Hybrid Simulationof Structural Collapse Andreas Schellenberg, Tony Yang and Bozidar StojadinovicUniversity of California, Berkeley

Ken ElwoodUniversity of British Columbia

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

Response Simulation with Second-Order EffectsDynamic loading excites a structure:Inertia Energy dissipation (damping)Resistance

Second order effects are included in the resistance of the structureHowever, they may be simulated in the computer

Outline of TalkSecond-Order Effects and Structural CollapseImplementation in OpenSees and OpenFrescoStructural Collapse of Portal-Frame ExampleSummary and Conclusions

Second-Order EffectsDefinition: effect of loads on the deformed geometryP-D: change of global geometryP-d: change of member geometryP-MM interaction (section level) also local buckling

Simulation to Structural CollapseSecond order effects are essential for simulating collapse of structures that displace substantiallyTypically civil structures are tested using shaking tablesHowever, structural collapse is difficult and expensive to investigate using shaking table tests

Advantages of using Hybrid SimulationGravity loads and resulting geometric nonlinearities are modeled analyticallyTherefore, no complex active or passive gravity load setups are necessary Actuator movements will limit displacementsThus, there is no need to protect expensive test equipment from specimen impactOnly critical, collapse-sensitive elements of a structure need to be physically modeled

Corotational Formulation (2D)

Implementation in a Hybrid ModelProvide the geometric transformations such that the effect of axial loads is accounted for in the computer part of the hybrid modelPhysical part of the model:Model material and cross-section level responseComputer part of the model:Model the second-order effect of axial loadProvide the rest of the structure

Implementation at nees@berkeleyUsing:OpenSees to provide the nonlinear geometric transformation facilitiesOpenFresco to provide the hybrid simulation frameworkOpenSees Navigator to graphically build the model, run the test and post-process the hybrid simulation results

Geometric Transformations Global SystemExperimental BeamColumnBasic System A(simply supported beam)Basic System B(cantilever beam)geometric transformation in OpenSees (Linear, PDelta, Corotational)

OpenFresco Components

FE-SoftwareExperimental SiteExperimental SetupExperimental ControlControl Systemin Laboratoryinterfaces to theFE-Software, stores data and facilitates distributed testing transforms between the experimental element degrees of freedom and the actuator degrees of freedom (linear vs. non-linear transformations)interfaces to the different control and data acquisitionsystems in the laboratoriesOpenFrescolocaldeployment

OpenFresco Components

networkdeploymentFE-SoftwareExp.SetupExp.ControlControl Systemin LaboratoryNTCP ServerControl PluginwithtransformationControl Systemin LaboratoryTCP/IPNTCP ServerControl Systemin LaboratoryActorExpSiteExp.ControlControl Systemin LaboratoryActorExpSiteShadowExpSiteNTCPExpSiteControl PluginwithouttranformationTCP/IPNTCPNTCPOpenFrescoOpenFrescoOpenFrescoExp.SetupShadowExpSiteExp.SetupNTCPExpSite

OpenSees Navigator User Interface

OpenSees Navigator User Interface

OpenSees Navigator User Interface

Example: Portal Frame TestProperties 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

Response Animation w/o Gravity Load

Response Animation with Gravity Load

Response Comparison: Global Level

Response Comparison: Element Level

FindingsBenefits:Second-order effects can be simulated without applying the axial force on the physical specimenThe specimens and test setups are less expensiveThe 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

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

Future WorkConduct large-scale simulationsConduct simulations where the axial load will be physically applied on the specimen

Download OpenSees Navigatorhttp://peer.berkeley.edu/OpenSeesNavigator

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