@phdthesis{8688590,
  abstract     = {{Due to the development of structural sealant glazing systems, also known as bonded glazing, in the 1960s, architects and engineers became able to design totally glazed façades light in weight, with a free-form and a maximum transparency. As these traditional façades demonstrated a number of implicit advantages, such as thermal deficiency, poor acoustic performance and condensation problems, new façade design concepts were developed, such as double-skin façades. Such a façade consists of a single outer glass layer and an inner insulating glass unit with a ventilated cavity in between. The width of this cavity can be reduced to typically 0.2 m, however an optimisation in favour of net usable floor area, i.e. the number one requirement in construction projects, is still possible. A structural optimisation can be realised by using alternative materials with a higher stiffness, i.e. steel instead of aluminium, by increasing the material efficiency, i.e. using material properties to their maximum, and by increasing the structural efficiency, i.e. maximisation of the involvement of components in the overall structural behaviour.

In this doctoral dissertation, two-sided bonded glass-steel frames using structural silicone and hybrid polymer adhesives are investigated for their structural performance. Firstly to enable an optimisation of the structural body of a double-skin façade element in terms of reducing cavity width. Secondly to perform fundamental research on the potential use of façade elements as contributor to the stabilisation system of the building. The research focusses on four structural levels, i.e. material level, connection level, element level and façade level. 
Two structural silicone adhesives, i.e. Sikasil® SG-500 (SI500) and Dow Corning® 993 (DC993), and one hybrid polymer adhesive, i.e. Soudaseal 2K (SO2K), are selected as suitable adhesives for the considered application. Using H-shaped specimens, experimental data for different loading conditions, i.e. tension, compression and simple shear, and for different loading regimes, i.e. monotonic and cyclic loading, are produced. Hyperelastic material models are calibrated based on the experimental data for all possible combinations of the load conditions. The goodness-of-fit and the suitability of the models is assessed. The potential of representing hyperelastic material behaviour using constitutive models calibrated for multiple deformation states determined through experimental tests on H-specimens is demonstrated. The calibrated hyperelastic material models are subsequently implemented in the finite element models of continuous adhesive glass-metal connections and bonded glass-steel frames after which the most suitable material model is selected and finite element model is validated before performing parametric studies.

Continuous adhesive glass-metal connections using the selected adhesives are investigated for their performance under out-of-plane bending, e.g. wind pressure or suction. The lateral stiffness and strength of the connections is determined experimentally and a parametric study is performed using a validated finite element model. The use of the hybrid polymer adhesive results in a higher stiffness due to the reduced recommended thickness of the adhesive layer compared to the minimum advised adhesive thicknesses of the structural silicones. Increasing the width-to-thickness ratio of the adhesive layer results in increased stiffness and strength of the continuous adhesive glass-metal connection. An analytical spring model using rigidity factors which depend on the aspect ratio of the joint and the Poisson coefficient of the adhesive material can be used to determine the structural behaviour of such connections. Welded steel corner connections whether or not stiffened by two-sided bonded glass panes are experimentally tested to determine the rotational stiffness. Parametric studies using validated finite element models demonstrate an increased rotational stiffness with an increase of the width of the adhesive joint or steel section and the section thickness. The thickness of the adhesive layer is important for values below 5 mm.

The horizontal in-plane stiffness of medium-scale 1.2 m by 1.2 m two-sided bonded glass-steel elements using the structural silicone and hybrid polymer adhesives is experimentally investigated using a custom-made test setup. The experimental data are used to validate finite element models which are then used for parametric studies. The horizontal in-plane stiffness increases with an increasing width-to-thickness ratio of the adhesive layer. The glass thickness has a negligible effect when the horizontal in-plane load is directly introduced into the steel frame. It is demonstrated that the use of relatively flexible adhesives imply the need for additional setting blocks to improve composite behaviour between glass and steel, even for double-sided bonded glazing. An existing mechanical spring model is adapted to predict the horizontal in-plane stiffness of two-sided bonded glass-steel elements. Principles of effective length and effective joint width-to-thickness ratio are implemented in the analytical model.

