No abstract

No abstract

No abstract

The rocking response of a freely standing two-rigid block 2-DOF system under ground excitation is comprehensively presented. The highly nonlinear governing equations of motion, properly established, under certain conditions may be linearised leading after integration to closed form solutions. The analysis is based on the assumption that friction at the interface between the two-rigid blocks or the lower block and the ground is sufficient to prevent sliding. All possible configuration patterns exhibited by the two-rigid block system during rocking motion are examined in detail. Attention is focused on the determination of the minimum amplitude ground acceleration among all patterns which leads the system to overturning instability. The effect of week damping is included in the analysis by reducing the relative angular velocity after impact. Conditions for overturning instability with or without impact, either between the two blocks or between the lower block and the ground, associated with an escaped motion in the phase-plane portrait, are thoroughly discussed. It is found that for moderately large values of excitation frequencies overturning instability occurs after impact. Beyond these values overturning instability without impact prevails. In case of overturning instability without impact, surprisingly enough, it was also found that there are ranges of values of excitation frequencies in which a monolithic rigid block as a 1-DOF system becomes more stable when divided into two equal rigid blocks, acting as a 2-DOF system.

No abstract

No abstract

No abstract

In light of recently published work highlighting the incompatibility between the concepts underlying current code specifications and fundamental concrete properties, the work presented herein focuses on assessing the ability of the methods adopted by some of the most widely used codes of practice for the design of reinforced concrete structures to provide predictions concerning load-carrying capacity in agreement with their experimentally established counterparts. A comparative study is carried out between the available experimental data and the predictions obtained from (1) the design codes considered, (2) a published alternative method (the compressive force path method), the development of which is based on assumptions different (if not contradictory) to those adopted by the available design codes, as well as (3) artificial neural networks that have been calibrated based on the available test data (the later data are presented herein in the form of a database). The comparative study reveals that the predictions of the artificial neural networks provide a close fit to the available experimental data. In addition, the predictions of the alternative assessment method are often closer to the available test data compared to their counterparts provided by the design codes considered. This highlights the urgent need to reassess the assumptions upon which the development of the design codes is based and identify the reasons that trigger the observed divergence between their predictions and the experimentally established values. Finally, it is demonstrated that reducing the incompatibility between the concepts underlying the development of the design methods and the fundamental material properties of concrete improves the effectiveness of these methods to a degree that calibration may eventually become unnecessary. Keywords Artificial neural network • Design codes • Ultimate limit state • RC beams • Compressive force path method • Physical models Abbreviations CFP Compressive force path ANN Artificial neural network ULS Ultimate limit state List of symbols a v Shear span b Beam width d Effective depth x Depth of the compressive zone A s Area of tensile reinforcement A s ′ Area of compressive reinforcement A sw Area of transverse reinforcement v ∕d Shear span-to-depth ratio f c Uniaxial compressive strength of concrete f yl Longitudinal reinforcement yield stress f yw Transverse reinforcement yield stress s Spacing between shear links l Ratio of tensile reinforcement (l = A s ∕b × d) t Ratio of compressive reinforcement (t = A s � ∕b × d) w Ratio of transverse reinforcement (w = A sw ∕b × s) V c Shear resistance of the RC beam without the contribution of the shear links V s Shear resistance offered by of shear links V u Shear developing along the span of the RC beam at failure M u Bending developing along the span of the RC beam at failure M f Flexural moment capacity of the cross section of the RC beam