advance dynamic testing techniques in structural engineering

1

Prof. Samir P Parmar (CE-14103277)

Research Scholar, Dept. of Civil Engineering, IIT Kanpur

Mail: [email protected]

ADVANCED DYNAMIC TESTING TECHNIQUES

IN STRUCTURAL ENGINEERING

2 Contents of presentation

Introduction of dynamic testing methods

Effective force testing

Pseudo dynamic testing

Real time hybrid dynamic testing

3 INTRODUCTION

Quasi-static loading test method (QST)

Shaking table testing method (STT)

Effective force method (EFT)

Pseudo-dynamic testing method (PDT)

Real time pseudo-dynamic testing method (RTPDT)

Real time dynamic hybrid testing method (RTDHT)

4 Quasi-static loading test method (QST)

A test specimen is subjected to slowly changing prescribed forces or deformations by means of hydraulic actuators

Inertial forces within the structures are not considered in this method.

Purpose is to observe the material behavior of structural elements, components, or junctions when they are subjected to cycles of loading and unloading.

Dynamic nature of earthquakes are not captured

5 Shaking table testing method (STT)

Test structures may be subjected to actual earthquake acceleration records to investigate dynamic effects

Inertial effects and structure assembly issues are well represented

The size of the structures are limited or scaled by the size and capacity of the shake table

6 Effective Force Method Pseudo-dynamic testing Real Time Dynamic Hybrid Testing (new development)

m5x5a

:

m4x4a

:

m3x3a

:

m2x2a

:

m1x1a

:

F i

F2

F1

F i

Other testing methods (STT)

7 Effective force testing method (EFT)

Effective Force Technique

Hybrid Testing & Computing Real-Time Pseudo-

Dynamic Hybrid Testing System

Real-Time “Dynamic” Hybrid Testing System

m5x5a

:

m4x4a

:

m3x3a

:

m2x2a

:

m1x1a

:

Applies the inertial ground motion generated forces through synchronized actuators - NEW


applying dynamic forces to a test specimen that is anchored rigidly to an immobile ground; perform real-time earthquake simulation

these forces are proportional to the prescribed ground acceleration and the local structural masses.

based on a force control algorithm

m5x5a

:

m4x4a

:

m3x3a

:

m2x2a

:

m1x1a

:



Hybrid Testing & Computing Pseudo-Dynamic Hybrid

Testing System Real-Time “Dynamic”

Hybrid Testing System

F2

F1

Applies forces in substructure through actuators only – real time operation is a benefit but not a must

10 Pseudo-dynamic testing method (PSD)

applying slowly varying forces to a structural model

motions and deformations observed in the test specimens are used to infer the inertial forces that the model would have been exposed to during the actual earthquake

Substructure techniques

11 Real time pseudo-dynamic testing method (RTPDT)

Same as the PSD test except that it is conducted in the real time

Introduce problem in control, such as delay caused by numerical simulation and actuator

12


Hybrid Testing & Computing Real-Time Pseudo-Dynamic

Hybrid Testing System Real-Time “Dynamic”

Hybrid Testing System

Applies forces in substructure through shake table and actuators – real time operation is a must

13Real-Time Seismic Hybrid Testing

S I M ULA T EDS T RUCT URE

FULL OR N EA RFULL S CA LE T ES T EDS UBS T RUCT URES HA KI N G T ABLES

(100 t on)

REA CT I ONW A LL

I N T ERFA CE FORCESA CT I VE FEEDBA CK FROMS I M ULA T ED S T RUCT UREA PPLI ED BY A CT UA T ORS

A GA I N S T REA CT I ON W ALL

Fig.1. Real-Tim e Hybrid Seism ic Testing System (Substructure Dynamic Testing)

Real time Hybrid seismic testing System (Substructure Dynamic Testing)

14 Real time dynamic hybrid testing method (RTDHT)

based on shaking table test combined with substructure techniques.

part of the structure (the physical model) is constructed and tested on the shaking table

The rest part of the structure (the numerical model) is numerically modeled in the compute

the earthquake effect on the superstructure was calculated as a interface force and applied to the substructure by the actuators (force control based)