Full-scale 3.45 m by 1.45 m two-sided bonded glass-steel elements using the structural silicone Sikasil® SG-500 (SI500) are experimentally tested to determine the horizontal in-plane stiffness and strength. A finite element model is validated and used to determine a suitable failure criterion for cohesive failure in the adhesive layer. The shear stress and shear strain failure criterion are able to predict the observed failure load with an error of only 3%. The shear strength and ultimate shear strain of the structural silicone are obtained from the previously conducted material tests on H-specimens. The adapted analytical spring model is able to predict the horizontal in-plane stiffness with an error of only 3.1%. Buckling phenomena are explored using available numerical and analytical studies. The structural response of the 3.45 m by 1.45 m two-sided bonded glass-steel façade element under vertical in-plane gravitational loads, horizontal out-of-plane wind loads, barrier loads and thermal loads are numerically investigated. Near the in-plane load introduction points the need for additional stiffening of the steel members is demonstrated. The investigation of the structural response of the bonded glass-steel frame with stiffened corner connections under several load combinations demonstrates that the glazing can be designed based on the acting out-of-plane loads only. This is not valid anymore when stiffer adhesives create more composite behaviour or when setting blocks directly introduce the in-plane loads into the glass panes. For the structural design of the steel frame and the adhesive joints, load combination taking into account both out-of-plane loads and in-plane loads need to be considered. For complex bonded glass-steel façade elements transferring a complex combination of in-plane and out-of-plane loads, the use of finite element modelling appears to be inevitable. 

Structural design approaches for the structural body of a double-skin façade element that provides lateral stability are provided. The conceptual design fixes the geometry and dimensions of the façade elements. The load transfer concepts need to be decided on before developing structural systems. Next, the actions and load combinations in correspondence with applicable standards and regulations are determined. The preliminary design can be done after the material selection. The actual structural design is an iterative process with the preliminary design as a first step in the optimisation process. The structural design should be performed in the ultimate limit state, related to strength, and the serviceability limit state, related to deformations. The structural design with respect to the ultimate limit state comprises the verifications of the actual stresses in the glass panes, in the steel frame and in the adhesive layers under the most unfavourable load combination. Buckling calculations enable the determination of the buckling behaviour of the glass panes. In the serviceability limit state, the in-plane and out-of-plane deformations of the glass panes and the steel framing under the most onerous load combination should be within acceptable limits. A design example demonstrates the application of the proposed design approaches. 

Additionally, the durability and long-term performance of continuous adhesive glass-steel connections using Sikasil® SG-500 (SI500) are experimentally investigated. Therefore, a newly developed artificial ageing schedule including the most important environmental factors, i.e. moisture, temperature and UV-radiation, is presented and imposed on the adhesive connections. The effects of individual and combined influential factors on the lateral stiffness and strength of continuous adhesive glass-metal connections are determined. Excellent resistance of the structural silicone against moisture, thermal cycling and UV-radiation is demonstrated. Furthermore, excellent adhesion to both glass and galvanised cold-formed steel is maintained for all ageing procedures. The importance of quality control during the bonding process is emphasized and several procedural steps are explained and illustrated.}},
  author       = {{Van Lancker, Bert}},
  isbn         = {{9789463554282}},
  keywords     = {{Glass,Steel,Structural Silicone,Hybrid Polymer Adhesive,Façade Units,Two-Sided Bonded}},
  language     = {{eng}},
  pages        = {{xxiv, 482}},
  publisher    = {{Universiteit Gent. Faculteit Ingenieurswetenschappen en Architectuur}},
  school       = {{Ghent University}},
  title        = {{Experimental and numerical investigation of two-sided bonded glass-steel façade units}},
  year         = {{2020}},
}