Aside from these plywood sandwich panel non-proprietary standards, the SIP industry has relied heavily on proprietary code evaluation reports. In early 2009, SIPA partnered with NTA Inc, a product certification agency, to produce the first industry wide code report which is available to all SIPA members who qualify. Unlike previous code reports, the prescriptive provisions provided in the SIPA code report are derived from an engineering design methodology which permits the design professional to consider loading conditions not addressed in the code report.
Strips 35 mm in width were cut from 3-mm three-layer birch plywood obtained from a local manufacturer. Strips were pre-assembled without adhesive and glued into the imprinted groove pattern (Fig. 1) by using PVAc adhesive Soudal 67A (INVA Building Materials s.r.o, Praha, Czech Republic), which was equally applied to all the grooves prior to assembling. No adhesive was applied to hold the plywood pieces to each other. The sandwich panel was pressed at a specific pressure of 0.7 MPa for 45 min, followed by conditioning for 24 h at 24 °C and 65% relative humidity to ensure proper curing of the adhesive.
Plywood Sandwich Panel Factory
Three-point bending tests followed ASTM C393-06 to obtain shear stresses in the core as well as in the faces. The sandwich panel width allowed the inclusion of a complete iso-shape core unit (Fig. 3). The span between the supports (l) was 410 mm, and the sandwich panel width (b) was 112 mm. The face layer thickness was 5 mm, and the total panel thickness was 38 mm (Table 2). The loading rate was set to 6 mm/min to reach failure within 90 s.
SIP is a sandwich structured composite, consisting of an insulating layer of rigid core sandwiched between two layers of structural board, used as a building material. The board can be sheet metal, plywood, cement, magnesium oxide board (MgO) or oriented strand board (OSB), and the core can either be expanded polystyrene foam (EPS), extruded polystyrene foam (XPS), polyisocyanurate foam, polyurethane foam, or be composite honeycomb plywood sandwich panel.
The grid bonding in the impressed grooves is seen as a novel feature of the new sandwich structure. Using digital image correlation, a deformation evaluation was completed (Fig. 7). As is visible, the regions where the ribs were present showed lower deformation than the rest of the panel. Especially, vertical deformations (eyy) were significantly lower in area of the ribs. The eyy of area with ribs was mostly -0.0005 (-), while in the center of the sample eyy ranged from -0.0018 to -0.0210 (-).
plywood sandwich panels
Honeycomb Sandwich Panels
Plywood sandwich panel samples B1 and B2 cut from the sandwich panel were tested to determine the loads at failure, which were 2.14 kN and 1.66 kN, respectively (Table 4, Fig. 9). The core shear strength values of B1 and B2 were 0.27 MPa and 0.21 MPa, respectively. Flexural facing strength was measured at 11.19 and 8.66 MPa. Samples failed at the outer side of the lower facing. The flexural facing strength was lower than the data reported by Li et al.
Furthermore deformation evaluation (Fig. 8) by DIC showed that facings are distributing the most of the exx deformations during the bending. As is common, the top facing was distributing positive strain (+exx), reaching a maximal value of 0.0123 (-), while the bottom facing was distributing negative strain (-exx), which was -0.014 (-). The stress-strain curve is shown in Fig. 9. For future research, consideration of the application of various surface materials to enhance bending properties is recommended, e.g., veneer overlays (Kawasaki et al. 1999; Král et al. 2013; Král et al. 2014) or fiber glass reinforcement (Li et al. 2014).
The third component in SIPs is the spline or connector piece between SIP panels. Dimensional lumber is commonly used but creates thermal bridging and lowers insulation values. To maintain higher insulation values through the spline, manufacturers use Insulated Lumber, Composite Splines, Mechanical Locks, Overlapping OSB Panels, or other creative methods. Depending on the method selected, other advantages such as full nailing surfaces or increased structural strength may become available.