Safety of 5G Network Physical Infrastructures 173
To ensure that the basis for design provides an appropriate level of structural reliability (or probability of failure), partial factors are introduced to take into account the
effects of aleatory and epistemic uncertainties in the methods used to assess the characteristic values but also in the specified analysis and verification procedures. Therefore,
design values for resistances are determined by dividing the characteristic values by a
partial factor, γ R , (larger or equal to 1.0) and design values for load effects are obtained
by multiplying the characteristic values by a partial factor, γ S , (typically larger than 1.0).
LSD specifies the verification of the structural reliability for several limit states, that
is states beyond which the structure no longer fulfils the relevant design criteria:
Ultimate Limit States (ULS) in which all possible failure modes must be evaluated,
Serviceability Limit States (SLS) in which it is verified that specified service requirements are met (e.g. maximum number of hours per year where the signal level is reduced
below an acceptable limit), and other limit states such as fatigue resistance.
One should note that under certain hazard events, communication structures may be
allowed to lose their functionality while not collapsing. However, it is often when such
hazard events occur that demand for mobile communication services increase as civil
protection and emergency services intervene, people try to contact and connect with
their families, and remote access requests to businesses expand. In these situations,
systems already severely strained can be pushed beyond their operational limits.
Finally, several load combinations must be checked to guarantee that all reasonable
possible sets of physical conditions that can occur during a certain time interval, also
known as design situations, are taken into account. In general, three different design
situations are defined, each one representing a certain time interval with associated
hazards, conditions and relevant structural limit states: persistent, transient and accidental situations, which refer to normal, temporary and exceptional situations. Each
load combination is formed by the permanent loads, a leading variable action and the
relevant accompanying variable actions, which are multiplied by combination factors
(smaller than 1.0) in order to obtain concomitant actions values [30].
LSD has been established in the European Structural Eurocodes, namely BS EN 1990
[31,32], BS EN 1993 series, such BS EN 1993‐3‐1 [21,33], and in the USA, standard
TIA‐222‐G [22] for example. By using BS EN 1990 and BS EN 1993‐3‐1, it is possible for
the stakeholders to manage the target reliability level of the structure by specifying
three reliability classes (Table 8.1). Regarding the design working life, BS EN 1993‐3‐1
recommends using a value of 30 years.
Table 8.1 Reliability classification in accordance with Eurocodes for ULS.
Reliability
classes
Reliability index, β 1
(1 year reference period) Examples of mobile communication structures
RC1
4.2
Towers and masts whose failure would likely result only in
small economical, social and environmental consequences
RC2
4.7
All towers and masts that cannot be defined in RC1 or RC3
RC3
5.2
Towers and masts whose failure would result in severe loss
of human life, and/or in major economical, social and
environmental consequences
To ensure that the basis for design provides an appropriate level of structural reliability (or probability of failure), partial factors are introduced to take into account the
effects of aleatory and epistemic uncertainties in the methods used to assess the characteristic values but also in the specified analysis and verification procedures. Therefore,
design values for resistances are determined by dividing the characteristic values by a
partial factor, γ R , (larger or equal to 1.0) and design values for load effects are obtained
by multiplying the characteristic values by a partial factor, γ S , (typically larger than 1.0).
LSD specifies the verification of the structural reliability for several limit states, that
is states beyond which the structure no longer fulfils the relevant design criteria:
Ultimate Limit States (ULS) in which all possible failure modes must be evaluated,
Serviceability Limit States (SLS) in which it is verified that specified service requirements are met (e.g. maximum number of hours per year where the signal level is reduced
below an acceptable limit), and other limit states such as fatigue resistance.
One should note that under certain hazard events, communication structures may be
allowed to lose their functionality while not collapsing. However, it is often when such
hazard events occur that demand for mobile communication services increase as civil
protection and emergency services intervene, people try to contact and connect with
their families, and remote access requests to businesses expand. In these situations,
systems already severely strained can be pushed beyond their operational limits.
Finally, several load combinations must be checked to guarantee that all reasonable
possible sets of physical conditions that can occur during a certain time interval, also
known as design situations, are taken into account. In general, three different design
situations are defined, each one representing a certain time interval with associated
hazards, conditions and relevant structural limit states: persistent, transient and accidental situations, which refer to normal, temporary and exceptional situations. Each
load combination is formed by the permanent loads, a leading variable action and the
relevant accompanying variable actions, which are multiplied by combination factors
(smaller than 1.0) in order to obtain concomitant actions values [30].
LSD has been established in the European Structural Eurocodes, namely BS EN 1990
[31,32], BS EN 1993 series, such BS EN 1993‐3‐1 [21,33], and in the USA, standard
TIA‐222‐G [22] for example. By using BS EN 1990 and BS EN 1993‐3‐1, it is possible for
the stakeholders to manage the target reliability level of the structure by specifying
three reliability classes (Table 8.1). Regarding the design working life, BS EN 1993‐3‐1
recommends using a value of 30 years.
Table 8.1 Reliability classification in accordance with Eurocodes for ULS.
Reliability
classes
Reliability index, β 1
(1 year reference period) Examples of mobile communication structures
RC1
4.2
Towers and masts whose failure would likely result only in
small economical, social and environmental consequences
RC2
4.7
All towers and masts that cannot be defined in RC1 or RC3
RC3
5.2
Towers and masts whose failure would result in severe loss
of human life, and/or in major economical, social and
environmental consequences