PSI - Issue 5

Ivan Baláž et al. / Procedia Structural Integrity 5 (2017) 1057 – 1064 Ivan Baláž / Structural Integrity Procedia 00 (2017) 000 – 000

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6

where N = 0 kN in the critical section, ρ w (z) = W y,ef / W y is effective section modulus ratio, which depends on the reduction due to the local buckling of the plate between stiffeners and in the parts of longitudinal stiffeners, the global buckling of the whole bottom flange in compression combined with reduction due to the shear lag in the bottom flange and on the reduction of the upper flange due to the shear lag. Details of ρ w (z) calculation may be found in (Baláž, 1990). Details of shear lag calculation at SNP Bridge were published in (Baláž, Chladný, 1991, 1992). f (y) is transverse direct stress distribution according to (ČSN 73 6205, 1984) and (BS 5400, Part3, 1982) described by 4 th order parabola; f (y ) = 1.0 for the vertical webs points and f (y ) < 1.0 for the other upper and bottom flanges points. Good correlation between theoretical and loading test values may be seen in Fig. 3.

Fig. 3. Comparison of theoretical direct and shear stresses distributions taking into local buckling, global buckling and shear lag effects due to loading test action 73 kN/m in the critical section with the measured loading test values of direct stress in the upper flange

7. Strengthening of SNP Bridge

As it was written above the cross section of SNP Bridge was originally a single-cell box steel girder from the point of the last, most-inclined cable anchorage till the Bratislava end of the bridge, because the middle web of the box girder was omitted in this part of SNP Bridge. The proposal for the bridge strengthening was made in (Chladný,

Table 1. Rating factors of SNP Bridge parts for normal, exclusive and exceptional actions. Part of the bridge Normal action rating factors = V n / 320 kN Exclusive action rating factors = V r / 320 kN

Exceptional action rating factors = V e / 3 20 kN

a) ON736220

b) exception

c) exception, strengthe ning

a) ON736220

b) exception

c) exception, strengthe ning

a) ON736220

b) exception

c) exception, strengthe ning

Box girder Tower leg

< 0 < 0 < 0

0.82 1.92 1.49

> 1.0

< 0 10.

1.0

1.0

0.58 7.09 1.29

1.7

1.8

– –

– –

– –

19.6

8.66 4.38

Cables

0.14

15.

Key: the sign “– “ means that rating factor was not necessary to calculate (> 1.0), the rating factor 0.82 means that instead of required V n = 320 kN, only 0.82 x 320 kN = 262.4 kN was obtained