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[ARCHIVED THREAD] - Question for Civil Engineers

Posted: 10/6/2005 8:55:08 AM EDT

Two actually...

#1. What causes dirt roads to get those ripples in them that make if feel like you're driving on railroad tracks?

#2. I've seen several curbs that have split horitzontally at street level and then the top portion stands up like an inverted "V", kinda like ... __/\__ What causes this?

Posted: 10/6/2005 8:57:34 AM EDT

[#1]

Quoted:
Two actually...

#1. What causes dirt roads to get those ripples in them that make if feel like you're driving on railroad tracks?

Usually occurs at places where vehicles slow, or brake.......

It also occurs as vehicle suspension oscillate over the road.

Posted: 10/6/2005 9:02:16 AM EDT

[#2]

Quoted:
Two actually...

#2. I've seen several curbs that have split horitzontally at street level and then the top portion stands up like an inverted "V", kinda like ... __/\__ What causes this?

Tree roots under the asphalt?

Posted: 10/6/2005 9:03:16 AM EDT

[#3]

#1 I would think water erosion mostly.

#2 ? There has to be some kind of expansion for it to push up. Pre-tensioned rebar? Water freezing in cold months?

Posted: 10/6/2005 9:04:25 AM EDT

[#4]

Quoted:
Quoted:
Two actually...

#1. What causes dirt roads to get those ripples in them that make if feel like you're driving on railroad tracks?

Usually occurs at places where vehicles slow, or brake.......

It also occurs as vehicle suspension oscillate over the road.

Yep. On some freeways even the concrete slabs are affected by this.

Posted: 10/6/2005 9:04:29 AM EDT

[#5]

Bodies buried under the road...

Oh, sorry. I thought you typed EVIL engineers...

Posted: 10/6/2005 9:08:12 AM EDT

[#6]

Quoted:
#1 I would think water erosion mostly.

#2 ? There has to be some kind of expansion for it to push up. Pre-tensioned rebar? Water freezing in cold months?

Water freezing causes it too, but I see he's from Texas.

Posted: 10/6/2005 9:08:24 AM EDT

[#7]

This is really weird. This same exact question was asked last year with the same exact title. Was that you or is this a huge coincidence?

An answer was found but I don't remember what it was. I work in a civil engineering firm so it piqued my interest.

It's really weird that this would be asked again of the same people. It's not a quesion like "which round works best on a buck" or something.

Posted: 10/6/2005 9:16:42 AM EDT

[#8]

Here is another queestion. How are traffic lights timed? Do you have a base equation for lanes and estimated traffic flow, or does everything just go in a computer and tell you what to do? Are there studies done aftarwards to determine if the light timing is optomized?

I ask because Northern VA has its head up its ass in terms of light timing.
The lights on a main flow road should not stop drivers every other light when they are traveling the speed limit. Would NOVA please pull its head out of its ass!

I would bet good money that a traffic light timing re-evaluation would cut NOVA traffic congestion by at least 15%.

Posted: 10/6/2005 9:16:58 AM EDT

[#9]

This is civil enginering related.

cheat sheet

Posted: 10/6/2005 9:20:29 AM EDT

[#10]

buy both
oh, sorry wrong thread

Posted: 10/6/2005 9:40:36 AM EDT

[#11]

Quoted:
I ask because Northern VA has its head up its ass in terms of light timing.
The lights on a main flow road should not stop drivers every other light when they are traveling the speed limit. Would NOVA please pull its head out of its ass!

There are certain municipalities around here that time their lights to the speed limit, i.e., if you drive the speed limit you rarely hit a red light.

I wish all the towns/cities around here would do that.

Posted: 10/6/2005 9:41:48 AM EDT

[#12]

Traffic light timing is a complicated monster.
traffic flow
traffic counts (bus/truck/cars)
cross streets with lights
size of intersections
speed (or speed changes)
queing theory
reaction times
street geometry

Posted: 10/6/2005 9:46:19 AM EDT

[#13]

Quoted:
Traffic light timing is a complicated monster.
traffic flow
traffic counts (bus/truck/cars)
cross streets with lights
size of intersections
speed (or speed changes)
queing theory
reaction times
street geometry

I in no way think its an easy task. I just think a cross-eyed baby on pot with a full diaper could do a better job then what is currently set up in NOVA.

Posted: 10/6/2005 11:42:51 AM EDT

[#14]

Quoted:
This is really weird. This same exact question was asked last year with the same exact title. Was that you or is this a huge coincidence? An answer was found but I don't remember what it was. I work in a civil engineering firm so it piqued my interest.

It's really weird that this would be asked again of the same people. It's not a quesion like "which round works best on a buck" or something.

It's been bothering me for sometime but I don't think I asked this before.

