The Performance, Safety and Production Benefits of SPS Structures ...

Lloyd’s Register, together with the University ofStrathclyde, are conducting a series of Fire EngineeringAnalyses for a number of SPS designs in accordancewith recently introduced IMO guidelines (SOLASChapter II-2 Regulation 17). Based on the analysis of theDFDS Tor Line funnel casing constructed withprefabricated SPS plates, Lloyd’s Register presented thefollowing conclusion in the submission, which wassubmitted to the Danish Maritime Authority and is nowapproved.“From review of the extensive research and developmentand the fire engineering analysis carried out byIntelligent Engineering Limited and StrathclydeUniversity, some of which is reproduced in this report, itis concluded that for its intended use, SPS meets all therelevant safety objectives and functional requirements ofthe revised SOLAS Chapter II-2 and should beconsidered as at least equivalent to a conventionalinsulated stiffened steel plate of A-60 fire rating.”ENERGY ABSORPTIONTo increase its energy absorption capacity, a structuremust be simplified and designed to allow localizedprogressive plastic membrane action in the hull or sideshell plating to occur. Simplification is achieved byeliminating stiffeners and by introducing a plate structurewith equivalent in-plane buckling capacity and stiffnessto the stiffened plate, and flexural capacity to sustaintransverse loads. This is uniquely achieved with the SPSplate section. Furthermore, the ductile core eliminateshard spots over primary supports and providescontinuous support to the face plates, dissipatinglocalized bending strains. The net effect is an increase tothe puncture resistance and blast resistance. A furtherbenefit is that the polyurethane elastomer provides aneffective crack arrest layer. In the case of double hullproduct oil tankers, the inner cargo tank lining can beeffectively isolated from cracks that propagate from tears(sheared plating which may eventually occur under highenergy impacts) in the outer hull through the framingmembers into the inner hull, thus preventing oil outflow.Figures A.4(a) and (b) graphically illustrate the localimpact resistance of a stiffened steel plate and a SPSplate when subjected to a corner shaped impactor,simulating the impacts of ship hulls with floating semisubmergedcontainers or dead heads or grazing offwharfs or from grabs for tank tops in bulk carriers. Theimpactor was mounted on a pendulum swing with a massof 2 tonnes that was raised two metres and released. Theimpactor struck the plate at approximately 20 km/hr.The stiffeners of the steel plate were buckled where theyframed into transverses and the plating was holed orpunctured. The impacted faceplate of the SPS plate wasplastically deformed in the shape of the impactor andembedded into the elastomer core in the shape, but notpenetrated.Figure A.4(c) shows a plastically deformed stiffenedsteel plate icebreaker hull section. At the load points thehull plating was bent sharply (hard spot withconcentrated bending strains) and ruptured. FigureA.4(d) shows the outer hull of a 40,000 dwt SPS productoil tanker loaded with four 500T actuators. The hullplates, and longitudinal and transverse girders, weredesigned for both normal operating loads and tomaximize the energy absorption capacity for extremeloads events. The hull plating developed plasticmembrane action between longitudinal girders, whichextended into adjacent cells as the longitudinal buckled.Rupture of the outer SPS plating did not occur as theelastomer core effectively distributed the load anddissipated the bending strains.Figures A.4(e) and (f) show a stiffened steel hull sectionthat was subject to a terrorist bomb attack and twostructurally equivalent plates that were subjected tounderwater blast loads. In both cases the steel platesshear, tear and open. Not only is the hull ruptured butalso a significant portion of the blast energy wastransmitted to the structure or contents behind the hullplate causing secondary damage. The SPS plateeffectively contained the blast load through plasticmembrane action.The use of SPS plates coupled with the appropriateenergy absorption design philosophy improves the crashworthiness of the hull structure (maximizes the totalenergy absorption of the structure), provides a decreasedrisk of environmental pollution and asset protection.LATEST DEVELOPMENT PROGRAMMEIn addition to the programmes described above, IEcontinues to develop SPS technology. The objectives ofthe development are to improve understanding of thecharacteristics and capabilities of the technology, todevelop design methodologies and to test the suitabilityfor new applications.Among the latest developments are:• Ongoing classification approvals for specificapplications: These have been achieved with sixmajor classification societies.• General material type approval for the elastomercore: This has been granted by DNV and similarapprovals are being pursued with the others societies.• A programme to establish a set of ship designverification rules: Lloyd’s Register is developing aset of rules and procedures for design assessment ofship structures using steel composite construction.This will enable designers to work towards anestablished standard for strength.• Investigation and full scale testing of SPSperformance in ship collisions and grounding: Thiswork will compare the performance of SPS and all-17