The purpose of the article is to discuss brief review about requirements of the design of foundation for static equipments which are there in almost all major industries. Almost all engineering projects require software platforms for finalising designs is the situation in projects in the fields of power plants, pharmaceuticals, food and beverage and many more.
With this literature review a detailed practical example of how to carry out foundation design for Vessels and Heat Exchangers will be taken up in our next Webinar on August 11th. 2021, with focus on :-
- challenges involved in designing foundation for Industrial structures.
- Preferred Software Application which can simplify the tasks of a structural engineer to input the equipment related all information to consider for design calculation.
- Productivity increase in no time investment
- Extensive report generation of all the scenarios
- Structural Design team helping Engineering layout team in the site location.
Foundation Design for Static Equipment
Any construction project comprises of two major divisions viz. Superstructure and Substructure. Foundation is one of the essential parts of the structure that fixes it into the soil and provides support for the main structures viz, superstructure that appear above the soil level. In other words, the substructure transmits loads of super-structure to the soil and is termed as foundation.
From the last century the foundation project gained increasing important, settlements of the buildings or structures, bearing capacity of the soil are the two aspects must be carefully studied to avoid the risk of damage.
Thanks to the continuous development of Civil and Structural Engineering methodologies makes the design of structures progressively more safe, reliable and at the same time with reduced financial implications using application software.
Function of Foundation
The main function of foundation is to safely transfer loads from the structure constructed on it as well as its own self weight to the ground. So that the ultimate bearing capacity of the soil and the settlement of the whole structure remains within the allowable limit
Types of Foundation
In the construction workflow Foundation Design Engineers are the ones most often gets inputs as a last information but expected to provide design solution first. Hence the role of Structural Foundation Design Engineer is vital in every project.
Foundation for Oil and Gas Facilities
Mechanical equipment used on process plants can be categorised into two main types, namely static and rotating equipment.
Rotating Equipment is generally used in the oil and gas and process industries to describe mechanical components that use kinetic energy to move fluids, gases, and other process materials.
Static equipment in oil and gas facilities comprises of pressure vessels, heat exchangers, storage tanks, fired Heaters, Tanks, etc. In this article we ‘ll be seeing foundation design for static equipment. “Static equipment” in industries does not contain moving parts or whose operational characteristics are essentially static in nature.
A pressure vessel (Horizontal & Vertical Pressure Vessel) is a container designed to hold fluids, i.e, gases or liquids at a pressure significantly higher or lower from the ambient pressure. The type and configuration of a foundation for equipment may be dependent on the following factors:
- Equipment base configurations such as legs, saddles, solid base, grillage, or multiple support locations.
- Anticipated loads such as the equipment static weight, and loads developed during erection, operation, and maintenance.
- Operational and process requirements such as accessibility, settlement constraints, temperature effects, and drainage.
- Erection and maintenance requirements such as limitations or constraints imposed by construction or maintenance equipment, procedures, or techniques.
- Site conditions such as soil characteristics, topography, seismicity, climate, and other environmental effects.
- Economic factors such as capital cost, useful or anticipated life, and replacement or repair costs.
- Regulatory or building code provisions such as tied pile caps in seismic zones.
- Construction considerations.
- Environmental requirements such as secondary containment or special concrete coating requirements
Foundation for Horizontal Vessel and Heat Exchanger
There is no industrial plant without pressure vessels, steam boilers, tanks, autoclaves, collectors, heat exchangers, pipes, etc. Horizontal equipment, typically supported on pedestals that rest on isolated footings (spread footings), strap footings, pile caps, or drilled piers. Consequently, the pedestal is the logical means of support. The configuration of pedestals varies with the type of saddles on the vessels,
1.1 Design Considerations in Foundation Loading
Horizontal pressure vessels are generally having complex geometry comprising of various geometrical discontinuities high loading conditions and many engineers have difficulty in classifying the large number of different loadings into the standard “dead” and “live” categories. There is, therefore, a need to define additional categories of loadings and load combinations with appropriate load factors.
What Design Loads Are Considered for Foundation Design?
Dead loads, Vertical Loads (Imposed loads), horizontal loads such as wind and earthquake to subsurface soil in one of the most prime design requirements
Dead loads invariably consist of the weight of the equipment, platforms, piping, fireproofing, cladding, ducting, and other permanent attachments. There is a distinction between dead and operating loads. Designating the operating contents (liquid, granular material, etc.), of the equipment as dead loads may be inconvenient when considering the possible combinations of loads that may act concurrently, and when assigning load factors.
- Structure dead load (Ds) – Weight of the foundation and soil above the part of the foundation that resists uplift
- Erection dead load (Df) – Fabricated weight of the exchanger or vessel, generally taken from certified exchanger or vessel drawings
- Empty dead load (De) – Empty weight of the exchanger or vessel including all attachments.
- Operating dead load (Do) – Empty dead load of the exchanger or vessel plus the maximum weight of contents (including packing/catalyst) during normal operation. The eccentric load should also be added to the operating dead load weight.
- Test dead load (Dt) – (horizontal vessels only) Empty dead load of the vessel plus the weight of test medium contained in the system. The test medium should be as specified in the contract documents. Unless otherwise specified, a minimum specific gravity of 1.0 should be used for test medium. Cleaning load should be used for test dead load if cleaning fluid is heavier than test medium.
Live Loads Live loads also commonly include the lifted loads that are attached to the main piece of equipment, or directly to the foundation and the items it contains.
Temperature change of the equipment can produce horizontal thrusts at the tops of the supporting piers. For large piping, such forces may significantly affect the foundation design.
Wind Loads – When designing outdoor equipment foundations to be constructed most engineers will use the relevant provisions in that code for determining wind loads on equipment. Most codes, such as the older editions of the Uniform Building Code (UBC 79) specify wind pressures according to geographic area, height above grade, and equipment geometry.
Seismic Loads – Determining lateral force requirements for equipment is a challenge for non-building type structures. The applicability to equipment and nonbuilding type structures is less than clear, particularly when most of the codes use nomenclature applicable to structures rather than equipment. The performance of many types of vendor-manufactured, floor-mounted equipment (both rigid and nonrigid) in past earthquakes has demonstrated a typically high inherent strength for resisting seismic loads.
Hydrotest Load (Dt): Test weight equals the empty weight plus weight of the test fluid, usually water, required for hydrostatic test. This information shall be obtained from vessel drawings with Project Mechanical Group’s reference.
Bundle Load: Bundle pull load is applicable only to foundations supporting Heat exchangers with removable tube bundle. It is a longitudinal force, which results from tube bundle removal operation during maintenance. It is usually assumed to be a certain percentage of the bundle weight applied as a lateral force at the centreline of the exchanger.
Thermal Loads: Thermal load is defined as load resulting from thermal expansion or contraction of the exchanger/vessel in longitudinal direction.
Piping Loads: Nozzle loads and loads due to pipe supports attached to the vessel (including loads due to thermal expansion) shall be considered in foundation design. Design engineer to coordinate with Piping/Plant Layout Group for determination of piping loads.
The information here is intended to provide general information on the topics presented. The information provided should not be used as a complete substitute for professional services. A detailed experience, codes and standard knowledge will be the better guide in carrying out for practising Engineers.