SPS products have been developed to reach their full plastic capacity in flexure or compression without local buckling of either faceplate.
To understand the performance bond strength of SPS, flexural and compressive resistance, shear resistance and fatigue resistance need to be considered.
A suitably strong bond at the interface between the core and faceplates is required for composite action, across a full range of operating temperatures. As well as static loads, this may include dynamic loading events such as wave action or impact loads (grab or heavy cargo) that occur frequently.
Bond strength has been established to be a function of surface preparation, casting conditions, ambient temperature and type of metal. Bond strength design values are based on providing a reliability index that is equivalent to other structural connection details (welded or bolted).
Designs are undertaken to meet performance requirements of generally not greater than 2MPa. Design bond strengths typically range between 6MPa to 2MPa although IE looks to exceed these. Typically 10-14MPa is achieved in the field. Positests are undertaken to confirm bond strengths as part of IE’s production and Q&A procedures.
Flexural and compressive resistance
SPS plates consist of two metal faceplates bonded to an elastomer core with thicknesses that are tailored to give the desired strength and stiffness. The tensile strength of the plates is governed by the thickness of the faceplates. (The elastomer core provides continuous support to the faceplates, which precludes local buckling.) The flexural capacity is governed by the full plastic moment capacity of the faceplates.
The compressive resistance of SPS columns or plates is a function of the length, core-to-faceplate thickness ratio, the relationship of core shear stiffness to faceplate bending stiffness, core-to-faceplate bond strength and the boundary conditions. SPS core material characteristics have been engineered to provide stability to the faceplates to preclude local buckling and that the ultimate limit state for strength is based on either cross-sectional strength or inelastic global buckling
The fatigue resistance for SPS faceplates is consistent with the fatigue resistance associated with category type A details (parent plate material). At high stress range levels the interface shear is unaffected, even at a shear stress range of 3.9 MPa. Tests have determined that the SPS interface bond is essentially fatigue insensitive. Therefore the fatigue resistance of SPS structures is a function of the bolted or welded connection details and not the SPS plate.