Reassessment of the flexural behavior of high-strength reinforced concrete beams under short-term loads

This work aims at describing the behavior of high-strength reinforced concrete (HSRC) beams under short-term ultimate loads with concrete compressive strengths higher than 50 MPa. A plastic approach besides a cross sectional analysis is employed to primarily trace the nonlinear response of nineteen HSRC simply supported beams for which experimental results are available. This proposed theoretical approach is able to acceptably match the experimental data with minor overestimation of flexural moments. Closed-form expressions to evaluate ductility indexes regarding deflections and curvatures as well as plastic rotation capacities are also proposed herein. Predictions of the National Brazilian Regulation for design of concrete structures NBR6118 in terms of ultimate flexural moments are also computed for comparison. A complete assessment of ductility in which plastic rotation capacities are computed for the studied beams is also given. It is found that the flexural ductility of a member could be increased with the use of high strength concrete. The use of a maximum tension steel ratio to guarantee a minimum flexural of ductility is highlighted.

Seismic Performance of Eccentrically Braced Frames with Shear Link

The push-over nonlinear evaluation of four eccentrically braced frame performance was conducted to assess the plastic deformation and location of plastic hinges in buildings with six, nine, twelve and fifteen stories. The excessive plastification of out-of-beam members is revealed in the majority of these buildings while the AISC design provision allows the moderate plastification in these members. Therefore, the beams out of link might be in danger of fracture of web and flange. Likewise, this was controversial evidence in Chrischurch earthquakes. In order to modify this problem either using fixed connection of braced members or using the very short shear links which have less end moment force than out-of-link beams moment strength are recommended. By this modification, the response modification coefficients are calculated for these buildings which are almost equal to the provision value. The maximum plastic rotation of shear links recommended by provisions (0.08 radian) is the upper ultimate limit to prevent emerging of out-of-link member`s instability.

Mechanical Properties of a Novel Plastic Hinge Seismic Fuse Based on Frictional Energy Dissipation to Avoid Brittle Failures in Beam-to-Column Moment-Resistant Joints

Traditional steel structure joints are prone to brittle failure under seismic excitation, and it is difficult to precisely control the location of the resulting plastic hinge or repair these joints after an earthquake. Therefore, based on the energy dissipation principle of the friction pendulum isolation bearing and automobile braking device, a low-cost friction-based plastic hinge (PH) joint is proposed to provide predictable energy dissipation and realize quickly repairable structures. The proposed PH was analysed theoretically, and five half-scale specimens using different bolt and friction materials were tested using cyclic reversing load. The test results showed that models PH-1 and PH-2 with Grade 4.8 and 8.8 limiting bolts, respectively, both provided a plastic rotation angle greater than 0.03 rad, exhibited experimental moment capacities of 0.91 and 0.93 times their theoretical capacities, and exhibited ductility coefficients of 2.75 and 3.14, respectively. It was found that high-strength limiting bolts were unsuitable as they damaged difficult-to-replace PH components. The selected PH configuration experienced damage to only the limiting bolts and friction plates and exhibited good plastic deformation capacity and hysteretic energy dissipation performance that met the plastic rotation, ductility, and friction energy dissipation requirements. Thus, the proposed PH can be used to improve the seismic performance of beam-to-column joints and the frames they form.

Neutral Axis Depth versus Ductility and Plastic Rotation Capacity on Bending in Lightweight-Aggregate Concrete Beams

This article presents an experimental study on the evolution of the neutral axis depth at failure in the critical section with the flexural ductility and plastic rotation capacity of reinforced concrete (RC) lightweight-aggregate concrete (LWAC) beams. For this, the results of a previous experimental program involving RC LWAC beams tested in flexure until failure are used. The variable studies were the concrete compressive strength (between 22.0 and 60.4 MPa and dry density between 1651 and 1953 kg/m3) and the longitudinal tensile reinforcement ratio (between 0.13% and 2.69%). The flexural ductility and the plastic rotation capacity of the RC LWAC beams are characterized by a ductility index and a plastic trend parameter, respectively. The influence of the variable studies, as well as the relation of the flexural ductility and plastic rotation capacity with the values for the neutral axis depth at failure are analyzed and discussed. Some conclusions are drawn which can be useful for the design of RC LWAC beams for flexure. In particular, it is shown that the practical rule of limiting the neutral axis depth at failure to ensure ductile behavior, as used in normal-weight aggregate concrete beams, is also valid for RC LWAC beams.

Assessment of Different Steel Material Characteristics on Shear Links Performance

The inelastic behavior of shear links depends on their material ductility. In order to investigate the effect of cyclic characteristics of steel on shear links behavior, five experimental links constructed of various steel grades are modeled by finite element approach. These models are verified using experimental shear links results. Moreover, cyclic stress-strain material curve is used for simulating links behavior and the models can simulate strength degradation of flange and web local buckling appropriately. The overstrength and plastic rotation of the links are modified due to the influence of test setup configuration once the buckling occurs. It can be concluded that the links material characteristics can affect the overstrength and plastic rotation. In this study, the various strain hardening of different grades of steel are evaluated and the amplitudes of strain which can simulate strain hardening of links are determined for five materials.