PSI - Issue 64

Antonio Bossio et al. / Procedia Structural Integrity 64 (2024) 56–64 Author name / Structural Integrity Procedia 00 (2019) 000–000

59

4

Referring to MC10 §6, equation of Ω p,trMC10 is proposed:

, b f = = −  τ

0.2

f ⋅ 

l

1 tanh

(1)

 

 

Ω

, p trMC

10

0.1

f

⋅

τ

0

co

Referring to Eurocode 2 (EC2) §5.2.2 the value of Ω p,trEC2 , is calculated according to:

τ

  

  

1 0.4 1 −

, b f

(2)

1.4

=

= −

≤

Ω

, p trEC

2

l f

⋅

τ

0

A Simple Friction Model (SFM) was considered, too. The value of Ω p,trSFM is calculated according to:

τ

    = + ⋅ 1 µ

   

f

, b f

l

=

(3)

Ω

, p trSFM

τ

τ

0

0

where µ = friction coefficient of corroded steel = 0.3 as suggested by Coronelli (2002). Figure 2b shows the Ω p,tr ratio related to different models, calculated for a concrete strength class C25/30.

0%

50%

100%

Crack Propagation

3.0

MC10 SFM EC2

0.30%

10

Ω p.tr

x [ μ m]

2.0

0.15%

Section Lost

5

1.0

0.0

0

0.00%

R 3 [mm]

0.0

15.0

30.0

f l [N/mm

2 ]

7

25

42

Fig. 2. (a) Section lost vs increment of cracked concrete front R 3 , (b) Ω p,tr ratios vs internal pressure, f l , in case of concrete strength class C25/30.

4. Corrosion simulation At first, oxide accumulation inside the grooves around the rebar actually helps the bond. The pressure created by the expanding oxide pushes the rebar tighter against the concrete, increasing the bond strength. This is on the conservative side, before it gets worse once cracks appear in the concrete. As the crack opens wider (due to continued pressure from the oxide, Bossio et al. 2017 and Benenato et al. 2022) the lateral pressure holding the rebar in place is lost, and the bond strength goes back down to its original value (see the downward sloping vertical line in Figure 3a). From there, the bond strength keeps reducing steadily. This continues until the gap between the rebar and the concrete (caused by shrinking steel and growing oxide) becomes as wide as the height of the ribs on the rebar ( h rib ) (see Figure 3b). This larger gap allows the rebar to slip more easily, further reducing bond strength. Disengagement, where the rebar loses most of its grip on the concrete, becomes a major concern at this point. The study assumes a uniform corrosion of the rebar across its entire cross-section. This simulates what happens in lab tests where artificial corrosion is used to mimic, for instance, the effects of carbonation.