This study aimed to investigate the flexural behavior of T-section semi-precast reinforced concrete (RC) beams composed of recycled aggregate concrete (RAC) and natural aggregate concrete (NAC). The experimental program consisted of four large-scale T beams, including three semi-precast T-beams and a reference RC T-beam made of traditionally cast high strength natural aggregate concrete (HSNAC). The web of all the semi-precast beams composed of a precast U-shaped part, which contained the longitudinal and transverse reinforcement and was cast of HSNAC, and an inner RAC core. Normal strength RAC (NSRAC) or high strength RAC (HSRAC) was used as web core filler, and HSNAC or HSRAC was used for the beam flange. Two techniques were adopted to fill the web core: the traditional concrete casting and the placement of well-sized precast concrete blocks. The results indicated the applicability of RAC and NAC in one section to achieve comparable strength, deformability, and failure mode to those of the monolithically cast beam with NAC. In addition, using precast RAC blocks as filler in the web core of RC beams is a promising construction technique, which can be adopted as a critical design parameter to control development, propagation, and width of flexural and shear cracks to a large extent.

More than 40 models have been established to date to determine the axial compressive behavior of noncircular (square or rectangular) concrete sections confined with fiber-reinforced polymers (FRPs) under concentric loadings. In this study, these models were classified into four groups, represented by nine analytical models. The accuracies of these models to capture the cyclic response of seven noncircular RC columns subjected to axial and reversible horizontal loads were evaluated. Specifically, the predicted responses revealed that the studied models predicted a premature FRP rupture failure mode, and in turn the simulation process was aborted early, revealing a low deformability capacity. By scrutinizing the available results, it was concluded that the axial compression behavior of the FRP-wrapped concrete was dependent on the applied loads, e.g., concentric axial load or axial load and bending moment. Subsequently, one of the examined models was adopted and revised to consider this effect. The modified model can accurately and safely simulate the lateral response of RC noncircular columns retrofitted with FRP, and it can be expanded for general application after verification against a notably large number of noncircular columns.

Clock synchronization has been a challenging task in the design of wireless networks because the synchronization accuracy suffers from uncertain transmission delay and/or packet loss due to poor wireless channel conditions. To address this problem, this paper develops a robust clock synchronization schemes based on matrix completion theory to improve the accuracy in presence of random transmission delay and packet loss. We propose a matrix completion based maximum likelihood estimator (MC-MLE) to estimate the clock offset and clock skew under Gaussian transmission delay model. Thanks to the denoise feature of matrix completion, the proposed schemes outperform the maximum likelihood estimator (MLE) in the presence of packet loss and random transmission delay. That is, the proposed schemes are closer to the Cramer-Rao lower bound (CRLB) than the MLE when the timestamp packets are randomly corrupted. The robustness and accuracy of the proposed schemes are validated by numerical results.

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