This paper presents the experimental data to improve the ductility of prefabricated concrete piles under the earthquake and the suggestion of restoring force model for those piles.
Recently, prefabricated piles tend to be used for the pile foundation of medium and low storied buildings, because those piles are high workability and cost efficiency in comparison with cast-in-place concrete piles. On the other hand, the ductility of prefabricated piles are lower than cast-in-place concrete piles, because prefabricated piles are produced by centrifugal molding. However, the checking against deformation performance of building piles is unnecessary in the building standard law of Japan. Therefore, the ductility of piles is not enough, when the deformation becomes more excessive than assumed.
The second chapter shows the improved detail and the experiment result of SC and PRC piles. SC and PRC piles are the kind of prefabricated piles.
First, to improve the ductility of SC and PRC piles, the void of these filled with normal strength concrete. Furthermore, PRC piles were improved the details shown in the Fig. 2
Then, the result of the experiment is shown. The parameter of the experiment is that the infilled concrete exist or do not. In case of having infilled concrete, either pile were improved ductility under the reverse cyclic loading and constant axial loading, because compression fracture of pile concrete were prevented. Conversely, piles having the void were caused brittle fracture. After brittle fracture, SC pile was able to resist axial force. On the other hand, PRC pile was unable to resist it.
The next chapter has shown the evaluation method of the restoring force model for SC and PRC piles.
First, Flexural capacity of those piles are calculated by fiber model analysis. The difference of having infilled concrete or nothing were described by the stress-strain relationship of the concrete. Deformation performance of those piles is calculated by the total of Bending deformation, Shear deformation and Rotational deformation of pile head connection. Bending deformation is calculated by integration of pile curvature. Shear deformation is calculated assuming the elastic body. Calculation method for Rotational deformation is different by pile head connection type. In case of pile head connection with anchorage bars, Rotational deformation is calculated by integration of anchorage bar strain assuming the triangular distribution. Alternatively, in case of pile head connection embedding footing, Rotational deformation is calculated by equation (11) assuming that fixing ratio is 0.9.
Then, examination result about relationship between shear force and drift angle were simulated by the suggestion method of restoring force model. The subject of the simulation were five SC piles , two improved PRC piles and twelve conventional PRC piles. As a result, suggestion method using fiber model analysis were able to evaluate the relationship between shear force and drift angle in each pile type.
