MiddleArch

Here are various photos of some of the middle arch stones being fit between voussoirs assembled already positioned across the form on a couple of older bridge projects.

On a segmented arch these middle stones which complete the arch don't have to be special keystones, in that they don't have to be necessarily bigger or different than the other voussoirs. As long as they are properly shaped to fit snug in the arch they will work. 

As you can see, this middle voussoir on the Monarch Bridge we built is going to slip in very tightly. Care needed to be taken so that it fit enough to be snug, but not so tight as to force the other stones out of alignment. Some of the thickness of this stone needed to be chiseled away before it went in properly. If it had been too thick, and we had forced it into the opening, a bulge would have been created somewhere along the rest of the curve of the arch, and the integrity of the whole bridge structure would have been compromised. 

Here in this photo of the MacDougal Bridge in Russel Ontario, 

when Evan felt confident it was going to fit, the chunky middle voussoir was hammered down into place with a heavy stone.

It was pounded down until the bottom touched the wooden form, and thus completed the continuous look of the curve created by the other arch stones.  

The rest of the voussoirs needed for filling in the middle space that extends across the form are all carefully fit and pounded in the same way. Some of these last interior voussoirs can be difficult to wedge all the way to the bottom. You may not be able to see if they are flush the intrados, but you can tell when these stones go down far enough because of the sound of stone hitting against wood.

On another occasion at the Hubb Creek Bridge project a special 'keystone' did have to be made. Prior to the arch being built a suitable stone had been chosen and the letter K (for Karlo Estates) sandblasted onto the face. 

When the time came to fitting this pre-made keystone into the space left between the other voussoirs that we had already set in place, I was disappointed to see how loosely it fit. 

In order to correct this and not have to take apart the other arch stones that were fitting so well we decided to cut out a portion of the form, to allow the keystone to fit down lower and so fit more snugly between the voussoirs to the left and right. This turned out to be a perfect solution and ended up being a signature visual feature of the bridge.

As you can see, we were only able to do this 'recessing' of the keystone because the 2x4s that made up the supporting curved surface of the form, extended beyond the outer rib. This extension had been done in order to build Hubb Creek Bridge two feet wider than the 6 foot wide bridge form it had previously been designed for.  

Beginning the rows of voussoirs

On a dry stone bridge the voussoirs are shaped as close to parallel bedded trapezoids as possible and then laid in rows optimally with their best face down and their longest length up. This first 'grocery bag' size/shaped voussoir is being pinned from the back

The closer that voussoirs can fit together at their faces ( the exposed intrude side) the better.

Avoid using stones for voussoirs that are more like triangles than squares (that is, ones that get too narrow towards their upper end when placed face down on the form)

If their sides don't fit well and lock, as they butted together along the row, try other combinations of voussoirs until they do. Each odd shaped voussoir should lock in somehow to the other or at least overlap on one side to the one next to it.

It is best if the stones in a row of voussoirs are all the same thickness so that the next stones can be laid across the joints. Sometimes a pair of voussoirs can be laid together to make up the height of the other stones in a row of voussoirs. 

These arch stones can be pinned with thin wedge stones as they are put in so that each one fits fairly snug in the structure as it is being built. Aviod letting any wedges slip down and  thus create pivot points between stones. The pins should be near the top and only be used to allow the faces of the voussoirs to touch, rather than be a place where the stones rock against each other. 

From the side looking across the bridge the voussoirs should all be set so that they fan out slightly along the lines drawn on the form. These wedges are pushed in just far enough so that the voussoirs keep their orientation. The final 'shimming' which locks things permanently tight will be done when all the voussoirs in the entire arch have been set properly in place.

Achieve the proper angle along the rows of voussoirs by pinning each voussoir (therefore effectively wedging it) is quite structural and can be done instead of having to shape every voussoir. By this method many useful, more random shaped stones, that have little or no taper, can be used. A more informal rustic look is created if enough of the stones in the bridge are pinned. 

Shaping voussoirs, by sawing and chiseling every single one  along their length to give them the slight taper required to fit in a radiating pattern (so that they are absolutely flush with the others) can become an unnecessarily time consuming job. 

More on this point tomorrow...

The Springers.

The springers are special arch stones. They are the first row of tapered stones that the rest of the voussoirs spring from
Their bottoms are level. Their tops (in a segmented arch) angle towards the centre point of the circle below the form.



