Vertical Vessel Foundation Design Guidelines

First, for a static equipment foundation, view its general arrangement drawings (GA drawings) and understand that equipment is supported on the concrete foundation, the elevated steel structure, or the steel skid. If it is not clear from the provided GA drawings, then ask the vendor to clarify.

Here, we discuss the foundation design of static equipment called “vertical vessel”. If the vertical vessel is supported on the elevated steel structure and steel skid then first its steel structure and steel skid will be designed and after that, the foundation will be designed, however, the design methodology is different in that case, which will be discussed in another post.

In this post, the vertical vessels which are directly supported on the concrete foundation will be discussed. Normally, a vertical vessel foundation is designed as an isolated footing that has a single pedestal, however, if the spacing between the vessel supporting legs is large, then separate concrete pedestals can be provided for each supporting leg and the footing is designed as 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 following:

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