Non‑removable‑bottom‑form steel truss floor decking and composite slabs differ significantly in material composition, construction methods, and performance: the former leverages a lightweight, non‑removable bottom form and efficient construction as its core advantages, while the latter relies on conventional precast concrete elements combined with on‑site composite action.

　　Non‑removable‑bottom‑form steel truss floor decking and composite slabs differ significantly in material composition, construction processes, and performance. The former leverages a lightweight, non‑removable bottom form and efficient construction as its core advantages, while the latter relies on conventional precast concrete elements combined with on‑site composite action. Below is a detailed comparison of their differences across multiple dimensions:

　　Materials and Structural Design

　　Non‑removable bottom‑form steel truss floor deck: It is precast as an integrated unit, combining steel trusses with a permanent bottom form—such as magnesium‑crystal fiber cement panels. The bottom form typically has a thickness of 12–20 mm; it does not contribute to structural load-bearing and serves solely as a construction formwork. Structurally, it creates a two‑way load‑bearing system with high overall stiffness, making it suitable for large spans (6–12 meters).

　　Composite slab: Composed of a precast concrete bottom slab (60–80 mm thick) and an in‑situ cast composite layer (≥70 mm), with the bottom formwork removed after construction. Typically designed as a one‑way slab; when spans are large, increasing the thickness of the composite layer or adding secondary beams is required, which can reduce space utilization.

　　Construction Efficiency and Techniques

　　Production and Transportation:

　　Non-removable bottom formwork: short factory production cycle (approximately 7 days), lightweight bottom panel (20.8 kg/m²), easy to transport, and can be manually handled.

　　Composite slabs: long production cycle (approximately 28 days), heavy bottom slab weight (156 kg/m²), prone to cracking during transport, and require tower crane lifting.

　　On-site installation:

　　Non-removable bottom formwork: Enables formwork‑free construction, with the bottom formwork providing inherent load-bearing capacity. After installation, reinforcement is tied and concrete is poured, eliminating the need to remove the formwork and reducing the construction schedule by 30%–50%.

　　Composite slabs: A temporary support system must be erected, and after installation, formwork may be removed only once the composite layer has attained the required strength; the process is complex.

　　Performance and Cost

　　Structural Performance:

　　Non-removable bottom formwork: with a maximum total load capacity of 8.17–17 tons, it meets Class A1 fire‑resistance standards, is corrosion‑resistant, and allows for a thinner overall floor slab thickness (e.g., 110 mm versus 130–140 mm for composite slabs), thereby increasing the interior clear height.

　　Composite slabs: They require a large volume of concrete and impose a high floor‑load (approximately 325 kg/m² after completion). Their joints necessitate the use of cast-in-place construction joints, which can compromise structural integrity.

　　Economic efficiency:

　　Non-removable bottom formwork: reduces labor costs (cutting the number of production workers by two-thirds), eliminates the plastering process, provides ample space for embedded pipelines, and lowers overall construction costs.

　　Composite slabs: high steel and concrete content, limited transportation radius, and high implementation costs.