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Recently, there has been a growing interest in the use of sandwich panels that, beyond handling well-known bending stress, can withstand torsional stresses. This is particularly relevant for wall applications when the panels are equipped with photovoltaic or supplemental curtain wall modules. This research article presents a detailed exploration of the structural behavior of eccentrically loaded sandwich panels, with a specific focus on warping torsion. Experimental and numerical studies were conducted on polyisocyanurate (PU) core sandwich panels, commonly employed in building envelopes. These studies involved various dimensions and material properties, while omitting longitudinal joints. The experimental study provided essential insights and validated the numerical model in ANSYS. Enabling parametric variation, the numerical analysis extends the analysis beyond the experimental scope. Results revealed a high degree of correlation between experimental, numerical, and analytical solutions, regarding the rotation, as well as the normal and shear stress of the panel. Confirming the general applicability of warping torsion in sandwich panels with certain limitations, the study contributes valuable data for applications and design of eccentrically loaded sandwich panels, laying the foundation for potential engineering calculation methods. [ABSTRACT FROM AUTHOR]

A deep understanding of the material parameters and the behavior of sandwich panels, which are used in the construction industry as roof and façade cladding, is important for the design of these construction components. Due to the constant changes in the polyurethane (PU) foams used as a core material, the experimental database for the current foams is small. Nowadays, there is an increasing number of failures of façade and roof panels after installation. This article presents a variety of experimental investigations on sandwich panels from two manufacturers with a core of polyisocyanurate (PIR) rigid foam (density: 40 kg/m3). As part of this study, compression, tension, shear, and bending tests were performed in several spatial directions and over the range required by the standard. The results of the tests showed the orthotropy of the core material and the dependence of the material on the direction and type of load. The stress-strain curves showed linear and non-linear areas. Using the data from this experimental study, a numerical model was implemented which utilized the Hill yield criterion to represent the orthotropy of the core material. The present investigation suggests that the classical von Mises failure criterion, used in many studies, is not suitable for the foam system applied in these sandwich panels. Instead, the Tsai–Wu criterion is more appropriate for defining the failure stresses. [ABSTRACT FROM AUTHOR]

Lightweight building steel envelop systems with bio‐based insulation – conservation of resources and reduction of CO2 emissions The aim of the research project presented below is to develop five building envelope systems made of low‐carbon steel and innovative use of wood fibre insulation. Three sandwich panels (pitched roof, flat roof, façade), a double‐skin façade and a façade cladding (cassettes) will be developed. The project includes a series of tests to investigate all relevant properties of the systems: load‐bearing behavior, fire behavior, thermal insulation, acoustics, air‐, water‐ and vapor‐permeability. In addition, two full‐scale prototypes were built to study the behavior of the systems under real conditions. The determination of LCA indicators and a comparison in terms of carbon footprint (GWP) with conventional systems using an existing office building as a reference will also be carried out. An economic comparison between the expected delivery and installation price of the five innovative systems and that of the existing conventional systems is planned. The production of the sandwich panels can be easily integrated into the current production lines. [ABSTRACT FROM AUTHOR]

The INCSEB project is aimed at developing 5 ultra‐low carbon envelope systems made in steel and that incorporate innovative use of wood fiber insulation. The systems under development are: 3 sandwich panels (cladding, pitch & flat roofing), 2 claddings (double skin & façade with plank). INCSEB includes tests to study various behaviors: mechanical, fire, thermal calculation, acoustic insulation, air/water/vapor permeability. Interpretation and classification reports will be done for each type of test. 2 full scale prototypes will allow to estimate the durability in real life conditions. LCA indicators and comparison of carbon footprint (GWP) to conventional systems based on a real office building will be provided. An economic study of the projected price of the 5 systems compared to existing conventional systems is also planned. Besides, as far as the production of innovative panels is concerned, it appears that they can be integrated in current production lines. Finally, actions to facilitate the dissemination of results and industrial application will be organized: drafts of design and installation guides, publications, submission of 3 amendments to relevant EN standardization committees, workshop, BIM objects. Lastly, the manufacturers plan to apply for patents protection. [ABSTRACT FROM AUTHOR]

Lightweight steel constructions made of sandwich panels are an economical solution for wall and roof claddings, especially in industrial construction. The panels consist of two thin sheets of steel and a core with thermal insulating properties. In the mounted state and at high temperatures on the outer face of the panel, damage to the components may occur due to blister formation. In a current research project, the influence of defects in sandwich panels with a PIR‐foam core is examined. This article presents the results of experimental tests regarding the influence of various parameters, such as face temperature, production defects and design of the longitudinal joint on blistering in sandwich wall panels with a PIR‐core. The aim is to identify the necessary conditions for the occurrence of blisters. Using an optical strain measuring method (Digital Image Correlation), the temperature‐induced deformations and strains in the covering nose of sandwich wall panels with hidden fastening are measured and will be analyzed with regard to blistering. First results reveal a significant dependence on the geometry and design of the covering nose. [ABSTRACT FROM AUTHOR]

