Study on ratcheting of beams under the combination of gravity and seismic load

Abstract

Ratcheting is one common phenomenon under excessive earthquakes. This study focuses on clarifying the ratcheting mechanism of beams subjected to the combination of gravity and seismic loadings. The sinusoidal excitations or their combinations represented the seismic loadings. Gravity acted as load-controlled loading and was applied by the self-weight of the beam as well as the additional mass put at the free end of the beam. A cyclic acceleration was applied at the base of the beam to provide the source of dynamic loading assumed as seismic loading. Equivalent loading conditions were put in experiments as in numerical analysis to validate the nonlinear finite element analyses. The analogy between thermal ratcheting and vibration ratcheting was considered to investigate the characteristics of cyclic accelerations. The frequency effects on the applied alternating accelerations were also investigated in this research. The results show that input waves containing the lower frequency components than the natural frequency are more damageable comparing to that containing higher frequency ones. Besides, the component with lower frequency contributes more to the occurrence of ratcheting. The characteristics of dynamic loading due to base acceleration depend on the loading frequency. The low-frequency acceleration acts like load-controlled loading, while the high-frequency acceleration is close to displacement-controlled loading.

Keywords

• ratcheting
• beam
• seismic loading
• gravity
• frequency ratio