# Ask the Structural Engineer! **URL:** \ **Category:** In My Humble Opinion\ **Created:** [May 20, 2003, 7:34pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365 "2003-05-20T19:34:53Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Eve](https://avatars.discourse-cdn.com/v4/letter/e/9e8a1a/32.png) [@Eve](https://boards.straightdope.com/u/Eve)\ **Post date:** [May 20, 2003, 10:23pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/21 "2003-05-20T22:23:10Z")
Will _no one_ think of the giant apes?! ---
**Author:** ![Strainger](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/strainger/32/244_2.png) [@Strainger](https://boards.straightdope.com/u/Strainger)\ **Post date:** [May 20, 2003, 10:38pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/22 "2003-05-20T22:38:26Z")
Sorry Eve, I’m not involved with civil structures. Get King Kong climbing the International Space Station, or better yet, installing a valve in an aircraft Bleed Air System, and maybe I can help. ---
**Author:** ![culture](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@culture](https://boards.straightdope.com/u/culture)\ **Post date:** [May 20, 2003, 10:44pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/23 "2003-05-20T22:44:56Z")
> [@](#): > > \*Originally posted by Eve \* > \*\*I was watching the crappy '70s remake of _King Kong_ this weekend, and I was wondering: _could_ Kong have climbed the World Trade Center? Now that we all know exactly how the towers were constructed, I thought, “Hmmm . . . The windows were probably just the right size for finger-grips, assuming he could break the glass and Jessica Lange didn’t impede his progress. But wouldn’t the pre-fab exterior panels just have peeled off with the weight of a giant ape climbing them?” > > Now, the Empire State Building: _there’s_ a structure that could withstand both a plane crash _and_ a giant ape! \*\* Yeah, I have to figure KK could not have actually climbed the WTC. Way to much weight for the facade, which as you noted is only lightly attached. OTOH, his bones could not carry the imposed load either, so let’s not get too picky. ---
**Author:** ![culture](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@culture](https://boards.straightdope.com/u/culture)\ **Post date:** [May 20, 2003, 10:47pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/24 "2003-05-20T22:47:30Z")
> [@](#): > > \*Originally posted by Strainger \* > **What kinds of analysis packages do y’all (culture and Finite Elephant) use for building construction? Not really looking for names, I’m more curious as to whether you use general purpose packages or more specialized packages that include various modules to eliminate the rigmarole of modeling from scratch.** SAP2000 Non-linear (Structural FEA), EMRC/NISA non-linear (Solid FEA), ETABS (Building Design), RAM (Component Design) ---
**Author:** ![Why\_A\_Duck](https://avatars.discourse-cdn.com/v4/letter/w/13edae/32.png) [@Why\_A\_Duck](https://boards.straightdope.com/u/Why_A_Duck)\ **Post date:** [May 20, 2003, 10:47pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/25 "2003-05-20T22:47:42Z")
So **Finite** , are ya linear or non-? – WA Duck, Submarine Structural Engineer ---
**Author:** ![lightingtool](https://avatars.discourse-cdn.com/v4/letter/l/57b2e6/32.png) [@lightingtool](https://boards.straightdope.com/u/lightingtool)\ **Post date:** [May 20, 2003, 10:51pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/26 "2003-05-20T22:51:18Z")
Beleive it or not, I was going to post this in GQ. Timely start for your thread! I work in theatre. Often, people will discuss bringing in a SE to determine the amount of weight we can hang from a point, to see if a beam will pull out of a wall if we use it as a pin rail, etc. How the hell do you folks figure that out? Do the higher-ups say SE but mean something else? Also, do you do on-location work often, or does your job keep you behind a desk, drafting all day? Thanks ---
**Author:** ![FranticMad](https://avatars.discourse-cdn.com/v4/letter/f/c68b51/32.png) [@FranticMad](https://boards.straightdope.com/u/FranticMad)\ **Post date:** [May 20, 2003, 11:07pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/27 "2003-05-20T23:07:03Z")
Another theater question. I’ve known two theater groups to rent/buy a building with a structural support in the middle of the audience area, which blocked the view. The supports were about 1 foot square, standing vertically. What would it take to remove a supporting column and replace it with a horizontal steel beam across the ceiling? How do you calculate the forces involved? How expensive? Will insurance companies agree to cover such a renovation? ---
**Author:** ![Strainger](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/strainger/32/244_2.png) [@Strainger](https://boards.straightdope.com/u/Strainger)\ **Post date:** [May 20, 2003, 11:08pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/28 "2003-05-20T23:08:48Z")
> [@](#): > > SAP2000 Non-linear ( **Structural** FEA), EMRC/NISA non-linear ( **Solid** FEA)(bolding mine) Is “solid” more general than “structural” (e.g. can include thermal elements as well) or is “solid” used to denote, say, brick and plane elements vs. beams, shells, and spars/trusses? Never heard of either of those packages. Are they geared toward modeling building material behavior? ---
