PSI - Issue 5

Hołowaty J. et al. / Procedia Structural Integrity 5 (2017) 1043 – 1050 Hołowaty / Structural Integrity Procedia 00 ( 2017) 000 – 000

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Table 2. Chemical composition of the steels ( % ). Bridge No. Sample C Mn Si

P

S

Cu

Cr

Ni

Al

1

Plate t = 12

0.258

0.496

0.169

0.024

0.043

0.258

0.014

0.055

0.001

L200× 100×14

0.030

0.319

0.004

0.031

0.024

0.051

0.010

0.037

0.002

2

Web I360

0.028

0.516

0.00

0.062

0.025

0.051

0.00

0.042

0.004

3

Web I380

0.037

0.528

0.00

0.088

0.042

0.051

0.00

0.035

0.003

Top flange I600 B

0.016

0.644

0.00

0.040

0.015

0.029

0.00

0.170

0.007

4

5

Plate t = 10

0.025

0.400

0.001

0.041

0.020

0.229

0.00

0.00

0.00

0.018 ÷0.30 0.03 ÷0.35

traces ÷0.33 0.04 ÷0.75

0.01 ÷0.33 traces ÷0.18

0.02 ÷0.46

0.01 ÷0.06

Wrought steel

-

-

-

-

0.004 ÷ 0.16

0.004 ÷0.115

0.11 ÷0.14

0.11 ÷0.14

0.03 ÷0.04

0.01 ÷0.02

Mild steel

S235

max 0.17 max 1.40

-

max 0.025 max 0.025 max 0.55

-

-

-

The mechanical properties of the bridge steels were determined via static tensile testing at room temperature on circular fivefold specimens with different gauge diameters (Table 3). The steel specimens from each bridge were machined under different conditions: naturally-age S and normalized N. As previously mentioned, the parameters for specimens N are comparable with the steel properties at the time of delivery i.e. at the time of bridge construction. Only for bridge No. 3 were additional specimens in full annealing condition prepared, with their condition marked as A. These specimens, similar to normalized ones, were heated at a temperature of 930 °C for an hour and then cooled down at the same time as the oven. Heat treatment is used to relieve stresses and form a uniform and refined microstructure. The process gives steel good ductility, low hardness and good workability and is a metallurgical process which is used on non-alloy steels. However, normalization is used with low and medium-carbon steels. The aim of this process is to recrystallize and obtain a microstructure with no residual stresses, which is uniform and fine grained. Compared to annealing, the process improves steel’s mechanical properties, in particular its hardness and toughness. Good ductility and the finest grain size is achieved, with machinability occasionally improved.

Table 3. Results of tensile and hardness tests on the steels.

Specimen diameter ( mm )

Brinell hardness

f yL ( MPa )

f u ( MPa )

A 5 ( % )

Bridge No.

Type of specimen

f yH ( MPa )

f u,B ( MPa )

HB 158 121 116 121 117 159 114 126 132 105 127 125 131 98

1 2 3 4 5 1 2 3 4 5 3

8

350 340 277 276 230 262 356 281 287 319 281 336 277 305

341 335 252 253 221 254 337 265 260 285 242 317 258 275

542 357 381 387 359 372 543 376 388 408 373 451 392 399

27 28 29 38 34 23 25 26 39 39 35 28 36 35

530 405 390 405 392 339 532 382 422 441 354 427 417 438

10 10 10

S

7 8

10

N

10 10

7

A

10