Application of a mobile measuring device for the planar evaluation of the current in-situ stress condition in glass

The load-bearing capacity of glass as a structural material as well as sustainability and resistance of a built-in glass against appearing loads and forces is assuming an ever-greater importance. Next to analytical and numerical calculations of maximum load-bearing capacity and the ultimate limit state, there is no generally accepted standardized non-destructive inspection method available, with which it is possible to estimate the prevalent load situation and predominant stress conditions, particularly in relation to mechanical or adhered connections. Within the research project “BiGla”, a measuring instrument based on photoelasticity was developed, which enables to measure and monitor occurring load states during the installation process, as well as the utilization of glass components subjected to significant load changes during their life cycle. Based on the combined examination of photoelasticity and its synergism with the finite element analysis it becomes possible to transfer qualitative measurement results into quantitative evaluations of predominant stress conditions. Achieved results, gained during experimental investigations under laboratory conditions, as well as during extensive field tests, are presented in this publication

Zur Bemessung von SL-belasteten Anschlüssen im konstruktiven Glasbau

For the design of glass structures the connection method is of great importance since the relevant stresses of point-fixed glass occur in the ultimate vicinity of the holes. If no further constructive means are provided, these stress peaks cannot be dissipated with subsequent glass breakage. This phenomenon also applies for in plane glass connections with bolts in bearing, where bolt forces act on the glass through ductile interlayers (mortar) that are placed between the glass and the steel bolt. However, until today, there are no construction standards for connections with only one bolt as well as for connections with several bolts under combined sectional forces and moments. Furthermore, imperfections, tolerances, brittle behaviour and scattering of the material properties have to be considered. This thesis addresses developing an engineering model for lapped glass joints with bolts in bearing and the derivation of rules for the design. Based on the stress function of Airy an analytical calculation method could be developed, in which local bearing stresses under bolt loading are superposed by net section stresses. Both stress states can be described by stress functions. Thus any bearing condition is addressable. By means of reverse composition of the two stress fractions the stress-strain-state of panes consisting of elastic-isotropic materials with arbitrary hole pattern under any boundary condition can be determined depending on the bolt load, the pane thickness, the hole diameter and the relevant width resulting from the joint geometry. Further the analytical solution could be reduced to a simple design equation, which enables the determination of the relevant stresses depending on bolt forces acting on the single hole, the diameter of the hole and the glass thickness. Thereby also the influence of the erection and fabrication tolerances as well as design parameters had to be systematically examined by Finite Element calculations that had been performed so far for the first time. The effects could be numerically discovered and coefficients for the design equation could be derived. Also a non uniform bolt force distribution has to be taken into account for long bolt rows parallel to the force direction. To ensure a sufficient load bearing capacity of the entire detail, the interlayer material cannot be neglected. Therefore, theoretical examinations were performed. The effect of erection and fabrication tolerances as well as geometrical parameters on the stresses in the mortar could be determined. The results serve as an approach for the verification of the interlayer against the bolt forces, the diameter of the hole and the glass thickness. The definition of the material resistance bases on former research results and examinations. All theoretical studies were verified by numerous experimental tests under monotony loading after prior cyclic service loading. In analogy to the analysis, the tests have been realised for joints under normal forces as well as under combined shear forces and moments. The stress-strain-distributions, which were determined by strain gauges and the analysis of the fracture pattern coincide with the theoretical results. Finally, it was shown that effective resistant stresses governing the load bearing capacity of bolted connections under in plane loading is lower compared to those effective resistant stresses that control failure in case of plate loading. The thesis closes with derivations for partial safety factors and proposals for the codification

Zur Bemessung von SL-belasteten Anschlüssen im konstruktiven Glasbau

For the design of glass structures the connection method is of great importance since the relevant stresses of point-fixed glass occur in the ultimate vicinity of the holes. If no further constructive means are provided, these stress peaks cannot be dissipated with subsequent glass breakage. This phenomenon also applies for in plane glass connections with bolts in bearing, where bolt forces act on the glass through ductile interlayers (mortar) that are placed between the glass and the steel bolt. However, until today, there are no construction standards for connections with only one bolt as well as for connections with several bolts under combined sectional forces and moments. Furthermore, imperfections, tolerances, brittle behaviour and scattering of the material properties have to be considered. This thesis addresses developing an engineering model for lapped glass joints with bolts in bearing and the derivation of rules for the design. Based on the stress function of Airy an analytical calculation method could be developed, in which local bearing stresses under bolt loading are superposed by net section stresses. Both stress states can be described by stress functions. Thus any bearing condition is addressable. By means of reverse composition of the two stress fractions the stress-strain-state of panes consisting of elastic-isotropic materials with arbitrary hole pattern under any boundary condition can be determined depending on the bolt load, the pane thickness, the hole diameter and the relevant width resulting from the joint geometry. Further the analytical solution could be reduced to a simple design equation, which enables the determination of the relevant stresses depending on bolt forces acting on the single hole, the diameter of the hole and the glass thickness. Thereby also the influence of the erection and fabrication tolerances as well as design parameters had to be systematically examined by Finite Element calculations that had been performed so far for the first time. The effects could be numerically discovered and coefficients for the design equation could be derived. Also a non uniform bolt force distribution has to be taken into account for long bolt rows parallel to the force direction. To ensure a sufficient load bearing capacity of the entire detail, the interlayer material cannot be neglected. Therefore, theoretical examinations were performed. The effect of erection and fabrication tolerances as well as geometrical parameters on the stresses in the mortar could be determined. The results serve as an approach for the verification of the interlayer against the bolt forces, the diameter of the hole and the glass thickness. The definition of the material resistance bases on former research results and examinations. All theoretical studies were verified by numerous experimental tests under monotony loading after prior cyclic service loading. In analogy to the analysis, the tests have been realised for joints under normal forces as well as under combined shear forces and moments. The stress-strain-distributions, which were determined by strain gauges and the analysis of the fracture pattern coincide with the theoretical results. Finally, it was shown that effective resistant stresses governing the load bearing capacity of bolted connections under in plane loading is lower compared to those effective resistant stresses that control failure in case of plate loading. The thesis closes with derivations for partial safety factors and proposals for the codification

Analysis of bonded hybrid steel-glass-beams by small scale tests

To realize architectural attractive transparent and lightweight constructions bondedhybrid steel-glass beams have been developed, where flanges of steel and webs ofglass are assembled to I-shaped profiles using adhesives. The load-bearing capacityof such beams is governed – apart from the mechanical and strength characteristicsof the adherent - by ageing, temperature and creeping. By means of small scalepush-out-tests the properties of different adhesive geometries, the influence of themanufacturing process and the general load carrying behaviour of bonded hybridsteel-glass-beams are shown