchor bolts and keep them out of the mat.
Step-5 : Anchor Bolt Check :
Design of anchor bolts shall be based on the following considerations. Corrosion allowance should be considered when required by the project design criteria.
Tension Check:
The maximum tension force in the anchor bolts (Tmax) may be calculated according with following formula:
Tmax = 4*M / (Nb x BCD) - (De1 or De2) / Nb
Where, M = total maximum moment on foundation BCD = Bolt circle diameter Nb = no. of anchor bolt
Use De1 or De2 whichever is critical.
The above formula provides a conservative value of Tmax compared to the concrete transformed section method.
Shear Check:
When anchor bolts are utilized to resist shear, the unit shear per bolt shall be calculated as follows:
Vmax = V / Nb where, V = total shear force on anchor bolt.
When oversized anchor bolt holes are provided in the vessel base plates or when anchor bolt sleeves that are not grout-filled are used, anchor bolts should be designed to resist tension only.
Frictional resistance to shear between the vessel base plate and the concrete or grouted bearing surface shall be utilized to resist shears induced by wind or by other static loads. Frictional resistance shall not be employed to resist shear induced by seismic loads. For seismic-induced shear, adequate mechanical means shall be provided to resist horizontal shear, either by means of properly detailed anchor bolt / bolt hole arrangements or through a combination of anchor bolts, shear lugs, or other anchorage devices. The static coefficient of friction between steel and concrete or between steel and cementitious grout shall be considered as 0.4 or specified in project design criteria.
Tension Shear Interaction check:
When anchor bolts are subjected to combined shear and tension loads, the design shall be based on satisfying interaction formula (say Appendix-d of ACI 318).
Please note that anchor bolt edge distance, spacing and load capacity shall be as per project design criteria.
Step-6 : Load combinations for foundation sizing / Pile loads and Foundation design:
You need to create the load combination per your project design criteria. However, I have created this load combination based on ACI 318:
Load combination for Foundation sizing and Pile load calculation (un-factored load calculation):
LC1: Do + Dp
LC2: (De1 or De2) + Wind LC3: De2 + Seismic LC4: Do + Dp + Wind LC5: Do + Dp + Seismic LC6: Dt + 025*Wind
Load combination for Pedestal and Foundation design (factored load calculation):
LC7: 1.4*(Do + Dp)
LC8: 0.75 [1.4 De2 (or 1.4 De1)] +1.6 Wind LC9: 1.2 De2 +1.0 E LC10: 0.75 (1.4 Do + 1.4 Dp) + 1.6 Wind LC11: 1.2 (Do + Dp) + 1.0 E LC12: 0.75 (1.4 Dt) + 1.6 (0.25 W)
The weight of the foundation and of the soil on top of the foundation shall be included as dead load in all of these load combinations.
Now from above steps, you have learnt the following:
Different types of loads on foundation Different criterias for the pedestal sizing Maximum tension and shear force on each anchor bolt A sample load combinations.
To complete the foundation design, your work will be to create following calculation sheets:
o A calculation sheet for anchor bolt embedment length check (ex: ACI 318 appendix-D).
o A calculation sheet for foundation sizing (considering soil bearing pressure, Sliding, Buoyancy and overturning) or pile load (tension, compression and shear on each pile) calculation and check with soil consultant for acceptable values.
o A calculation sheet for foundation and pedestal reinforcement calculation per your project design criteria.
In this page I will talk about Horizontal vessel / Horizontal Drum equipment foundation load calculation. Following is a picture of Horizontal vessel / Drum:
Now you will follow the following steps to start the foundation load calculation and design:
Step-1 : Review of vessel drawing (Vendor Equipment Drawing)
You need to review Vessel drawings from foundation design point of view and check whether you have all the following information:
Vessel Erection weight (De1): Vessel Empty weight (De2): Vessel Operating weight (Do): Vessel Hydrotest weight (Dt): Wind Shear and Moment in transverse direction Seismic Shear and Moment in transverse direction (if the Project site is at Seismic zone) Vessel operating temperature and confirm with Mechnaical discipline Total length of vessel and spacing of saddle supports Vessel Center of Gravity location with respect to saddle Anchor bolt location on fixed and sliding saddle Detail of equipment saddle (fixed and sliding)
Step-2 : Verification of foundation location, elevation and external fittings loads
You need to review Plot plan, Equipment location drawings and 3 -D Models and check whether you have all the following information:
Verify the area available for foundation. Verify Foundation location and Elevation Pipe supports and Nozzle loads on Equipment (Dp) Location and size of Platforms around the vessel Locations of underground pipes Electrical and Instrument duct banks Locations and extent of adjacent foundations Verify the location and extent of new/existing foundations not shown in 3D model or plot
plan.
Step-3 : Description of Foundation Loads:
Please follow this section to understand the different loads on foundation:
Vessel Erection weight (De1): The erection weight is the fabricated weight of the vessel, plus internals, platforms, etc., that are actually erected with the vessel. Data from Equipment drawing.
Vessel Empty weight (De2): The empty weight is the in-place weight of the completed vessel, including the fabricated weight of the vessel, plus the weight of internals, piping, insulation, and platforms, but excluding the weight of fluids or products which will be contained in the vessel during operation. Data from Equipment drawings.
Vessel Operating weight (Do): Vessel Empty weight (De2) + Weight of Fluid inside the vessel. Data from Equipment drawings.
Vessel Hydrotest weight (Dt): Vessel Empty weight (De2) + Weight of test water
Pipe supports and Nozzle loads on Equipment (Dp): Please Coordinate with the Pipe Stress Group for determination of nozzle loads and loads due to pipe supports attached to the vessel.
Wind Shear and Moment (W): You will find this load data in vendor drawings. However, you have to calculate this load based on project design basis. During wind load calculation, you need to consider the pipes and platforms attached with the vessel. Transverse and longitudinal wind load shall be calculated per design project criteria. No allowance shall be made for shielding of winds by nearby equioment. The calculated design moments and shears due to wind load should be compared to those shown on the vessel drawings and maximum loads shall be used for foundation design.
Seismic Shear and Moment (E) (if the Project site is at Seismic zone): You will find this load data in vendor drawings. However, you have to calculate this load based on project design basis. During seismic load calculation, you need to consider the pipes and platforms attached with the vessel. The longitudinal seismic force shall be resisted by the fixed end pier only unless the piers are tied together by tie beams below the base plates. Transverse seismic forces shall be resisted by both piers using saddle or base plate reactions as the basis for computing base shear. The calculated design moments and shears due to seismic should be compared to those shown on the vessel drawings and maximum loads shall be used for foundation design.
Thermal Load (T): The thermal load is defined as the load which results from thermal expansion or contraction of the exchanger/vessel in the longitudinal direction. The maximum thermal force is equal to the maximum static friction force (frictional resistance) acting at the equipment sliding support before the saddle begins to move. The frictional resistance equals the coefficient of friction (see project design criteria) times the vertical support reaction.
The thermal load considered in foundation design shall be the smaller of the following:
1. The maximum pier reaction at the sliding end times the coefficient of friction of the sliding surfaces
2. The force required to deflect each pier one-half the amount of the total thermal expansion between supports (assuming thermal loads of equal magnitude, but opposite directions, act on each pier).
Generally, for short piers, the frictional force discussed in item (a) above governs the design.