Sandwich panels in the construction industry are used as roof and facade elements and usually consist of two thin face layers of steel and a thicker core of polyurethane (PU) or mineral wool in between. The PU core material is constantly being further developed. In addition to improvements in the physical properties, this further development also leads to changes in the mechanical properties. As a result, the design rules that were established for older foam systems must be reviewed at regular intervals. There is a great need for research into the temperature‐dependent behavior of the foam system. As these elements are used as roof and facade elements, they are directly exposed to climatic conditions. High temperatures are generated on the cover sheets due to solar radiation. The PU rigid foam changes its mechanical properties in this temperature range. Tests on small parts and components show a change in the stiffnesses and strengths, as well as the load‐bearing behavior under elevated temperature. Consideration of the temperature in the design is therefore of great importance. In view of the continuous further development of the foam system, statements regarding the core material from older research must be reconsidered. [ABSTRACT FROM AUTHOR]

Determination of the shear properties of sandwich core materials A comparison of the core materials of sandwich panels has revealed inconsistent relationships between their stiffness moduli at different core thicknesses. Therefore, two test methods for determining the shear properties of the core material of sandwich panels were assessed theoretically and experimentally. The results show that for the shear beam test according to EN 14509 a more precise definition of the load distribution plates is necessary and that the usual neglect of the indentation at the support is only justified for thin and medium panel thicknesses. The investigations on the square shear test have shown the influence of the eccentricity between the joint plane and the top edge of the specimen and resulted in the development of a new test setup. The findings from the investigations provide the basis for more realistic modelling of the load‐bearing behavior of sandwich panels in the future. [ABSTRACT FROM AUTHOR]

Moment support interaction of multi‐span sandwich panels Self‐supporting double skin metal faced sandwich panels are usually designed and installed as multi‐span beams. In this case, there is always an interaction at the intermediate supports between the compressional normal force in the face sheet and the support reaction orthogonally to it, which can reduce the bending capacity. Many effects influencing the reduced load‐bearing capacity are not taken into account in current approval practice (and design). Within a research project funded by the DFG, experimental, numerical and analytical investigations were therefore carried out on sandwich panels. The main influences on the reduced wrinkling stress under an applied transverse compressive load were quantified and a possible solution was identified in order to take them into account in the future, e.g. within the scope of the approval tests. [ABSTRACT FROM AUTHOR]

Due to their excellent combination of space enclosing, heat insulating and supporting function, steel sandwich panels – mostly flat – are used for roofs and walls of standard industrial buildings. Because freely formed structures generally are playing an increasing role in contemporary architecture, curved sandwich panels would offer a high potential to architectural design. Simultaneously, the advantageous load‐bearing capacity could further increase the benefits of their usage. The necessary design strategy, the manufacturing technology for the curved cover plates and their overall mechanical behavior – all of these 3 main keys have been investigated in an interdisciplinary research project with architects, structural‐ and mechanical engineers. It has been one of the main goals in this project to find an applicable, efficient strategy for singularly produced panels (lot size 1: serial production with quantity = 1) in favour of a maximum flexibility for individual geometries. [ABSTRACT FROM AUTHOR]

Sandwich panels with a core of corrugated cardboard The goal of a research project of the Institute for Steel Construction and Materials Mechanics was to determine the utilization of corrugated cardboard as a core material for sandwich panels for roof and wall cladding. In contrast to common core materials, corrugated cardboard is recyclable and consists of renewable raw materials. The bearing behaviour depends mainly on the paper types and on the orientation of the anisotropic material inside the panel. The weakest orientation has similar stiffness and strength as common core materials. However, these can be exceeded many times by other core orientations. Investigations of the most important building physical parameters have shown that the fire behaviour is slightly better than that of most PU‐sandwich panels. The thermal conductivity in the weakest core orientation is comparable to that of mineral wool, the stronger core orientations show higher thermal conductivity. [ABSTRACT FROM AUTHOR]

Examination of the interaction of bending and compression at the support of sandwich panels The interaction of bending moment and the compression at the support of sandwich panels is assessed experimentally. DIN EN 14509 [1] gives a 3‐point‐bending‐test in which the span depends indirectly on the thickness of the panel. The span is the decisive factor since it gives the ratio of moment to compressive force. Therefore, it was analysed how long the span shall be to represent real systems well. The parameter‐study led to the conclusion that the span might be between 1 m and 12 m for realistic results. DIN EN 14509 [1] usually asks for 4 m to 6 m. Tests were performed to improve the understanding of the relevant mechanisms [2–5]. The over‐ resp. under‐estimation of the span leads to deviations in the serviceability criterion of up to ± 20 % (wall) and ± 30 % (roof). Finally, a recommendation is given to consider these deviations in practical design. [ABSTRACT FROM AUTHOR]

