Section 25.5.1/Lap Splice Requirements
ACI 318-19 Section 25.5 covers lap splice classifications, required lap lengths, and placement requirements for reinforcing bars in concrete members.
Contact lap splices are classified as either Class A or Class B based on the stress level in the bars and the percentage of bars spliced at the same location. Class A splices require a lap length of 1.0 times the tension development length (ld). Class B splices require 1.3 times ld. Class B is required when more than one-half of the bars are spliced within the lap length, or when the bar stress exceeds 0.5fy at the splice. In practice, most lap splices in beams, columns, and walls are Class B because designers commonly splice all bars at the same location. Lap splices must not be used for bars larger than No. 11 except in compression-only members. Bars in a lap splice must be in contact throughout the lap length or spaced no farther apart than one-fifth the lap length or 6 inches, whichever is less. Transverse reinforcement is required through the splice region per Section 10.7.6 for column splices.
Why this section exists
Reinforcing bars are manufactured in standard lengths (typically 20, 40, or 60 feet) and must be spliced where the required bar length exceeds the available bar length. The lap splice transfers tensile force from one bar to the next through the surrounding concrete via bond stress. The Class A/B system ensures longer laps where more bars are spliced at the same location because multiple splices create a higher demand on the concrete bond in that region. The prohibition on lapping bars larger than No. 11 reflects the difficulty of developing adequate bond for large bars in a practical lap length, requiring mechanical splices or welded splices for No. 14 and No. 18 bars.
What plan reviewers look for
Plan reviewers check the structural drawings for lap splice locations, lengths, and classifications. They verify the lap length matches the required class (1.0 ld for Class A, 1.3 ld for Class B) with the development length calculated per Section 25.4.2 including all applicable modification factors (bar spacing, cover, transverse reinforcement, coating, lightweight concrete). They check that lap splices in columns are located in the middle half of the column height where stresses are lowest. They verify that column tie spacing is reduced through the splice region. For walls, they check that horizontal and vertical bar splices are staggered.