Step-4 : Load combinations for foundation sizing / Pile loads and Foundation design:
You need to create the load combination per your project design criteria. However, I have created this load combination based on ACI 318:
Load combination for Foundation sizing and Pile load calculation (un-factored load calculation):
LC1: Do + Dp + T LC2: (De1 or De2)+ Wind LC3: De2+ Seismic LC4: Do + Dp + Wind + T LC5: Do + Dp + Seismic + T LC6: Dt + 025*Wind
Load combination for Pedestal and Foundation design (factored load calculation):
LC7: 1.4*(Do + T + Dp )
LC8: 0.75 [1.4 De2 (or 1.4 De1)] +1.6 Wind LC9: 1.2 De2 +1.0 E LC10: 0.75 (1.4 Do +1.4 T + 1.4 Dp) ± 1.6 Wind LC11: 1.2 (Do +T + Dp) + 1.0 E LC12: 0.75 (1.4 Dt) + 1.6 (0.25 W)
The weight of the foundation and of the soil on top of the foundation shall be included as dead load in all of these load combinations.
Step-5 : Anchor Bolt Check :
Maximum shear and tension on anchor bolt shall be calculated based on above load combinations and shall be compared with project acceptable value. Anchor bolt embedment length shall be checked per any project approved code (ex: ACI 318 appendix-D).
Step-6 : Pedestal Sizing and reinforcement:
Unless controlled by other factors, the minimum pier dimensions in each direction should equal to the dimensions of the base plate plus 100mm. Piers shall be sized in 50mm increments. The minimum thickness of the pier should be approximately 10% of the pier height, with a minimum of 250mm.
Pier size should be adjusted to ensure the factored vertical force on the pier does not exceed the value of 0.1Agfc¢ (Refer ACI 318 section 10.3.5)
Piers should be designed as axially loaded cantilever flexural members
When the size of the pier cannot be adjusted and the value of the axial load exceeds 0.1Agfc¢, the piers should be designed as compression members subjected to combined flexure and compressive axial load.
For piers with slenderness ratio equal to or exceeding 22, moment magnification effects should be considered (refer section 10.13 of ACI 318). In calculating the slenderness ratio, a "K" factor of 2 should be used. The P-M column interaction check may also be considered in pier design.
Shears on piers along both the longitudinal and transverse directions of the equipment shall be checked per code requirements (refer ACI 318, Chapter 11).
Reinforcement should normally be arranged symmetrically. Both the fixed end and sliding end piers shall be sized and reinforced identically. For pier height less than 7 feet, the vertical reinforcement may be extended from the foundation with no dowels being required.
A double tie shall be placed at the top of piers, spaced 50mm and 125mm below the top of concrete (or below the bottom of grout), to protect the top of concrete piers against cracking.
Step-7 : Slide plate :
Slide plates are placed at the sliding end pier to allow longitudinal movement of exchangers and vessels due to the thermal growth. The steel slide plate on the sliding end is generally coated with Dow Corning G-n Metal Assembly Paste or similar lubricant in order to reduce the coefficient of friction. Slide plates should be galvanized or painted to prevent corrosion.
For large movements and/or heavy horizontal vessels, it may be necessary to use slide plates with low coefficient of static friction, such as lubrite, teflon, etc. Design of lubrite and teflon slide plates shall be in accordance with the recommendations of the slide plate manufacturer, as the coefficient of static friction varies with the temperature and pressure at the bearing surface.
Typical coefficients of friction (m) are as follows
0.15, for mild steel slide plates coated with Dow Corning G-n Metal Assembly Paste 0.20, for mild steel to mild steel without lubricant 0.06, for teflon slide plates with bearing pressure over 100 psi
Now from above steps, you have learnt the following:
Different types of loads on foundation Different criterias for the pedestal sizing Maximum tension and shear force on each anchor bolt A sample load combinations.
To complete the foundation design, your work will be to create following calculation sheets:
o A calculation sheet for anchor bolt embedment length check (ex: ACI 318 appendix-D).
o A calculation sheet for foundation sizing (considering soil bearing pressure, Sliding, Buoyancy and overturning) or pile load (tension, compression and shear on each pile) calculation and check with soil consultant for acceptable values.
o A calculation sheet for foundation and pedestal reinforcement calculation per your project design criteria.
In this page I will talk about Shell & Tube Exchanger equipment foundation load calculation. Following is a picture of Shell & Tube Exchanger:
Now you will follow the following steps to start the foundation load calculation and design:
Step-1 : Review of vessel drawing (Vendor Equipment Drawing)
You need to review Vessel drawings from foundation design point of view and check whether you have all the following information:
Vessel Erection weight (De1) Vessel Empty weight (De2) Vessel Operating weight (Do) Vessel Hydrotest weight (Dt) Weight of Tube Bundle Wind Shear and Moment in transverse direction Seismic Shear and Moment in transverse direction (if the Project site is at Seismic zone) Vessel operating temperature and confirm with Mechnaical discipline Total length of vessel and spacing of saddle supports Vessel Center of Gravity location with respect to saddle Anchor bolt location on fixed and sliding saddle Detail of equipment saddle (fixed and sliding)
Step-2 : Verification of foundation location, elevation and external fittings loads
You need to review Plot plan, Equipment location drawings and 3 -D Models and check whether you have all the following information:
Verify the area available for foundation. Verify Foundation location and Elevation Pipe supports and Nozzle loads on Equipment (Dp) Location and size of Platforms around the vessel Locations of underground pipes Electrical and Instrument duct banks Locations and extent of adjacent foundations Verify the location and extent of new/existing foundations not shown in 3D model or plot plan.
Step-3 : Description of Foundation Loads:
Please follow this section to understand the different loads on foundation:
Vessel Erection weight (De1): The erection weight is the fabricated weight of the vessel, plus internals, platforms, etc., that are actually erected with the vessel. Data from Equipment drawing.
Vessel Empty weight (De2): The empty weight is the in-place weight of the completed vessel, including the fabricated weight of the vessel, plus the weight of internals, piping, insulation, and platforms, but excluding the weight of fluids or products which will be contained in the vessel during operation. Data from Equipment drawings.
Vessel Operating weight (Do): Vessel Empty weight (De2) + Weight of Fluid inside the vessel. Data from Equipment drawings.
Vessel Hydrotest weight (Dt): Vessel Empty weight (De2) + Weight of test water
Pipe supports and Nozzle loads on Equipment (Dp): Please Coordinate with the Pipe Stress Group for determination of nozzle loads and loads due to pipe supports attached to the vessel.
Wind Shear and Moment (W): You will find this load data in vendor drawings. However, you have to calculate this load based on project design basis. During wind load calculation, you need to consider the pipes and platforms attached with the vessel. Transverse and longitudinal wind load shall be calculated per design project criteria. No allowance shall be made for shielding of winds by nearby equioment. The calculated design moments and shears due to wind load should be compared to those shown on the vessel drawings and maximum loads shall be used for foundation design.
Seismic Shear and Moment (E) (if the Project site is at Seismic zone): You will find this load data in vendor drawings. However, you have to calculate this load based on project design basis. During seismic load calculation, you need to consider the pipes and platforms attached with the vessel. The longitudinal seismic force shall be resisted by the fixed end pier only unless the piers are tied together by tie beams below the base plates. Transverse seismic forces shall be resisted by both piers using saddle or base plate reactions as the basis for computing base shear. The calculated design moments and shears due to seismic should be compared to those shown on the vessel drawings and maximum loads shall be used for foundation design.
Thermal Load (T): The thermal load is defined as the load which results from thermal expansion or contraction of the exchanger/vessel in the longitudinal direction. The maximum thermal force is equal to the maximum static friction force (frictional resistance) acting at the equipment sliding support before the saddle begins to move. The frictional resistance equals the coefficient of friction (see project design criteria) times the vertical support reaction.
The thermal load considered in foundation design shall be the smaller of the following:
The maximum pier reaction at the sliding end times the coefficient of friction of the sliding surfaces
The force required to deflect each pier one-half the amount of the total thermal expansion between supports (assuming thermal loads of equal magnitude, but opposite directions, act on each pier).
