Takayoshi OTSUKA, Toru KOBAYASHI, Toshimitsu MIZUMA
Nippon Civic Consulting Engineers Co., Ltd.
Symposium on Material Design and Performance of Concrete Structures

Key words: shield tunnel, segment lining, performance-based design method, the limit state design method, beam-spring model

Background
There is currently a trend in structural design away from the conventional allowable stress method towards performance-based design, whereby required performance at various state limits is set. In Japan, a practical limit state design method has already been established especially for reinforced concrete building structures, but not for tunnels because of the added difficulties of accounting for externally applied loads such as soil pressure.

Research Summary
In order to apply the limit state design method, a set of limit states for reinforced concrete segment lining structures was established. The limit states included were:
・ the crack width limit state;
・ joint opening limit state;
・ damage limit state;
・ cross-section failure/distortion ultimate limit state; and
・ failure due to fire ultimate limit state.
A study was performed to determine the required performance and design verification method for each of these states. A road shield tunnel of 12 m external diameter was assumed and trial design calculations were carried out using a 3-ring beam-spring model. Calculations were performed for both the limit state design method and the conventional allowable stress design method. Often, design inconsistencies arise using the allowable stress method because of limits on the allowable compressive stress. It was found that the limit state design method could resolve these inconsistencies.