Specimen during the test Specimen after the collapse 0

EP-01 326,90 331,37 16,51 15,81 16,21 Collapse mode: mode 1

Note: collapse of bolt B followed by the collapse of bolt A cracks on the welds between web and flanges

Specimen during the test Specimen after the collapse 0

100 200 300 400

0 2 4 6 8 10 12 14 16 18 20 22 24

Force (kN)

Displacement (mm)

Transducer A

Transducer B

Transducer C

EP-01 bolt A 0,55 1858,9 89,70(*)

EP-01 bolt B 0,55 5485,1 317,65

(*) bolt A strain gauge malfunctioning

0 100 200 300 400

0 100 200 300 400 500 600

Force (kN)

Bolt's axial load (kN) EP-01 Bolt A EP-01 Bolt B

0 100 200 300 400

0 1000 2000 3000 4000 5000

Force (kN)

Bolt's axial deformation (µm/m) EP-01 Bolt A

EP-01 Bolt B

ε _y

[mm/s] [kN] [mm] [mm] [mm]

EP-02 326,90 396,90 16,26 14,42 14,67

Collapse mode: mode 1

Note: contemporaneous collapse of both the web-flange weld and the bolt B

Specimen during the test Specimen after the collapse 0

100 200 300 400

0 2 4 6 8 10 12 14 16 18 20 22 24

Force (kN)

Displacement (mm)

Transducer A

Transducer B

Transducer C

EP-02 bolt A 0,55 4560,5 265,84

EP-02 bolt B 0,55 4484,8 265,06

Bolt EP-02 A after the collapse Bolt EP-02 B after the collapse 0

100 200 300 400

0 100 200 300 400 500 600

Force (kN)

Bolt's axial load (kN) EP-02 Bolt A EP-02 Bolt B

0 100 200 300 400

0 1000 2000 3000 4000 5000

Force (kN)

Bolt's axial deformation (µm/m) EP-02 Bolt A

EP-02 Bolt B

ε _y

ε _y

EP-03 326,90 347,27 21,57 21,11 22,66 Collapse mode: mode 1

Note: collapse of bolt A followed by the collapse of bolt B cracks on the welds between web and flanges

Specimen during the test Specimen after the collapse 0

100 200 300 400

0 2 4 6 8 10 12 14 16 18 20 22 24

Force (kN)

Displacement (mm)

Transducer A

Transducer B

Transducer C

EP-03 bolt A 0,55 4574,6 246,59

EP-03 bolt B 0,55 6402,8 306,44

Bolt EP-03 A after the collapse Bolt EP-03 B after the collapse 0

100 200 300 400

0 100 200 300 400 500 600

Force (kN)

Bolt's axial load (kN) EP-03 Bolt A EP-03 Bolt B

0 100 200 300 400

0 1000 2000 3000 4000 5000 6000

Force (kN)

Bolt's axial deformation (µm/m) EP-03 Bolt A

EP-03 Bolt B

ε _y

EP-04 0,07 270,92 15,97 14,54 15,55 Collapse mode: mode 1

Note: collapse of bolt A

cracks on the welds between web and flanges

Specimen during the test Specimen after the collapse 0

100 200 300 400

0 2 4 6 8 10 12 14 16 18 20 22 24

Force (kN)

Displacement (mm)

Transducer A

Transducer B

Transducer C

EP-04 bolt A 0,55 5436,5 281,32

EP-04 bolt B 0,55 4437,5 266,12

Bolt EP-04 A after the collapse Bolt EP-04 B after the collapse 0

100 200 300 400

0 100 200 300 400 500 600

Force (kN)

Bolt's axial load (kN) EP-04 Bolt A EP-04 Bolt B

0 100 200 300 400

0 1000 2000 3000 4000 5000 6000

Force (kN)

Bolt's axial deformation (µm/m) EP-04 Bolt A

EP-04 Bolt B

ε _y

EP-05 0,07 302,67 21,70 21,60 21,97 Collapse mode: mode 1

Note: collapse of the welds between web and flanges

Specimen during the test Specimen after the collapse 0

100 200 300 400

0 2 4 6 8 10 12 14 16 18 20 22 24

Force (kN)

