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This study investigates the behavior of hybrid beam-column connections with numerous detailing methods to be incorporated into precast concrete moment-resisting frames under simulated reversed cyclic loading, and ultimately develops a design procedure. Seismic performance of moment-resisting precast concrete beam-column connections was investigated through simulated reversed cyclic load tests. In addition, nonlinear finite element analysis (FEA) of typical monolithic and precast concrete connections was carried out using a modified concrete damage plasticity model. Good agreement was achieved between experimental and numerical results, which indicates that the FEA model is capable of capturing failure modes of the investigated precast concrete connections. Simple detailing modifications resulted in major improvements in the performance of connections in terms of load-displacement curves, stiffness, and energy dissipation. Finally, a design procedure was developed for the investigated connections based on failure modes and investigated limit states. [ABSTRACT FROM AUTHOR]

The present study pertains to the influence of variation of FRP (Fiber Reinforced Polymer) proportion in tension reinforcement on the flexural behavior of RC beams with FRP and steel reinforcing bars. A total of 25 beams, including FRP-, steel- and hybrid FRP-steel reinforced ones, were tested to failure under four-point bending. Two types of FRP bars, GFRP (Glass Fiber Reinforced Polymer) and BFRP (Basalt Fiber Reinforced Polymer), were used and both over- and under-reinforced beams were tested. The beams in each group were designed to have close flexural capacities to fully reveal the effect of FRP proportion in the tension zone on beam ductility for a fixed bending capacity. A new analytical model was developed for estimating the bending capacities of beams. Different deformation and curvature ductility definitions were adopted and an energy-based definition, revealing the expected tendency in beam ductility, was determined. The test results revealed that the presence of even a single FRP bar in the tension zone results in reductions up to 40% in beam ductility as compared to the beam with full steel reinforcement. Each additional replacement of a steel bar with FRP was found to cause a further decrease up to 20% in beam ductility. [ABSTRACT FROM AUTHOR]

Each year a large number of concrete bridges are subjected to impact by overheight vehicles or vehicles carrying overheight objects. Most bridge owners in the United States are concerned with the increasing trend of bridges impacted by overheight vehicles, thereby increasing the urgency to evaluate the resistance of bridges to lateral impact loads. The present integrated numerical and experimental study investigates the behavior of a critical connection, between girders and floor beams, in a type of bridge that is considered to be particularly vulnerable, prestressed concrete through-girder (PCTG) pedestrian bridges. PCTG pedestrian bridges comprise precast, prestressed concrete girders connected by cast-in-place, reinforced concrete floor beams and a cast-in-place deck. The deck is connected to the floor beams only, and the floor beams are joined to the girders using embedded concrete anchors. The investigation combines three-dimensional finite-element analyses with physical testing to elucidate the load-deformation characteristics of the girder-floor beam connections. A series of six girder-floor beam connection subassemblage specimens were built and tested, three of which were subjected to vertical loading, while the other three specimens had a combination of vertical and horizontal load. Three types of anchors were investigated, including two types of loop inserts and one bolt insert. The study revealed that specimen response depends upon the characteristics of the embedded concrete anchors. Deterioration of specimen load capacity was found to be associated with concrete cracking, formation of a cone breakout surface, yielding of the anchors, and fracture of the inserts. The floor beam-girder subassemblages were able to resist large displacements after attaining peak load, even though postpeak load carrying capacity was undermined in most cases. DOI: 10.1061/(ASCE)0733-9445(2007) 133:11 (1670) CE Database subject headings: Bridges, girder; Beams: Connections; Concrete, precast; Bridges, pedestrian; Lateral loads; Deformation; Finite element method; Impact loads.

This paper investigates the bilateral teleoperation with the possibility of continuously variable scaling during real-time operation. The algorithm proposed for this purpose provides the operator with the ability to change the scaling gains of force and velocity loops during operation. The controllers are derived to enforce exponentially decaying error dynamics on systems which have inner loop disturbance compensation. The proposed architecture assumes the scale factors as continuous functions of time which have continuous derivatives that are also included in the mathematical derivation. Unlike the existing studies, the presented framework allows real-time adaptation of scaling gains, which provides the user with the ability to conduct coarse and fine motion in the same operation. The Lyapunov stability proof of the proposed method is made and the margins of the controller gains are identified for practical operation. Furthermore, the operational accuracy is enhanced by the application of a PD force control loop which is also new for scaled bilateral teleoperation. The realization of PD loop is made using an α - β - γ filter to differentiate the force signal. The algorithm is validated on a setup consisted of two single DOF motion control systems. In order to provide a complete analysis, a wide range of experiments are made, velocity and force scales having sinusoidal patterns with different amplitudes and frequencies. Moreover, comparison with a classical bilateral control architecture is made to highlight the flexibility of the proposed control method. The efficacy of the proposed approach is solidified by the successful tracking responses obtained from these experiments. [ABSTRACT FROM AUTHOR]

This article presents a novel master-slave control configuration that is experimentally demonstrated to improve teleoperation performance under random network delay. This is achieved via the design of a proactive haptic sensing system based on a laser range sensor on the slave side, which in turn allows for the proactive transmission of force control from the master to the slave, thus compensating for Internet-based network delays. The proposed configuration introduces three main contributions to the literature of bilateral control systems: (1) fully decoupled position and force control systems, which allow for the controller gains of each loop to be tuned independently, eliminating the trade-off common to most previous literature; (2) a novel approach that exploits the slow variation nature of the environment parameters, resulting in a lower bandwidth requirement in comparison to previous force control methods; (3) capability to measure the slave environment location and the prediction of the contact force as a result, which provides the human operator with the capability to generate the reaction force proactively on the master side. The conducted experiments demonstrated a significantly improved performance in terms of synchronized forces and positions despite the random network delay between the master and slave systems. [ABSTRACT FROM AUTHOR]