Hopefully lot of them can be 'hand-dressed' from appropriate shaped rocks found in the tons of random material needed in the building of a dry stone bridge.

Some of them might need to be sawn.

This is done by finding a likely candidate stone for a springer and sawing straight lines at the right depth and correct angle, and then chiselling in the strips of material away. In the photo above you can faintly see the remaining saw lines after the material has been removed. A template was used to trace the angle on this big springer stone. 

It is the angle and shape shown in this diagram.

It is best if the springers made from the template have some thickness at the nose rather than have the stone come to a point, so that they are stronger and less likely to break .

This nose will become part of the intrado which is the name for the underside of the arch. 

Supporting the Form

The form used for supporting a dry stone bridge while it is being built can be held in place in a number of ways. Most often temporary, fairly thick, beams need to be used for the form to rest on.These beams or heavy planks need to be positioned in such a way that they can be dropped down and the form lowered and slid out sideways after the bridge arch is built and has become self supporting. In the photo above the beams that support the form are resting on big stones bedded in the creek. Wedges will be slid between the top stones and the beams to bring the form to the correct height. These wedges will be removed later when the dry stone arch is completed.

The form for Crown Bridge was supported by a crib of cedars.   The posts in the crop running parallel to the direction of the bridge were knocked out after the bridge was completed so that the form could be lowered and taken away.

Springdale bridge in Port Hope was supported by 4 by 4s laid on 12 inch blocks. Later after the bridge work is done, the blocks will be smashed and the form will drop down.

On a couple of bridges I have used four pairs of these block wedges under the supporting beams.

Plastic is sometimes used between the wedges so that the wood doesn't bind when the time comes to spread them to lower the beams supporting the form.

Other types of arches

Of course there are several different types of arches, not just the semi circle arch and the segmented arch. 

At a recent workshop Patrick McAfee and I were teaching last February, we took the opportunity during a huge downpour to go inside and discuss some of these various kinds of arches and vaults and their different applications. 

Then our students went back outside and built three segmented  arches.

Here are some of these other shapes that can be used in bridges as well. 




One example of an elliptical arch. 

A superb example of an elliptical dry stone bridge was built in 2013 in Australia by my good friend Gavin Rose. The link to the web site where he describes the building of this bridge is http://www.ttms.com.au/grampians-national-park.html

(photo by John Daley)

There is also the pointed (or Gothic) arch
Here is a flattened Gothic arch stone bridge built over the Sudbury River in Aiken's Park near Hopkinton Massachusetts.

Gothic arches end up needing to be taller than circular or segmented arches and are therefore less useful in going over wide spans. For long bridges they are used in combination. Usually they require a higher approach both sides of the bridge too. 

Although I have seen ogee arches, I have never seen one used in a  bridge 

The catenary arch is very close to a parabolic curve. There are many bridges whose arches approach some sort of  parabolic curve. These would be stronger than segmented arched bridges.

The jack arch (or flat arch) is just that - an arch that has little or no curve. A bridge of this type would require the maximum of lateral resistance (in the form of stone mass) on ether side of the span to stop the arch from spreading.


                         


This is a kind of corbelled arch bridge. It relies predominantly on tensile strength, not compression strength, and therefore, even with using massive stones, is a weaker arch. 

It and other bridges is found on a very good site where you can see more arches at http://traveltoeat.com/the-arch-in-architecture-and-history/


Through a series of posts in Thinking With My Hands from October 5th to 31st ,2013, I discussed a lot of these different types of arches. 



Arch # 1

Arch #2

Arch # 3

Arch # 4

Arch # 5

Arch # 6

Arch # 7

Let's do some exploring along The Catenary Trail

Arch # 8

Arch # 9

Arch # 10

Arch #11

Arch # 12

Arch # 13

Arch # 14

Arch # 15

Arch #16

Arch # 17

Before advent of the arch Part 1

Before the advent of the arch. Part 2

Before the advent of the arch. Part 3

Before the advent of the arch. Part 4

Determining the radius if you know the segment length and the height of the arc

In the example of the segmented arch form I had to make in the previous post, the segment length (span of the bridge ) equaled 12 feet.  

For half a form, the measurement is six feet. 

The height of my bridge was three feet. 

Therefore the radius for a segment of a circle, according to the equation below, equals 7 1/2 feet

From calculating that radius, I determined where the axis was, and then cut my arc from the ply wood, and also drew my radiating lines at the same time.  

