Safety of 5G Network Physical Infrastructures 183
In particular, in monopoles with tubular cross‐section or with a radome mounted on
the top, the vortex shedding phenomena causes a random pressure in the plane perpendicular to the direction of the wind flow. If the frequency caused by vortex shedding
coincides with the fundamental frequency of the structure, significant resonant vibrations will occur [3,6]. Because this condition occurs for a critical wind speed that is
often observed, the assessment of the fatigue resistance may also become important.
Although this phenomenon is widely known, its complexity makes the currently used
empirical‐based procedures for the assessment of the response too simple. Diverse
failures caused by these phenomena were observed and are well documented [3,60].
Also, the presence of ice on the structure increases the mass, changes its dynamic characteristics and could severely alter the behaviour under wind action on the structure
due to the increase of the exposed area coupled with potential asymmetries of the structural geometry [3,6]. These design shortcomings could be aggravated by fabrication
faults, for example in the welding of the stiffeners where undersize welds are often used.
In structural design, many aspects are frequently ignored when using numerical
model simulation, for example, soil‐structure interaction, a more refined mass distribution and/or stiffness loss. The dynamic analysis of tall slender structures is commonly
performed in the frequency domain, based on the frequency dependent character of
both wind loads and mechanical properties of the structure. These factors depend on
several parameters, including the first natural frequency of the structure, its damping
and the characteristics of the wind [4,5]. Consequently, the numerical models currently
available and commonly used by the industry do not reflect the actual field conditions
and do not provide adequate information of the correct structural behaviour [3]. Also,
several studies highlight the great difficulty in the adequate consideration for structural
analysis of non‐structural elements, which are protected and/or allow protection of the
structure when exposed to wind action [8,9]. Shield effect is a well‐known fact. However,
there is no well‐defined method available for the quantification of this important phenomenon. Thus, there may be a significant reduction of the current design values of the
wind pressure at areas where there are head frames and/or multiple antennas, which are
often determined by a simple sum of the wind action on each element [9].
In this context, there is also an urgent need for the development of the knowledge in
this technical and scientific field. It is vital to perform an extensive review of the state‐
of‐the‐art and develop new approaches for the analysis and design of this type of
structures.
8.4.3 Maintenance Failures
Before the exponential growth in the use of cellular phones, maintenance failures were
mainly due to inappropriate maintenance operations, for example, the collapse of a very
high guyed mast (over 300 m in height) during maintenance. Nowadays, with the huge
number of small existing communication structures, the major failures occur more
likely due to the lack of maintenance. In the 1990s, communication networks significantly expanded. During this period, governments and telecommunication companies
intended to cover the national territories with the best possible network. As a result,
there was a large‐scale deployment of communication structures to respond to their
needs. After this period, it was recognized as essential to maintain these structures in
good structural conditions using periodic inspections, maintenance and occasional
testing. Like any infrastructure, maintenance is essential to ensure the extension of the
In particular, in monopoles with tubular cross‐section or with a radome mounted on
the top, the vortex shedding phenomena causes a random pressure in the plane perpendicular to the direction of the wind flow. If the frequency caused by vortex shedding
coincides with the fundamental frequency of the structure, significant resonant vibrations will occur [3,6]. Because this condition occurs for a critical wind speed that is
often observed, the assessment of the fatigue resistance may also become important.
Although this phenomenon is widely known, its complexity makes the currently used
empirical‐based procedures for the assessment of the response too simple. Diverse
failures caused by these phenomena were observed and are well documented [3,60].
Also, the presence of ice on the structure increases the mass, changes its dynamic characteristics and could severely alter the behaviour under wind action on the structure
due to the increase of the exposed area coupled with potential asymmetries of the structural geometry [3,6]. These design shortcomings could be aggravated by fabrication
faults, for example in the welding of the stiffeners where undersize welds are often used.
In structural design, many aspects are frequently ignored when using numerical
model simulation, for example, soil‐structure interaction, a more refined mass distribution and/or stiffness loss. The dynamic analysis of tall slender structures is commonly
performed in the frequency domain, based on the frequency dependent character of
both wind loads and mechanical properties of the structure. These factors depend on
several parameters, including the first natural frequency of the structure, its damping
and the characteristics of the wind [4,5]. Consequently, the numerical models currently
available and commonly used by the industry do not reflect the actual field conditions
and do not provide adequate information of the correct structural behaviour [3]. Also,
several studies highlight the great difficulty in the adequate consideration for structural
analysis of non‐structural elements, which are protected and/or allow protection of the
structure when exposed to wind action [8,9]. Shield effect is a well‐known fact. However,
there is no well‐defined method available for the quantification of this important phenomenon. Thus, there may be a significant reduction of the current design values of the
wind pressure at areas where there are head frames and/or multiple antennas, which are
often determined by a simple sum of the wind action on each element [9].
In this context, there is also an urgent need for the development of the knowledge in
this technical and scientific field. It is vital to perform an extensive review of the state‐
of‐the‐art and develop new approaches for the analysis and design of this type of
structures.
8.4.3 Maintenance Failures
Before the exponential growth in the use of cellular phones, maintenance failures were
mainly due to inappropriate maintenance operations, for example, the collapse of a very
high guyed mast (over 300 m in height) during maintenance. Nowadays, with the huge
number of small existing communication structures, the major failures occur more
likely due to the lack of maintenance. In the 1990s, communication networks significantly expanded. During this period, governments and telecommunication companies
intended to cover the national territories with the best possible network. As a result,
there was a large‐scale deployment of communication structures to respond to their
needs. After this period, it was recognized as essential to maintain these structures in
good structural conditions using periodic inspections, maintenance and occasional
testing. Like any infrastructure, maintenance is essential to ensure the extension of the