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Concrete In Australia : March 2013
42 Concrete in Australia Vol 39 No 1 Table 2. Details of lapped splice length specimens. Specimen No: Effective depth d (mm) Tensile steel area Ast (mm2) Lapped splice length Ls (mm) Clear spacing sL (mm) Loading type fc (MPa) fct.f (MPa) Ec (MPa) fsy (MPa) fsu (MPa) SL--1 119 452 10db = 120 0 Static 38.0 3.5 30,500 561 721 SL--2 119 452 15db = 180 0 Static 38.0 3.5 30,500 561 721 SL--3 119 452 20db = 240 0 Static 38.0 3.5 30,500 561 721 SL--4 119 452 15db = 180 0 Cyclic 38.0 3.5 30,500 561 721 SL--5 119 452 15db = 180 28 Static 38.0 3.5 30,500 561 721 SL--6 119 452 15db = 180 28 Cyclic 38.0 3.5 30,500 561 721 lapped splice is Ls. For this initial series of lapped splice tests, both static and cyclic loading regimes were adopted. Mid-span deflection together with the location and width of primary cracks were measured throughout the test. In addition to the two loading regimes, static and cyclic, the variables considered were the lap length Ls and the clear spacing between the bars being spliced together, sL. Details of the six lapped splice specimens are given in Table 2. ey represent the first six of a planned total of thirty-six splice specimens, in which lapped splices in beams (with and without transverse reinforcement) and slabs will be studied, both under short-term static loads, after 50,000 cycles of service loads and after prolonged periods subjected to sustained loads and shrinkage. e first series of sustained load tests is currently underway, but the results are not yet available. When interpreting the results of the static and cyclic load tests, cracked section analysis can be readily undertaken to check the stresses that develop in the lapped splice at all levels of loading up to and including anchorage failure. 3.2 Test results Development length specimens: e maximum load Pmax measured in each specimen during the test is given in Table 3, together with the corresponding maximum stress that was developed in the monitored bars at the critical section (i.e. the maximum stress in the bars with anchorage length Ld ). For the static load tests, the load required to produce the first crack Pcr is also recorded in Table 3. Specimen DL-14 with a development length of just 60 mm (5db ) suffered bond failure immediately at first cracking, so it was not possible to determine the steel stress corresponding to the maximum average ultimate bond stress. Of the cyclic load tests, specimens DL-4, DL-13 and DL-17 were all subjected to in excess of 50,000 cycles of load, before being loaded monotonically to failure. Each cyclic load specimen was cycled between 10% and 50% of the peak static load determined from the identical static load specimens DL-2, DL-11 and DL-16, respectively. Specimen DL-9 suffered a sudden bond failure after 25,080 cycles of load (cycling between 10% and 60% of the peak static load determined from DL-7). e anchorage length Ld required by AS3600-2009 to develop the failure stress σst is also shown Table 3, together with the factor of safety associated with the code approach (taken as the ratio of Ld in the specimen to Ld required by the Standard). When considering the minimum development lengths specified in codes of practice, it is generally agreed that a factor of safety in the range 1.5 to 2.5 is reasonable and appropriate. For the static load tests, the factors of safety obtained from AS3600-2009 are generally in that range (except for DL-11 and DL-12 marginally under and DL-6 somewhat higher). With the exception of DL- 4, all the cyclic load tests are below the acceptable range. For three of the cyclically loaded specimens, the steel stress at failure of the anchorage was below that obtained in the corresponding statically loaded specimen with factors of safety reducing to a low of 1.30 for Specimen DL-13. Figure 4 illustrates selected data from Table 3. e results from Figure 4 indicate that the effect of concrete cover on the development length is perhaps not as significant as is indicated in the current code approaches, with statistically little difference in the steel stress at failure between the specimens with 25 mm cover and those with 40 mm cover. e factors of safety obtained from AS3600-2009 therefore are consistently lower for the specimens with 40 mm cover than those with 25 mm cover. e maximum load Pmax measured in each specimen during the test is given in Table 4, together with the corresponding maximum stress that was developed in the bars of the lapped splice at mid-span. Each of the cyclic load test specimens was subjected to 40,000 cycles of load, before being loaded monotonically to failure. Each specimen, SL-4 and SL-6, was first loaded beyond cracking and then cycled between 10% and 50% of the peak static load determined from the identical static load specimens SL-2 and SL-5, respectively. e lap splice length Ls required by AS3600-2009 to develop the failure stress σst is also shown Table 4, together with the factor of safety associated with the code approach (taken as the ratio of Ls in the specimen to Ls required by the Standard). When considering the minimum lapped splice lengths specified in codes of practice, it is generally agreed that a factor of safety in the range 1.5 to 2.5 is reasonable and appropriate. For the contact lapped splices (SL-1 to SL-4, with sL = 0), the factors of safety obtained from AS3600-2009 are all in that range, with no reduction in the factor being observed in the specimen subjected to cyclic loading. e factors of safety obtained using AS3600-2009 for this test program are in agreement with and support the conclusions reached in earlier Australian test programs (11 and 12) and support the recent amendments to the Australian Standard. For the non-contact lapped splices (SL-5 and SL-6, with sL = 28 mm), the factors of safety obtained from AS3600-2009 are 2.24 and 2.28, respectively. Again, there was no reduction in