Effect of Footing Size on the Dynamic Behaviour of Cohesionless Soil-Foundation System

Abstract

The current study examines the influence of footing size on the dynamic behaviour of machine foundation systems placed on a prepared foundation bed of cohesionless soil. Large-scale block foundation tests are performed on rigid reinforced cement concrete (RCC) square foundation of two different sizes (F1: 550 mm × 550 mm × 200 mm and F2: 650 mm × 650 mm × 200 mm). Steady–state vertical harmonic loading is applied to the footings at three different magnitudes of eccentric force settings (mee), using a Lazan type mechanical oscillator. The dynamic response is recorded in terms of displacement, velocity, and acceleration amplitudes. Results are reported in the form of magnification factor (M) versus frequency ratio (fr) response. Further, the natural frequency (fn), equivalent dynamic stiffness (k), and total damping ratio (D) are evaluated using the corresponding displacement amplitude (zr) and the operating frequency (fmr) at resonance condition, obtained from the tests for both the footings F1 and F2 at different eccentric force settings. The results attained from this study are compared to those reported in the existing literature.KeywordsDynamic responseMachine foundationBlock vibration testSize effectCohesionless soil