Bar Selection Criteria

This section discusses the significance of the Bar Selection Method and Bar Selection Bias parameters and the effect each has on the optimization process.

Bar Selection Method

Minimum Reinforcement Area - For this option, the bar set areas and associated lengths are used to calculate the total reinforcement volume, which is used to find the optimum reinforcement for the full beam line. The bias (see below) that is selected by the user in the Design Criteria dialog box is used to increase the reinforcement volume of bars that are not part of the bias bar size group. This weighted biasing of bars that are not part of the bias group ensures that bar sets are only picked from outside the group when they provide a significantly more economical design.

Minimum Reinforcement Spacing - For this option, the reinforcement spacing is checked to ensure that the minimum code required spacing is achieved. Given the bar sets with the minimum spacing the program will try to pick the smallest bars possible after the bias has been applied to the spacing for all bars that are not part of the bias bar size group. This will provide a design that tries to reduce the reinforcement area once the minimum spacing has been achieved.

Maximum Reinforcement Spacing - This option works in a similar manner to the Minimum Reinforcement spacing by trying to provide the largest bar spacing and smallest reinforcement area possible.

Bar Selection Bias

Bias Bar Size: This option identifies which bar sizes are preferred by the engineer. The bars in the Bar Table are divided into three groups. Assuming #3 through #18 bars are in the table then:

Small size = #3, #4, #5and #6
Medium size = #7, #8, #9 and #10
Large size = #11, #14 and #18

The amount of bias increases or decreases the critical parameter used in the Bar Selection Method when a bar is not a part of the preferred bar size. The increase in the value is based on how far the bar size is from the preferred bar size. Assuming Medium bar size is selected then a #5 bar set will have double the percent increased compared with a #6 bar because a #5 bar is two bar sizes away from the #7 (medium) bar size. The amount of bias is most effective when minimum reinforcement area is selected.

Bar Selection Example

Consider an example where 1.1in² of flexural reinforcement is required. The following outcomes can be expected based on user selections:

Minimum Bar Area, Medium Bar Size and Medium Bias:2-#7 (1.2in²) is selected over 10-#3 (1.1in²) because it is not part of the medium bar size, so its area is increased before comparing it to the 2-#7.
Minimum Bar Area, Small Bar Size and Medium Bias: 10-#3 (1.1in²) is selected over 2-#7 because it is part of the small bar size and has the smallest bar area of any bar set combination.
Maximum Bar Spacing, Small Bar Size and Large Bias: 2#7 (1.32in²) will be selected over 3-#6 because even though it is not part of the small bar size its spacing and reinforcement area are considered preferable to 3-#6 because the spacing is larger.

Note: The option to Keep all bars in layer the same size and Adjacent bars may differ in size by in the Design Criteria – Bar Selection tab are enforced only when possible. In some situations adjacent bar sets cannot satisfy the above two options because of code prescribed capacity, spacing, and other such criteria. It is therefore possible that even though the user has prescribed a change of only one bar size between adjacent bars the final design will produce adjacent bar sets with a larger difference in bar size to meet other code prescribed limits.