Report No.: CCEER-03-3

Title: Seismic Performance of RC Bridge Frames with Architectural-Flared Columns

Authors: Hisham Nada, David Sanders, and M. Saiidi.

Date: January 2003

Sponsoring Agency: California Department of Transportation (Caltrans))

Performing Organization:
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557


Design of flared columns to resist earthquake loading is a complicated issue due to the changing cross section along the column length. It was believed that if the flares had low longitudinal and transverse reinforcement ratios, they would fail during earthquakes. Therefore, the column core would be the element remaining to resist the earthquake. Past earthquakes have shown that flared columns are susceptible to premature shear failures. In the 1994 Northridge Earthquake, shear failures were caused by plastic hinge formation at the base of the flare and a subsequent increase in the level of column shear demand above design levels. This study presents an experimental and analytical study that is examining new details for flared columns, base hinges and joints. The purpose is to maintain the aesthetic value of the flare without impacting the system performance. The primary feature is a gap at the top of the column and the amount of transverse flare reinforcement. Four bents were tested using the shake table to examine dynamic effects as well as column and beam interaction. The test specimens had different amounts of confining reinforcement in the flare. An analytical non-linear finite element analysis study was conducted using the DIANA program to explore different parameters effects. A strut-and-tie model was created based on the finite element analysis that is capable of predicting the yielding, maximum load carrying capacity of system and the stresses in different parts of the structure.