In designing tower foundations to save on installation or retrofitting costs, the engineering fee might be a little higher, but the resulting design can save a considerable amount of money by using a performance-based analysis, according to the Telecommunications Industry Foundation’s newest white paper.
The installation of new foundations and the modification of existing foundations for telecommunication structures represent significant capital investment costs.
The money invested limits the use of that capital for other telecommunications infrastructure. For the industry to support the demand for telecommunications infrastructure as effectively as possible, all analysis methods that can minimize cost should be considered.
The Telecommunications Industry Foundation (TIF) has issued a white paper intended to encourage effective foundation design in accordance with the codes and standards that apply while allowing options to be considered that can avoid unnecessary costs due to simplified design methods.
In many instances, limited space at the site or relatively poor soil conditions can require the use of specialized foundation systems or layouts that increase construction costs. The resulting designs may require foundations with large footprints, deep installation depths, or the need for soil anchors when space is limited. Based on these factors, the telecommunications industry is impacted when excessive foundation costs limit investment, network redundancy, and technology upgrades by wireless carriers.
Rigid body behavior is a typical assumption for foundation analysis in the industry. While this assumption allows for relatively simple calculations, it may not correlate well with the actual behavior and may, in fact, penalize the calculated foundation capacity.
An analysis that considers the flexible behavior of the foundation and stiffness of the soil can better assess the true behavior to allow optimized results. This is especially true in the case of drilled pier foundations with large lateral and overturning forces. Current industry practice also typically analyzes the tower using a model that assumes the supporting foundation is fully fixed or pinned.
The support reactions resulting from this analysis are then applied to the foundation in a separate set of calculations that do not consider the impact of foundation movement on the structure. Due to this separation in the analysis process, some assumptions must be made for the foundation analysis that may not allow the full capacity of the foundation to be realized.
The method proposed in this white paper requires a comprehensive review of the combined behavior of the foundation and structure that allows the foundation capacity to be optimized.
Consequently, current industry practices for foundation analysis may result in sub-optimal designs. Therefore, alternate methods of analysis are needed to find more cost-effective solutions.
Specifically, the TIF paper advocates for the consideration of performance-based analysis for foundations. It is likely that this will require some additional engineering effort; however, the engineering costs will often prove to be considerably less than costs associated with the foundation installation or upgrade that would otherwise be required when using other analysis methods.