The writing of the code is done by members of various association (ACI, NCMA, BIA, TMS, etc,) and professionals that write numerous. The ACI code is published and distributed by ACI. That is the reason for historic testing records to develop the design standards since masonry has always been a wall-based strength of actual samples instead of individual materials. In high rise buildings, many engineers place a maximum strength limit of the grout supplied to maintain compatibility and reaction of all materials. The ACI 530 "Code and Specifications" and most masonry texts explain the process in detail. The main difference is the high slump for 100% contact and suction of the water out of the mix as necessary. During this period and the final curing the CMUs absorb the excess water and provide a moist curing environment. The grouting rate is specified and final consolidation is required. In a CMU unit grout meeting ASTM requirements must be 8"to 11"slump with fine aggregate. There is a subsrantial difference between actual bonding between CMUs and concrete. RE: CMU Lap Splice vs ACI 318 Lap Splice MrHershey (Structural) 21 Oct 14 21:57 You're using 50% more of the steel strength, so you need 50% more lap. (12-1) of ACI 318-05 multiplied by the 1.3 splice factor: If you plug db=0.625 inches, fy=60 ksi, f'c=f'm=4 ksi, and the maximum spacing/cover amount allowed by each code (cb+Ktr/db)=2.5 for ACI 318, K=5db for TMS 402) into the equations for both concrete and CMU, you'll get the following:Įq. So you're using ~50% more of the rebar strength in concrete design than in masonry design. Equivalent to CMU would be to use Omega of 1.67 with ASD combinations, which reduces your 60 ksi to 36 ksi. Concrete lets you go to 60 ksi, but then goes Phi factor of 0.9, plus LRFD load factors. Typically CMU reinforcing is limited to 24 ksi stress. RE: CMU Lap Splice vs ACI 318 Lap Splice JedClampett (Structural) 21 Oct 14 18:34Īgree with Jed. Has anyone else noticed this before? Does anyone know why this is the case? I'm having a hard time convincing myself that coarse grout and medium weight CMU can develop and splice a bar in a shorter distance than concrete. I understand 12.2.3 can decrease the lap splice length in concrete based on confinement of transverse reinforcement, but TMS 402 also has a provision to reduce the lap splice length. For CMU (f'm=2000 psi) the lap splice comes out to about 20 inches but for concrete (f'c=4000 psi) it comes out to 31 inches using the provisions of 12.2.2. When I detailed it, then double checked it, I noticed that for a #5 bar, the tension lap splice length for CMU is less than the Class B tension lap splice length for the concrete. I had #5's at 24 inches in the CMU and #5's at 12 inches centered in the stem of the retaining wall, so I extended alternating bars from the stem to lap splice the CMU vertical reinforcement. The test results were also compared with the predictions by the ACI 408R 03 and Eurocode 2 provisions.I recently designed a retaining wall that had a CMU screen wall above it for IBC 2012. For D22 and D32 bars, the use of either transverse reinforcement or thick concrete cover was recommended to develop the specified yield strength of 600 MPa (87 ksi). The results showed that the reinforcing bar splices gave a satisfactory performance for all D13 (diameter = 13 mm ) bar splices. The average bar stresses resulting from this test were compared with the predictions by the ACI 318 provisions. Most of the specimens were designed to satisfy the Class B splice length specified by ACI 318. Concrete strengths ranged from 24.7 to 55.3 MPa (3582 to 8021 psi). The test parameters were the reinforcing bar diameter, concrete cover thickness, concrete strength, and stirrup spacing. Twelve simply supported beams and slabs with reinforcing bar splices were tested under monotonic loading. Keywords: bond Class B splice high-strength steel splice lengthĪn experimental study was performed to evaluate the applicability of ACI 318 to the Class B splice of 600 MPa (87 ksi) reinforcing bars. Title: Experimental Study for Class B Lap Splice of 600 MPa (87 ksi) Reinforcing BarsĪuthor(s): Won-Seok Choi, Hong-Gun Park, Lan Chung, and Jin-Keun Kim
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