PSI - Issue 64

Saim Raza et al. / Procedia Structural Integrity 64 (2024) 1200–1207 Raza / Structural Integrity Procedia 00 (2024) 000 – 000

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Fig. 3. Design post-tensioning loads for various eccentricities of the tendon in the proposed ribbed formwork topology for span lengths of 4 to 6m

4. Printing feasibility of the slender formwork for ribbed concrete slab To assess whether it is practically feasible to print a ribbed slab formwork with a thickness of just 30 mm, the 3D concrete printing of the proposed design was performed using the robotic arm printing facility at the Structural Engineering laboratory in Empa. In the printed geometry, the width of each filament was 30 mm and the height was 10 mm. The printing toolpath path consisted of back-and-forth movements between the ending and starting positions of adjacent layers due to the open geometry of the formwork. The concrete material flow rate during the printing was set to 1 l/min and the robot speed was 56 mm/s. In the used printing system, the amount of accelerator dictates both the initial yield stress and the rate at which the filament undergoes hardening, thereby controlling the buildability of the layers. An accelerator dosage of 26 ml/l was used during the printing of the formwork. The formwork was successfully printed to a height of 2m, as shown in Fig. 4, which demonstrates the feasibility of the proposed concept.

Fig. 4. 3D concrete printing of the ribbed formwork with 30 mm thickness and 2m span