Analysis and Development of Advanced Sandwich Elements for Sustainable Buildings

Building industry represents nearly 40 % of primary energy consumption in most countries registered in the International Energy Agency. This makes the building sector the highest energy consuming sector in industry worldwide. To fulfil energy reduction objectives, European Union (EU) countries and companies are looking for solutions to lower the energy demands from the building sector.

Therefore, ambitious targets for energy consumption of new buildings are being implemented, and by the year 2020 nearly zero energy buildings will become a requirement in the EU. As a consequence of these requirements as well as general requirements for increased efficiency and sustainability, the building sector is experiencing a growing demand for modular, lightweight building elements having a high degree of insulation, a long life time, a low CO2 emission, a low consumption of raw material, and an attractive surface with minimum maintenance.

The need for improvement, innovative structures and production methods therefore grows. In this challenging environment, precast thin-walled High Performance Concrete (HPC) Sandwich Panels offer an interesting solution to all actors involved in the value chain of the building, from the architects and the manufacturers to the end owners.

However, the literature available with respect to analysis and/or design of thin-walled HPC sandwich panels is scarce. The goal of this work was to develop a framework for analysis and optimization of the precast thin-walled High Performance Concrete Sandwich Panels. The present framework was led at three levels.

The first level experimentally investigated material and mechanical properties of shear connectors, insulation layer and HPC. Material characterization included assessment of time dependent strength, fracture properties, stiffness and shrinkage for HPC. In a second stage, the structural level was described to study the influence of the various constituents of the sandwich panel on the behaviour of the panel under shear and bending loading.

The experimental investigations focused on using the metallic, Basalt Fiber Reinforced Polymer (BFRP) and Carbon Fiber Reinforced Polymer (CFRP) connecting systems in combination with rigid foam. The experimental program included testing of small-scale specimens by applying shear (push-off) loading and semi-full scale specimens by flexural loading.

Further, two full-scale thin-walled HPC sandwich panels were exposed to flexural loading. Both the material level and the structural level were described through experimental and numerical investigations. A non-linear 3-D FEM model was developed using commercial programme Diana. Results of FEM analysis were found in good agreement with the experimental results.

The FEM model was capable predicting behaviour of HPC sandwich panel exposed to shear and flexural loading with reasonable accuracy. Further, numerical study was performed to assess the risk of early age cracking and to analyse the robustness of thin-walled sandwich panels at early ages. The approach investigates the constrained shrinkage that the external HPC plate is subjected to.

The modelling approach studied crack propagation in dependence on the stiffness of the restraints as well as distance between the restraints. The analysis predicts when cracking occurs and, if it occurs, how severe the consequences are. Finally, the third level was concerned about structural and cost optimization of the proposed sandwich system.

The optimization procedure was performed to find the structurally and thermally efficient design of load-carrying thin-walled precast HPC sandwich panels with an optimal economical solution. The optimization approach was based on the selection of material’s performances and panel’s geometrical parameters as well as on material cost functions in the sandwich panel design.

The strength based design of sandwich panels is in competence with the format of Eurocode 2. The optimization process outcomes in complex of design recommendations, which fulfil the requirement of minimum cost for those elements.