Bundle Pull Load (Lb): The bundle pull load is applicable only to foundations supporting exchangers with a removable tube bundle. It is the longitudinal force which results from the tube bundle removal operation during maintenance.This force shall be applied at the center of bundle elevation. In case of stacked exchangers, the more (most) critical load due to bundle pull, applied at the center of the respective bundle, shall be used. The force due to bundle pull shall be resisted by the fixed end pier only. Bundle pull load may be omitted if a bundle pulling extractor is used for removal of the bundle. The method of bundle removal should be listed in the project design criteria. Unless the project design criteria dictates otherwise, the bundle pull load is considered to be 100% of the bundle weight. Bundle pull load should be
considered as live load for assigning load factors.
Step-4 : Load combinations for foundation sizing / Pile loads and Foundation design:
You need to create the load combination per your project design criteria. However, I have created this load combination based on ACI 318:
Load combination for Foundation sizing and Pile load calculation (un-factored load calculation):
LC1: Do + Dp + T LC2: (De1 or De2)+ Wind LC3: De2+ Seismic LC4: Do + Dp + Wind + T LC5: Do + Dp + Seismic + T LC6: Dt + 025*Wind * LC7: De2+ Lb
Load combination for Pedestal and Foundation design (factored load calculation):
LC8: 1.4*(Do + T + Dp ) LC9: 0.75 [1.4 De2 (or 1.4 De1)] +1.6 Wind LC10: 1.2 De2 +1.0 E LC11: 0.75 (1.4 Do +1.4 T + 1.4 Dp) ± 1.6 Wind LC12: 1.2 (Do +T + Dp) + 1.0 E LC13: 0.75 (1.4 Dt) + 1.6 (0.25 W) LC14: 1.4*De2+ 1.7*Lb
The weight of the foundation and of the soil on top of the foundation shall be included as dead load in all of these load combinations.
Step-5 : Anchor Bolt Check:
Maximum shear and tension on anchor bolt shall be calculated based on above load combinations and shall be compared with project acceptable value. Anchor bolt embedment length shall be checked per any project approved code (ex: ACI 318 appendix-D).
Step-6 : Pedestal Sizing and reinforcement:
Unless controlled by other factors, the minimum pier dimensions in each direction should equal to the dimensions of the base plate plus 100mm. Piers shall be sized in 50mm increments. The minimum thickness of the pier should be approximately 10% of the pier height, with a minimum of 250mm.
Pier size should be adjusted to ensure the factored vertical force on the pier does not exceed the value of 0.1Agfc¢ (Refer ACI 318 section 10.3.5)
Piers should be designed as axially loaded cantilever flexural members When the size of the pier cannot be adjusted and the value of the axial load exceeds 0.1Agfc¢,
the piers should be designed as compression members subjected to combined flexure and compressive axial load.
For piers with slenderness ratio equal to or exceeding 22, moment magnification effects should be considered (refer section 10.13 of ACI 318). In calculating the slenderness ratio, a "K" factor of 2 should be used. The P-M column interaction check may also be considered in pier design.
Shears on piers along both the longitudinal and transverse directions of the equipment shall be checked per code requirements (refer ACI 318, Chapter 11).
Reinforcement should normally be arranged symmetrically. Both the fixed end and sliding end piers shall be sized and reinforced identically. For pier height less than 7 feet, the vertical reinforcement may be extended from the foundation with no dowels being required.
A double tie shall be placed at the top of piers, spaced 50mm and 125mm below the top of concrete (or below the bottom of grout), to protect the top of concrete piers against cracking.
Step-7 : Slide plate :
Slide plates are placed at the sliding end pier to allow longitudinal movement of exchangers and vessels due to the thermal growth. The steel slide plate on the sliding end is generally coated with Dow Corning G-n Metal Assembly Paste or similar lubricant in order to reduce the coefficient of friction. Slide plates should be galvanized or painted to prevent corrosion.
For large movements and/or heavy vessels, it may be necessary to use slide plates with low coefficient of static friction, such as lubrite, teflon, etc. Design of lubrite and teflon slide plates shall be in accordance with the recommendations of the slide plate manufacturer, as the coefficient of static friction varies with the temperature and pressure at the bearing surface.
Typical coefficients of friction (m) are as follows:
* 0.15, for mild steel slide plates coated with Dow Corning G-n Metal Assembly Paste * 0.20, for mild steel to mild steel without lubricant * 0.06, for teflon slide plates with bearing pressure over 100 psi
Now from above steps, you have learnt the following:
Different types of loads on foundation Different criterias for the pedestal sizing Maximum tension and shear force on each anchor bolt A sample load combinations.
To complete the foundation design, your work will be to create following calculation sheets:
A calculation sheet for anchor bolt embedment length check (ex: ACI 318 appendix-D). A calculation sheet for foundation sizing (considering soil bearing pressure, Sliding, Buoyancy
and overturning) or pile load (tension, compression and shear on each pile) calculation and check with soil consultant for acceptable values.
A calculation sheet for foundation and pedestal reinforcement calculation per your project design criteria.
References has been taken from,
1. Design of structures and foundations for vibrating machines by S. Arya, M. O'Neill and G. Pincus2. Foundation analysis and design by J. E. Bowels3. Dynamics of bases and foundations by D. Barkan4. Design of Machine Foundations - Lecture Notes of Professor M.H. El Naggar, Department of Civil
Engineering, The University of Western Ontario, London, Ontario, Canada, N6A 5B9
In this page I will talk about the rigid block foundation for Centrifugal (Pump) and Reciprocating machines (Compressor). We are considering the concrete block is infinitely rigid and thus a lump mass model can be considered in computer 3D modelling. To start the design of a block foundation, we need to follow the following steps to collect the design data:
Step-1 : Review of pump / compressor drawing (Vendor Equipment Drawing)
The machine data pertinent to the dynamic analysis and design of the block foundation should be obtained from vendors.
Plan dimension of pump / compressor base frame Height of rotor / shaft center line from the bottom of skid Anchor bolt location, size and embedment depth Weight of machine parts and the rotor parts (pump / compressor rotor and motor rotor) Location of center of gravity both vertically and horizontally Operating speed of machines and power rating of motor (RPM) Magnitude and direction of unbalanced forces. For reciprocating machines both primary and secondary unbalanced forces and couples
and respective CG locations needs to be checked. Limit of deflection and vibration amplitudes at center line of rotor.
Step-2 : Collection of Geotechnical / soil data (Pl discuss with soil consultant and look into project design criteria)
The Geotechnical data are used for evaluating the soil / pile stiffness and damping coefficients, and are required for both static and dynamic design and analysis of of block foundations. Following soil parameters are required:
Soil weight density Poisson's ratio Dynamic shear modulus (G) Shear wave velocity (vs) Dynamic modulus of sub-grade reaction (ks) Allowable soil bearing pressure or pile load carrying capacity for design of foundation
Step-3 : Categorization of rotating machines based on machine speed:
The rotating machines are categorized based on machine speed. Following are different categories of machines:
Low Speed machine: The low speed machines operate at a speed range of less than 500 RPM. High tuned foundations, having first natural frequency more than machine's operating speed, should be designed for this type of machines. In this case machine do not pass the resonance during machine start up and coast down condition.
Intermediate speed machine: The intermediate speed machines operate at a speed range 500 RPM to 1000 RPM. Foundations should be designed for this type of machines high
tuned or low tuned side whchever more practical. If the foundation is low tuned, dynamic amplitude shall be checked during start up and coast down condition.
High Speed machine: The high speed machines operate at a speed range of more than 1000 RPM. Low tuned foundations, having first natural frequency less than machine's operating speed, should be designed for this type of machines. In this case machine will pass the resonance during machine start up and coast down condition. Dynamic amplitude shall be checked during start up and coast down condition. You need to ensure that there is no adverse effect to machine operation during the resonant conditions.
Variable Speed machine: The variable speed machines operate at a speed range as prescribed by vendor. Foundations should be designed for this type of machines high tuned or low tuned side whchever more practical. A detail dynamic analysis of foundation is required for a range of machine operating speeds to ensure that the dynamic design criteria are met.
