Manual for Design and Detailings of Reinforced Concrete to Code of ...

Version 2.3 May 2008span > 10 m except for cantilever as similar to BS8110 is also included.Flanged Beam One or two-waySupport condition Rectangular Beam b w /b < 0.3 spanning solidslabCantilever 7 5.5 7Simply supported 20 16 20Continuous 26 21 26End span 23 18.5 23 (2)Note :1. The values given have been chosen to be generally conservative and calculation mayfrequently show shallower sections are possible;2. The value of 23 is appropriate for two-way spanning slab if it is continuous over one long side;3. For two-way spanning slabs the check should be carried out on the basis of the shorter span.Table 3.1 – effective span / depth ratio(vi) Maximum spacing between bars in tension near surface, by Cl. 9.2.1.4 ofthe Code, should be such that the clear spacing between bar is limited by70000βbclear spacing ≤ ≤ 300 mm where βbis the ratio of momentfyredistribution. Or alternatively, clear spacing ≤47000 ≤ 300 mm. So the70000βb 70000×1simplest rule is = = 152 mm when using high yieldfy460bars and under no moment redistribution.f s(vii) Concrete covers to reinforcements (Cl. 4.2.4 and Cl. 4.3 of the Code)Cl. 4.2.4 of the Code indicates the nominal cover required in accordancewith Exposure conditions. However, we can, as far as our buildingstructures are concerned, roughly adopt condition 1 (Mild) for thestructures in the interior of our buildings (except for bathrooms andkitchens which should be condition 2), and to adopt condition 2 for theexternal structures. Nevertheless, the “Code of Practice for Fire ResistingConstruction 1996” should also be checked for different fire resistanceperiods (FRP). So, taking into account our current practice of usingconcrete not inferior than grade 30 and maximum aggregate sizes notexceeding 20 mm, we may generally adopt the provision in our DSEGManual (DSEDG-104 Table 1) with updating by the Code except forcompartment of 4 hours FRP. The recommended covers are summarizedin the following table :15