ACI 550.6-19 Acceptance Criteria for Special Unbonded Post- Tensioned Precast Structural Walls Based on Validation Testing and Commentary.
R3.1 For a generic precast wall system to be accepted based on this document, a design procedure should be developed before validation testing. The design procedure should be based on a consideration of material properties and force transfer mechanisms, and its development will usually require preliminary, and possibly extensive, physical testing that is not part of the validation testing. Derivation of a method to calculate the stiffness of the walls, including those of the test modules, would be one outcome of the preliminary development program. Other outcomes should include methods for calculating E n , E nt , and E pr . This requirement for the development of a design proce- dure before the validation testing is consistent with experi- ence from the development of the special hybrid moment frame system that is the subject of ACI 374.1 and 550.3. The National Institute of Standards and Technology (NIST) carried out the basic development program for the innovative hybrid frame system. With financial help from a contractor, multiple small-scale hybrid frame subassemblages, designed to differing nominal engineering design values, were tested to failure along with similar specimens of monolithic construction, and a design procedure for hybrid frames developed from that information. To be able to use the hybrid frame concept in practice, ACI 374.1 was written to define the conditions under which the same R and C d factors could be used for special hybrid frames as those used for monolithic special moment frames designed to Chapter 18 of ACI 318. The contractor then used that hybrid frame system for a 39-story condominium building in San Francisco. To validate that the performance of that building would be satisfactory, subassemblages that were half-scale models of typical interior, exterior, and corner column connections were tested in accordance with the requirements of ACI 374.1. The foregoing represents the use of ACI 374.1 for prequalifying hybrid frames for a specific structure.
3.3 The design procedures shall be used to design the test modules, and shall be documented in the test report. R3.3 The justification for the small number of test modules specified in Chapter 4 is that a previously developed design procedure is being validated by the test results. Thus, the test modules for the experimental program should be designed using the procedure intended for the prototype wall system, and values for stiffness and strength should be predicted for the test modules before the validation testing is started. In practice, most building designers produce designs with more robust sections and more reinforcement than required for the design forces and code requirements. Test specimens, however, should be representative of walls that have properties closest to those satisfying exactly the nominal engineering design values rather than specimens with more robust sections and reinforcement because the authority having jurisdiction is likely to limit the allowable maximum stresses to those achieved in the testing. Because the strength and stiffness of coupled walls depend on the degree of coupling between walls, the procedure also should define how to calculate the degree of coupling.ACI 550.6 pdf download.