1. TEMPLATE DESIGN © 2008
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Experimental Testing and Analysis of a Beam
Column Connection on Liquefiable Ground
Background
Earthquake-induced soil liquefaction occurs in saturated soils
where the pore spaces between grains are completely filled
with water. When an earthquake occurs, the relative strength
and stiffness of the soil decreases due to large cyclic motions
causing the grains to move readily about each other. When
this happens, the ability of the soil to support the foundations
of structures decrease.
Historical cases such as the Niigata earthquakes in 1964 and
2004 represent these performance failures of buildings due
to combined ground shaking and permanent deformations.
Research Objectives
Beam-Column System Design SAP2000 Models of System Expected Results
Structural Fuse
Future Research
Column-Frame Connection
Strain gauges are placed by the fuse to measure bending
moments, and vertical linear variable differential transformers
(LVDT’s) are placed at the tip of the beam to measure its vertical
displacement.
Once our system is fabricated and tested, we expect to get a
similar moment- rotation plot shown below. Each “loop” on
the plot represents one cycle of motion that the piston
applies. We expect there to be space between each loop on
our plot because this implies that the material is flexible and
is absorbing energy. On the contrary, if the loops were tightly
packed, the material is stiff and not absorbing as much
energy.
Beam-Column Connection and cross sectional are (left). Structural
fuse and cross sectional area (right).
Instron Universal Testing Machine (left). Complete system design
with frame (right).
Jalila Elfejji, Dr. Shideh Dashti, Dr. Abbie B. Liel, Juan Carlos Olarte
University of Wisconsin-Madison, University of Colorado at Boulder
The goal of our research is to analyze how earthquake
accelerations on liquefiable soils affect the behavior and
damage potential of buildings. In the future, we will
construct both a physical and numerical model of a 3-
story, nonlinear, moment resisting structure on soil to
evaluate its behavior on liquefied ground. However, our
focus this summer was the design and fabrication of a
prototype beam-column connection of this soon to be
built structure. This is to ensure that it will hold similar
structural characteristics to that of real buildings in terms
of stiffness, strength, ductility and degradation.
We are testing for the moment-rotation relationship at
the beam-column connection as well as the vertical
displacement at the tip of the beam. We do this by
applying a vertical cyclic load at the tip of the beam using
an Instron Universal Testing Machine. A frame was also
designed in order to keep the system securely fastened
on the machine. This is represented by the red lines on
the drawing.
The fuse is an important structural component of our
design. It localizes plastic behavior ensuring that damage
will first occur at the beams before the columns.
Parallel Axis
Theorem
Moment
of Inertia
SAP
Beam-
Column
SAP
Beam-
Column
w/Frame
OpenSees
Beam-
Column
Tip
Displacemen
t
(mm)
9.66 9.66 9.6
Tip Rotation
(rad)
0.046 0.046 0.045
Connection
Rotation
(rad)
0.013 0.013 0.012
Instrumentation
Along with a physical model, a numerical model of the
beam column system was developed. In order to model
the fuse, we used the cross sectional area of the real fuse
and found the moment of inertia using the parallel axis
theorem. We set that value equal to the moment of inertia
for a rectangular section and solved for the base. This
value is what was used as the base and height of the the
solid square cross section of the fuse on SAP2000.
Numerical Model of Beam-Column
Parallel Axis
10mm
1.6mm
d
I= 1907.55 mm^4 b=12.29 mm
Strain
Gauge
LVDT
We expect there to be yielding at the ends of
the fuse, but the fuse itself will remain intact.
Source: Soil Dynamics and Earthquake Engineering (2012)
References:
Dashti, Shideh, and Abbie B. Liel. Performance of Buildings on Liquefiable Soils: Evaluation and Mitigation : n. pag. Print.
Trombetta, N.W. , H.B Mason, Z Chen, T.C Hutchinson, J.D Bray, and B.L Kutter. "Nonlinear dynamic foundation and frame
structure response observed in geotechnical centrifuge experiment." Soil Dynamics and Earthquake Engineering 32: n. pag.
Web.
We will eventually build a
3-story structure that will
be tested on liquefiable
soil, shake table, and a
centrifuge. From there we
hope to analyze the
sliding, tilting, and lateral
drift of the structure,
acceleration and
frequency within the
ground, pore water
pressure of the soil, and
techniques to help
mitigate hazards due to
liquefaction.