There are two methods for defining tendons in RAM Concept. The most commonly used is the Manual Tendon layout method. This feature has been available since the inception of the software. However, a more sophisticated and more powerful means of laying out tendons exists, and is the subject of this article. This method is referred to as the automated tendon method, and consists of capabilities accessible on the Tendon Parameters and Generated Tendon layers. There are several advantages this option has that lead not only to time savings in the initial modeling, but that also make revisions to the layout much more easily accommodated.
Review of Manual Tendon Method
Before discussing the automated tendon feature, a review of the Manual Tendon method is in order to illustrate how the two methods differ. Manual tendons are defined on the Manual Tendon layer under the Prestressing folder. Note that there are separate folders for both principal span directions (latitude and longitude).
Figure 1 – Creation of manual tendons is done on the Manual Tendon layer. There are separate folders for latitude and longitude principal directions.
On the Manual Tendon plan, each tendon is represented by a line segment. This segment is the geometric entity the user creates and modifies (both geometry and associated properties) to establish a tendon layout. Each tendon has high and low points, from which a complete profile is interpolated, and a number of strands. Adjacent tendons that share an endpoint also share the profile elevation at the common point. As such, changing the profile elevation for one tendon also changes the elevation of the common point for the other tendon. There are commands available for placing multiple tendons at once. This includes laying down a multi-span tendon line with successive clicks, as well as placing distributed tendons over an area of the slab using a polygon.
Figure 2 – Multi-span banded tendon defined on the Manual Latitude Tendon layer.
The first limitation in the manual modeling of tendons (Manual Tendon layer) in RAM Concept lies in the fact that once tendons are placed, there is no association between each of them (aside from the profile elevation of a common point). Each tendon maintains its own geometric location and profile, and changes to one tendon do not affect other tendons. This can lead to a significant effort in revising tendon layouts to accommodate changes to the floor. For example, Figure 3 shows a situation where a slab boundary revision has been made, and the manual tendons within the area now need to be revised one by one to update them for the new plan geometry.
Figure 3 – Manual tendons requiring one-by-one revision for a change in slab edge location.
The second limitation with the manual modeling of tendons in RAM Concept is that the user must specify a number of (and possibly spacing of) tendons, whereas it may be preferable to specify an effective force, from which a number of tendons is determined. There are tools available in RAM Concept that estimate the balance load that a region of tendons produce, but there is no means of specifying an effective tendon force. This must be done by back calculating from a number of (and possibly spacing of) tendons.
Automated Tendon Methodology
The automated tendon feature set was created to allow the generation and manipulation of large blocks of tendons at once, reducing the need to edit tendons one at a time to accommodate revisions to concrete geometry and loads. The analysis and design routines treat generated individual tendons the same as manual tendons. In fact, generated tendons can be copied from the Generated Tendon plan and pasted on to the Manual Tendon plan, at which point they become manual tendons. It may be advantageous to use both manual and automated tendons on a single floor to capitalize of the strengths of each method. However, since both sets of tendons are always considered it is important if using both to make sure that the same tendons are not defined on both layers in which case they would be double counted.
The automated tendon features are accessed in the Tendon Parameters and Generated Tendon layers as shown in Figure 4.
Figure 4 – Creation of automated tendons is done on the Tendon Parameters and Generated Tendon layers.
Figure 5 – Tendon Parameters plan (left window), with resulting tendons on Generated Tendons plan (right window).
Tendon Parameters
There are three RAM Concept objects that are primarily used when defining automated tendons: banded tendon polylines, distributed tendon quadrilaterals, and profile polylines. These objects are drawn and displayed on the Tendon Parameters layer. The Generated Tendon plan then displays the resulting individual tendons once the tendon generation is complete. The generated tendons are displayed the same way that manual tendons are, except that the generated tendons are not editable. They can be revised only via the objects on the Tendon Parameters layer.
A more detailed discussion of these objects is now given.
Banded Tendon Polyline
The Banded Tendon Polyline defines the plan location of a single tendon or group of tendons. An example of this is illustrated in the left-most window in Figure 5. The highlighted (yellow) polyline extends north-south and its associated parameters are shown in the dialog to the right. This includes properties such as the number of strands, number of strands per tendon, width over which the tendons are placed, and tendon type (bonded/unbonded). The commands for drawing these entities are available under the Tools menu when the Tendon Parameters plan is active.
