PT Anchor Tests (University of Minnesota, Duluth)

  • Monostrand Post-Tensioning Anchor Evaluation Tests (March 13, 2012 - November 01, 2013)
    • The monostrand post-tensioning (PT) anchorage tests will focus on key variables related to self-centering wall systems: post-yield cyclic loading, PT splices, anchorage capacity after a seismic event, and durability details. Tests will be conducted prior to the shake table and wall-floor sub studies to finalize the test details. The PT anchorage system will also be investigated post-test, if needed, to analyse any unexpected phenomena observed in the large-scale tests. Two manufacturers of 7-wire monostrand anchorages will be tested under monotonic and cyclic loading procedures. Standard monostrand tests provide a baseline to compare results of previous research and to evaluate effects of post-yield cyclic loading and splices. Splices are an important part of the testing program because they are needed to tie the wall into the foundation and to extend the tendons in tall multistory structures. Splices will be investigated extensively in the monostrand tests as they are also significantly more complex in multi-strand tendons. To investigate the remaining capacity of a tendon after the first major seismic event, samples from the tendons and anchorages used in the shake table tests will be tested to failure simulating loading from an aftershock or another major seismic event. Durability is a key component to any post-tensioned system. The most widely used internal unbonded PT tendon system in practice is a greased/sheathed monostrand system (PT coating with extruded plastic sheath). Unbonded internal multi-strand systems are much less common. For the systems described in this project, details will be developed for a greased system applicable to multi-strand PT tendons in walls.
  • Multi-strand Post-Tensioning Anchor Evaluation Tests (August 20, 2012 - December 07, 2012)
    • The multi-strand post-tensioning (PT) anchorage tests will focus on key variables related to self-centering wall systems: post-yield cyclic loading, anchorage capacity after a seismic event, rotation between multi-strand anchorages, and durability details. Tests will be conducted prior to the shake table and wall-floor sub assemblage studies to finalize the test details. The PT anchorage system will also be investigated post-test, if needed, to analyse any unexpected phenomena observed in the large-scale tests. Two manufacturers of 7-wire multi-strand anchorages will be tested under monotonic and cyclic loading procedures. Multi-strand anchorages have unique challenges in quantifying their response in a self-centering wall system. Even in a straight tendon, strands will tend to twist along the length between the dead and live end anchorages. This rotation can have an effect on the behaviour of the tendon under large deformations and has the potential to reduce the failure load of the tendon. Additionally, previous research has indicated that stress concentrations at the nose of the wedge within anchorages can reduce the failure load of the tendon and greatly reduce ultimate strains. This behaviour will be verified and addressed through extensive testing of a modified wedge geometry that balances the normal force on the strand more evenly over the length of the wedge, thus reducing the stress concentration at the nose. Durability is a key component to any post-tensioned system. The most widely used internal unbonded PT tendon system in practice is a greased/sheathed monostrand system (PT coating with extruded plastic sheath). Unbonded internal multi-strand systems are much less common. For the systems described in this project, details will be developed for a greased system applicable to multi-strand PT tendons in walls.

Single Rocking Column (Iowa State University)

  • Free Vibration Testing of Rocking Column (April 02, 2012 - July 24, 2012)
    • The procedure for this experiment consists of constructing a single reinforced concrete column, and offsetting the column by an initial angular displacement, and measuring the free-rocking motion of the column once released. The test set-up will have a mass that will be able to be set at different positions on the rocking column. This will result in changes to the dynamic properties of the system, and changes to the time history response. By changing the dynamic properties of the system, correlations between what affects the response of a rocking system can be drawn based upon which parameters where changed and by how much. Also, another set of tests will be conducted using externally mounted #5 steel bars as hysteretic dampers allowing about 14% energy dissipation in the system. The goals of these experiments will be to gain a better understanding of the energy dissipation mechanisms operating within rocking structures, and to be able to accurately predict the free rocking motion of a controlled rocking structure. Although these experiments will aid in better predicting the time history of controlled rocking structures, it will also be a valuable trial run for much more expensive shake table testing. The specimen dimensions and testing protocol for these tests have been made to match that of a scaled down version of the PreWEC system that will be tested dynamically in this project.

