Longitudinal

• Required As

  The required area of steel is calculated for top and bottom flange based on maximum negative and positive moment at the location of each POI. Load Combinations Service I Final for RC and Ultimate I for PTare considered in this evaluation . CIP RC/PT Girder first calculates the capacity provided by the PT tendon, and if the demand is lower, required rebar is reported as zero. If the demand is higher, required additional rebar is calculated to satisfy the demand.

  The bar location for the calculation of this area is based on the cover distance specified by the user. However, CIP RC/PT Girder adds one inch to the clear cover to determine the centroid location of rebar to avoid recalculating the demand based on a change in bar size.

  In the case of sections with no prestressing (reinforced section)the method shown below is used to calculate the reinforcement first as a singly reinforced section, and if that is not sufficient as a doubly-reinforced section. The cracking moment is not checked, otherwise included in the calculation of the demand. In the case that the section is too small to carry the demand, the design might fail. This is calculated and flagged in CIP RC/PT Girder, however is only reported in the required As design graph as a 92,900 mm2 of rebar.

The procedure is as follows (Ref. Park and Paulay, Chapter 10):

Rectangular sections will be designed as either singly- (As, tension steel) or doubly-reinforced (As and A's, compression steel).

T-sections (I-section will be treated as T-section for flexure design) will be designed as singly-reinforced (As).

As required will be the maximum of A _s1+A _s2 and A _smin

This can also be written as 0 = Ad²+Bd + C

Then, d can be calculated as,

• Calculate jd
  
  
• Calculate A _srequired is maximum of A_s shown below and A _smin
  
  

• Layout

  CIP RC/PT Girder uses the required area of steel to determine the number of bars needed at each POI location. This information is then used to determine the bar layout. The longitudinal bars can be laid out in two ways: by number of bar increments, and by bar length. Bar locations determined by CIP RC/PT Girder do not include the extension and development lengths and bar locations are the locations where the rebar is assumed to be fully developed.

  To layout the bars by increment of bars, CIP RC/PT Girder obtains the locations along the bridge length, where a multiple of bar areas can satisfy the required rebar area. Once these locations are determined, CIP RC/PT Girder finds the ranges of bars that can satisfy the required bars. Note that in this case, the bar ends may fall at any location relative to each other.

  To lay out the bars by length increments, CIP RC/PT Girder determines the locations falling at multiples of the given increment, and then determines the number of bars needs at these locations to satisfy the demand. CIP RC/PT Girder will then determine the ranges of bars of equal numbers to lay a set of bars. Note that in this case, the bars are located at even increments, but the number of bars may vary by any number.

  The interactive nature of the bar layout process allows the users to modify the bar numbers and lengths and see the effect of their revision visually in graphical form. The final selection may be copied to the model information for use in further analysis or saving in the input file.

Shear Reinforcement

CIP RC/PT Girder uses the required area of stirrup per unit length (Av/s) to determine the stirrup spacing. The Av/s is calculated the same way as described in the shear capacity calculation. CIP RC/PT Girder uses the number of legs specified at the section and the stirrup size to determine the total area of stirrup. Based on the required area and the total area, CIP RC/PT Girder calculates the minimum theoretical spacing at each POI. CIP RC/PT Girder will then determine the locations where a multiple of the required spacing will be sufficient to satisfy the demand. This information is then used to determine the ranges where stirrup can be laid out with given spacing increments. Note that CIP RC/PT Girder does not check the detailing requirements such as minimum and maximum spacing; however, the maximum spacing of stirrups is limited to 300 mm.

The interactive nature of the stirrup layout process allows the users to modify the ranges and their spacings and see the effect of their revision visually in graphical form. The final selection may be copied to the model information for use in further analysis or saving in the input file.