## 1 Introduction
Nine test samples of SCS slabs are made with stud bolt connectors and are put under concentrated load at the centre of the slab. The observed failure modes included concrete core crack, lower plate slip and upper plate buckling, and stud bolt separation. To study load vs. displacement at the centre and load vs. interlayer slip behaviour, stud bolts diameter and concrete thickness were varied. The results of the tests were compared with the results of sandwich slabs with J-hook connectors [24], and better behaviour was observed. One theoretical model was used to predict the bending strength of the slabs. The results of the theoretical model were consistent with the test results. Researches on the CSC shear connectors proposed by [PERSON] et al. [23] have been limited to theoretical studies due to the practical problems of the two end welding, especially in slabs. In 2017 and 2018, [PERSON] and [PERSON] [30; 31] investigated and compared the performance of CSCs for interlayer shear behaviour using Push-out tests in two states of one end welded and two ends welded. The interlayer shear strength of the CSCs in the two ends welded form was approximately twice that of the one end welded. In addition, in two end welded state due to bonding of faceplates, there was no sudden failure, and thus more ductility and energy absorption were provided. Therefore,they proposed a method to perform the two end welded of CSCs, which could help to make easily in construction site and improve structural performance [32]. In this method, as shown in Figure 1(a), in the first step, steel faceplates are accurately measured and lined for the installation of the CSCs and creation of the holes required for plug weld. Plug weld is done by filling the holes with arc welding to connect steel faceplates to the inaccessible end of the CSC connectors. Then, the one end of CSCs is welded on steel faceplates. In the following, in accordance with Figure 1(b), the two steel faces are located in the opposite position, so that the other end of the CSCs can be welded to steel faceplates using plug weld. Finally, the space between the two steel faces is filled with concrete materials, as shown in Figure 1(c) experimental studies of SCS beams interconnected by two ends welded CSCs showed acceptable results in terms of ultimate strength as well as ductility and energy absorption under static load compared with one end welded ones. Research on the behaviour of SCS slabs with two ends welded CSCs can also be important. One of the most critical developments in composite sandwic of SCS is possible to use in structures where light weighting is an important criterion, such as ship-hull. Therefore, in this study, the SCS sandwich slab that consists of lightweight concrete (LWC) core sandwiched in between two steel plates interconnected by proposed two ends welded CSC shear connectors under concentrate quasi-static load is assessed. For this purpose, two SCS slabs manufactured with LWC core and steel fibres reinforced LWC core are investigated and compared with that containing normal weight concrete (NWC) core. For this reason, the failure modes of the slabs and the load-displacement relationship are also measured. Besides, the obtained results are compared to those performed in the previous investigations of the ones of the J-hook SCS system [24] and stud bolt SCS system [29]. For a reasonable comparison, the geometrical characteristics of the specimens and the cross-sectional area of the shear connectors are approximately equivalent to those of the selected reference specimens.