Use of European Standards in the Australian Tunnelling Industry

E. S. Bernard TSE P/L, Sydney

European Standards in Australia

What is required in a standard?

• Conformance to a Quality System

• Depends whether it is a material specification or a testing standard,

• Consistent products or outcomes is the main objective,

• Achievable products or outcomes is desirable.

European Standards in Australia

Why would anyone bother using European standards in Australia?

• Do they offer advantages over other standards?

• Are they cheaper to perform?

• Do they offer lower variability?

Design Guides

European standards are referenced in design guides such as 2010 Model Code

• Model Code is not a legally binding document, and is more a collection of ideas than a code.

• The fib Model Code 2010 purports to be an international guide to concrete design, but in fact references only European standards

• European standards differ markedly from other standards for FRC, but not for plain concrete – so the present focus is on FRC

Problems with European Standards

European standards come with baggage!

• Non-Europeans cannot be members of the code committees

• Committee membership is dictated by petty nationalism, only European member countries need apply

• Contrast this to ASTM International where any person from any country can be a member

• Why would Australians use standards over which they have no influence?

Problems with European Standards

Accreditation

• Accreditation of Australian labs to EN standards is expensive and problematic

• Some FRC specifications are extremely expensive to fully comply with

• FRC standards are based on a „standard concrete‟ using sand and aggregate imported from France – NO EXCEPTIONS!

• Only a 250 L planetary concrete mixer is permitted for defining performance of standard concrete, no agitator trucks allowed!

Problems with European Standards

Plain concrete

• Most European standards for plain concrete are very similar to Australian and ASTM standards, only a few unusual standards offer advantages

• Why would an Australian lab bother to gain accreditation for tests that are almost identical and offer no advantages?

• ASTM standards offer a level of specialisation that provides for numerous properties missing in Australian standards. The problem is finding labs that can do the tests.

European Standards

Fibre Reinforced Concrete

• EN14488 Part 3, Sawn shotcrete beam

• EN14488 Part 5, Square panel

• EN14561 notched beam

• None of these standards offer precision estimates on performance.

• All are vaguely written with minimal descriptions of the test machine requirements and no references to provide supporting data.

European Standards

EN14488 Part 3 sawn shotcrete beam

• 75x125 mm sawn beam on 450 mm span

• COV in residual strength >30% for 3 beams

• What can you do with data displaying such high variability?

• This test has caused numerous problems on projects around the world and should not be used other than as a last resort when only small amounts of concrete are available.

Effect of number of samples n

Larger correction factor appears associated with non-Normal data

4

1

0.75

nc

n

inf

1.02

0.24

COV n

COV n

0.50

0.60

0.70

0.80

0.90

1.00

0 10 20 30 40 50

Eqn. (7)

Eqn. (9)

Co

rre

ctio

n F

acto

r

Number of Specimens, n

EN14488.3 Beam tests

EN14488.3 should only be used as a last resort

European Standards

EN14488 Part 5 Square panel test

• 600x600x100 mm sawn square panel

• COV in residual strength of >12% for 3 panels

• Expensive to cut, capture of rebound if no splayed sides are used in mould

• Base is seldom flat, so load-deflection record can have multiple peaks

• Mode of failure changes with toughness

• Friction responsible for 40% of energy absorption and no control of loading surface

EN14488 Part 5 Square Panel

Specimen results are obscured by high friction with base

EN 14488 panel test

Research in Norway demonstrated that friction with supports

is responsible for about 40% of energy absorption

0

10

20

30

40

50

60

70

80

90

0 4 8 12 16 20 24 28

Deformasjon (mm)

La

st

(kN

)

Standard

Grease

Kvadratiske platerSquare panels

No friction

Displacement

Load

(kN

)

EN 14488 panel test

Non-flat base causes multiple peaks in curve producing

essentially useless results.

Q-chart Design of FRS linings

EN 14561 beam test

Central point load and notch lead to higher estimates of performance

than are achieved with ASTM C1609.

Problems with European Standards

EN14561 Beam test

• MOR and residual strength are higher than for un-notched beams

• Maximum permissible fibre length is 60 mm, as opposed to 50 mm in other beam tests.

• Variability in performance is at least as high as for ASTM C1609, population COV reported as ranging from 25-35% in post-crack residual capacity in RILEM papers

• This test method provides no guidance in respect of supporting roller design and friction limitations and thus bias is uncontrolled.

