Hanson provides services at
AT&T tower sites nationwide

Hanson’s association with AT&T began in the late 1940s and has developed into a successful partnership. Over the years, Hanson’s working relationship with AT&T has included developing satellite-receiving earth stations and hundreds of network junction and urban switching centers. AT&T has also called on us to provide tower attachments, upgrades and modifications at its communications sites nationwide.

Here are highlights:

Attachments

Hanson performed all necessary field surveys, RF engineering, structural engineering, materials specification and procurement, and construction installation on approximately 60 tower attachments nationwide for AT&T's tower attachment tenants.

Attachments primarily consisted of three types of antennas—whip, panel and dish. Attachments were made to self-supporting towers, guyed towers, concrete silo towers and building roof tops.

RF engineers reviewed frequency interference and antenna separation from existing antennas. Structural engineers reviewed existing towers to determine if they could support additional wind and ice loads imposed by the proposed antennas. During the structural review, engineers investigated the possibility of gaining additional structural capacity by removing and salvaging existing nonfunctional antennas.

Installation drawings included a detailed materials list for the mounts transmission line support and grounding.

Upgrades

Alascom, a subsidiary of Pacific Telecom, retained Hanson to perform foundation inspections and investigations for 25 existing communication tower sites in Alaska. The tower heights ranged from 250 to 350 feet.

Hanson conducted foundation investigations that included field sampling, lab testing and evaluating tower foundation capacities at all 25 sites. Concrete tower foundations were also examined for long-term freeze/thaw deterioration. The site locations began near Fairbanks, continued west to the Canadian border, then continued south to the Kenai Peninsula. Site conditions included glacial and windblown eolian soils, shallow bedrock and alluvial floodplain deposits at extremely remote locations. Two of the sites were located in a permafrost range with the existing towers supported on refrigerated deep-pile foundations. Complete geotechnical and concrete inspection reports were prepared for each site.

Of the 25 sites investigated, 18 required no remedial repairs or modifications. At three of the sites, concrete foundation pads required additional rock anchoring. At two of the sites, remedial repairs of frost-damaged concrete foundation pedestals were necessary. Placement of surficial insulating blankets overlapped by a protective layer of sand and gravel was recommended for the two permafrost sites to help maintain consistent cold ground conditions adjacent to the refrigerated deep-pile foundations. We completed field drilling and inspection work at the 25 sites within three weeks, and the project was completed within the budget requirements.

Modifications

To upgrade its nationwide communications network, AT&T installed additional microwave antennas on several self-supporting towers. In many cases, the additional wind loads acting on the new antennas exceeded the recommended tower foundation uplift capacities, requiring foundation strengthening. As part of its tower modification program, AT&T retained Hanson to reevaluate the original tower uplift capacities and to recommend measures for minimizing foundation strengthening.

Hanson noted that the original tower foundation uplift capacities had often been based on conservatively assumed backfill soil parameters, since backfill compaction records were usually not kept during the original construction of the towers in the 1950s and '60s. We recommended field visits to each tower modification location, with the backfill soils sampled and tested in our laboratory to determine the compacted soil types and strengths. We also performed in situ testing (i.e., shear vane or portable penetrometer) to determine the soil backfill strength and density. Based on our investigations, we were able to eliminate foundation strengthening for about 80 percent of the tower sites. The foundation strengthening required was minimized at the remaining sites.