Base Plate on sides 1

[upk]

Let's say you have a weak A307 bolts installed on top of concrete. You want to strengthen the base plate yet you don't want to add more bolts on top. What would happen if you add base plates on the sides? Does anyone do this? Can it cause

a) Increase in tensile strength of the part in tension?

b) even increase the strength of the compression side

c) pryout failure of the two adjoining plates?

d) breakout failure

e) can you develop the side base plates as tension block?

If no one does it. What is the failure mode of it?

 

[racookpe1978]

Sketch a "traditional" square concrete pad under a traditional baseplate. Doesn't have to be real accurate, but then sketch the "pullout cones" of the principle stress loads around each of the bolts.

So, you see on the sketch where the concrete could be in tension?

Now, on the sides of the same concrete pad, if there were sideplates attached, show the extra anchor bolts inserted into the concrete from each of the sides, or from two opposite sides.

Can you see where those added "pullout cones" are going to overlap the already-stressed tension cones from the vertical anchor bolts?

If you can arrange the side plates so there is no extra tension in the upper part of the concrete pad, your idea may work. Otherwise, you're weakening the upper part of the concrete with more drilled holes, then adding more tension to the same volume of concrete with the new bolts.

 

[upk]

In base plate design illustrations, the concrete underneath are shown empty. What if there is many reinforcement below base plate.

See pic of the actual concrete base before pour. The anchor bolt used is the weak A307. The longitudinal bars are grade 60. In pullout cones.. does it also occur irregardless of what kind of reinforcement you have inside the concrete? Supposed the load can survive the A307 yield strength.. would the reinforcement help in suppressing pullout cones?

 

[BAretired]

Where is the pic?


BA

 

[upk]

or

http://imagizer.imageshack.us/v2/800x600q90/908/qn27BN.jpg

 

[upk]

pls check out

http://www.pbase.com/techroof/image/161552678

 

[KootK]

X2 for racookpe1978's comments. Additionally, one would need to consider the stiffness of the original baseplate and what a realistic sharing of load between the top mounted and side mounted bolts might be. That alone might render the concept unfeasible.

pullout cones.. does it also occur irregardless of what kind of reinforcement you have inside the concrete? Supposed the load can survive the A307 yield strength.. would the reinforcement help in suppressing pullout cones?

The rebar definitely helps. If you're using ACI appendix D, you'll get a modest boost for having some rebar crossing the failure cones. If you're designing the connection using a strut and tie based algorithm, like Widiato's method, then you might be able to squeeze considerably more capacity from the system but the detailing of reinforcement, particularly it's development on either side of assumed failure cones, will become very important.

If you post a sketch of your anchor bolt layout and your loads, we'll likely be able to offer a good deal more help.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[upk]

If you post a sketch of your anchor bolt layout and your loads, we'll likely be able to offer a good deal more help.

This is the actual real anchor layout

(or see

http://www.pbase.com/image/161555922

if no image above).

The anchor is the A307 16mm with depth about 1 foot J shape that is distance about 2.8" to 3" inches to edge. What rule do you use for anchor near the edge.. ACI said it must not be less than 1.5 Hef where Hef is the height of the anchor. The anchor is 1 foot size.. so if the rule is to be followed.. it must be 1.5 feet (18 inches) from edge, the actual is about 3 inches to edge. Even if the depth of the anchor is just 4 inches.. the 1.5 Hef would make it 6 inches away from edge.. so pryout is a danger huh? But with reinforcement below it.. I wonder how it functions with pryout.

The load would be center support for gable rafter beams (side w8x21 5.5 meters) connecting at middle. The sides also use the same anchor layout. See below:

X------W------X

The W is the middle supporting the 2 rafters from sides. The 2 rafters are connected at middle and carried by the baseplate. IN extreme seismic shaking where the wide flange can flex and even bend in the weak axis. The connections must be strong.. so is your estimate, would the present anchor bolts be sufficient?

This is why I plan to use the very expensive Hilti chemical anchors to put it about 100 mm away from edge to reinforcement the poor A307.

 

[KootK]

This is the actual real anchor layout

What I'd really need to see is a dimensioned sketch showing the bolts, base plate geometry, and column cross section. Additionally, a sketch showing the loads on the connection would be very helpful.

Given that the framing that you're supporting here is pretty light, I'd be very surprised if the connection couldn't be made to work with the A307 bolts. A307 bolts are generally inferior to A325 bolts but will certainly have some reliable capacity that you can utilize. The bigger issue may well be the use of hooked anchor bolt ends. Again, there is some capacity, but it's not usually the best way to go where anchor bolts are expected to resist tension.

I would proceed as follows:

1) Evaluate what you've got using ACI 318 Appendix D or your country's equivalent standard. It may be fine fine as is.

2) If #1 doesn't work, look into a more sophisticated evaluation procedure like Widianto's: Link.

3) If neither #1 nor #2 work, revisit the concept of adding supplemental fasteners.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[BAretired]

The anchor bolts appear to be pretty widely spaced. I'll bet they are outside the base plate entirely. I think we are talking about the column with the epoxy filled void which has been addressed by several others including mes7a, hocho, skylite and upc...have I missed anyone? If so, the column size is 500 x 500 and the existing anchor bolts appear to be spaced at about 400 each way.