15 Block Diagrams of Various Testing Methods

Excitation Specimen Response

16 Open Loop Test

> Quasi-Static Loading: Cyclic Loading

> Shaking Table: Ground Motion

Specimen Response

Quasit-static; Shaking Table Test

17 Open Loop Control (in concept)

Effective Force Test

Specimen ResponseExcitation

Mass Multiplier & Actuator Application

Effective Force

18 Closed Loop Test


Solution of ModelsEquation of Motion

applied displacement

force measured

Pseudo-dynamic Test Method

19 Closed Loop TestRESPONSE ANALYSIS (Superstructure)

EXCITATIONSpecimen

(SUBSTRUCTURE)SUBSTRUCTURE

RESPONSE

SUPERSTRUCTURERESPONSE

STRUCTURERESPONSE

measuredforce (q)

dislacment command

CONTROL IMPLEMENTATION

Pseudo-dynamic Test with Substructure

20 Closed Loop Test

Real-time Hybrid Dynamic Test

Simulator/Controller>RESPONSE ANALYSIS (Superstructure)>DELAY COMPENSATION

EXCITATIONShake Table

Specimen(SUBSTRUCTURE)

SUBSTRUCTURERESPONSE

SUPERSTRUCTURERESPONSE

STRUCTURERESPONSE

measureddisplacement

force command

externalforce (p)

21Summary of dynamic test methods

Advantages Disadvantages

PDT

Size of the specimen can be large or very large

Inertial forces are not true forces and distorted by discrete parameter model, actuators and computers

Rate effects are neglected because of quasi-static loading

RTPDT

Size of the specimen can be large or very large

Inertial forces are not true forces and distorted by discrete parameter model, actuators and computers

Actuator time delay is introduced

STT True inertia forces in assembly Size of the specimen is limited

RTDHT True inertia forces on the specimen Specimen can be large or very large

Part of the inertia forces are simulated with errors (same as PDT)

Actuator time delay is introduced

22 Effective Force Testing

a Mx Cx Kx 0

Equation of motion

Subscript refers to motion relative to a fixed reference frame (absolute displacement)

xa g x x I xa g x x I

x tg eff Mx Cx Kx M P

23 Open Loop Control (in concept)

Effective Force Test

Specimen ResponseExcitation

Mass Multiplier & Actuator Application

Effective Force

24 Effective Force Test – Hardware Components

Servo-Hydraulic Actuators

Servo-Hydraulic Control System

Elastic Spring

Measurement Instrumentation (DAQ)

Computer Simulator Controller

25Effective Force Test – Hardware

Configuration

xPc SoftwareSCRAMNetDSP Read/

Write

DSPSignal

Generation

CONTROLLER

SCRAMNet

Test SoftwareControl

Servo-Controller

Servo-Hydraulic Control

STS

DAQ HardwareSignal

Conditioners

`

Structure

DAQ

`

xPC SoftwareSCRAMNetAnalog I/O

Analog I/OSCRAMNet to

Analog I/O Bridge

26 Effective Force Test -Dynamic force controlSeries elasticity and displacement feedback

Actuator with Displacement Control Structure

Command Signal

Compensator

Load Cell

Series Spring, KLC

Target Force

Measured Force

1 / KLC

27Effective Force Test -Dynamic force control

Series elasticity and displacement feedback

KLCGActuator

2

1ms cs k

Actuator inClosed-loop

Displacement Control

Series Spring

Structure

Compensation

1/KLCActuator

1G

C

StructureDisplacement

ActuatorDisplacement

DesiredForce

AchievedForce+

++

-

ActuatorDisplacement

Feedback

2

2

Achieved ForceCG

Desired Force 1 CGLC

ms cs kms cs k K

Ideal: C = 1/G

28 Effective Force Test -Dynamic force control

The advantages of using the series spring

the actuator can be well tuned and operated in displacement control

it provides for one more parameter than can be altered in the control design (the oil stiffness cannot be)

the term KLC(1-CG) in the transfer function indicates that the smaller the value of KLC the less sensitive is the transfer function to deviations of C from 1/G

29 Effective Force Test – Effect of Time Delay

The dynamic characteristics of hydraulic actuators inevitably include a response delay , which is equivalent to negative damping

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.0 2.0 4.0 6.0 8.0 10.0

Frequency (Hz)

