RAM Concept Tendons [FAQ]

Applies to
 Product(s):RAM Concept
 Area: Modeling; Analysis; Design

Why are some tendons shown at the wrong elevation in the tendon perspective?

The soffit elevation at each profile point is determined during the Analyze All and Calculate All commands. If one of these commands is not performed since the drawing (or moving, etc.) of a tendon, or since a change in the mesh, the tendon elevations in perspectives are not accurate.

The same is true for elevations optionally shown as text on the plans.

It is quicker to analyze (but not using “Calculate All”) with Process > Analyze All. This avoids processing the design calculations.

How can I place a manual tendon relative to the top surface, rather than up from the soffit?

If you use manual tendons, they can be placed with an elevation relative to either surface or soffit. If you use the "Above soffit" approach and enter say 6.25” for the high points, then high points will stay 6.25” up from the soffit even if the slab thickness changes.

On the other hand, if you use the “Top cover” option with a small positive cover (or if you use the “Above surface” option with a small negative number), then the top of the strand will maintain the distance from the top surface and increasing the slab thickness will result in tendons with more drape.

What do the terms “Latitude” and “Longitude” mean?

In the USA, Britain and other countries it is typical practice to place all the tendons in one direction in a concentrated band over column lines. If the designer is using another practice then we recommend that you still use the Latitude and Longitude tendon layers because it makes editing the PT easier. i.e. Put the tendons in the X direction on one layer and the Y tendons on the other. Latitude and Longitude are just layer names.

Do I have to draw the tendons for a post-tensioned slab?

Yes. It is not difficult, and encourages you to address detailing issues before they become field problems.

How do I draw tendons?

See Chapter 26 Defining Tendons for details. It's important to note that the program allows you to manually define tendons on the manual tendon layers, or you can generate tendons based on user defined tendon parameters.

Can I harp tendons?

Yes. Any tendon segment can be declared to be harped. The “half-span” tendon tool is useful for any harp point (or any low point) that is not at mid-span. Multiple harp points can be located in any span by using multiple tendon segments.

Does it matter which way I draw “half” tendons?

Yes. The inflection point is measured from the first point clicked and the profiles are specified in the order of the points clicked. To be compatible with the tendons created using the Full Span Tendon tool, we strongly recommend that you always start at the high point.

Can I terminate some strands past a column?

This can be done with one of two methods.

The tendon can be “forked” such that the number of strands decreases. As shown in Figure 37-1, if the transition is from 15S (15 strands) to 10S (because an adjacent span does not require that many strands) then terminate 5S using a half span tendon. It is common to terminate strands at quarter span and at the slab centroid.

Note: You should only use this method for tendons with no jacks attached. This is because a jack attached to tendons of different lengths has inaccurate seating (wedge draw-in) loss calculations.

Figure 37-1 Termination of strands (no jacks)

The second method can be used when jacks are modeled. If the total number of strands is 15S then one tendon with 10S needs to be continuous with an additional tendon with 5S alongside. It is common to terminate tendons at quarter span and at the slab centroid.

Figure 37-2 Termination of strands / tendons (jacked). Plan alignment of tendons is subjective.

Does Concept check to make sure the number of strands in connected tendon segments is consistent?

Yes. you will get a warning to that effect during the calculation when the strand number changes.

How does Concept calculate friction losses?

Concept only calculates friction losses if jacks are specified. Concept performs friction loss calculations considering the (elevation view) curvature of the tendons, the (plan view) horizontal kinks in the tendon and the jacking and friction parameters. The stress in the tendon is assumed to vary linearly along each tendon segment.

Does Concept calculate elongations (extensions)?

Yes, if jacks are specified. Use the Visible Objects dialog to view "Jack Elongation" on the manual tendon standard plans.

Do the elongations (extensions) include the effect of the seating distance (wedge draw-in)?

Yes. The elongation reported includes the deduction of the seating distance.

Why do I get the warning:  "An error has been found.   A non-external tendon is out of a cross section in design strip x-x" 

RAM Concept is checking one of the design sections in that design strip. The particular section has been trimmed. It may have been trimmed due to the cross section trimming method (e.g. using Max rectangle trimming could trim off any beams or drop panels in the section) or because of the slope limit which prevents adjacent sections from rapidly jumping in depth. Where there error occurs, there is a tendon passing through this section within the part of the section that was trimmed off.

To fix the problem either revise the strip trimming methods and/or verify the cross section in perspective view. You may need to revise the design strips in plan or move the tendon in some cases.

Note, a similar problem can happen with user reinforcement that is placed outside the limits of any trimmed cross section. See [[RAM Concept - Reinforcing bar out of cross section]] for details.

Can Ram Concept identify tendon clashes?

Our 3D graphics for tendons are very accurate and you can visually inspect them using tendon perspective plots, but we don’t call out or highlight clashes in Ram Concept.

See Also

[[RAM Concept Tendon Parameters]]

Cross Section Trimming

[[RAM Concept - Reinforcing bar out of cross section]]