Design and Structural Verification of a Modular Multi-Level Aluminum Access Stair System for Maintenance and Construction Applications

Abstract

Modular access towers are increasingly used in construction, industrial maintenance, rooftop servicing, and excavation applications where conventional scaffold stair systems may be limited by installation time, relocatability, available footprint, and project-specific fabrication requirements. This study develops and evaluates a configuration-aware structural verification framework for a multi-level aluminum access stair system assembled from repeatable welded and bolted modules. The objective is to determine whether modular stair-tower configurations can satisfy strength, stability, connection, and anchorage requirements under site-specific gravity and environmental loading while maintaining the flexibility required for repeated assembly and reconfiguration. The methodology combines three-dimensional finite-element analysis in SAP2000, code-based aluminum member checks, analytical utilization and reserve-factor calculations, and separate verification of bolts, welds, base anchors, and tie-off anchors. A primary Colorado installation was assessed for dead, live, snow, wind, and seismic actions using 6061-T6 aluminum members. A separate Florida installation was reviewed as an independent cross-project case under a higher basic wind speed of 168 mph. Controlled manufacturing drawings for standard and compact towers ranging from one to ten stair modules were also examined to evaluate the influence of module count, total height, structural mass, footprint, and tie-back spacing. All reported structural components satisfied the unity utilization criterion. The governing 3 in × 3 in × 0.25 in aluminum angle reached a utilization ratio of 0.941. The base-anchor and tie-off-anchor interaction ratios were 0.752 and 0.651, respectively. A two-bolt field connection provided 16.57 kips of shear capacity against a demand of 12.39 kips. The results show that structural adequacy depends not only on individual member strength but also on inter-module load-path continuity, anchorage, connection reliability, lateral-restraint spacing, and site-specific environmental actions. The proposed framework provides a transferable engineering basis for comparing configurable lightweight access structures and supports future parametric optimization and experimental validation.