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Date: 23 November 2017
Two-Column Bent Seismic Performance  


Topic Name: Two-Column Bent Seismic Performance
Category: Civil Engineering
    
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Research persons: David Sanders, Associate Professor of Civil Engineering & M. Saiid Saiidi, Professor of Civil Engineering

Location: Bridge Research and Information ,Civil Engineering ,
Department/258 University of Nevada, Reno Reno, NV 89557
Tel: (775) 784-6664 ,Fax: (775) 784-1390, United States

Details

The design of structural bridge elements like columns, beam-column joints,
and cap beams has changed tremendously over the past 30 years. Many experimental
tests have been done in order to determine the behavior of bridge bents under
seismic loading. Most of those tests were performed under static-cyclic loading,
whereas only a few of those tests were dynamic to simulate real-time earthquake
effects. Based on the literature review, most studies have focused on
retrofitting older columns and/or single columns versus new design criteria on
systems. Therefore, this study will be investigating two-column bridge bents
under dynamically loading by testing them with real-time earthquakes on a shake
table. The main research objective is to investigate the seismic performance of
two-column bridge bents with different aspect ratios using current Caltrans
design criteria. There are 3 bents to be tested. The three specimens are
identical except for the aspect ratios, which are 2.5, 4.5, and 6.64. The first
test will be of the bent with a column aspect ratio of 2.5. The bents will be
tested by using increasing levels of the Sylmar earthquake motion until failure
occurs.
Test Model
Based on the 0.3-scale model developed from a previous study, three specimens
were designed using current CALTRANS specifications and recommendations. The
current design included column confinement, ductility, column shear capacity,
longitudinal and transverse reinforcement of cap beams, and the beam-column
joints. The new design configuration for the specimens is shown in Fig. (1).
Strain gages were attached to the longitudinal and transverse reinforcement in
both columns and beams to determine when yielding occurs and strain profiles
across the section. Novotechniks (displacement transducers) were installed in
the expected plastic hinge zones and at the beam-column joints in order to
record curvature and shear deformations, which will be used to obtain the
concrete strains at critical sections. In addition, accelerometers and
potentiometers were added to record frame displacement and acceleration during
testing. A total of 150 data acquisition channels will be used for the tests.
Data will be sampled at 160 samples per second.

Loading System
One of the features of the present study is to load each specimen with mass
(lead bricks) on the top and along side the cap beam to simulate the inertia
mass and the axial compression force. The amount of lead weight was calculated
based on the scale ratio between the model and prototype. To produce realistic
stresses in the system, the weight causes an axial load in each column of 0.05
f'cAg . Ag is the gross area of each column. Steel buckets were designed to
contain the lead blocks. Fig. shows the lead buckets placed on the specimen
from the previous study. The specimen with the aspect ratio of 6.64 will look
the same as this.
 


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