中井 正一

This paper describes the development of a simplified nonlinear analysis to predict behavior of a horizontally loaded piled raft foundation. In the proposed method, two new effects have been introduced to the previous method. One is the change of ultimate soil resistance against piles due to the contact between the raft and the underlying soil. The other is the rotation of the raft due to the bending moment from piles and also to the change of the contact pressure distribution caused by the pile movement. A comparison with centrifuge test of piled raft foundations and freestanding pile groups indicates that the proposed method can give a fairly good prediction of the behavior of a horizontally loaded piled raft foundation.

An extensive study of the dynamic behavior of piled foundations with very short piles has been made by a series of centrifuge model tests and three dimensional finite element analyses. It was found from the model tests that the addition of very short piles to a piled foundation reduces, bending moments and shear forces of the piles at their head. It was also found from the series of finite element analyses that the earthquake response of a building is not affected very much due to the difference of the type of foundation (piled/piled raft) or of the connection condition of the pile at its head (rigid/pin). However, it was pointed out that the contribution of very short piles to the pile bearing shear forces is about 30 to 40 per cent and is found effective from the view point of earthquake resistance.

The knowledge about the condition of the ground is crucial when considering earthquake disaster mitigation. However, collecting information on the ground condition over a wide area is not an easy task. In order to address this issue, the authors have looked at the fact that the land use is closely related to the soil condition and micro topography. The objective of this paper is to investigate an approach to infer the ground and landform conditions based on the land use and its change. The authors have already examined the method in which detailed digital land use information was used. In this paper, a new approach where satellite (Landsat/TM) data are effectively used to identify land use is discussed.

It is well known that the surface soil condition and the micro topography are influential to the seismic intensity of the ground and hence to the seismic damages. In this paper a study in which maps in the old times are compared with those in the present time is first made to come up with the topography. This topography is then compared with H/V spectra computed from the microtremor observations that have been conducted at a total of 155 locations in the city of Chiba. It was confirmed that the H/V spectra have strong relationship with micro topography. It was also found that the ratio between horizontal and vertical amplitudes of the computed fundamental mode of Rayleigh waves corresponds well with observed H/V spectra from the viewpoint of frequency dependency.

Abstract: Analysis is one of the key issues in realizing complex large structures. In spite of the tremendous accumulation of methods and theories in the field of structural analysis, there is still a need to include newly developed methodologies into analysis codes for production use. This paper describes the initial development of a platform to accommodate the future needs in this area. The system being developed is a knowledge‐based system which first accepts the user's description of an analysis problem, comes up with a suitable analysis method and a corresponding computational algorithm, then develops a program along with input data to solve the problem, and finally gives a result to the user. Program generation is done by selecting appropriate building‐block codes from a program database. To construct a prototype system, a problem solving model called an ‘organizational model’ is introduced, which is developed to imitate the problem solving in a real life. The main part of the system, which functions as described above, is written in CLOS (common LISP Object System), while generated codes are written in either FORTRAN or C++. The performance of the prototype system shows that this approach can be effective. Copyright © 1992, Wiley Blackwell. All rights reserved