Dynamic analysis of multilayered glass slab under pedestrian excitation

Abstract Laminated glass walkways depend on their polyvinyl butyral (PVB) interlayers to make the glass plies act together, yet PVB loses stiffness with temperature, load duration and age. This study examines how interlayer degradation changes the dynamic behaviour of a five-layer laminated glass panel under pedestrian excitation. A multilayer thin-plate formulation gives the neutral-surface position and the layer-wise bending and torsional rigidities, and the equation of motion under a sequence of moving bipedal footfalls is solved in closed form by modal superposition and the Laplace transform. Frequency bounds for full and zero composite action, together with a partial-interaction estimate, relate the interlayer shear modulus to the natural frequencies. A three-dimensional finite element model of a panel based on an in-service glass footbridge is then analysed by modal, harmonic response and full transient analyses, for a rigid-bond and a degraded interlayer with the same geometry, supports, mesh, damping and loading. The closed-form time histories agree closely with the transient finite element results, and the partial-interaction estimate reproduces the finite element frequencies of the bending modes. Degradation lowers every natural frequency, the higher modes most, and amplifies the displacement, velocity and acceleration produced by walking. Velocity and acceleration grow more than displacement because the lowered fundamental frequency moves towards a walking harmonic. The principal stress in the glass also rises but stays far below the strength of fully tempered glass, and the deflection remains within the adopted limit; the peak acceleration of the degraded panel, however, exceeds the recommended comfort limit. Vibration serviceability, rather than glass strength or deflection, therefore governs the degraded panel. Because the frequency bounds need only geometry and elastic properties, a measured fundamental frequency can be used to screen the condition of the interlayer without destructive testing.