Construction AM Question

[Ambrug20]

Problem #11.6

My questions is: Where is 16.3 come from and units lcy –what is this

A test strip shows that a steel-wheeler roller, operating at 3mph, can compact a 0.5 ft. layer of material to a proper density in four passes. The width of the drum is 8.0 ft. The roller operates 50 min per hour. The number of rollers requires to keep us with a material delivery rate of 540 bank cubic yds/hr in (1 bank cubic yard = 0.83 ccy):

a. 1

b. 2

c. 3

4. 4

Solution: first calculate the roller production:

Ccy/hr = (16.3 x 8ft x 3mph x 6 inch x 50min/60min)/4 passes = 489 ccy/hr

489 ccy/hy / 0.89 = 589.2 bcy/hr

Thus, 540 / 589.2 = 0.92 < 1

Therefore, only one roller is required to keep up with delivery of material.

Production = (2.5 icy/cycle x 45 min/hr) / 0.85 min/cycle = 132 lcy/hr

My questions is: Where is 16.3 come from and units lcy –what is this

 

[sac_engineer]

Problem #11.6
My questions is: Where is 16.3 come from and units lcy –what is this

A test strip shows that a steel-wheeler roller, operating at 3mph, can compact a 0.5 ft. layer of material to a proper density in four passes. The width of the drum is 8.0 ft. The roller operates 50 min per hour. The number of rollers requires to keep us with a material delivery rate of 540 bank cubic yds/hr in (1 bank cubic yard = 0.83 ccy):

a. 1

b. 2

c. 3

4. 4

Solution: first calculate the roller production:

Ccy/hr = (16.3 x 8ft x 3mph x 6 inch x 50min/60min)/4 passes = 489 ccy/hr

489 ccy/hy / 0.89 = 589.2 bcy/hr

Thus, 540 / 589.2 = 0.92 < 1

Therefore, only one roller is required to keep up with delivery of material.

Production = (2.5 icy/cycle x 45 min/hr) / 0.85 min/cycle = 132 lcy/hr

My questions is: Where is 16.3 come from and units lcy –what is this

16.3 is a conversion factor to have a result in ccy/hr because your input parameters have different units.

(5280 ft/mile) x (1 cubic yard / 27 cubic feet) x (1 foot / 12 inches) = 5280/27/12 = 16.3

lcy = loose cubic yards. 1 yard of loose soil will be compacted to 0.83 yards.

 

[Ambrug20]

Problem #11.6
My questions is: Where is 16.3 come from and units lcy –what is this

A test strip shows that a steel-wheeler roller, operating at 3mph, can compact a 0.5 ft. layer of material to a proper density in four passes. The width of the drum is 8.0 ft. The roller operates 50 min per hour. The number of rollers requires to keep us with a material delivery rate of 540 bank cubic yds/hr in (1 bank cubic yard = 0.83 ccy):

a. 1

b. 2

c. 3

4. 4

Solution: first calculate the roller production:

Ccy/hr = (16.3 x 8ft x 3mph x 6 inch x 50min/60min)/4 passes = 489 ccy/hr

489 ccy/hy / 0.89 = 589.2 bcy/hr

Thus, 540 / 589.2 = 0.92 < 1

Therefore, only one roller is required to keep up with delivery of material.

Production = (2.5 icy/cycle x 45 min/hr) / 0.85 min/cycle = 132 lcy/hr

My questions is: Where is 16.3 come from and units lcy –what is this

Thanks, you are life saver. These construction problems does not going easy for me. could you help withone more problem. i will upload it and need to know where 1.5 in second formula come from

 

[civilized_naah]

16.3 is a conversion factor to have a result in ccy/hr because your input parameters have different units.
(5280 ft/mile) x (1 cubic yard / 27 cubic feet) x (1 foot / 12 inches) = 5280/27/12 = 16.3

lcy = loose cubic yards. 1 yard of loose soil will be compacted to 0.83 yards.

Agreed! However, doesn't the problem seem incomplete if we don't know how many passes are made per hour, i.e. at what rate ground is being covered? Right now we know:

3 mph = 15840 ft/hr x 8 ft wide x 0.5 ft deep = 63360 cu.ft in 4 passes = 15840 cu. ft per pass = 587 cu. yd. compacted soil per pass (ideal) - converted to 587x50/60 = 489 cu. yd (actual) per pass because of 50 mniutes active per hour.

