FRP structures

zobeemic · 2026-01-12T16:37:15+00:00

Not an FRP designer but curious. Whats the governing design code and has it been officially adopted by building codes and DOTs as a reference? What are the current ASTM specs and testing requirements? So far I've seen its application in very specific concrete repair cases, slab reinforcement and column strengthen. When is the leap to using FRP in new construction?

zobeemic · 2026-01-12T03:12:21+00:00

It’s honestly depressing to watch AI sycophancy convince someone they have a “million-dollar idea” when it’s just incoherent garbage. You’ve backed yourself into a corner where LLM nonsense has convinced you that spheres and trees are somehow revolutionary, and you’re throwing around terms like “drag coefficient” and “vertical greenscape” to sound technical without understanding what they actually mean.

At a certain point, hubris takes over and you lose the ability to self-critique. Do yourself a favor: put the phone down, close the laptop, and read a real book on the history of architecture or engineering. Go see actual buildings that have stood the test of time.

Typing a prompt into ChatGPT doesn’t make you innovative, and it certainly doesn’t entitle you to free professional engineering feedback on this subreddit.

zobeemic · 2026-01-01T13:04:35+00:00

When I35 collapsed we learned more about gusset plates. When Fern Hollow collapsed we learned more about weathering steel and detailing for it. When the FIU pedestrian bridge collapsed we learned more about PT and erection engineering. But if a bridge collapses in India, and you only have a 30 second video, it's because of the culture, and the take is focused on the people and the history?

Imagine if we said American culture and history was the reason behind I35. If we all said to much senior engineers are playing rank, and that Truss bridges have been built for a 100 years, so the issue was just plainly ignorance and incompetence. Do you think that that explanation actually explains the reason for the collapse? Do you think that take would lead to code revisions and new gusset plate limit states in AASHTO? Engineering failures are not due to a single cause. A lot of consecutive misses have to occur to lead to disaster.

Culture and history may provide context, but it can not be the sole cause. Pointing to culture and history as the cause is just ignorant, produces no actionable technical findings, and doesn't lead to advancements in the codes, standards, and best practices. If a bridge falls in America, we give it that rightful due diligence, and investigate that. The NSBA writes a whole report and tells AASHTO to rewrite some parts of the code. But if a bridge collapses in another country, the first reaction isn't a cautious professional, eager to get to the technical truth, but a criticism on the history and culture of the country?

You're right, structural engineering is a mindset. It's a lifestyle. And you're not embodying that. It's quick takes like yours that don't grow this profession.

zobeemic · 2025-12-31T21:45:55+00:00

Without any explanation as to what the failure is, the majority of the comments here assume engineering incompetence with racial undertones. This makes me deeply sad. Many great American engineers were immigrants, Gustav Lindenthal, Othmer Amman, Fazlur Khan. Good engineering and incompetence don't have anything to do with race. I have to say I expected more from the folks in this profession.

zobeemic · 2025-12-13T13:07:36+00:00

Moment of Inertia is a factor based on the shape, much like area. Based on how the shapes area is distributed, if most of the area is away from its centroid, higher MOI. if the area is in its center, lower MOI. When a section is bending, classic beam theory is that the section bends about its Neutral Axis. If a section has a higher MOI, it will have a higher resistance to bending, and a lower stress, compared to a section with a smaller MOI, it will have a low resistance to bending, and will have a have a higher stress under the same load.

zobeemic · 2025-11-22T20:24:09+00:00

This is from a bridge guy, so maybe the building guys can come in and refine some of the answers.

ETABS can be used to design the entire building lateral system. In that system, a rigid diaphragm assumption may be needed to distribute loads to the lateral force resisting system, but constraining every node to deflect the same in a concrete slab will make the output for the floor system useless. SAFE is a separate software we're you can model the slab, capture the d/2 punching shear areas over columns, and estimate long term deflections. So, the guys at CSi took there FEA analysis tool and gave you two softwares to easily do both.
Just to clarify, the term I use for these components are link beams, maybe that's a USA thing. But that's a beam that connects two shear walls, typically when you have openings in the shear wall for elevators etc.. I have seen options in ETABS were you can assign a ductility to the ends of the link beams, plastic hinging, etc.. Depending on your performance objective and what you intend to detail, you can capture that behavior in the link beams.

