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Reinforced concrete integrated T-beam, 1-way slab, and column calculator

Jonathan Ochshorn

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Directions: Enter values in the yellow fields for "units and criteria," "material properties," "geometry," "loads," "moment values," and "number of rebars" (bars) as well as the bar size for slab reinforcement.

Press "update" button.

moment values and beam-girder spans
Fig. 1. Schematic view of T-beams, girders, and columns, showing moment value coefficients and centerline spans (A and B) for typical girders and beams. One-way slabs, spanning between beams and forming the top flanges of the T-beams, are not shown.

The calculator computes required steel area and selects bars (or spacing) for 1-way slabs, T-beams, and columns. Columns are designed based on the number of occupied floors selected. Bar fit is not checked by this calculator. See Table A-5.3 in the text (2nd edition) for bar fit limits. "Cover" for slab and beam reinforcement is here defined as the distance from the outer face of the concrete to the centerline of the reinforcing bar or bars. In other words, subtracting this cover dimension from the slab or beam thickness gives the effective depth. Both the beam and girder width refer to the "stem" width below the slab, and not the effective width of the T-beam. Required steel for girders is not computed.

Calculations and results, shown below to the left, are based on Building Code Requirements for Structural Concrete (ACI 318-14) and Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7-10). For T-beams and 1-way slabs, criteria for the use of moment values must be met; for columns, it is assumed that buckling is not an issue, i.e., that the ratio of height to minimum cross-sectional dimension is no greater than about 12. "Interpolated" R-ρ calculations give exact solutions; use the "tabular" setting to check answers based on approximate tabular values found using Table A-5.9 in the text (2nd edition). Dead load is automatically calculated based on the selected weight of reinforced concrete; except that column weight is excluded from column dead load. Beam and girder spans, A and B, are measured to centerlines; calculator uses specified beam and girder thicknesses to establish clear span dimensions. To find stirrup spacing, insert computed value for "Maximum shear force for beam at face of support, Vu" into stirrup spacing calculator. "Number of spaces" is defined as n in Figure 1 above. For the structure shown in Figure 1 with beams at the third points of the girder, n = 3. For beams at the quarter points, n = 4, etc. Floor beams and slabs are designed based on dead and live loads; roof beams and slabs are designed based on dead loads plus the greater of snow or roof live (maintenance) loads. When the "number of occupied floors above column" is set to zero, the slabs and beams will be designed based on dead and roof loads. Otherwise, the beams and slabs will be designed based on dead and live loads. Columns are designed based on the governing combined loads (considering dead, live, roof live-maintenance, and snow loads per ASCE/SEI 7-10), as summarized in Table A-2.7 of the text (2nd edition).

Lateral forces and lateral force-resisting systems are not considered in this calculator.

More detailed explanations and examples can be found in my text.

  Units and criteria      
  units R-rho calculation live load reduction?  
  Material properties      
  number of spaces  
  column type
  Moment values      
  slab neg moment slab pos moment beam neg moment beam pos moment
  Number of bars     Slab reinforcement
  beam neg moment beam pos moment column bar size
  Effective width  
  for pos-mom T-beams  
beam or girder spans less than or equal to 0  
beam or girder width less than or equal to 0  
beam or girder thickness less than or equal to 0  
dead, live, roof or snow load less than 0  
beam width too wide for girder span  
girder width too wide for beam span  
slab thickness greater than beam thickness  
concrete weight less than 0  
slab negative moment steel ratio too high  
slab positive moment steel ratio too high  
slab thickness less than or equal to 0  
beam negative moment steel ratio exceeds maximum  
beam positive moment steel ratio exceeds maximum  
need at least 6 bars for spiral column  
number of floors above column less than 0