Step-4 : Preliminary sizing of foundations:
A block foundation consists of massive concrete blocks, piers and mat foundation. The preliminary sizinng of block should be based on the following:
Weight of the block foundation should be at least 4 times the weight of reciprocating machines and 3 times the weight of centrifugal machines.
The width of foundation should be at least 1.5 times the vertical distance from the bottom of foundation to the center line of the shaft / rotor.
The center of mass of machine foundation (machine+foundation system) should coincide with the centroid of the soil foundation or pile group resistance. Horizontal eccentricity should be limited to 5% of the corresponding foundation dimension.
For a rigid mat, following criteria to be followed:
o Minimum thickness of the mat will be 600 mm or 1/5 th of least foundation dimensions or 1/10 th of largest foundation dimensions, whichever is greater .
o Maximum thickness of the mat will be 1500 mmo Minimum thickness of mat, t = 0.0012 x (ks x (a)4)1/3 ft, ks = soil dynamic modulus
of subgrade reaction, lbs/in3, from soil report, a = maximum cantilever projection (inches), measured from face of block (Refer: Foundation analysis and design by J E Bowles)
Step-5 : Requirement for dynamic analysis of foundations:
Dynamic analysis of concrete foundations are not required for all the foundations supporting rotating equipment. You need to refer your project design criteria for the conditions for dynamic analysis. Following are the general criteria for not performing any dynamic analysis of foundation supporting rotating equipment:
Dynamic analysis is not required if the weight of machine is less than 25kN. Dynamic analysis is not required if the power rating of motor is less than 200hp.
If you are not doing any dynamic analysis of concrete block foundation, then follow Step-4 for foundation sizing and put it into 3D model for any interference check.
If you are doing the dynamic analysis of concrete block, then follow the following steps.
Step-6 : Calculation of un-balanced forces for dynamic analysis of foundations:
If unbalance force is not mentioned in the Vendor equipment drawing, then you will calculate the force as follows:
Un-balance force for pump: Fpump = mp-rotor x e x w2
Un-balance force for motor: Fmotor = mm-rotor x e x w2
Where, mp-rotor = weight of pump rotor, mm-rotor = weight of motor rotor
w = circular frequency = 2 x pi x (f / 60), f = speed of machine from vendor drawing (RPM).
e = rotor eccentricity, depends on machine speed
Eccentricity Table ( Refer reference -1)
Machine Operating Speed (f in RPM) Eccentricity e (mils)
Pump / compressor f < 3000 (1.8-107) / (f)2
Pump / compressor f > 3000 (12000/f)1/2
Motor f < 1500 1.5
Motor 1500< f < 3000 1
Motor f > 3000 0.5
Now you are having all the information to start the foundation analysis and design. You can put all the above data in any computer software program (say - Dyna5) or use any text books to calculated the natural frequencies of foundation. You can also use the different tables that I have attached here (click for the table).
Natural frequency analysis of foundation:
This rigid block has six degree of freedom. So, you will calculate all the following uncouple natural frequencies:
1. Sliding Frequency along horizontal X-direction2. Sliding Frequency along horizontal Y-direction3. Sliding Frequency along vertical Z-direction4. Rocking Frequency about X, rotational mode5. Rocking Frequency about Y, rotational mode6. Rocking Frequency about Z, rotational mode
When the CG of foundation system is far above the foundation base, coupling effect needs to be considered to calculate the foundation natural frequency. In this case sliding mode and rocking mode frequencies overlap each other and as a result foundation dynamic analysis may be more critical. You can calculate the coupled natural frequency using the formula mentioned in the table.
Coupled condition: 1. Sliding along X & Rocking about-Y and 2. Sliding along Y & Rocking about X
Once, analysis is completed, please check the foundation for the following conditions:
Resonance Frequency Check:
Calculate resonanace frequency and check that the ratio of machine frequency vs resonance frequency (f / fd) is either less than 0.8 or greater than 1.2 in all six degrees of freedom.
Resonance frequency can be calculated as follows: fd = fn / (1-2 x D2)½
where, fn = foundation natural frequency, D = Damping ration (see table 5 and 12)
Soil Bearing Pressure / Pile Capacity Check
Soil bearing pressure or pile load should not exceed 75% of the allowable. Please avoid any foundation
upliftment in seismic / wind condition.
Maximum Velocity check:
Maximum velocity should fall in "Good Condition" per table-1 of attached table
Environmental condition
Maximum displacement amplitude of vibration at foundation level should lie within or below "Zone-B" of figure -1 and it should fall below the Zone "Troublesome to persons" of figure -2 in the attached table.
Reinforcement:
Reinforcement shall be provided per project approved design code. However, you can use minimum reinforcement as follows:
0.2% rebar on all face of concrete block and mat.
1% rebar for all concrete pedestal.
Rebar spacing should not be more than 300 mm.
Anchor Bolt:
Anchor bolt shall be checked for start-up and coast down contion.
Design of Concrete Ring Beam for Storage Tank
In this page I will talk about the design philosophy of ring beam for storage water tank. The granular fill foundation of the tank shall be designed per project design criteria / specification. This type of foundation is mostly common to all project site. However, sometimes we design concrete ring beam around the tank foundation. Following are some reasons for design of concrete ring beam, though this is more costly and take longer to construct than granular fill ring:
Sometimes clients ask to provide concrete ring beam around tank foundation. Prevent uplift of the tank due to wind or earthquake Prevent edge failure of the soil at the tank shell Prevent local uplift of the tank due to internal pressure.
Now you will follow the following steps to start the foundation load calculation and design:
Step-1 : Review of Tank detail drawing (Vendor Drawing)
You need to review tank drawings from foundation design point of view and check whether you have all the following information:
Tank Dimension, Diameter and Height Type of Roof (Floating or fixed roof), weight of roof Detail of tank shell and weight of tank shell Detail of tank base plate, location of base sump, annular plate and total weight of base plate Detail of anchor bolt (BCD, no of bolt and dia of bolt) and anchor bolt fixing detail Location and detail of man-hole at bottom portion of tank Product density and and maximum height of product Maximum height of water inside the tank for the hydrotest* Internal pressure or suction Live load Wind Shear and moment on tank shell Seismic shear and moment on tank shell
Step-2 : Verification of foundation location, elevation and external fittings loads
You need to review Plot plan, Equipment location drawings and 3 -D Models and check whether you have all the following information:
Verify the area available for foundation. Verify Foundation location and Elevation Pipe supports and Nozzle loads on tank (Dp) Location and size of Platforms around the tank Locations of underground pipes Electrical and Instrument duct banks Locations and extent of adjacent foundations Verify the location and extent of new/existing foundations not shown in 3D model or plot plan.
Step-3 : Loads on concrete ring beam and on the confined compacted granular fill in-side the ring:
You need to place concrete ring beam in such a way that outer surface of the tank shell should be the center of ring beam. Consider the following loads on ring beam and on granular compacted fill inside the concrete ring.
