1. 1
Experimental Testing and Analysis of the Seismic Response of an
Inelastic Structure on Liquefiable Ground
Jalila Elfejji
Undergraduate Researcher
Shideh Dashti
Assistant Professor
Abbie B. Liel
Assistant Professor
Juan Carlos Olarte
Graduate Student Researcher
University of Colorado Boulder
August 5, 2014

2. 2
Abstract
Earthquake-induced soil liquefaction is the process in which the relative strength and
stiffness of a granular soil decreases due to large cyclic earthquake motions. When this
happens, the ability of the soil to support the foundations of structures decreases, leading
to detrimental damage on surrounding infrastructures such as foundation settlement,
tilting, and damaging of underground facilities. The objective of this research is to
analyze how ground accelerations within liquefiable soils affect the performance and
damage potential of inelastic structures. In order to achieve this goal, a physical and
numerical model of a 3-story, nonlinear, moment-resisting frame is being developed in
order to evaluate its behavior on liquefied ground. Geotechnical centrifuge and fuse
calibration tests of our frame is being conducted to give us a clear understanding of the
relationship between ground shaking, liquefaction, building displacements, and building
damage. Prior to the complex centrifuge tests of the entire soil structure system, we
conduct scaled component tests of a beam-column connection at 1g with no centrifuge
acceleration. These tests will help ensure that our scaled frame holds similar structural
characteristics to those of real buildings, especially in terms of strength, stiffness,
degradation, and ductility. We are also developing numerical models of the 3-story frame
and beam-column connection in SAP2000® and OpenSees, to properly validate the
numerical models under 1-g and fixed-base conditions before adding the complexities of
soil behavior. Our research will be used in future centrifuge tests of liquefaction impacts
on soil and structures in order to further develop reliable and performance-based
mitigation techniques of this important hazard.
Introduction
1.) Liquefaction
Liquefaction occurs in saturated soils where the pore spaces between grains are
completely filled with water (Johansson 2014). When an earthquake occurs, the strong
shaking motions causes the grains to move readily about each other, allowing the soil to
behave like a liquid. Historical cases such as the Niigata earthquake (1964) and Fukuoka
earthquake (1966) represent these performance failures of buildings due to combined
ground shaking and permanent deformations (Kerciku 2008). Other cases of damage such
as the Adapazari earthquake (1999) led to excessive foundation settlement, tilting and
sliding, as shown in Figures 1 and 2 (Bird 2004). However, other forms of potential
damage could include vertical gaps between pile-supported structures damaging piping,
sewage systems, underground facilities, and uplifting of parking lots (Tokimatsu 2012).
Figure 2 Foundation Settlement due to liquefaction
(Bird 2004)
Figure 1 Tilting due to liqufaction
(Bird 2004)

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These events emphasize how important it is to understand the process of liquefaction in
order to successfully mitigate its risks and occurrences in urban areas within the U.S and
on a global scale.
Geotechnical centrifuge testing is an effective tool to evaluate the response of
scaled models of soil-structure under increased gravity and hence, realistic confining
pressures. In addition, a 1-D servo-hydraulic shaking table can apply earthquake motions
to the model specimen while spinning in the centrifuge. Centrifuge tests will be carried
out on liquefiable soil with and without the mitigation strategies in order to evaluate the
effectiveness of liquefaction remediation strategies in the context of building
performance.
Prior to the complex centrifuge tests of the entire soil structure system, the scaled
model structures need to be designed, analyzed, fabricated, and tested extensively, which
was the focus of our research this summer. Due to their critical role in the performance of
structures, particular attention was paid to the design and fabrication of a beam-column
connection of the soon to be built 3-story structure, in order to calibrate numerical
simulations of nonlinear buildings. After studying the response of this connection, the
entire building will be constructed and tested alone, under fixed-base conditions, initially
without soil. Then the response of the integrated system will be studied in future phases
of the research.
Testing Objectives
The focus of our 10-week research is to analyze and test the design of one beam-column
connection of the future 3-story structure (Figure 3). By doing so, we hope to understand
the moment-rotation behavior under cyclic loading, which is an important aspect of
building response during earthquakes. Also, the testing of this connection will ensure that
it will hold similar structural characteristics to that of real buildings in terms of strength,
stiffness, ductility, and degradation. This structure will be used in future centrifuge tests
of liquefaction impact on soil and structures and the mitigation of this important hazard.
Figure 3 Beam Column Connection from 3-story
structure

