# tscarborough



## jshuatree (Feb 21, 2010)

if u have the rise of an arch and the span can u get the radius


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## Crosby (Jan 11, 2009)

jshuatree said:


> if u have the rise of an arch and the span can u get the radius


Really??


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## jshuatree (Feb 21, 2010)

yes really I know I ask all the hard ones ....is this even possible without just keep on adjusting your line till u get it right Im looking for a formula I can do it through trial and error


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## Crosby (Jan 11, 2009)

what type are you building?


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## jshuatree (Feb 21, 2010)

Im not building one Itjust seems like there should be a formula of some kind ...and Im always trying to learn everything even the stuff in the trade that arent used much anymore like steriotomy....but it would be a segmental


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## Crosby (Jan 11, 2009)

jshuatree said:


> Im not building one Itjust seems like there should be a formula of some kind ...and Im always trying to learn everything even the stuff in the trade that arent used much anymore like sterionimy


there is a lot of different arches, if everything was a perfect circle we wouldn't need a saw.


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## Crosby (Jan 11, 2009)

I'm sorry i didn't see you edited your post so you want to know about a segmental arch it' a semi circle


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## jshuatree (Feb 21, 2010)

pleease explain


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## Crosby (Jan 11, 2009)

u sure your not talking about the The Alan Parsons Project, steriotomy


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## Crosby (Jan 11, 2009)

what would you like me to explain?


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## jshuatree (Feb 21, 2010)

did I spell it wrong steriotomy the practice of cutting and shaping stone...explanation of how a jack arch is like a segmental and is it possible to get the radius with just the rise and the span of an arch without using the trial and error method


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## Crosby (Jan 11, 2009)

jshuatree said:


> did I spell it wrong steriotomy the practice of cutting and shaping stone...explanation of how a jack arch is like a segmental and is it possible to get the radius with just the rise and the span of an arch without using the trial and error method


it's not, a jack arch is flat that needs steel, a segmental is a curve that is actually less than a semi circle which the curvature holds it together..


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## jshuatree (Feb 21, 2010)

sorry i read that wrong I thought i saw jack arch...i know about segmentals gothics semicircle ...for the segmental it seems if u have the rise and span there should be a way to get the radius without jacking around with the line so much


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## Crosby (Jan 11, 2009)

when you are level on your columns where you start your arch you pull a line assuming your line/columns are level you figure out your rise from there, the rest is mathematics.


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## Crosby (Jan 11, 2009)

This will help http://en.wikipedia.org/wiki/Semicircle I have the benefit of carpenters but if your interested in theory ur all set.


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## jshuatree (Feb 21, 2010)

thanx thats gonna come in handy


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## Crosby (Jan 11, 2009)

no problem, you should to pull a line on the first course of your columns from end to end to keep em straight or else it will look like it's walking away.


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## Crosby (Jan 11, 2009)

once i get my square wall line for my piers i shoot a laser up and hang drop lines and pull another line ( spring line) where the arches start. hanging lines is key if u can..


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## bytor (Jan 23, 2010)

I think this is the formula that you're after:

h = the rise of the arch (from your level 'span' line)
l = the span of the arch


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## bytor (Jan 23, 2010)

Crosby said:


> a jack arch is flat that needs steel ..


A properly built 'jack' arch will not require steel


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## Crosby (Jan 11, 2009)

the formula in this business is production, period... I'm a layout guy, i run everything to grade flash,weep, hang the lines, 3 courses,mark the heights/poles and I'm on the next one....the bombers follow me they don't have to think about **** just lay brick...it works and i work with some talented guys if u sneeze they got 50 on u and you can sell it.


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## Crosby (Jan 11, 2009)

for the record anything over 2' requires steel. Thats code here, a jack arch is the weakest of them all. My question is why wouldn't you??


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## greg24k (May 19, 2007)

Crosby said:


> for the record anything over 2' requires steel. Thats code here, a jack arch is the weakest of them all. My question is why wouldn't you??


 Why wouldn't what?


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## jvcstone (Apr 4, 2005)

code is code--nothing to do reality. What Bytor is talking about are the millions of jack arches that were (are) built before "code" or even steel that hold up well for centuries. As long as there is no spreading of the wall (caused generally by faulty foundation movement) a properly constructed jack arch will hold up just fine. Admittedly, a bit of radius does make for a stronger arch.

JVC


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## Crosby (Jan 11, 2009)

greg24k said:


> Why wouldn't what?


add steel man, you need steel under a jack arch.. it's flat .not only that it should be flashed properly as part of a drainage system in a cavity wall including weep holes.


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## Crosby (Jan 11, 2009)

jvcstone said:


> code is code--nothing to do reality. What Bytor is talking about are the millions of jack arches that were (are) built before "code" or even steel that hold up well for centuries. As long as there is no spreading of the wall (caused generally by faulty foundation movement) a properly constructed jack arch will hold up just fine. Admittedly, a bit of radius does make for a stronger arch.
> 
> JVC


yeah your right but they were not jack arches holding up for centuries,, jacks are flat, they can't take the load like the historic arches your refering to... none of them are flat..they all are gothic, tudor, etc, the aqua ducts are still standing anything with a curvature will last . walls built today around the average home are cavity walls intended to drain water..where does your solution fit in, no flashing, no weeps, no nothing!!bound to fail...


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## jvcstone (Apr 4, 2005)

> jacks are flat,


I know what a jack arch is--have built hundreds of them during a 35 year career. (with steel btw) Just saying that the steel is a convenience, and a proper jack (not talking a course of soldiered bricks or stone) can withstand the load without it. Can show you plenty of jacks around here that are 100-150 years old and doing just fine--of course they are over openings in real masonry walls,--not 4" veneer.

