Computer Modeling - Level of Effort
Computer Modeling - Level of Effort
(OP)
Typically working on low-rise buildings (3-Story or less), I use hand calculations, spreadsheets, and Enercalc when performing calculations for design.
I have access to better analysis programs such as RISA and Ram Systems. I have noticed that these programs have the capabilities to design just about everything including masonry walls and steel joists.
I usually do not use them because it seems like using a backhoe to build a sand castle. I wanted to know at what point other engineers go from using hand calc's and spreadsheets to building a full blown computer model for their designs? Is there a big increase in efficiency to using the complete computer model for smaller building? Does anyone have a rule of thumb for switching from one analysis method to another (like a sq. ft threshold)?
Any input is welcome
I have access to better analysis programs such as RISA and Ram Systems. I have noticed that these programs have the capabilities to design just about everything including masonry walls and steel joists.
I usually do not use them because it seems like using a backhoe to build a sand castle. I wanted to know at what point other engineers go from using hand calc's and spreadsheets to building a full blown computer model for their designs? Is there a big increase in efficiency to using the complete computer model for smaller building? Does anyone have a rule of thumb for switching from one analysis method to another (like a sq. ft threshold)?
Any input is welcome






RE: Computer Modeling - Level of Effort
When something is difficult such as too many load combinations, composite WF beams, etc, I would rather invest time in inputting a more intense computer program (past history when I was an employee working on a lot of heavy commercial stuff)
RE: Computer Modeling - Level of Effort
I go to STAAD or RISA pretty quickly...I also like to use software and hand calcs/ spreadsheets together as a way to double check myself.
RE: Computer Modeling - Level of Effort
If I design a beam manually, and the loads, span, etc. change, then the revised design is probably a complete re-work. Those changes are usually very fast with a computer program, such as moving a load 2 ft to the left, and running it again. Save the file over the old one, write the new size on the drawing, and move on.
The computerized revision is often a lot cleaner also. Using a uniformly loaded simple beam for example, say the span increased from 20 ft to 24 ft. Sure, I can scale up the moments by the ratio L^2 and the deflections by the ratio of L^4, mark out the old ones, and select a new beam pretty quickly, but that's going to be hard to follow months or years later.
So many parts ended up redesigned on my projects that it would've been much, much more maddening and slower with manual calcs.
RE: Computer Modeling - Level of Effort
One of the other big advantages in my mind is the ability to try out different senarios with little effort. Want to consider floor joists instead of beams? The change takes a matter of minutes, and the program does a tonnage take-off. Need to check floor vibration? Change the concrete thickness, concrete weight, and even beam spacing effortlessly. Want to design and do a take-off of WF vs. tube columns? Again, a matter of minutes.
And then when all is said and done, you have the confidence that you did not make a math error, and the program forces you to think through all the proper design parameters... sidesway amd k-factors, load combinations,bracing criteria,etc. And having complete and organized calculations all done for you doesn't hurt either.
As you can tell, I am a RAM fan. It's not as easy with STAAD or RISA as it is with RAM, but I wholeheartedly vote for modeling software. It's not cheap, but well worth the price.
RE: Computer Modeling - Level of Effort
Of course - I am proficient with RISA and can load it up in matter of minutes - so it is worth the effort
RE: Computer Modeling - Level of Effort
I will usually use RAM SS to do preliminary design. I don't really get to cute with the designs. I will use RAM to design the beams, columns and give me preliminary numbers on the LFRS. I will also use it to help with the design of joist with varying loads when I have multiple drift and RTU combinations but will not use it for simple joist designs.
I find it easy to run multiple building configurations for my clients. I am currently working on a structure that has had 4 different iterations in about 2 weeks. Each one gets sent to the contractor for an exact bid on the structural requirements. I am working on another project where the client wanted pile loads in 1 day on two different framing schemes (4 stories).
Once we are awarded the project, I will use RAM to back check the lateral forces in the building (I will run those by hand). I will then use STAAD to run a 2D frame analysis of the building (I don't like how RAM distributes the loads in the LFRS). If the building is a simple warehouse, I will use spreadsheets and tables to design the building and use RAM to check my analysis.
Pretty complicated I guess.
RE: Computer Modeling - Level of Effort
Sometimes I do go to hand calculate something. However, when it changes, it's just down right annoys me to have to redo them. Usually, I would have been better to invest the time up front to model it instead of having to change calculations and carry them through on my notes or spreadsheets.
RE: Computer Modeling - Level of Effort
Is it easier to spend all that time working modifying wall panels with all the openings in the program to get the reinforcing necessary?
RE: Computer Modeling - Level of Effort
RE: Computer Modeling - Level of Effort
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Computer Modeling - Level of Effort
EIT
RE: Computer Modeling - Level of Effort
RE: Computer Modeling - Level of Effort
What don't you like about it?
I use RAM all the time for lateral load distribution. It works pretty well for simple diaphragm box structures.
RE: Computer Modeling - Level of Effort
RE: Computer Modeling - Level of Effort
Well geez, how often is that?? Maybe I live region with very flat terrain, but it's not too often I find myself dealing with a structure embedded into the side of a hill.
So, I guess math and physics be damned?
Do you accurately model your diaphragms?
RE: Computer Modeling - Level of Effort
EIT
www.HowToEngineer.com
RE: Computer Modeling - Level of Effort
However, simple design problems are often extremely complicated when you throw it into a design program.
A FEA program will not do tributary area based force distribution, without fudging the stiffness modifiers.
RE: Computer Modeling - Level of Effort
Do I accurately model my diaphragms..... I try to do the best that I can. How do you accurately model a flexible diaphragm in RAM? I don't think RAM has that option..... or maybe I have been using it for so long they have now added it and I just haven't figured that out yet.
I also have many projects that are embedded into the sides of hills.
I love RAM.... I use it for gravity load distribution all the time especially when I have those pesky drift loadings. I take the frame distributions as an advisement to make sure my numbers are somewhat accurate. I just like a little more control during my frame analysis (which is why I use STAAD).
Don't worry, I never have any members that end up failing in the completed RAM model but passing in the STAAD models.
RE: Computer Modeling - Level of Effort
In all cases, diaphragms can ever be sloped, and you can have multiple diaphragms of the three catagories at each story level.
RE: Computer Modeling - Level of Effort