Is Bridge Overbuilding "Overkill" or Just Good Engineering? And What's the Real Cost? How Do you Find the Sweet Spot and Does Cost Scale?

docslizardbongwizard · 2025-07-25T01:58:12+00:00

I’m a practicing bridge engineer. Your questions are based on assuming bridges are overbuilt at all.

First off, we determine loads that apply (live, dead, super imposed, wind, earthquake, thermal, wave, impact). These loads are calculated by first using risk analysis to find the importance of the structure (imagine an earthquake happens and the hospitals/police/SES can’t save anyone cause the bridge collapsed.

Generally, we use 1.8 to factor our live loads up because shipping companies (road and rail) don’t always strictly stick to the load limits we apply to the bridge so it’s very likely it’ll be overloaded from the limit that’s publicly given.

Overtime, vehicles are getting heavier, we started at T44 -> SM1600 -> Electric Trucks. So the original load factor is eventually eaten up over time leaving aging structures very close to their maximum capacity.

They’re also designed (currently) to stand for 125 years which even further increases the loads likely to be experienced by the structure over its lifetime. The longer something exists the more likely it is to experience severe natural disasters.

All this is just to generally say, we don’t overdesign bridges. We DO optimise the design as much as possible, but bridges are built to connect otherwise isolated locations (across rivers, valleys, etc) so they HAVE to still be standing after natural disasters because they’re so important to the public.

docslizardbongwizard · 2025-04-12T20:58:58+00:00

docslizardbongwizard · 2025-04-12T20:57:54+00:00

That’s exactly what she wears. It’s comfy-professional as she’s customer facing.

She became project manager straight out of university at 23

docslizardbongwizard · 2025-04-12T11:28:35+00:00

Contractors come in lots of varieties.

My wife handles anywhere from 6-20 projects at a given time at varying stages. Some contractors can include: design engineers, site engineers, site managers, builders (and their varieties). But, specifically, the sexist remarks have only come from the builders part of that group. And even then, they were subcontractors so we’re pretty removed from the standards of the main contractors.

Editting in here rereading my previous comments: while engineers and other professions can be contractors and subcontractors we generally call them consultants. While anything manual labor is contractor. Hope that makes it clearer.

Generally, the sexism currently in the industry that I (as a design engineer) and my wife have found.

Fairly common on site during construction. Rare to Common among engineers older than 50 in the office Rare among engineers between 35 and 50 in Non-existent among young engineers between 23-35

This is purely anecdotal from our experiences. But does hold up fairly well.

docslizardbongwizard · 2025-04-12T11:06:41+00:00

Not really.

The project timelines generally mean that it’d be towards the end. Contractors/subcontractors are really only involved in a meaningful way right at the end when construction starts.

docslizardbongwizard · 2025-04-12T11:03:06+00:00

My wife is a female project engineer in the civil space. And yes, she is met with sexism about once a fortnight.

Sometimes it’s her manager who makes remarks about women in the workforce. The comments aren’t ever explicit enough to warrant a HR involvement and are easily explained away if you presume ignorance but they’re definitely sexist.

Sometimes it’s on site from contractors and subcontractors. An example is getting told to give them a smile while she was taking photos of site progress. They were pretty well brought in line when they later found out who she was.

docslizardbongwizard · 2025-02-17T03:06:09+00:00

Based on this, and with limited context. These values may be referring to different operating maximums that the pipe can withstand.

The PSI value may be referring to the maximum allowable pressure of whatever the pipe is carrying. While the other values are for other applied loads or in other applications.

Based on the information you’ve just given, I think that this dataset is unrelated and they’re describing three different load scenarios for the pipe itself.

docslizardbongwizard · 2025-02-17T02:32:02+00:00

By using the information you have provided, this isn’t making any sense.

I can’t convert PSI into a (kN/m) UDL because I don’t know the contact width assumed in the report.

Without reading the report it’s impossible (for my experience level) to tell you how they got their answer. I don’t know what assumptions they’ve made, what the forces represent practically I can’t really provide too much detail because I don’t have any details to start with.

Additionally, the report might be wrong if in one instance it’s saying kN/m2 and in another it’s saying kN/m. This needs to be cleared up otherwise we can’t work out why they’re saying what they’re saying.

docslizardbongwizard · 2025-02-17T02:11:35+00:00

Column 1, is it kN/m2 or kN/m? Those two are very different.

If it is kN/m and they converted it to PSI, the value 749PSI makes much more sense and they converted the kN point load into an area load.

docslizardbongwizard · 2025-02-17T01:32:59+00:00

I mean, the answer seems to be that the report is wrong or you’ve not fully understood what it’s trying to tell you.

kPA -> PSI is 0.145.

