# 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:** 3
**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, 12:09pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/41 "2003-05-21T12:09:55Z")
> [@](#): > > - As for insurance, structural engineers have incredibly high liability and often pay an arm and a leg for coverage. \*\* Hodge is more or less correct on his other responses, but I think the question above is about whether or not the theater’s insurance would cover. I am not an insurance agent, but I doubt it. ---
**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, 12:16pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/42 "2003-05-21T12:16:25Z")
> [@](#): > > \*Originally posted by Ranchoth \* > \*\*How thick would I have to make a Copper cuirass in order to equal the strength of a cuirass made out of steel? \*\* Copper isn’t a very common structural material. Based on a quick check of material properties, I’d say at least twice or three times as thick, depending on the alloy. If it were my body part, I’d stick with steel. ---
**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, 12:24pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/43 "2003-05-21T12:24:46Z")
> [@](#): > > \*Originally posted by OxyMoron \* > **I think if I had everything to do over again, I’d seriously consider structural engineering.** Funny. I’d have gone into computer science. \*\*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? \*\* [/QUOTE] I think that with the current state-of-the-art in analysis and materials, that another Tacoma Narrows is unlikely. I think that the Biggest Unknown is in seismic design. Every time the earth shakes, we find out more we didn’t know before. Other than seismic, I think the increasing emphasis on speed of design and construction will probably lead to another Hyatt Regency. The Hyatt Regency wasn’t just one design mistake, but a string of bad snap judgements and missed warning signs, mostly owing to a tight construction schedule. ---
**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, 12:41pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/44 "2003-05-21T12:41:56Z")
> [@](#): > > \*Originally posted by Jinx \* > **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!)** A lot of pre-computer analysis was done with very clever approximate methods, such as Portal Frame Analysis and Moment Distribution, both of which are still taught in school (or at least were). These methods required a lot of calculation, but not as much as a stiffness matrix method. Legend has it that SOM ran a computer model of Sears Tower once (and only once) to verify their hand calculations. It cost $10,000 to do. In 1972. > [@](#): > > **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?)** Ah, yes, vibration. I am not a bridge engineer, so I can’t speak to vibration in bridges, but a floor system of steel beams in the 22-30 foot range have a natural frequency that resonates at most people’s walking pace. If the system is light enough, your walking will cause it to feel like it’s bouncing. It’s especially noticable in open areas such as shopping malls, where ther damping effect of furniture and partitions is minimal. I imagine that certain bridges may resonate with the frequency of a truck’s suspension rebound in a similar manner. > [@](#): > > \*\*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? \*\* I’m a building engineer, so I don’t usually deal with those things, but we all get the same magazines. Based on those, yes, there is quite an industry based on inspecting those things. Of course, writing a report is one thing. Having the DOT pay to do anything about it is another. ---
**Author:** ![culture](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@culture](https://boards.straightdope.com/u/culture)\ **Post date:** [May 21, 2003, 1:27pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/45 "2003-05-21T13:27:31Z")
> [@](#): > > \*Originally posted by CanvasShoes \* > \*\*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. \*\* Definately designed by an architect! ---
**Author:** ![culture](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@culture](https://boards.straightdope.com/u/culture)\ **Post date:** [May 21, 2003, 1:32pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/46 "2003-05-21T13:32:14Z")
> [@](#): > > \*Originally posted by OxyMoron \* > \*\*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? \*\* Finite elements. This is the technology currently used to model structures on computers. This technology is very powerful but unfortunately allows unqualified people to perform complex analysis without really understading what they are doing. This is very dangerous and we see screwed up analysis all the time. Good thing structures have big factors of safety. I believe the most likely next tacoma narrows will be a long-span roof (such as a stadium) collapse where the analysis, performed using finite element, was performed improperly. ---
