Experimental methods and techniques: the Structural ...home.deib.polimi.it/schiaffo/CS/structural...

Experimental methods and techniques:

the Structural Engineer's viewpoint

Dario Coronelli and Roberto Felicetti

Dept. Civil and Environmental Engineering

PhD course: Experimental methods and techniques

in computer science and engineering

D. Coronelli, R. Felicetti

2

Objectives of this presentation

to convey the following aspects

- structural viewpoint on experimental mechanics

- current applications of experimental methods in Structural Engineering

- close relation between structural models and experiments

- added value from Computer Science

across different perspectives

from material characterization to structural behaviour

new structures vs. existing ones

real structures vs. virtual ones

the perfect recipe for a messy presentation...


3

definitions of "structures"

the arrangement and interrelationship of parts in a construction

a complex system considered from the point of view of the

whole rather than of any single part

how is a "structural behaviour" involved in experimental tests ?

global and local response of complex structural arrangements

the primary object of structural experimental tests

non uniform loading in material characterization tests

parasitic effects in apparently simple tests on small samples

the loading equipment is itself a structure

loads and boundary conditions have to be imposed

the structural model becomes part of the experimental test

not all the structures can be tested as a whole


4

Applications of experimental methods in Structural Engineering

Testing for Characterizing New Materials NM

Testing for the Design of New Structures NS

New types of structures and loads

Laboratory specimens and test methods

Numerical Analysis

Testing for the Assessment of Existing Structures ES

Measurement: Geometry, Materials Properties, Loads

Deterioration: Observation and Measurement

Models: Strength, Deterioration

Testing for Study of Historical Structures HS


5

basalt fibre technology is similar to glass fibre

the molten rock (~1300°C)

flowing in a rhodium-platinum bushing

is drawn by blowing with air or steam

nice properties

• heat and chemical resistance

• high tensile strength and stiffness

• well matched density to cement

open issues

• brittleness in the long term

• sensitivity to Alkali Silica Reaction

• bond properties in cement paste

one example: testing the potential of mineral fibre (basalt)

for improving the fracture toughness of cementitious composites

a recurring issue in material characterization:

the difficult instatement of uniform load/strain conditions

filament properties

diameter = 12 μm

max load = 0.2 N

max stress =1500-2000 N/mm2


6 bond tests on single basalt filaments specimen preparation

special

moulds

0.3 mm = 25∙Ø


7 bond tests on single basalt filaments • displacement controlled tests

• a laboratory scale as a load measuring device

displacement measurement sample positioning on the scale plate


8

elastic limit

load-displacement curves

0.0

5.0

10.0

Av. shear

str

ess (

N/m

m2)

0.0 0.1 0.2 0.3

Displacement (mm)

the change of slope indicates the onset of debonding


0 1 2 3 4 5

Displacement U ( m)

0.00

0.05

0.10 1__ = 1.7 Ø

P (N)

PE

f = 2.5 N/mm2 Lb= 0.32 mm

step A

y = 100 N/mm2 Ø = 11 m

PE Ø___

y

0 1 2 3 4 5

Displacement U ( m)

0.00

0.05

0.10 1__ = 1.7 Ø

P (N)

PE

f = 2.5 N/mm2 Lb= 0.32 mm

Pmax Ø Lb f + y - 2 f _______

Lb

step A

B

C = Pmax

y = 100 N/mm2 Ø = 11 m

0 1 2 3 4 5

Displacement U ( m)

0.00

0.05

0.10 1__ = 1.7 Ø

P (N)

PE

f = 2.5 N/mm2 Lb= 0.32 mm

Pmax Ø Lb f + y - 2 f _______

Lb

step A

B

C = Pmax

unstablestressdrop

fibre pull-out

y = 100 N/mm2 Ø = 11 m

y = 100 N/mm2

0.0 0.5 1.0x / Lb

0

50

100

step APE

step C

Pmax

step B

(N/mm2)

f = 2.5 N/mm2

Lb - acrit = 1__ acosh y__

f

0.00.51.0 a / Lb

0 1 2 3 4 5

Displacement U ( m)

0.00

0.05

0.10

P (N)

PE

f = 2.5 N/mm2 Lb= 0.32 mm

step A

B

y = 100 N/mm2 Ø = 11 m

Ø 10÷15 µm

x,u P, U

Lb

ainterfacialcrack

bonded(elastic diffusion)

debonded(slip-friction)

y

f

u

k1 k 500 000 N/mm³

K = ·Ø·k 20 000 N/mm²

FIBRE(Ef = 72 000 N/mm²)

= 1

Ø

4·K

Ef

0.6

Ø

CEMENT

9

y = 100 N/mm2

0.0 0.5 1.0x / Lb

0

50

100

step APE

step B

(N/mm2)