Mag

nitu

de

Experimental

Numerical

30 Effective Force Test – Predictive Control

KLCT = e-s

2

1ms cs k

Actuator Series Spring

Structure

1/KLC+

++

-

20 0 0 0

1

LCm s c s k K

+

+

T0-

+Model of Structure-

Spring SystemDelayModel

PredictiveDisplcement

CorrectiveDisplcement

Smith Predictor

31 Effective Force Test – Predictive Control

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.0 2.0 4.0 6.0 8.0 10.0

Frequency (Hz)

Mag

nitu

de

Without compensationWith compensation

32 Effective Force Test – Software

•Simulink®•Real-time Workshop®5•XPC Target

33 Pseudo dynamic testing

Define a model of the structure system Define the desired excitation – usually base acceleration Calculate the expected response of structure – displacement Use an actuator to apply the desired displacement in the

structure Measure the resistance force in the structure (or estimate it from

measurements) Repeat the above steps – start from second

i i i i Md Cd R f

34 Pseudo-dynamic testingInput excitation fi (desired)

Impose di+1 on the structure

Measure ri+1

Set i - 1 = I

-1

i+1 i+1 i+1 i iΔt Δta = m+ c f -r -cv - ca2 2

i+1 i i i+1Δtv =v + a +a2

2

i+2 i+1 i+1 i+1Δtd =d +Δtv + a2

35


Solution of ModelsEquation of Motion

applied displacement

force measured

Pseudo-dynamic Test Method

Pseudo dynamic testing

36 Pseudo-dynamic testing – Hardware components

Servo-Hydraulic Actuators

Servo-Hydraulic Control Systems

Measurement Instrumentation

On-line computer

37Pseudo-dynamic testing – Hardware

Configuration (Local)

Matlab SoftwareIntegration Algorithm

Simulation Interface

SCRAMNet

SIMULATOR


Write

DSPSignal

Generation

CONTROLLER



Analog I/O Bridge

DAQ

SCRAMNet


Servo-Controller


Flex Test

SV

DAQ HardwareSignal

Conditioners

`` `

38 Pseudo dynamic testing

Discretized equation of motion of the structure at time intervals for ,

i i i i Md Cd R f it i t 1i toN

Equation solved in computer step by step, with Ri as the reaction

force measured from the specimen under test. Result is the displacement command of next step that will be applied to the specimen at each node of mass by actuators.

39 Pseudo dynamic test—integration algorithm

Both explicit and implicit time-stepping integration algorithm can be applied for solving equation of motion in Pseudo-dynamic tests.

Explicit methods compute the response of the structure at the end of current step based on the state of the structure at the beginning of the step.

Central difference method (Takanashi et al. 1975), Newmark- Beta method (1959), Modified Newmark’s method (1986), The γ-function pseudodynamic algorithm (Chang et al. 1997) Unconditionally stable explicit method(Chang, 2002)

(continued on next)

40Pseudo dynamic test—integration algorithm(continued) Implicit methods require knowledge of the structural response at the target

displacement in order to compute the response.

the displacement is dependent on other response parameters at the end of the step

iteration is required in the algorithm to satisfy both the imposed kinematic conditions and the equilibrium conditions at the end of the time step

Newmark – Alpha method (Hilber et al. 1977) Hybrid implicit algorithm (Thewalt and Mahin, 1987) Newton iteration (Shing, 1991)

,

41 Pseudo dynamic test—integration algorithm(continued) Implicit iteration algorithm provide improved stability

characteristics and permit the used of larger integration time steps

Iteration on experimental model is not practical since structure materials are path dependent

Explicit methods are easier to implement

Explicit integration methods are preferred for PSD simulation when stability limits are satisfied for the structural model under investigation

42 Pseudo dynamic test—integration algorithm(continued)Example: Modified Newmark’s Method

11121 )1()(

iiiiii tfRRddMdM

iiiitt dddd 2

2

1

)(2 11

iiiit dddd

111

1 )1(22

)2(2

iiiiii t

RRfMddd

Substitute into and solve for

43 Pseudo-dynamic testing – sub structuring principle

May fabricate only part of the structure whose hysteretic behavior is complex and apply the test to this part

Remaining part treated in the computer

44 Pseudo-dynamic testing – sub structuring principle

subscripts a and e denote the degrees of freedom within the analytical and experimental substructures.