Shake Table Test (NEES@UNR)

  • Shake Table Testing of Precast Rocking Wall with Side column_1 (PreWEC-s1) (June 27, 2013 - June 28, 2013)
    • One of the essential considerations in seismic design of structures is to provide life safety. While the focus on life safety is to protect the buildings, occupants, substantial economic losses ensue when an earthquake causes structural and non-structural damage and permanent deformations. Beginning with the PREcast Seismic Structural Systems (PRESSS) program, one of the concepts that have been studied by several researchers is the use of seismic resilient systems to improve the earthquake performance of buildings beyond life safety, by mitigating structural damage. Rocking precast concrete wall is one of the practical examples originated from this concept. These walls designed with unbonded post-tensioning as primary reinforcement, which helps the system to self-center while minimizing structural damage during major seismic events. Main source of energy dissipation in Single Rocking Walls (SRW) generated from impact of the rocking body on the footing. However, in order to come up with supplemental damping for such systems, a PreWEC concept previously established. PreWEC systems are basically single rocking walls connected to side/ end steel columns using special energy dissipating oval “O” shaped mild steel connectors. These external dampers are welded to steel columns from one side and to wall steel embedment plates from the other side. While subjected to lateral loads, special, replaceable connectors placed between the wall and columns experience relative vertical displacements due to the gap opening at the base of the wall system. This results in connectors enduring large inelastic deformations and providing the necessary energy dissipation for the system. Precast Rocking Wall with Side column_1 (PreWEC-s1) consists of a concrete precast wall connected to a footing block with (5) 0.6" diameter PT strands. In this test unit, 8 “O” shaped steel connectors used to dissipate energy. These external energy dissipaters are welded to the steel side columns hinged to the base from one side and to the wall steel embedment plates from the other side.
  • Shake Table Testing of Precast Rocking Wall with Side column_2 (PreWEC-s2) (July 29, 2013 - July 30, 2013)
    • One of the essential considerations in seismic design of structures is to provide life safety. While the focus on life safety is to protect the buildings, occupants, substantial economic losses ensue when an earthquake causes structural and non-structural damage and permanent deformations. Beginning with the PREcast Seismic Structural Systems (PRESSS) program, one of the concepts that have been studied by several researchers is the use of seismic resilient systems to improve the earthquake performance of buildings beyond life safety, by mitigating structural damage. Rocking precast concrete wall is one of the practical examples originated from this concept. These walls designed with unbonded post-tensioning as primary reinforcement, which helps the system to self-center while minimizing structural damage during major seismic events. Main source of energy dissipation in Single Rocking Walls (SRW) generated from impact of the rocking body on the footing. However, in order to come up with supplemental damping for such systems, a PreWEC concept previously established. PreWEC systems are basically single rocking walls connected to side/ end steel columns using special energy dissipating oval O shaped mild steel connectors. These external dampers are welded to steel columns from one side and to wall steel embedment plates from the other side. While subjected to lateral loads, special, replaceable connectors placed between the wall and columns experience relative vertical displacements due to the gap opening at the base of the wall system. This results in connectors enduring large inelastic deformations and providing the necessary energy dissipation for the system. Precast Rocking Wall with Side column_2 (PreWEC-s2) consists of a concrete precast wall connected to a footing block with (3) 0.6inch diameter PT strands. In this test unit, 12 O shaped steel connectors used to dissipate energy. These external energy dissipaters are welded to the steel side columns hinged to the base from one side and to the wall steel embedment plates from the other side, as shown in the drawings.
  • Shake Table Testing of Single Rocking Wall_1 (SRW1) (July 27, 2012 - July 27, 2012)
    • One of the essential considerations in seismic design of structures is to provide life safety. While the focus on life safety is to protect the buildings, occupants, substantial economic losses ensue when an earthquake causes structural and non-structural damage and permanent deformations. Beginning with the PREcast Seismic Structural Systems (PRESSS) program, one of the concepts that have been studied by several researchers is the use of seismic resilient systems to improve the earthquake performance of buildings beyond life safety, by mitigating structural damage. Rocking precast concrete wall is one of the practical examples originated from this concept. These walls designed with unbonded post-tensioning as primary reinforcement, which helps the system to self-center while minimizing structural damage during major seismic events. Main source of energy dissipation in Single Rocking Walls (SRW) generated from impact of the rocking body on the footing. However, in order to come up with supplemental damping for such systems, a PreWEC concept previously established. PreWEC systems are basically single rocking walls connected to side/ end steel columns using special energy dissipating oval O shaped mild steel connectors. These external dampers are welded to steel columns from one side and to wall steel embedment plates from the other side. While subjected to lateral loads, special, replaceable connectors placed between the wall and columns experience relative vertical displacements due to the gap opening at the base of the wall system. This results in connectors enduring large inelastic deformations and providing the necessary energy dissipation for the system. Single Rocking Wall-1 (SRW1) consists of a concrete precast wall connected to a footing block with (4) 0.5inch diameter PT strands.