Figure 6 – Commands for drawing automated tendons, available on the Tendon Parameters layer.
Whereas with manual tendons a single segment always produces a single half-span tendon, multiple tendons encompassing multiple spans can be created with a single banded tendon polyline using the generated tendon method. In Figure 5, four tendons, each with four strands, are produced from the single tendon polyline drawn in the left window. The number of tendons, spacing of the tendons, and strands per tendon can be controlled through the properties associated with the tendon polyline. Figure 7 shows four different choices of tendon grouping resulting from different tendon polyline parameters. The left-most image uses 16 strands, with all 16 strands in one tendon. The second image uses 16 strands with a Max Strands/Tendon value of one, with the tendons placed over a two foot width. The third image uses a Max Strands/Tendon value of four, producing four tendons of four strands over two feet. The right-most image uses the same settings as the third, except over a width of four feet rather than two.
Figure 7 – Four different choices of tendon grouping for the 16-strand tendon polyline in Figure 5.
While for manual tendons the number of strands must be input, another benefit of using banded tendon polylines is that the input can specify either number of strands or effective force. A toggle controls the input mode. This toggle is associated with each tendon entity and not the model as a whole so each method can be used throughout the model where appropriate.
With the manual tendon method, each line segment corresponds to a tendon half-span. The profiling of banded tendon polylines is determined by any profile polylines that intersect it. This behavior will be discussed in more detail in a subsequent section.
Distributed Tendon Quadrilateral
The Distributed Tendon Quadrilateral defines the plan location of a region of uniformly distributed tendons with a single orientation. This object can be used to generate tendons with units of number of strands for effective force per unit length. Distributed Tendon Quadrilateral objects with like orientations and systems properties can also be drawn overlapping to accomplish increasing the force at distinct locations. As with the banded tendon polylines, these objects do not contain any profiling information. The profiling of the generated distributed tendons is controlled by any profile polylines that intersect them. This is described in more detail in the following section.
Profile Polyline
The Profile Polyline object is a polyline that has an associated vertical elevation and controls the profile for any banded tendon polyline and distributed tendon polyline that intersects it. The elevation references can be set to absolute, above surface/soffit, or top/bottom cover. All elevations are to the center of gravity of strand (CGS). Profile Polylines can be generated automatically from the span segment information, or drawn/edited manually. The commands for drawing profile polylines are available under the Tools menu when the Tendon Parameters plan is active.
Figure 8 – Command for setting profile elevations of automated tendons.
Figure 9 – Tendon Parameters plan, with profile polylines (yellow) drawn to control the profile of N-S tendon.
Unlike with manual tendons, the banded tendon polylines and distributed tendon quadrilaterals drawn on the Automated Tendon plan have no profile geometry associated with them (see the dialog in Figure 5). Instead, the profile is determined entirely from profile polylines. The profile polylines allow the profiles of multiple tendons at once to be easily revised by simply moving or adjusting the elevation of the polyline. This is particularly helpful when tendon layouts are non-uniform, vary in length, and contain sweeps.
It is also possible to define banded tendon polylines and distributed tendon quadrilaterals that extend outside the slab edge as this is often desirable for design plan representation. This is in contrast to manual tendons, where design errors will be generated if any tendons occur in empty space. As a result of this, changes to slab geometry can be more easily accommodated since banded tendon polylines and distributed tendon quadrilaterals do not necessarily need to align with the edges of slabs or openings. An example of this is shown in Figure 10.
Figure 10 – Use of the automated tendon method automates tendon revisions when slab geometry changes.
Another benefit of the banded tendon polyline method is that end points of a tendon polyline drawn on the Automated Tendon plan do not need to correspond to the physical tendon endpoints, as they do on the Manual Tendon plan. An example of this is shown in Figure 11. The sweeping tendon is placed using eight segments to form the polyline. The high points of the tendon are at the ends of the polyline with the low point near the center of the polyline.
Figure 11 – Single-span tendon defined using eight polyline segments.