As existing antenna mounts age in the field and become overstressed because of changes in loading demand, the industry has increasingly recognized the need for consistency and transparency in the way antenna mounts are designed and analyzed. As a result, the Telecommunications Industry Association (TIA) has released both new and revised standards within the past year. The rationale for the changes incorporated in these standards can be difficult to decipher, and their implications for standard business practices going forward are worth examining. The following information will address common questions regarding these standards — particularly TIA-5053 — and other general mount engineering practices.
Q: What is the TIA-5053 standard and why was it created?
A: TIA-5053 is a standard created to address multiple issues regarding the design of antenna mounts and their use in the field.
Issue 1: Design differences among manufacturers.
Historically, antenna mount design criteria and methodology have varied widely among manufacturers, making comparisons difficult. For example, it might appear that Manufacturer A’s antenna mount, designed for four 96-inch antennas at 90 mph wind speeds, has greater capacity than Manufacturer B’s mount designed for four smaller 60-inch antennas at 120 mph wind speeds. However, the second mount may actually have more capacity because of the higher wind speed it was designed for, in addition to other unknown design criteria, including antenna centerlines and exposure. Because of the number of criteria involved in mount design, it has been nearly impossible up to this point to compare mounts from two manufacturers for actual capacity without additional information, or a separateindependent mount analysis of each mount. The TIA-5053 standard addresses these inconsistencies between manufacturers by specifying a complete list of criteria for the design of antenna mounts. They include:
1. Modeling guidelines
2. Loading conditions
3. Load factors
4. Equipment placement
5. Maintenance loads
6. Load combinations
Thus, the TIA-5053 standard enables customers to make apples-to-apples comparisons between mounts made by different manufacturers.
Issue 2: Idealized designs vs. real-world installation practices.
When mounts are installed in the field, loading configurations frequently diverge from the loading intended by the mount’s design. For example, today’s mounts are rarely installed in the field with loading that is both vertically and horizontally symmetrical on the mount, as intended for optimal capacity according to the mount design. Mounts designed and classified to the TIA-5053 standard will take into account loading symmetry tolerances in the reported capacity that will reflect real-world installation variances. However, if the loading is installed outside of the allowed symmetry tolerances, the classification becomes invalid.
Issue 3: Limited or obscure rating documentation on mounts.
Mount analyses have become more prevalent in the past several years because of concerns that existing mounts are being loaded beyond their design capacity. Toengineers, the widespread presence of overstressed mounts in the field comes as no surprise. Mounts commonly have issues that prevent them from achieving their theoretical capacity. General condition issues include rust, corrosion and missing bolts. Installation issues include incorrect orientation of main mount members and improper installation of the mount-to-tower connection. And in practice, loading is rarely installed symmetrically, which further deviates from the design intent. Final loading configurations frequently consist of weight and wind areas that the mounts were not designed to handle, even in the most optimal installation conditions.
Many customers receiving mount analysis deliverables express shock and disbelief at the prevalence of overstressed mounts. Carriers have only begun to realize the can of worms that has been opened, as the expense of correcting previously undiscovered issues rises exponentially. Although the purchase of mounts designed and classified per the TIA-5053 standard will not have an immediate financial effect, it will provide many long-term benefits to those footing the bill. Not only will it provide transparency into what is installed in the field, enabling increased accuracy in budget planning for future equipment deployment, but also it may lessen the need for mount analysis and modification design for multiple future deployments.
Q: Are manufacturers required to design and classify mounts to TIA-5053?
A: No. TIA-5053 is a voluntary standard. However, if a manufacturer reports that a mount is classified in accordance with this standard, then the entirety of the standard must be incorporated into the mount design.
TIA-5053 was written to apply broadly in the industry. Special cases may fall outside of this standard, but it is geared to include 85 percent of all mounts.
Q: Does TIA-5053 only apply to new mounts?
A: No. TIA-5053 also can be used to classify existing mounts. However, it may not be cost-effective to do so because additional engineering time will be required to determine the mount classification. In addition, because of symmetry requirements and other site-specific criteria listed in the standard, ensuring that an existing mount conforms to the standard may require relocating existing loading in order to fall within the allowable symmetrical tolerances. If an existing mount cannot be classified in accordance with TIA-5053, it should be analyzed in accordance with TIA-222.
Q: Do I have to precisely match the design loading configuration in order for a mount classification to be valid?
A: No. For example, if a mount is classified for four antenna positions, as long as the symmetry requirements are met, as many as four antennas of varying sizes and weights may be installed in any of the four positions, as long as the design-factored forces are not exceeded at any loading position (see Figure 1).
Q: How can a mount in the field be identified as a classified mount?
A: Refer to Table 1. Mounts are classified into categories based on their intended use. Each mount classified in accordance with the TIA-5053 standard will have a designated code comprised of letters and numbers toidentify its category, maximum horizontal design force per mount pipe location, maximum vertical design force per mount pipe location and allowed vertical offset. In addition, the TIA-5053 standard requires submission of specific documentation with classified mounts.This documentation will provide clarification on design intent and proper assembly of all components.
Q: How will TIA-5053 help the various stakeholders in the industry?
