PSI - Issue 70

Maheshwar Bose et al. / Procedia Structural Integrity 70 (2025) 137–144

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4.4 Inter story Drift & Drift Ratios Inter-story drift is a crucial parameter for effectively evaluating structural behaviour. It provides a more dependable measure of both structural and non-structural damage compared to absolute displacements. This study examines the story drift of a six-story irregular L-shaped building incorporating steel bracing in various configurations. Notably, the drift ratio in all models remained below the 0.4% limit specified by the Indian standard code except in unbraced condition under NF ground motion. Therefore, only critical model graph is shown in Fig. 3. In every scenario, the maximum story drift occurred at the third floor. Furthermore, the use of steel bracings for lateral load resistance resulted in a more uniform drift distribution. According to the Indian standard code, the story drift in any story should not exceed 0.004 (0.4%) times the story height under the action of design base shear. While observing the graph, there found a drift spike at story 5 in unbraced condition i.e. at 15m height. The reason being the NF Earthquake generates high- velocity pulses that excites lower to mid stories, creating localized drift spikes. Also, there may be a possibility of Plastic hinge formation and thus failure occurs.

Fig.3: Drift ratio for Imperial Valley (NF) (Non-Linear)

4.5 Response Spectrum Analysis It is the widely adopted linear dynamic analysis technique used in earthquake engineering to estimate the peak response of structures under seismic loading. This method assumes that the total response of a multi degree of freedom structure can be decomposed into the series of independent modal contributions, each corresponding to a specific natural vibration mode. These modes, much like harmonics in a vibrating string, capture the dynamic characteristics of the structure. RSA involves evaluating the maximum response — such as displacement, velocity, or pseudo acceleration of an equivalent single degree of freedom system across a range of natural periods or frequencies, typically for a defined damping ratio. The RS itself is a plot that represents the peak response values of these SDOF systems subjected to a specific ground motion. It is observed that systems with shorter natural periods tend to experience higher accelerations, while those with longer periods generally exhibit larger displacements. This method provides valuable insight into the potential dynamic behavior of a structure without requiring time-dependent analysis for each scenario. Table.5. Spectral acceleration of the RSM of different model

Unbraced

Eccentric

V-Braced

X-Braced

STOREY

OUTPUT CASE

Ux

Ux

Ux

Ux

mm/s 2 739.87 519.25 478.64 541.15 545.97 398.46

mm/s 2 863.63 775.29 676.57 615.36 572.24 460.74

mm/s 2 946.36 841.54 739.83 665.92 617.95 546.29

mm/s 2 944.14 849.89 757.4 685.36 633.68 564.25

Story_6 Story_5 Story_4 Story_3 Story_2 Story_1

RSX RSX RSX RSX RSX RSX