Questions regarding code requirements for reinforcement lap splice lengths
for masonry per the 1997 UBC:
1. Section 218.104.22.168 gives splice lengths for working stress design and
Section 222.214.171.124 gives splice lengths for strength design. Why are the
splice lengths different depending on the method of design? (i.e., how does
the rebar know which design method was used?)
2. For working stress design of reinforced masonry, the development length
would be 48 bar diameters for 60 ksi steel per Section 2126.96.36.199. Section
2107.2.12 requires lap splice lengths to be increased by "not less than 50
percent of the minimum required length" if moment design tensile stress is
greater than 80 percent of the allowable steel tensile stress. Thus if the
reinforcement at mid-height of a vertically spanning wall is within 20
percent of the tensile area required for lateral wind or seismic load, must
the splice length be increased to 72 bar diameters (if spliced near
mid-height of wall)? Does one have to design for 80 percent of normal
"allowable tensile stress" to avoid an increase in splice lengths?
3. Section 2188.8.131.52 also requires a 30 percent increase in splice length
where splices are located close together (e.g., bars each face within one
grouted cell). Are the 50 percent and 30 percent increases additive if both
conditions apply at a splice location (e.g., highly stressed bars at the end
of a shear wall, placed within once cell)?
4. If a one-third increase in allowable stress is taken for wind or seismic
loads, how are the limits based on Fs applied (before or after the 1/3
increase is applied)?
William C. Sherman, PE
Camp Dresser & McKee, Inc.
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