LICENTIATE THESIS - Luleå tekniska universitet

the equations to calculate the design shear resistance and the design fatigue strength are
changed. These changes give that the new draft is much more conservative than the
EC2- 1 (1991)(see later sections).
In the MC90 (1993), also presented in a Fib textbook (1999), a more refined method is
proposed based on work by Stemland et al (1990) and others:
⎛ 2 ⎞
log N1 = ⎜12 + 16Sc,min + 8Sc,min ⎟(
1 −S c ,min ) for N1 ≤6
⎝ ⎠
log N = 0.2 log N ⋅ log N − 1 for N > 6 and ∆S
≥0.3 −3S
/8
( )
2 1 1 1 c c,min
( )
log N ⋅ 0.3 −3S
/8
log N for N 6 and S 0.3 3S /8
2 c,min
3 = 1 > ∆ c < − c,min
∆sc
with ∆s
= S −S
c c,max c,min
The equations are illustrated in Figure 3.1 for the two cases R = S c,min/S c,max = 0 and
= 0.5.
Some observations can be made:
- EC2 is the most conservative code (the new draft, EC2-draft (1999), is even more
conservative).
- Aas-Jacobsen (and the Swedish code) is somewhat less conservative for Sc,min > 0.
- MC90 gives lower N-values for N < 6 and low Sc,min -values. But it gives higher
N-values for N > 6 in comparison to EC2 and Aas-Jakobsen.
- UIC gives always the same S c,max = 0.5. For R=0 and N < 6 this is conservative
but for N > 6 it can be un-conservative. For higher R-values the change from
conservative to un-conservative will take place for higher N-values, see Figure
3.1.
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