Presented at the XXIV Nordic Concrete Research Symposium in Stockholm, August 17-19, 2022.

1. Aug. 17, 2022 J Silfwerbrand, KTH 1 (12)
Design by Testing –
Lessons Learned from Full-Scale Loading Tests
on Industrial Fibre Concrete Floors
Johan Silfwerbrand
KTH Royal Institute of Technology, Stockholm
24th NCR Symposium, Stockholm, Aug. 17, 2022

2. Outline
 Design by testing according to Eurocodes
 Industrial fibre concrete floors – types & design
methods
 Problems & possible solutions
 Lessons learned
 Concluding remarks
Aug. 17, 2022 J Silfwerbrand, KTH 2 (12)

3. Design by Testing according
to Eurocodes
 Mentioned in EC 2 & described in EC “0”, Annex D
 Design by testing may be used…
 (i) if suitable design models are missing,
 (ii) if large number of similar components are
going to be used or
 (iii) to confirm design assumptions.
 The design by testing should fulfil required safety
level.
Aug. 17, 2022 J Silfwerbrand, KTH 3 (12)

4. Industrial Concrete Floors
Aug. 17, 2022 J Silfwerbrand, KTH 4 (12)

5. Design of Industrial Fibre
Concrete Floors
 Slabs-on-grade are ≠ load-carrying structure 
not dealt by Euro- or most other design codes
 Pile-supported slabs: Is it considered load-
carrying or not?  Different design methods give
very different results.
 Conservative design leads to too thick and
uneconomical FC slabs.
 Less conservative design leads often to slabs that
perform well. But why? Are there neglected
factors that contribute to the load-carrying
capacity?
Aug. 17, 2022 J Silfwerbrand, KTH 5 (12)

6. Possible Benefical Effects
Factor
1. Arch action
2. Membrane effect
3. Load redistribution
4. Contribution from the ground
between the piles
Aug. 17, 2022 J Silfwerbrand, KTH
F
6 (12)

7. Design by Testing
Advantages Disadvantages
Straight-forward way to include
unknown beneficial effects
Difficulties & costs to perform a
sufficiently large number of tests
Possibility to evaluate which
design method that is best
Major cracks & damages (not
desired by the client)
Increased knowledge on the real
performance
Difficulties to create the
necessary ultimate load
Aug. 17, 2022 J Silfwerbrand, KTH
40 kN/m2 =
4,1 m
2 m
7 (12)

8. Basic Factors Influencing
Load-Carrying Capacity
 Slab thickness
 Concrete strength
 Fibre content
 Fibre distribution & fibre orientation in the
thickness direction
 Contact with & stiffness of underlying grade
 Pile spacing
 Pile characteristics (size of pile head, load-carrying
capacity)
 Horizontal restraint (due to friction or any rigid or semi-
rigid support)
Aug. 17, 2022 J Silfwerbrand, KTH 8 (12)

9. Which Slab Part Should be
Loaded?
A. Interior part between pile heads – positive
moment
B. Interior part above pile head – negative moment
Aug. 17, 2022 J Silfwerbrand, KTH 9 (12)

10. The Swedish Experience
 The real industrial floor cannot
be tested in ULS.
 Tests on SLS are possible.
 Make at least one test at a
suitable location.
 Combine it with a relatively
large number of cores.
Aug. 17, 2022 J Silfwerbrand, KTH 10 (12)

11. Coring
 Large number of cores for
estimating mean value &
scatter of slab thickness,
concrete strength, fibre
content, fibre distribution &
any contact with the
underlying ground.
Aug. 17, 2022 J Silfwerbrand, KTH
h = ?
Any contact?
11 (12)

12. Concluding Remarks
 Loading tests on fibre concrete industrial floors
may constitute a part of the quality assurance.
 Due to problems with load levels, number of tests
& damage costs, they cannot be the sole method.
 Combinations with coring is a promising
alternative.
 Research on hidden & unquantified factors is
urgent.
Aug. 17, 2022 J Silfwerbrand, KTH 12 (12)