drp181
Structural
- Aug 22, 2003
- 8
When detailing columns as "members not designated as part of the lateral-force-resisting system" per ACI 318-02 (or -05) Section 21.11, the two possibilities are: (1) the forces under the design displacements are less than the member strengths, and (2) the forces under design displacements exceed the member strengths, or are not checked. The first category is covered in Section 21.11.2, and the second in 21.11.3.
Section 21.11.2.2 requires members to conform to Section 21.4.3, which in turn requires lap splices in the middle half of the column clear height (21.4.3.2). However, Section 21.11.3 does NOT appear to require following 21.4.3.2, which would mean that lap splices would NOT be required to be in the middle half of the clear height. Generally, the requirements of 21.11.3 are more restrictive, since it allows the designer to not check the columns under the design displacements. For lap splices, though, it appears to be less restrictive.
Is this a correct interpretation of the code? Are lap splice requirements loosened because of the increased tie requirements? Or is the intent of the code to require mid-height splices for all columns in high seismic zones?
Adding to the confusion, the 2003 IBC in Section 1908.1.6 adds the following revision to ACI 21.11.2.2: "Lap splices of longitudinal reinforcement in such members need not satisfy Section 21.4.3.2 in structures where the seismic-force-resisting system does not include special moment frames." This would reduce the above difficulties to only those buildings in high seismic zones with special moment frames, and only when looking at columns not part of the moment frames. However, the inconsistency would still seem to be present in this case, where the designer could skip the design displacement check and get around the mid-height splice requirement.
Thanks in advance for any light you can shed on this issue.
Section 21.11.2.2 requires members to conform to Section 21.4.3, which in turn requires lap splices in the middle half of the column clear height (21.4.3.2). However, Section 21.11.3 does NOT appear to require following 21.4.3.2, which would mean that lap splices would NOT be required to be in the middle half of the clear height. Generally, the requirements of 21.11.3 are more restrictive, since it allows the designer to not check the columns under the design displacements. For lap splices, though, it appears to be less restrictive.
Is this a correct interpretation of the code? Are lap splice requirements loosened because of the increased tie requirements? Or is the intent of the code to require mid-height splices for all columns in high seismic zones?
Adding to the confusion, the 2003 IBC in Section 1908.1.6 adds the following revision to ACI 21.11.2.2: "Lap splices of longitudinal reinforcement in such members need not satisfy Section 21.4.3.2 in structures where the seismic-force-resisting system does not include special moment frames." This would reduce the above difficulties to only those buildings in high seismic zones with special moment frames, and only when looking at columns not part of the moment frames. However, the inconsistency would still seem to be present in this case, where the designer could skip the design displacement check and get around the mid-height splice requirement.
Thanks in advance for any light you can shed on this issue.
