Akira Nishimura

WS3b4 – SAFETY EVALUATION AND RESIDUAL LIFE PREDICTION OF CONCRETE BRIDGES

ABSTRACT This paper describes a method for safety evaluation of concrete bridges and its verification based upon field tests performed either under static loading by test trucks for the application of the system identification method or under dynamic loading by falling mass for the application of the modal analysis. The safety factors for flexural and shear failures were evaluated from these test results. Then, they were verified through the ultimate load test carried out in field on the reinforced concrete main girders isolated by cutting off from the bridge system. Finally, residual life of the bridge was predicted by applying the fuzzy set theory which deals with the subjective information of bridge engineers.

Secular change in structural reliability of friction-type bolted joint of galvanized members.

Hot dip galvanized bridges have become popular for prevening corrosion due to exposure and reducing maintenance costs during the life time of steel bridges. The reliability of galvanizd friction type joints with high strength bolts may differ from that of ordinary joints of uncoated members. This difference is caused primarily by the iron-zinc alloy and pure zinc layers of the surface of the member. The present paper reports the results of investigation on the behavior of hot dip galvanized friction type joints with high strength bolts under short-duration static load and the secular change of bolt tension. The results are then applied to evaluate the reliability of galvanized joints having bolt tension lower than the specified value as well as of slip-load occurrence.The main conclusions derived from this study can be summarized as follows: After a month, the loss in bolt tension was 10-13% for the hot dip galvanized surface as compared to the initial bolt tension. The secular change of bolt tension and the slip coefficient calculated by using the residual bolt tension could be expressed by use of the regression method based upon the exponential creep law. The probability of slip occurence decreased with increasing duration after the bolt clamping of he joint. The maximum value of the probability calculated was rather small, ranging from 4.8×10-7 to 6.6×10-7.

EFFECT OF OPEN SOCKET ON CABLE TENSION ESTIMATED BY VIBRATION METHOD

The method of estimating tension of bridge cables by measuring their natural frequency, so-called vibration method, is convenient on construction site of structures with cables, Concerning the method some papers have been reported hitherto. In these reports cables are assumed to be clamped on both ends. However, for the estimated tension of cable supported by open sockets, vibration of the sockets has a notable effect, which has not been investigated. In order to get reliable and accurate estimation for tension of cables with open socket, some experimental works were performed and reported in this paper.