• Crack width is directly measured or calculated as rigid body rotation based on deflection measurements

EN 14561 beam test

Notch is supposed to overcome fibre alignment problems with

boundaries, but research results are contradictory on this issue.

Alternatives

Australian and ASTM Standards

• Australian standards very similar for plain concrete

• There are no Australian standards for FRC

• The main alternative to European FRC standards are ASTM standards

• ASTM C1609/C1609M and ASTM C1550

• Several labs are already accredited for these tests in Australia

• New ASTM standards are under development including 1200 mm diameter panel

ASTM C-1550 Panel tests

The focus of ASTM standards development is consistency of outcomes and low cost so that numerous specimens can be tested. ASTM C-1550 tests are more reliable and cheaper than EN14488 Square

panels or beams for shotcrete

Performance Testing

• Quality control testing has been used in Australian mines and tunnels for many years, this has yielded the following design guide

ASTM C-1609 Beam tests

ASTM C-1609 tests involve no notch, no „standard‟ concrete, cheaper to perform due to simpler test set-up

ASTM C-1609 support rollers

Friction in supporting rollers can lead to very high bias in residual strength results, up to 200% over-estimate.

ASTM C-1609 support rollers

ASTM beam standards will soon be based on standard roller design that eliminates inter-lab bias to produce more consistent data.

1200 mm round panel test

The large panels have a 50% larger diameter and support radius, and

thickness of 150 mm, thus area is 12 times larger than 150 mm beam and

mean performance correlates well with 150 mm thick beams.

Residual Strength Estimation

Residual strength estimation in 1200 mm panels is based on yield line

(plastic) model of moment distribution at hinges and elastic distribution of

strain through the cross-section, which is very similar to the theory used for

beams.

Basis of residual strength estimation has passed rigorous scrutiny by

design engineers who like the fact that the same theoretical basis is used

for both types of specimen.

Population COV for residual strength in 1200 mm panels is 11%. This is

less than half the variability displayed in any beam test.

Rd

rPf p 23

2fb = PL/bd 2

Beams Panels

EN14561 and Crack Widths

• EN14561 offers the sole advantage that post-crack performance is assessed in terms of crack width, but this can be calculated from ASTM C1609 and panel results when crack locations are measured.

• How are crack widths used in design?

• Can be used in 2010 Model Code or in FEA

2010 Model Code

• This is a guide, not a code. There is little continuity between sections, and many parts are confusing and ambiguous.

• This guide is a starting point for design, not the end point. Designers are free to expand on the ideas contained in it which is good because there is nothing new in this guide.

• Ductility requirements for FRC are much lower than for conventional reinforced concrete, more like L-grade mesh

• Maximum „allowable‟ crack width is 2.5 mm, but how this is achieved for a strain-softening material is not explained.

• Creep and age-dependent changes in performance are not considered, nor is seismic or concentrated point loading.

2010 Model Code

• The Model Code intimates incorrectly that only fibres that exhibit time-dependent changes in length under load suffer creep in cracked FRC. This is patently wrong because slip occurs at the boundary between fibre and concrete and steel FRC exhibits very clear creep rupture that is easy to measure and is documented in published papers.

• Performance at 28 days is assumed to hold at all other ages. There is no account taken of very significant falls in performance with age observed in steel FRC as strength of concrete exceeds 50 MPa.

Embrittlement

2010 Model Code takes no account of age-dependent changes in toughness. The fall in toughness that occurs with aging of steel FRC is therefore not considered.

Permanent FRC Linings

2010 Model Code makes the revolutionary claim that flexural capacity is determined using rectangular stress block for concrete in compression and varying stress

block for fibres in tension. Every other model of FRC behaviour makes the same assumptions but permits any type of fibre and steel bars to be used.

Alternative methods of design

2010 Model Code has nothing to offer for hard-rock FRS lining design. Q-chart and work by Barrett & McCreath (1995) offer far superior models of behaviour and

are proven. European standards have nothing to contribute for shotcrete.

Summary

European standards…

• Are the “closed shop” that is tightly guarded

• Are more expensive than alternatives

• Are not provided by most labs in Australia

• Offer no advantages in terms of either accuracy or variability

• Can be subject to high friction-induced bias due to lack of control over support conditions

• Offer the sole advantage of expressing FRC flexural performance in terms of crack width