1. Experimental Testing and
Analysis of a Beam-Column
Connection on Liquefiable Soil
Jalila Elfejji, Dr. Shideh Dashti, Dr. Abbie B. Liel, Juan Carlos Olarte
University of Colorado at Boulder
University of Wisconsin-Madison
July 26, 2014
8. SAP2000 Beam-Column Connection with Fuse
I= 1907.55 mm^4 b=12.29 mm
Parallel Axis
10mm
1.6mm
d
Parallel Axis
Theorem
Moment
of Inertia
9. Deformation Results of Beam-Column System on
SAP2000 and OpenSees
SAP
Beam-
Column
SAP
Beam-
Column
w/Frame
OpenSees
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
Liquefaction occurs in saturated soils where the pore spaces between the grains are completely filled with water
When an earthquake occurs, the strong shaking causes the grains to move apart from each other causing the soil to behave like a liquid
An example of this are sand boils, where the grain move upwards and outwards until it reaches the surface
When liquefaction occurs the relative strength and stiffness of the soil decreases, making It hard for the soil to support structures
An example of damage due to liquefaction is in Niigata Japan (1964 and 2004), where an earthquake hit the city, and most damage was due to liquefaction
Tilting, sliding, and foundation settlement, uplifting of roads, and damage to underground facilities
Research Objectives
Goal of our research is to analyze how earthquake accelerations in liquefiable soil affect the behavior and damage potential of structures
Eventually build a 3-story structure to test on liquefiable soil and then on a centrifuge
Focus of this summer is the design and fabrication of beam column-connection
This will ensure that our 3 –story structure will hold similar structural characteristics to those of real buildings, especially in terms of strength, stiffness, degradation, and ductility
What we are testing for is the total deformation of the connection: moment-rotation relationship at the connection and tip displacement
We will do this by applying a cyclic vertical load at the tip of the beam using an Instron Universal Testing Machine
One of the challenges of our design was securing the beam and column to the machine so that that the piston applying the load would lie perfectly aligned with the tip of the beam
Built a frame to secure this (red)
Beam and Column are made out of square hollow steel tubing (why?)
Important structural component of connection in the fuse which is a reduced cross sectional area of the beam
Fuse localizes plastic behavior at the end of beams ensuring that damage will occur first to the beams before the columns
Columns transfer gravity loads so its damage could be fatal
Just as important as the beam column connection is the connection between the column and the frame
We want the connection to be pinned, or only rotate in one direction.
We do this in order replicate this moment and shear force diagram, that can only happen with it pinned at both ends
Along with a physical model, I developed a numerical model of our system on SAP of the beam column system and fuse
Challenge with this was modeling the cross section of the fuse
SAP only has solid cross sections with no missing area as options
Used parallel axis theorem to find the moment of inertia of the real cross section and set that equal to the moment of inertia for a rectangular section
b and h are same (square section)
Even though different cross section, same moment of inertia, so similar results
Another SAP model of beam column system with the frame
Frame should not effect deformation results
Comparisons of tip displacement, tip rotation, connection rotation values of the beam column system alone, system with the frame, and beam column system on OpenSees which was modeled by my mentor Juan
Talk about Instrumentation
Strain gauges placed at fuse location to measure bending moments in the XZ plane of the beam column connection
LVDT’s at the tip of the beam in order to measure vertical displacement (why do we do this?)
Once system is fabricated and tested we expect to get a similar moment rotation relationship plot on the left
This was a study done by which is similar to ours
Expect loops on plot to be more spread apart that means material is very flexible and absorbs more NRG, on the contrary where loops are more tightly packed means less flexible material and doesn't’t absorb as much NRG
Earthquakes are a release of NRG, idea of building is to absorb NRG, concrete is more stiff, our steel has more damping effects
Expect yielding at the ends of the fuse
Build a 3-story steel structure, and place it on a shaking table, then on liquefiable soil, and than in a centrifuge at 70g
Structure: tilt, settlement, inner story drift, lateral displacement
Soil: pore water pressure, acceleration, settlement under the foundation
Ground Motion: Frequemcy, accelration, and duration of motion
Mitigation: what mechanism to use to reduce these risks (densification and drainage)