  • Shake Table Testing of Single Rocking Wall_2 (SRW2) (August 09, 2012 - August 09, 2012)
    • One of the essential considerations in seismic design of structures is to provide life safety. While the focus on life safety is to protect the buildings, occupants, substantial economic losses ensue when an earthquake causes structural and non-structural damage and permanent deformations. Beginning with the PREcast Seismic Structural Systems (PRESSS) program, one of the concepts that have been studied by several researchers is the use of seismic resilient systems to improve the earthquake performance of buildings beyond life safety, by mitigating structural damage. Rocking precast concrete wall is one of the practical examples originated from this concept. These walls designed with unbonded post-tensioning as primary reinforcement, which helps the system to self-center while minimizing structural damage during major seismic events. Main source of energy dissipation in Single Rocking Walls (SRW) generated from impact of the rocking body on the footing. However, in order to come up with supplemental damping for such systems, a PreWEC concept previously established. PreWEC systems are basically single rocking walls connected to side/ end steel columns using special energy dissipating oval O shaped mild steel connectors. These external dampers are welded to steel columns from one side and to wall steel embedment plates from the other side. While subjected to lateral loads, special, replaceable connectors placed between the wall and columns experience relative vertical displacements due to the gap opening at the base of the wall system. This results in connectors enduring large inelastic deformations and providing the necessary energy dissipation for the system. Single Rocking Wall-2 (SRW2) consists of a concrete precast wall connected to a footing block with (6) 0.5 inch diameter PT strands.
  • Shake Table Testing of Single Rocking Wall_3 (SRW3) (June 17, 2013 - June 19, 2013)
    • One of the essential considerations in seismic design of structures is to provide life safety. While the focus on life safety is to protect the buildings, occupants, substantial economic losses ensue when an earthquake causes structural and non-structural damage and permanent deformations. Beginning with the PREcast Seismic Structural Systems (PRESSS) program, one of the concepts that have been studied by several researchers is the use of seismic resilient systems to improve the earthquake performance of buildings beyond life safety, by mitigating structural damage. Rocking precast concrete wall is one of the practical examples originated from this concept. These walls designed with unbonded post-tensioning as primary reinforcement, which helps the system to self-centre while minimizing structural damage during major seismic events. Main source of energy dissipation in Single Rocking Walls (SRW) generated from impact of the rocking body on the footing. However, in order to come up with supplemental damping for such systems, a PreWEC concept previously established. PreWEC systems are basically single rocking walls connected to side/ end steel columns using special energy dissipating oval O shaped mild steel connectors. These external dampers are welded to steel columns from one side and to wall steel embedment plates from the other side. While subjected to lateral loads, special, replaceable connectors placed between the wall and columns experience relative vertical displacements due to the gap opening at the base of the wall system. This results in connectors enduring large inelastic deformations and providing the necessary energy dissipation for the system. Single Rocking Wall-3 (SRW3) consists of a concrete precast wall connected to a footing block with (6) 0.6 inch diameter PT strands.
  • Shake Table Testing of Single Rocking Wall_4 (SRW4) (July 18, 2013 - July 19, 2013)
    • One of the essential considerations in seismic design of structures is to provide life safety. While the focus on life safety is to protect the buildings, occupants, substantial economic losses ensue when an earthquake causes structural and non-structural damage and permanent deformations. Beginning with the PREcast Seismic Structural Systems (PRESSS) program, one of the concepts that have been studied by several researchers is the use of seismic resilient systems to improve the earthquake performance of buildings beyond life safety, by mitigating structural damage. Rocking precast concrete wall is one of the practical examples originated from this concept. These walls designed with unbonded post-tensioning as primary reinforcement, which helps the system to self-center while minimizing structural damage during major seismic events. Main source of energy dissipation in Single Rocking Walls (SRW) generated from impact of the rocking body on the footing. However, in order to come up with supplemental damping for such systems, a PreWEC concept previously established. PreWEC systems are basically single rocking walls connected to side/ end steel columns using special energy dissipating oval O shaped mild steel connectors. These external dampers are welded to steel columns from one side and to wall steel embedment plates from the other side. While subjected to lateral loads, special, replaceable connectors placed between the wall and columns experience relative vertical displacements due to the gap opening at the base of the wall system. This results in connectors enduring large inelastic deformations and providing the necessary energy dissipation for the system. Single Rocking Wall-4 (SRW4) consists of a concrete precast wall connected to a footing block with (6) 0.6 inch diameter PT strands. Height of Link beam decreased to 11.5 from the wall base for this test.