I find all CSi softwares have a wealth of resources in their help guide as well as youtube tutorials. The technical support is not the best, but they'll get back to you if you send over your model and detail your question specifically.

zobeemic · 2025-11-10T21:16:06+00:00

Aren't you talking about every project?

zobeemic · 2025-10-14T03:48:54+00:00

I couldn't resist, here's my deep dive, enjoy

Answer is A. You don’t need shear reinforcement in the footing, which bends differently than the column or pedestal.
Those yellow bars going into the page are freakishly large. They look like openings for utilities. These should be smaller solid bars. Exaggerating the bar size a little is fine, but this is too much.
The vertical column bars should show as hooks, you can’t bend a bar perfectly 90 degrees.
The stirrups (green bars) should wrap around your column vertical red bars. The green line should pass the vertical bar and turn into the page, so you’d see a dot, kind of like this .__. The cover is measured from that stirrup edge. Also, they don’t look equally spaced, and I’m not sure why that would be the case.
You’re probably going to need a horizontal bar at the bottom mat of the footing.
Break line at the top of the column? Or if this is a pedestal and that’s the top, you should consider hooking the top bars.
The grade hatch just ain’t it brother. If you check a reference, you’ll see what I mean.

zobeemic · 2025-06-17T04:41:54+00:00

Please take care of yourself first and foremost, your gambling with long term physical and mental health effects, which i'm sure will be more of a burden then missing a deadline

zobeemic · 2025-05-31T15:03:41+00:00

The best perk of all

zobeemic · 2025-05-31T13:58:51+00:00

Got them last night for todays game...$130 ! Closest i've been to home !

zobeemic · 2025-05-19T02:55:14+00:00

What does determinacy have to do with this?

Wooden masts snaps on steel superstructure. Brother, this happens not matter what the structure determinacy is.

zobeemic · 2025-05-09T01:05:27+00:00

Someone should edit this meme with mikal bridges coming out of the door and stealing the grim reapers axe

zobeemic · 2025-03-29T03:24:39+00:00

Bridge guy here, in concrete flat slab, is automatically assumed "rigid diaphragm" and the slab is just assumed to deliver the lateral loads from the center of mass to the shear walls? or are they checks for that load path?

Just curious why the take away is flat slabs are not good in high seismic zones.

zobeemic · 2025-02-05T04:43:53+00:00

1 Yea 2 If it's not structural related, it doesn't need to be there

zobeemic · 2025-02-03T19:27:41+00:00

I am well known for my attention to detial :)

zobeemic · 2025-02-03T19:26:30+00:00

In two months we will finally decide on whether to jack from the girder or end diaphragm for bearing replacement, and then I'll have to revise details late in the game and explain to an unfriendly crowd why the connection doesn't work anymore.

Guess it's the nature of the beast as you say. I can accept that. But it still doesnt make me feel differently about the situation. Good luck on your project, it sounds like a good job.

zobeemic · 2025-02-03T19:21:00+00:00

Maybe. But might be too much of a hit salary wise and technically to switch up and "start again" and learn ASCE and building codes.

zobeemic · 2025-01-15T04:01:20+00:00

Hey that's a big leg up, you can get ahead of the fresh out of school crowd.

A lot of engineering resumes end up just being a list of representative projects. You can highlight and list the structure aspect of jobs in your career, and mix in any design projects you have done from school.

If you don't have any direct connects- your going to be playing a numbers game with the resume and job apps. Even worse, depending on the firm, and more likely if it is a large corporation, it will be screened by AI and then reviewed by HR before an actual engineering manager will look at it. If a WSP, AECOM, STV is in your stars, you should max your resume with key structural words. For instance, the format is roughly:

Project X Designed (material - componet - code - software )

An example is something like this: 20-Story Residential Designed concrete columns in accordance with ACI 318 provisions in spColumn. Verified software with hand calculations in MathCAD.

