Laying Long runs and string sag - Contractor Talk - Professional Construction and Remodeling Forum

lukachuki · 01-17-2007, 08:45 AM

Ok here's the details. Our masonry crew is going to begin building a Polo ring 300' x 150' x 5'out of 8" block. The 300' sides of the ring are going to have a 2% drop in it which equals 6' over the 300' run. The footer has been put in (50 yds) and the corner batter boards are up.

2 Questions:

1. What kind of tricks do you guys have for keeping these long runs exactly to grade. We all know that string sags (i've heard 1" every 100' or so) but anyone know how to get it to cooperate? I'm sure there are some fairly simple tricks but I am unaware at this point. I know what I think I need to do but I will wait to tell you guys before I embarrass myself.

2. Does a wall this long need vertical expansion joints to prevent cracking and if so what is the best way to do it.

Thanks

concretemasonry · 01-17-2007, 10:43 AM

The 2% drop is very significant!! Federal guidlines for freeways limit slope to 10% max. Are you going to attempt to build to the slope of the land like SOME California sound barrier walls or level to make things look correct and match everthing around the ring?

As far as laying to the "line", I leave that to those that know more or have better techniques than me. - there always ways to put in elevation controls along a wall.

Regarding the joints (not expansion joints, but actually control joints since concrete shrinks more than it expands), for something that long you will get cracks. The decision is where they occur. It would be best to have control joints to break things up and have points for some elevation control.

A block wall will crack. It starts with a crack near the center and additional cracks will break each panel about in half and will continue on and on, depending on the block curing/age, temperature swings, moisture changes(weather), height and amount of horizontal steel.

I saw a very long strip shopping center back wall (12" block, 18' high, 750' long) built without any joints, but with joint reinforcement every other course. The wall did crack as you would expect. The cracks were not at all that large and very very uniform in width and spacing (20 to 24' apart). This was built about 1975 and the center has been changed in front, but the back is the same and the walls are still fine after a couple of coats of paint. You can see the cracks, but no big thing. At the time it was built, the owners (mason contractors) knew it would crack, but accepted it.

Point out to the owners that they can expect cracks.

I would worry more about the wall stability unless it was properly vertically reinforced. Since you will be reinforcing it somwhat, it appears there will be an opportunity to break the wall into sections. This will also give you an opportunity to set points. Walls like this have been known to turn into sidewalks.

A 5' high wall can be very dangerous if not designed properly. - Make sure someone else is responsible for the structural design.

Dick

stacker · 01-17-2007, 11:09 AM

we get down on the line and sight it with our eyes.
i would put control joints in a wall that long for sure.

lukachuki · 01-17-2007, 11:23 AM

Don't have much time to comment now but thanks for the replies. What would be an accepted way to do the control joints? And how often would you put them in the wall? Every 30' would work well with the durawall ladder wire.

Gotta Go.

stacker · 01-17-2007, 12:24 PM

25' to 30'

jvcstone · 01-17-2007, 12:29 PM

Hi Tim,

Think we had a thread on here a while back about line trigs (twigs).

Essentially a trig is a lead build at points in a run other than corners used to twig the line to to prevent that sag, and also wind deflection. Each of those midpoint leads can be built to a transit shot to insure what ever grade you need (or level) Do a search for it.

JVC

concretemasonry · 01-17-2007, 01:22 PM

Don't forget about some vertical steel!!

tkle · 01-17-2007, 04:04 PM

Footing and first course lines I'll shoot in a stake about every 50' for my heights.With 6' slope in 300' I'd put them at exactly 50' with a foot drop on each one.Sight down the stakes and run a line the entire length to range it in.If your stakes aren't plumb you'll get a wiggle.I wet set my 1st course using a torpedo on each block getting them as perfect as possible.When starting the wall,recheck your 1st course for height and range cause they won't be perfect.Generally when doing longer walls I'll do it 50 to 100 feet at a time depending on the size crew.Usually 1 tender and 2 masons for each 50'.I build leads at both ends or simply drive a stake to hold my line spotting a block at the end and the at the end of my 50' run.You should know from checking the first course if you need to correct any heights at this time.Pull the line the entire 300' to range it in.Use trigs on the block that you spotted to hold your line in place.Check bond and plumb as you go up.Finish a course spot another block. I'd put expansion every 30' using half blocks so it's like two ends butting together.Vertical 1/2" steel at midpoint, at the top and through the expansion or durawall (better)every other course.

concretemasonry · 01-17-2007, 05:03 PM

If you really want the joints to work, don't run the Dur-O-Wal through the control joints. Run a bar through the joint with one end greased to let it slip in the bond beam. - Nothing fancy, but just basic.

tkle - Hate to butt in, but 1/2" vertical steel where? I know it goes in the center of the wall, but what about spacing?

tkle · 01-17-2007, 06:45 PM

Quote:

Originally Posted by concretemasonry

If you really want the joints to work, don't run the Dur-O-Wal through the control joints. Run a bar through the joint with one end greased to let it slip in the bond beam. - Nothing fancy, but just basic.

tkle - Hate to butt in, but 1/2" vertical steel where? I know it goes in the center of the wall, but what about spacing?

