Hybrid Simulation of Structural Collapse

1. Hybrid Simulationof Structural Collapse Andreas Schellenberg, Tony Yang and Bozidar Stojadinovic University of California, Berkeley Ken Elwood University of British Columbia

2. Hybrid Simulation • Hybrid simulation is an experimentally based testing method for investigating the response of a structure to dynamic excitation using a hybrid model • A hybrid model is an assemblage of one or more physical and one or more numerical, consistently scaled, partitions of a structure • The equations of motion of a hybrid model under dynamic excitation are solved during a hybrid simulation test

3. Response Simulation with Second-Order Effects • Dynamic loading excites a structure: • Inertia • Energy dissipation (damping) • Resistance • Second order effects are included in the resistance of the structure • However, they may be simulated in the computer

4. Outline of Talk • Second-Order Effects and Structural Collapse • Implementation in OpenSees and OpenFresco • Structural Collapse of Portal-Frame Example • Summary and Conclusions

5. Second-Order Effects • Definition: effect of loads on the deformed geometry • P-D: change of global geometry • P-d: change of member geometry • P-MM interaction (section level) also local buckling

6. Simulation to Structural Collapse • Second order effects are essential for simulating collapse of structures that displace substantially • Typically civil structures are tested using shaking tables • However, structural collapse is difficult and expensive to investigate using shaking table tests

7. Advantages of using Hybrid Simulation • Gravity loads and resulting geometric nonlinearities are modeled analytically • Therefore, no complex active or passive gravity load setups are necessary • Actuator movements will limit displacements • Thus, there is no need to protect expensive test equipment from specimen impact • Only critical, collapse-sensitive elements of a structure need to be physically modeled

8. Corotational Formulation (2D)

9. Implementation in a Hybrid Model • Provide the geometric transformations such that the effect of axial loads is accounted for in the computer part of the hybrid model • Physical part of the model: • Model material and cross-section level response • Computer part of the model: • Model the second-order effect of axial load • Provide the rest of the structure

10. Implementation at nees@berkeley • Using: • OpenSees to provide the nonlinear geometric transformation facilities • OpenFresco to provide the hybrid simulation framework • OpenSees Navigator to graphically build the model, run the test and post-process the hybrid simulation results

11. Geometric Transformations Experimental BeamColumn Global System Basic System A (simply supported beam) Basic System B (cantilever beam) geometric transformation in OpenSees (Linear, PDelta, Corotational)

12. OpenFresco Components local deployment FE-Software OpenFresco interfaces to the FE-Software, stores data and facilitates distributed testing Experimental Site transforms between the experimental element degrees of freedom and the actuator degrees of freedom (linear vs. non-linear transformations) Experimental Setup interfaces to the different control and data acquisition systems in the laboratories Experimental Control Control System in Laboratory

13. OpenFresco Components network deployment FE-Software OpenFresco NTCPExpSite NTCPExpSite ShadowExpSite ShadowExpSite Exp.Setup Exp.Setup TCP/IP TCP/IP NTCP NTCP OpenFresco OpenFresco ActorExpSite ActorExpSite NTCP Server NTCP Server Exp.Setup Control Plugin with transformation Control Plugin without tranformation Exp.Control Exp.Control Control System in Laboratory Control System in Laboratory Control System in Laboratory Control System in Laboratory

14. OpenSees Navigator User Interface

15. gravity loads modeled analytically OpenSees Navigator User Interface

16. Defining experimental components (OpenFresco) OpenSees Navigator User Interface

17. Example: Portal Frame Test • Properties of Model: • num. DOF = 8(2 with mass) • Period: T1 = 0.291 sec • Damping: z1 = 0.02 • P = 50% of fPn • Crd-Trans: P-Delta, Corotational • ExpElements: EEBeamColumn2d • ExpSetups: ESOneActuator • ExpControl: ECxPCtarget • SACNF01: pga = 0.755g

18. Response Animation w/o Gravity Load

19. Response Animation with Gravity Load

20. Response Comparison: Global Level

21. Response Comparison: Element Level

22. Findings • Benefits: • Second-order effects can be simulated without applying the axial force on the physical specimen • The specimens and test setups are less expensive • The physical setups are protected from falling structural elements • Shortcomings: • Interaction of axial force and element resistance at the local level is not accounted for properly (local buckling, P-MM interaction) • Rate effects are not accounted for

23. Conclusions • Second-order effects can be effectively simulated using a hybrid model: • The effect of axial load can be modeled in the computer using appropriate geometric transformations • Collapse of structural systems due to second-order effects can, thus, be simulated • OpenSees and OpenFresco implementation has been successfully demonstrated

24. Future Work • Conduct large-scale simulations • Conduct simulations where the axial load will be physically applied on the specimen

25. Download OpenSees Navigator http://peer.berkeley.edu/OpenSeesNavigator

26. Thank you! Development and operation of the nees@berkeley equipment site is sponsored by NSF Special thanks to Dr. Eiji Kohama for all the help with the portal frame tests