Arriving soil = 540 cy.yd. per hour = eqauivalent to 448.2 cu. yd./hr compacted.

Am I missing something?

 

[sac_engineer]

Thanks, you are life saver. These construction problems does not going easy for me. could you help withone more problem. i will upload it and need to know where 1.5 in second formula come from

The 1.5 factor is used for calculating volume of dry loose material. You have to calculate backwards from the wet condition to the dry. The combined dry materials (cement, aggregate) contain more air voids and has a greater volume (i.e lower density) compared to the volume under wet conditions for the same weight (i.e. higher density) because you're replacing most of the air voids with a smaller volume of water to make the concrete mix thick and cohesive.

 

[civilized_naah]

Am I missing something?

No, I got it. In 1 hour, longitudinal travel = 3 miles = 15840 ft, which is like going over a length of 3960 ft four times. Thus, in 1 hour, compacted earth volume = 3960 ft (L) x 8 ft (W) x 0.5 ft (T) = 15840 cu. ft = 587 cu. yd. Working 50 minutes per hour, compacted volume = 489 cu.yd. (compacted) = 589 cu.yd. (bank measure). Arriving soil = 540 cu. yd. bank measure.

 

[sac_engineer]

16.3 is a conversion factor to have a result in ccy/hr because your input parameters have different units.
(5280 ft/mile) x (1 cubic yard / 27 cubic feet) x (1 foot / 12 inches) = 5280/27/12 = 16.3

lcy = loose cubic yards. 1 yard of loose soil will be compacted to 0.83 yards.

Agreed! However, doesn't the problem seem incomplete if we don't know how many passes are made per hour, i.e. at what rate ground is being covered? Right now we know:

3 mph = 15840 ft/hr x 8 ft wide x 0.5 ft deep = 63360 cu.ft in 4 passes = 15840 cu. ft per pass = 587 cu. yd. compacted soil per pass (ideal) - converted to 587x50/60 = 489 cu. yd (actual) per pass because of 50 mniutes active per hour.

Arriving soil = 540 cy.yd. per hour = eqauivalent to 448.2 cu. yd./hr compacted.

Am I missing something?

You're not missing anything. You did the same calculation but you're incorrect to think that the problem is about compaction of soil "per pass". We know how many passes it takes to compact the soil. The number of passes is only a time multiplier when determining the rate of soil delivered. If it only took 2 passes, then it would only take half the time to compact the same amount of soil.

Based on your calcs, you are comparing the rate of soil delivered (equivalent to 448.2 cu yd compacted) to the compacting rate of each roller (489 cu yd per working hour). Thus, only 1 roller can meet the 540 lcy rate of delivery.

 

[civilized_naah]

i will upload it and need to know where 1.5 in second formula come from

130 sq. ft x 5 in = 54.17 cu. ft. of concrete will typically weigh 54.17x145 = 7,854 lb

With the weight ratio = 1:2:4 and typical water cement ratio = 0.4, cement is about 1/7.4 of total weight = 1061 lb

Using SG of cement = 3.15, cement volume = 1061/(3.15x62.4) = 5.4 cu. ft

Which is way lower than what the listed answers are. I have never seen a factor of 1.5 used to adjust between dry and wet volumes (though I recognize that the adjustment MUST be made. Sorry to complicate the issue further.

 

[sac_engineer]

i will upload it and need to know where 1.5 in second formula come from

130 sq. ft x 5 in = 54.17 cu. ft. of concrete will typically weigh 54.17x145 = 7,854 lb

With the weight ratio = 1:2:4 and typical water cement ratio = 0.4, cement is about 1/7.4 of total weight = 1061 lb

Using SG of cement = 3.15, cement volume = 1061/(3.15x62.4) = 5.4 cu. ft

Which is way lower than what the listed answers are. I have never seen a factor of 1.5 used to adjust between dry and wet volumes (though I recognize that the adjustment MUST be made. Sorry to complicate the issue further.

It's a tricky question because the 1:2:4 ratio in the question is assumed to be by volume, not by weight since you're not given any densities, so you can't just add 0.4 to 7. Because you're working with volume only, you need to include the 1.5 factor for dry loose material.

