Masonry Lap Lengths
Reinforcement Masonry Lap Lengths
Lap splice lengths for reinforcement on masonry projects are an important specification to consider on design drawings. When a project utilizes a typical masonry closed-end masonry block, mason contractors will need to lift blocks over the vertical bar that projects above the bottom courses to lap with vertical bars above.
Lap splice lengths for reinforcement on masonry projects are an important specification to consider on design drawings. When a project utilizes typical masonry closed-end masonry block, mason contractors will need to lift blocks over the vertical bar that projects above the bottom courses to lap with vertical bars above. The longer the lap, the more labor costs are incurred. However, designers must also ensure the proper transfer of stresses from one bar to another within the lap splice. This article hopes to clarify tips to consider while calculating lap splice (or development) lengths, and best practices for detailing lap lengths on design drawings.
According to the masonry code, TMS 402 Building Code Requirements for Masonry Structures (formerly MSJC), development length of reinforcement shall be the minimum of 12 inches or the length calculated by the following equation:
ld = length of reinforcement development or splice length
db = diameter of reinforcement bar
fy = reinforcement yield strength
� = 1.0 for bars #3-#5 – 1.3 for bars #6-#7 – 1.5 for bars #8 and larger reinforcement
K = minimum ( cover, clear spacing, 9 x db )
f’m = masonry design strength
See full article for Examples:
#1 Development Length Table – Based on TMS 402 Equation 6-1
#2 Developement Length Table – Based on TMS 402 and IBC
#3 Old method comparison for Development Lengths, Bars Centered
#4 Old method comparison for Development Lengths, Bars Each Face
#5 Masonry Wall Schedule with LAP Lengths
Confinement of Reinforcement
Lap splice lengths can be reduced if the lap splice is properly confined by transverse reinforcement per TMS 402. Providing a #3 or larger bar transverse to the lapped bars and within 8” from each end of the lap splice allows the lap splice length to be reduced by the confinement reinforcement factor per equation below. However, the lap splice length shall not be less than 36db. The clear space between the transverse bars and lapped bars shall not exceed 1.5”, and the transverse must fully develop beyond the intersection with lapped bars in grouted masonry.
Asc = area of the transverse bar, not greater than 0.35 in2
db = diameter of reinforcement bar
Additional Tips for Designers
Using a wall schedule is a good way to show that the same bar may have different lap lengths required in different situations, as is shown in WALL TYPE W1 and W2. Lap lengths do vary based on all the variables shown in the equation on page 1.
Masonry Lap Lengths increase when:
– Using lower f’m
– Increasing bar size, and/ or
– Decreasing reinforcement cover or spacing distance between reinforcement
Ways to avoid long msonry lap lengths are to use the maximum allowed f’m , use smaller bar diameters when possible, try to avoid tight bar spacings, and try to avoid small reinforcement covers (double reinforced walls) when possible.
When there is a situation where a larger lap distance is needed (larger bars are needed, small spacing, and/ or double reinforced walls are needed) as shown in WALL TYPE W4 and W5, it may be advisable to consider using a reinforcement coupler instead of lapping the reinforcement bars.
Reinforcement couplers can be a threaded splice coupler or a mechanical sleeve coupler. Couplers must be selected carefully as masonry cells are confined spaces and may not have sufficient space for all types of couplers.
Masonry Lap Lengths:
In conclusion, considering ways to reduce lap splice lengths (use of higher f’m, centering bars within cells where possible, selecting smaller bar diameters, confinement of laps, etc) will help towards constructability and labor costs, possibly offsetting any additional material costs. Implementing wall, lintel, or pier schedules specifying lap splice lengths specific to reinforcement conditions in lieu of more general statements in General Notes will also lead to more efficient masonry detailing.
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