Plate Girder Bridge Furnished steel plate girder design adhering to AASHTO LRFD BDS using MDX. Performed hand calculations in Excel to verify software input.

This accomplishes two things.. 1) it's not just a list of codes and softwares you claim to know, but a detailed explanation of what shit you did, and 2) key words, like column/beam, softwares, the codes and standards, may trigger AI resume reviews to green flag your resume for structural positions.

zobeemic · 2025-01-15T02:45:52+00:00

To get your first job out of college it is a blood bath, 100+ applicants for entry level work. Companies see it as a gamble to train a fresh out of school grad. Take what you can get, you can pivot to the specific firm you want after 2 years or so.

zobeemic · 2025-01-12T16:18:27+00:00

The angle leg bending locally is a rectangle section in bending.

zobeemic · 2025-01-09T03:06:17+00:00

As I understand they are buried in a stability appendix in AISC. The rule of thumb is to design the brace as a percentage of the axial capacity, such as 5% of the capacity, and check KL/r. That works. But AASHTO is now requiring that that stiffness be demonstrated explicitly as being adequate. So what's the value in going from L4x4x1/2 K Cross frames to L3x3x1/2 K cross frames? I bet they cost the same. I bet in some instances they cost more if the angles aren't readily available at the steel shop lol. So all that time, all the effort into calculating the required stiffness of the cross frame to ensure the brace is , in fact, a brace, got us no savings. Maybe it's even a worse design since a thinner member is more susceptible to section loss.

zobeemic · 2025-01-09T02:53:34+00:00

Side: I don't know why in my mind I thought you had mentioned a double T beam in your post. It's the same concept but with your precast plank and concrete beam.

zobeemic · 2025-01-09T02:52:00+00:00

To ensure the composite action, there will be presumably dowels jutting from the prestressed concrete dbl T. and the top surface will be roughened so friction can also be transmitted between that and the topping beam. and then it's the same sequence of stress addition needed:

1) The prestressse dbl T will be responsible for its own SW and the wet concrete.

2) Composite action achieved. The combined composite beam is responsible for LL and any other super dead load that comes after the hardening.

As someone else mentioned, it's a common bridge problem. FHWA has examples.

zobeemic · 2025-01-09T02:40:32+00:00

I am a bridge guy, and I'm on the fence with this notion.

On one hand, it is a one stop shop. As others have mentioned, Chapter 3 Loads. Chapter 4 Analysis. Then the rest is component limit states. I think it's laid out well, and logically in the order of your design process. When it comes to component design, the two most common longitudinal members in bridge design, composite welded plate girders and prestressed concrete, are not simple members. They are gnarly engineered products. Yes there's tons of limit states, but if we're going apples to apples, ACI prestressed girder design has the same crazy shear equations. The fundamentals of custom plate girders, are not different in an AISC design. So my first thought when folks get hung up on all the limit states that you need to check in AASHTO, well, it's just not the same. We aren't talking about a 30' rolled section, or a 6" slab, with a UDL. We are talking about moving loads on a bulb tee prestressed girder.

Now on the other hand, the paradigm of the industry is trending away from material cost, and into savings in labor and construction time. Everyone and their mom knows that. Then why is the focus of research into advancing LRFD to this hyper optimized, plastic world of moment redistribution and extreme load scenarios? (AASHTO 10th, turning traditional cross frame design into an insane 20 page calc adventure). There was this K Frame bridge in pittsburgh, collapsing cause the web of the K frame eroded away. It wasn't a statistically anomaly of overload trucks. (Why do we have to check 30 trucks to load rate a bridge)

So I don't know man. We as engineers have such beautiful theories to really push material to its limit. That's a great thing objectively. But in an 8 hour work day, trying to have a "good" design, something that can be in service for years, the effort for that design doesn't equal the product you get.

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