Here are some links that help explain how you go about determining the radius for a predetermined bridge span if it is going to be segmented arch. 

www.handymath.com/cgi-bin/rad2.cgi?submit=Entry

www.mathopenref.com/chordsintersecting.html

www.mathopenref.com/arcradiusderive.html

Ribs and Lobsters

The design I use to make the form , often called the 'centering' that goes under a dry stone bridge or arch (until the stones support themselves) looks a lot like a large lobster trap.

The one I am assembling here for the Hubb Creek dry stone footbridge project near Wellington Ontario is a twelve foot span.

The form was made in two sections, from 4 sheets of 3/4 inch plywood. The two halves of the form will be scabbed together with squares of plywood.

The arc of the bridge was to be a segmented Roman arch shape. I have used four sheets of plywood and equally spaced the curved 'ribs' to make a form with a twelve foot span and a width of six feet.  

Having determined that the distance across the bottom of the segment is to be 12 feet ( the width of the stream) and the height of the arc to be 3 feet on a flat surface, I fix an axis and draw a circle with a radius where the line of a twelve foot span segments the circle at three feet along a perpendicular axis. See tomorrow's post to see how this is calculated.

This gives me the height I want for the form and thus the shape of the ribs for the arc of the bridge. I lay each of the four sheets down (one at a time) with one edge along the bottom segment and a corner aligned with my axis and then trace the half rib shape on to my plywood. 

Before cutting the outside ribs, don't forget to draw radiating lines from the fixed axis while the plywood is flat, so you have guidelines for determining the angle that each of the voissoirs should be oriented when the form is made up and supported in place at the actual bridge site. It is better to draw the lines now than try to guess the angles later. 

Trying to re-establish the the centre point of the arc in order to draw radiating lines after the form is made can be pretty tricky. We had to turn this form upright and on its side (and then measure out so many inches to an axis point 6 feet high) to be able to draw the radius lines for our MacDougal Bridge form, because we had forgotten to draw them when the ribs were not attached. 

I cut the rib out with a jig saw or sometimes even a skill saw.
After I have cut one, by rotating the first rib around the plywood sheet I've cut it from, and placing properly I was able to get another full rib out each sheet of plywood. See tomorrow's post to see how this is calculated.

Since plywood only comes in 8 foot lengths, for the 12 foot span bridge, I made both halves six feet long at the base and three feet high. Keeping the form in two halves made it easier to transport in my truck too and also lighter to carry to bridge site. 

The four ribs (of the one half of the form) are spaced at 24 inches and secured with 2x4s and deck screws in five or six places.  A couple of braces are screwed in place diagonally between the ribs to stop the form leaning sideways with all the weight of the stones. Several 2x8 6 foot long boards are screwed to the bottom of the form to give it stability.  The other half is made the same way.

At the site the two halves are scabbed together and the form is then carried into place. To keep it lighter most of 2x4s that will create the surface of the arc will be aded to the top of the form later.

Next: how to temporarily support the form over the stream until the stone arch is built.

Bridge Foundations

The abutment foundations we built for that first bridge in Port Hope are not the only kind we've used. The foundations described below have also worked well and in a couple of other cases I've discovered a combination of stone and concrete has been quite a suitable solution for small dry stone footbridges of this type. Below is a description of two other ways it can be done if the situation allows for it.

Here at the public bridge in Russell Ontario, ten foot wide, four foot deep holes were dug by machine and U shaped forms were assembled of plywood and then concrete poured to make the abutments. Less concrete was needed because of the clever U shape design. Clear gravel was used to fill up the four feet of depth around the abutments and tapered back to eventually be the support the tails of the bridge. 

Stones were embedded in the fresh concrete to be a resistance to any sheering action across the top of the flat surface of the abutment. Re-bar or long bolts can be used here instead.

In Wellington Ontario we used concrete forms again but created six inch high steps in combination with embedded re-bar to act as resistance to the lateral push of the arch.

At Bruce's bridge we dug precise 8x8 by 8 foot deep holes in the hard subsoil and then added clear sharp 3/4 gravel to within 12 inches of the surface. After compacting it thoroughly we built our bridge on top of this dense gravel foundation. Lateral movement of the bridge was avoided by bedding the first larger foundation stones below grade into the gravel. 

