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STRUCTURAL ANALYSIS

NWTE has produced over 600 tower structural analysis reports.

A structural analysis is performed when changes to a tower’s appurtenance configuration are made. This usually happens when additional antennas and feed lines are to be installed, increasing the amount of wind load and weight to be supported by the tower. Each tower is evaluated per the requirements of the TIA/EIA-222-F Standard, “Structural Standards for Steel Antenna Towers and Antenna Supporting Structures.” NWTE will also provide analyses per the recently published TIA-222-G revision of the Design Standard.

NWTE uses RISATower (formerly ERITower)—a sophisticated software program—to perform each structural analysis. The program allows the engineer to build finite element models of guyed and self-supporting towers and monopoles. The engineer inputs tower geometry, structural member sizes and materials, guy wire information, connection data, appurtenance information, wind speed and ice thickness. The program calculates and applies wind and ice loads in the model. Program output includes stresses in each structural member and guy wire, tower deflections, and foundation loads.

NWTE finds out if stress levels, deflections (if microwave antennas are installed), and foundation loads are within the allowable limits per the Design Standard. NWTE then issues a structural analysis report which includes tower elevation and plot plan sketches showing structural member and guy wire sizes, an appurtenance list, a cross section sketch showing locations of feed lines, a list of structural member stresses, and recommendations, if any, for strengthening the tower. NWTE can also provide construction drawings for tower structural modifications.

The following graphs are typical examples of how NWTE uses sophisticated computer modeling to perform precise tower analyses.

Deflection Chart

The above graph, for instance, shows twist and sway levels at different tower elevations.

tower stress levels

The second graph, above, shows stress levels in a tower’s structural members.

guy tower model

The third graph, above, shows a computer model of a guyed tower.