Displacement (mm)

Transducer A

Transducer B

Transducer C

EP-05 bolt A 0,55 6266,1 323,05

EP-05 bolt B 0,55 8754,0 863,29

Bolt EP-05 A after the collapse Bolt EP-05 B after the collapse 0

100 200 300 400

0 100 200 300 400 500 600

Force (kN)

Bolt's axial deformation (kN) EP-05 Bolt A

EP-05 Bolt B

0 100 200 300 400

0 1000 2000 3000 4000 5000 6000 7000 8000

Force (kN)

Bolt's axial deformation (µm/m) EP-05 Bolt A

EP-05 Bolt B

ε _y

ε _y

EP-06 0,07 304,24 15,19 13,98 15,28 Collapse mode: mode 1

Note: collapse of bolt B

cracks on the welds between web and flanges

Specimen during the test Specimen after the collapse 0

100 200 300 400

0 2 4 6 8 10 12 14 16 18 20 22 24

Force (kN)

Displacement (mm)

Transducer A

Transducer B

Transducer C

EP-06 bolt A 0,55 5384,0 354,34

EP-06 bolt B 0,55 8065,5 466,37

Bolt EP-06 A after the collapse Bolt EP-06 B after the collapse 0

100 200 300 400

0 100 200 300 400 500 600

Force (kN)

Bolt's axial load (kN) EP-06 Bolt A EP-06 Bolt B

0 100 200 300 400

0 1000 2000 3000 4000 5000 6000 7000 8000

Force (kN)

Bolt's axial deformation (µm/m) EP-06 Bolt A

EP-06 Bolt B

ε _y

EP-07 160,00 321,68 13,58 13,04 13,69 Collapse mode: mode 1

Note: collapse of bolt B followed by the collapse of bolt A

Specimen during the test Specimen after the collapse 0

100 200 300 400

0 2 4 6 8 10 12 14 16 18 20 22 24

Force (kN)

Displacement (mm)

Transducer A

Transducer B

Transducer C

EP-07 bolt A 0,55 1727,9 93,18(*)

EP-07 bolt B 0,55 5078,5 429,72

(*) bolt A strain gauge malfunctioning

Bolt EP-07 A after the collapse Bolt EP-07 B after the collapse 0

100 200 300 400

0 100 200 300 400 500 600

Force (kN)

Bolt's axial load (kN) EP-07 Bolt A EP-07 Bolt B

0 100 200 300 400

0 1000 2000 3000 4000 5000

Force (kN)

Bolt's axial deformation (µm/m) EP-07 Bolt A

EP-07 Bolt B

ε _y

EP-08 160,00 341,00 20,98 19,88 20,83 Collapse mode: mode 1

Note: collapse of bolt B followed by the collapse of bolt A

Specimen during the test Specimen after the collapse 0

100 200 300 400

0 2 4 6 8 10 12 14 16 18 20 22 24

Force (kN)

Displacement (mm)

Transducer A

Transducer B

Transducer C

EP-08 bolt A 0,55 5955,1 407,26

EP-08 bolt B 0,55 8139,1 399,61

Bolt EP-08 A after the collapse Bolt EP-08 B after the collapse 0

100 200 300 400

0 100 200 300 400 500 600

Force (kN)

Bolt's axial load (kN) EP-08 Bolt A EP-08 Bolt B

0 100 200 300 400

0 1000 2000 3000 4000 5000 6000 7000 8000

Force (kN)

Bolt's axial deformation (µm/m) EP-08 Bolt A

EP-08 Bolt B

ε _y

EP-09 160,00 324,57 16,64 15,36 16,55 Collapse mode: mode 1

Note: contemporaneous collapse of both bolts

Specimen during the test Specimen after the collapse 0

100 200 300 400

0 2 4 6 8 10 12 14 16 18 20 22 24

Force (kN)

Displacement (mm)