JVC


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## Crosby (Jan 11, 2009)

My apologies sir, i just realized i stepped out of line... i have learned more here than i have contributed, sorry if i offended anyone. My experience is limited to my years, sometime i get ahead of myself.


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## jvcstone (Apr 4, 2005)

> My apologies sir,


None needed friend. Lively discourse is how we all learn from one another.

JVC


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## Tscarborough (Feb 25, 2006)

You have the formula up there, of course you can calculate it. Personally, I do not like iron in arches, and iron does not last nearly as long as masonry. Most of the issues I see with windows have to do with the steel rusting, expanding, and popping the joints (usually brought on by poor flashing, admittedly).

The amount of masonry that an arch has to support is also calculable , and it is not a very high number in relation to the opening width. Jack arches do not need iron, and if yours do then they are decorative arches not a structural jack arch.


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## stuart45 (Oct 7, 2009)

Although a Jack arch is flat, it is set out on the radius of a segmental arch, and all the joints radiate to a single striking point, so it is really a segmental with the ends extended top and bottom to form the flats. Ideally it should be built with gauged or rubbed brickwork with joints no more than 1/8 inch thick. Done properly it will easily bridge a 4 ft opening and there are many examples here a few hundred years old still in good nick.


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## Crosby (Jan 11, 2009)

I was being a stubborn, argumentative, jackass last night/this morning. Sometimes I can’t see past the end of my nose, I was rereading my posts and I can’t believe I was even arguing the point..Way to much Jamison, no excuse for my behavior. I've been shut down since we got pounded with snow here, my wife is ready to shoot me in the face, from the same sort of stubbornest I displayed here. Can’t learn **** if the ports are not open, and I have a lot to learn.


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## 4th generation (Mar 28, 2008)

Don't beat yourself up about it ,we are all here to learn and contribute where possible .These are some of the finest masons & tradesmen around and it can be a humbling experience. & The winter can get anyone depressed, however its only 4 wks till spring.


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## jvcstone (Apr 4, 2005)

crosby said:


> Way to much Jamison


At least your taking good care of yourself:thumbsup:

JVC


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## CanCritter (Feb 9, 2010)

bytor said:


> A properly built 'jack' arch will not require steel


 
ditto....no iron needed in a properly constucted jack arch

and yes there is a formula....l have one formula thats 2 pages long and will give the dimensions of every cut and voussiors in a arch..

l should aslo clarify that l would use a angle iron on a jack arch just for the added security given that most would be on wooden framed houses and could experience frezze thaw cycles and some shifting...for me it would just be added security and in the end cant find fault with folks doing that


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## stuart45 (Oct 7, 2009)

I usually draw the arch out full size on a board to get the sizes for the templates and cutting boxes. The bricks can also be laid out and checked once cut.


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## Rockmonster (Nov 15, 2007)

To get back to the initial question, my formula is r=1/2span(squared) +ht(squared) over 2ht.....I don't know how to type this out as Bytor did....but this is a formula I use all the time in segmental arches......trial and error is for guys that don't get geometry....


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## CanCritter (Feb 9, 2010)

stuart45 said:


> I usually draw the arch out full size on a board to get the sizes for the templates and cutting boxes. The bricks can also be laid out and checked once cut.


 

this is generaly what l do,,lm more hands on than a pencil pusher as theres real world varibles that dont work well with formulas sometimes,,,basicly build your form and layout and git at it


Crosby...."it works and i work with some talented guys if u sneeze they got 50 on u and you" 

thats the diffrence between a journeyman and a shoemaker


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## jshuatree (Feb 21, 2010)

Tscarborough said:


> You have the formula up there, of course you can calculate it. Personally, I do not like iron in arches, and iron does not last nearly as long as masonry. Most of the issues I see with windows have to do with the steel rusting, expanding, and popping the joints (usually brought on by poor flashing, admittedly).
> 
> The amount of masonry that an arch has to support is also calculable , and it is not a very high number in relation to the opening width. Jack arches do not need iron, and if yours do then they are decorative arches not a structural jack arch.


 
this brings up another qu like over garage doors you see alot of cracking whatis the best way to prevent this


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## stacker (Jan 31, 2006)

jshuatree said:


> this brings up another qu like over garage doors you see alot of cracking whatis the best way to prevent this


i always will lag my iron into the header when going over garage doors.this helps to keep the iron from moving.also a 6-8 inch lap over the brick is what i call for.i will also use jack legs under the iron until the wall has had a chance to set up.generally about 3-4 days.


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## NJ Brickie (Jan 31, 2009)

jshuatree said:


> this brings up another qu like over garage doors you see alot of cracking whatis the best way to prevent this


If it a block building the best way to cross over large openings with brick work is to use a steel I beam with a long flange on the bottom as your lintel in the block work. The long flange acts as your angle iron. If it is a stick framed building then do as Stacker suggested.


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## Tscarborough (Feb 25, 2006)

Technically, lagging loose lintels is not an approved method. The angle should be sized to support the load without lag bolts, the issue being that an undersized angle lagged to a header will cause the angle to roll outward. If it is not undersized, there is no need to lag it.

The calculations for a relief angle (lagged angle) are different than for a loose angle.

In practice, it does not matter for normal (<20' spans with no natural arching) garage openings, so long as you are using at least 6x4x5/16" for openings 16-18 foot.


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