Criteria - Deflection

Selecting the Criteria > Deflection command will cause the Deflection Criteria dialog box to appear, displaying the current deflection criteria for beam design optimization. Change these criteria by selecting different options and/or entering new values.

Note: Deflections are not considered in the Design of the beams, that is, no consideration is given to deflection when calculating the amount of reinforcing required during optimization. However, following a beam design the optimized reinforcing and section properties of the beam are considered to calculate the deflection in the beam and compare against the criteria specified by the user.

Setting	Description
Don't check deflection for span/depth (ln/h) less than	Select this option to restrict deflection checks to concrete beams with a specified minimum span-to-depth ratio. The span length considered is the clear span length. This feature can be used to limit which beams are checked as permitted by Table 9.5(a) in ACI 318-99 10. By specifying a sufficiently large value for this limit the user can effectively 'switch off' deflection checks if so desired. The minimum ratio allowed is 1.0.
Minimum Allowable Span-to-Deflection ratios	Ln/d indicates a minimum span-to-deflection ratio. Note that the span lengths in this check are based on the clear length (face-to-face) span length. Delta indicates an absolute maximum deflection value. A delta value of `0.0` indicates no limit for that condition. The criteria to use is based on assignment made using the Assign > Deflection Criteria command. The first criteria in the list is used by default for newly created beams. For more information please refer to the technical section on calculating beam deflections.
Long Term Deflection	The time dependant deflection factors are based on the length of time that long term deflection is to be measured at per ACI 318-99 9.5.2.5. The Initial Time Dependant Factor is used to determine the long term deflection due only to dead load. That is, the portion of long term deflection that occurs prior to the attachment of the non-structural (live load) elements. This factor is defaulted to 0.0 so as to assume the live loads are applied relatively soon after completion of construction. The actual long term deflection against which the allowable deflection criteria will be checked is calculated as the Final Long Term deflection less the Initial Long Term deflection. The percentage of Live Load Sustained is that percentage of the live load that is considered relatively static so as to result in long term deflection on the structure. This percentage of the full live load is applied to the structure for the calculation of the final long term deflection. For the calculation of the long term deflection all live load is considered to have been applied to the structure concurrently, that is, no skip loading is considered in the calculation of long term deflection. For more information please refer to the technical section on long-term deflection.
Effective Moment of Inertia	Select the method by which the program will calculate the effective moment of inertia (Ieff) for each of the deflection calculations. If the ACI is selected then Ieff is calculated per ACI 9.5.2.3 eqn (9-7) for each deflection check (Dead Load, Live Load, Long Term and Net) independently. If Use I From Analysis is selected then the same moment of inertia used in the analysis (Ig x Cracked Section Factor) will be used in the calculation of each of the beam deflection checks. Clicking Cancel will cancel any changes made and return you to RAM Concrete Beam Design. Clicking OK will cause a warning message dialog box to appear on the screen stating that proceeding with this command will clear all previously optimized beam designs. You are given the option to continue the deflection criteria change by clicking Yes or canceling the change by clicking No.