Transcript Collaborative Research: Behavior of Braced Steel Frames With

NEES Equipment Site
University of Minnesota
http://nees.umn.edu
Multi-Axial Subassemblage Testing (MAST)
• 6 Degree-of-Freedom (DOF) Control Technology
• Ability to test large-scale structural subassemblages
• Teleoperation of hydraulic equipment
• Real-time data and visual information sharing via
telepresence
MAST 6 Degree-of-Freedom Testing Machine
The University of Minnesota Multi-Axial Subassemblage Testing (MAST) system enables
multi-axial quasi-static cyclic tests of large-scale structural subassemblages, including
portions of beam-column frame systems, walls, and bridge piers. Six-degree-of-freedom
control technology, employed by the MAST system, advances the current state of
technology in which boundary effects are often reduced to simple uniaxial loading
configurations because of difficulties encountered in imposing multiple-degree-of-freedom
states of deformation and load using conventional structural testing means. The system is
unique in size and scope and greatly expands the large-scale earthquake
experimentation capabilities both nationally and internationally.
Researchers examined the damage of a 8.3m
(27'-3") tall tee-shaped concrete wall that was
subjected to a series of multidirectional
deformations at the MAST facility.
As shown in the photograph above, the MAST system employs a stiff steel crosshead in
the shape of a cruciform, which is controlled with six-degree-of-freedom control
technology. Four ± 1470 kN (± 330 kip) vertical actuators, capable of applying a total force
of ± 5870 kN (± 1320 kips) with strokes of ± 510 mm (± 20 in.) mount between the
crosshead and the strong floor. Two sets of actuator pairs with strokes of ± 400 mm (± 16
in.), provide lateral loads up to ± 3910 kN (± 880 kips) in the horizontal orthogonal
directions. The actuator pairs are secured to an L-shaped strong wall with universal type
swivels. The vertical clear distance permits specimens up to 8.8 m (28 ft. 9 in) in height to
be tested. The horizontal clear distance between the vertical actuators can accommodate
specimens up to 6.1 m (20 ft.) in length in the two primary orthogonal directions. Larger
specimens may be oriented along the diagonal directions.
The stiff steel crosshead and six-degree-of-freedom control technology enable control of
the position of a plane in space. This feature makes it possible to apply pure planar
translations, as well as the possibility of applying gradients to simulate overturning (e.g.,
axial load gradient in the columns of a multi-bay frame, or wall rocking). Any degree-offreedom may be programmed in either displacement control or load control, and degreesof-freedom may be constrained in a master-slave relation to be a linear combination of
the values of other degrees-of-freedom. As an example, using the mixed-mode control
capabilities of the MAST system, it is possible to program any lateral displacement
history, and at the same time specify overturning moment as a constant times the lateral
force, while simultaneously maintaining an independent history of axial load on the test
specimen. The system is also equipped with four ± 980 kN (± 220 kip) ancillary actuators
with strokes of ± 250 mm (± 10 in.), which can be used to apply lateral loads at
intermediate story levels, gravity loads, or simulated specimen boundary conditions. An
example of a test incorporating the ancillary actuators to simulate a simple boundary
condition for a slab-column connection test is shown in the figure to the right.
In addition to quasi-static ramp and hold testing protocols, the MAST laboratory also
supports hybrid testing using either a local or remote (user provided) computation engine
for local or distributed testing. The equipment is capable of supporting Simcor and
OpenFresco protocols.
The MAST laboratory has a wide array of instruments including LVDTs, string
potentiometers, tiltmeters, and load cells. These instruments are seamlessly integrated
into MAST’s data acquisition system with a variety of custom designed quick connect
boxes. The data acquisition system allows for any combination up to 248 ¼-bridge strain
sensors and 172 voltage (@±10V) channels to be sampled simultaneously at a rate of up
to 10Hz.
Testing of a Slab-Column Connection
MAST also offers the use of a Metris (formerly Krypton) K600 optical dynamic measuring
machine. The K600 system is a CCD camera-based system that is used to monitor the
position of infrared LEDs in 3D space. Where traditional instruments are typically limited
to one or two measurable degrees of freedom, the advantage of the K600 system is the
ability to measure 3D positions of single points on a specimen and rotations of planes on
a specimen. MAST has 41 LEDs which can be run simultaneously @ 100Hz.
In conjunction with the contributions of NEESit Cyberinfrastructure software, the
teleobservation/teleoperation infrastructure provides relevant information needed for both
monitoring and interpretation of experiments. As such, this facility incorporates real-time
teleobservation of all visual monitoring information (video feeds) during an experimental
run and real-time transmittal of all acquired sensor data. Full real-time teleoperation of 10
video cameras and 8 still image cameras, and limited real-time teleoperation of hydraulic
equipment is available.
The MAST facility fits into an integrated data-centric approach for experimentation,
computation, theory, databases, and model-based simulation facilitated through the
NEEScentral collaboratory. One of the most powerful features of this integrated approach
to model-based simulation is an accumulated database of experimental results, which
features the ability to “replay” tests and to couple experimental responses with computer
simulations. The project team for the operational phase of the facility includes Carol
Shield (PI), Catherine French, Paul Bergson, Drew Daugherty, Angela Kingsley, Jon
Messier, and Jane Zirbes, (Dept. of Civil Eng.), and Douglas Ernie (Dept. of Electrical and
Computer Eng.)
MAST Control Room – supports teleparticipation
Carol Shield
Principal Investigator
This equipment site receives operational support from the National Science Foundation under Cooperative Agreement No. CMS-0402490. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not
necessarily reflect the view of the National Science Foundation.