**Author:** ![culture](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@culture](https://boards.straightdope.com/u/culture)\ **Post date:** [May 21, 2003, 1:37pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/47 "2003-05-21T13:37:09Z")
> [@](#): > > \*Originally posted by Strainger \* > \*\*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? \*\* EMRC/NISA is a general purpose program that has shell (thick, thin and hybrid), beam, solid (4 and 8 node) and gap elements (amoung amny others). It can model pretty much anything. SAP2000 is intended to model only beams, although it does have shells for shwar walls and diaphrams. It works great for buildings but miserable for anything else. Much faster than EMRC NISA when modeling buildings, however. ---
**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, 1:38pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/48 "2003-05-21T13:38:50Z")
culture’s right. There have been several instances of structural collapse (Hartford Arena comes to mind) caused by the inability of the engineer to translate the idealized computer model to the real-world structure and vice versa. Mario Salvadori’s _Why Buildings Fall Down_ is an interesting and accessible read on the subject. ---
**Author:** ![culture](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@culture](https://boards.straightdope.com/u/culture)\ **Post date:** [May 21, 2003, 1:41pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/49 "2003-05-21T13:41:29Z")
> [@](#): > > \*Originally posted by UncleBill \* > \*\*Where did you get all those degrees? \*\* Texas A&M and the **M** ental **I** nstitute for the **T** ouched ---
**Author:** ![culture](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@culture](https://boards.straightdope.com/u/culture)\ **Post date:** [May 21, 2003, 1:54pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/50 "2003-05-21T13:54:10Z")
> [@](#): > > \*\*Mario Salvadori’s _Why Buildings Fall Down_ is an interesting and accessible read on the subject. \*\* Gordon’s _Structures, or Why Things Fall Down_ is better IMHO, but both are a good read. Gordon’s book covers civil and mechanical engineering concepts. Mario Salvadori’s _Why Buildings Stand Up_ is also good. Wearne’s \* Collapse: Why Buildings Fall Down\* gives several interesting in-depth case studies but is more technical and of limited interest to non-engineers. I keep all four on the desk right in front of me to keep these things in my mind. I spend a lot of time investigating structural failures in my practice. ---
**Author:** ![culture](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@culture](https://boards.straightdope.com/u/culture)\ **Post date:** [May 21, 2003, 1:55pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/51 "2003-05-21T13:55:34Z")
Thanks to Finite Elephant, Hodge and Others for the backup. ---
**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, 2:03pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/52 "2003-05-21T14:03:49Z")
You’re welcome, **culture**. I apologize for any thunder-stealing. And BTW, I went to Illinois. Twice. I highly recommend grad school as a means of going into career stasis during a recession. And since I’m cleaning up loose ends, my firm uses RAM, RISA, Robot, SAFE, and the usual assortment of one-trick programs. I’m in the Rust Belt, so our practice is mostly in steel. ---
**Author:** ![culture](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@culture](https://boards.straightdope.com/u/culture)\ **Post date:** [May 21, 2003, 2:04pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/53 "2003-05-21T14:04:51Z")
> [@](#): > > \*Originally posted by lightingtool \* > \*\*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 \*\* We do this all the time. At some of the mega concerts, the producers want to hang 20,00 to 50,000 pounds from our carefully designed stadium roof. Therefor we get hired to supervise the rigging. We even get to watch some of the concerts from the ceiling framing to monitor things. ---
**Author:** ![culture](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@culture](https://boards.straightdope.com/u/culture)\ **Post date:** [May 21, 2003, 2:10pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/54 "2003-05-21T14:10:12Z")
Opps, forgot about SAFE. We use that too, as well as RISA 3D sometimes. ---
**Author:** ![culture](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@culture](https://boards.straightdope.com/u/culture)\ **Post date:** [May 21, 2003, 2:36pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/55 "2003-05-21T14:36:15Z")
> [@](#): > > \*Originally posted by Finite Elephant \* > \*\*You’re welcome, **culture**. I apologize for any thunder-stealing. > > And BTW, I went to Illinois. Twice. I highly recommend grad school as a means of going into career stasis during a recession. > > And since I’m cleaning up loose ends, my firm uses RAM, RISA, Robot, SAFE, and the usual assortment of one-trick programs. I’m in the Rust Belt, so our practice is mostly in steel. \*\* My minion did the same thing (UICU/two times). He is working out pretty well so far. UI was one of my top five picks for grad school. Could resist the call of the east coast however. ---
