Civil Engineering Reference
In-Depth Information
The main discrepancies with the current building codes are mainly related with
the design loads and the safety factors. The structural analyses are based on the
most unfavourable load combinations, however, the direct use of the load distri-
butions prescribed by the designing codes, developed for standard buildings, leads
to several inaccuracies due to the non-linear behaviour of membrane structures and
their large de
ection behaviour. Super position of load effects is not applicable to
membrane structures and a different
fl
load distribution can easily result
in an
unexpected de
ection which can lead to water ponding and snow drift with the
progressive collapse of the structure. On the other hand, seismic loads, which are
particularly insidious for standard building, are generally negligible due to the low
mass of tensioned membrane structural systems. Even the concept of tributary area
for live loads is not literally applicable to membrane roofs. In addition, the unique
surface forms prevent the direct use of the coef
fl
cients for the snow distribution and
the wind pressure provided by the designing codes for standard geometries.
In the European context, the common approach for the design of buildings and
other civil engineering works and construction products is provided by a series of
ten European Standards (EN 1990
EN 1999) known as EN Eurocodes. Their area
of applicability is extremely wide from the basis of structural design to the actions
on structures, in addition they describe the design procedures and the theoretical
aspects concerning each main building system (concrete, steel, composite steel and
concrete structures, timber, masonry, geotechnical design, design of structures for
earthquake resistance, aluminium). The design of the rigid frame supporting the
tensile structure is generally carried out according to the prescriptions reported in
each Eurocode (steel, timber and aluminium), however, the most demanding part of
the project, the membrane or the cable net, is at the discretion of the designer.
The only European Standard currently available about membrane structures is
the EN 13782:
2005
-
. Its area of applicability is
mainly restricted to the safety requirements for tents which need to be observed at
design, calculation, manufacture, installation, maintenance, operation, examination
and testing of mobile, temporary installed tents of more than 50 m
2
ground area.
Nonetheless, it offers the only reference to membrane structures and deals with the
fundamental terms and de
“
Temporary structures-Tents-Safety
”
nitions, the general requirements for design, analysis and
examination, principles of numerical analysis, the design actions, the veri
cation of
stability and equilibrium, the ground anchorages, the other structural components,
the special design and manufacture criteria, the manufacture and supply, the
examination, the competence, procedures for approval, examination and tests, the
tent topic, the use and operation, the burning behaviour and the aerodynamic
coef
cients for round shape tents.
The characteristics, the requirements and the test methods for coated fabrics
intended for temporary structure and tents are summarised in the European Standard
EN 15619:2008+A1:2010
“
—
Rubber or plastic coated fabrics
Safety of temporary
—
structures (tents)
Speci
cation for coated fabrics intended for tents and related
structures
. It introduces the idea of different level of performance for each charac-
teristic which allows the choice of the appropriate level of each characteristic (mass
per unit area,
”
tensile mechanical behaviour,
tear strength, coating adhesion,
