The cable bands (hereafter, “bands”) of suspension bridges are major members made of cast steel material that couple together the main cables and the hanger ropes, which are composites of several strands of steel wires; they maintain their position through the friction force that results from the fastening force (axial force) of the several cable band bolts (hereafter, "bolts") that fasten the bands. We have confirmed that the bolt axial force decreases with the passage of time; due to this, the friction force decreases and it is possible that the band will slip due to the hanger’s tensile force, so management of the bolts’ axial force through maintenance, measuring the bolts’ axial force and performing additional tightening in cases where axial force is low, is necessary.

Cable band (transverse prestressing type)

Slippage force and slippage resistance force in the band

In order to reduce the aforementioned maintenance work, we have analyzed the results of the measurements of bolt axial force and hanger tensile force that have been done up until now, have revised the safety factor for slippage, which had previously comprehensively been designated as “3,” and have formulated a management manual for the maintenance. From now on, we will conduct maintenance management while obtaining data on decrease in axial force and checking safety allowances.

However, because the Kurushima-Kaikyo Bridges are different from other suspension bridges in that their bolts are fastened vertically, it is necessary to take into consideration the bolts’ axial varing force besides slippage, such as due to hanger tensile force. In order to investigate bolts’ axial varing force, we carry out measurements while loading vehicles are running on the bridge as well as studying the maintenance management manual.

Kurushima-Kaikyo Bridges’ cable band

Investigation with loading vehicles on the Kurushima-Kaikyo Bridges