Geotechnical Data:
Before starting the design, you need to collect the following information about soil:
Allowable Bearing Pressure Density of Soil Co-efficient of earth pressure at rest (Ko)
Loads on Ring beam:
Total weight of tank shell (vertical load), kN / m (DL) Total weight of roof , for fixed roof case. For floating roof, part of the roof weight will come on the
ring beam, kN / m (DL) Total live load on roof , for fixed roof case. For floating roof, part of the live load will come on the
ring beam, kN / m (LL) Part of annular base weight on ring beam, kN / m2 (DL) Part of product / test water load on ring beam, kN / m2 (PL) Seismic shear and wind shear on ring beam, kN / m Part of internal pressure / suction load on ring beam, kN / m2(IP)
Loads on compacted granular fill inside the ring beam:
Floating roof weight on compacted granular fill, kN / m2(DL) Annular base weight on compacted granular fill, kN / m2 (DL) Live load on floated roof, kN / m2 (LL) Product / test water load on compacted granular fill, kN / m2(PL) Internal pressure / suction load on compacted granular fill, kN / m2 (IP)
Following load combimations can be used for soil bearing pressure check (at bottom of ring beam level) :
Load Combination: LC1 - Self weight of soil / Beam + Self weight of tank + Product weight + Internal pressure
Load Combination: LC2 - Self weight of soil / Beam + Self weight of tank + Product weight + Internal Pressure + Live Load
Load Combination: LC3 - Self weight of soil / Beam + Self weight of tank + Product weight + Internal pressure + Wind Load
Load Combination: LC4 - Self weight of soil / Beam + Self weight of tank + Product weight + Internal pressure + Seismic Load
Load Combination: LC5 - Self weight of soil / Beam + Self weight of tank + Product weight + Internal pressure + Live Load + Wind Load
Load Combination: LC6 - Self weight of soil / Beam + Self weight of tank + Product weight + Internal pressure + Live Load + Seismic Load
Load Combination: LC7 - Self weight of soil / Beam + Self weight of tank + Test water weight
Load combinations for Ring beam design for Hoop tension:
Load Combination: UC1 - 1.7 x (Surcharge load of confined soil) + 1.7 x Surcharge load of (Self weight of tank + Product weight + Internal pressure)
Load Combination: UC2 - 1.7 x (Surcharge load of confined soil) + 1.7 x Surcharge load of (Self weight of tank + Product weight + Internal pressure)+ 1.4 x surcharge of Live Load
Load Combination: UC3 - 1.7 x (Surcharge load of confined soil) + 1.7 x Surcharge load of (Self weight of tank + test water weight)
Step-4 : Determination of concrete ring beam size:
The ring wall should be a minimum 300 mm thick and extend to a suitable bearing stratum, whch may be natural ground or built-up compacted granular material. It should be 500 mm below ground level and extend below frost line. The bearing capacity of the soil below the ringwall should be calculated using a strip foundation analysis loaded with vertical load as mentioned in step-3.
API 650, appendix-B, clause B.4.2.2 states that it is desireable that the ringwall width be such that the average unit soil loading under the ring wall will be approximately equal to the earth pressure under the confined earth at the same depth (in maximum liquid level condition).
Once, the ringwall thickness is determined from above condition, it should be reviewed to ensure that excessive quantities of concrete are not used for tanks with low liquid levels and that the permissible ground pressure for the width of the wall is not exceeded.
Please note that, soil bearing pressure under the ring beam and under the confined earth at same depth should not exceed the allowable soil bearing pressure for any of the above described load and any load combinations.
Step-5 : Determination of Hoop Tension on concrete ring beam and reinforcement calculation:
The concrete ring beam shall be designed for hoop tension. This hoop tension will be generated from surcharge load due to confined soil and loads on confined soil.
Load calculation:
Surcharge due to confined soil: Sursoil = 0.5 x (height of ringwall)2 x soil density x Co-efficient of earth pressure at rest (Ko)
Surcharge due to uniform load on confined soil: Surudl = (Load on confined soil) x (height of ringwall) x Co-efficient of earth pressure at rest (Ko)
Total Hoop tension (T) = (Sursoil + Surudl) x (0.5 x centerline diameter of ring beam)
Factored Hoop Tension load can be calculated as per step-3.
Required area of Hoop reinforcement is, Ast = (Factored Hoop tension) / (0.9 x yeild stress of rebar---fy)
The ringwall must also be designed to take care circumferential bending moments due to the vertical load being applied eccentrically to the ringwall center line.
The ringwall should be reinforced on both faces, with vertical reinforcement (stirrups) closest to the concrete surfaces. Not more than 50% of the hoop reinforcement should be lapped at any one position.
Step-6 : Anchor Bolt Design:
Anchor bolt shall be checked per design criteria and Tenssion & Shear load supplied by vendor. If wind and shear forces are not supllied by vendor, you need to calculate the anchorage load from API 650.
Anchor bolt shall be designed for ductility failure. If required, additional reinforcement to be provided around the anchor bolt.
Foundation Design Philosophy for Equipment on Skid
In this page I will talk about the foundation design philosophy for Equipment on skid. These equipment are static in nature and are resting on Channel section or Wide beam section. A very simple analysis and design is required to produce a Foundation for equipment on skid. You need to follow the following steps to complete the foundation design:
Step-1 : Review of Equipment Drawing (Vendor Equipment Drawing)
Plan dimension of Equipment base frame Height of Equipment Anchor bolt location, size and embedment depth Empty weight of Equipment (De) Operating weight of equipment (Do) Location of center of gravity both vertically and horizontally
Step-2 : Verification of foundation location, elevation and external fittings loads
You need to review Plot plan, Equipment location drawings and 3 -D Models and check whether you have all the following information:
Verify the area available for foundation. Verify Foundation location and Elevation Pipe supports and Nozzle loads on Equipment (Dp) Location and size of Platforms around the Equipment, if any Locations of underground pipes Electrical and Instrument duct banks Locations and extent of adjacent foundations Verify the location and extent of new/existing foundations not shown in 3D
model or plot plan.
Step-3 : Description of Foundation Loads:
Please follow this section to understand the different loads on foundation:
Equipment Empty weight : The empty weight is the in-place weight of the Equipment, including the fabricated weight of the equipment, plus the weight of internals, piping and insulation, but excluding the weight of fluids or products which will be contained in the equipment during operation.
Equipment Operating weight : Equipment Empty weight (De2) + Weight of Fluid inside the Equipment
Pipe supports and Nozzle loads on Equipment (Dp): Please Coordinate with the Pipe Stress Group for determination of nozzle loads and loads due to pipe supports attached to the Equipment.
Wind Shear and Moment: Most of the time you will not find this load data in vendor drawings. You need to calculate this load based on project design basis. During wind load calculation, you need to consider the pipes and platforms attached with the equipment.
Seismic Shear and Moment (if the Project site is at Seismic zone): Most of the time you will not find this load data in vendor drawings. You need to calculate this load based on project design basis. During seismic load calculation, you need to consider the pipes and platforms attached with the equipment.
Step-4 : Block Sizing Criteria:
Concrete foundation block supporting equipment, shall be sized according to the following criteria:
Face-to-face Block size shall be the larger of the following:
(a) Bolt center line distance + 200mm
(b) Bolt center line distance+ 8 x bolt diameters
(c) Bolt center line distance + sleeve diameter + 150mm
(d) Out to out dimension of skid + 100mm each side
(e) Bolt center line distance + 2 x (minimum bolt edge distance)
It is desirable to make the pedestal deep enough to contain the anchor bolts.
Step-5 : Anchor Bolt Check :
Design of anchor bolts shall be based on the following considerations. Corrosion allowance should be considered when required by the project design criteria.
Tension Check:
The maximum tension force in the anchor bolts (Tmax) may be calculated according with following formula:
Tmax = M / (Nb x BCD) (Equipment weight) / Nb
Where, M = total maximum moment on foundation due to wind or seismic
BCD = Bolt center line distance
Nb = no. of anchor bolt
Shear Check:
When anchor bolts are utilized to resist shear, the unit shear per bolt shall be calculated as follows:
Vmax = V / Nb where, V = total shear force on anchor bolt.
When oversized anchor bolt holes are provided in the vessel base plates or when anchor bolt sleeves that are not grout-filled are used, anchor bolts should be designed to resist tension only.
