Journal of Constructional Steel Research 66 (2010) 256–276 Contents lists available at ScienceDirect Journal of Constructional Steel Research journal homepage: www.elsevier.com/locate/jcsr Fatigue performance of lightweight steel–concrete–steel sandwich systems X.X. Dai, J.Y. Richard Liew * Department of Civil Engineering, National University of Singapore, Singapore article info Article history: Received 14 November 2008 Accepted 10 July 2009 Keywords: Energy dissipation Fatigue life Lightweight concrete Hooked connector Hysteretic response Plastic deformation Sandwich structure Steel–Concrete–Steel composite Stiffness degradation abstract This paper investigates the static and fatigue strength behavior of a composite sandwich system, which consists of a lightweight concrete core sandwiched in between two steel plates and interconnected by J- hook connectors. For this purpose, fibre-reinforced lightweight concrete, of density less than 1450 kg/m 3 , and novel J-hook connectors that are capable of resisting tension and shear have been developed. Fatigue tests were carried out to study the fatigue behaviour of sandwich beams by varying the maximum applied load and load range. It is found that maximum applied load and load range affect fatigue performance independently. The maximum applied load has a significant effect on fatigue performance when the difference between it and the load range is large. Test evidence shows that considering only the load range, without taking into account the maximum applied load, may over-predict the fatigue life of the sandwich structural system. Finally, a three-parameter fatigue design equation, taking into account both the load range and maximum applied load, is proposed based on regression analysis of test data. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction A lightweight sandwich composite structure is defined as a three-layer system, consisting of two thin outer skins of high strength material separated by a low density and lightweight core material. Since the mid-1980s carbon or glass fiber reinforced poly- mer (CFRP/GFRP) composites have been used increasingly in ship construction [3–9]. They consist of two stiff and relatively high- density CFRP/GFRP skins separated by a thick, light and structurally weaker core, generally PVC foam. However, these FRP sandwiches were used only for small to medium vessels due to their low stiff- ness and high cost. A newly developed sandwich system known as the Sandwich Plate System (SPS), consisting of steel face plates with a polyurethane core in between has been successfully used for ship deck rehabilitation work [10,11]. However, large scale adop- tion of the SPS to build larger ship structures has not been realised due to high materials cost, problem of welding the panel joints at the site and questions over the durability of the polymer when ex- posed to extreme temperature. In the 1990s, Klanac et al. [12] and Kujala et al. [13] introduced all metal sandwich panels by using laser welding technology. The two metal face sheets are laser welded to the corrugated metal core to form a structural efficient panel which has high stiffness-to- weight ratio and superior manufacturing accuracy and efficiency. * Corresponding address: National University of Singapore, Department of Civil Engineering, BLK E1A, #07-03, 1 Engineering Drive 2, Singapore 117576, Singapore. Tel.: +65 65162154; fax: +65 67791635. E-mail address: cveljy@nus.edu.sg (J.Y. Richard Liew). However, the face plate thickness must be thin enough for laser welding. The thin face plates are not protected by any infill ma- terials and thus they are also prone to perforation due to impact objects. Concrete is one of the alternate infill materials that can be used for sandwich construction due to its relatively lower cost and good performance over a long service life. In fact, concrete was used to build merchant ships after the First World War. Scarcity of steel during World War II also resulted in the production of many concrete ships [14]. However, ships built of normal weight concrete typically carry a weight penalty of more than 50% to that of steel ships. This implies a corresponding reduction of cargo capacity, speed and fuel efficiency. This prompts the research into a novel structural composite form which utilizes ultra-lightweight concrete and structural steel for novel ship construction. Fatigue failure is of one of the key concerns in the design of bridges and ship structures. Fatigue analysis is normally carried out based on the S–N curve approach [15], as shown in Eq. (1), under the assumption of a linear cumulative damage law, the so called Miner’s rule [16], as shown in Eq. (2). N f × (S ) m = K (1) k  i=1 n i N i = C (2) where N f is the number of cycles to failure, m and K are constants determined by regression analysis of fatigue test data and S is the applied stress range, n i is the number of cycles applied by stress magnitude ∆σ i , N i is the number of cycles to failure of stress magnitude ∆σ i , and C is constant and usually assumed to be 1.0 for design purposes. 0143-974X/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jcsr.2009.07.009