Concrete

The fragmentize breadths predicted by the diametrical labels exit been cypher for a range of change parameters alter hear payoff mark (Figure 9) Varying get through (Figure 10) Varying parapet pose with constant financial backing field of ope symmetryn and idiom. (Figure 1 1) Varying boundaryinate spacing with constant advantage surface ara and maximum air to AS 3600. Figure 12) bulletin board system 5400 results have been plot using a Ms / MGM ratio of 0. 1 and 1. tout ensemble results have used long bourne measure outs where available. Larger discrepancys of these interprets may be found on the Powering presentation associated with this paper. The pursuance observations can be made from the graph results The bulletin board system 5400 results using the two unlike appoint ratios gave substantially different results, with the spunkyer(pre titulary) ratio giving increased crevice widths. The notice board 8110 results were both roughly centrally placed between the two notice board 5400 results, or close to the lower values.The Recoded 2 results were usually reasonably close to the incriminate of the separate results. The CUBE-Flip-1990 results were consistently the lowest for high marque stresses and high cover hybridize values. Results with varying spacing were close to Recoded 2 results. The IAC 318 results were consistently the highest, world close to and sparingly higher than the pep pill bound bbs 5400 values. both dissolve widths increased approximately linearly with increase steel stress Crack widths increased with increase cover, with Recoded 2 reaching a constant value at 70 mm cover, and the CUBE-PIP code at 35 mm cover.The other codes continued to increase more than linearly up to 100 mm cover. All codes predicted increasing press stud width with increasing break spacing and constant reinforcement ara steel stress. Figure 9 Varying emphasis reinforcement stress Figure 10 Varying cover Figure 11 Va rying bar spacing with constant reinforcement ara and stress Figure 12 Varying bar spacing with constant reinforcement argona and maximum stress to AS 3600.When the steel stress was adjusted to the maximum allowable at a lower place AS 3600 (I. E. minify for increasing bar spacing and increasing bar diameter) the predicted piece of cake widths were reasonably fork over in the spacing range 50 to 200 mm, then tended to reduce with greater spacing. DEFLECTION The main differences in shape up to the counting of deflections be summarized low Australian and American codes are based on the Brannon comparability, using a uniform fair effective stiffness value.Australian codes allow for overtaking of accent rigidifying through a reduction of the tick offing import link to the free concrete shrinking. Allowance for shrinkage bend in the Australian codes is simplify and will underestimate curvature in symmetrically reinforced regions. British codes allow only a low tensio n value for check overed sections, which is further trim back for long term deflections European codes dupe an intermediate approach for batty sections, tit an allowance for loss of tension change.British and European code provisions for shrinkage curvature are essentially the same impelling stiffness, calculate according to AS 3600, Recoded 2, electronic bulletin board 5400, and BBS 8110, and with no tension stiffen, is plotted against bending result for the same concrete section used in the crack width analysis. Figure 13 shows results with no shrinkage, and Figure 14 with a shrinkage of 300 Microscopic. RESEARCH ABOUT THE METHODS apply IN DIFFERENCE CONCRETE STANDARDS AS 3600 limits the maximum reinforcement stress under serviceability clogs to a truism value dependent on either the bar diameter or the bar spacing, whichever feasts the greater stress.AS 5100 has the same limits, with an additional requisite to check for lower limits under indissoluble loads for elements in exposure sorts 82, C or U. Recoded 2 limits stresses in essentially the same way, except that the limits are presented as maximum bar spacing or diameter for a specified stress, kind of than vice versa. The Recoded 2 limits are related to 3 different values of nominal crack width, 0. 2 mm, 0. 3 mm or 0. 4 mm, under pseudo-static loading. The relevant crack Edith depends on the exposure classification and type of member.Code Provisions for Crack comprehensiveness Limits As well as stress limits, Recoded 2 has detailed provisions for the calculation of design crack widths, which are summarized under The base formula for crack width crack spacing x (mean steel strain mean concrete strain) makes no allowance for variation in crack width between the level of the reinforcement and the surface of the concrete, however the crack spacing is mainly related to the cover depth, and the crack width is directly proportional to crack spacing, so the depth of cover has a signifi cant effect on crack widths.The expression for Seems ECMA limits the effect of tension stiffening to 40% of the steel strain. For long term effects the tension stiffening coefficient is minify by 1/3, from 0. 6 to 0. 4. The British concrete design codes specify a design crack width at the surface of the concrete as follows The basic approach is standardised to Recoded 2, except that the crack width is projected from the reinforcement level to the concrete surface. The main differences between BBS 5400 and BBS 8110 are BBS 5400 includes a factor to reduce the effect of tension stiffening, depending on the ratio of live load fleck to dead load moment (Ms / MGM).The effect of this is to reduce tension stiffening effects to zero for a load ratio of 1 or greater. The tension stiffening coefficients are differently formulated. The IAC requirements are based on stress limits derived from the Surgery-Lutz equation The IAC 318 equation makes no allowance for tension stiffening, and pred icts crack width at the upper bound of those studied in this paper. Results are usually similar to those from the BBS 5400 equation using a Ms / MGM ratio of 1 .AS 3600, AS 5100, and IAC 318 AS 3600 and AS 5100 provisions for simplified calculation of deflections are identical other than a typographic error in AS 5100), and are both based on the Brannon equation, which is in any case used in IAC 318. The equation in IAC 318 is differently formulated, but will give identical results for the same faulting moment and section stiffness values. The AS 3600 version of the equation is shown below left is calculated for the maximum moment section, and applied along the full length of the member beingness analyses.The calculation of the cracking moment in the Australian codes (but not IAC 318) includes an allowance for the shrinkage induced ductile stress in the unchecked section, which contributes to loss of tension stiffening AS 3600 and AS 5100 provide a factor KC , applied to the cal culated deflection, to account for the additional deflection receivable creep and shrinkage KC = 2- 1. 2(ASS / East) brand that for a symmetrically reinforced section KC reduces to the minimum value of 0. , being the effect of creep deflection alone. 6. 4. 2 OBSESS,BBS 8110 Deflections in BBS 5400 and BBS 8110 are calculated from integration of section curvatures. The cracking moment and curvature of cracked sections allows for a short term concrete tensile stress of 1 Amp, reducing to 0. 5 Amp in the long term. shoplifting curvatures in BBS 8110 are find from the free shrinkage strain, and the first moment of area of the reinforcement about the cracked or unchecked section, as appropriate.BBS 5400 uses a similar approach, but tabulates factors based on the compression and tension reinforcement ratios. 6. 4. 3 Recoded 2 and CUBE-PIP 1990 (MAC 90) The European codes also provide for calculation of deflections by integration of section curvatures, but provide a different expression for the stiffness of cracked sections shrinkage curvatures are assessed using a similar method to that given in BBS 8110