**Author:** ![UncleBill](https://avatars.discourse-cdn.com/v4/letter/u/d26b3c/32.png) [@UncleBill](https://boards.straightdope.com/u/UncleBill)\ **Post date:** [May 20, 2003, 11:27pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/29 "2003-05-20T23:27:10Z")
> [@](#): > > \*Originally posted by culture \* > \*\*A structural engineer’s error killed about 150 people in the Kansas City Hyatt Collapse in 1983. \*\* The original engineering design by Gillum-Colaco International was sufficient to hold the walkways, the modications were made by Havens Steel Company to avoid threading a long rod were the cause of the tragedy. The Engineering firm failed in not sufficiently reviewing the design change made by the construction company, not in providing a good initial design. The engineers still lost their licenses in MO and TX, and GCI could no longer do engineering work. The engineers had signed the bad drawings. [More here.](http://www.uoguelph.ca/~ajenney/webpage.htm) Where did you get all those degrees? ---
**Author:** ![Hodge](https://avatars.discourse-cdn.com/v4/letter/h/5f9b8f/32.png) [@Hodge](https://boards.straightdope.com/u/Hodge)\ **Post date:** [May 20, 2003, 11:28pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/30 "2003-05-20T23:28:33Z")
Until **Culture** or **Finite** come along, I’ll take a stab at the following: > [@](#): > > Often, people will discuss bringing in a SE to determine the amount of weight we can hang from a point, to see if a beam will pull out of a wall if we use it as a pin rail, etc. How the hell do you folks figure that out? There are a multitude of factors that need to be taken into account: The length of the unsupported span, the size and type of beam (I Beam, Wide Flange, Hollow Structural Section, etc.), grade of steel, type of connection at the ends (bolted, welded, Moment Conn.?, etc.), where the point load will be applied, how heavy it is, whether or not it will be a static load or a dynamic load that could introduce transverse or tortional bending, and so on. I’ll have to leave the technical details of the calculations to the pros, however. > [@](#): > > Do the higher-ups say SE but mean something else? No. An SE does exactly what you’ve described. > [@](#): > > Also, do you do on-location work often, or does your job keep you behind a desk, drafting all day? It’s a requirement of the job that structural engineers make on-site reviews. In my office, the boss-man is out on site visits slopping around in the mud and arguing with the site super about about rebar most mornings of the week. On the other hand, if the engineer is only responsible for, say, steel joists then it’s the design engineer for the overall job who’s obligated to make the site reviews. > [@](#): > > What would it take to remove a supporting column and replace it with a horizontal steel beam across the ceiling? How do you calculate the forces involved? How expensive? Will insurance companies agree to cover such a renovation? This type of thing is done all of the time. Typically one would install temporary shoring posts to support the ceiling before removing the post and installing the new beam. This is actually rather simple to calculate (I’m told) so the true expense won’t be from the engineer but from the contractor and, depending on the situation, can get very costly. As for insurance, structural engineers have incredibly high liability and often pay an arm and a leg for coverage. ---
**Author:** ![Strainger](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/strainger/32/244_2.png) [@Strainger](https://boards.straightdope.com/u/Strainger)\ **Post date:** [May 20, 2003, 11:34pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/31 "2003-05-20T23:34:48Z")
> [@](#): > > (from **lightingtool** ) How the hell do you folks figure that out? First, you need to calculate the stresses in the structure of concern. To do this, calculate axial, bending and shear loads on the structure using [static equilibrium equations](http://physics.uwstout.edu/strength/beams/beam41.htm) (sum of forces=zero; sum of moments=0). Then, based on these loads and the geometry of the structure, you can calculate the maximum stresses in the component(s) using hand calculations aka closed form equations. Some equations either easy enough to remember whereas others are complex enough to where you need to look them up in a textbook. Alternatively, particularly for complicated structures and loading, you can use the [Finite Element method](http://www.sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/num/widas/history.html) to calculate stresses. Once you have your stresses, you compare it to the strength of the material, i.e. the maximum allowable stress before the material fails. The strength criteria include ultimate (stress at which breaking occurs, pretty much), yield (stress at which permanent deformation occurs), and fatigue (strength at a given number of load cycles). For each criterion you also need to account for shear or tensile loading, since shear strength of a given material is generally much lower than tensile strength (for the material with which I’m familiar, anyway). How is the strength determined? Initially from testing to derive empirical results. Each material also has a standard to which it is to be fabricated, to ensure robustness. ---
