TNX on the art of tower design

Tower Numerics (TNX) is the developer of industry standard software for tower analysis and design. Their software is built from the ground up for the tower industry, and has been proven and refined over twelve years. The program started as ERI Tower, when it was written by the industry pioneer Dan Horn in response to the need for a dedicated and powerful, yet easy to use package for tower analysis and design. Peter Chojnacki was working at RISA Technologies when they acquired ERI Tower. He wrote numerous features of what became known as RISATower as users came up with design issues that required advanced modelling techniques. In September 2010 Peter’s company Tower Numerics acquired the rights to RISATower, changed the name to tnxTower, and focused exclusively on providing tools for design of communication and wind turbine towers.

TowerXchange: Tower Numerics’ tnxTower software is described as developed from the ground up for the tower industry - what does that mean in practice?

tnxTower is the most popular tower design program in the US. Our software is used for the analysis and design of new and existing towers, since any equipment changes made for co-locations require structural evaluation, and possibly strengthening of the tower. Our software implements standards that govern telecom tower design, enabling practitioners to run analyses to determine if the structure can carry the load.

What is unique about tnxTower is that our software was designed exclusively for the telecom tower industry. Before the telecom towers sector was as hot as it is now, general purpose design software, traditionally used to model buildings, industrial facilities or bridges, would be used for towers. You can try to design a tower in these general purpose programs, but in the tower industry you need to be fast and efficient - speed of turnaround is very important - so you need a streamlined system tailored to telecom towers with utilities to create and modify models very quickly.

Software not specifically meant for towers lacks many essential features, such as automated bracing generation, load application based on ancillary input, ancillary databases, and many others. Such software may contain a lot of superfluous elements that distract from the main objectives and complicate the design process. Tower design standards, which codify loading and strength requirements, are not usually implemented in those packages.

Simplicity is the key to tnxTower - we have a simple, streamlined user interface, easy to understand inputs, with no cryptic commands, and clear and concise outputs. Nonetheless, tnxTower can handle virtually all complexities of tower analysis, such as load optimization and non-linear cable analysis. The program is not a black box, however, and users have access to detailed output data for verification purposes.

In addition to being a software publisher, we do our best to be an educational resource for the industry as well. Our website includes materials on topics related to tower design for the benefit of our users and anyone else who is interested. We work with equipment manufacturers on expanding the range of items we include in TNX equipment databases distributed with the program.

TowerXchange: What is unique about the design requirements of telecom towers?

Telecom tower design combines principles of structural mechanics with elements of aerodynamics. One of the main objectives is to properly associate geometry of the structure and attached ancillaries with forces generated by wind from varying directions. Wind forces need to be amplified due to the height of the structure and topography of the site. Presence of ice and escalation of its thickness with height or wind load reduction due to components shielding each other are important considerations. Further, dynamic effects of uneven wind action need to be accounted for. It is a fascinating area of engineering, but like all engineering disciplines requires simplifications. Design standards, such as TIA-222-G, help engineers create practical and viable designs by simplifying the rules. This largely eliminates the need to undertake substantial “academic” work every time a new design is made or an existing tower configuration is modified.

TowerXchange: For our less technically inclined readers, please introduce us to the key information you need to know about a piece of equipment to determine what effect adding it to a structure will have on the capacity of that tower.

At a minimum, the software input for a given piece of equipment must include its weight, front and side areas, shape, and position on the tower. Except for the position on the tower, all other parameters are stored in tnxTower database, enabling reuse of pre-defined equipment on other projects. Different shapes of antennas result in different forces, even if the antennas have the same outline (projected) area. For instance, flat panels attract greater force than circular shapes of the same projected area. Height to width ratio of an antenna is also a factor. These parameters are automatically accounted for either in the tnxTower database values or at the analysis runtime. Another aspect to consider are multiple, adjacent ancillaries. In such cases the total loads tributary to these items may be reduced due to shielding effects. tnxTower handles all calculations automatically, and includes additional important considerations, such as ice accretion, air flow characteristics, wind speed increases, and others.

There are many different aspects of the antenna and feed line placement that influence the stresses in the structural members of a tower. Repositioning of the ancillaries on the tower, if practicable, can have a beneficial effect, when the altered, combined effect of wind pressure results in a reduction of member forces.

