An experimental investigation of the effect of the placement angle on the collapse of ice screw anchors

Ice screws are used as anchors for ice climbing, especially on vertical ice walls. The mechanical properties of modern ice screws must comply with international standards; nevertheless their reliability greatly depends on the mechanical characteristics of the ice and on the actual screw placement. The placement is an important issue; in particular the angle between the axis of the ice screw and the ice wall is a relevant and physically measurable factor for ice screw reliability, thus potentially significant for ice climbing safety. This work is focused on the effect of the placement angle on the collapse load of ice screws. The topic was recently investigated by several authors mainly using artificially "laboratory" ice; different results, often contradictory in terms of collapse loads and suggested placement were obtained. To improve knowledge on ice screw failure and increase ice climbing safety, a scientific analysis was carried out. Both static and dynamic (shock) tests on ice screw specimens placed in a natural environment (waterfall ice) have been performed with different placement angles (-20 degrees, 0 degrees, +20 degrees). The experimental results as well as their statistical analysis are reported and discussed. Attention was also paid to the effect of the ice properties on the collapse of the ice screw anchors. (C) 2012 Elsevier Ltd. All rights reserved.