Tailor Made Concrete Structures – Walraven & Stoelhorst (eds)
© 2008 Taylor & Francis Group, London, ISBN 978-0-415-47535-8
Non destructive tests for existing R.C. structures assessment
S. Biondi & E. Candigliota
Department of Design, Rehabilitation and Control of Architectural Structures, Pricos, University
“G. D’Annunzio”, Chieti-Pescara, Italy
ABSTRACT: In this paper in-situ non destructive tests for r.c. structure diagnosis are discussed. Three existing
sport domes were analyzed in order to evaluate their global behavior and to design their seismic assessment.
A wide program of in situ (non destructive) and laboratory (destructive) tests was carried out. Some literature
proposals are used for test data interpretation and to validate non linear F.E.M. structural analyses.
1
INTRODUCTION
In Italy a great part of the territory wasn’t classified
as seismic up to 2003, so that lower intensity earthquakes caused important structural damages and loss
of human life. For this reason new Codes were produced, in all of which diagnosis of existing r.c. frames
is considered.
In the Abruzzo Region (Lanciano, Ortona and
Vasto) three recently built sport domes, with r.c. structures based on older seismic codes, were analyzed in
order to evaluate their seismic behavior.
A wide program of in situ and laboratory tests was
carried out regarding r.c. elements of these buildings.
In particular the actual concrete strength is detected by
means of combined non-destructive methods (rebound
index and ultrasonic pulse velocity). Some cylindrical
concrete specimens are extracted for compressive laboratory tests. Some literature proposals are used and
discussed in this paper for test data interpretation.
ν, concrete mass density γ (kg/m3 ). Four different formulas are considered for any kind of measure (direct,
semi-direct, indirect):
2.3 SonReb method for compressive strength
In the SonReb method two equations are used, based
on rebound index and pulse velocity:
2.4 Ultrasonic pulse velocity for laboratory test
2 THEORETICAL BACKGROUND
2.1 Rebound index for compressive strength
The equivalent cube compressive strength RcR (in
MPa) can be determined by using rebound index I :
2.2
Some concrete cylindrical specimens are extracted
(Ø = 75 ÷ 95 mm diameter) with various slenderness
ratio 1,00 ≤ l/ Ø ≤ 2, 36. These specimens are preliminarily tested using ultrasonic apparatus [using
(2) ÷ (4)] and then in compression; in this case two
correlations between cylindrical fc and cubic Rc compressive strength are considered:
Ultrasonic velocity for compressive strength
The same strength RcV (in MPa) can be determined by
means of dynamic Ecd and static elastic modulus Ec ,
using ultrasonic pulse velocity V (km/s), Poisson ratio
where CØ , Cr and Cd are correction coefficients that
depend on core diameter, rebar presence (never in this
case), damage to drilling (Dolce et al. 2006).
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0,80
55
45
(6.1)
(6.2)
(2)
(3)
(4.1)
(4.2)
0,60
(6.1)
(6.2)
(2)
density
0,40
35
0,20
25
0,00
-0,20
15
-0,40
5
1
3
5
7
9 11 13 15 17 19 21 23
Figure 2. Non-dimensional compressive strength for laboratory specimens.
Figure 1. Compressive strength for laboratory specimens.
75
3 TEST RESULTS
(6.2)
(1)
(5.2)
65
A great number of in situ tests were carried out (62
rebound and 73 ultrasonic tests, the latter for 161 different direct, semi-direct or indirect measures). In this
paper an evaluation of combined method efficiency is
discussed based on in laboratory concrete specimen
tests (23 cylindrical specimens).
(2.S)
(5.1)
55
45
35
25
15
3.1
5
Ultrasonic pulse velocity for laboratory tests
First of all, ultrasonic method efficiency on core
was evaluated. In laboratory compressive strength,
depending on specimen slenderness and drilling damage, eq. (6), is compared with theoretical values due
to pulse velocity, (eqs. (2) ÷ (4) with γ actual mass
density). In Figure 1 the results are ordered in terms
of eq. (6.1) values (in MPa); the better correlation is
obtained using eq. (2) with actual density.
In Figure 2 non-dimensional values, obtained from
eqs. (6) and (2), are compared with actual concrete
density (average γ = 2200 kg/m3 ). Each nondimensional value ξa = (x − x)/x is obtained considering
current value, x, average value, x, and measure range,
x = xmax − xmin . Figure 2 shows a good agreement
between pulse velocity estimation, (2), and compressive strength, (6). Compressive strength strictly
depends on concrete density while Code concrete
density, γcode = 2400 kg/m3 , overestimates ultrasonic
pulse velocity strength.
3.2
1
3
5
7
9
11 13 15 17 19 21 23
Figure 3. Compressive strength for laboratory and in-situ
tests.
75
(6.2)
(1)
(5.2)
65
(2.S)
(5.1)
55
45
35
25
15
5
1
2
3
4
5
6
7
8
9
Figure 4. Compressive strength for laboratory specimens
and in situ tests (considering only direct ultrasonic tests).
Combined method for in situ tests
In Figure 3 a comparison of laboratory tests, eq. (6.2),
with in situ tests before core extraction [pulse velocity using mass density γ = 2350 kg/m3 , (2.S), rebound
index medium, (1), SonReb method, (5)] is carried out.
Both a large rebound index overestimation and a
large scattering of in situ pulse velocity are evident:
the first due to concrete carbonation degree, the second
due to semidirect and indirect measurement influence.
This scattering dramatically affects combined
method results. Otherwise if only direct pulse velocity
measure in situ is used, the combined method results
are more efficient, Figure 4.
1038
4
CONCLUSIONS
In situ tests have shown a great, sometimes discouraging, dispersion of results, also for within the same
building (due to building phases) and the same element
(due to environmental and casting conditions, loading
and cracking levels).
An extreme difficulty to reach unitary conclusions
can be pointed out. This difficulty was higher for buildings with structural elements of wide dimensions or
with large reinforcement ratio.
Concrete strength determination by means of the
combined non-destructive method has shown high
levels of difficulty due to direct, indirect and semidirect ultrasonic pulse velocity dispersion (Biondi &
Candigliota 2008, in prep.). For existing r.c. buildings, the direct pulse velocity for combined method
is strongly recommended in order to obtain correct
compressive strength evaluation.
REFERENCES
Biondi, S. & Candigliota, E. 2008. In situ tests for seismic
assessment of r.c. structures. Proc. 14th World Conference on Earthquake Engineering, Beijing, China, 12–17
October 2008. Paper ID 05-01-0447.
Dolce, M., Masi, A., Ferrini, M. 2006. Estimation of the
Actual In-Place Concrete Strength in Assessing Existing RC Structures. Proc. of the 2nd International Fib
Congress, Naples, Italy, 5–8 June 2006. Paper ID 9-10.
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