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How does a structural glazing system handle differential movement between glass, aluminum, and structure?
Differential movement is managed by designing joints and connections that isolate glass from rigid structural displacement while providing controlled load transfer. Glass, aluminum, and building structure have different coefficients of thermal expansion and stiffness characteristics; to avoid imposing peel stresses on adhesives or over-stressing glass, designers provide movement joints, sliding or floating bearings at mechanical fixings, and flexible adhesive layers sized for expected elongation. Primary strategies include: 1) Movement allowance: specifying clearances at glass edges to accommodate thermal and structural drift; 2) Flexible adhesive systems: using structural silicones with high elongation and low creep to absorb relative displacements; 3) Secondary mechanical supports: point anchors or spider fittings with bearings that allow rotation and limited translation; 4) Isolated back-up framing: thermally broken subframes that separate the glazing interface from the main structure, limiting heat- or load-induced movement transmission; 5) Design for differential deflection: ensuring glass spans and support spacing limit flexural stresses under service loads; 6) Controlled sequence of load transfer during installation to avoid pre-stressing adhesives. For seismic situations, oversized boltholes, sliding plates and slotted connections allow large in-plane and out-of-plane displacements. Proper detailing also includes edge cover caps and gaskets that compress rather than shear, and adhesives applied in bead geometries that reduce peel stress concentration. Final verification is accomplished via movement envelope calculations and mock-up testing to ensure the glazing system can accommodate the predicted differential movements throughout operational temperature and load ranges.