Engineering Structures 31 (2009) 2045–2059 Contents lists available at ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct Impact tests on steel–concrete–steel sandwich beams with lightweight concrete core J.Y. Richard Liew ∗ , K.M.A. Sohel, C.G. Koh Department of Civil Engineering, National University of Singapore, BLK E1A, #07-03, One Engineering Drive 2, Singapore 117576, Singapore article info Article history: Received 11 August 2008 Received in revised form 9 March 2009 Accepted 9 March 2009 Available online 8 April 2009 Keywords: Contact law Elastic–plastic analysis Lightweight concrete Low velocity impact Sandwich composite Shear connector Steel–concrete composite abstract This paper studies the impact performance of Steel–Concrete–Steel (SCS) sandwich beams consisting of a lightweight concrete core sandwiched between two face plates that are connected by J-hook connectors. Impact tests were carried out by dropping free weights on to sandwich beams to investigate their structural response against impact loads. Test results revealed that the proposed J-hook connectors provide an effective means to interlock the top and bottom steel face plates, preventing them from separation during impact. The use of fibres in concrete core and J-hook connectors for composite action enhances the overall structural integrity of the sandwich beams when compared with those without such enhancement. An elastic–plastic analysis method is developed to predict the force-indentation relationship of sandwich sections subjected to local impact. Dynamic analysis based on the local force- indentation relationship is carried out to predict the impact force and global response behavior of the sandwich beams. The predicted results are compared with those obtained from the tests to validate their accuracy so that they can be used to evaluate the performance of sandwich beams under low velocity hard impact. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction Steel–Concrete–Steel (SCS) composite systems are cost effec- tive structural systems that have found applications in submerged tube tunnels, protective structures, building cores, bridge deck, gravity seawalls, floating breakwater, anti-collision structures, nu- clear structures, liquid containment, impact resisting structure for volcanic shelters, ship hulls and offshore structures, in which resis- tance of impact and explosive loads is of prime importance [1–5]. Recently, Bergan and Bakken [6] proposed the use of SCS sandwich panels with a lightweight concrete core for ship hull construction. In SCS sandwich construction, the two steel face plates act as per- manent formwork providing two impermeable skins for the struc- ture upon completion. SCS sandwich construction combines the advantages of both steel and reinforced concrete to provide pro- tection against impact, blast and fire loads. In addition, the smooth steel surfaces can be readily protected, inspected and tested so that the integrity of the structure can be easily assured throughout its service life. The performance of a SCS composite structure is dependent upon efficient interaction and transfer of stresses between the steel plates and the concrete core. This can be achieved using mechanical shear connectors which prevent vertical separation ∗ Corresponding author. Tel.: +65 65162154; fax: +65 67791635. E-mail address: cveljy@nus.edu.sg (J.Y.R. Liew). in addition to longitudinal slip. Types of shear connectors used for sandwich composite construction include headed shear studs, angle shear connectors and mechanically fixed through connectors such as Bi-Steel [7]. However, the use of headed stud connectors is not suitable for lightweight concrete cores due to its low bearing capacity. Through connectors (such as those used in Bi-steel), which require friction welding, are not suitable for shallow depth panels of thickness less than 200 mm [7]. Therefore, a novel J-hook connector system (Fig. 1) is proposed to fill this gap when a shallow core (depth < 100 mm) is required in sandwich composites to produce slim-deck design [1,9]. Most of the previous studies have been focused on the ultimate strength behaviour of SCS sandwich structures under static or quasi-static loading [1–3,10–15]. However there have been a few studies on the impact behaviour of SCS sandwiches or double skin composite structures. Bambach et al. [16] conducted experimental and analytical studies on the transverse impact response of concrete filled steel hollow sections. Sohel et al. [8] conducted impact tests on SCS sandwich beams with angle shear connectors welded on the face plates. Most of the test specimens failed prematurely by tensile separation of the face plates, local buckling of face plates and crushing of the concrete core leading to poor impact performance. Since then, a further improvement was made using J-hook connectors and the static flexural strength behaviour was investigated by Liew and Sohel [1]. This paper further extends the work to study the performance of sandwich beams with J-hook connectors under impact loads. 0141-0296/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.engstruct.2009.03.007