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STRUCTURAL ANALYSIS

NWTE has produced over 1,500 tower structural analysis reports.

A structural analysis is performed when changes to a tower’s appurtenance configuration are made. It is common for tenants on a tower to require replacement of existing antennas and/or placement of additional antennas, associated radio equipment and feed lines, thus increasing the amount of wind load and weight to be supported by the tower. Each tower is evaluated per the requirements of the TIA-222-G or TIA-222-H Standard, “Structural Standards for Steel Antenna Towers and Antenna Supporting Structures,” depending on which revision is currently adopted by the jurisdiction.

NWTE uses tnxTower (Tower Numerics, Inc.)—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 structural member and guy wire forces and capacities, tower deflections, and foundation loads.

NWTE determines if structural member forces, 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 forces and capacities, and recommendations, if any, for strengthening the tower. NWTE can also provide construction drawings for tower structural modifications.

Typical graphical output from tnxTower is shown below.

Deflection Chart

Figure 1: Guyed tower deflections.

tower stress levels

Figure 2: Structural member demand–capacity ratios.

guy tower model

Figure 3: Guyed tower isometric view.