Height-Dependent Seismic Performance of Ordinary Moment Frame Buildings with Solid Slabs on Dropped Beams in Tripoli, Libya: A Nonlinear Pushover Analysis

Reinforced concrete (RC) buildings with ordinary moment frames (OMFs) and solid slabs on dropped beams represent the predominant mid-rise residential structural system in Tripoli, Libya. These buildings are typically designed for gravity loads alone, with little or no explicit seismic detailing. This study investigates how building height affects the seismic response, damage evolution, and performance compliance of this typology. Three configurations — 8, 10, and 12 stories — share identical plan geometry, material properties, and site hazard parameters. Each configuration was modeled in ETABS and analyzed using nonlinear static pushover analysis, with concentrated plastic hinges assigned at the ends of beams and columns. Performance was evaluated against ASCE 41-17 acceptance criteria at the target displacement corresponding to the unreduced MCE­_R demand.

The findings showed that the three configurations satisfied the Immediate Occupancy performance level in both principal directions. Increasing height reduced lateral stiffness, lengthened the fundamental period, and progressively degraded displacement ductility along the stronger direction, highlighting the need for explicit seismic detailing as building height increases.

Keywords: Pushover Analysis, Ordinary Moment Frame (OMF), Building Height, Performance-Based Earthquake Engineering, Target Displacement, Inter-Story Drift, Tripoli.