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The material properties of steel and concrete vary depending on the loading rate to which they are subjected. To realistically evaluate the seismic performance of reinforced concrete (RC) columns, it is necessary to simulate the loading rate that structures will experience during seismic events as accurately as possible. Real‐time dynamic testing is preferred over quasi‐static testing for this purpose. On the other hand, the seismic performance of RC columns also depends on the axial force applied to the column. However, due to the large axial stiffness of RC columns, accurately controlling the axial force during the test, particularly in real‐time testing, is challenging. Consequently, only a few component‐level dynamic tests have been conducted for RC columns. This study aims to explore the influence of axial force and loading rate on the seismic performance of RC columns. To this end, both slow and fast cyclic loading tests were conducted on square cross‐section RC columns subjected to four different axial forces. By utilizing a robust actuator control method along with a specially designed load transfer element, the axial force was successfully controlled, while the lateral displacements were imposed on the columns in real‐time. The results include lateral strengths, postyield responses, damage patterns, rebar strains, and their rates, all of which constitute unique experimental data that can contribute to a deeper understanding of the actual seismic response of RC columns. [ABSTRACT FROM AUTHOR]

A network interface program for controllers (NICON) for pseudo-dynamic hybrid simulations is presented. The program is implemented as an independent program residing between the simulation model and an actuator controller with various functions necessary for hybrid simulations, such as communication, coordinate transformation, error compensation. These functions are generalized to allow for a generic configuration of actuator setup theoretically with any number of control points and control degrees of freedom. Application examples of NICON to hybrid simulations of civil infrastructures subjected to earthquakes or fire are presented. [ABSTRACT FROM AUTHOR]

The vertical component of ground motions can affect the seismic performance of reinforced concrete (RC) piers as significant as its horizontal counterpart. However, real‐time testing for RC piers subjected to both horizontal and vertical ground motions has been scarcely conducted due to the difficulty in multi‐axial control of actuators. In this study, the seismic response of a bridge RC pier was investigated by conducting real‐time hybrid simulation (RTHS), where the RC pier was physically tested in the laboratory and the bridge superstructure was numerically modeled. The test setup that can synchronously apply both horizontal and vertical ground motions was constructed by using three dynamic actuators and a flexible loading beam (FLB). The lateral response of the RC pier was investigated by varying the intensities for vertical ground motions, while the same intensity for horizontal ground motion is used. It was found that the axial force from the dead load of superstructure can significantly affect the initial stiffness, strength, and post‐yield response of the RC pier. For the selected earthquake ground motions, however, the intensity of vertical ground motion did not make a substantial difference in the lateral response, although there was a notable difference in the fracture pattern. [ABSTRACT FROM AUTHOR]

Several actuators need to be controlled to impose a multi‐degree of freedom displacement boundary conditions on a specimen in multi‐axial hybrid simulations or conventional multi‐axial displacement‐controlled tests. As the displacement boundary conditions are typically defined in the Cartesian coordinate system, kinematic transformation is required to transform the boundary conditions into actuator strokes. In previous studies, the kinematic transformation was carried out assuming no elastic deformation of the reaction system where the actuators and specimens are mounted. Accordingly, the kinematic transformation becomes inaccurate if the elastic deformation are not negligible, thereby impacting the accuracy of the experiments. There are methods to compensate for these errors by instrumenting specimens, but the existing methods often require many iterations or do not monotonically approach the target displacements. This study proposes a new method for kinematic transformation from the Cartesian system to the actuators' local coordinate systems. The method adopts a model identification technique by which the influence of the elastic deformation can be effectively considered in calculating the actuator strokes. Numerical verification and experimental validation with the proposed transformation method are carried out. The results show that the proposed transformation method can decrease the number of iterations to achieve the target displacement boundary conditions and thus avoiding overshooting the displacement boundary conditions and reducing the interaction between actuators. It is expected that the proposed method can reduce the overall time to run a multi‐axial hybrid simulation or multi‐DOF displacement‐controlled experiments. [ABSTRACT FROM AUTHOR]

