Investigations on Linear Silicone Joints for Glass-Metal Elements with Composite Structural Behavior

A trend towards adhesive connections instead of mechanical ones can be observed for transparent facades in recent years. Furthermore, research efforts are made to increase the efficiency regarding material use by designing systems with composite structural behavior. In this article, experimental and numerical results obtained for linear structural silicone joints between glass and stainless steel substrates, investigated separately under tensile and under shear loading, are discussed. The two selected adhesives, Dow Corning® 993 and Sikasil® SG-550, are approved for structural sealant glazing systems and are planned to be used within a novel concept for façade elements with composite structural behavior, consisting of a glass pane and a filigree metal framing. For an adhesive joint with prismatic geometry, the influence of different lengths, widths and thicknesses of the joint on its mechanical performance is assessed experimentally under tensile loading, while under shear loading only different thicknesses are investigated. Both under tensile and under shear loading, a dependency of the failure engineering stresses on the joint thickness is noticed. In a second step, the suitability of selected hyperelastic models is assessed for predicting the load versus displacement behavior of the investigated linear adhesive joints. The parameters required for these models are determined based on uniaxial tensile tests on dumbbell specimens

Experimental and simulation data for point-by-point wire arc additively manufactured carbon steel bars loaded in uniaxial tension

Wire arc additive manufacturing is considered to allow a reduced material consumption for structural steel components by efficiently distributing the material only where necessary. Parts produced with this technology exhibit an irregular, imperfect geometry, which influences their structural behaviour. This paper describes a dataset, which includes geometry information for point-by-point wire arc additively manufactured steel bars, force and displacement measurements from performed uniaxial tensile tests on such bars, and force and displacement values from geometrically and materially non-linear simulations of the bars with imperfect geometry. The geometry data was obtained by 3D scanning the steel bars. Moreover, a script is provided that allows processing the scanned geometry data such that it can be used to generate suitable finite element meshes for geometrically and materially non-linear analyses. The force and displacement data from the uniaxial tensile tests were collected through measurements with a load cell for the force and with the help of digital image correlation measurements for the displacements. The non-linear simulations of the experiments were conducted with the computer aided engineering software Abaqus on processed approximations of the irregular scanned geometry. The described dataset can be used for better understanding the influence of the irregular geometry on the structural behaviour of wire arc additively manufactured parts. Moreover, researchers can apply the data to validate finite element simulation models and approaches for predicting the structural behaviour of different wire arc additively manufactured parts.ISSN:2352-340

Ductility and Buckling Behaviour of Point-by-Point Wire Arc Additively Manufactured Steel Bars

The wire arc additive manufacturing (WAAM) technology in combination with computational design shows a big potential for realising novel force-flow optimised and material-efficient connections. This contribution deals with point-by-point WAAM, a material deposition strategy that allows to place material precisely where structurally needed or aesthetically desired. This could be applied, among others, for realising a novel optimised type of steel nodes between custom-oriented profiles, as they occur in freeform steel-glass grid-shells. In this paper, the structural behaviour of robotically fabricated straight WAAM steel bars under uniaxial tensile and compressive loading is discussed. The focus is set on the ductility exhibited by such components as well as on the buckling behaviour observed under compressive loading. Experimental tests were conducted, both under tensile and under compressive loading to assess the influence of the irregular geometry on the structural performance. Furthermore, it was studied to what extent a prediction of the ductile structural behaviour, of the compressive load-bearing capacity and of the post-buckling behaviour is possible by finite element simulations. This contribution presents and discusses highlights of the obtained results.ISSN:2509-707

Linear adhesive connections at the edge of laminated glass panes: an experimental study under tensile, compressive and shear loading

Adhesive connections experience in recent years an increasing popularity in the field of structural glass. Generally, linear adhesive joints are positioned on the surface of glass panes as in the case of structural sealant glazing systems. However, due to the existing trend for larger glass elements and implicitly glass panes with higher thickness, connections with adhesive joints at the edge of laminated glass panes become more interesting. In this article, experimental results for such linear adhesive joints with glass and stainless steel substrates, tested under tensile, compressive and shear loading, are presented and discussed. Three different cross section geometries of the joints are investigated: rectangular, L-shaped and U-shaped. For each of these cross sections, two silicone adhesives approved for structural sealant glazing systems and one structural acrylic adhesive are included in the experimental programme. All tests are performed at ambient conditions. Beside the mechanical behaviour in the form of load versus displacement results, also the failure modes and patterns are analysed. Regarding the interaction of the adhesives with the interlayer material under compressive loading, it is observed that at certain loads bubbles start to form in the interlayer and subsequently a delamination is initiated for all three adhesives. Moreover, the specimens with acrylic adhesive exhibit delamination as well under tensile and under shear loading. The results from this experimental study provide novel findings for linear adhesive connections at the edge of laminated glass panes and represent a basis for further investigations and developments on such joints.ISSN:2363-5142ISSN:2363-515

