RCDC Beam design - effective depth Calculation

Question

Bentley Team, 
 How is the effective depth for beam being calculated for a beam with two or more numbers of layers in RCDC software? 
 Please provide the basis and validation for the same. 
 I could find some formula related to effective depth in FAQ in the link below, but that is not giving correct value for the design I have. 
 https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/41953/rcdc-beam

Abhisek M · Answer

Hello, 
 In RCDC the effective depth of a beam is calculated in the fllowing manner. If D is the total depth and d is the effective depth, then d = D - Clear Cover - 16mm -12.5mm d= D- Clear Cover -28.5mm 
 Here, clear cover thickness includes stirrup dia. For effective depth calculation it is assummed that 2 layers of reinforcement is present and effective depth is calculated from the top most fibre to the mid depth of spacer bar. Though it is conservative in some cases, but we are in safer side. Considering this fact, a value of 16mm is considered as the bar dia of bottom most layer reinforcement. Then 25mm spacer bar is considered for which we take half the depth in claculation as 25/2=12.5mm. 
 After getting the d value it is again rounded down to nearest 5mm interval, which in turn make the aforementioned 28.5mm value, 30mm. 
 Can you please check and let me know if this matches with your calculation?

Nidhi Valia · Answer

Hi Request you to kindly note following: All cover is assumed to be cover to longitudinal reinforcement. Assumption of number of layers of reinforcement: At design time the number of layers of reinforcement is assumed as under to arrive at the effective depth, d: D < 400 mm 1 layer 400 mm >= D <=1200 mm 2 layers 1200mm > D <= 1350 mm 3 layers 1350 mm > D <= 1800 mm 4 layers 1800 mm > D <= 2250 mm 5 layers 2250 mm > D <= 2700 mm 6 layers 2700 mm > D <= 3250 mm 7 layers D > 3250 mm 8 layers Detailing Philosophy: The reinforcement required is computed as per the effective depth for the number of layer of reinforcementas per table above. Rebars will be arranged in multiple layers if requiredand the style of detailing selected. The maximum number of layers usedwill be limited to thoseassumed when computing the effective depth. In case it is not possible to provide the required reinforcement using the largest rebar arranged in the maximum possible layers the number of layers will be automatically increased. With the increase in number of layers the effective depth and the reinforcement required will be computed again. When providing rebars across the section of the beam, the minimum and the maximum spacing criteria and the preferred number of rebars will be considered. The rebars wil be symmetrically arranged across the section. In case the number of bars are varying across the section, the auto detailing will ensure that the symmetry will be maintained.eg. 6 bars will reduce to 4 and not 5 bars OR 5 bars will reduce to 3 and 4 bars.

Nidhi Valia · Answer

Hello Mr. Paresh, 
 Sharing the attached sheet for your reference and clarification. 
 Thanks 
 Deff and Ast calculation.xlsx

Abhisek M · Answer

Please refer the explanation and the excel sheet available in below link. 
 https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/59381/how-the-effective-depth-is-calculated-in-beam-design-and-what-is-the-impact-of-maximum-aggregate-2-size-on-effective-depth

Abhisek M · Answer

Please refer the explanation and the excel sheet available in below link. 
 https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/59381/how-the-effective-depth-is-calculated-in-beam-design-and-what-is-the-impact-of-maximum-aggregate-2-size-on-effective-depth

Nidhi Valia · Answer

Hi, 
 The clear cover that is considered in RCDC is the clear cover to the main Longitudinal Bar and not the Link . 
 So, in the above example, the Deff for column would be calculated as: 
 Deff = 500 - 40 - 25/2 = 447mm. 
 Hope this clarifies. 
 Thanks

RCDC Beam design - effective depth Calculation

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