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ACI detailing and design manual


Hamza Ahmad
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  • 5 months later...

Aoa dear experienced fellows.

Can anyone let me know how can we do the detailing of a 15"x30" rcc column with 4.5 in2 of Ast. Do we have to use ACI SECTION 7.7 Equations for the purpose or any other fomula or thumb rules etc.

Any suggestions in this regards are highly appreciate.

Thnx 

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On 15/02/2018 at 1:13 PM, Hussain Abid said:

Can anyone let me know how can we do the detailing of a 15"x30" rcc column with 4.5 in2 of Ast. Do we have to use ACI SECTION 7.7 Equations for the purpose or any other fomula or thumb rules etc.

Any suggestions in this regards are highly appreciate.

When the amount of required area of vertical reinforcement for a column is known (as we normally obtain from structural software like ETABS & SAP2000 etc.), its detailing involves following steps:  

a. Converting the reinforcement into number of bars. Actually required number of bars is calculated by dividing the area of reinforcement by the area of different bars one by one. For example, in the stated case, required number of bars for a #6 vertical bar (bar cross-sectional area=0.44 sq.in.) will be 4.5/.44=10.22 bars. For a #5 bar (bar area=0.307 sq.in.) will be 4.5/.307=14.6 bars. Similarly, for a #8 bar (bar area=0.785 sq.in.), required number of bars will be 4.5/.785=5.7 bars. 

b. Selecting the number of bars to be provided. Following are the important points to be considered while deciding 'bar size' and 'number of bars provided'.

(1) Number of selected bars is generally an even number. For square or rectangular columns, minimum 4 vertical bars are required. Whereas for curcular columns, at least 6 bars are required. number.The 'number of bars provided' is obtained by rounding up the required number of bars to next higher even number. Based on calculations made in the previous paragraph,  12 #6, 16 #5 or 6 #8 vertical bars may be used to furnish a reinforcement area of 4.5 sq.in. in the given column.

(2) The area of provided bars must be equal or a bit more than the required reinforcement area obtained from design calculations (or a structural software).

(3) The configuration of selected bars & placement of ties within the column cross-section, should be in line with the following code provisions:

i. ACI 315 Figures 13 and 14 (column bar configurations)

ii. ACI 318-08 Section 7.7 (concrete cover requirements)

iii. Applicable provisions of ACI 318-08 Chapter 21, keeping in view the seismic requirements & structural frame type.

Regards.

 

 

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1 hour ago, Hussain Abid said:

It would be nice if you could elaborate the same case with beams reinforcement.

 

im attaching screenshot for the beams b/w grids F &H. im unable to make out the three values 0.9,0.2,0.9   and 0.6,0.6,0.4.  These values show the top and bottom reinforcement values, how to interpret these values? 

SCREENSHOT.jpg

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8 hours ago, Hussain Abid said:

It would be nice if you could elaborate the same case with beams reinforcement.

Firstly, conversion of reinforcement area for flexural (longitudial) beam reinforcement to 'number of bars' is similar to that for the vertical reinforcement of columns. However, for deciding the 'number of bars provided' in case of beams, we round the calculated value to next higher integer number only, whether it is even or odd. For example, if required steel area is 0.9 sq.in., and #5 bar is to be used, then required number of bars =0.9/0.307=2.93. In this case, we may use 3 #5 bars for the beam. (Whereas, in case of a square or rectangular column, we needed to use at least 4 bars.)

Secondly, in case of a beam, required number of bars are to be provided along the relevant (top or bottom) face of the beam only, depending upon whether we are detailing the reinforcement for the negative or positive bending moment. In case, required number of bars (as calculated in previous paragraph) exceeds the maximum number of bars permissible in one layer, required number of bars will be provided in layers, separated vertically by spacers.

Thirdly, total area of reinforcement provided, must be within the steel areas corresponding to Minimum & Maximum steel ratios prescribed by ACI 318 for the beams. 

Fourthly, detailing of all type of beam reinforcement needs be in accordance with relevant provisions of ACI 318 and ACI 315 (whether seismic or non-seismic, as applicable).

 

7 hours ago, Hussain Abid said:

im attaching screenshot for the beams b/w grids F &H. im unable to make out the three values 0.9,0.2,0.9   and 0.6,0.6,0.4.  These values show the top and bottom reinforcement values, how to interpret these values? 

Out of three reinforcement values shown along (the top or bottom side of) a beam, two outer values (0.9 & 0.9 at left & right sides of top face, and 0.6 & 0.4 at left & right sides of bottom face of the beam under discussion) indicate the amount of reinforcing steel required at the relevant (top & bottom) faces of the two supports. Whereas, the middle values (0.2 on the top, & the 0.6 on the bottom side) indicate the amount of reinforcing steel required at the mispan of the beam,  on the top & bottom faces respectively.

HTH

Regards.

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