Frictional resistance to shear between the equipment skid and the concrete or grouted bearing surface shall be utilized to resist shears induced by wind or by other static loads. Frictional resistance shall not be employed to resist shear induced by seismic loads. For seismic-induced shear, adequate mechanical means shall be provided to resist horizontal shear, either by means of properly detailed anchor bolt / bolt hole arrangements or through a combination of anchor bolts, shear lugs, or other anchorage devices. The static coefficient of friction between steel and concrete or between steel and cementitious grout shall be considered as 0.4 or specified in project design criteria.
Tension Shear Interaction check:
When anchor bolts are subjected to combined shear and tension loads, the design shall be based on satisfying interaction formula (say, Appendix-d of ACI 318).
Please note that anchor bolt edge distance, spacing and load capacity shall be as per project design criteria.
Step-6 : Load combinations for foundation sizing / Pile loads and Foundation design:
You need to create the load combination per your project design criteria. However, I have created this load combination based on ACI 318:
Load combination for Foundation sizing and Pile load calculation (un-factored load calculation):
LC1: Do + Dp
LC2: (De) + Wind LC3: Do + Seismic LC4: Do + Dp + Wind LC5: Do + Dp + Seismic
Load combination for Pedestal and Foundation design (factored load calculation):
LC6: 1.4*(Do + Dp)
LC7: 0.75 [1.4 De] 1.6 Wind LC8: 1.2 Do +1.0 E LC9: 0.75 (1.4 Do + 1.4 Dp) 1.6 Wind LC10: 1.2 (Do + Dp) 1.0 E
The weight of the foundation and of the soil on top of the foundation shall be included as dead load in all of these load combinations.
Now from above steps, you have learnt the following:
Different types of loads on foundation Different criterias for the concrete block sizing Maximum tension and shear force on each anchor bolt A sample load combinations.
To complete the foundation design, your work will be to create following calculation sheets:
o A calculation sheet for anchor bolt embedment length check (ex: ACI 318 appendix-D).
o A calculation sheet for Concrete block sizing (considering soil bearing pressure, Sliding, Buoyancy and overturning) or pile load (tension, compression and shear on each pile) calculation and check with soil consultant for acceptable values.
o A calculation sheet for foundation and pedestal reinforcement calculation per your project design criteria.
Pipe rack Design PhilosophyIn this page I will talk about the pipe rack design philosophy. Pipe rack is the main artery of any plant. This carries the pipes and cable trays (raceways) from one equipment to another equipment within a process unit (called ISBL piperack) or carries the pipe and cable trays from one unit to another unit (called OSBL pipe rack). Some times you will also find the AIR COOLED HEAT EXCHANGERS on the pipe rack.
There are different types of pipe rack:
Continuous Piperacks (conventional pipe rack) system Non-continuous Piperacks system Modular Pipe rack
Conventional / Continuous Pipe rack
Continuous Piperacks (conventional pipe rack) system: This is essentially a system where multiple 2-dimensional (2D) frame assemblies (commonly called bents), comprised of two or more columns with transverse beams, are tied together in the longitudinal direction utilizing beam struts (for support of transverse pipe and raceway elements and for longitudinal stability of the system) and vertical bracing to form a 3D space frame arrangement. Piperacks supporting equipment such as air-cooled heat exchangers must utilize the continuous system approach.
Step-1: Data collection for pipe rack design:
Due to the “fast track” nature associated with most of the projects, often the final piping, raceway, and equipment information is not available at initiation of the piperack design. Therefore, as a Civil/Structural Engineer, you should coordinate with the Piping group, Electrical, Control Systems, and Mechanical groups to obtain as much preliminary information as possible. When received, all design information should be documented for future reference and verification. In the initial design, the Engineer should use judgement when applying or allowing for loads that are not known, justifying them in the design basis under "Design Philosophy" (a part of your calculation)
The following should be reviewed for design information:
Plot plans and equipment location plans 3D model showing piping layout, cable tray layout, Piperack bent spacing and
elevation of support levels in the transverse direction , Elevation of longitudinal beam struts and locations of vertical bracing. and location of pipe bridge, if any.
Piping orthographic drawings. Vendor prints of equipment located on the rack, e.g., air coolers and
exchangers.The vendor prints should include the equipment layout, mounting
locations and details, access and maintenance requirements, and the magnitude and direction of loads being transmitted to the piperack.
Electrical and control systems drawings showing the routing and location of electrical and instrumentation raceways and/or supports.
Underground drawings that show the locations of buried pipes,concrete structures and foundations, duct banks, etc. in the area of the piperack.
Pipe rack construction material (Steel, Cast-in-situ concrete, Pre-cast concrete) shall be as per project design criteria.
Please note that, Unless specifically explained in the project design criteria, no allowance or provisions should be made for future additions for pipe or raceway space and related loading.
Step-2: Design loads consideration:
Following loads are to be considered for the pipe rack design:
Piping Gravity load (D): In the absence of defined piping loads and locations, an assumed minimum uniform pipe load of 2.0 kPa should be used for preliminary design of piperacks. This corresponds to an equivalent load of 6 in (150 mm) lines full of water covered with 2 in (50 mm) thick insulation, and spaced on 12 in (300 mm) centers. This assumption should be verified based on coordination with the Piping Group, and concentrated loads should also be applied for any anticipated large pipes. When the actual loads and locations become known, as the project develops, the structural design should be checked against these assumed initial load parameters and revised as required. A concentrated load should then be added for pipes that are 12 in (300 mm) and larger in diameter. The concentrated load P should be:
P =(W - s x p x d), s = Spacing of piperack bent, p = pipe weight considered (kPa), d = pipe diameter W = pipe concentrated load.
Where consideration of uplift or system stability due to wind or seismic occurrences is required, use 60% of the design gravity loads as an "all pipes empty" load condition.
Loading due to hydrostatic testing of lines should be considered in the design if applicable. Coordinate the testing plan(s) with Construction, Startup, and/or the Piping Group as necessary, in order to fully understand how such loads will be applied to the piperack structure. Under most normal conditions, multiple lines will not be simultaneously tested. The hydro-test loads do not normally need to be considered concurrently with the other non-permanent loads, such as live load, wind, earthquake, and thermal. Typical practice is to permit an overstress of 15% for the hydro-test condition. Because of these considerations, the hydro-test condition will not normally govern except for very large diameter pipes. Electrical Tray and Conduits (D): Electrical and control systems drawings and/or the project 3D model should be reviewed to determine the approximate weight and location
of electrical trays, conduits, and instrumentation commodities. Unless the weight of the loaded raceways can be defined, an assumed minimum uniform load of 1.0 kPa should be used for single tier raceways.
Self weight of Pipe rack (D): The weight of all structural members, including fireproofing, should be considered in the design of the piperack.
Weight of Equipment on pipe rack (D): Equipment weights, including erection, empty, operating, and test (if the equipment is to be hydro-tested on the piperack), should be obtained from the vendor drawings.The equipment weight should include the dead weight of all associated platforms, ladders, and walkways, as applicable.Special Loads: Special consideration should be given to unusual loads, such aslarge valves, expansion loops, and unusual piping or electrical configurations.
Live Load (L): Live load (L) on access platforms and walkways and on equipment platforms should be considered, as applicable.
Snow Load (S): Snow load to be considered on cable tray and on large dia pipes. This load shall be calculated per project approved design code and project design criteria. Generally, you need to consider 100% snow load on top tier and 50% on other tier of pipe racks.
Wind Load (W): Transverse wind load on structural members, piping, electrical trays,equipment, platforms, and ladders should be determined in accordance with project approved design code. Longitudinal wind should typically be applied to structural framing, cable tray vertical drop (if any), large dia pipes vertical drop (if any) and equipment only. The effects of longitudinal wind on piping and trays running parallel to the wind direction should be neglected.
Earthquake Loads (E): Earthquake loads in the vertical, transverse, and longitudinal directions should bedetermined in accordance with the project design criteria. Vertical, transverse, and longitudinal seismic forces generated by the pipes, raceways, supported equipment, and the piperack structure should be considered and should be based on their operating weights. Pipes must be evaluated for seismic loads under both full and empty conditions and then combined with the corresponding gravity loads.