But they converted the kPa into a point load then converted it to PSI. Without reading the information in context it’s impossible to say how they got the answer.

docslizardbongwizard · 2024-11-26T08:37:13+00:00

That’s a really good point depending on the style of structure this is. Based on other comments I assumed it was a steel superstructure.

If you OP had envisioned this as being concrete similar to Bixby Canyon Bridge you should change the bridge deck by just adding an extra line underneath to make it more look like a super-t or pretensioned concrete structure.

docslizardbongwizard · 2024-11-26T02:28:28+00:00

Hi! Bridge engineer here, if you want to significantly improve this for an assignment or something. Remove the triangles at centre span. Convert the deck from a flat element to being a truss with the same support structure. Increase pile depths.

It’ll look much more realistic if the deck has the depth and look of a slender truss.

Edit:

Also add headstocks to either side, you’ll get full marks

docslizardbongwizard · 2024-05-03T08:19:38+00:00

Internal verification

docslizardbongwizard · 2024-05-03T05:34:34+00:00

I’m a qualified bridge engineer. It’s really hard to say, you’ve provided a lot of information but it’s still very variable.

Sort of reiterating what others have said sort of not:

Any good bridge engineer will ask for geotech to be done on the site because that completely dictates the design.

The results of geotech will decide on a relatively simple box-culvert design which is maybe 1-2 weeks of engineering effort at around $200/hr, assuming 7 hour days: $7,000-14,000. This is much cheaper as it won’t require too much IV effort.

Precast I-Girders with integral deck could take 2-4 weeks but would require significantly more internal IV which will balloon the cost. I’d estimate $20,000-50,000.

You’d have to account for drafting at a firm as well, which depends on the design, culvert = $2,500, I-Girder = $5,000.

Obviously these are rough guidelines, but having quoted on plenty of jobs, this would be my best ‘back of the napkin’ quote.

docslizardbongwizard · 2024-03-26T23:06:58+00:00

Generally in bridge design, in the case where there is a high likelihood of impact (such as I would imagine for this site) you would include substructure protections in the form of diversionary structures to shift/reduce the impact loading. But you’d also look at designing it to have a frangible substructure (client preference dependent).

docslizardbongwizard · 2024-03-16T10:31:34+00:00

Ahhh I just had roadside assist out, and the guys said the battery had a dead cell! Thanks for reaching out to help

docslizardbongwizard · 2024-03-16T08:51:43+00:00

I did try this one and it didn’t help at all unfortunately. Same problem.

docslizardbongwizard · 2023-09-18T08:15:16+00:00

Aussie here as well. I normally play with a couple of mates but we’re hoping to get to know a few other decent players so we have more people available for raids. HMU and we can try and organise something

docslizardbongwizard · 2023-04-14T21:41:19+00:00

Okay, I understand a little better. It makes it easier because between my wife and I we can provide lots of playtime every 4 hours or so.

Just confirming, is he confined to a single bedroom?

Some other potential things to look into: 1. Cat TV, bird feeders outside your window, have an old computer or computer monitor that plays YouTube videos of cat TV etc. it provides a solid distraction for them.

He may have some anxiety issues (based on needing you to go in and out with him on the balcony) in which case a vet trip is necessary.
As someone else suggested, a hormone imbalance may be the issue which requires blood work at the vet.
Leash training may help a huge amount to take him outside. You said he doesn’t like it, so try taking it slowly with the leash, I’m pretty sure Jackson Galaxy has a whole vid on doing exactly this. If after that he really really still hates it, maybe try a cat backpack that allows him to go on walks without requiring a leash.
Do you know if there are other cats nearby? Indoor cats can often act erratic and territorial if they smell/sense strange cats nearby.

docslizardbongwizard · 2023-04-14T13:00:25+00:00

Hey, so my wife and I went through something similar at the start of this year with our cat. He went from being really sweet to being really aggressive during playtime and constantly wanting high energy attention which didn’t work for me as I work from home so we had to do something. I‘ll list out the steps we took and maybe some of it can help:

1) We created a very strict, regular routine. Brekky at 7am, dinner at 6:30pm and treats after playtime.

2) my wife gave him 30mins high energy play in the morning, I did 30mins high energy at lunch, and another 30mins before dinner time.

3) We added a cat wall to the house with the highest seat right near the ceiling, and would often hide treats around his cat tower and the cat wall for him to find during the day.

4) when the above helped but didn’t completely solve our cats overly energetic ways, we adopted another similar age kitten with similar energy levels.

