Beam Design Aid Calculation: As received

1. Beam Design Aid Calculation
Posted by Ackerley Acton May 30, 2012 - 588 views - Filed in Civil Engineering
It is still difficult to directly design a reinforced concrete beam even if dimensions and material
properties are known. The use of design aids are commonly used to streamline the design process
instead of laboriously using a trial-and-error approach. The design aid shown below is used for
design or analysis. Values of Mu/ bd 2
are in units of PSI. It can be used to directly solve for act
knowing factored actual moment Mu, f’c, fy, b and d.

2. Example 1
GIVEN: A rectangular concrete beam with dimensions is shown below (stirrup bars

3. not shown). Use concrete f’c = 4000 PSI and grade 60 bars.
REQUIRED:
1) Determine the usable moment capacity Mu of the beam using formula.
2) Determine the usable moment capacity Mu of the beam using Table 2.
Step 1 – Determine usable moment capacity Mu of the beam using formula:

4. Step 2 - Determine the usable moment capacity Mu of the beam using Table 2:
From Table 2 above:
Example 2
GIVEN: The concrete beam below. Use the following:
 Concrete f’c = 4000 PSI
 Steel grade 60
 Concrete cover = ¾”
 #8 bars are to be used for main tension bars
 #3 stirrups
REQUIRED: Design the rectangular beam such that h =1.5b and pact = ½ (pmax).
wu = 2 KLF (includes anticipated beam weight = 300 PLF)

5. Step 1 – Determine maximum factored moment, Mmax:
Step 2 – Select values from Table 2:
Step 3 – Solve for “b” and “d” by substituting Mmax for Mu in above equation:

6. Step 4 – Select beam dimensions:
From above, use b = 12” and d = 18”
Step 5 – Determine required area of main tension bars:

7. From above, pact = 0.0107 = As/bd
Step 6 – Determine number of #8 main tension bars:
Step 7 – Check beam height with “Minimum Thickness of Beams” Table:
From Table:
h = 21” which is approximately = 20” as designed
Step 8 – Check originally assumed beam weight:

8. It was assumed that the beam weight = 300 PLF (See Step 1).
Actual beam dimensions:
Recall:
Beam Weight = 250 PLF < 300 PLF (assumed) OK
Step 9 – Draw “Summary Sketch” labeling all information necessary to build it:

9. Source: faculty.delhi.edu
Prepared by: zone4info.com