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Utilities’ use of lattice box structures is not a new concept. In fact, utilities have used the design in substations for well over a hundred years. In recent years, utilities have looked at their existing lattice box structures and asked themselves: Can this structure support new upgraded equipment or should we replace it? But how do you determine if this existing structure can have an extended service life? 

Ready for Reuse?

The benefits of lattice box structures stand true from when they were originally built. They offer:

  • A relatively compact footprint for use in substations due to the ability to mount electrical equipment vertically on multiple tiers
  • Support for the bus conductor and incoming/outgoing transmission line
  • The ability to support numerous pieces of equipment and conductor lines without the need to have individual support structures and foundations for each piece of equipment
  • Easy access to the field crews to provide maintenance operations

But the question still stands: can this structure support new, upgraded equipment? With recent advances in computer software, answering this question has become more straightforward.

Lattice box structures can now be modeled, analyzed, and retrofitted (as required) using industry standard computer software. The repetitive nature of these structures allows for an engineer to create a model of a single column and girder type and copy and paste these assemblies together to form a complete model of the structure in relatively little time. The software creates a 3D model of the structure and provides a convenient way to automatically check member strengths, deflections, and applicable member end forces.

In fact, now that these models can be created in a simple and straightforward manner, the reuse of existing infrastructure is becoming a more pronounced and preferred alternative in today’s substation world. A number of Leidos’ projects involve investigating existing lattice box structures for reuse with modern equipment, typically to realize cost savings for our utility clients. This cost saving is achieved by reusing the existing structure and associated foundations (with retrofits if necessary) and avoiding the cost of demolition, new fabrication of structures, new installation of foundations, and overall construction time.

The Option to Replace

Building conventional steel support structures and installing new foundations remain the main alternative to reusing existing structures. This requires designing and detailing all of the new structures and foundations to be installed and typically results in numerous individual support structures with their own individual foundations. In addition, the conventional steel support structure needs a larger footprint in the existing substation, which may require a yard expansion. In the cases where these new steel support structures are replacing existing lattice box structures, the cost of demolition and outage time needs to be accounted for in the construction schedule.

Summary

Extending the service life of existing lattice box structures, in lieu of the conventional replacement, can be evaluated at a relatively modest cost in comparison to total replacement. Utilities across the country are beginning to recognize these cost savings through the use of modern structural analysis. Although every substation project is unique, reusing existing infrastructure is always a welcome alternative to replacement.

To learn how Leidos can help with your utility’s unique substation project or any of your utility’s toughest engineering challenges, visit our Power Delivery Services page.
Baker Tee, PE, is a lead civil/structural engineer for substation projects with 10 years of experience. He primarily reviews calculations and drawings relevant to all structural aspects of substation design, such as equipment support structure design, foundation design, rigid bus design, transformer oil containment, and construction specifications. He has extensive experience in existing structure evaluation and retrofit design. He earned both an M.S. and B.S. in civil engineering from the University of Illinois.