If Hilti anchors are to be installed at a closer spacing, they would also be contained within the column reinforcement cage. Four anchors should be sufficient, sized to resist seismic loads.

BA

 

[upk]

BA. the base plate is also 500 x 500mm.. i dont trust the A307 without any data and its 2.5 inches at the edge corner of each column and the Hilti technical told me it should be at least 80mm (3.2 inches) or suffer pryout failure (i read and see the Aci appendix D on breakout tension cones and other failure mode and it horrified me. so to avoid months of worried. ill add 4 hilti chemical bolts with 75.3 ksi strength at 4 inches from edge of every middle side edge. right inside the reinforcement cage for added strength. no harm in that. it will be implemented within 24 hours(the contractor just waiting and getting inpatience. i just cant afford torques wrench to tighten so we will just manual wrench on the nuts. hope this is sufficient isnt it.

the hilti chemical bolts will be 16mm and 4 inches in length. the 20mm would be too big and we dont have concrete drilling machine more than 4 inches.

 

[upk]

This is the 0.5x0.5 mtr base plate for the column top shown earlier:

The blue dot is the A307 bolts (1 foot embediment) located about 3" from edge corner. The red dots are the additional expansion bolts. Unfortunately. There is no stocks of the Hilti chemical bolts so have to use local GI expansion bolts (5" embediment is the longest I can find), I wonder what is the yield strength of GI expansion bolts? The light blue wide flange is the 1 foot support of the rafter.

The contractor made the base plate 0.5x0.5 mtr instead of the smaller one in the plan because he can't find any anchor bolts that is 7 inch deep. The designer said the corners can be used if the base plate is thick. We have 16mm base plate. But learning the A307 is not A325. I told the contractor to add the additional bolts the designer has designated.

This is the column actual sections (all the columns have similar reinforcements)

This will carry the rafters shown below (using w8x21 5.5 foot rafter and 2x6" 1.8 mm purlins spaced at 0.6 mtr with light roofing material).

I'm concerned about seismic loading.. kootk said the rafters will flex back and forth... I read in ACI that the metal plates can have moments and compression, tension side too. So I wonder if the A307 can make it with additional bolts at middle. The designer has already left the company and last thing he said was to make the plate thicker if we want to use the corner A307 or put additional anchors at mid part. I wonder if metal plates have interaction diagram too where there is particular failure moment and failure axial load. ?

 

[BAretired]

If the designer has left the company, the company should assign the work to somebody else. You need to get some competent engineering performed right away; it should have been performed long ago. You can't make these decisions on site while erecting structural steel; and you can't expect to get such detailed advice from Eng-Tips or any other online source.

Holes in base plates should be drilled in the shop in accordance with approved shop drawings prior to shipping to the site. If steel is to be primed, primer should be applied in the shop before shipping.

BA

 

[upk]

The contractor tried to acetylene the 16mm hole (see pics below) but unfortunately (or fortunately) they can't make it smaller than 20mm.. so I spent extra bucks to have the manual drilling of all holes in the 9 plates by machine shop.

(the holes were done by the steel were epoxied primered)

You said you haven't seen steel being primered on site. Here's the picture of it being primered on site.

Note very important that in my country.. 100% of contractors do it that way because they ordered from the steel supplier the raw pure naked steel then contractor primered it at site.. no one did it at shop (because they have no shop just to waterproof them before delivery.. this is true in all major contractors and builders).

By the way. I followed all your instructions. I let the structural firm verified the computations of the contractor overdesigned larger plates and more anchor bolts and it is ok. The wife of the structrual engineer head was jus pissed with me year ago when I visited their company dozen times for the epoxy void and carbon fiber wraps asking questions and discussions computations they could have overlooked. So if I'm learning how to compute manually.. it is just to verify their design.. not to design on my own.. I'll always have them updated of an changes.

 

[hokie66]

Just curious, what kind of primer are you using and how is it being applied?

The wife's attitude may explain a few things.

 

[upk]

It's epoxy primer applied directly on the steel. The contractor workers won't even want to remove the rust first.. but I insisted they remove the rust with steel brush. But they do so lightly only. Someone (you perhaps) said the steel must be sandblasted to white first.. no contractor in our country do that.. we directly applied it. Also many contractors use red oxide because it can suppose to last longer.. but my contractor said when red oxide is used.. you can't tell the rust from the red oxide paint months or years later because they are both colored red so can't tell which is already rusting... so i allowed them to use epoxy primer.. but they are bad to even apply it even while raining.. the local product is like this

http://www.boysen.com.ph/products.do?item_id=951

The wife only wants to deal with big project because they design 40-storeys. So she looked down on my 2 to 3 storey. But the company has made some mistakes like suggesting pure epoxy on column 2 inches voids (from honeycomb) and forgot some stirrups and I had to pay for the carbon fiber retrofit design. So the only way to have peace of mind is to learn how to compute manually and become a structural engineer so can verify the project. In our country. most structural engineers are civil engineers. We don't have a course in structural engineering.. so I may one day join them to verify their design and perhaps write an article about danger of epoxy repair in column void to strengthen my position over the contractor and designer.

 

[JStructsteel]

Is everything going on overthere under a giant big top tent?

 

[upk]

No they are putting epoxy primer under the sun and even while a bit of rain.. so new rusts form in parts of steel missed. In our country. This is the normal thing contractors do with laborers only earning $10 for working 10 hours a day. Such poor practice I know.