Lightweight constructions made of sandwich panels became well established for roof and wall claddings of industrial structures. Due to their good heat insulation, their excellent weight to load ratio and high load‐bearing capacity as well as the economical manufacturing and erection process, sandwich structures are build frequently. Besides the mentioned advantages the linear manufacturing process of sandwich panels usually limits the possible building cubature to rectangular shapes. In an interdisciplinary project, architectural, civil engineering and mechanical engineering institutes of Technische Universität Darmstadt are working on a design concept building shell structures with linear manufactured curved sandwich panels. A preliminary study indicates that arched sandwich beams have a high potential regarding the load‐bearing capacity. The comparison between arched and single span sandwich beams shows that, even for asymmetric loads, resulting stresses in the two‐hinged arches are significantly lower than in the related simply supported single span beams. To verify the results of the numeric study full‐scale tests on curved sandwich panels will be performed. Furthermore, an assessment of the load‐bearing behavior of the panels joints loaded with axial forces is planned. Based on the results further numeric studies will be conducted to investigate the behavior of whole shell structures following the developed design principle by taking into account realistic load cases for exemplary building applications, giving special attention to asymmetrical loads. Moreover, further research regarding the requirements for supporting structures as well as for the connection between the shell structure and the supporting structure is necessary to take into account the high axial forces, which are not common in sandwich structures. [ABSTRACT FROM AUTHOR]

Within the scope of a research project, the pull‐through resistance of direct fixings of sandwich panels under cyclic loading was determined on small‐scale sandwich specimens. The tests were carried out on wall panels with lined steel face sheets. Various core materials (PU foam, mineral wool), face sheet thicknesses, panel depths and various screw manufacturers were combined. From the test results, cyclic reduction factors for fixings on the mid and end support were determined according to prEN 14509‐2. [ABSTRACT FROM AUTHOR]

Diaphragm effect of sandwich panels. Full scale tests were carried out within the scope of [5] to investigate the diaphragm action of sandwich panels. Shear diaphragms were constructed to assess the load carrying action of the sandwich panels bracing the structure. The bearing behaviour of the various components contributing to the shear diaphragm effect was investigated in more detail on smaller experimental set ups. These small scale tests include investigations into the screw connections between the sandwich panels and the substructure, as well as a series of tests on the load transfer through the longitudinal joint between the individual panels. The most untapped potential for improvement of the bearing capacity has been found to be the influence of the longitudinal joint. An increased force transmission in the longitudinal joint leads to higher values of stiffness and maximum bearable load of the shear diaphragm. Various methods to improve the contribution of the joints were developed. Of these, the hook-and-loop tape joint reinforcement has been found to yield the best results. Therefore, this reinforcing method has also been investigated in full scale tests. The use of hook-and-loop tape in the longitudinal joint makes the panels acting as one big plate. The impact on the screw connection has been successfully reduced by improving the load transfer in the longitudinal joints. [ABSTRACT FROM AUTHOR]

Das Ziel der durchgeführten Optimierung liegt darin, die mechanischen und geometrischen Eigenschaften der Sandwichbauteile so auf einander anzupassen, dass sich eine möglichst hohe Tragfähigkeit der Elemente ergibt. Gleichzeitig werden die entstehenden Materialkosten berücksichtigt. Eine parallele Berücksichtigung der Tragfähigkeit und der Materialkosten führt zu einer Mehrzieloptimierung mit zwei konkurrierenden Zielen. Zusätzlich fließen die Gegebenheiten, die aus den Produktionsprozessen und der Anwendung der Paneele resultieren, in die Berechnungen als Randbedingungen ein. Der Aufsatz basiert auf [1], wobei es sich um eine Optimierung von Sandwichwandbauteilen mit einem PUR-Kern und Stahldeckschichten handelt. Optimization of wall sandwich panels. The aim of the conducted optimization is an adjustment of the mechanical und geometrical properties of sandwich panels in a way that a high load bearing capacity of the elements can be achieved. At the same time the emerging material costs shall be considered. A simultaneous consideration of load bearing capacity and material costs causes an optimization problem with two competitive objectives. Conditions coming from the production processes and the use of the panels are intergraded in the optimization calculations as constraints. This article is based on [1], where an optimization of wall sandwich panels with a PUR-core and steel cover sheets is done. [ABSTRACT FROM AUTHOR]