Transducer A

Transducer B

Transducer C

EP-09 bolt A 0,55 5783,9 301,87

EP-09 bolt B 0,55 6014,1 343,92

Bolt EP-09 A after the collapse Bolt EP-09 B after the collapse 0

100 200 300 400

0 100 200 300 400 500 600

Force (kN)

Bolt's axial load (kN) EP-09 Bolt A EP-09 Bolt B

0 100 200 300 400

0 1000 2000 3000 4000 5000 6000

Force (kN)

Bolt's axial deformation (µm/m) EP-09 Bolt A

EP-09 Bolt B

ε _y

EP-10 160,00 335,10 23,17 22,26 23,22 Collapse mode: mode 1

Note: bolts snug tightened

collapse of bolt B followed by the collapse of bolt A cracks on the welds between web and flanges

Specimen during the test Specimen after the collapse 0

100 200 300 400

0 5 10 15 20 25 30

Force (kN)

Displacement (mm)

Transducer A

Transducer B

Transducer C

EP-10 bolt A Snug tightened 929,16 55,71(*)

EP-10 bolt B Snug tightened 7804,9 409,27

(*) bolt A strain gauge malfunctioning

Bolt EP-10 A after the collapse Bolt EP-10 B after the collapse 0

100 200 300 400

0 100 200 300 400 500 600

Force (kN)

Bolt's axial load (kN) EP-10 Bolt A EP-10 Bolt B

0 100 200 300 400

0 1000 2000 3000 4000 5000 6000 7000 8000

Force (kN)

Bolt's axial deformation (µm/m) EP-10 Bolt A

EP-10 Bolt B

ε _y

bolts had the same characteristics of those used for the tests on the T-stub assemblies, namely bolt M20, class 10.9. The tests were performed under loading control, with different loading rates, according with the loading history reported in Figure 34. A first cycle of loading and unloading was performed in the elastic range, followed by a ramp of loading with a low loading rate and a loading ramp characterised by the loading rate . In particular, the following tests were performed: one test with 0,16 / , one with 16,00 / , one with 160,00 / , two with 325,00 / and two with 625,00 / (the maximum value of the loading rate was limited by the equipment capability). All the bolts were preloaded with a pretorque of 0,55 , in compliance with the preloading adopted in the T-stub tests.

Figure 34: Loading history for the tests on the bolt assemblies (graph not in scale)

The load was applied using a MTS actuator with maximum capacity in tension and compression of 1000 kN, placed within the same test rig as the one adopted for the tests on the T-stubs. A specific setting was built up to apply the tensile load to the bolt assemblies (Figure 35) and the bolts were fixed to the lower support of the rigid frame. To estimate the bolts deformation, two transducers were used. The transducers allowed to measure the displacement of the setting to which the bolts were fixed (Figure 35).

Figure 35: The testing set-up

reported. For each specimen the following data are collected:

• the loading rate ;

• the maximum load measured during the tests;

• the displacements measured by the two transducers, associated with the maximum load;

• the displacement calculated as the mean value between the displacements measured by the two transducers, associated with the maximum load;

• the force vs. displacement curves obtained from transducers measures for each specimen;

• the photography of each specimen after the collapse has occurred.

The results are ordered according to their loading rate, from the lower to the higher. At the end, all the results

are collected in a summarizing table (Table 5) and the curves are gathered in Figure 39.

[kN/s] [kN] [mm] [mm] [mm]

B-01 0,16 256,85 2,50 2,22 2,36

Specimen after the collapse

load transducer A transducer B displacement

[kN/s] [kN] [mm] [mm] [mm]

B-03 16,00 308,64 2,25 2,05 2,15

Specimen after the collapse

B-05 160,00 263,48 2,46 2,30 2,38

Specimen after the collapse

load transducer A transducer B displacement

[kN/s] [kN] [mm] [mm] [mm]

B-02 325,00 301,83 2,47 2,25 2,36

Specimen after the collapse

B-07 325,00 277,47 2,44 2,23 2,34

Specimen after the collapse

load transducer A transducer B displacement

[kN/s] [kN] [mm] [mm] [mm]

