## 1 Introduction  
Sandwich panels crafted with concrete skins and insulating cores are a competitive solution for building structural components with energy-efficient added value (see a review in [PERSON] et al.) [1]. The concern about climate change and sustainable solutions drives research towards greener and more bio-based engineering sandwich technologies according to [PERSON] et al. [2]. In the present work, a solution based on the vegetal FRCM and polystyrene core serves as a lightweight construction solution with noteworthy insulating properties for building enclosures. The mechanical properties of these panels depend significantly on the composite action between materials. An adequate material connection is crucial, as insufficient bonding may result in a problematic stress distribution within the panel, potentially causing detachment failure or a substantial decrease in mechanical strength. In this order, different authors like [PERSON] et al. [3] developed a composite shear connector system of a glass-fiber-reinforced polymer (GFRP) used to transfer interface shear forces in a precast concrete sandwich panel. This study developed push-off, pullout, and flexural teststo evaluate the structural performance of the shear connectors, and the effect of the bond between concrete and insulation was evaluated with push-off tests. The results showed satisfactory performance with a lower bound of 90% of composite action for specimens with a 100 mm thick insulation wythe and full composite action for most panels with 50 mm thick insulation. [PERSON] et al. [4] studied a numerical model by evaluating zig-zag functions by enforcing the continuity of transverse shear stresses at layer interfaces, being able to predict accurately the distribution of stresses and displacements in laminated plates and sandwich panels. Another study by [PERSON] et al. [5] presented experimental and numerical methods to analyze the structural behavior related to a sandwich panel with a glass-fiber-reinforced polymer (GFRP) plate connection system, where double-shear tests were conducted on sandwich specimens to characterize the available shear capacity provided by the connectors and panel configuration. The authors conclude that for well-balanced composite action, it is necessary to use the least amount of material in the plate connectors and an increased amount of bending capacity of the outer panel to avoid a significant drop in the load after the peak load. At the same line, [PERSON] et al. [6] presents an experimental campaign at elevated temperatures for panels stiffened by structural ribs, insulation layers, and steel shear connectors. The results highlighted insulation shear failure from differential thermal expansion at the interface with concrete, where the shear connectors induced stress concentrations, leading to local failure. A study presented by [PERSON] et al. [7] carried out push-through tests on a precast-concrete-insulated sandwich panel using combined angled and horizontal connectors, where basalt-fiber-reinforced polymer and steel connectors were used. This study evaluated various connector inclination angles and diameters, diagonal connector orientations relative to the loading, and panels with or without an active foam-to-concrete bond. The results show that steel connectors failed by yielding in tension and inelastic buckling in compression. In the case of larger-diameter basalt-FRP connectors, they pulled out under tension and crushed in compression, and smaller-diameter basalt-FRP connectors ruptured in tension and buckled in compression. Also, it is demonstrated that the strength and stiffness improved with the connector angle and diameter. [PERSON] et al. [8] performed 24 double-shear tests on precast-concrete-insulated sandwich panels using stainless-steel plate connectors. The authors analyzed parameters like connector directions, insulation effects, cavity widths, and connector heights.