a

e

a

e

a

e

aaT

ea

eaee

a

e

aaT

ea

eaee

ff

RR

dd

CCCC

dd

MMMM

aeaaeaaeaeeeeeeeeee dKdCdMfdKdCdM

dKdCdMfdKdCdM Teze

Teae

Teaaaaaaaaaaa

ee e e ea aD d f D d

Taa a a ea eD d f D d

Tested part. Calculate displacement command for next step. Interface force: Analytical part. Calculate interface state used in interface

force.

ea aD d

45 Pseudo-dynamic testing – Hardware Configuration (Internet)

NTCP ServerTCP/IP

NTCP PluginSCRAMNetSimulation Interface

SIMULATION INTERFACE


Write

DSPSignal

Generation

CONTROLLER



Analog I/O Bridge

DAQ

LAN/WAN

SCRAMNet


Servo-Controller


Flex Test

SV

DAQ HardwareSignal

Conditioners

Matlab SoftwareTCP/IP

Integration Algorithm

SIMULATION COORDINATOR

Analysis Site

Remote Substructure Site

`

`` `

46 Pseudo-dynamic testing –Software

Response analysis – Mat lab Simulink

Controller implementation – Matlab Stateflow

47 Dynamic hybrid testing - I

Combined use of earthquake simulators, actuators and computational engines for simulation

Details later in the presentation

Physical Substructure

Computational Substructure

Ground/Shake Table

Shake Table

Structural Actuator



Response Feedback `

48Dynamic hybrid testing - II

Shake Table

Laminar Soil Box

Foundation

Well understood

Focus of interest

`

Structural Actuator

49Real-time dynamic hybrid testing - II

Acceleration input:Table introduces

inertia forces

Shake Table

Laminar Soil Box

Foundation

`

Structural Actuator

Response Feedback

Distributed mass

Has to operate in Force Control

50



Ground/Shake Table

Shake Table

Structural Actuator



Response Feedback `

Substructure Testing – Unified Approach

31 1 3 3 2

2First story contributionto shake table acceleration Third story contribution

to shake table acceleration

1 2

Shake table acceleration,

Actuator Force, 1

t

a

ku s u s x x

m

F s m

1 3 3 3 2

First story contribution Third story contributionto actuator force to actuator force

1u s k x x

51 Unified approach to substructure testing

If , then the control requires a shake table and an actuator to implement the substructure testing.

If , then the controller require just an actuator to implement the substructure testing as pseudo-dynamic testing:

Note: In pseudo-dynamic testing, inertia effects are computed. In dynamic hybrid testing ( ), the actuator should

operate in force control.

1 30 and 0s s

1 30 and 0s s

1 30 or 0s s

52 Hybrid Controller Implementation (UB-NEES)

Design done jointly between MTS and UB

Physical Substructur

e


Ground/Shake Table

Shake Table

Structural Actuator


MTS ActuatorController (STS)

MTS Hydraulic PowerController (HPC)

MTS Shake TableController (469D)

SC

RA

MN

ET

I

SCRAMNET II

Compensation ControllerxPC Target

Real-time Simulator

General PurposeData Acquisition

System

Network Simulator

Data Acquisition

Optional Optional

HYBRID CONTROLLERUB-NEES NODE

CONTROL OFLOADING SYSTEM

Physical Substructur

e

Hybrid Testing

• Flexible architecture using parallel processing

53 Implementation of RTDHT

Structure

Actuator

ShakeTable

54 Substructure response

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.0 2.0 4.0 6.0 8.0 10.0

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.0 2.0 4.0 6.0 8.0 10.0

Hybrid test

Shake table

Second (simulated)floor

Structure

Actuator

ShakeTable

First (physical)floor

55 Shake Table at University of California, USA

Schematic representation of NEES/UCSD Shake Table.

Reference:

56 Multishaker facility at SUNY-Buffalo

57 Fast hybrid test (FHT) system of University of Colorado-Boulder

58 IIT Kanpur, Pseudo Static Laboratory

59 Fatigue Testing Facility of IIT Kanpur, India

60 Fatigue Testing Facility of IIT Kanpur, India

Actuator (Mass Shaker)

61 Mass Shaker and other instruments

Special Thanks to Dr. Samit Ray Chowdhury,IIT Kanpur

advance dynamic testing techniques in structural engineering

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