Friction Loading (Tf): Friction forces caused by hot lines sliding across the pipe support during startup and shutdown are assumed to be partially resisted through friction by nearby cold lines. Therefore, in order to provide for a nominal unbalance of friction forces acting on a pipe support, a resultant longitudinal friction force equal to 7.5% of the total pipe weight or 30% of any one or more lines known to act simultaneously in the same direction, whichever is larger, is assumed for piperack design. Friction between piping and supporting steel should not be relied upon to resist wind or seismic loads.
Anchor and Guide Loads (Ta): Piperacks should be checked for anchor and guide loads as determined by the Pipe Stress Group. It may be necessary to use horizontal
bracing if large anchor forces are encountered. For conventional pipe rack systems, it is normally preferred to either have the anchors staggered along the piperack so that each support has only one or two anchors, or to anchor most pipes on one braced support. For initial design, when anchor and guide loads are not known, use a longitudinal anchor force of 5.0 kN acting at midspan of each bent transverse beam (refer project design criteria). Guide loads are usually small and may be ignored until they are defined by the Pipe Stress Engineer. For non-continuous pipe rack systems, piping may be transversely guided or anchored at both cantilever frames and anchor bays. Longitudinal anchors may be located only at anchor bays.
Please note that, all friction forces and anchor forces with less magnitude, (say ~ 5.0 kN), applied to the top flange of the beam, may be considered as resisted by the total beam section. When anchor loads have large magnitude and are applied to the top flange of the beam, the effect of torsion must be addressed.If the beam section is inadequate to take care of this torsional force, alternatives to be considered, such as provide horizontal bracings at the load locations.
Step - 3: Load Combinations and allowable deflection of pipe rack:
You need to create the load combinations per your project design criteria. However, I have refered here some load combinations.
Please note the following:
Earthquake load is a factored load. For load combinations that include wind or earthquake loads, use only the non-
friction portion (anchor and guide portion) of the thermal loads, i.e., friction loads are not combined with wind or seismic loads. Friction loads are considered to be self-relieving during wind and earthquake and should only be combined with anchor and guide loads when wind or earth-quake loads are not considered.
Hydrostatic test loads need not be combined with wind and earthquake loads unless there is a reasonable probability of the occurrence of either of these loads during hydrostatic testing.
For calculation of foundation soil bearing pressures or pile loads, stability checks against overturning, sliding, and buoyancy, and deflection checks, the following unfactored load combinations (ACI 318) shall be used:
1. D2. D + L + SL + Tf + Ta3. D + Tf + Ta4. D + 1.3W + Ta5. D + L + 0.5SL + 1.3W +Ta6. D + L + S +0.65W + Ta7. 0.9De + 1.3W + Ta8. D + E/1.4 + Ta
9. D + 0.2S + E/1.4 + Ta10. 0.9De + E/1.4 + Ta
Load Combinations for design of foundations (ACI 318):
1. 1.4D2. 1.4D + 1.7L +1.7S3. 1.4D + 1.4Tf +1.4Ta4. 0.75 (1.4D + 1.7L + 1.7S + 1.4Tf + 1.4Ta)5. 0.75 (1.4D + 1.7L + 1.7S + 1.4Ta) + 1.6W6. 1.2D + 0.2S + 1.0E + 1.2Ta7. 0.9De + 1.6W + 1.2Ta8. 0.9De + 1.0E + 1.2Ta
Steel Design load combinations: (AISC - LRFD)
1. 1.4D2. 1.2D + 1.6L + 0.5S + 1.2Tf + 1.2Ta3. 1.2D + 1.6S + 0.5L + 1.2Tf + 1.2Ta4. 1.2D + 1.6S + 0.8W + 1.2Ta5. 1.2D + 1.6W + 0.5L + 0.5S + 1.2Ta6. 1.2D + 1.0E + 0.5L + 0.2S + 1.2Ta7. 0.9De + 1.6W + 1.2Ta8. 0.9De + 1.0E + 1.2Ta
De is the minimum dead load on the structure.
FINAL ANCHOR AND GUIDE LOAD CHECK:
Where the design of transverse beams has been based on anchor loads as explained in step-2,a final check of beams (and other affected members) should be made when final definition of these loads is available from the Pipe Stress Engineer.Based on the Engineer's experience and judgement, an overstress in any element (of up to 10%) can be considered, provided proper justification is given. Where such overstress cannot be properly justified, modifications should be made to the piperack structure in order to bring the stress levels within the normal allowables. Modifications could entail the addition of horizontal bracing to the transverse beams to resist significant loads from the anchor(s), replacing and/or adding members, strengthening members (i.e.,cover plating, etc.), and/or relocating the anchor and guide load(s).
ALLOWABLE HORIZONTAL AND VERTICAL DEFLECTION:
Allowable deflections of piperack structures shall be as per project design criteria. However, you can consider the following as limit of deflection:Lateral deflection produced by load combinations that include wind or seismic forces:Piperacks supporting equipment: h/100, unless a more stringent requirement is given by the manufacturer of the equipment.Piperacks supporting piping and raceway only: h/200 or as per project
design criteria.Lateral deflection produced by sustained static forces such as pipe and anchor loads: h/200 or as per project design criteriaVertical deflection of beams due to gravity pipe loads:as per project design criteria h is the total height of the pipe rack structure.
Step-4: Framing of Continuous/Conventional Pipe rack:
Frames Main piperacks are usually designed as moment-resisting frames in the transverse direction. In the longitudinal direction, there should be at least one continuous level of beam struts on each side. For piperacks with more than one tier, the beam struts should be located at a level that is usually equal to one-half tier spacing above or below the bottom tier. Vertical bracing in the longitudinal direction should be provided to carry the longitudinal forces, transmitted through the beam struts, to the baseplate / foundation level.
Transverse Beam
Transverse beams must be capable of resisting all forces, moments, and shears produced by the load combinations. Transverse beams are generally a moment-resisting frame, modeled and analyzed as part of the frame system. The analysis model must reflect the appropriate beam end conditions. In the design of beams, consideration should be given to
Large pipes that are to be hydro-tested. Anchor and friction load with large magnitude (see step-2, anchor and friction
load)
Central Spine:
For steel piperacks with spans of more than 6 m, a center spine consisting of a system of horizontal braces and struts located at midspan of each level of piping should be considered . This additional light horizontal framing greatly increases the capacity of the transverse pipe support beams to resist friction and anchor forces, and also serves to reduce the unbraced length of the beam compression flange in flexure and to reduce the unbraced length of the beam about the weak-axis in axial compression. This concept reduces the required beam sizes and provides a mechanism for eliminating or minimizing design, fabrication, or field modifications that could otherwise be required due to late receipt of unanticipated large pipe anchor forces.
Longitudinal Beam Strut
For typical continuous piperack systems, the longitudinal beam struts should be designed as axially loaded members that are provided for longitudinal loads and stability. Additionally, the longitudinal beam struts that support piping or raceway should
be designed for 50% of the gravity loading assumed for the transverse pipe or raceway support beams, unless unusual loading is encountered. This 50% gravity loading will account for the usual piping and raceway take-offs. Normally, the gravity loading carried by the beam struts should not be added to the design loads for the columns or footings since pipes or raceway contributing to the load on the beam struts would be relieving an equivalent load on the transverse beams. Concentrated loads for large pipes may be treated as in step-2.
For any continuous piperack system where the anticipated piping and raceway take-offs are minimal or none, the 50% loading criteria does not apply. In such cases, the beam struts should be designed primarily as axially loaded members. Do not provide beam struts if they are not needed for piping or raceway support, or for system stability. Conversely, the 3D model should be checked to verify that beam struts subjected to unusually large loads (such as at expansion loops) have been given special consideration. All longitudinal beam struts, including connections, should be designed to resist the axial loads produced by the longitudinal forces.
