Special hybrid moment frames composed of discretely jointed precast and post-tensioned concrete members (ACI T1.2-XX) and commentary (T1.2R-XX)

This document defines procedures that can be used to design special hybrid moment frames composed of discretely jointed precast concrete beams post-te nsioned to concrete columns. Such frames are suitable for use in regions of high seismicity or for structures assigned to satisfy high seismic perform ance or design categories. After a major seismic event, that moment frame c an be expected to exhibit minimal damage in beam-column regions and negligi ble permanent displacements. Such moment frames do not satisfy the prescrip tive requirements of Chapter 21 of ACI 318-99 for frames of monolithic cons truction. According to Section 21.2.1.5 of ACI 318-99, their acceptance req uires demonstration by experimental evidence and analysis that the frames h ave strength and toughness equal to or exceeding those provided by comparab le monolithic reinforced concrete frames that satisfy the prescriptive requ irements of Chapter 21. This document describes the procedures that the des igner must use to demonstrate through analysis that such frames have streng th and toughness at least equal to those of comparable monolithic frames. Among the subjects covered in this standard are requirements for: 1. Materials, and especially the special reinforcement that is debonded in the beam adjacent to the beam-column interface; 2. The framing system, and especially the roles of the post-tensioning tend ons, the special reinforcement, and the floor slab; and 3. The beams of the moment frame, and especially their required prestress f orce level, the contribution of the special reinforcement to their probable moment strength, and the calculation of that strength. The commentary describes some of the issues addressed by the Innovation Tas k Group and Collaborators in developing the standard. The commentary references documentary evidence, additional to the reference s of ACI T1.1R-01 and Chapter 21 of ACI 318R-99, that supports this standar d. No comparison is made, however, either within the body of this standard or in its commentary, of the performance of test modules satisfying the pre scriptive requirements of ACI 318-99 with modules that, although not satisf ying the prescriptive requirements of ACI 318-99, satisfy this standard. Su ch comparisons, both experimental and analytical, are available in the refe rences cited in the commentary.