Deflection Criteria

The Criteria > Deflection command is used to define the deflection criteria considered for beam design optimization.

Note: Deflections are not considered in the Design of the beams. 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 in calculating the deflection in the beam, and the deflections are compared against the criteria specified by the user.

Setting	Description
Don’t check deflection for span/depth (ln/h) less than	This option is used to restrict deflection checks to concrete beams with a specified minimum span-to-depth ratio. The span length considered is the clear (face-to-face) 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 clear (face-to-face) span length is used for this check. For cantilevers the span length is doubled for the calculation of deflection to length of span ratio. Delta indicates an absolute maximum deflection value. A delta value of "0.0" indicates no limit for that condition. The default or alternate criteria is used based on the assignment made in the RAM Modeler for each beam. Beams are automatically assigned the default values unless the Layout > Beams - Deflection Criteria command in the RAM Modeler is used to override the assignment. For more information please refer to the technical section on calculating beam deflections.
Long-Term Deflection	The time-dependent 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. Note that this factor is not the actual length of time, but a factor based on the length of time (ξ per ACI 9.5.2.5). Refer to the technical section for more on how this factor is applied. The Initial Time Dependent Factor (ξ) is used to determine the long-term deflection due only to dead load for the time prior to the addition of the live 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 which assumes 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, plus the Immediate Live Load Deflection. This is as described in "Notes on ACI 318-99, Portland Cement Association" and the technical section below. 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 live load is applied to the structure for the calculation of the final long-term deflection. For more information please refer to the technical section on long-term deflection.
Effective Moment of Inertia	The user can select the method by which the program will calculate the effective moment of inertia (I_eff) for each of the deflection calculations. If the ACI is selected then I_effis calculated per ACI 9.5.2.3 Eq. (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 (I_g x Cracked Section Factor) will be used in the calculation of all of the beam deflection checks, no modification will be made for reinforcing or deflection type (Dead, Live etc).