Glass panel under shear loading

Danijel Mocibob
EPFL, 2008
EPFL thesis

Abstract

The latest trends in contemporary architecture are fully transparent pavilions: a single storey building free of any steel or concrete frame, where glass panels are used as unique vertical structural elements to support the roof and as wind bracing to stabilize and stiffen the building. In this application, individual glass panel is supported on two sides (roof and foundation) and subjected to in-plane shear force (lateral wind), out-of-plane distributed load (perpendicular wind) and in-plane compression force (self weight of the roof, snow). While several studies on glass plate behaviour under distributed load and column buckling exist, shear buckling of two sides supported glass panel has not been investigated yet. Therefore, research on this topic gives original and innovative importance to both theoretical (glass panel under shear loading) and practical (use of glass envelope for building stabilization) applications. Two structural concepts are developed: point support concept - the glass panel is attached to the substructure by bolted connections at corners linear support concept - the glass panel is glued to the substructure by two shorter sides. The local behaviour of the connection devices and the global behaviour of the glass panel under in-plane shear force are studied by means of experimental investigations, numerical modelling and parametric analyses. Experimental investigation and numerical simulation of connection devices was conducted in order to better understand the behaviour of different types of glass/substructure bolted (for point support) and glued (for linear support) connections. Deformation, stress distribution and local influence on the surrounding glass were analyzed. From these studies, the most suitable connection device for load introduction was chosen and implemented in the glass panel. Tests on full size glass panels were conducted in order to estimate the shear buckling behaviour of a glass panel. Also the influence of different boundary conditions (point and linear) and load interaction (in-plane shear force with out-of-plane distributed load and in-plane compression force) on global glass panel behaviour were analyzed. The specimen deformation, the stress distribution and the failure mode have been analyzed. Advanced numerical models of point and linear supported glass panel were implemented using the Finite Element Code Ansys. Elastic buckling analysis was used to determine the critical shear buckling force, shear buckling coefficient and shear buckling mode shape, further used as the initial geometrical imperfection. By means of nonlinear buckling analyses the global glass panel behaviour was studied analysing glass panel deformations, stresses distribution and support reactions. The influence of initial imperfection shape was investigated as well as the interaction of in-plane shear force with out-of-plane distributed load and in-plane compression force. The models were validated by comparing their results with experimental measurements. The parametric study was carried out to identify the most important parameters, evaluating their influence on shear buckling behaviour. The influence of the glass panel and connection device geometrical/material properties on critical shear force, global deformation, stress distribution and support reaction could be determined. A simple method for preliminary design of glass panels subjected to in-plane shear force was proposed by developing formulas, graphs and curves for determining the glass panel shear buckling resistance. Finally, this study led to some recommendations for practical use of glass panels in fully-transparent pavilions as structural elements.

Official source

https://infoscience.epfl.ch/record/125889?ln=en

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Danijel Mocibob
EPFL, 2008
EPFL thesis

Abstract

Official source

https://infoscience.epfl.ch/record/125889?ln=en

About this result

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Field observations as well as experimental tests have shown that both the strength and displacement capacity of reinforced concrete (RC) members might be significantly reduced by the presence of lap splices. This degradation applies in particular if the longitudinal reinforcement is spliced in regions where inelastic deformations concentrate, which is frequently the case for RC building walls or bridge piers. In fact, these members often feature lap splices above the foundation level, where seismic demands are largest and damage is likely to occur. In performance-based earthquake engineering (PBEE), which now sets the standards for seismic assessment, deformation rather than force capacities are compared to the demand; however, past experimental studies on spliced members have focused on the characterization of the strength rather than the deformation capacity of lap splices. Further-more, these tests were primarily performed on spliced RC beam and column specimens, typically subjected to mono-tonic loading. Experimental investigations on the deformation capacity of members with lap splices under cyclic loading are underrepresented. This applies in particular to walls, despite the fact that splicing of longitudinal reinforcement in their plastic hinge regions is common construction practice. In line with the available experimental work, most of the developed empirical and analytical expressions aim solely at quantifying the force capacity of lap splices. The preceding observations have motivated the following objectives of the present work: (i) investigate the displacement capacity of spliced RC walls through experimental tests; (ii) propose expressions characterizing the deformation capacity of lap splices subjected to monotonic and cyclic loading; and (iii) develop numerical and mechanical models suitable for practicing engineers to simulate the behaviour of RC members with lap splices. Existing experimental programmes on spliced RC walls, including the cyclic test of two units recently carried out at the structural laboratory of EPFL, are first reviewed and collected in a database. The review of the experimental data shows that the failure of the outermost lap splices, located in the boundary element, typically triggers the failure of the RC wall. Moreover, the main parameters influencing the deformation capacity of lap splices are identified. Building on these findings, an experimental programme on spliced RC wall boundary elements is designed using lapsplice length, confining reinforcement, and loading history as variable parameters. From the obtained results, an empirical expression for the lap-splice strain capacity is derived. A 2D shell element model is first developed to simulate the global force-displacement response of the walls in the aforementioned database. The lap splice response is considered through a new equivalent uniaxial steel stress-strain law. Secondly, an axially equilibrated displacement-based beam element model is proposed in which the lap splice response can be included by using the derived strain limit expression. Finally, a novel mechanical model describing the behaviour of spliced RC wall boundary elements is presented. It extends the tension chord model by accounting for anchorage slip and the presence of lap splices.

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EPFL2008

Structural Response of R-UHPFRC - RC Composite Members Subjected to Combined Bending and Shear

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EPFL2012

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Talayeh Noshiravani

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EPFL2019