Thanks for the note on dur-a-wal.Never was sure.Never had a problem but might as well do it right.Local specs call for it midway on a six foot wall.I'll put it on the 4th course making it 40" above the footing steel and 40" below the top steel.Same with a 5'4" wall though the top spacing will be less.I've been using more dur-a-wal lately.I think it does a better job.No vertical steel is required with the Dur-a-wal but I still like to throw 1 in the top.Butt in all you like,I appreciate your input.

stacker · 01-17-2007, 06:52 PM

we have always used dura wall on every other course.this generally allows for the dura wall to be one course below a bond beam,and one course above.
and like concrete says 'DONT run dura wall thru a control joint.keep the dura wall 2-3 inches from the control joint.in the bond beam course use a slip joint.this will keep the bond beam complete but also allow for movement.

tkle · 01-17-2007, 07:57 PM

Just realized my screw up.I was talking about horizontal steel.Vertical steel I'll place 24"O.C.Sorry for the confusion.If you'll excuse me I'll go eat some pie now.
http://www.orco.com/OWS/6high_wssw_16.pdf

http://www.orco.com/OWS/6high_wssw_14.pdfl

tkle · 01-17-2007, 08:00 PM

J

concretemasonry · 01-17-2007, 09:13 PM

tklt -

I was wondering about the verticals. I don't know you were from Orange County area. That is a wwell accepted design.

I have seen a lot of the Orco walls through the years. Good products, good information and good people.

tkle · 01-17-2007, 10:33 PM

Quote:

Originally Posted by concretemasonry

tklt -

I was wondering about the verticals. I don't know you were from Orange County area. That is a wwell accepted design.

I have seen a lot of the Orco walls through the years. Good products, good information and good people.

Most of the cities will accept those spec.s even with the verts @40"s O.C.
Actually I don't know any that don't.They are signed.I always go with 24" with a top bar.Probably overkill but I worry about earthquake damage in this area. 6.0
I've dealt with Orco when they only had the Orange county plant.Now they're all over Southern Cal.Unfortunately the quality of their block is suffering because of it,but I have always gotten good service and good information.

concretemasonry · 01-17-2007, 11:06 PM

tkle -

Orco and similar companies always have to be conservative on the general information they give. - They don't want to end up in court.

Most of the time you can save money by hiring an engineer because he will usually go for less reinforcing if he has all the information on the job.

I have spent a good deal of time starting in 1970 with some of the Muth family and employees at various meetings. I also spent one very late News Years eve (so late I missed the Rose Bowl parade the next day) with them trying to start a new production line at the Riverside plant.

tkle · 01-18-2007, 04:50 AM

Quote:

Originally Posted by concretemasonry

tkle -

Orco and similar companies always have to be conservative on the general information they give. - They don't want to end up in court.

Most of the time you can save money by hiring an engineer because he will usually go for less reinforcing if he has all the information on the job.

I have spent a good deal of time starting in 1970 with some of the Muth family and employees at various meetings. I also spent one very late News Years eve (so late I missed the Rose Bowl parade the next day) with them trying to start a new production line at the Riverside plant.

When it comes to a garden wall,I tend to go over on the steel anyway.Number 4 is cheap,at least in comparison to the total cost of the job.On an engineered structural wall I won't.I'm not an engineer and don't want to second guess them.
Started the trade in 1976 in O.C.Only really dealt with the original plant a few times.Needed a P.O.number back then.They have a plant in Banning now that I deal with,but frankly I'm starting to lean towards Angelus.Their block seem to be slightly straighter.

lukachuki · 01-18-2007, 09:44 AM

Quote:

Originally Posted by jvcstone

Hi Tim,

Think we had a thread on here a while back about line trigs (twigs).

Essentially a trig is a lead build at points in a run other than corners used to twig the line to to prevent that sag, and also wind deflection. Each of those midpoint leads can be built to a transit shot to insure what ever grade you need (or level) Do a search for it.

JVC

Thanks JVC,

Good advice. I remember that conversation, although it was mostly about definitions if I remember correctly I will look it up. I was thinking that this is what needs to be done although I had forgotten it was called a trig (twig).

lukachuki · 01-18-2007, 09:55 AM

Mr. Big Fish, Tkle, and stacker thanks for your input. As always it is amazing that people are willing to give this info away for free. Like the idiot that I am this wall is unengineered (will not happen again) so I am interested in the overkill solution. I guess one question that springs to mind is this. How exactly do you put a slip joint in a bond beam to tie all your 30' sections together, yet still allow for movement?

One other question. How much does a lightweight 8" block weigh. Their is a great deal of difference in the weight of a LW block around here and my masons are begging for the light LW blocks. The ones that I ordered weigh in at 28 lbs. so i'm not sure if I will have a mason revolt or not.

tkle · 01-18-2007, 10:35 AM

I'm always willing to give information to those looking to do quality work.As CM commented grease your overlap.If your wall is to be solid grouted you might consider getting all bond beam block.Slightly lighter but you can tell the difference after picking up a few hundred in a day.Myself when laying heavier block,I just end up laying less at the end of the day.

weights: http://www.orco.com/tech_average.htm