LICENTIATE THESIS - Luleå tekniska universitet

Evaluation of Concrete Structures
and the last level is very complicated since it is connected to so-called γ-values (factors
for loads, traffic etc.). These “levels” cannot be found in BBK94.
In Table 5.1 you can see a summary of the number of load cycles the Lautajokki
Bridge could manage with the compared codes. In the table the more refined methods
from the different codes are compared.
If we compare the results in Table 5.1 we can see that there are differences. The
calculation with EC2-2 (1995) gives the least conservative values. The Swedish code is
slightly more conservative than the EC2-2, but they are still fairly similar. The new
version of Eurocode, EC2-draft (1999), is by far the most conservative one.
For example: for the strength class C30 at P = 30 tons the Swedish Code gives that the
bridge should manage 2000 cycles before failure, the EC2-draft (1999) gives 50 cycles
and the EC2-2 (1995) gives 3800 load cycles. We then have in mind that the bridge
managed 6M cycles without failure (full-scale test performed at LTU, 1996), which
points out that none of the three compared codes is especially accurate.
Table 5.1 Number of load cycles (n in million load cycles) for the Lautajokki
bridge. Comparison between EC2-1 (1991)/EC2-2 (1995), BBK94 (1994) and
EC2-draft (1999) at different strength classes.
A) Strength Class Code Number of load cycles, n
[M cycles]
22.5 tons 25 tons 30 tons
Swedish 0.90 0.10 0.002
C30 EC2 1.9 0.19 0.0038
Draft 0.053 0.004 0.00005
Swedish >1 >1 0.8
C40 EC2 223 31 1.1
Draft 0.44 0.039 0.0007
Swedish >1 >1 >1
C50 EC2 3093 519 26.8
Draft 1.8 0.18 0.0036
Swedish >1 >1 >1
C60 EC2 8929 1615 95.6
Draft 5.1 0.5 0.012
Swedish >1 >1 >1
C80 EC2 34659 6900 486
Draft 18.8 0.06 0.06
A) Strength classes according to EC2-draft (1999).
What are the differences between the three codes? Some of them are:
- The expression to calculate the shear force capacity, see Table 5.2.
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