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Methods
1.) Design of Beam-Column Connection
By testing a column-beam connection, we expect to see nonlinear behavior based on
moment vs. rotation curves due to the fact it absorbs a lot of energy, implying significant
deformation than in nonlinear curves. Both the beam and column are made out of hollow
square steel tubing, with the beam welded to a small plate, which will be bolted to the
column (Figure 4). The dimensions of the beam and column will be half of its true length
on our 3-story structure in order for us to replicate the important loading conditions.
2.) Structural Fuse
An important component of our design is a fuse placed at the end of the beam to ensure
its nonlinear properties, which are important for understanding damage in earthquakes
(Figure 4). The fuse localizes plastic behavior at the end of the beam ensuring that
damage will first occur at the beam before the column. Because columns transfer gravity
loads, they are essentially more important than beams, and its failure could be fatal in real
building scenarios.
Figure 4 Beam-Column Connection and cross sectional are (left). Structural fuse and cross sectional area (right).
3.) Design of Frame
We will be applying a series of sine waves with different load amplitudes at the tip of the
beam using an Instron Universal Testing Machine. Figure 5 shows the loading protocol
that is very similar to what we will be using for our experiment. A frame was designed
and fabricated in order to securely fasten the beam-column structure to the machine. We
had to keep in mind that the piston applying the load must be aligned with the tip of the
beam and in order to secure the middle frame to the machine, we can remove the bottom
piston and use the base plate to bolt the frame to the machine. Figure 6 shows the Instron
FUSE

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Universal Testing Machine and what the complete beam-column system will look like
once fabricated, with red and diagonal lines representing the frame.
Figure 6 Instron Universal Testing Machine (left). Complete system design with frame (right).
The frame was broken up into four parts: top frame (Part 1), vertical frame (Part 2),
middle frame (Part 3), and bottom frame (Part 4). 4 wholes were drilled across the width
of frame parts 1, 2, and 4 in order to adjust its height if necessary.
(Figures 7-10) show the dimensions of each frame section.
Figure 5 SAC Loading Protocol (Krawinkler 2000)

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Figure 7 Top Frame (Part 1)
Figure 9 Middle Frame (Part 3) with bolted connection
Figure 10 Bottom Frame (Part 4)
Figure 8 Vertical Frame (Part 2)

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4.) Design of Column-Frame Connection
Just as important as the beam-connection is the connection between the column and the
frame. Our connection design includes a column that will be pinned at both the top and
bottom, attached to parts 1 and 3 of the frame. We chose pinned connections because the
dimensions of the beam and column are half the length of what it will be on our 3-story
structure, making the bending moment zero at the middle of beam and column under
earthquake loading. Part of the column end will be shaved down and removed in order to
create two “semi-circular teeth” in which a small steel cube will fit snug and bolted
between the teeth then welded on the plate and bolted to the frame (Figure 11). This
allows the column to rotate freely in one direction without creating friction with the plate.
Figure 11 Column-Frame
Connection
5.) SAP2000® Models
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 was
used as the base and height of the solid square cross section for the fuse on SAP2000®
(Figure 12).
Figure 12 SAP2000 Beam –Column System
Parallel Axis
Theorem
Moment of
Inertia
p
Parall 10
1.6
d
ParpParallel Axis
d