0.00.51.0 a / Lb

y = 100 N/mm2

0.0 0.5 1.0x / Lb

0

50

100

step APE

(N/mm2)

0.00.51.0 a / Lb

shear-lag model

pulled rod embedded in an elastic medium

elastic diffusion scale length 1/ ≈ 1.7∙Ø

total diffusion length ≈ 5∙Ø

elastic limit PE ≈ 5.3 Ø2 y

critical bonded length 1/ acosh(√ y/ f) ≈ 4.3∙Ø


10 toughness indicators and comparison with the slip-friction model

Lf / 2

x

w

Lb(x, a)

w

f


11

fixed rotation

direct tension

hinged platens

direct tencion splitting bending

increasing "structural" effects

material characterization often implies

tackling the not uniform distribution of stress and strain

• improving the test methods

• devising appropriate interpretation techniques (inverse analysis)


12

Testing for design and verification of new structures

5.2 Design assisted by testing

Design may be based on a combination of tests and calculations.

Testing may be carried out, for example, in the following circumstances:

• if adequate calculation models are not available;

• if a large number of similar components are to be used;

• to confirm by control checks assumptions made in the design.


13

an effect often neglected in the design of precast shell elements

2nd order effects due to loading + deformation

sagging curvature

the compressed chord

behaves like an arch

(downward thrust)

the pulled strands

behave like a rope

(uplift action)

some experience earned

by testing precast thin-shell elements


14

0.000 0.002 0.004 0.006

Curvatura [1/m]

0

100

200

300

400

500

Mo

me

nto

[kN

·m]

M0 = 290 kNm

Multth

= 1030 kNm

a hyperbolic paraboloid shell element


15

a long span hollow-core roof element


16 the devil is in the detail...

bent rebar at a re-entrant angle


17

Design of New Structures - NS

Testing and Numerical Modelling


NS - Member Response, Testing and

Analysis

18

one-way beam two-way slab


Member Response, Testing and Analysis 19


20


21


Measured

Displacement

on outer surface

Relevant phenomena on internal surface

22


Laboratory Test 23


Numerical Model

NLFE 3D

Abaqus v.13.0

24


25


26


27

NS – New types of structures


28


29

• Mexico City, 1985


30


31 Testing for the Design of New Structures NS

TEST SPECIMEN: Structure and substructure

RESPONSE at study: Global and Local

• force, displacement, strain, crack opening

INSTRUMENTS

Measurements inside the Specimen

• Steel

• Concrete

FAILURE MODES and strain/crack patterns


Punching shear

failure

32


Attuatore

cerniera

biellebielle

funi controvento

nel piano orizzontale

cerniera cerniera

puntelli

(non a contatto)

Montante

contrasto

spinta

testa pilastro

mobile

travi

ancorate

a terra

biellebielle

33


Numerical modelling

(Coronelli, 2010; Coronelli and Corti, 2014))

PRE: Test set-up Design

POST: Test interpretation

Pushover analysis

(Model implemented in SAP 2000 v.15)

34


35


36

fire testing of structural assemblies

effects of fire on structural members

• rise of temperature (often with gradients)

• decay o mechanical properties (strength, stiffness)

• thermal strain (possibly restrained)

mutual interaction between

thermal and mechanical loads

• strain under load ≠ unloaded strain

• load-deflection interaction (buckling)

• stability of protective layers


the thermal curvature requires

a self-adapting loading system

(hydraulic jacks in parallel

hinged beams, etc)

Typical experimental setup: horizontal furnace

in most cases

just one isolated bay can be tested

37


38 virtual extension of the tested structure

burning compartment

Fabienne Robert

CERIB, Epernon, France

cold

compartment

cold

compartment

stiffness

of the cold

sub-structure


39

• vertical jacks: dead load

• horizontal jacks: tension-compression

• eccentric vertical jacks: rotations

• read displacements/rotations

• compute the target forces

• impose the target forces

closed loop interaction between numerical and real parts of the structure

[F] = [K]∙[u] + [c]

stiffness

matrix

initial

conditions

measured

displacement


40

FULL SCALE 6m x 4m , 4.1m

MULTIDIRECTIONAL LOADING

•18 vertical jacks in compression 300 tons (1) - 50 tons (4) : stroke = 500 mm

30 tons (4) - 5 tons (9) : stroke = 400/500

•9 horizontal jacks C : 125 tons and T : 60 tons (3) : stroke 500

C : 50 tons (6) : stroke 400 mm

•2 specific vertical jacks 30 tons (2) for connections : stroke 1000

and rotation 10

TEMPERATURE RISE – POWER

16 MW (16 gas burners)

Temperatures of up to 1320

C

structural fire testing laboratory at CERIB (France)


41

see Model-based Strategies for Real-time Hybrid Testing - J.E. Carrion and B.F. Spencer, Jr.