The bridge is 8 years old and has showed no sign of movement or slumping.

Shaping Stone 2

I believe that 'shaping' should differentiated from 'splitting' stone in that it involves breaking a stone across its narrower thickness. It can also involve breaking a stone to create a rough face and/or obviously giving it some sort purposeful shape. 

Splitting on the other hand involves opening a stone up along its grain or sometimes across, (sometimes using feather and wedges or a 'tracer') but usually involves bigger pieces than ones we will be shaping and splitting generally is done more at the rough beginning stages of a project. 

I rarely 'split' stones unless perhaps I come across a stone that is layered and has a fault or a fissure where it seems like it would be easy to chisel open to separate it into two matching halves. The twin stones with newly revealed surfaces are sometimes called 'shiners'. Shiners are rarely used structurally, that is, with their faces showing out in a dry stone wall because they are generally too thin and the bulk of the stones can't be embedded into the wall deep enough.

Shaping is more likely to be what we do to the stones in normal dry stone walling. It is what you see going on in this photo above. The stone is too long and the wrong 'shape' to go into the abutment we are making for the bridge. If we need to make a new face on a stone we can cut (shape) it this way too. 

To use the stone we have to shape it with a chisel and hammer. Ironically the chisel is a two inch 'splitter'. It has a carbide tip blade and a one inch shank (which makes it easy to grip and sends the blow of the hammer down with more force into the stone) 

Granted, a single hammer known as a walling hammer could be used inserted to do this kind of shaping but it involves more of a gradual chopping away at one side of the stone to get the stone to the right size. I prefer to just cut across the stone the way you see it is being done here along the line scratched on the stone in the photo above.

I use a three pound lump hammer holding the splitter firmly gripping it nearer the pointed end of the chisel. The chisel blade has to be positioned exactly along the line I want it to break. It needs to touch the stone's surface in at least two points so that the chisel isn't resting on a high point which would only allow the force of the blow to one small (directionless) point. With the chisel blade touching the surface in at least two places on the line, the force of the blow is spread/connected? along the length of the chisel width at least, and so sends the message/energy of the impact along the proper orientation. 

Enough hard whacks will eventually tell the stone where it should think about breaking. If it the stone I am shaping is fairly flat and big enough I sometimes put a straight piece of metal ( T-bar or rail or even a pry bar) under it parallel to my line  so that the blow from the hammer is sent directly down below along the line where the stone is resting. Sometimes if it is taking a while and I want to make sure it breaks in the right place I turn the stone over and chisel the other side too.

Eventually the stone will break and usually if it is the right kind of stone (granite sandstone and limestone are good) it will produce a clean flat straight break which can often be used as a 'face'. 

Shaping Stone

Before going any further on the story of the bridge we built in Port Hope in 2004 let's talk about splitting, shaping  and dressing stone material. We needed to know how to do these things to be able to make some of the stones we used in the bridge.

This seemingly demanding task of trying to change the shape of rocks and stones has been going on for a long of time. Not that it always takes a long time, though it can, but it's certainly been going on since the beginning of time. 

Workers in stone in early civilizations in almost every part of the globe discovered all sorts of clever ways (some of their techniques still remain a mystery ) of prying/removing chunks of rock out of the ground or cutting slabs away from outcroppings of bedrock, and then taking these big rocks and making them smaller, shaping them perfectly and even decorating their surfaces with textures and intricate designs. Various theories on how the Incas and other ancient people did this with such accuracy and on such a spectacular scale makes for great reading. 

The methods employed by humble dry stone wallers however are not wrapped in any great mystery, nor are their ways a closely guarded secret that only a few craftsmen ever properly grasp to become truly proficient. Stacking stones is not rocket science. Nor is the shaping, splitting or even the dressing of stones.  Only a few tools are needed along with a certain understanding of some basic methods. Whether one is building a wall, a cairn, a seat, or a small bridge, the things you have to know about the subject are pretty simple. 

See tomorrow's post.

Less than a year later

Less than a year later and with Norman's help we organized the first DSWAC 'pack horse' dry stone bridge building workshop in Canada. A handful of enthusiastic stone aficionados signed up for the course a couple months before the event ( at 100 dollars for three days hands-on instruction ) and together that October we made bridge building history at 

Port Hope Ontario's first Canadian Dry Stone Wall Festival.

