Observed Damage - Overview

The Ji Lu cable stayed bridge offers a unique opportunity to see the force of an earthquake applied to a cable stayed structure first hand.  The Ji Lu case study in one of forensics.  The damage is there, reasons for the damage are unknown.  Only with careful observation of the damage can the behavior during the earthquake be understood.

Though very minor damage was distributed throughout the structure, major damage was concentrated in just a few areas.  In the main span deck, around the area of the central pylon, there was severe concrete cracking, spalling, and reinforcing bar buckling.  

Figure 1 - Fault Normal pulse with a period matching the transverse mode correlating to the damage observed

The central pylon, also in this area, saw concrete cracking and cover shedding.  At the ends of the span, in the supporting bents, there was heavy shear cracking, and evidence of large lateral offsets and concrete pounding.  The foundations, just above the pile cap, saw cracking and flexural yielding and a cable stay, on the North side, fractured.

The overall damage pattern documented suggests large movement in a transverse mode where the tower moves opposite to the direction of the central pylon (Figure 1).  This is used to calibrate the period of vibration in the investigation. 

Evidence for this being that the most heavily damaged side of the central pylon is opposite the largest measured lateral offset at the end piers.  Further, the nature of the damage in the main span at the central pylon area is indicative of large plastic rotations the direction consistent with this assumption.