For #1, I should mention that in every circumstance (3) that I've seen, the curbs are part of a divided median and they split within about 6 months of being poured.

Posted: 10/6/2005 11:58:03 AM EDT

[#15]

Quoted:
There are certain municipalities around here that time their lights to the speed limit, i.e., if you drive the speed limit you rarely hit a red light.

I've seen some like that, but it seems in the same respect, if you hit one light red, you'll hit them all red.

Posted: 10/6/2005 12:00:50 PM EDT

[#16]

Quoted:
Quoted:
There are certain municipalities around here that time their lights to the speed limit, i.e., if you drive the speed limit you rarely hit a red light.

I've seen some like that, but it seems in the same respect, if you hit one light red, you'll hit them all red.

Yup, and those that are timed for 45 mph work just fine at 90mph!

Posted: 10/6/2005 12:06:47 PM EDT

[#17]

Wash boarding, the "ripples" on gravel roads, are caused by the natural frequency of the unsprung mass and the spring rate of the vehicles traveling over these roads.

The frequency or spacing of the wash boarding is related to the speed of the vehicle by the equation of

frequency = (k/m)^1/2

where k is the spring rate and m is the unsprung mass.

Believe it or not, most vehicles have very close ratios of k/m. Because of this, it is most comfortable to travel at speeds that cause this formation because the dampers (shock absorbers) isolate the harshness of the ensuing vibrations.

Not a civil engineering question as they don't do so well in dynamics which is the study most closely associated with this subject...

Posted: 10/6/2005 12:19:50 PM EDT

[#18]

Quoted:
This is civil enginering related.

href=cheat sheet

I don't get the O or V measurement ??
Something aint jiving, No such thing as a perfect circle

Posted: 10/6/2005 12:39:03 PM EDT

[#19]

I'm a chemical engineer.

They say we're not civil.

Posted: 10/6/2005 1:05:09 PM EDT

[#20]

Quoted:
I'm a chemical engineer.

They say we're not civil.

Ha! I'm a mechanical engineer. We build weapons systems. Civil engineers build targets.

Posted: 10/6/2005 1:18:18 PM EDT

[#21]

Washboards are created by the motor grater when the road top is dry and packed hard, the blade on the grater jumps up and down due to the hardness of the roadtop. They are also caused by the other reasons stated in the above posts, but the motor grater is the main cause of them around here.

Posted: 10/6/2005 2:25:19 PM EDT

[#22]

Quoted:
Washboards are created by the motor grater when the road top is dry and packed hard, the blade on the grater jumps up and down due to the hardness of the roadtop. They are also caused by the other reasons stated in the above posts, but the motor grater is the main cause of them around here.

Really? That is bad practice in operation. My cousin runs a grader for the county and he can leave the surface glass-smooth in gravel, packed sandstone or blackland, it doesn't matter. If the blade hops, the operator needs to set the rake and draft better.

A grader is analogous to a carpenter's plane.

Posted: 10/6/2005 3:36:44 PM EDT

[#23]

Don't ask an engineer. Find a road scholar.

Mild Bill
and I apologize.

Posted: 10/6/2005 4:27:35 PM EDT

[#24]

Quoted:
Wash boarding, the "ripples" on gravel roads, are caused by the natural frequency of the unsprung mass and the spring rate of the vehicles traveling over these roads.

The frequency or spacing of the wash boarding is related to the speed of the vehicle by the equation of

frequency = (k/m)^1/2

where k is the spring rate and m is the unsprung mass.

Believe it or not, most vehicles have very close ratios of k/m. Because of this, it is most comfortable to travel at speeds that cause this formation because the dampers (shock absorbers) isolate the harshness of the ensuing vibrations.

Not a civil engineering question as they don't do so well in dynamics which is the study most closely associated with this subject...

Wrong again nancy boy.

The rutting of the road is caused by the fore and aft bouncing of the vehicle. HOWEVER, the best thing to do is avoid the speed that caused the rutting. The excitation freq. being near the natural frequency of the vehicle causes resonance, resulting in the peak amphiltude of displacement.

I guess you forgot that civil engineers RULE THE WASTELAND of earthquake loading.

The reason the curbs split is because the dirt settles under the curb. The curb usually has no steel reinforcement. Concrete is weak in tension. Bottom of the curb is in tension when the dirt settles.

The light timing thing is governed by computer programs and induction coils under the roadway called "loops".

You can cure any highway related problem in the land with enough money and with politicians with enough balls to pend it wisely.

Can't have 800,000 cars driving on a road that was at peak capacity in 1955 and not expect jams.

The science of highway engineering is very well advanced but there's NEVER ENOUGH MONEY.

Posted: 10/7/2005 3:56:38 AM EDT

[#25]

Thanks.

[ARCHIVED THREAD] - Question for Civil Engineers

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