New tower site planning is a complex challenge, given the many interrelated decisions. Requirements that drive the need for the tower influence its height, which then affects tower type and land size. Given these interdependent components, it can be difficult to find another way to examine options.
Because cost is normally a dominant driver for capital projects, identifying the right way forward with cost analysis and insights to break out components can be a great benefit for new tower project teams.
Tower Types
There are generally two large tower types for utilities to consider:
- Self-support towers are lattice-type steel structures usually featuring three or four tower legs supported by a foundation. Self-support towers typically require a smaller land site area.
- Guyed towers are mast-type structures made up of truss members that are supported with a symmetric array of guy lines and need a small foundation. Guyed towers typically require a larger site.
Monopole towers should also be considered because of their limited intrusiveness and ease of erection, due to their small footprint and relative size. However, these are typically built for one-off applications that can withstand the lower height, and reduced stability and rigidity. For the larger tower types, land area needs differ between the two, and there are other cost drivers that utilities should consider with each of these options.
Cost Considerations
With new tower site projects, costs can affect the selection of tower design and, in turn, determine the actual location for the project. Understanding the cost considerations — whether utilities are evaluating a self-support tower or guyed tower — can provide needed clarity.
- Steel costs: As a commodity, steel is priced based on weight. Therefore, the cost of a tower is directly proportional to the total quantity of steel required to build it. A self-support tower requires more steel in its design than a guyed tower, which means guyed towers of equal height are less costly.
- Foundation costs: The size and depth of a tower foundation depends on tower height, antennas and appurtenances. For self-support towers, in particular, foundation size considerations must be based on how appurtenances affect loading and forces on the tower. As a practical matter, there can be large variations in foundation size depending on the site.
In general, self-support towers require larger foundations to carry the overall bending moment from the tower. Because the larger foundations take time to cure, this can also affect the project schedule.
A guyed tower requires foundations at the base of the tower and at each guy anchor. However, the base foundation is significantly smaller than for a similarly sized self-support tower because it only carries the vertical load and a small horizontal shear force and bending moment.
Guyed towers are kept upright with additional bearing support from guy anchor foundations, which carry all of the tower’s tensile forces. These smaller foundations, for tower and anchor points, are also generally easier to install and faster to cure, which can positively affect a project schedule.
- Erection costs: Both tower types are assembled on the ground or erected piece by piece, so these costs are not usually significantly different.
Self-support towers use mobile cranes or, in some cases, helicopters for erection. These towers have heavier and larger sections, which can affect the crane size requirements and labor cost.
Guyed towers use the same erection methods, but the lighter, smaller and less labor-intensive sections often result in lower labor costs. However, the additional cost to string and tension the guy wires offsets labor savings.
- Land use costs: Self-support towers generally require lower land use costs than guyed towers, based on differing site requirements, but this is contingent on the location of the site and landowner willingness to sell/lease land or otherwise accommodate a tower.
- Maintenance costs: Expenditures tend to be similar between self-support and guyed towers in terms of maintenance requirements. Self-support tower maintenance is straightforward, focusing on the condition of the steel tower members and bolts, but these towers have more surface area needing inspection.
A guyed tower has variables beyond maintaining steel, members and bolts. Checking and maintaining guy wires, guy tensioning, anchors and the area around the anchors requires time and care.
As utilities plan new tower sites, there are many variables to consider, all of which affect the project cost. By evaluating the different cost elements between tower types and considering how the cost will be affected based on other project decisions, project teams gain additional insight during the planning process.
With utilities facing increasing demand for widespread, reliable communications networks, they must take a strategic approach to new tower sites as they build out their infrastructure. Explore additional considerations in depth.
