How to set steel into concrete.

Date 04-16-2010 13:31

A local visitors bureau wants a new sign. The major element will be the steel structure[see attachment], intended to imitate the New River Gorge Bridge. I want to know what a resonable depth would be to set the posts in concrete. The soil may not be deep enough to permit digging by standard methods, and I may have to anchor it into sandstone. Assuming a hard packed clay soil, what would appropriate dimensions be to set the posts into poured concrete? i.e. what volume of concrete would I need [assuming a cylindrical shape] and what dimensions? I am imagining a 12" diameter form, 24" deep, set down from the surface by 8" to allow for topsoil and landscaping. Would a cold galvanizing paint be worth applying to the steel set in the concrete? This is intended to imitate a bridge built with A242 Corten steel, so I am leaving it unpainted. I am still working my way through the basics of calculating bending moments in beams and engineering basics, so I can't make any more than a guess as to what is appropriate for this situation. Wind loads would be minor, 60mph gusts are quite rare here, and the area is well drained. Can anyone shed some light on this?

Attachment: CVBSign2.JPG (43k)

By hojopens3 (**)

Date 04-16-2010 13:50

i would just drill 2 holes--- 18" x 36'', fill with 3500 mix concrete, set anchor bolts, or once concrete sets use a hiliti drill and use some 3/4 x 6 redheads with a 3/4 x 10 x 10 base plate, will be plenty

By Bob Garner (***)

Date 04-16-2010 14:09

The International Building Code (ICC) section 1805.7.2 has the design info you want for the pole footing. It has the magic formula for the diameter and depth of the hole. But you will have to know the wind load at the top of each pole and the soil strength. Table 1804.2 in the Code gives some practical strength values of different soils.

Let me know if I can send you these code pages (maybe 3 pages). Where will the sign be located? Maybe I can look up some wind speeds and loads for you.

Bob G.

By 803056

Date 04-16-2010 14:28 Edited 04-16-2010 14:35

That's a good looking sign.

I had several friends that worked on that bridge back in the late "70's". The conversations always included a mention of the winds they had to contend with when they were working over the gorge.

I would have to imagine there are some reasonably high sustained winds around noon time over the gorge. The wind velocity would drop off quickly as you get further away from the gorge edge. I would check with the "authorities" to verify the maximum wind speed over the gorge if your sign is anywhere near the edge of the gorge. I believe the Department of Environmental Protection usually collects that type of data. They usually have a data collection station on the bridge or close to it.

Bob has some good information. Basing your design on an established code is good practice.

Good luck. It looks like an interesting job.

Best regards -Al

By Iron Head 49 (***)

Date 04-16-2010 14:44

Another thing that may be helpful, is bell the bottom of each hole. This will help with bearing as well as uplift. If the holes are not too deep it is easy to bell them with a fencing bar.

By Bob Garner (***)

Date 04-16-2010 14:50

I didn't pay attention to the word, "Gorge". You could be in a so-called special wind region. It would be good to check with your local code officials to see how they are going to beat on you and especially if they will require a permit. I have the wind maps for most special wind regions but local code folks frequently like to write their own.

Bob G.

By Bob Garner (***)

Date 04-16-2010 15:07

I did some further research. There is a special wind region south of Fayetteville, which I presume is the gorge you are talking about. The region surrounding this area has to be designed for a 90 mph wind (whether that's realistic or not - Codes and all). I don't know what the wind speeds are in the special wind region.

As is usually the case, things just get more difficult.

Bob

By G.S.Crisi (****)

Date 04-16-2010 18:55

I assume that cost isn't a big concern in this case (as long as we don't speak of a million dollars), so I can send you the Anchor Bolts Engineering Standard that we used, back in my days of erector engineer, in the construction of a new oil refinery in the province of Mendoza, Argentina. 60 mph, or more, winds are frequent in the region, and most important, the province of Mendoza is a Grade 4 Earthquake Zone, which means that the worst earthquakes on earth can occur there. The last one happened in 1944.
A lot of anchor bolts types are depicted on that Engineering Standard, all of them designed for Grade 4 earthquake. I can send you a copy and you may choose the one that suites you better. However, it's not in electronic format, just printed, so I'll send it by Priority Air Mail. If you agree, send me a Private Message through this Forum with your mailing address. Depending on which city of the USA you live in, it'll take 6 - 10 days to reach you.
Of course, there will be no charge at all. It'll be a pleasure to be of service to you.
Giovanni S. Crisi
Sao Paulo - Brazil

By devo

Date 04-17-2010 01:18

Gotta love this forum! Thanks for all the replies. Yes, it is in the area south of Fayetteville, WV and the sign itself will be located about 7 miles south of the Gorge itself. I am now thinking about going the bolts in concrete route, similar to what I have seen on other signs around here. That way, I can pour the concrete and set the bolts one day, and then erect the sign after it cures. With the nuts above and below the plate, I should be able to level and adjust things just fine. As far as erection goes, I think I am going to assemble a crew of friends and do it Amish style. It's only 430 or so pounds..... PM's sent to all who so graciously offered extra help, if you ever want to come and see some of the best whitewater in the east, give me a call, I'm a better raft guide than I am a welder.

By DaveBoyer (*****)

Date 04-17-2010 03:40

If You keep the top of the concrete above grade, You won't get the rusting that comes along with soil contact. The bolted base sounds like a good idea to Me as well.

By Bob Garner (***)

Date 04-19-2010 15:15

For what it's worth, you will notice that the electric utility industry typically set their columns on double-nut anchor bolts with no grout below the baseplate. Their theory is to allow air to circulate below the baseplate and preclude rust. As long as the space between the top of concrete and bottom of baseplate is no more that 1 1/2 times the bolt diameter, bolt bending should not be an issue.

I would love to hit the whitewater again but old age is keepin' me and the wifey on dry land. We loved the Class 5's on the American River!