Impact of configuration irregularity (L-shape) on the seismic performance of low-to mid-rise reinforced concrete frame buildings in Nepal | |
| Author | Hirachan, Bisesh |
| Call Number | AIT Thesis no.ST-25-22 |
| Subject(s) | Framing (Building)--Earthquake effects--Napal Earthquake resistant design--Napal |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Structural Engineering |
| Publisher | Asian Institute of Technology |
| Abstract | Nepal’s rapid urbanization, narrow plot geometry, and the shift toward preserving traditional courtyard-style planning have increased the prevalence of L-shaped buildings. Their inherent irregularities, including differential wing motion, stress concentration at re entrant corners, mixed vibration modes, and lateral-torsional coupling, demand detailed seismic evaluation. This study investigates their performance using eight structural models ranging from symmetric to L-shaped configurations. Response Spectrum Analysis (RSA) and Linear Time History Analysis (LTHA) is performed on all models to understand elastic behavior, while Nonlinear Time History Analysis (NLTHA) is conducted on the two irregular forms to capture inelastic responses.The analysis shows that increasing plan irregularity leads to shorter periods and reduced mass participation while torsional irregularity and diaphragm rotation increase with asymmetry and height. Linear analysis shows up to 120% amplification in drift, 19% higher roof displacement, and progressive increases in base shear and overturning moment from RRM to ILM3. Local demands concentrate at the re-entrant corner, where columns and beams experience the highest shear, torsion, and bending moment. However, the axial demand is the highest for the corner column under seismic loading. NLTHA further confirms that nonlinear effects dominate in mid-rise irregular frames, with linear analysis overestimating drift by up to 2.5 times and underpredicting overturning moment due to P Δ action. Overall, the findings show that even moderate projection irregularity (>30%) governs seismic behavior, highlighting the need for nonlinear evaluation in mid-rise MRF, thus, bridges the gap between elastic and inelastic behavior by showing that LTHA can be misleading for mid-rise frames, while NLTHA reveals trend reversals, early yielding, and realistic energy dissipation. Findings challenge the 15% projection limit, show NBC’s torsion limit (1.5) is more appropriate for Nepal, and confirm that the fundamental period of L-shaped buildings depends on both configuration and height. The results also show that balanced stiffness can control torsion even with equal projections and identify re-entrant corners, L-corners, and beam–column joints as critical detailing zones. |
| Year | 2025 |
| Type | Thesis |
| School | School of Engineering and Technology |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Structural Engineering (STE) /Former Name = Structural Engineering and Construction (ST) |
| Chairperson(s) | Pennung Warnitchai;Anwar, Naveed (Co-Chairperson) |
| Examination Committee(s) | Krishna, Chaitanya;Thanakorn Pheeraphan |
| Scholarship Donor(s) | AIT Scholarship |
| Degree | Thesis (M. Eng.) - Asian Institute of Technology, 2025 |