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Concrete In Australia : December 2013
Concrete in Australia Vol 39 No 4 53 as slabs and some band-beams. The author has addressed some cases with low (but not zero) shear reinforcement (Gurley, 2011b.) Diagonal concrete struts do indeed come into play when the content of shear reinforcement is low. The economics of the method remain to be established clearly, though one would expect better economy from a method that is “straight-forward and logical” (Boyce) as compared to the present empirical main code method: Vu = Vuc + Vus. The economy of this author’s method will improve if one accepts that φ = 0.80 for shear reinforcement, putting it on par with the strut-and-tie method as suggested by Boyce. The author accepts Boyce’s comments in his last paragraph. If the paper is rewritten it will be modified accordingly. Reference Gurley, C.R ., 2011b. Upper-bound yield-line rigid-plastic plane stress analysis of core coupling-beams in tall buildings. ICE London Magazine of Concrete Research 62(4): 265–273, doi: 10.168/macr.9 .00199. Response to Anthony Bayadi The discussion from Bayadi raises issues as to the syllabus documents for civil/structural courses taught by TAFEs in NSW and interstate. TAFEs are not free to teach whatever they like. There are about 10 federally-funded “skills councils” writing or approving syllabus documents for training courses in Australia. Most of these syllabus documents can be downloaded from training.gov.au if one has the correct eight to 10 character code. The skills council that includes civil engineering is the SkillsDMC. The DMC stands for drilling, mining and civil, although the SkillsDMC nowhere mentions the term civil engineering. Nevertheless, this is the only civil engineering course approved by the Australian Government and eligible for a significant federal subsidy. Within the SkillsDMC system, the code for civil concrete structures is RIICWD533A. 2nd and 3rd characters are I for ink. There has also been a TAFESA course in structural engineering written by an Adelaide-based committee mostly consisting of structural engineers and drafters and including several national firms. This course has been taught by TAFEs in Adelaide and in Sydney (Ultimo), Canberra, RMIT and Tasmania. This course has not had federal registration but our understanding is that it will be taken over by SkillsDMC soon. Consult Australia has been negotiating with SkillsDMC initially through the Consult Australia Adelaide office, but now negotiates through Jonathon Russell at its Sydney head office. These two courses are the basic sources for what should be taught in TAFE civil/structural engineering courses anywhere in Australia, but there is always some room for interpretation. The author would always support the proposition that the first responsibility of TAFEs is to teaching drafting, meaning CAD. The syllabus documents do include subjects, usually with names more than five words long, which would once have been called statics or simple equilibrium. TAFE civil/structural engineering students learn early on to construct shear-force and bending-moment diagrams for simply-supported spans and cantilevers. The difficult question is: How far does one go towards providing education for the breed once known as design drafters? These are people with an intelligent appreciation of their work sufficient enough to make occasional estimates in order to progress the job until a design engineer has caught up and checked it out. One suggests that, for concrete structures, this does include an intelligent understanding of L/d ratios including usual values (not mentioned in AS3600) and how to do single-cycle iteration to a somewhat more accurate value. It also includes how to calculate usual minimum reinforcement content for slabs, beams and columns. In addition, it is necessary to know the extent of bottom rebar and top rebar and why they are as they are. This may often permit drafters to finish some drawings subject to a design-check that leads to modifications that are fairly minor. The existing courses seem to go further and, in terms of reinforced concrete design require: (1) design for moment – meaning how many main reinforcing bars go exactly where and why and (2) design for shear – meaning how many ties/stirrups and where they go. This brings us to the present paper: Question 1: Should TAFE students be taught about design of shear reinforcement in beams at all? Strictly a yes or no question. Question 2: Should TAFE courses be limited to minimum shear rebar at maximum spacing as described in the paper? Question 3: If one wants to go beyond that then the options are: Q3.1 The empirical method (meaning no underlying theory) AS3600 c8.2 .2(a): Vu = Vuc + Vus first adopted by an ACI- ASCE Joint Committee in the late 1950s, which addressed a then immediate problem in terms of hanger collapses in the US, under snow load as one remembers. That joint committee only ever thought that this was to be temporary. Why has it survived, at least in Australia, 60 years later? David Herbert agrees that the AS3600 method Vu = Vuc + Vus is past its use-by date. Q3.2 The lower-bound S&T method introduced in Stuttgart and Zurich from about 1984 but, perhaps, requiring specialised finite element software. See AS3600 sections 7 and 12. See also Beletich, Hymas, Reid and Uno 2013, the usual text-book at TAFE Sydney Tech Ultimo. Q3.3 The present “exact” alternative provided in the author’s paper. See AS3600 c6.7 . This method is basically a Danish yield-line method (for plane-stress) to which one has added some bells and whistles – in particular the notion that a partial anchorage force can be used with dogleg hinges. One did suggest the term dogleg some decades ago. The statics is not much, if at all, ahead of what students do in earlier classes. TAFE students, and of course, university students of civil/ structural engineering will have a long, perhaps 40-50 year, career ahead of them. Do we want to limit our teaching to the current edition of AS3600 knowing that the code will 49-56 - Discussion.indd 53 49-56 - Discussion.indd 53 26/11/13 12:42 PM 26/11/13 12:42 PM