Design of embedded pipelines in seismic areas require consideration of the interaction between pipeline and surrounding soil. The soil‐pipe interaction is often numerically modeled using Winkler springs, where a simple bilinear or trilinear soil resistance‐displacement relationship is employed. As Winkler spring modeling approach requires experimental data for calibration of spring parameters, extensive experimental studies have been carried out. However, most tests in previous studies have been carried out for pipeline specimens subjected to monotonic load, in which pipe lateral‐vertical response coupling is hardly investigated. In the present research, a novel test method that enables testing of a pipe specimen under lateral or vertical cyclic loading is investigated. In the proposed method, a soil box is mounted on a 6‐degree of freedom (DOF) displacement‐controlled table, such that soil‐pipe interaction in the lateral/vertical direction can be investigated. A series of tests considering various parameters such as pipe diameter, burial depth, soil density, and loading condition were performed. Test results provided evidence of the effect type of loading has on soil‐pipe interaction and the strong coupling between pipe response along lateral and vertical directions. [ABSTRACT FROM AUTHOR]

There has been growing interest in seismic hazards in permafrost regions as development in those regions has increased. Because major infrastructure, such as natural gas pipelines, has been constructed in permafrost regions, it is necessary to evaluate the seismic safety of such a network system. As frozen soil's dynamic properties differ from those of its unfrozen state, the characteristics of seismic waves propagated through frozen soil layers in permafrost differ from those propagated through unfrozen soil. Thus, the dynamic properties and composition of frozen soil layers located between bedrock and the ground surface need to be realistically considered in evaluating the seismic hazards of permafrost regions. The frozen soil layer's composition greatly depends on soil temperatures which vary seasonally and are gradually increasing due to global warming, therefore it is necessary to consider soil temperature variation. In this study, comprehensive parametric site response analysis was carried out based on measured data regarding seasonal and annual temperature variation to investigate seismic hazards. The soil temperature variation between summer and winter and temperature increases due to global warming were the main considerations. The analysis results clearly show that the soil temperature variation significantly impacts seismic hazards in the permafrost region, leading to different site response characteristics than those in the non‐permafrost region. [ABSTRACT FROM AUTHOR]

Though often overlooked, the impact of seismic transient ground deformation on natural gas (NG) pipes can be highly adverse. Particularly, pipe elbows may undergo excessive in-plane bending demand and buckling. In this paper, a critical scenario of a pipe coupling two industrial structures typically found in an NG processing plant is studied. High strain and cross-sectional ovalization on the elbows are probable during an earthquake due to the out-of-phase oscillation of the two structures imposing asynchronous displacement demands at the two pipe ends. A parametric study was first performed to investigate various structure-pipe-structure configurations that increase seismic demands to pipe elbows. Simultaneous mobilization of divergent oscillation between two supporting structures at the low-frequency range, a lower pipe-structure stiffness ratio, a shorter length of straight pipe segments in the linking pipe element, and a higher pipe internal pressure have led to the onset of critical strain demands in pipe elbows. To validate this observation, an experimental campaign was developed in which a full-scale linking pipe element was physically tested by means of hybrid simulation (HS). The study shows that the seismic interaction of the structures coupled with the pipe is nonnegligible and can even be critical for the integrity of the coupling pipe. The finding depends on the structural system's dynamic and geometrical properties as well the frequency content of the earthquake excitation. [ABSTRACT FROM AUTHOR]

Summary: In a building subjected to seismic loading, large compressive force may develop in reinforced concrete (RC) coupling beams because of axial restraint imposed by the neighboring shear walls against the elongation of the coupling beams during the failure process. The axially compressive force can increase the shear stiffness and strength of the coupling beam and may change its failure mode. In this paper, a novel coupling beam testing procedure adopting hybrid simulation method is proposed in which the axial restraint is determined through hybrid simulation and the calculated axial restraint is imposed on a specimen during the test. RC coupling beams were tested by adopting both the proposed test procedure and the conventional testing approach in which the effect of the axial restraint is not accounted for. Test results depict a clear difference in the response of the coupling beam, such as shear capacity and failure mode, depending on the consideration of the axial restraint during the test. The test outcome demonstrates the usefulness and applicability of the proposed test procedure. [ABSTRACT FROM AUTHOR]