https://www.ideals.illinois.edu/bitstream/handle/2142/3629/NSEL.Report.006.pdf?sequence=2

Experimental testing methods in structural dynamics

quasi-static loading

predefined displacement or force time history

to investigate the hysteretic or cyclic behavior

of structural materials or components under earthquake loading

interaction with the structure and rate dependent behavior

of the structure are not considered

shaking-table test

the entire structure is subjected

to a ground acceleration history

dynamic effects and rate dependent

behavior can be completely modeled

reduced scale model due to limitations

on the size and payload capacity E-Defense - Japan UC San Diego

North Carolina State Univ.

https://www.ideals.illinois.edu/bitstream/handle/2142/3629/NSEL.Report.006.pdf?sequence=2


42 hybrid (or pseudodynamic) testing

the structure to be tested is divided into a physical component and a numerical model

the physical component is representative of the stiffness of the structure

the numerical model includes the mass of the structure (lumped at discrete locations)

and the structural damping

during the test:

the dynamic response

is calculated numerically

using time step-integration

the calculated displacements

are applied to the test specimen

(discrete DoF)

the forces required are measured

and fed-back to the model

to calculate the displacements

in the next time step


43 implementation issues

numerical time step integration

Newmark method

Central Difference Method

(explicit)

management of time delays

1.compute target displacement

2.send target displacement

3. impose target displacement

4.measure restoring force and

displacement

5.send force and displacement

6.update response

ramp-hold loading procedure continuous pseudo-dynamic


44

Distributed pseudodynamic

distributing the different substructures at geographically separated facilities

using the internet to link them with the main simulation computer

Fast-MOST Multi-Site Online Simulation Test

Computational Sites: Buffalo (deck)

UIUC

Lehigh

Experimental Sites: Berkeley

Boulder

Buffalo http://nees.buffalo.edu/

Real-time hybrid testing

the imposed displacements and response analysis are executed

at a signficantly higher speed, approaching the real time scale

rate dependent components can be tested

high performance physical testing system, computers and software for

numerical calculations and data acquisition are required


45

Testing for the assessment of existing structures

two main tasks:

collecting the required information

historical survey, geometrical survey, structural details, material quality

possible distress, patologies, etc

data processing

hand computation, numerical analysis, categorization of structural condition

two corresponding lines of research:

developing new tools for onsite inspection

viability, reliability, low cost, readily available results

developing new procedures or strategies for data processing

scalable level of detail, safety assessment or maintenance planning


46 developing new low cost tools for onsite inspection

consumer electronics and portable computers allow interesting developments

in many cases the problem is to make objective and measurable

what is already perceived and recognized by a skilled inspector

discoloration of fire damaged concrete

300 - 600°C pink or red

600 - 900°C whitish grey

900 -1000°C buff

0

10

20

30

40

50

fatto

re d

i rifle

ssio

ne (

%)

400 500 600 700

lunghezza d'onda (nm)

rossoblue

800°C

400

200

20°C

verde

malta cementizia

Øobiettivo = 8 mm

media di 12 misuredeviazione std = 3-5%

600

spectrophotometer


original picture

0.00

0.05

0.10

0.15

0.20

0.25

1

R-B

Red-Blue difference

-0.002

0.000

0.002

0.004

0.006

0.008

0 20 40 60 80

depth (mm)

color variation (x - y)

average

ordinary concrete(masked aggregate)

breakpoint

a digital image: millions of colour measurements

normalized Red-Blue difference

0.00

0.05

0.10

0.15

0.20

0.25

1

R-B / R+B

side view of a concrete core

0.31 0.32 0.33

0.33

0.34

0.35

x

y

ordinaryconcrete

flash illuminantauto white balance

D65

200

1

1 800°C

600

400

20

full image

masked aggregate

std dev ellipse (masked aggr.)

Mont Blanc tunnel [4]

47


48

Delam Tool http://soundingtech.com/

Chain drag

identification of delaminated areas

in industrial concrete floorings


49

- floor area: 8200 m2

- 7.5 km to be scanned

~15 mm

why the common inspection methods

are so sketchy?


