Fresh concrete used in 3D printing should ensure adequate yield stress, otherwise the printed concrete layer may suffer intolerable deformation or collapse during the printing process. In response to this issue, an analytical study was carried out to derive the initial yield stress and hardening coefficient of fresh concrete suitable for 3D printing. The maximum shear stress distribution of fresh concrete was calculated using a stress transformation equation derived from the equilibrium condition of forces. In addition, the elapsed time experienced by fresh concrete during the printing processes was estimated and was then substituted into the elapsed time-yield stress function to calculate the yield stress distribution. Based on these results, an algorithm capable of deriving both the initial yield stress and the hardening coefficient required for printing fresh concrete up to the target height was proposed and computational fluid dynamics (CFD) analyses were performed to verify the accuracy of the proposed model.

The dual potential capacity model (DPCM) was proposed in this study to evaluate the shear strengths of short and deep reinforced concrete (RC) members with the shear span‐to‐depth ratios less than 2.5. In the proposed model, the nonlinear flexural analysis considering the bond mechanism between steel reinforcements and surrounding concrete was conducted to estimate the local stress increase in the steel reinforcements between flexural cracks, and the shear demand force of the cracked tension zone in an RC section can also be determined on this basis. The crack concentration factor was introduced to consider the size effect in estimation of the potential shear capacity corresponding to the shear demand force to be resisted by the cracked tension zone. For the compression zone, different plasticity models were adopted depending on the shear span‐to‐depth ratio to estimate the potential shear capacity of the intact compression zone. For the verification of the proposed model, a total of 466 test results of RC short and deep beams with various shear span‐to‐depth ratios less than 2.5 were collected from existing literature, and accuracy of the proposed model was verified in detail by comparing the shear strengths of the RC short and deep test specimens estimated from the proposed DPCM with those of the test results.

In structures manufactured using 3D concrete printing, cracks can easily propagate along the interface between printed layers. Therefore, it was necessary to determine the interlayer bond strength. In this study, direct shear and tensile tests were performed to determine the interlayer bond stability of the 3DCP members. To confirm the appropriateness of the mix proportion used to fabricate the specimens, the open time available for printing was identified via a mixing test, and the extrudability and buildability were verified via a printing test. In addition, direct shear and tensile tests were performed using the specimen manufacturing method (i.e., mold casting and 3D printing) and printing time gap (PTG) between the laminated layers as key test variables. The interlayer bond strengths of the specimens, according to the variables obtained from the test results, were compared and analyzed based on the interfacial shear strength standards presented in the current structural codes. In the direct shear test, failure occurred at the interlayers of all the specimens, and the interlayer bond strength tended to decrease with increasing PTG. In addition, the interlayer bond strength of the direct shear specimens exceeded the interfacial shear strength suggested by current structural codes. In contrast, in the direct tensile test, interlayer surface failure occurred only in some specimens, and there was no distinct change in the interlayer bond strength owing to PTG.

Half precast concrete slabs with inverted multi-ribs (Joint Advanced Slab, JAS), which enhance composite performance between slabs by introducing shear keys at connections between the slabs and improve structural performance by placing prestressing tendons and truss-type shear reinforcements, have recently been developed and applied in many construction fields. In this study, flexural and shear tests were performed to verify the structural performance of JAS members. Towards this end, two flexural specimens and four shear specimens were fabricated, and the presence of cast-in-place concrete and the location of the critical section were set as the main test variables. In addition, the flexural and shear performance of the JAS was quantitatively evaluated using a non-linear flexural analysis model and current structural design codes. Evaluation results confirmed that the flexural behavior of the JAS was almost similar to the behavior simulated through the non-linear flexural analysis model, and the shear performance of the JAS can also be estimated appropriately by using the shear strength equations presented in the current design codes. For the JAS with cast-in-place concrete, however, the shear strength estimation results differed significantly depending on the way that the shear contributions of the precast concrete unit and cast-in-place concrete were calculated. Based on the analysis results, this study proposed a design method that can reasonably estimate the shear strength of the composite JAS.