**Author:** ![Ranchoth](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranchoth/32/1066_2.png) [@Ranchoth](https://boards.straightdope.com/u/Ranchoth)\ **Post date:** [May 21, 2003, 12:00am UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/32 "2003-05-21T00:00:26Z")
How thick would I have to make a Copper cuirass in order to equal the strength of a cuirass made out of steel? ---
**Author:** ![lightingtool](https://avatars.discourse-cdn.com/v4/letter/l/57b2e6/32.png) [@lightingtool](https://boards.straightdope.com/u/lightingtool)\ **Post date:** [May 21, 2003, 12:23am UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/33 "2003-05-21T00:23:40Z")
Thanks for the responses. I’ve read them all about 8 times, as well as the link, and I think I understand. One more question that stems from my personal experience doing theatre in a barn during my wild and crazy youth: How would one determine all that when dealing with a wooden structure that was built 40 to 50 years earlier? (ok, two more) Do any of you folks do any earthquake safety work on pre-existing buildings? What’s that process like? Thanks ---
**Author:** ![OxyMoron](https://avatars.discourse-cdn.com/v4/letter/o/e9a140/32.png) [@OxyMoron](https://boards.straightdope.com/u/OxyMoron)\ **Post date:** [May 21, 2003, 3:28am UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/34 "2003-05-21T03:28:29Z")
I think if I had everything to do over again, I’d seriously consider structural engineering. So here’s my big-picture question: is there any building technology currently in use that you think is being pushed beyond its reasonable limits? IOW, what’s the next Tacoma Narrows, in your opinion? ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [May 21, 2003, 3:29am UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/35 "2003-05-21T03:29:59Z")
Three questions: a) FEA - how old is this technique, and what did you guys do before it existed? Beyond a very basic structure, could it be done with PCs? (The matrices must have been a nightmare!) b) Why, exactly, do bridges and elevated walkways “bounce”? Is it due to the use of pre-stressed steel beams that makes even the tiniest vibration like a mini earthquake? How many people call in to complain some bridge is going to collapse because its bouncing while I sit in traffic on it (as traffic goes by in the other direction, for example?) c) Those old, heavily-rusted out bridges, high-tension towers, and such…does anyone really inspect them with NDT to make sure they’re sound? If so, how often? Or, is that a job for ME’s? ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [May 21, 2003, 3:31am UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/36 "2003-05-21T03:31:29Z")
> [@](#): > > \*Originally posted by Jinx \* > **…Beyond a very basic structure, could it be done WITHOUT PCs? (The matrices must have been a nightmare!)…** Sorry! - Jinx! ---
**Author:** ![Trigonal\_Planar](https://avatars.discourse-cdn.com/v4/letter/t/0ea827/32.png) [@Trigonal\_Planar](https://boards.straightdope.com/u/Trigonal_Planar)\ **Post date:** [May 21, 2003, 6:19am UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/37 "2003-05-21T06:19:53Z")
Depending on the bridge design, one end of the platform is anchored to prevent any horizontal and vertical movement (its “pinned”). The other end is free to move (or, has a “roller” connection). This allows the bridge to expand and contract with temperature changes. But since the one end is not secured, it also means it can bounce up and down. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [May 21, 2003, 6:43am UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/38 "2003-05-21T06:43:08Z")
Do you have any pet peeves about badly designed structures (or any product for that matter)? Perhaps some design trends which look purposeful but are just for show and undesirable from an engineering standpoint? ---
**Author:** ![CanvasShoes](https://avatars.discourse-cdn.com/v4/letter/c/74df32/32.png) [@CanvasShoes](https://boards.straightdope.com/u/CanvasShoes)\ **Post date:** [May 21, 2003, 7:52am UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/39 "2003-05-21T07:52:01Z")
Well darn!! I want to find the engineers that are responsible for designing the little, teensy, playing card-sized “platforms” (and I use that term Veerrreeee lightly) that are used in grocery store checkout stands. Supposedly they are there for a purse, or checkbook so that you can get out your credit card from INSIDE the purse, or put the checkbook on the little stand and actually write a checkto pay for your groceries. I’d like to know WHY they didn’t make them big enough to actually do the job. ---
**Author:** ![Finite\_Elephant](https://avatars.discourse-cdn.com/v4/letter/f/a88e57/32.png) [@Finite\_Elephant](https://boards.straightdope.com/u/Finite_Elephant)\ **Post date:** [May 21, 2003, 12:04pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/40 "2003-05-21T12:04:00Z")
> [@](#): > > \*Originally posted by Why A Duck \* > \*\*So **Finite** , are ya linear or non-? > > – WA Duck, Submarine Structural Engineer \*\* It depends on the situation, silly! Seriously, given the level of software and speed of computers available today, we do a lot more non-linear analysis than is probably strictly necessary. Single story post-and-beam systems have been designed for millenia without knowing the effects of p-delta. [Previous page](https://boards.straightdope.com/t/ask-the-structural-engineer/176365.md?page=1) [Next page](https://boards.straightdope.com/t/ask-the-structural-engineer/176365.md?page=3)