PSI - Issue 10

N.G. Pnevmatikos et al. / Procedia Structural Integrity 10 (2018) 195–202 N.G. Pnevmatikos et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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law the fatigue damage index and the fatigue life were calculated and shown in Fig.6. For low cycle fatigue a non linear time history analysis subjected to Aigio earthquake excitation, with a scale factor of two, was performed. With such a strong earthquake the members reach the yield limit and experience inelastic deformation. Plastic rotation vs. time at connection was obtained and shown on Fig.7. By applying the reservoir method, the spectrum of plastic rotation was calculated and is shown on Table 4. Table 2. combinations of fatigue method and analysis case which were performed with respect of the level of earthquake excitation. Fatigue method Analysis Method Linear time history Nonlinear time history 1/3 Aigio earthquake excitation Aigio earthquake excitation 2 times Aigio earthquake excitation High cycle fatigue S-N (fatigue chart from EC3 part 1-9) x - - Low cycle fatigue - x x

Stress vs. time diagram

σ (Μ Pa)

Time (sec)

Fig. 5. Stress at connection vs time diagram for linear dynamic analysis of frame subjected to 1/3 of Aigio ground motion

Table 3. Stress variation spectrum obtained by reservoir Method

Peaks and valleys

Δσ (Mpa) 282,67

Number of cycles (n i ')

Δσ

Τ1 Τ2 Τ3 Τ4 Τ5 Τ6 Τ7 Τ8 Τ9

(P1-T1) (P2-T2) (P1-T3) (P3-T4) (P4-T5) (P6-T6) (P5-T7) (P7-T8) (P9-T9)

1 1 1 1 1 1 1 1 1 5 1

213,3 183,3 129,3 106,6

90,7 77,4 65,4 52,2

Τ10 Τ11

(P10-T10) (P8-T11)

27,04 32,67

Using a low cycle fatigue model (Eq.(1)) (Vayas et al. (2003)), the number of rotation range cycles N is calculated. From the reservoir method the number of cycles n i is obtained. Applying the Miner’s law (Eq.(2)), the fatigue damage index and corresponding fatigue life were calculated for different slope of fatigue curve, m, and shown in Fig.8.