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:
Horizontal Vessel                                  

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:
    • 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.
For typical foundation for a Horizontal Vessel click here

I hope this page will be very helpful to you to understand the basic foundation loads of a Horizontal Vessel.

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Disclaimer: This page is prepared based on experience on Civil Engineering Design. All definitions and most of the explanations are taken from different text books and international design codes, which are referenced in the contents. Any similarity of the content or part of with any company document is simply a coincidence. Subhro Roy is not responsible for that.