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Concrete In Australia : December 2013
56 Concrete in Australia Vol 39 No 4 DISCUSSION PAPER reinforcement fixed diagonally through the joint area. Headed shear reinforcement is normally fixed vertically as shear reinforcement in flat-plate/flat-slab construction. This sounds like a great idea and one would really like to see some more detailed thought directed at the practicality of such designs and whether or not one could reasonably do this in just one or both vertical planes. Also some testing. It seems obvious that headed rebars have much better anchorage than normal ties particularly at a compression face and particularly in slabs just 200-250 mm thick. One would eventually like to see some fire tests to prove that diagonal ties do not require any/much cover over the head to resist loss of strength from fire particularly at a re-entrant corner. They are, after all, embedded in a much larger volume of concrete. For fire, top cover is a lesser issue than bottom cover! In 1972, the author went to Christchurch, New Zealand, for the structural design of a block development including a 12-storey building with a façade-transfer floor at one or two storeys above ground. The beam-column joints supporting the transfer floor were reinforced with 50% X-rebars running from top in the beam one side, diagonally through the joint zone to bottom of the beam on the other side. These X-rebars were in just the one façade vertical plane. The author saw this building again in April 2012 (under CERA escort) at a distance of about 10m. There was then no visible damage despite the earthquake in February 2011. Figure 2: Reinforcement of joint zone perhaps using headed shear reinforcement as X-bars. Figure 1: Panel-zone beam/column joint under major horizontal load: wind, earthquake or explosion. 49-56 - Discussion.indd 56 49-56 - Discussion.indd 56 25/11/13 4:15 PM 25/11/13 4:15 PM