Deflection Checks in RAM Concept

A deflection check feature that allows users to check deflection limits during the design calculations was added in RAM Concept Version 8 Update 4.

This article describes how to use this new program feature.

Defining Deflection Checks and Deflection Limits

Deflection Check criteria must be specified in the Deflection Check Table (Criteria > Deflection Checks) before deflection limits are checked during the design calculations.

Figure 1. Deflection Check Table

To add a Deflection Check to the table, click on the Add Deflection Check button, enter the information below in the dialog, and then click OK.

• Specify a Name for the new deflection check.
• Select a loading, load combination, or load history step using the Deflection Result Layer menu.
• (Optional) Select a loading, load combination, or load history step using the Diff. Result Layer menu. If a selection is made for the Diff. Result Layer, then the calculated deflection represents the deflection from the Deflection Result Layer less the deflection from the Diff. Result Layer. If None is used for the selection, then the calculated deflection represents the layer from the selected Deflection Result Layer only.

After a Deflection Check is added, deflection limits can be specified in the Deflection Check Table.

Deflection limits are defined using the properties described in the list below. When defining the upward or downward deflection limit properties, a value can be input in the table or No Limit may be selected.

Downward Limit - downward deflection limit defined as an absolute deflection.

Downward Limit (L/Δ) - downward deflection limit defined as a proportion of the span length.

Upward Limit - upward deflection limit defined as an absolute deflection.

Upward Limit (L/Δ) - upward deflection limit defined as a proportion of the span length.

Deflection Measure - how the deflection is measured, which can be Total or Relative. Total deflections are measured from the undisplaced shape. Relative deflections are measured relative to the displacements at the end of a span or check line. See figures below for a summary of each option.

Figure 2. Deflection Check Measures for Typical Span 

Figure 3. Deflection Check Measures for Span with Support at One End (Point 1)

Assigning Deflection Checks

After the Deflection Check are defined, they can be assigned to design objects like span segments and deflection check lines.

Span segments are the objects used to generate design strips in RAM Concept. They are typically modeled between supports and define the structural span, or in some cases a portion of the structural span.

To assign one or more Deflection Checks to a span segment, check the boxes next to the appropriate Deflection Check listed in the Deflection Check box in the General tab of the Span Segment property dialog.

Figure 4. Assigning Deflection Checks to Span Segments

Deflection Check Lines are new RAM Concept objects that designed exclusively for deflection checks. Like span segments, they are typically modeled between supports, most often diagonally across a given bay as shown in the image below. Deflection Check Lines are also useful for checking deflections at localized areas away from supports, for example at slab edges or at transfer loads.

Deflection Check Lines are modeled on the Design Strip Layer and grouped by Latitude and Longitude Span Sets similar to span segments. To model a Deflection Check Line, do the following:

1. Choose Tools > Deflection Check or click the Deflection Check Tool 
2. Click at the deflection line start point.
3. Click at the deflection line end point. The two clicks (Step 2 and Step 3) define the deflection line spline.

To assign one or more Deflection Checks to a deflection check line, check the boxes next to the appropriate Deflection Check listed in the Deflection Check box in the General tab of the Deflection Check Line property dialog.

Figure 5. Selected Deflection Check Line with Deflection Check Assignments

Understanding the Deflection Check Calculation

The deflections used for deflection checks are calculated as follows:

• Each span segment or deflection check line is subdivided into stations along the object. The subdivision of span segments is based on design cross section locations. The subdivision of deflection check lines is based on the user-defined minimum number of divisions and max division spacing properties.
• The total deflection at each station along the object is determined for the Layer and Diff Layer defined with the Deflection Check.
• A downward and/or upward deflection limit is determined at each station based on the user-defined Deflection Check Criteria. For total deflection limits, the limit matches the user-defined Downward Limit and/or Upward Limit. For span ratio deflection limits, the user-defined span ratio limit (L/D) is converted into a deflection limit by dividing the span length by the span ratio limit. When the relative deflection measures are used, the input deflection limit is converted to a limit that can be directly compared to the calculated total deflections. This is done by adding the displacements at the first and last station to the input deflection limit.
• The total deflection is compared to the upward and/or downward deflection limits.

Note: Calculated deflections represent the deflections at point locations along the spine of span segments or deflection check lines. Deflections are not integrated across the cross section length or design strip width for span segments similar to the way design forces and moments for cross sections are determined.

Understanding the Deflection Check Calculation

When a Deflection Check is defined, a Status Plan, Deflection Checks Plan, and a Std Deflection Plan are automatically generated for the check on the Deflection Checks Layer.

The Status Plan displays the spline line for each deflection check line and span segment with a deflection check assignment. After the calculations are run, these lines are displayed in green with a status of “Δ OK” if the calculated limits are within the defined deflection limits. When the calculated deflection i outside the defined deflection limits, the lines are displayed in red with a status of “Δ Failed.” Failure locations are marked across the spline line. If a Deflection Check references a load history layer and the analysis is completed without the load history calculations, “Δ Needs Calc” will be displayed for the status. Results will be displayed after the load history calculations are completed.

Figure 6. Deflection Check Layer - Status Plan

The Deflection Checks Plan displays the calculated deflection and deflection limit for each deflection check line and span segment with a deflection check assignment. Plotted results represent the envelope results for the layers defined with the Deflection Checks. No information will be displayed in this plan if the check references a load history layer and the analysis is completed without the load history calculations.

Figure 7. Deflection Check Layer - Deflection Checks Plan

The Std Deflection Plan plots the total standard deflection contours for the deflection check. The results are based on the Layer and Diff Layer defined with Deflection Check. This plan can be used to compare total deflection results with the results displayed on the other Deflection Checks plans.

Using Deflection Checks with PT Design Optimization

The PT Design Optimization feature processes deflection checks like other design code rules. Possible design solutions that result in deflections outside the limits of the specified deflection check are not considered valid designs. During the optimization, property values of optimizable tendon and/or profile polyline objects are automatically adjusted to control deflections within the specified limit.

Use caution when using deflection checks that reference load history layers with PT Design Optimization as this can increase the total optimization time by 10x or more. This significant increase in calculation time is a result of the iterative, non-linear load history analysis and the rigorous calculations that are performed at each design section in the model. For best performance, we recommend referencing only load combination and/or loading layers in specified deflection checks when optimizing PT designs. After the optimization completes, a more comprehensive deflection investigation can be performed by loading the best trial and running the load history calculations.