A: It will assist these categories of stakeholders in the following ways:
Engineers:Prior to the use of the TIA-5053 standard, it was nearly impossible for an engineer to be able to compare in-field conditions of an existing mount to the original design intent because of minimal information provided from the manufacturer regarding the entire list of criteria incorporated in the mountdesign. Documentation provided with mounts classified in accordance with the TIA-5053 standard will provide transparency to engineers regarding design criteria and will enable them to easily compare installed loading versus maximum design loading.
Mount manufacturers:TIA-5053 provides an industry standard for mount design and promotes the installation and the use of mounts in a manner that is in line with the design intent. In addition, it helps them more easily respond to questions regarding the capacity of their mounts. Finally, it allows them to easily demonstrate how their products compare with those of other manufacturers.
Contractors and installers: TIA-5053 simplifies the purchasing process by making it possible to easily compare products of different manufacturers. Documentation requirements will promote installation in accordance with the manufacturer intent (e.g., allowable tie-back angles).
Carriers (owners): Currently, a majority, if not all, tower owners maintain that the mount is completely owned by the carrier. With the enforcement of the TIA-222-H standard, mount analyses will be a required step in the structural analysis process. Through the purchase of mounts classified in conformance with TIA-5053, carriers will be able to mitigate many of the costs associated with mount analysis, reanalysis and modification design, along with reducing the risk of failures in the field resulting from inadequate and incorrect installation.
Q: Is it better to modify or replace a failing mount?
A: From the perspective of an engineer, the best course of action will depend on the degree of modification required and on the feasibility and cost comparison of modification versus replacement. This can also be driven by the local carrier market based on their current budgets and forecasts for future technology installs. It’s prudent for decision-makers to keep in mind that extensive modifications to mounts usually result in a noticeable capacity stress ratio increase to the tower. For example, one complex mount modification performed by the SSOE Group resulted in a 60 percent increase in both the front and side areas of the mount following modification, likely leading to a significant increase in the tower capacity stress ratio.
Q: How can the results of mount analyses performed bytwo engineering vendors be so different?
A: There is no widely accepted industry standard for the way an engineer performs a mount analysis. Mount analysis deliverables vary, from a direct load comparison only to a rigorous analysis using finite element analysis software. Current standard design codes do not specify guidelines for the nuances involved in mount analyses. To help engineers perform mount analysis to the same standards and to drive consistency between engineering vendors, the TIA is developing a white paper on best practices for mount analysis, with the participation of over 20 engineering firms and mount manufacturers across the industry.
Q: Why am I getting such a high mount capacity stress ratio from just from one radio addition?
A: It is often assumed that the structural adequacy of a mount is similar to that of a tower, in that all existing structures are adequate under existing loading conditions and that changes in mount capacity stress ratio should reflect loading additions similar to the way these changes affect tower capacity stress ratio. That is, a small equipment change or addition will have a minimal effect on the structure capacity stress ratio. However, there are a couple of reasons why mounts cannot be compared to towers in this way.
If there is no mount analysis on record, it is likely the mount has not been analyzed before and many mounts are overstressed under as-is conditions for reasons discussed in “How to Analyze Antenna Mounts to Avoid Costly Consequences” (AGL Magazine, December 2015). Therefore, it is possible that the mount will be overstressed even if loading is removed.
In addition, swapping an older technology antenna for a new one is not equivalent because of the significant increase in size and weight of new equipment when compared to overall loading on the mount. The mount is also a much smaller structure relative to the equipment it holds than the tower, so loading changes will have a larger impact on its capacity stress ratio. For one mount analysis on what would be considered a typical loading scenario, the addition of one antenna and one radio per sector caused the equipment weight to increase by 59 percent, and the front and side wind areas to increase by 40 percent and 46 percent, respectively. For another mount analysis, the addition of one radio per sector caused increases in area and weight per sector (see Table 2).
Q: It doesn’t look as though the proposed mount is any sturdier than what is currently installed. Why do you recommend this mount be used?
A: There are many different aspects of a mount that determine its overall performance and capacity, many of which cannot be easily pinpointed through visual observation alone. The article “Mount Analysis Case Study: Why Small Modeling Changes Make a Big Difference” (AGL Magazine, November 2016) demonstrates how many seemingly small changes in mount or loading configuration result in large capacity stress ratio changes. In addition, manufacturers are now designing their mounts to support heavier loading conditions than they were five to 10 years ago.
Q: What changed in TIA-222-H regarding mount analysis requirements?
A: TIA-222-H took prior requirements for mount analysis and expanded upon them, explicitly stating them in a separate chapter in the standard.
Q: When will TIA-222-H be enforced?
A: The TIA-222-H Standard was published in October 2017 and will be recognized and referenced by the 2018 “International Building Code” (IBC). As jurisdictions adopt the 2018 IBC, mount analyses will need to comply with TIA-222-H in order to meet with jurisdictional requirements.
All stakeholders in the mount analysis industry will benefit from these recently published standards, which promote consistency and a leveling of the playing field across all aspects of the industry. With 5G and possibly even larger associated equipment loads on the horizon, the standardization of mount design and analysis through these standards will ensure that the antenna mount industry is ready to address any and all loading challenges.
Michelle Kang, P.E., and Ismaias Recinos, P.E., are structural engineers at SSOE Group (www.ssoe.com), a global engineering, procurement and construction management firm. Each has experience working on towers, mounts, rooftop sites and other specialty structures for various clients throughout the United States.
This article originally ran in the July, 2018 issue of AGL Magazine.