Design Memorandum

TO:                  All Design Section Staff

FROM:            Bijan Khaleghi
DATE:             July 15, 2009
SUBJECT:       Skin Reinforcement Requirement

This design memorandum supersedes design memorandum issued on February 10, 2009 on skin reinforcement requirement for flexural members.

The requirement of the LRFD Section “Control of Cracking by Distribution of Reinforcement” for skin reinforcement shall be modified as follows:

If the depth of non-prestressed or partially prestressed members, h, exceeds 3.0 ft., longitudinal skin reinforcement shall be uniformly distributed along both side faces of component for a distance dt/2 from the tension face.  It shall be permitted to include such reinforcement in strength computations if a strain compatibility analysis is made to determine stress in the individual bars or strands. Equation shall be revised as follows:


dt = distance from extreme compression fiber to centroid of extreme tension steel (in.)

The total area of longitudinal skin reinforcement (per face) need not exceed one-fourth of the required flexural tensile reinforcement As+Aps.  The maximum spacing of skin reinforcement shall not exceed either dt/6 or 12 in.


This revision is consistent with other revisions recently made to Articles and The February 10, 2009 memorandum on skin reinforcement requirement was based on the AASHTO T-10 early approval of the ACI requirement for skin reinforcement. This was not approved for the 2009 final ballot items. The February 10, 2009 memorandum is withdrawn since the ACI requirement for skin reinforcement is less conservative than the current AASHTO LRFD requirement.

If you have any questions regarding these issues, please contact Bijan Khaleghi at 705-7181.

cc:   Mohammad Sheikhizadeh, Bridge Construction - 47354

       F. Posner, Bridge and Structures – 47340

Note:  For a PDF of this design memo, click here.