Example 1: Strengthening a slab with externally bonded CFRP strips - Strengthening of Concrete Structures with Adhesively Bonded Reinforcement - page 41

Table 4.2 Individual values obtained in situ for near-surface tensile strength.

n 1 2 3 4 5

f fctm,surf,i [N/mm 2 ]

2.2 2.5 2.0 2.4 2.3

Mean value: 2.28 N/mm 2

Standard deviation: 0.19

4.1.3.2 Concrete compressive strength
Concrete of class B25 was able to be ascertained from the as-built documents according
to DIN 1045 [94]. Following a test on the member according to DIN EN 13 791 [95], the
result was a strength class of C20/25. Therefore, the values according to DIN EN 1992-
1-1 [20] Tab. 3.1 for C20/25 concrete will be used for the design. This results in a mean
concrete compressive cylinder strength f cm = 28 N/mm 2 and a characteristic concrete
compressive cylinder strength f ck = 20 N/mm 2 .

4.1.3.3 Type and quantity of existing reinforcement
The as-built documentation reveals that a type R 443 steel mesh was used as the
reinforcement. Therefore, according to [96], this is a type BSt 500M (IV M) steel rein-
forcing mesh to DIN 1045 [94] or DIN 488-2 [97]. Consequently, we can assume a yield
stress f yk = 500N/mm 2 and a modulus of elasticity E s = 200 kN/mm 2 . As given in [96], a
type R 443 mesh has longitudinal bars with an area a sl = 4.43 cm 2 /m, which consists of
pairs of Ø6.5mmbars@150mm c/c, and transverse bars with a sq =

0.95 cm 2 /m, made up

of Ø5.5mm bars @ 250mm c/c.

4.1.3.4 Position of existing reinforcement
The as-built documents indicate a concrete cover of min c 2.0 cm,

according to DIN 1045 [94]. A survey according to [98] has revealed that

= 1.0 cm, or nom c =

the

reinforcement is positioned as shown in Figure 4.2.

4.1.3.5 Strengthening system
Commercially available externally bonded CFRP strips with a characteristic tensile
strength f Luk = 170 kN/mm 2 are to be used

for the strengthening. According to the manufacturer, strips with dimensions of ( t L ×

2200N/mm 2 and modulus of elasticity E L =

b L )
50 × 1.4mm, 80 × 1.4mm and 100 × 1.4mm are currently available ex stock. In order

Fig. 4.2 Type and position of existing reinforcement