Foundation Design Philosophy for Equipment on Skid-Help

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.

I hope this page will be very helpful to you to understand the basic foundation loads of a Skid Mounted Equipment.

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.


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.




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


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.

Typical foundation and oil containment drawing for a Transformer

For requirement of firewall refer NFPA-850 chapter-5.


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.


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.

Foundation Design Philosophy for Horizontal Vessel

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.




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)



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 beused. 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 () 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


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.


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.

Foundation Design Philosophy for Equipment on Skid-Help

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