TowerXchange: Tell us how your users can calculate the effect of additional tenancies on the most stressed component of a tower.

We help our users handle additional equipment in a staged manner. First, let’s have a look at what is involved in a standard structural calculation for a tower.

Normally you would consider 12 different wind directions for calculations based on different, code mandated criteria, and need to generate up to 38 independent load combinations, which in turn will require running 38 analyses. For many towers additional, dynamic considerations are required, which may double the number of the load combinations and analyses. This is before any equipment variances are considered. Any change of the equipment configuration will require running all of the analyses again. It is a very large number of calculations, but it can be very efficiently handled with our software.

If the equipment mounted on a tower is added to or removed, then you have to rebuild your computer models with different equipment sets. tnxTower has a facility to specify all the equipment on a tower and assign classification categories to different equipment types, such as antennas, feed lines, or dishes. The user can then model existing, reserve, future, or other equipment combinations and loading, driven by the policies and agreements of the tower owner.

With tnxTower you can create different load cases for different scenarios, for example for two, three or five tenants. Our program automatically runs the multiple analyses for different scenarios and gives reports for different situations. We help engineers who work in a multi-tenant environment use a single model - one file that contains all the current information and future load scenarios for a tower.

tnxTower makes it easy to add information about tower reinforcement and to manage reinforcement schemes. For example, users can define members with different sizes or as reinforced members, or they can modify bracing patterns. We recently introduced a monopole reinforcement module, which is important to help squeeze the maximum capacity form existing monopoles in regions where tower owners are running out of capacity on existing towers and where zoning restrictions make permitting and building new towers difficult.

TowerXchange: One of the challenges facing telecom tower operators in emerging markets is that towers may lack their original drawings. What can be done to evaluate such towers and make them suitable for structural upgrades to increase capacity?

There’s no magical way to recreate drawings. Member sizes, lengths, and other geometry data as well as steel properties are critical in assessing the capacity of the structure. In addition, bolt numbers and their patterns or the extent of corrosion can make a big difference. For those reasons there is no substitute for a proper tower mapping.

Tower mapping report is usually prepared following a site visit, during which an extensive survey of the structure is performed. Technicians need to climb the tower to gather information on which the tnxTower input can later be based.

3D tower evaluation surveys are occasionally used, but most of the time it’s done through visual inspection and photography. Since telecom towers are tall, slender structures, 3D scans are cost prohibitive in many cases, and their accuracy may often be insufficient.

TowerXchange: How does tnxTower help tower manufacturers integrate design and manufacturing processes?

tnxTower is used by most of the big US manufacturers. Some of them use our software in their workflow - they have front-end facilities that prepare input data and then run tnxTower analyses to obtain parameters for the manufacturing process. So in a way we provide an interface between structural design and manufacturing. There are ways to provide an even tighter integration of the manufacturing with tnxTower, and we are looking into them as well.

TowerXchange: Finally, please sum up how you would differentiate TNX from your competitors.

Tower Numerics specializes in the tower design software - this is our only business. tnxTower has been conceived for telecom tower design from the outset and this focus shows throughout. It is a single, stable package, capable of designing monopoles, self-supporting and guyed towers, or any hybrid types.

tnxTower is a sophisticated finite element analysis program, with advanced capabilities, such as non-linear cable analysis, yet we aim to make our data entry simple and understandable. All user data is channelled through self-explanatory input pages, and graphic feedback is present at all stages. The straightforward input does not prevent tnxTower from being able to handle the most complex tower projects, as the interface permits a great deal of flexibility in the tower model definition.

tnxTower output is unquestionably the best in the industry. Our presentation of information to the user is clear, concise and on target. For instance, most users need only a specific subset of the whole output. More extensive reports that provide the whole picture are always available, however, in case users need to do additional diagnostics or verifications.

Our loading optimization algorithms reduce tnxTower wind forces to the full extent permitted by the TIA Standard. The program includes facilities to manage equipment loading scenarios, which can be an enormous time saver for multiple tenant tower projects. On the design side, the program not only checks strength of members and connections, but is also able to optimize member sizes to automatically produce the most economical structures. Monopoles can be designed and reinforced, providing a way to increase the often critically important capacity for additional tenants.

In a nutshell, we give our users extra leverage that provides cost and efficiency benefits.