**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, 3:07pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/56 "2003-05-21T15:07:55Z")
> [@](#): > > \*Originally posted by culture \* > \*_Gordon’s Structures, or Why Things Fall Down is better IMHO, but both are a good read. Gordon’s book covers civil and mechanical engineering concepts. Mario Salvadori’s Why Buildings Stand Up is also good. Wearne’s \* Collapse: Why Buildings Fall Down_ gives several interesting in-depth case studies but is more technical and of limited interest to non-engineers. > > I keep all four on the desk right in front of me to keep these things in my mind. I spend a lot of time investigating structural failures in my practice. \*\* I’ve read, and love, both of the Salvadori books, and will now try the Gordon. Interesting that the technology you identify as problematic is something used in creating a design, rather than something intrinsic to the design itself. ---
**Author:** ![Arfur](https://avatars.discourse-cdn.com/v4/letter/a/57b2e6/32.png) [@Arfur](https://boards.straightdope.com/u/Arfur)\ **Post date:** [May 21, 2003, 3:09pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/57 "2003-05-21T15:09:58Z")
I live in Chicago. I am not a paranoid nut, however I keep hearing about this fault line in southern Illinois. How screwed would we be here in Chi-town, if a big one hit down south? A.) I live in a simple wood frame house, an old one. B.) How about our downtown? Thanks. ---
**Author:** ![Spectre\_of\_Pithecanthropus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spectre_of_pithecanthropus/32/12343_2.png) [@Spectre\_of\_Pithecanthropus](https://boards.straightdope.com/u/Spectre_of_Pithecanthropus)\ **Post date:** [May 21, 2003, 3:38pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/58 "2003-05-21T15:38:20Z")
> [@](#): > > \*Originally posted by Hodge \* > \*\*Does your hatred of architects burn with the fire of a thousand suns? Or does it merely smoulder like BBQ charcoal, only flaring up at the approach of architectural flesh? > > **Hodge** (structural draftsman) \*\* Which brings up a good point. Why _would_ **culture** hate architects? For that matter, maybe he can enlighten us as to the division of responsibilities on a building project. It seems like the architect gets most of the credit, but the structural engineers have to vouch for the solidity of every cubic centimeter of the finished work. Do architects and s.e.'s often work together in the same firm, with each carrying out different responsibilities. ---
**Author:** ![culture](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@culture](https://boards.straightdope.com/u/culture)\ **Post date:** [May 21, 2003, 3:38pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/59 "2003-05-21T15:38:37Z")
> [@](#): > > \*Originally posted by Arfur \* > \*\*I live in Chicago. I am not a paranoid nut, however I keep hearing about this fault line in southern Illinois. How screwed would we be here in Chi-town, if a big one hit down south? > A.) I live in a simple wood frame house, an old one. > B.) How about our downtown? > Thanks. \*\* You are probably thinking of the New Madrid fault centered in Memphis. If the big one hit, you will be safest in a one-story wood frame house that has wood siding. Old multi-story masonry buildings are the worst. Modern hi-rises are pretty safe as they tend to be more carefully engineered. How bad Chicago will get it when the New Madris fauly goes (and it will) is very hard to say. However, Chicago is rated a seismic zone 1 which means if you do get large ground motion in chicago you are screwed as the buldings are not built to resist it (However, zone 1 also implies geologist think you will not get large ground motions). Memphis, however, is doomed if they get a magnitude 8 quake, because they have not had a signficant quake since 1830 so they citizens tend to forget it can happen. ---
**Author:** ![culture](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@culture](https://boards.straightdope.com/u/culture)\ **Post date:** [May 21, 2003, 3:46pm UTC](https://boards.straightdope.com/t/ask-the-structural-engineer/176365/60 "2003-05-21T15:46:39Z")
> [@](#): > > \*Originally posted by Spectre of Pithecanthropus \* > \*\*Which brings up a good point. Why _would_ **culture** hate architects? For that matter, maybe he can enlighten us as to the division of responsibilities on a building project. It seems like the architect gets most of the credit, but the structural engineers have to vouch for the solidity of every cubic centimeter of the finished work. Do architects and s.e.'s often work together in the same firm, with each carrying out different responsibilities. \*\* This is kind of a runnuing joke in the industry. Architects and SEs have a love-hate relationship. Architects are vital to gettinga building built, but so are SEs. SEs feel the architects get too much credit for the results. Look at the plate on most buildings. It list the owner, architect and contractor, but requently the SE is left off. Architects get larger fees than SEs. The architects is normally the prime design professional (i.e. the SE works for the architects), and SEs feel this gives the architect too much control over the SEs design. However, overall, the architects and SEs get along just fine as they are our best clients, and it is hard to hate the hand that feeds you. [Previous page](https://boards.straightdope.com/t/ask-the-structural-engineer/176365.md?page=2) [Next page](https://boards.straightdope.com/t/ask-the-structural-engineer/176365.md?page=4)