抄録
In general, Nuclear Power Plants (NPPs) are designed for a postulated earthquake event. Two conceptual stress limits which are Primary stress limit and Primary plus Secondary stress limit are required to meet in the design codes for seismic loads on essential structures such as a piping induced by the seismic event. The past researches proposed an interpretation that seismic response of structure is comprised of load-controlled load and displacement-controlled load, whereas most design codes consider the seismic response corresponds to load-controlled load which should be limited with the Primary stress limit to prevent a plastic collapse.Although these limits are considered to qualify two independent loads which consist of load-controlled load and displacement-controlled load, all of design codes for NPPs give weight at qualifying the load-controlled load since the load-controlled load, the pure Primary Stress components, is believed to govern a plastic collapse on structures, whereas no plastic collapse has ever occurred on any experimental tests. Past researches proposed an interpretation where seismic response is comprised of load-controlled load and displacement-controlled load. An interpretation of the each term in the equation of motion was proposed in the former researches PVP2015-45287 which found a structure excited by a lower frequency than the natural frequency which is considered as an excitation at Rigid condition could result in plastic collapse because of a minimal recovering force counteracting the deformation. This result implies that the current design codes which assume elastic-behavior may include significant over-conservatism to ensure the adequacy of structures under seismic condition. As many experimental results are showing, very large seismic loads which excessively exceed the design limit barely caused failure in piping components. This paper investigates the relationship between inertia forces and element forces on a single mass cantilever model applying a bi-linear material property against several random time-history loads which are adjusted to represent the said excitation conditions. This paper also clarifies the correlation between deformations due to the excitations and the inertia/element forces observed on the models.
