Schubtragfähigkeit von Wänden aus Kalksand-Planelementen mit geringem Überbindemaß  -  Experiment und rechnerische Simulation

Shear load bearing capacity of masonry walls made of calcium silicate element units with a low overlap length — Experimental and numerical simulation analysis.

The shear force resistance capacity VR of masonry walls subjected, in their plane, to loads from winds or earthquakes, amongst other things, depends on the overlap length of the units ü or on the ratio of the overlap length and the height of the unit ü/hast. The currently permissible overlap length, according to German design standards and norms, of ü ≥ 0.4 hast can not always be adhered to in building practice, when using element units. In such cases and according to general technical approval code (abZ) of the German Institute for Building Technology (DIBt) for calcium silicate element units within the range 0.4 >ü ≥ 0.2 hast or 12.5 cm, a reduced permissible calculation value of the characteristic shear strength fvk of 60 % of the value according to DIN 1053-100:2007-09 (ü ≥ 0.4 hast ) has been used to date. This high loss of load bearing capacity, based on results of older experiments with ob solete test setups, was to be tested in the course of the inclusion of element units in the calculation standards for masonry walls, with a new shear calculation concept.
As a result, extensive experimental and theoretical tests were carried out on 17.5 cm thick and 2.50 m high shear walls made of masonry calcium silicate element units and ungrouted butt joints. The objective was to quantatively determine the influence of low overlap length ü/hast< 0.4 on the shear resistance of these masonry walls and in particular with static-cyclical horizontal displacement at the wall top. The vertical load pressure (σ = 0.5/1.0/1.43 N/mm²), the overlap length (ü/hast = 0.2/0.4) and the fixing at the top and bottom of the wall were varied and used as experimental parameters.
Within the range of normative calculation with low overlap lengths 0.2 ″ ü/hast ″ 0.4, the investigations showed no significant load bearing capacity loss. With more extensive theoretical Finite Element analyses for the normal building practice spectrum of overlap lengths 0.2 ″ ü/hast ″ 1.0 for walls with a vertical load of 0.5 N/mm² or 1.0 N/mm², a reduction of load bearing capacity of maximum 12 % to 16 % was calculated.
The transmission of the horizontal shear load from the top of the wall to the bottom of the wall takes place through a diagonal compression stress field. Cracks may occur in the overlap area of the element units as a result of stress concentration, which are limited to the overlap area and do not cause any impairment to the load bearing capacity of the wall. This capacity is only then exhausted when the trans missible, diagonal compression stress can no longer be absorbed, especially at the bottom of the wall with cracked masonry.