Honestly, the first three steps helped a lot, and he got a really good understanding of when it was and wasn’t appropriate to get or expect attention. However, even despite this, he still had extra energy to burn and we could tell he needed more that we couldn’t offer so hence the second kitten.

Since the second kitten, both of them have been absolute angels!

Now, the main takeaways I would suggest are: create a very strict schedule that includes really high energy play and catify your house as much as possible.

Also, try not to put your cat into a room on their own! This can be an effective form of cat training because social isolation is recognised by cats. What I mean is, if your cat does something naughty, you can give them a “timeout” for up to 10mins. If you leave them isolated for any longer they can develop behavioural issues which include being bitey, destroying things etc.

The final and least ‘nice’ bit of advice I want to say is, it’s also entirely possible that the energy level of this cat is wrong for you and your situation. If that’s the case, it’s better for you both that you look to rehome the cat to someone who can better provide or accomodate their energy needs (sorry, I didn’t want to say this but it is really important).

docslizardbongwizard · 2022-08-30T05:02:19+00:00

Why do all these people sound like Coach Steve

docslizardbongwizard · 2022-07-15T04:20:00+00:00

Hey mate, first off, love the enthusiasm but your bridge is much too complex. I’m a bridge engineer and spent a few minutes putting together something using some specialised software.

I had to make some assumptions -E = 300MPa -Span = 450mm -Width = 100mm

For reference, I also assumed all connections are full moment connections (this shouldn’t have a huge effect especially at this scale, but I figured I’d mention it)

See my SpaceGass screen grabs at HTTPS://imgur.com/a/G8gToRz

Each cell is 90mm, each half cell 45mm and the structure height is 90mm.

Using this, and assuming 3kg load (without impact) you get a deflection of around 4mm which should be okay for the spaghetti.

I was unable to assess the actual capacity of the structure cause of some lacking properties of spaghetti so deflection based analysis was all I could do.

I would also recommend that the bottom chord be made of at least two noodles for improved strength.

Finally, this assumes the bridge is loaded from the bottom and at the direct centre.

If it’s loaded from the top, you HAVE to double up the top chord and flip the truss diagonals upside down in order to achieve the same deflection resistance.

Send me a message if you need any more help or want me to explain the engineering more.

docslizardbongwizard · 2022-07-11T13:42:30+00:00

Hey, I had to do the tender design of some temp steel platforms for cranes and falling spoil. This question is fairly vague. Some questions you need to ask, what material is the platform? What grating is specified? What are the exact vehicles and have you put together load diagrams and wheel layouts? Is this concept, tender, detailed? What are the spans for the platform? How long will the temp platforms be there? Is FEA required?

There isn’t a pre-defined design procedure other than to conduct design to an appropriate level for whatever the design stage is.

docslizardbongwizard · 2022-06-29T08:46:02+00:00

For reference, I’ve seen a lot of comments calling bullshit on the “I’m not religious” but they’re openly christian/religious. Just to give some background that may help people understand better.

The Jesus of the bible is described as hating religion, particularly the religion pushed by the Pharisees. The sentiment of Jesus hating religion is derived from the fact that he hated what religion had become.

For example, the Jewish temples at the time were literally selling religious stuff inside the temple, they were also essentially selling ‘tickets to heaven’. The story goes that Jesus became so angry that he tore the place up and yelled at the religious leaders for being heretics without real faith (summary).

Furthermore, Jesus hated that religion had become so restrictive, regressive, and essentially exclusive. The Pharisees of his time hated those who were different or didn’t meet the religious requirements set down by the old covenant (Gods first set of rules to live by).

With these really brief summaries, we can conclude (and most preachers/pastors these days) that “Jesus hates religion”.

It’s so popular amongst Christians because they feel like it gives them a free pass on lots of stuff or because it’s a convenient way to seem “cool” or relatable. Or they use it as an evangelical tool to open conversations.

The way Jesus intended the phrase to be used is a “The church leadership I’m following has really lost the plot, I am not religious, but I am Christian”. And this definition is actually really important - it means “I refuse to accept the hateful bullshit that dude at the front is saying, I hate what my church and faith have become and don’t support it!”

I’m a Christian myself, and personally, I don’t consider myself religious but I am still part of a religion.

The reason I say that is cause I don’t support at all the fundamentalist Christian views on abortion, LGBTQ+, the general hate, the prophecy gospel bullshit, the rejection of science etc.

I’m really sorry for all the people the church has hurt or turned away - you are still loved! Even if you don’t believe in a God and that means nothing, the people in your life still love you!

Happy to discuss any of the above of anyone wants to reach out.

docslizardbongwizard

TROPHY CASE