Vertical Vessel Foundation Design Guidelines

When designing the foundation for a vertical vessel, it is essential to begin by reviewing the general arrangement (GA) drawings. These drawings help identify whether the vessel is supported directly on a concrete foundation, on an elevated steel structure, or mounted on a steel skid. If the support system is not clearly indicated in the GA drawings, it is important to seek clarification from the equipment vendor to ensure accurate foundation design.

This post focuses on the design of foundations for vertical vessels supported directly on concrete foundations. In cases where the vessel is mounted on an elevated steel structure or skid, the structural elements must be designed first, followed by the foundation. That methodology differs and will be covered in a separate post.

Typically, vertical vessels supported on concrete foundations use an isolated footing with a single pedestal. However, if the vessel has multiple supporting legs with significant spacing, separate pedestals may be used for each leg, and the foundation is then designed as a combined footing.

Data Provided by Vendor

Loading Data

The following loads are provided by the vessel vendor, which is generally mentioned in the general arrangement drawing of the vessel:

Equipment Weight

Equipment weight at the following conditions:

1. At empty condition              
2. At operating condition          
3. At hydro test       

Wind Forces and Moment

 Maximum horizontal wind force and maximum wind moment is provided at the base of the vessel

Seismic Forces and Moment

 Maximum horizontal seismic force and maximum seismic moment is provided at the base of the vessel

Fixing Detail

The following fixing detail is mentioned in the provided GA drawing of the vessel.

1. Numbers, diameter, orientation, and Bolt circle diameter (BCD) or c/c distance of anchor bolts.
2. Base Plate detail

Note: These details should be marked in the civil foundation drawing and a reference of the GA drawing of vessel will be included in the civil foundation drawing

Data Provided by Soil Technician

From Soil Technician, we require following information as required in the general footing design:

1. Net or Gross bearing capacity of soil at best suitable depth for isolated or combined footing
2. Water table depth(if present)
3. Soil improvement suggestion if required
4. Density of existing soil

Data Provided by Piping

1. Height of Pedestal above ground is provided by the piping engineer as per their piping.

Calculation Performed By Civil Engineers

1. Calculate Civil Dead Load = Footing Self-weight + Pedestal weight +  Soil weight
2. Make the following service load combinations :

• Civil Dead Load + Equipment Test Wt
• Civil Dead Load + Equipment Empty Weight + Wind
• Civil Dead Load + Operating Weight + Seismic

3. Make the following design load combinations :

• 1.4 Civil Dead Load + 1.4 Equipment Test Wt
• 1.2 Civil Dead Load + 1.2 Equipment Empty Weight + Wind
• 1.2 Civil Dead Load + 1.2 Equipment Operating Weight + Wind
• 1.2Civil Dead Load + 1.2 Operating Weight + Seismic

 
4. At service load combination, ensure foundation stability in the following :

• Overturning
• Sliding
• Bearing pressure
• In uplifting

5. At design combination, calculate the following:

• Pedestal reinforcement
• Embedment length of anchor bolt(Nos and dia are provided by the vessel vendor)
• Footing reinforcement
• Please check carefully that the vessel ID, location, orientation, and fixing detail are the same as those marked in the vessel general arrangement drawing.
• Send foundation drawing for IDC (Inter-Disciplinary checks).

Note: if you are designing a square isolated footing, you can use this calculator: “https://knowledgesharingplatform.com/vertical-vessel-footing-design-calculator/“