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A model of the beam-column system with the frame was also developed as well
as another beam-column system on OpenSees. The results for the tip displacement, tip
rotation, and connection rotation are very close to each other for all 3 models ensuring
that they are accurate in design (Figures 13-14).
Figure 14 Displacement and Rotation Results
6.) Instrumentation
Strain Gauges and LVDT’s
Strain-gauge configurations are based on the Wheatstone bridge, which have four
resistive legs that act as sensing elements (See Figure 15). When a physical phenomena
such as change in strain is applied to a specimen, the resistance of the sensing elements
changes in the bridge, and depending on the number of active legs on the bridge, there
can be three different configurations of strain-gauge bridges: quarter bridge, half-bridge,
and full-bridge (Sciammarella 2012). For the purpose of testing our model connection,
strain gauges will be placed on the top and bottom of the fuses to capture non-linear post
yield strain in this location (Figure 16). We can then calculate the rotation at the fuse
using information from other calibration tests.
Along with strain gauges, we will place a vertical LVDT (Linear Variable
Differential Transformer) at the tip of the beam in order to measure its displacement up to
(Figure 16). An LVDT is an electromechanical transformer that converts rectilinear
motion of an object to a corresponding electrical signal, measuring displacements
anywhere from a few millimeters to a couple inches (Macro Sensors 2014).
SAP
Beam-
Column
SAP
Beam-
Column
w/Frame
OpenSees
Beam-
Column
Tip
Displacement
(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
Figure 15 Location of Strain Gauges and LVDT’s
Figure 13 Beam- Column System with Frame

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Expected Data
Once our system is fabricated and tested, we expect to get a similar moment- rotation plot
shown in Figure 17 which was a previous experiment conducted in San Francisco with a
similar experimental set-up as ours. 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 responding in a nonlinear manner and is damping
energy. On the contrary, if the loops were tightly packed with one another, the material
being used is not as stiff therefore not damping as much energy as we want. Along with
the moment-rotation plot, we expect our fuse to behave similar to that in Figure 17, with
yielding at the ends, but the fuse itself still remains intact.
Figure 17 Soil Dynamics and Earthquake Engineering (2012)
Figure 16 Strain Gauge (Sciammarella 2012)
Strain Gauge
LVDT
ffdssdf

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Future Directions
As part of our future research, our team will build a 3-story, nonlinear, moment resisting
structure that will be tested on liquefiable soil, a 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, as well as develop new
techniques to help mitigate hazards due to liquefaction. Figure 18 shows these possible
test set-ups.
Figure 18 Drawings of Proposed Centrifuge Tests

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References
Johansson, J. (2014, June 10). Soil Liquefaction. Retrieved from
http://www.ce.washington.edu/~liquefaction/html/main.html
Kerciku, A. A. (2008). FAILURE OF SHOWA BRIDGE DURING THE 1964 NIIGATA
. The 14th World Conference on Earthquake Engineering, 8.
Shideh Dashti, A. L. (2014, June 9). Performance of Buildings on Liquefiable Soils:
Evaluation and Mitigation. Retrieved from www.nsf.gov:
http://www.nsf.gov/awardsearch/showAward?AWD_ID=1362696&HistoricalAw
ards=false
Tokimatsu, K. (2012). LIQUEFACTION-INDUCED DAMADE TO BUILDINGS IN
URAYASU CITYDURING THE 2011 TOHOKU PACIFIC EATHQUAKE .
International Symposium on Engineering Lessons Learned from the 2011 Great
East Japan Earthquake, 10.
Sciammarella, C. A., & Sciammarella, F. M. (2012). Strain Gage Rosettes: Selection,
Application and Data Reduction. Experimental Mechanics of Solids (). : .
Chang J. Barbera; Raychowdhury, Prishati; Thomas, Jeremy (April 22, 2006). Centrifuge
Testing of Combined Frame-Wall-Foundation Structural Systems. Retrieved from
https://www.dropbox.com/sh/vlw5uudlpul9ywn/AAAuxSIWLanKdzWScNsDAS
5qa/Chang%20et%20al%202006.pdf
Performance of Buildings on Liquefiable Soils: Evaluation and Mitigation. Retrieved
from file:///C:/Users/Manu/Downloads/Liquef-
Proposal%20Description_vf%20(1).pdf
Trombetta, N.W.; Mason, H.B.; Chen, Z; Kutter, B.L. (2013). Soil Dynamics and
Earthquake Engineering. Retrieved from Trombetta2013_SDEE%20(3).pdf
Macro Sensors (2014). What is an LVDT. Retrieved from
http://www.macrosensors.com/lvdt_tutorial.html