Structural behaviour of point-by-point wire arc additively manufactured steel bars under compressive loading

Wire arc additive manufacturing combined with optimization tools for computational design shows a big potential with respect to the current efforts in the architecture, engineering, and construction industry of reducing the consumption of materials by using them more efficiently. These technologies allow to design and fabricate steel components, connections, and structures with material deposited only were structurally necessary. The findings presented in this paper focus on wire arc additively manufactured bars, robotically printed by point-by-point deposition and subjected to compressive loading. Such elements can be used for realizing stand-alone components or connections between existing parts, either alone or in combination with continuous deposition, and are generally susceptible to flexural buckling due to their slenderness. The influence on the flexural buckling behaviour of aspects like printing directions, slenderness, and support conditions was investigated by experiments and finite element simulations. In addition, the irregular geometry of the wire arc additively manufactured bars was evaluated based on three-dimensional scans, the identified characteristics were correlated with the flexural buckling results, and the relevance of the irregular surface geometry in predictive buckling simulations was assessed. The experiments showed consistent results indicating that such bars could be produced in a reliable and repeatable manner. The conducted simulations with the scanned geometry and an elastic-plastic material model allowed for an overall satisfactory prediction of the flexural buckling resistance. With regard to future design approaches, it was shown that the existing buckling curve for solid sections is suitable for point-by-point wire arc additively manufactured nearly straight bars and simulations with a constant equivalent diameter can be used for predicting the flexural buckling resistance if a rather low equivalent geometric imperfection is assumed.ISSN:0143-974

Structural behaviour and micro-structural characteristics of coloured kilned glass panels

In recent years, the architecture, engineering and construction industry is increasingly embracing digital design approaches and robotic production methods. This is as well noticeable in the façade design sector, especially when it comes to architectural design tasks dealing with complex geometries or adaptive components. Although glass is mainly used in facades due to its transparency, it often determines significantly the aesthetic appearance of a building and has to control the transmitted light and the visibility between exterior and interior. Recently, a novel method for producing polychromatic glass panels by fusing granular glass powder of different colours onto the surface of annealed float glass in a kilning process was developed at ETH Zurich. By using a multi-channel tool attached to a robotic arm for placing the granular powder onto the glass surface, digitally designed patterns can be realised precisely and repetitively. This paper focuses on the structural behaviour and the micro-structural characteristics of this novel type of coloured glass panels for façade applications. The bending strength of such glass panels was determined based on four-point-bending tests and was compared to that of annealed float glass. A non-negligible decrease in the bending strength was observed. Furthermore, the reasons for this reduction in structural performance were analysed based on microscopic investigations. It was observed that both the kilning process and the density of deposited granular powder had an influence on the surface microstructure. The presented results are essential for the production of polychromatic kilned glass as well as for future applications of this type of glass panel in façades.ISSN:2363-5142ISSN:2363-515

Enabling a Ductile Failure of Laminated Glass Beams with Iron‐Based Shape Memory Alloy (Fe‐SMA) Strips

Laminated glass beams are used as structural elements to support transparent roofs or to transfer wind loads acting on transparent facades. However, in case of breakage, laminated glass beams only exhibit a low residual load-carrying capacity provided by the interlayers. A more efficient solution is to add a filigree ductile reinforcement on the tension side of the laminated glass beams, for instance by adhesive bonding. By these means, the post-cracking behaviour of the beams and their redundancy can be improved and a ductile failure behaviour can be achieved. Moreover, an additional pre-stressing of this reinforcement allows increasing the initial glass cracking resistance. Despite their obvious potential, an application of pre-stressed laminated glass beams in real projects is prevented by the rather complicated necessary procedures for pre-stressing. This contribution discusses first experimental results on a novel concept for pre-stressed laminated glass beams with adhesively bonded strips made of an iron-based shape memory alloy (Fe-SMA). The pre-stress can be applied in this case by heating up the Fe-SMA. The feasibility of the concept is analysed based on results from four-point-bending tests on medium-scale simple, reinforced and pre-stressed laminated glass beams.ISSN:2509-707

