Ji Lu Investigation - Elastic Investigation
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The first step in the analysis of the Ji Lu Cable Stayed bridge was an elastic model.  The elastic model varied test the effects of different ground motions, boundary conditions, and structural assumptions.  The elastic model also served as baseline of study for further non-linear investigation.

Use SAP2000, each of the four nearby ground motions were analyzed.  Different combinations of different ground motions were run and their effects on the overall structural behavior of the system was considered.  The different ground motions were run in conjunction with different boundary conditions for the bridge and different structural assumptions for its members.

The critical response parameters for the study are the flexural demands at the base of the main pylon, the flexural demands in main span girder at the pylon, the displacements at the top of the bridge, and the displacements at the span ends.

The elastic study yielded the following observations:
Week axis plastic hinging was unlikely the cause of the damage at the main span pylon connection.
The transverse bending properties of the main span are very important for determining the structures dynamic characteristics.  The tower properties change overall dynamic behavior very little.
The precast wings were active in resisting bending force in compression.
Spalling above the main span was unlikely due to flexural hinging of the tower base above the deck.
The transverse mode with the most mass participation is bounded between period of 2.1 and 3.8 seconds.
Stiffening the deck in the transverse direction increased lateral displacements at the top of the bridge.
Restraining the vertical degree of freedom at the end spans reduced the longitudinal motion of the tower and consequentially effects all other response parameters..
There are coupling effects between the vertical, transverse, and longitudinal ground motions that manifest in end span displacements.  Thus, vertical restraint cannot occur at the end spans for realistic behavior.  The Gap model with a vertical release is most representative.
Elastic model predictions of the end displacement are far less than those recorded in the field.  


[Elastic Structural Models] [Ground Motion Variation] [Periods of Vibration] [Elastic Study Results]