In this tutorial we will show how SAFE can automate the application of post-tensioning in a slab to balance a portion of the self-weight. In this case our target is 60 to 80 percent. The floor plate similar to what might be encountered in residential construction consists of an 8-inch slab, 12-inch square columns and 8-inch thick walls all constructed of 5000 psi concrete. The pre-stressing tendons shown here in green are made up of half inch diameter strands with an area of 0.153 inches square. The jacking stress is 216 ksi with total losses of 40.5 ksi The banded tendons run in the X direction and for simplicity's sake we'll place only one tendon in each band. The program will then report the total number of strands needed in each band. The distributed tendons are placed in the Y direction with an approximate spacing of 38 inches on center. The program will automatically determine the vertical profiles of the tendons. The concrete design code used will be ACI 318 19. We will start our tutorial with the slab, columns, and walls already drawn in plan. The overall dimensions are approximately 108 feet by 92 feet. We will have eight grids in the X direction and six in the Y with spacing of between 8 and 28 feet in each direction A quick check of the material properties confirms that we have 5000 psi concrete and a 416 grade 270 steel for our pre-stressing tendons Next we will review the tendon property Here we verify the material property and the size of the strand make sure it is 0.153 inches square Next we will define the static load patterns Two default load patterns are defined. Dead with a self-weight multiplier of 1, and a live load with no self-weight multiplier. Next we will add a PT final load pattern. This pattern is defined for the application of post-tensioning forces on the model after all losses have occurred and a PT transfer load pattern for the application of PT forces prior to the occurrence of long-term losses Based on the load patterns defined, the program automatically defines associated load cases. Load cases determine how the load patterns are applied and analyzed. All the load cases should be linear static analyses which is what is shown on the form Now we will add the support lines. Support lines can be used to help position design strips and subsequently tendons as support lines identify the load path for slab spans Support lines may either be drawn or added using grid lines We will add support lines using grids starting in the X direction. Support lines may be assigned to either layer A or layer B and for the X direction we will use layer A. The support lines will be added at grid lines containing supporting objects such as columns and walls. Note how the support lines follow the layout of the columns even when the columns do not lie exactly on a grid line such as at grid lines C and D. In the Y direction we will add support lines using layer B If we wish to use a different geometry for a support line we can select it delete it and then simply redraw it Click the select object button to leave the draw mode Next we will add the design strips using the support lines. The design strips will be used to automate the layout of the post-tensioning. Because the design strips in this tutorial are being added to the model using the support lines the layers associated with the design strips will be inherited from the support lines, that is, the design strips in the X direction will be layer A and those in the Y direction will be layer B. We select the support lines in both the A and B layers and go to the add design strips using selected support lines command This model will have column strips only and no middle strips as is typically done for post-tensioned slabs so we leave the create Middle Design strips box unchecked and click ok Now select all the design strips and go to the edit strip width command We will select the auto widen entire strip option so that the program will automatically set the strip widths We are now ready to add the tendons select the design strips in layer A only and go to the add edit tendons add tendons using selected strips command Remember that the tendons in the layer A or X direction are to be banded. Set the bandwidth equal to zero - this will cause the program to simply report the number of total strands required in each band and for the banded tendons we will use a parabola shape. Lastly verify that the maximum and minimum balancing ratios are 0.8 and 0.6. By adding the tendons to the design strips rather than individually drawing them, the program will automatically determine the number of strands needed and the vertical profile to balance the percentage of self-weight specified here Now select the design strips in layer B Again we add tendons to the design strips but this time the tendons in the Y direction will be distributed with a spacing of 38 inches on center and they will have a shape of reverse parabola we will use the same balancing ratio target Any spurious or unwanted tendons may be selected and deleted just like any other object To review the tendons generated by the program hold down the control key and right click on a banded tendon to display a selection list. This form shows that multiple objects exist at the same location select the tendon object and click ok A tendon vertical profile form is now displayed. Click in any of the edit boxes in the span data table and the associated section of tendon is highlighted. Note how the program has draped the tendon over the structural support points. If changes are needed, click on a span and edit the data in the table or simply grab one of the control points and drag it to a new location. Note that anchorage and stressing ends are illustrated by different icons. In the lower right corner the number of strands required in this banded region is displayed. Click on the tendon loads button and we see that the tendon is stressed from the J end with a jacking stress of 216 ksi Click the tendon losses button and we see that the loss at stressing is 27 ksi and that the long-term loss is 13.5 ksi If we control right click on a distributed tendon we see that the program has calculated two strands per tendon which based on our spacing of 38 inches on center works out to be approximately 17 kips per linear foot. For the profile note how the support points of the tendons are at the banded tendon locations The post-tensioning tendons added by the program were to balance a percentage of the self-load. Next we will assign loads in addition to the self weight. Turn off the display of the tendons and select the slab object Go to the assign shell loads uniform command select the dead load pattern and enter 35 in the uniform load edit box. This will be a gravity direction load. Click apply and leave the load assignment form open. Click on the get previous selection button but this time select the live load pattern and enter 50 into the loads edit box click ok to leave the form Now we may start the analysis by clicking on the Run Analysis and Design button Once the analysis is complete the deformed shape for the dead load case appears. We will change the display to Shell stresses forces Note that we have Dead, Live, PT final, PT transfer, and PT final HP which is a load case that the program automatically added for the hyperstatic analysis. Select the PT transfer load case and then shell stresses top face and the S11 component Next we will display slab design information We will use the strip based design and for the display type, because we have post-tensioning in the model we have several choices. In addition to enveloping flexural reinforcement, which is the larger of the reinforcing calculated by the strength or stress design we have shear reinforcement, the flexural strength reinforcement by itself stress reinforcement by itself, and three levels of stress checks - transfer, normal, and long term. Select the stress check long term - this is a check based on two combinations Dead plus PT final and Dead plus 0.5 Lve plus PT final check layer B only and compressive for the stress type Moving the cursor over the design strips displays the stress check values This concludes this tutorial on the automated post-tensioning capabilities of SAFE