The property I had chosen to build the bridge on was in the town my family and I had just recently moved to. There was a good bed and breakfast there off main street that had a beautiful 4 acre property with a gentle swale going through a grassy clearing near the huge Victorian house. I made a scary cold call and proposed the idea of having a bridge built there to the owner who I had never met. He was was not as surprised or as cautious as I had been expecting. Instead he listened intently and was quite enthusiastic as I told him I had chosen his property for a very unusual stone project. When I inquired whether he would object to the idea of me constructing a traditional Scottish style dry stone bridge somewhere on his estate, at a cost to him of only the twenty four tons of stone material, he replied "Am I an idiot? " Which I took to mean that he was all for it.

As the days got closer he got more and more enthusiastic about the free bridge he was going to get and offered to serve lunches to everyone who would be working on the project.

Before the three day public event during which I hoped to complete the bridge, a fair amount of prep work had to be done. Enough suitable stone material had to be procured. This was coming from a stone quarry I had recently discovered about an hour away. 

The foundation holes had to be dug and the abutments built up to the height of finished grade either side of the creek we were planning to span. Holes are usually not much fun to dig but these were. The excitement of what we were going to be creating was mounting by the shovel full. It was a hot day and shirts came off almost immediately. 

The 6 by 4 foot squares had to be dug to below the creek bed, which fortunately was not flowing during that uncomfortably hot week back in late September 2004. Large limestone slaps, similar, but slightly smaller than the squarish huge chunks of armour stone used by landscapers, were lowered into the holes and fitted in a dove tail fashion to create a kind of dry stone crib below grade. From these bases there would be support to spring the bridge off of. 

These two 'abutments' had to be low enough to not move with the frost.

My hope was that if they did move at all they would both move the same amount and at the same time and in the same direction so that the bridge would still stay tight. 

This bridge was to be an experiment. I needed to see if dry laying stone was a suitable method for building small foot bridges in Canada. I had already by that time built many smaller dry stone garden arches and realized that as long as the matching bases were dug evenly, with the same size and depth of footprint into similarly undisturbed ground, over time, very little evidence of conflicting movement occurred across the arches. Would a dry stone bridge have the same success? 

Epiphany Bridge

Not long after it was built I was taken to see this very old looking dry stone bridge. I am not that old. Nor in fact was the bridge. The bridge had been built by Master Craftsman Norman Haddow and Dieter Schneider several months before. 

It was however the first dry stone bridge I had ever seen in the flesh. 

While visiting Scotland in 2003 ( meeting and working with certified wallers, researching how the DSWA was run and getting advise from their members on establishing a similar organization in Canada) I had an opportunity to meet Norman and travel with him to see examples of good quality 'dry stane dyking'. Norman was eager to show me the bridge which had just been built using local boulders and a random selection mostly the mica schist stone found on the large estate which is located near the village of Butterstone in the Highlands. 

We drove up some narrow roads and then walked quite a distance to get to what seemed like a very remote part of Scotland. As we walked Norman informed me that the design of the bridge was based on the bridge at Glenn Lion (another remote area of Scotland) which he had visited with his family many times as a boy and he had always been fascinated with. 

He told the story of how he had been commissioned to build this new bridge by a wealthy landowner to replace the wooded one which was situated over the 'burn' (the Scottish word for stream or brook) where the man had proposed to his wife many years prior. Obviously it was to be a very special project to commemorate that engagement and a successful marriage which had lasted five decades. At first Norman was reluctant to take on the challenging task of building a completely mortarless stone arched bridge, but after some continued persuading by the landowner he agreed to do it. I'm so glad he did as it was from that bridge that many other bridges arose.

I had a bit of an epiphany when I saw it. In all my travels I had never seen anything as fittingly beautiful, as that sturdy stone bridge. I couldn't imagine it ever having not been there. I was also quite sure I hadn't seen or heard of any bridges built like it anywhere in Canada either. I remember starting to get really excited. I took many photos of it with Norman standing, or rather squatting, near it. (He explained the scale of the bridge looked more impressive that way) He took the photo of me there. Standing or squatting, after seeing Norman's lovely bridge I was suitably 'impressed'. I understood for the first time how it was actually possible to span distances by carefully fitting random stones together in a proper arched configuration. From that day on I became absorbed with the idea of building one someday somewhere in Canada. That was back in 2003

The Construction

The bridge sprang off four large boulders which were found on site and moved with heavy equipment close to where they needed to be placed in pairs on opposite sides of the burn, after which they were barred into their final position manually. More very large rocks were bedded together in the earth over these boulders creating the two stone cribs which formed the abutments for the future bridge either side of the burn. They protruded roughly to the height of the level that the water was known to rise during spring run off. Next Norman and Dieter carefully fixed in place the wooden form that had been constructed by local carpenters (to temporarily take the weight of the bridge arch) It was propped in such a way that the supporting wedges could be removed and the form could be slid out from under the structure after the two sides of the arch were built up and joined at the top so that the bridge would be then able to support itself.

