experimental evidence needed to achieve the code-validation of the hybrid
precast wall system as “special” reinforced concrete (RC) shear walls is
specified in ACI ITG T5.1. Among the subjects covered in ITG T5.1 are requirements
for the design of test specimens and their configurations, as well as requirements
for testing, assessing, and reporting satisfactory performance. Draft design
guidelines (pending experimental validation) can be found in ACI ITG T5.2.
The project will capitalize on the research outcomes by specifically addressing each of the mandatory acceptance criteria in ITG T5.1 using test specimens designed based on ITG T5.2. The final project deliverables will demonstrate the performance of hybrid wall structures in response to these mandatory criteria. The following four major research tasks will be conducted by the project:
1. Design and Fabricate Test Specimens: Six 0.4-scale walls will be tested. The main parameters will be: (1) relative amounts of mild steel and PT steel; (2) wall length; (3) presence of panel openings; and (4) wall detailing at base. One test specimen will be a fully emulative wall with no PT steel to provide benchmark comparisons. The specimen properties will be determined from full-scale prototype walls designed based on ACI ITG T5.2. A pre-determined length of the mild steel bars at the wall base will be unbonded by wrapping inside plastic sheathing to prevent low-cycle fatigue fracture of the steel. Closed steel hoops will be used to confine the concrete at the base. The use of steel “armor” plates at the wall base corners will be considered. High-performance fiber-reinforced grout will be used at the wall joints. As required by ACI ITG T5.1, unless the full-scale prototype wall is comprised of a single panel, each test specimen will contain a minimum of two wall panels – the bottom panel will model the critical base panel and the top panel will model all of the upper story panels.
2. Conduct Validation Experiments: The walls will be tested under tributary gravity loads and reversed-cyclic lateral loads based on ACI ITG T5.1. The lateral load will be applied at the resultant of the assumed 1st mode lateral force distribution. Owing to the “damage-free” characteristics of the system, each specimen may be subjected to multiple tests. The walls will ultimately be tested to failure (within equipment limits). The behavior of the walls will be monitored using an array of sensors to develop the performance data needed for ITG T5.1 validation.
3. Conduct Pre- and Post-Test Analyses and Validate Analytical Models: Pre-test analyses of the walls will be conducted to establish the expected specimen behavior. Post-test correlation of the experimental and analytical results will lead to validated analytical models for the system.
4. Assess Specimen Behavior and Validate Design Procedure: Task 4 will assess the seismic behavior of the specimens to validate the classification of the proposed system as special RC walls based on ACI 318 and ITG T5.1. The test results will be compared with design expectations (e.g., lateral force and displacement capacities) to validate the design methods, leading to a validated Design Procedure Document. The project will also develop linear-elastic/effective-stiffness models and simplified nonlinear models that can be used as design tools.
Codification and Utilization Procedure
Upon successful completion of the research, the following four-step Codification and Utilization Procedure will be used for the implementation and transfer of the results into practice:
1. The development of a white paper summarizing the results and the code changes needed to implement the technology;
2. The involvement in the research of a design/build contractor or the equivalent combination of a designer, precast producer, and contractor interested in implementing the methodology;
3. The submission of any necessary codification proposals to the ASCE/SEI 7 Code Committee; and
4. The submission of any necessary codification proposals to the ACI 318, 374, and 550 Committees.
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