## 2 Experimental Review of Prefabricated Lightweight CFST Framework-Composite Slab Structures
### Experimental Design and Fabrication of Specimens
#### 2.1.2 Design of a Composite Slab  
Two types of composite slab were prepared for the experiment including a sandwich panel and a concealed steel-truss panel. Three designs of the sandwich slab were prepared without an opening, with a window opening, and with a door opening. The specimens were designed with a column spacing of 3900 mm and a floor height of 2700 mm. The concealed steel-truss and sandwich panels were designed with thicknesses of 150 and 240 mm, respectively. Sandwich panels were spliced together to form a slab without an opening. The sandwich panel measured 590, 3540, and 240 mm in height, length, and thickness, respectively. It comprised three layers with each measuring 80 mm in thickness. The dimensions of the sandwich panel could be changed, according to the design of the column spacing and floor height. Thus, it was suitable for different spatial layout designs of rural buildings. The middle layer of the sandwich panel was a graphite-polystyrene board, serving as the heat-insulation layer of the slab, whereas the outer layers comprised cast-foamed concrete and served as the structural layers. The thickness of the middle heat-insulation layer can be increased or decreased, according to the different energy-saving building standards and the requirements of different regions. Additionally, foamed concrete layers have a smaller thermal conductivity than normal concrete and masonry blocks, which contributes to the improved heat-insulation performance of the slab. The outer structural layers of foamed concrete also protect and improve the fire-resistance and durability of the middle heat-insulation layer. A single layer of \(\phi\)3@50 orthogonal galvanised cold-drawn steel wire mesh with 30-mm cover thickness was embedded into each of the outer structural layers of foamed concrete to improve strength. The wire meshes in the two structural layers were connected with \(\phi\)3  
Figure 1: Image and figure showing stiffener-reinforced L-brackets welded to the column and connected to the beam with M12 high-strength bolts. wires diagonally embedded across the heat-insulation layer, which form a spatial wire truss framework that enabled the outer structural layers and middle heat-insulation layer to form an integrated unit for load bearing. A steel-tie bar of \(\phi\)6@200 was attached to each end of the panel for connection with the columns of the framework. The structure was partly embedded into the panel with a buried depth of 300 mm and exposed a straight length of 105 mm. It was welded with the single layer of the orthogonal galvanized cold-drawn steel wire mesh using a minimum of three welding points. Two sandwich panels were connected with a tongue-and-groove joint. The bottom edge of the panel was of a groove design and the top edge was a tongue design. Figure 2 showed the structural design of the sandwich panel. A wall with an opening was formed by splicing sandwich panels both with and without openings. Panels with openings were designed with a steel tie bar at the edge for connection with the framework with no steel tie bar at the opening edge. Either a door or a window was connected to the edge without a steel tie bar. The length of a panel with an opening can be changed according to different sizes of doors and windows. The door opening of the specimen measured 1800 mm in height and 800 mm in width. The panels for the door opening measured 1370 mm in length. The window opening of the specimen measured 1000 mm in height and 1400 mm in width. The panels for the window opening measured 1070 mm in length. The tongue-and-groove joint between the two sandwich panels had the tongue along the top edge and the groove along the bottom edge of the panels. By inserting the groove along the bottom edge of one panel into the tongue along the top edge of a panel, the perpendicularity of the two joined panels was ensured. The seams between the joined panels were filled with foamed concrete and then scraped until it was level.