Experimental study on the construction-stage deformation and load transfer of scaffold bays in waffle slab formwork supporting systems

Six representative scaffold-bay specimens derived from practical waffle slab formwork supporting systems were tested to investigate construction-stage deformation and load transfer along the complete supporting assembly. The specimens comprised a modular ringlock scaffold frame, adjustable screw jacks, primary beams, secondary beams, and formwork panels, and covered variations in scaffold height, bay spacing, upright tube size, primary-beam type, secondary-beam arrangement, and design construction load. The axial strain response of the uprights, the overall load–displacement response, and the deformation distribution along the load-transfer path were examined. The results showed that the uprights mainly remained in axial compression within the design load range, although the load sharing among the four uprights was not fully uniform. The overall vertical stiffness was governed by the combined effects of the upper transfer configuration, including the primary-beam type, secondary-beam arrangement, bay dimension, and screw-jack extension. Stiffer or denser upper transfer arrangements led to more stable load–displacement responses, whereas configurations with larger bay dimensions or lower beam-layer stiffness produced larger vertical deformation and made the upper beam layer more influential in the system response. The deformation decomposition at the design load indicated that the total vertical displacement was not governed by scaffold compression alone; the beam layers and contact-related deformation also made appreciable contributions. A stiffness interpretation was therefore established by separating the elastic axial shortening of the uprights from the additional non-elastic deformation associated with contact adjustment, gap closure, and compatibility between transfer layers. Based on this decomposition, a nonlinear stiffness formulation was developed to describe the load-dependent deformation response of the supporting system. The proposed framework provides an experimental and analytical basis for evaluating construction-stage deformation and determining elevation adjustment requirements in waffle slab construction.