System Tests (NEES@UMN)

  • Wall-Floor Sub assemblage Test at NEES (MAST) (March 14, 2012 to Present)
    • Subassemblage tests will be conducted at NEES@UMN (MAST) to investigate the wall-floor connection concepts and the interaction of the rocking wall with the surrounding building system. The quasistatic nature of MAST prevents investigation of dynamic energy losses associated with wall rocking. Tests will be conducted on 1/3 scale portions of the prototype structures featuring PreWEC systems attached to 5.5 x 5.5m floor diaphragms in plan. Pinned-ended steel columns with appropriate stiffness will provide vertical direction restraint to simulate gravity columns supporting the boundaries of the floor diaphragm. The MAST crosshead will provide the boundary condition at the top of the wall and as such will be programmed to simulate the effects of the missing floors of the prototype structure above the subassemblage including the gravity and lateral loads. Ancillary actuators will be used to apply additional lateral loads to the modeled floor slab to pseudo-statically simulate the inertial effects to be transferred from the floor to the wall through the wall-to-floor connections. The tests may be performed using a combination of force-controlled and displacement-controlled reverse cyclic loads as appropriate to simulate the seismic effects. Lateral drifts of up to at least 3.5% will be applied to the PreWEC systems. In total, three subassemblage tests will be conducted to assess the behavior of the different floorwall connections and system interaction, including the one with the RC floor. In each test, the PreWEC and floor will be extensively instrumented to observe the specimen behavior including at least 60 strain gauges, 50 displacement devices, and several load cells. The MAST’s Nikon Metrology K600 Coordinate Measuring Machine will be deployed to characterize the strain variation in critical regions of the wall-floor system by monitoring LEDs mounted on short anchors embedded in the wall panel and floor system. Test results will be used to evaluate the performance of the PreWEC and floor systems and the analytical models.