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Concrete In Australia : March 2013
44 Concrete in Australia Vol 39 No 1 the capacity of the lap splice due to cyclic loading. e non- contact splices were of similar strength to the contact splice and able to develop a similar stress. is is not intuitively obvious. Intuitively, with the full perimeter of each bar within the non- contact lap length able to bond with the surrounding concrete, one would expect a higher strength than a contact splice of the same length. 5.0 CONCLUSION e test results reported here are from the first stages of an on-going test program to determine the effects of cyclic loading and sustained loading on the required development length and lapped splice length of deformed bars in tension. A close examination of the test specimens indicates that the load at which bond failure occurs depends on the spacing of primary cracks within the development or lap length and the proximity of the nearest primary crack to the critical cross- section. e average ultimate bond stress that develops at failure in a development or lap length is dependent on the number of cracks that cross the developing bar within the anchorage length. To properly assess these effects, a number of identical specimens will need to be tested to assess the variability of the results and the influence of crack location and spacing. ese tests are currently being planned. It is noted that as Ld became smaller and the number of primary cracks within the development length decreased, the average ultimate bond stress determined from the load at failure increased. is effect is not accounted for in the existing methods for predicting the required development length, including that specified in AS3600-2009. Notwithstanding the above, the factors of safety in relation to the predicted stress development obtained using the procedure in AS3600-2009 were unsatisfactorily low in several of the static load specimens, in particular DL-3, DL-8, DL-12 (all with a Ld = 20db) and DL-11 (with Ld = 15db). ACKNOWLEDGEMENT e work has been undertaken with the financial support of the Australian Research Council through an ARC Discovery grant to the first author. is support is gratefully acknowledged. REFERENCES 1. Standards Australia, "Australian Standard for Concrete Structures (AS3600-2009)", Sydney, 2009. 2. ACI Committee 318, "Building Code Requirements for Structural Concrete (ACI318M-08) and Commentary", American Concrete Institute, Farmington Hills, Michigan, 2008. 3. Eurocode 2, "Design of concrete structures Part 1-1: General rules and rules for buildings", British Standard, BS EN 1992-1-1:2004, European Committee for Standardisation, Brussels, 2004. 4. Standards Australia, "Australian Standard for Concrete Structures (AS3600-2001)", Sydney, 2001. 5. Goto Y., "Cracks formed in concrete around deformed tension bars", ACI Journal, 68(4), 1971, pp 244-251. 6. Gilbert R.I., "A review and critical comparison of the provisions for the anchorage of reinforcement in North American, European and Australian Standards", Concrete in Australia, Concrete Institute of Australia, 33(3), 2007, pp 33-40. 7. Gilbert R.I., "Lapped Splice Lengths for Tensile Reinforcing Bars in Slabs -- Experimental data", Committee document -- BD-002, Standards Australia, 14 August 2008. 8. Tepfers R (1979). "Cracking of concrete cover along anchored deformed reinforcing bars", Magazine of Concrete Research, 31(106): 3-12. 9. Tepfers R (1982). "Lapped tensile reinforcement splices", Journal of the Structural Division, ASCE, 108(1): 283-301. 10. Canbay E & Frosch RJ (2005). "Bond strength of lap- spliced bars." ACI Structural Journal, 102(4): 605-614. 11. Canbay E & Frosch RJ (2006). "Design of lap-spliced bars: Is simplification possible?", ACI Structural Journal, 103(3): 444-451. 12. Yeow, J.X. (2008). " e Development Length and Lapped Splice Length in Reinforced Concrete", Bachelor of Engineering Honours esis, University of New South Wales. 13. Gilbert, R.I. (2008). "Experimental Data -- Lapped Splice Lengths for Tensile Reinforcing Bars in Slabs", Submission to BD-002, 14th August 2008. 14. Dux, P.F. & O Moore, L.M. (2009). "Lapped Splices in Reinforced Concrete Slabs -- an Experimental Review of Current and Proposed Code Revisions", Concrete 09, Biennial Conference of the Concrete Institute of Australia, September, Sydney. At section at mid-span under maximum load, Pmax AS3600-2009 db (mm) Lap length Ls (mm) Max. Load, Pmax (kN) Crack Load, Pcr (kN) Ast (mm2) d (mm) Mmax (kNm) st (MPa) Ls (mm) Factor of safety Comments SL--1 12 10db=120 27.0 19.6 452 119 17.4 349 296 2.47 Bond failure - static load SL--2 12 15db=180 38.6 19.0 452 119 24.4 488 414 2.30 Bond failure - static load SL--3 12 20db=240 44.9 22.0 452 119 28.1 563 478 1.99 Bond failure - static load SL--4 12 15db=180 41.3 452 119 26.0 520 441 2.45 Bond failure (40,000 load cycles) SL--5 12 15db=180 37.5 16.0 452 119 23.7 475 403 2.24 Bond failure - static load SL--6 12 15db=180 38.3 452 119 24.2 484 411 2.28 Bond failure (40,000 load cycles) Specimen No. Table 4. Test results -- lapped splice length specimens.