RAM CONCEPT

Question

Hello, 
 I have modeled the weird shape mat slab that we have in one of our projects. But the reinforcement I am getting is so huge. I mean I have already inputted user reinforcement #6@9"O.C T&B and in addition to that I am getting huge reinforcement. Can you please help me with this? Not sure if this has to do with design strips. 
 I also wanted to ask about meshing. How much small element can I have? In the above model I have 3'. Does this element size dependent on something? 
 I have attached the model in drop box link so that you can have a look at it. It didn't let me upload it here since the size was 9MB. Any suggestions for such a complicated slab would be much appreciated. 
 Dropbox link - www.dropbox.com/.../AAD-7w6-IvmXX6mqcRwCGJNoa 
 Thanks, 
 Ankith Patel

Karl G · Answer

There are some very large cantilevers, like the one marked in the image below. Are you counting on soil support in this area? If so, modeling an area spring would help reduce moments. Otherwise, you will need something much thicker than a 9" slab. 
 
 Section 19.1.1 in the RAM Concept Manual (excerpt below) has some general guidance on mesh size. 
 
 Regarding design strips, I recommend using the "Orient Span Cross Section" tool so that the cross sections within the design strips are perpendicular to the user reinforcement that is modeled. Chapter 23 "Defining Design Strips" in the RAM Concept Manual has more information on using that tool

Karl G · Answer

First, I would change the slab area behavior of the main slab so that it is two-way and not one-way. 
 
 Next, there also appears to be redundant distributed user reinforcement callouts that result in multiple individual bars at the same location. For example, the 3 set of user bars shown in the image below are all modeled at the top of the slab. It seems like only one of those groups should be modeled. A similar problem occurs with the bottom bars. 
 
 Then, I would invest time in cleaning up the design strips. Specifically, I would: 
 1. Model a separate span segments over each of the perimeter beams. I would use a full-width strip with a manual strip boundary so that the strip includes the beam and an appropriate effective slab. The design system should be set so that it is designed as a beam and not a two-way slab. 
 2. For other span segments, manually define a support width so that the first/last cross sections are at the face of the supports. Also, make sure that they are all designed as two-way slabs with torsion design not set to "Beam". Defining a support at each end of the span segment should resolve the problem with the Design Status Plan. 
 3. If shear reinforcement is detailed for the cross section at the face of the support, ignore it as the program checks reinforcement at all sections and the critical section for shear is a distance "d" away from the location. More on that point can be found on the web page below: 
 https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/3094/ram-concept-shear-reinforcement-faq 
 The revised design strip layout should look something like this:

Karl G · Answer

1) The cover is a property of the span segment. You can edit the span segment, change the values marked below, and re-run the calculations to update the program bar location. You cannot change the properties of program reinforcement. Instead, you would need to view the selection properties of the program reinforcement, change them to user bars, and then change the values. 
 
 2) Program reinforcement is always detailed perpendicular to the cross sections. The span set will govern how and where the reinforcement is displayed on the respective plans in RAM Concept only.

Karl G · Answer

1) The web page below has instructions for modeling manual strip boundaries: 
 https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/4511/manual-design-strip-boundaries-tn 
 2) You will need to edit the span segment, uncheck the box for Detecting Supports and Edges Automatically, and then enter values for the support widths.

Karl G · Answer

Due to the area spring, the program was looking for supports above the slab when generating the design strips and detecting the supports. To resolve the problem, I copied the area spring to the clipboard, deleted the area spring from the model, generated the strips, edited the span segments and unchecked the box to detect the supports automatically, and then pasted the area spring back into the model.

Karl G · Answer

This error occurs when there is a series of span segments defining a frame, and at one of the columns the span segment on one side has different support conditions defined then the span segment on the other side. For example, the span segment to the left of the column has a support detected of some width, but the span segment on the right has no support.

Karl G · Answer

Click on Edit - Cut to copy to clipboard and remove the area springs from the model. Then, click on Edit - Paste to paste it from the clipboard back into the model. 
 To eliminate the design strip error, look for adjacent span segments and make sure that for each end both span segments that end at a give point have supports identified. Reports - Calc Log will identify the problem span segments by number.

Karl G · Answer

1) For the longitude strip parallel to the beam, I would set the skew angle to 0 so that the cross sections are perpendicular to the beam span. For the latitude directions, there are irregular middle strips and other conditions that are causing a problem for span detailing. You can eliminate the program reinforcement in that direction by editing the span segments and setting MS Span Detailer to None. 
 2) The program uses the finite element for all slabs whether they are two-way slabs, drop caps, or drop panels. The design of drop caps and drop panels should be handled differently. That is accomplished with cross section trimming. See section titled "Notes on Drop Caps and Drop Panels" at the link below for more discussion. 
 https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/4514/cross-section-trimming-tn#drop 
 3) Is this question associated with a different model? The area in the PDF does not seem to match with the file at the dropbox link. I will need to review the file to answer your question.

Karl G · Answer

The issues with the reinforcement noted in your PDF are associated with span detailing. RAM Concept uses span detailing to extend program reinforcement to certain percentages of the span. This program reinforcement is largely detailed in an initial design pass that excludes the user reinforcement (we do not want to span detail user reinforcement since it may be far in excess of what is required). Later design passes, include the user reinforcement and keep program reinforcement when it is determined that it is required, including span detailing. 
 In your model, you have modeled continuous mats of top and bottom reinforcement over the entire slab. If you plan to detail continuous reinforcement, then bar cut-offs along a span do not apply and you could turn span detailing off. Other modeling issues that can create problems for span detailing: 
 1) A support is not detected at one end. When this happens, the program considers the strip a cantilever strip and the top reinforcement is extended across the entire span. 
 2) Widely varying column or middle strip widths between adjacent strips in the same frame. 
 3) Elevation or anchorage differences between the detailed program reinforcement and the defined user reinforcement. These differences can make comparisions between the two difficult and force the program to keep program reinforcement that is detailed in the initial pass when it would not be required.