Construction: Temporary structure question

You are assigned to be the project manager of a 20-story concrete building. The concrete structures from the second level to the top level are consistent. The construction schedule plans for one floor slab concrete pour per week. You need to estimate how many steel jacks it would need to support the floor slabs after formworks are removed. The dimension of the slabs is 88 ft by 106 ft. Spacing of the jacks supporting the slab is 10 ft or less and from edge to edge of the slab. The jacks supporting a floor slab can be removed if the concrete of that floor slab achieve 90 percent of the design strength or more. How many jacks in total do you need approximately?

A/ 120

B/ 500

C/ 400

D/ 200

If the pouring take a full week, then after 28 days to achieve 90% on the second floor you could move the shoring to reshore the 5th floor, you would need 4 sets of 120 which is 480 I would choose b 500.

I agree with EngEngr.

10*12 = 120.. Then 4 weeks worth of jacks are needed.

dastuff said:

I agree with EngEngr.
10*12 = 120.. Then 4 weeks worth of jacks are needed.

Click to expand...

That's correct.

Did I win something?? Thanks for the question good one for reshoring, any more?

So what if the question said 75% strength?

I know in the field, we normally assume 75% strength to be reached in 7 days. In this example, that would mean you only need one set of jacks times 120 jacks per floor. The answer would be 120.

I'm just trying to think of how they could twist something like this. I guess they could also take out the edge to edge part, which means you wouldn't need as many supports.

Any other twist anyone knows of?

If they were going to assume a different time period they would probably give you some concrete test results. They can also toss in some damaged shores which will need to be replaced.

Thanks for the tips. Do you have any problems to share that ask either of these?

A formed concrete wall 15' tall is being filled at a rate of 10ft/hr with 150 lb/cf concrete. The cement is type II w/ a retarder

Using ACI 347 what is the depth to the uniform load on the form work,

a. 5.6'

b 6.2'

c 9.4'

d 13.5'

what is the maximum load

a. 1178

b. 1285

c. 1404

d. 2250

In reference to the first question of this topic...

Shoring/Reshoring of multi-story buildings..

I am looking at the 7th edition of SP-4. They have the Tables showing shoring/reshoring steps and what loads are trasmitted, etc. However there are (4) TABLES. 5-2, 5-2A, 5-3, 5-3A. From what I can tell, one of them 5-2 is just the dead load of the slab where 5-2A factors in weight for construction live load as well as the matl weight of the shores and forms..

However, I can't tell the difference between 5-2 and 5-3. Also, are these types of questions going to be qantitative, if so, which one is applicable. Would they tell us to 'ignore construction live loads' which basically tells us which of the two tables to look at.. I suppose a qualitative question, could probably be answered by either one..

It looks like one has 2 levels of shoring, 1 of reshoring, while the other has 1 level of shoring with 2 levels of reshoring.. Is there a rule of thumb of which one to use?

The lateral pressure equation has a temperature in it. Was this left out or is there something standard we would be safe to assume?

Also, I had thought the pressure was the same for lateral earth pressure 1/3H, however 1/3 of 15'-0 is 10 from the top or 5 from the bottom, to me it was not clear if it was asking from the top or bottom.. at either rate, 10 nor 5 are answers.. 5.6 and 9.4 are both close.. I would ASSUME it meant from the top with would be 10, so 9.4?

Mike

Sorry assume 70F and from the top, Mike you need to use 347-4 which is an appendix in SP-4

Part A

Answer is C. 9.4'

use equation 2.4 of ACI 347 (pmax = CwCc (150+43,400/T + 2800R/T) this gives you the maximum load.

Then use equation 2.1a of ACI 347 (p = wh) solve for h.

Part B

Answer is C. 1404lb/ft2 (see Part A eq. 2.4)

You win, you can select any prize from our lovely gift selection.

Is it just me or is anyone else's SP-4/ACI347 tab-less? In other words, does anyone have any pointers as to what's important in this book? I've heard it was nearly useless but of course I bought it anyway.....lol. Any help is appreciated.

Thanks

I only have the ACI 347. I was able to download it and I wasn't about to shell out $250 for the SP-4. I'm actually still on the fence about whether to stick with the Construction Section or go back to Water Resources/Environmental. Sorry I couldn't be of more help.

At least you can switch back, in NC you have to list your depth on your application and that's what you're stuck with....arghhh!

What you need are the design calcs from 347-04 they are different than CERM, you probably need 5-6 pages.

I have found two tables in the SP-4 showing the sequence for reshoring..

One has two levels of shores with one level of reshores while the other has one level of shores with two levels of reshores..

Would they have to specify this or is there a rule of thumb when to use I am a Gigantic DoucheBag

I would just look in ACI 347-2R-4 it has the whole sequence of shoring/reshore and a methods for estimating forces during shoring and reshoring. They have a specific sequence I am not aware of a rule of thumb.