Performance of Glass to Iron-based Shape Memory Alloy Adhesive Shear Joints with Different Geometry

Previous research has shown that glass beams with external, mechanical post-tensioning along their edges show better structural performance than glass beams without any such reinforcement. The initial and post-fracture load-bearing capacity of glass beams can be increased by reinforcing them with stainless steel or fiber-reinforced plastic (FRP) tendons that are post-tensioned and connected to the beam edges. However, post-tensioning of stainless steel or FRP bars or strips is complex and challenging because it often requires special setups, such as hydraulic jacks. Iron-based shape memory alloys (Fe-SMAs) are promising post-tensioning materials due to their efficient activation procedure and good mechanical properties. The target prestress level can be introduced by heating the Fe-SMA to a specific temperature followed by cooling down naturally to ambient temperature. As a contribution to assessing the feasibility of strengthening glass elements with adhesively bonded Fe-SMA strips, this paper focuses on the bond behavior of glass-to-Fe-SMA lap-shear joints based on numerical investigations. A finite element model is developed to evaluate the effect of adhesive thickness, Fe-SMA strip thickness and bond length on the structural behavior of glass to Fe-SMA lap-shear joints.ISSN:0289-801

Application of an iron-based shape memory alloy for post-tensioning glass elements

Previous research has evidenced that by adding a ductile reinforcement on the tension side of a glass beam, for instance by adhesive bonding, its post-cracking behaviour and redundancy were improved, while an additional pre-stressing of this reinforcement further helped to increase the initial cracking resistance. Past investigations used steel tendons or stainless steel strips, which required rather complex setups and procedures for mechanical pre-stressing. This study aims to introduce an easier-to-apply procedure with strips made of an iron-based shape memory alloy (Fe-SMA), which has the property of remembering its initial shape after a phase transformation from austenite to martensite. The Fe-SMA strips can be anchored to a parent structure as pre-strained strips, in case of a glass substrate by adhesive bonding. After activation of the Fe-SMA through a heating and cooling process, a tensile stress is generated in the strip, which applies a compressive stress field into the parent structure. This work discusses the results from first feasibility investigations dealing with the choice of adhesive and identifying a suitable activation procedure for Fe-SMA strips adhesively bonded to glass elements. The effective bond length, which needs to be considered when defining the anchorage length, was determined for two structural adhesives. While for the high-strength, brittle 2c-epoxy adhesive SikaPower (R)-1277, shorter bond lengths of a little more than 120 mm were sufficient, for the more ductile 2c-methacrylate adhesive Araldite (R) 2047-1, longer bond lengths were necessary for the same load level (more than 240 mm). Furthermore, an activation procedure by electrical resistive heating was applied, which (i) allowed sufficient heating of the Fe-SMA for activation, (ii) avoided too high instant temperature changes in the glass and (iii) did not affect the required anchorage bond length.ISSN:2363-5142ISSN:2363-515

Corrosion behaviour of point-by-point wire and arc additively manufactured steel bars

Robot-assisted point-by-point wire and arc additive manufacturing is considered a promising technology for optimising the production of metallic connections used in complex nodes, space trusses or grid shells. While mechanical properties of such elements were proved suitable for structural applications, a lack of knowledge exists concerning their durability. We investigate the corrosion performance of low carbon steel bars produced by point-by-point wire and arc additive manufacturing. Metallurgical analyses show uniform microstructure along the length of the steel bars. Corrosion initiation tests in simulated atmospheric exposure reveal the influence of geometry on corrosion, in particular, the presence of concave areas. The surface state and postprinting cleaning processes were investigated with microscopy and electrochemical techniques. These experiments indicate a detrimental effect of oxide scales due to the wire and arc additive manufacturing process on the corrosion behaviour of the steel. The results of the study show that special care must be given to the geometry and surface state of wire and arc additively produced low carbon steel components in case of long-term use.ISSN:0947-5117ISSN:0043-2822ISSN:1521-417