Why is it important to focus on weight and wind load for a wireless tower?

There are many major areas where weight and wind play a key role. These include: Performance, revenue, expenses (more weight and space on the tower increases leasing costs) and safety.

When you think about it, it’s easy to see how weight and wind can impact the performance of a wireless system on a tower. Improperly designed, configured or installed equipment on a tower—or even choosing the wrong mount—can cause misalignments and even total failure. Drawing a direct line from those kinds of impacts to revenue is easy.

In terms of expenses, in many cases,  the cost of leasing tower space is based largely on how much loading a base station antenna adds to the tower structure. That’s why wireless operators often use wind load data presented by base station antenna manufacturers when deciding on which antennas to deploy. Therefore, it is important for operators and tower owners to fully understand how wind load data is calculated so fair comparisons can be made between various antennas and mounts.

Safety must always be paramount to operators as well. As networks become larger and more complex, overweighted towers or configurations that present wind resistance can cause equipment to loosen or mounts to fail, which can represent a danger to residents nearby. The safety of maintenance crews must always be taken into consideration, since overloaded towers or those with little concern for weight and wind load can present a danger to even veteran crew climbers.

Deploying more and more antennas in order to meet growing demand only results in antenna towers and support structures being pushed to the limits of their load capacity.

As you look at modernizing your network, it is important to understand the impact your antenna and antenna mounting choice has on the overall tower load. Frontal wind loading and overall weight are important factors. Performance factors aside, antenna mounts with better frontal loading design and lesser weight will decrease overall tower weight and wind load issues. Base station antenna mounts add load to the towers not only due to their mass, but also in the form of additional dynamic loading caused by the wind. Depending on the aerodynamic efficiency of the antenna mount, the increased wind load can be significant.

Additionally, there are other location specific factors to consider when calculating antenna wind load. These include geographic location, tower height, tower or building structure, surrounding terrain, and shielding effects from other mounted antennas.

Although the antennas have evolved to offer as many as eight connectors in the same space and weight (i.e. engineers have figured out how to fit the same RF performance into the same size package and form factor), up today the challenge of weight and wind load of the antenna mounts (impacting the total antenna-mounting system) have not been addressed. LTE installations involve dozens of components, including antennas, RRUs, trunk and sector fiber, matching connectors, and jumper cables. Plus, there’s a long list of support components—such as hangers, hoists and junction boxes—all mounted on a structural support. With this amount of gear, it can be very problematic to manage all this on existing TDMA/GSM sector frames designed for smaller and lighter antennas and less equipment. You also have to consider the tower structure itself may be designed to hold much less equipment.

A quick history lesson.

When we consider weight and wind load as they relate to the structural support variables of a tower, it’s important to start with a bit of a history lesson. Overall,  as the technology has grown, evolved and changed, so have structural supports and mounts. First, we had robust structures with heavy-duty mounts. As antennas decreased in weight and size, so did the structures and mounts. As a result, less loading needs led to less robust structures. But, as heavier 3G antennas and equipment rolled onto the market, loading was impacted, deflection increased, and issues with twist and sway became more and more prevalent.

Now, with LTE technology,  there are even heavier antenna piping and antennas, as well as RRUs, fiber boxes and other necessary equipment.

Failures to address the appropriate mounts and structures have started to become more evident as towers have fallen or been damaged due to vibration and torsion. Bottom line, years ago tower mounts were designed to meet lower criteria. For example, under the old criteria, a tower from just ten years ago was designed to meet 150 mph loading, which was considered a strong design for the antennas and equipment it had to support. Now, that same tower does not meet the set criteria!!!

FASMETRICS SA F-CAT systems are designed for this specific purpose: to relax the tower from both weight and wind loading in order the existing operational towers to meet these criteria, even with four times higher weights than its predecessors.

Why structural support is so important.

As we’ve discussed, when there is a need to increase capacity, modernizing a network by adding new LTE equipment to existing networks is a good option. However, a migration from older technology to LTE can add an average of 750 lbs of equipment and an additional 50 square feet per sector of effective projected area (EPA) to the top of the tower, which can have a tremendous impact on performance. Although well-made mounts can help antennas maintain optimum performance, too little attention is paid to the impact of mounts, such as their physical properties and their ability to support LTE components for the long term.

Less expensive, low-grade structural components such as mounts, brackets, and fasteners may have difficulty preventing antenna tilt, twist, sway and vibration. Over time, these issues can cause antennas and entire networks to underperform. When low-quality mounts fail, sites can—and do—go down. Operators must pull personnel and equipment from other sites to restore connectivity, negatively affecting productivity. And, of course, there’s the potential to destroy personal property or cause serious injury or death. Other possible ramifications of a structural failure due to weight and wind load issues include:

• Expenses are impacted by the deployment of emergency mobilization crews, expedited equipment shipping costs, labor overtime.
• Customers may switch carriers if they consistently experience dropped calls and slow data rates, negatively impacting operator image and revenue.
• Urban cell site downtime can result in a significant loss of roaming charge revenues, as well as negatively impact the company’s image.
• Customers or public safety officials may have difficulty communicating during emergencies, affecting safety and security, which could also lead to litigation.

Top structural support considerations

When engineers design towers today, or look at the prospect of adding equipment, such as an antenna, there are several critical factors they should look at closely to ensure future tower stability and network performance.

Among these critical factors are mounts.

Tower mounts should be chosen carefully based on the projected weight of the antennas. Any overloading can create movement that can have a negative impact on safety and performance. In fact, failure to choose the right mount can result in damage or destruction of structure legs, with the possibility of the tower falling. Overloaded mounts can also result in twisting and instability from the tensional forces, which can lead to network failures. In simple terms, overloading of an existing infrastructure occurs when the tower and mounts are saddled with an amount of equipment the structure was not designed to handle.

Engineers and operators who take a piecemeal approach to tower construction or network modernization risk putting their entire system at risk. In addition to the obvious safety issues, performance can be degraded, which can ultimately lead to loss of revenues.

While reducing cost is always a top priority, operators that price shop for the best bargains risk piecing together a structure comprised of multiple low-quality components that ultimately cannot safely withstand the elements or ensure network dependability. When you consider the significant  expenditures involved in creating a wireless network path, installing poor-quality mounts is akin to mounting the cheapest tires on a high-performance race car.

The evolution of the structural mount.

In the past, 250 pounds per sector was the standard, with a recommended EPA (effective projected surfaced area) of 16. Towers were designed for those criteria. Nowadays, however, many mounts on multi-operator towers in the U.S. exceed those limits substantially. So, should one mount fail in one carrier sector, the resulting tower tension, vibration and instability may multiply the impact on the other three sectors. This can cause an entire structure to fail or, at the very least, cause the system to perform poorly for some or all of the other carriers. The resulting loss of revenues can be devastating.

So, when it comes to structural support, the key takeaways are to approach network modernization for towers holistically and as a complete system. And make sure you choose a single supplier with the expertise to deliver LTE antenna mounting solutions that enhance structural integrity and properly support the weight and wind load criteria for today’s 4G equipment.

The evolution of the cell tower structure has made weight and wind load an industry-wide issue that must be addressed. And that’s not just for safety concerns. Structures that fail to take into account weight and wind load when implementing upgrades or modifications risk bringing their network down—or, at the very least, degrading performance. In today’s competitive market with discerning consumers who demand reliable services, you don’t want to risk losing customers. The good news is that here at FASMETRICS SA we have many very good solutions for upgrades that allow for adding antennas, connections, mounts and equipment that can help your structures remain stable for continued performance. We are a trusted single-source partner that can ensure that your structure meets or exceeds requirements for safety and performance.