15

implementation of the impact acoustics technique

over a long linear path: a hand-driven hammering-trolley

50


17 data processing 51


18

data processing

two frequency peaks can be recognized:

one connected to the hammer mechanism (information about the blow intensity)

one ascribable to the delaminated pavement (related to crack extension)

besides the frequency drop

also the sound loudness

increases with the size

of delaminated area

52


21

statistical frequency of loudness

indicator

the definition of a colour scale

allows to draft a damage map

53


22

the damage map of the inspected pavement

about 8 hours data recording - 2 GBytes in digital audio files

85.000 tapped points - 2400 are more or less likely to experience a detachment

54


55

+ +

re-thinking ordinary tools

-10

-5

0

5

10

am

plit

ud

e (

kN

)

drill bit

-4

-2

0

2

4

am

plit

ud

e (

V)

0 50 100 150

time ( s)

ultrasonic sensor

bit delay

(26 s)

time

of flight

AIC picker

AIC picker

t0 t1 t2

the time of flight of mechanical pulses

is monitored in real time (80 pulses/s)


56

hot face

cold

face

depth

- sensitive and reliable method

- high definition of the results (10-20 pulses/mm)

- not influenced by the inherent heterogeneity of the material

- remarkable repeatability of the results

a scan of the pulse velocity is obtained


57

Object of study:

System made of Parts and Elements

Assessment of SAFETY (ISO 2394):

Load effect < Strength

S < R

R requires measurements on the real structure

Deterioration effects

ISO 2394:1998 General principles on reliability for structures

ES – Assessment


58

Geometry: Survey

A = cross section

R = R (Ac, As)

Material properties: Sampling, Testing

f = strength

R = R (fc, fs)

Model: R = R( A, f )

ES Testing for the Assessment of Existing Structures


59

ES – DETERIORATION eg. Reinforced Concrete

ATTACK: Industrial Pollution, Marine Environment, Fumes, De-Icing Salt


Corroded Steel Cross-section Measurement

Laboratory In situ

60


61


62


63


64

Deterioration: Measurement and Observation

MEASUREMENT of quantities involved in Strength

(eg Material Properties and Geometry with deterioration)

Difficulties (No Standard Methods)

OBSERVATION of Damage and RATING

«Low, Medium, High, Very High»

Easily carried out visually – requires experience

ES - Strength and Deterioration Processes


Condition Rating - Example 65


66


67


68


69


70


71


72

Photographs/ Video

Image processing

Computer vision

Visual Methods and Digital Techniques


Prestressed Concrete

Visible damage

Hidden damage

73


Prestressed Concrete

Invisible damage

74


Topics and Links

Structural Health Monitoring

http://shm.sagepub.com

Digital Image Correlation

Computing and Cultural Heritage

http://jocch.acm.org

ICT assistance in monitoring and restoration, Tools for reconstruction and

processing of digital representations

Archives of Computational Methods in Engineering

http://www.springer.com/engineering/computational+intelligence+and+c

omplexity/journal/11831

75


Conclusions

The "structural" viewpoint involves the complex interrelationship

among the different parts composing a structural system

and the loading equipment

This perspective applies to any scale, from small material samples

to big structures exceeding the actual size of the lab facility

Design of New structure types and members:

combined use of testing and models (prediction and/or interpretation)

Existing and deteriorating structures:

standard measurement techniques missing

urgent need for some construction types

visual/digital developments of qualitative assessment

76


References

Coronelli D., (2007) “Condition rating of RC structures: a case study” Journal of Building Appraisal,

2007, Volume 3, Number 1, 2007 , pp. 29-51

Zandi Hanjari, K., Lundgren, K., Plos, M., Coronelli D. (2013). Three-dimensional modelling of

structural effects of corroding steel reinforcement in concrete. SIE, Structure and Infrastructure

Engineering (ISSN:1573-2479), vol. 9., pp. 702- 718.

Coronelli, D., Corti, G., (2014) Nonlinear static analysis of flat slab floors with a grid model ACI

Structural Journal Vol.111 No.2 March April, 343-351

Coronelli, D., Martinelli, L., Foti, F. “Analisi e progetto di piastre alleggerite in C.A. con azioni sismiche

/ Analysis and design of voided reinforced concrete slabs for seismic loading", 2015 (in Press)

Felicetti R. (2005), "Digital camera colorimetry for the assessment of fire damaged concrete", Proc. Fib

Task Group 4.3 Workshop Fire Design of Concrete Structures: What now? What next?, Milan,

Dec. 2-4, 2004, Gambarova P.G., Felicetti R., Meda A. and Riva P. (Eds.), Starrylink, Brescia,

2005, p.211-220

Felicetti R. (2006), "The Drilling Resistance Test for the Assessment of Fire Damaged Concrete",

Journal of Cement and Concrete Composites, V.28, p.321-329.

Felicetti R. (2010), "Assessment of an industrial pavement via the impact acoustic method", European

Journal of Environmental and Civil Engineering, V.14, p.427-439, DOI 10.3166/EJECE.14.427-

439.

Felicetti R. (2012), " Bond properties of mineral micro-fibre", Bond in Concrete 2012, Brescia, 18-20

June, 8 p.

77

Experimental methods and techniques: the Structural ...home.deib.polimi.it/schiaffo/CS/structural...

Documents

Transcript of Experimental methods and techniques: the Structural ...home.deib.polimi.it/schiaffo/CS/structural...