Perfectly flat, suitably thick, squarish stones work best in the construction of a challenging bridge like this one. Most of the local stone available for the bridge was predominantly rounded and consequently Norman and Dieter strove to find enough naturally flat bedded stones to do the job.

These valuable flatter stones (voussoirs) were carefully laid in bands, basically upright with their best faces down (forming the intrado) across the wooden arch, so that each row leaned up against the previous one, ensuring that all of the rows were gently leaning in a radial pattern up against the initial row of larger 'springer' stones. This was repeated until the rows of stones met almost in the middle. 
Finally across that remaining gap, where the rows nearly met, a row of the best 'keystone-like' stones were wedged in securely. All the radiating stones over the form were then pinned with granite wedges of varying sizes. Pinning and wedging the structure thoroughly ensured that even the slightest wiggling of the larger stones in the arch would be eliminated 

The rows of stones at this point in the construction look quite jagged (like a hedgehog's back, says Norman) A second and third layer of more horizontal stones was then built into and over top of the radiating rows of voussoirs so that the arch becomes thicker and heavier. This extra weight actually helps make the bridge even sturdier. Providing a bridge has proper solid built up sides (abutments) that can not move, it is a known principle of physics that the stone arch will become stronger as additional weight is added to it.

Abridgement

Perhaps those of us who love dry-laid stonework and/or build with stone, using only stone (no mortar) can better understand what it is about a dry stone bridge that makes it so profoundly attractive  - and so 'right'. 
Many of us can certainly appreciate the rewarding sense of accomplishment Anne Halliday must feel having recently completed her first bridge at the Westwood Hotel Golf and Country club near Glasgow Scotland.

Unlike thousand of others made with steel, wood or concrete, a properly built dry stone structure like this beautiful arched bridge that Anne built, is not just a thing of beauty, it is also a delightful demonstration and resonating expression of what it is we associate the word 'bridge' to mean.

It is this expressive manifestation of the 'dry stone bridge' alone that so mysterious spans the gap of our own imagination of what 'bridging' is. 

We begin to understand not only why and how it 'stands', but even what it is a 'bridge' stands for.

While some of us will never get over the charm of a dry stone bridge (when we do indeed have the pleasure coming across one) we recognize that it intrinsically capsulizes, in its unique structural design, all that is involved in the concept  of  'comprehending' , literally 'trying to get over' something.  

The stones are all joined together in a magical pattern to actually reach across the opening, which is less like an 'understandable opening' and more like a challenging expanse of nothingness presenting a kind of invisible barrier. 

A bridge of this type that is uniquely constructed of skillfully fitted stones in an arch is in itself the 'abridgement' of the concept of dry stone walling. It epitomizes the artistry and craftsmanship involved. 

Such a bridge will always represent more than the sum of its parts (the stones) 

Sadly there are relatively few dry stone bridges here in Canada that are built of dry laid stone. Not many can be found even back in Britain or Ireland or the rest of Europe either. And while there there are still very few being built Anne's project does represent a growing movement, a new resurgence in the interest in building permanently with stone, and without mortar. 

It mostly involves using common sense (and physics) to fit the stones together. Skilled artisans like Anne are helping demystify the concept of working with this plentifully available and naturally structural material.  All that is required is a dedication to building properly with stone the way people simply used to in the past, with an understanding that bridges needed to be built way before manufactured products and speciallized technology came along. 

The stones in Anne's bridge rely solely on their own friction and weight to keep the whole arch suspended in air.

They join together in a continuous bond facilitating not just our 'getting across' the real bridge (and also the concept), but they also help us to make that intuitive connection between form and function.

Click here to see more photos and read what Anne Halliday has to say about building her bridge

To see the a previous Thinking With My Hands post I wrote about Anne and her bridge visit Anne Halliday and her Bridge