This page discusses the optimized results from the RAM Concept PT Optimization Tutorial. Comparisons are made between the best solution found by the Optimizer and the base design, which was found by manually iterating the tendon quantities.The optimized results were produced using the Optimization settings shown in the image below.
The PT, Rebar, and SSR costs are summarized in the table below. The Optimizer reduced the total reinforcement cost by approximately 6%. Note that the best solution found by the Optimizer increased the PT Cost from the base model and reduced the Rebar and SSR Costs. During manual iterations, engineers tend to focus primarily on PT quantity only. One of the advantages of the optimizer is that also includes rebar and SSR costs in the optimized cost and, as a result, considers possible solutions that are typically not considered in a manual design.
In general, the Optimizer increased PT quantities (total PT 28% higher than base design) in almost all banded and distributed spans. See the image below for examples. In the images, the quantities in red are associated with the best solution found by the Optimizer and the quantities in yellow are associated with the base design.
The differences in tendon profiles are minor and affected the end spans only.
Mild reinforcement savings (54% cost reduction) were associated with the elimination of top reinforcement added for strength design (ACI 318-14 8.5.2) at some of the columns and the elimination or reduction of bottom reinforcement added for minimum requirements in nearly all spans (ACI 318-14 188.8.131.52). These differences can be observed by comparing the Bottom Reinforcement Plan on Layers – Rule Set Designs – Service Design and the Top Reinforcement on Layers – Rule Set Designs – Strength Design in each model.
SSR savings (13% cost reduction) were associated with a decrease in the number of studs and an increase in stud spacing along most rails. At one location (see corner column with base design boxed in image below), the Optimizer completely eliminated the stud rails .
The SSR cost reductions are the result of lower unbalanced moment for the governing strength load combinations due to the PT force and profile changes. The image below shows the Balance Loading reactions in the optimized design (red values) and base design (yellow values) at the column where the stud rails were eliminated. Note the higher Mr moments in the optimized design. This higher moment counteracts the gravity moments and effectively reduces the unbalanced moment at the column, which reduces the punching shear stress.
The unreinforced punching shear stress ratio at the column above was 1.11 in the manual design. When the unreinforced stress ratio demand exceeds capacity and the stress ratio increases, it is not obvious that a PT quantity or profile change can reduce the punching shear stress and eliminate required reinforcement. The Optimizer does a good job of finding these possible solutions.
Deflections are not considered during the optimization. However, we have found that optimized designs naturally result in reasonable deflections. The maximum deflection for the Service Load Combination: D+L are shown in the image below for the optimized model. Note that the total deflection in the optimized model was decreased from about 0.5 inches to 0.39 inches. This lower deflection was associated with the higher PT forces.
The deflections for the Initial Service Load Combination after optimization are shown in the image below. Note the area of negative (upward) deflection at the top of the cantilever. This occurred due to the increase in PT force and a slight overbalancing of the dead load. If this deflection is a concern, we recommend making some final changes to the tendon force and/or profiles in that area after loading the best result for the optimization.