MS13.4 - Hybrid analyses, experimental tests and numerical modeling in earthquake engineering

Hybrid testing provides an efficient and less costly way to explore the response of structural systems to realistic dynamic or seismic loading. However, the required equipment to execute hybrid tests are high-cost tools. To get insight in the hybrid testing methodology, a small-scale set-up has been developed in this project. An Arduino UNO controls the system that imposes the displacement to a linear actuator. Connecting the small-scale set-up, i.e. the Arduino UNO, to MATLAB allows imposing a time his-tory to the physical substructure. A load cell measures the restoring force which will be communicated to MATLAB by the Arduino UNO. Numerical integration based on the Gravouil-Combescure scheme with Classic Lagrange Multipliers (CLM) determines the displacement for the next time step. This paper describes hot spots of the methodology and the results of a demonstrative experimental test. The experiment consists of a 4 degree of freedom (DOF) numerical model combined with a 1 DOF physical specimen. The installed linear actuator only has one gearing option, which leads to a possible overshooting loop. Interesting conclusions can be drawn from the analysis of the small-scale set-up in view of its future upscaling and implementation of the hybrid test method at laboratory scale. Firstly, the linear actuator requires a non-negligible amount of time to reach the imposed displacement which imposes boundary conditions in the MATLAB directives. Secondly, a velocity-controlled actuator is essential in the exploitation of hybrid testing. Thirdly, the displacement tolerance influences the stability of the system. If one increases the displacement tolerance, the risk of an overshooting loop decreases. However, the accuracy might be influenced. Good balance must therefore be found between stability and accuracy.

In order to reduce the numerical cost of dynamic time history analysis, this research proposes to extend the application of the Proper Orthogonal Decomposition (POD) to reinforced Concrete (RC) structures with material nonlinearities subjected to earthquakes. To achieve this time economy in nonlinear dynamic analysis, the structural model is reduced by projection on the POD modes. Material nonlinearity in reinforced concrete structures is due to steel ductility and concrete damaging. In this work, it is modeled by the fiber section technique for 1D members (beams and columns) and by the layered shell approach for 2D elements (walls). Two reduction techniques are used. The first one is for structures studied for a single base excitation. In this application, a full model nonlinear time history analysis is conducted on an initial small duration portion of the earthquake. The obtained results are statistically analyzed to find the most dominant POD modes. Then, these POD modes are used to reduce the dynamic system. Next, the analysis for the remaining portion of the earthquake is conducted on a reduced model. The second technique is for structures studied for multiple earthquakes. In this approach, a full model nonlinear time history analysis is conducted for one selected earthquake. Based on the obtained results, a principal component analysis is conducted to find the dominant POD modes. Then, these POD modes are used to reduce the dynamic system. Next, the remaining earthquakes are entirely analyzed using the reduced dynamic model. For the conducted tests, reduced models gave very close results to the full models at a fraction of the time cost (time economy up to 96%). Thus, this work demonstrates that the POD method can be used to reduce the numerical cost of dynamic time history analysis for RC structures with material nonlinearities subjected to earthquakes.

Wide attention and research have been focused on the vibration control of thin wall structures immersed in fluid environment, for which fuel containers, vessel shells and underwater robotics are among the most frequent examples. Designing such structures with respect to the desired vibration property increasingly requires application of microstructured plates and shells. In this work, we propose a finite element framework that allows predicting vibration behaviours for composite plates with periodic microstructures in the context of fluid-structure interaction (FSI). In this regard, inertial effects of the fluid are taken into account by considering a fluid induced added mass, which we calculate based on one or both sides of the composite plate. We then perform vibration analysis by prescribing Bloch boundary conditions to the periodic unit cell, which we model using a Mindlin plate finite element that integrates the FSI effect. We validate the numerical framework by considering a fluid-structure coupled system, composed of a periodic composite plate which is fixed to a number of fluid cavities filled with ideal fluid. Based on this configuration, we investigate the influence on the plate vibration due to the fluid properties which include the fluid density, the number and size of the fluid cavities. Simulations revealed that the first two parameters present significant effect on the structure vibration since both the band gap range and position can be controlled by using different fluid densities and numbers of cavities. Meanwhile, we confirmed negligible impact on the vibration mode shape due to FSI since its effect mainly remains on the inertial mass of the structure. To confirm the effectiveness of our band gap predictions, we further performed dynamic response simulations in the frequency domain and considered extra cases of microstructure design. Comparison between the band gap calculation and frequency response analysis based on the considered cases validates the accuracy and adaptability of the proposed numerical approach, which can be used to assist the microstructure design of composite plates with FSI for specified vibration behaviours.

A novel sliding-stretching seismic isolator is illustrated in this work. The device is inspired by the tendons and bones of human limbs, using 3D-printed components and metallic parts [1]. The isolator is made of a unit cell formed by a central post that carries the vertical load and slides against a base plate. The central post is linked to four corner posts by stretchable membranes (“tendons”) and rigid members (“limbs”). In the present work, a scalable approach to the design of this system is illustrated. It is worth mentioning that the displacement capacity of the developed device depends only on the geometry of the rigid members, while the vibration period of the unit can be easily tuned by dynamically varying the elongation of the tendons in the nonlinear stress–strain regime.A comparative analysis on the estimated cost of the presented seismic isolator and the ones available on the market is also presented.