 

[Ambrug20]

i will upload it and need to know where 1.5 in second formula come from

130 sq. ft x 5 in = 54.17 cu. ft. of concrete will typically weigh 54.17x145 = 7,854 lb

With the weight ratio = 1:2:4 and typical water cement ratio = 0.4, cement is about 1/7.4 of total weight = 1061 lb

Using SG of cement = 3.15, cement volume = 1061/(3.15x62.4) = 5.4 cu. ft

Which is way lower than what the listed answers are. I have never seen a factor of 1.5 used to adjust between dry and wet volumes (though I recognize that the adjustment MUST be made. Sorry to complicate the issue further.

It's a tricky question because the 1:2:4 ratio in the question is assumed to be by volume, not by weight since you're not given any densities, so you can't just add 0.4 to 7. Because you're working with volume only, you need to include the 1.5 factor for dry loose material.

:screwloose: Thanks all of you, guys, who answer and discussed my questions. I would never know about these coefficients if you wouldn't tell me. It’s all tricky to me. I am doing Transportation in the Depth, so I only need to learn morning part of the Construction (which is a lot). Can somebody recommend me a good handbook to help with cement ratio and etc. :tardbang:

 

[sac_engineer]

:screwloose: Thanks all of you, guys, who answer and discussed my questions. I would never know about these coefficients if you wouldn't tell me. It’s all tricky to me. I am doing Transportation in the Depth, so I only need to learn morning part of the Construction (which is a lot). Can somebody recommend me a good handbook to help with cement ratio and etc. :tardbang:

I did the transpo depth exam in Oct 2009. Lots of horizontal curve, vertical curve, and safe stopping distance.

I wouldn't worry about bringing additional concrete mix references since there will probably be only 1 question in the morning. The CERM covers it well, but your sample questions should be enough to bring to the exam.

My advice is not to get bogged down on every topic in the test plan for the breadth portion of the PE exam. Try to be proficient in about 80-85% of the material. Otherwise, you'll end up spending too much time on topics you're not strong in. When I prepared, I didn't bother with any of the environmental topics because that is my weakest subject and I knew I can be more proficient in my stronger subjects. Also, I had to prepare for the surveying and seismic exams (California requirement for PE), so I had to make some sacrifices. In the end, I passed all 3 exams on the first try.

Good luck!

 

[Ambrug20]

:screwloose: Thanks all of you, guys, who answer and discussed my questions. I would never know about these coefficients if you wouldn't tell me. It’s all tricky to me. I am doing Transportation in the Depth, so I only need to learn morning part of the Construction (which is a lot). Can somebody recommend me a good handbook to help with cement ratio and etc. :tardbang:

I did the transpo depth exam in Oct 2009. Lots of horizontal curve, vertical curve, and safe stopping distance.

I wouldn't worry about bringing additional concrete mix references since there will probably be only 1 question in the morning. The CERM covers it well, but your sample questions should be enough to bring to the exam.

My advice is not to get bogged down on every topic in the test plan for the breadth portion of the PE exam. Try to be proficient in about 80-85% of the material. Otherwise, you'll end up spending too much time on topics you're not strong in. When I prepared, I didn't bother with any of the environmental topics because that is my weakest subject and I knew I can be more proficient in my stronger subjects. Also, I had to prepare for the surveying and seismic exams (California requirement for PE), so I had to make some sacrifices. In the end, I passed all 3 exams on the first try.

Good luck!

That would be my second try. I did Transportation in October 2009 and failed. Like you said, I didn’t go deep in all of the AM areas except Water Recourses and Open channels. In the result I had “0%” on construction and 25% on structural. I graduated 20yrs ago in Russia. Not saying that Russian colleges not strong, but just very little to remember of structure and Geo-tech (never used it during these years). So, this time I am trying to improve my ability and shoot for at list 60% at the morning. And of cause planning to spend lot of time with Transportation and cover with higher score what was missing in the Breath part. That is my plan; I spend lot of time studying and hope that this time away from family and fun will be paid of.

thanks for your support :reading:

 

[IL-SE]

I don't remember anything that difficult on the morning PE. The very few construction problems were relatively straightforward. There will likely be a soil borrow-fill problem, so practice a few of those.

 

[txguy]

I don't remember anything that difficult on the morning PE. The very few construction problems were relatively straightforward. There will likely be a soil borrow-fill problem, so practice a few of those.

I agree