and Design of Cast-in-Place Anchors
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|Description: Anchors installed in plastic hinge zones|
The well-established design procedures for headed anchors, such as those stipulated in
318-11 and in CEB design guidelines, do not apply to the anchors
installed in concrete that likely be substantially damaged during an
earthquake. Plastic hing zones of concrete elements such as beams,
columns, walls and slabs may develop high levels of cracking and
cruching under seicmic loading. It is recommended that the anchor
reinforcement must be
provided for the anchors installed in plastic hinge zones.
| The tests in Phase II and Phase III of the NEES-Anchor project
indicated that the key role of reinforcement, in addition to carrying
the forces from the anchors, is to protect concrete around the anchors
from splitting, breaking out, and crushing. This understanding has led
to alternative designs and detailing for the anchor reinforcement.
The focus of the Phase V tests are to 1) identify the key parameters
for the desired performance of anchors in plastic hinge zones; 2)
observe the beahavior of anchors in plastic hinge zones with local confinement; and 3) verify the implemented anchor reinforcement detailing.|
|Phase III Experimental Program:|
The test setup and the instrumentation plan is shown below. Seven strain gages were installed on the longitudinal bars of the columns, especially near the test anchor. These strain gages will define the actual plastic hinge zones developed in the column. Column displacements are measured using string pots while the anchor displacements are measured using spring-loaded LVDT's.
|Finite Element Analyses:|
Finite element analyses have been conducted to verify the loading protocols for the columns. The column will be subjected to reversed cyclic displacement at 0.2 in. (elastic behavior), 0.4 in. (first yielding), 0.8 in., 1.2 in., 1.6 in., 2.4 in., and 3.2 in. For the test of Specimen T1, the test anchor will be subjected to monotonic tension till failure after the column loading is completed. Depending upon the observed behavior, the test will be repeated using Specimen T2, and the test anchor in Specimen T3 will be subjected to cyclic loading. If concrete near the test anchors is damaged significantly such that the full anchor steel capacity is not developed, the rest two specimens will be tested with the columns to be subjected to lower levels of cyclic displacements.
T1 (accidental high-speed loading)
(Front face) 02/08/12
T2 (monotonic tension, at zero position)
(Side face, anchor on the left) 02/23/12
T3 (cyclic tension, at -8Dy)
(Side face, anchor on the left) 03/03/12
S1 (monotonic shear, at zero position)
(Side face, back anchor broken) 03/10/12
Anchor shaft was exposed after the 1.5-in. cover spalled, leading to combined bending and shear on the anchor.
S2 (cyclic shear, with column loaidng)
(Side face, front anchor broken) 03/15/12
Again, anchor shaft was exposed after the cover spalled, leading to combined bending and shear on the anchor.
S3 (with FRP wrapping)
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