B-04 650,00 266,44 0,75(*) 2,14 2,14(**)

Note: (*) transducer A malfunctioning;

(**) the mean displacement is substituted by the displacement measured by transducer B

Specimen after the collapse

B-06 650,00 280,96 2,37 2,11 2,24

Specimen after the collapse

This allowed to measure also the bolt deformation during the tensile test. In addition, since the bolt was previously calibrated, also the axial load was calculated and compared with the load applied using the MTS actuator. Hereafter, the curves load vs. axial deformation (Figure 36) and load vs. axial load obtained from the calibration (Figure 37) are reported. In Figure 36 is the deformation corresponding to the yielding; in Figure 37, the curve associated to loads greater than 200 kN was dashed, since it was obtained by extrapolation. In both of the figures, the preloading of the bolt is observable.

In Figure 38, the load vs. time curves are represented. The curves allow a comparison between the load transmitted by the actuator and the axial load acting in the bolt, calculated on the basis of the axial deformation measured by the internal strain gauge. The two curves are overlapping and the initial difference between the two curves is due to the preloading of the bolt.

Figure 36: Load vs.axial deformation curve for the bolt B-02 assembly

8.2.4 Summary of the results and conclusions

In Table 5 the results of the tests are collected. For each bolt, the maximum load and the mean value of the displacement associated to the maximum load are reported. In Figure 39 the load vs. displacement curves of all the tests are collected.

Table 5 and Figure 39 point out quite a high dispersion of the results. It can be observed that the minimum

and the maximum values of the collapse loads were achieved with a loading rate of 0,16kN/s and 16 kN/s,

respectively, i.e. the two lowest values of loading rates adopted in the tests. The collapse loads associated to

higher values of loading rate are placed between these two boundary values. Therefore, a connection

between the loading rate and the maximum load achievable seems to be not distinguishable. As to the

maximum deformation capacity, the results collected in the Figure 39, seems to indicate a favourable

influence of the loading rate on the bolts ductility: the higher the loading rate, the higher the maximum

deformation capacity. However, the limited number of the tests performed and the natural dispersion of the

Figure 37: Load vs. axial load curve for the bolt B-02 assembly

Figure 38: Load vs. time curve for the bolt B-02 assembly

ID specimen Pretorque Maximum Mean

B-01 0,55 0,16 256,85 2,36

B-03 0,55 16 308,64 2,15

B-05 0,55 160 263,48 2,38

B-02 0,55 325 301,83 2,36

B-07 0,55 325 277,47 2,34

B-04 0,55 650 266,44 2,14

B-06 0,55 650 280,96 2,24

Table 5: Summary of the results of the tests on the bolt assemblies

Figure 39: Load vs. displacement curves of all the bolt assemblies

Symonds relationship parameters), a series of tensile tests on the structural steel of the T-stubs were carried out, at different loading rates. The tests were performed at the Technische Universität Braunschweig and the Rheinisch-Westfälische Technische Hochschule Aachen [8].

The results of the tests performed in quasi-static conditions are summarised in Table 6.

Joint component ID

specimen Cross section F max R m R eh R p0,2 A

mm ² kN MPa MPa MPa %

End-plate 10 mm x_dir

2X1 28,30 15896 562 373 373 32,6

2X2 28,15 15756 560 370 370 33,1

2X3 28,28 15710 556 372 368 35,4

End-plate 10 mm y_dir

2Y1 28,32 15809 558 382 378 30,9

2Y2 28,29 15807 559 380 377 30,8

2Y3 28,29 15751 557 382 378 26,0

Column HEB220

3X1 113,34 50016 441 300 292 34,9

3X2 112,59 49758 442 306 294 34,5

3X3 112,93 49622 439 304 284 36,1

Table 6: Mechanical properties of the steel of the columns and of the end-plates

Concerning Cower-Symonds relationship parameters, the following values were calculated: 3,44 and

473 for the column flange T-stub steel and 5 and 1130 for the end-plate T-stub steel.