Rules of Thumb for Structural System Selection

[mfstructural]

I wanted to start a thread on selection of structural systems and materials for new buildings/projects.
For example, let's say you get a set of preliminary plans from the architect to bid on. How do you decide what materials/structural systems to use?
Sometimes obviously the architect will designate a material, for example, they may want a particular building with masonry brick/CMU composite wall at the exterior.
Sometimes that's not the case, so what are the variables that would drive you to choose a given system over another. Like using steel framing with concrete on deck as opposed to a concrete flat plate construction? Cost? Ease of constructabllity?
Maybe someone has some rules of thumb they use?

 

[hokie66]

I think the most important factor is location of the project. In some areas, steel rules, in others concrete. For major developments, it may be worthwhile to do preliminary designs to enable costing of several solutions. For minor projects, the system to be used is usually self evident to a structural engineer who practices in that area.

 

[TLycan]

I think material and structural system are closely inter-related with each other, but the following factors, in my opinion, governs the Material and system:

1-Economy
in my country R.C. is 3times cheaper than steel

2-Spans
in large spans say(10meters) R.C. won't be the most optimum structural solution
3- clear height
for height, story height or total height, which is determined by the authorities and architectural the beam depth will govern the clear height
4-timing (some owners, their main objective is to finish the project fast)

For Example I 've been working with certain owner who wants that all of his hotels to be made of steel because of time reduction, though the R.C structure would have been fit better, from the economical point of view. but I understood later the difference in time between R.C and steel will be economically better for him; that is the renting and booking of the hotel in this time difference will make high revenue and compensate the difference between R.C and steel

 

[Eldorado]

Yes, local factors are important. In my area labor cost is much lower than in other parts of the country, so formwork is not that much of a cost add. Limestone is plentiful as are other components for cement, so concrete is plentiful.

Sometimes lead time dictates. For small steel jobs, I often have to use wide flanges and channels instead of steel joists.

 

[abusementpark]

I've heard you need 1000 shear studs on the job before going to a composite steel floor is economical over just doing a non-composite design. I have no idea how valid it is.

 

[mfstructural]

Good information. Any sources on approximate costs of concrete vs steel vs wood, etc? How do you quantify the costs? By square footage? I am in the Chicago area so costs are high I'm sure.

 

[TXStructural]

Labor rates in Chicago are more than twice the rates in Texas, Arkansas, and most central states. Consider that half the cost of construction is labor, probably more where you are. It's not just the material, but the level of complexity in the details and the uniformity of the structure that affects cost (principally through labor.)

Specifically, make sure that similarly situated and loaded members are identical, not just similar. For concrete, this means there are fewer piles of rebar and less confusion in placement. For steel, it means fewer shop drawings, and easier storage and hanging. For materials with repetitive members, uniformity can be the most valuable means to get an economical building. Do not minimize materials at the expense of constructibility.
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For information about concrete systems, visit a new CRSI online tool, developed for students and designers (pardon the elementary nature of some of the material) at:

http://concept.crsi.org

The embedded calcs were developed to provide a reasonable, DD-level design of different types of concrete floor systems.

For those who want the full architect- and student-level pitch for concrete, it's at

http://explorer.crsi.org