Monitoring Forces in Steel Wire Rope Nets: Evaluation of Short and Long Term Influences

139-142

Artikel aus einem Buch

200204829

ABSTRACT: Flexible steel wire rope nets are used as mitigation measures in avalanche starting zones. The purpose of these measures lies in the prevention of an avalanche release. Net systems are loaded by the uphill snowpack which results in pressure, tensile and shear forces in various parts of the structure. At the “Hafelekar” test site close to Innsbruck (Tyrol, Austria) at 2.254 m a.s.l. forces acting on the strut in the middle and the strut at the edge of the snow net were measured from 2006 to 2017. Furthermore two automatic weather stations provide continuous measurements of air temperature and snow height in the test site. The recordings provide the temporal evolution of forces over each winter period. Hence maximal values of forces per year and overall were determined. Since mitigation measures are dimensioned to withstand extreme values, a comparison between characteristic forces and the measured forces is given. With regards to the meteorological parameters the measurements indicate additional loading by precipitation events. Melting and sublimation processes lead to a reduction of the snowpack and therefore to decreasing forces acting on the structure. Beside seasonal variations throughout the winter period, the measured forces also indicate a diurnal variation. While resulting stresses in the structure increase during the night, they decrease during the day, if no precipitation event occurs. These fluctuations are observed in a range of ≈ 10% of the load and are correlated with heating and cooling of the snowpack which is associated with different bonding states in the snow cover.
Keywords: steel wire rope nets, avalanche mitigation, design load, diurnal variation, mitigation measures,
monitoring