Crowd-Induced Vibration Serviceability of Reinforced Concrete Lecture Theatre Floors: Taraba State University

Abstract

Overcrowding in Nigerian public university lecture theatres has created a severe structural loading problem that engineers have rarely confronted systematically: crowd-induced dynamic loading that far exceeds the live loads assumed at the design stage. This study investigates the vibration serviceability of reinforced concrete floor systems in six lecture theatres at Taraba State University (TSU), Jalingo, where observed peak occupancies reached as high as 211% of design capacity. In-situ ambient vibration testing via the Stochastic Subspace Identification (SSI) algorithm, calibrated finite element modelling in ETABS, and multi-harmonic crowd load simulation were combined to characterise structural responses across six loading scenarios. Fundamental floor frequencies of 4.08 to 6.83 Hz were recorded, with the lowest values concentrated in flat-slab theatres whose wide spans placed them squarely in the resonance band for the second harmonic of rhythmic crowd activities near 4.2 Hz. Modal Assurance Criterion (MAC) values of 0.84 to 0.97 across the first three bending modes confirmed adequate model fidelity beyond the fundamental frequency alone. A supplementary boundary condition study showed that semi-rigid column base assumptions improved the mean frequency prediction error from 4.8% to 2.1%, though serviceability classifications were unaffected. Parametric sensitivity analysis for three theatres whose structural details were estimated rather than drawing-verified showed that natural frequency predictions varied by no more than 4.9%, with compliance classifications unchanged across every perturbation. Under rhythmic crowd loading at 150% of design capacity, peak floor accelerations reached 0.61 m/s2 in the most critical theatre, exceeding the ISO 10137:2007 assembly area limit of 0.45 m/s2 by 36%. Dynamic amplification factors of 1.42 to 3.89 were recorded, driven primarily by near-resonance excitation of flat-slab floors. The study recommends graduated interventions ranging from administrative occupancy limits to structural retrofitting, and makes a case for explicit vibration serviceability provisions in Nigerian design standards for educational facilities of this nature.