When designing the longitudinal beam struts for flexural loads, the full length of the beam should be considered as the unbraced length for the compression flange.
Vertical Bracing
When moment-resisting frame design is not used in the longitudinal direction, vertical bracing should be used to transmit the longitudinal forces from the beam struts to the foundations. Knee-bracing or K-bracing is most often used for this purpose. Unless precluded by equipment arrangement or interferences, bracing should be placed equidistant between two expansion joints. Design calculations and drawings must reflect a break in the beam strut continuity between adjacent braced sections through the use of slotted connections or by eliminating the beam struts in the bays designated as free bays. The maximum length of a braced section should be limited to 48m to 50m. If the braced bay is not located equidistant from the free bays, the maximum distance from the braced bay to a free bay should be limited such that the maximum total longitudinal growth or shrinkage of the unrestrained segment does not exceed 40 mm.
Column
The columns must be capable of resisting all loads, moments, and shears produced by the load combinations.A moment-resisting frame analysis should normally be used to determine the axial load, moment, and shear at points along the columns.The frame analysis model should be based on the following:
Consider column base as hinge. Use 4 bolt connections for safety purpose
For design of steel columns subjected to flexural loads, the distance between the base and the first transverse beam or the knee brace intersection should be considered as the compression flange unbraced length.
Design Philosophy for Transformer Pit In this page I will talk about how to detemine the size of oil containment for transformer. Following is a typical picture of a transformer and its foundation with oil containment.
Now, you will follow the below steps to determine the foundation and size of spilled oil containment.
Step-1 : Review of Transformer drawing (Vendor Equipment Drawing)
You need to review transformer drawings from foundation design point of view and check whether you have all the following information:
Transformer Erection weight (De) Transformer Operating weight (Do) Plan dimension of Transformer base Height of transformer and location of oil tank Total volume of oil in the oil tank Transformer Center of Gravity location in empty condition and operating
condition for Seismic load calculation and application Anchor bolt detail (size, location, projection, etc..) and transformer supporting
details
Step-2 : Verification of foundation location, elevation and external fittings loads You need to review Plot plan, Equipment location drawings and 3 -D Models and check whether you have all the following information:
Verify the area available for foundation and containment. Verify transformer Foundation and containment location and Elevation
Electrical and Instrument duct banks Bus duct support and foundation detail, on and around the transformer pit
Locations of underground pipes Location of fire hose and sprinkler around the transformer Locations and extent of fire wall and construction type of fire wall Verify the location and extent of new/existing foundations not shown in 3D model
or plot plan.
Step-3 : Soil / Geotechnical information:
Following Geotechnical information are required to start the foundation and spilled oil containment:
Soil allowable Bearing pressure or pile capacity (Tension, compression and Lateral force capacity)
Soil density Active soil pressure co-efficient of soil Earthquake soil pressure co-efficient Ground water table location Frost depth (for winter snow)
Step-4 : Transformer Pedestal sizing criteria:
Transformer pedestal shall be sized according to the following criteria:
Face-to-face pedestal size shall be the larger of the following:
(a) Bolt c/c distance + 175mm
(b) Bolt c/c distance + 8 x bolt diameters
(c) Bolt c/c distance + sleeve diameter + 150mm
(d) Size of base frame + 200mm
(e) Bolt c/c distance + 2 x (minimum bolt edge distance)
It is desirable to make the pedestal deep enough to contain the anchor bolts and keep them out of the mat.
Step-5 : Transformer spilled oil containment sizing criteria:
Containment size shall be calculated for worst condition. It is assumed that worst condition will be happened when total oil is in the containment + Transformer on fire + Heavy rain fall. So, total containment volume will be, addition of following items:
Volume of transformer oil (mentioned in the equipment drawing) Transformer on fire: When transformer is on fire (refer IEEE-980 annex-B or
NFPA-850 chapter-6 ) all the hose pipe (deluge system) will spray the water on all four sides and top of the transformer. So total volume of water will be: Water volume = (Total surface area of the transformer (all 4 sides) + top plan area of transformer) xrate of water flow from hose pipe per unit area x total fire rating time.
Rain water: Total volume of rain water shall be calculated for total fire time. So volume of rain water = Rain fall intensity (mm/hr) x Plan area of containment x total fire rating time.
Generally, you will find that containment area is full of stones (40 mm down). In this case, we consider that 35% void is available to accommodate the above volume of oil and water mix. So, you need to increase the capacity of the containment accordingly.
Step-6 : Anchor Bolt Check :
Design of anchor bolts shall be based on the following considerations. Corrosion allowance should be considered when required by the project design criteria.
Tension Check:
The maximum tension force in the anchor bolts (Tmax) may be calculated according with following formula:
Tmax = M / (Ny x BCD) - (De / Do) / Nb
Where, M = total maximum moment on foundation BCD = Bolt c/c distance Ny = No. of bolt row Nb = no. of anchor bolt
Use De or Do whichever is critical.
Shear Check:
When anchor bolts are utilized to resist shear, the unit shear per bolt shall be calculated as follows:
Vmax = V / Nb where, V = total shear force on anchor bolt.
Frictional resistance to shear between the transformer base plate and the concrete or grouted bearing surface shall be utilized to resist shears induced by wind or by other static loads. Frictional resistance shall not be employed to resist shear induced by seismic loads. For seismic-induced shear, adequate mechanical means shall be provided to resist horizontal shear, either by means of properly detailed anchor bolt / bolt hole arrangements
or through a combination of anchor bolts, shear lugs, or other anchorage devices. The static coefficient of friction between steel and concrete or between steel and cementitious grout shall be considered as 0.4 or specified in project design criteria.
Tension Shear Interaction check:
When anchor bolts are subjected to combined shear and tension loads, the design shall be based on satisfying interaction formula (say Appendix-d of ACI 318).
Please note that anchor bolt edge distance, spacing and load capacity shall be as per project design criteria.
Step-7 : Load combinations for foundation sizing / Pile loads and Foundation design:
You need to create the load combination per your project design criteria. However, I have created this load combination based on ACI 318:
Load combination for Foundation sizing and Pile load calculation (un-factored load calculation):
LC1: Do LC2: (De) + Wind LC3: De + Seismic LC4: Do + Wind LC5: Do + Seismic
Load combination for Pedestal and containment mat foundation design (factored load calculation):
LC6: 1.4*(Do) LC7: 0.75 [1.4 De] 1.6 Wind LC8: 1.2 De +1.0 E LC9: 0.75 (1.4 Do ) 1.6 Wind LC10: 1.2 (Do) 1.0 E
The weight of the foundation and of the soil on top of the foundation shall be included as dead load in all of these load combinations.
Step-8 : Loads on containment wall
Containment wall shall be designed for following loads and load combinations:
Active soil pressure on the wall Surcharge load on wall due to live load on soil. You need to discuss with
construction about any site crane movement around the transformer pit.
Earthquake load on wall due to soil movement. Use Monobe Okabe Equation for Earthquake load calculation.
or requirement of firewall refer NFPA-850 chapter-5.
Now from above steps, you have learnt the following:
Different types of loads on foundation Different criterias for the pedestal sizing Maximum tension and shear force on each anchor bolt A sample load combinations.
To complete the foundation design, your work will be to create following calculation sheets:
A calculation sheet for anchor bolt embedment length check (ex: ACI 318 appendix-D).
A calculation sheet for foundation sizing (considering soil bearing pressure, Sliding, Buoyancy, uplift of foundation due to frost and overturning) or pile load (tension, compression and shear on each pile) calculation and check with soil consultant for acceptable values.
A calculation sheet for foundation, pedestal and containment wall reinforcement calculation per your project design criteria.
