Introducing a new block design for arches

I have been working on a new manufactured concrete block design which can be used to build arches, cylinders and domes.  This design is something of a departure from my earlier work: it is not triangular, but more rectangular in general shape.  This shape allows it to be easily produced on a standard block machine, it also allows for easy handling, cubing, stacking and shipping.  It takes maximum advantage of the mold volume to produce the largest number of blocks while minimizing wasted space in the mold. No core pullers are required.

The shape is rectangular, 8 inches by 16 inches, with a width of around 3 inches.  There are two grooves located in the block, these are used to locate and place reinforcing steel rebar.  The rebar also acts as supporting scaffolding while the block are laid.

Each block has a compound angle, which is at 45 degrees to the rectangular edges of the block.  This compound angle makes each block act as a wedge, or voussoir, like a conventional arch block: except that the wedge-shape occurs at 45 degrees to the face of the block, normal to the axis of rotation of the arch being assembled, to allow for the corrugated feature of the assembled arch,

These block weigh only 75% of the weight of a typical 8 " x 8" x 16" block.  This makes them easier to handle and place for the mason.  The key and keyway, and also the grooved recesses for the rebar create hand holds for ease of handling by the mason.  A small indentation in the bottom of one of the grooves is an indicator to show the mason the thinner end of the block.

Each subsequent layer of block is laid at ninety degrees to the previous layer, this herringbone stacking creates the corrugations.  The grooves for accepting rebar allows the block to be placed directly on top of the previous course: you don't have to 'thread' the block all the way down the rebar, it is very simple and easy to lay these block.

These block have two 'keys' that stick out and two 'keyways' that form recesses, creating an effective interlock between two adjacent block.  This feature, together with the two recesses which accept rebar, fully locate block and lock them into their proper position as they are laid.   The arch remains stiff as block are laid, this system for assembly works well.

The block are stacked to create corrugations in the arch.  These corrugations introduce a moment of inertia in the arch, resulting in higher strength and increased flexural rigidity: just like a tin can or a plastic bottle has ridges to make it stiffer.

Manufactured concrete block are anispotropic: the strength is not the same in all directions, there is a high-strength axis and a weaker axis in any manufactured block.  These new block are produced so that the high-strength axis of the manufactured concrete is always facing radially, toward the outside of the structure.  Conventional concrete block always have the high-strength axis facing vertically, with the low-strength axis facing outside, so that they are less strong (especially to impacts from outside).  This weakness of concrete block is dramatically demonstrated by FEMA P-320 testing, where a 2" x 4" piece of wood is fired through a cannon at a wall to simulate tornado conditions.  A regular unreinforced block wall will have holes poked right through it with the FEMA P-320 test. The block system described here is much stronger.

Multiple wythes or layers of block can be used to make this system even stronger, by making the arch even thicker.  By making the arch thicker, there is no limitation to the size of arch which can be built.

These block can be dry-stacked, or they can be used with mortar.  If they are dry-stacked, they will create an arch around 25 feet across.  By using mortar, the size of the arch can be adjusted, either larger or smaller by feathering or tapering the mortar thickness.  Different sized radii can be combined to build an arch with more than one center, creating beautiful designs and providing extensive design flexibility.

In addition to a round arch, these block can also assemble into a pointed or Gothic arch.

A US patent application for this design has been filed.  I worked on this design with 5 students from Alfred University's Inamori School of Engineering for their Senior Project.  These students are (listed alphabetically): Corey Bergendahl, Jacob Brown, Dillon Jones, Stephen Livoti, and Andrew Schermerhorn.  Each of these students did a great job in focusing on this technology for their Senior Project, they are all listed as co-inventors on the patent application.  These students were under the direction and supervision of their instructors, Dr. Ehsan Ghotbi and Dr. Eric Payton.  Below is a picture of 3 students (from left: Jacob, Stephen, Dillon) doing a dry stack test assembly.

High quality, high carbon, heat-treated molds made for this block system were made by Besser Proneq. This mold is suitable for a 3-at-a-time block machine, and works on either a Besser or Columbia type block machine.  It produces six block per cycle.  One of the block cavities has a removable insert, with the option available to create two half blocks with each cycle.  The mold can either produce six full blocks per cycle, or five full blocks and two half blocks.  The half blocks allow for the end of an arch to be made as a flush surface, an important feature.

An initial trial run of this mold and these block were made at Southern Tier Concrete Products Corporation in Alfred, New York.  This mold worked very well, it easily produced 6,000 block in this trial run.  The cycle time was around 10 seconds, or around 1.6 seconds per block.

Since these block only use 75% of the material used in a standard 8" x 8" x 16" and require less cycle time per block than a standard 8" x 8" x 16" block, it is expected that these block will sell for around the same price or even less than the cost of a regular block.  If we assume that each block sells for $1.50  then an arched roof can be built for around $7.00 per square foot, which includes rebar.  This represents an incredible value: very high strength, beautiful, maintenance free, fire resistant, rot proof, insect proof, building systems which can be expected to withstand tornadoes, hurricanes, and other severe weather events for less than $10 per square foot.   This system is also very energy efficient: it takes advantage of the thermal mass benefits which characterize masonry, and extends those benefits to the roof and the entire building.

This system provides extensive design flexibility: many different types of structures can be made from this one block.  It can be used to create round arches, pointed Gothic arches, multi-centered arches, cylinders, domes, arch rib sections, and even flying buttresses.  This design flexibility makes it appropriate for many different applications, from arched roofs for residential, commercial and public buildings, to tunnels, bridges, culverts, retaining walls, and many other infrastructure applications.

This block system is especially well suited for making arched bridges.  Currently, the US is facing an impending crisis with its infrastructure, and with its bridges in particular.  The example left for us by the Romans of using arches for their aqueducts proves beyond any doubt that the masonry arch system is effective, durable, and able to withstand the test of time: many aqueducts are over 2,000 years old and remain structurally sound to this day.

Currently I am building test structures using this new block.  I expect these structures to be completed over the summer.  Check back on this blog for progress and pictures of this system being used.

150th poem about masonry

I can hardly believe it:
what began as a dare,
still I concede it
caught me unaware -

Here is April's last day
looking back at the mix
of my silly foray
into poems of bricks.

It's been too much fun
but now at long last
my poems are done
they are in the past.

When you see a mason
just please remember
they might be tracing
poet's spark from an ember.

The spark, once lit
can burn with ease
those words will fit
those bricks in these.

Review

For five years now every April
I've endeavored to write
poems on masonry every day
the result's banal and trite.

Poorly conceived, poorly composed
poorly written and poorly done
thoughtless, reckless and poor
not even read by anyone.

Stilted and derivative
foolhardy and stupid
pretentious and sloppy
even hated by Cupid.

The worst of the worst
all too synthetic
these poems all suck
just plain pathetic.

Bridges

Bridges: they do connect us
their safety is important
Once broken, they wrecked us
their disrepair's a portent

Of ominous things to come
for this country's many millions
Broken bridges have become
A problem worth 52 billions

We need a better way
to make our bridges strong
we need it done today
and they should last quite long

But cutting edge design
can borrow from the past
aqueducts come to mind
those Roman structures last

They've lasted over 2 millenia
civilizations have come and gone
abuse? they've seen plenty o'
and they're still standing strong

The masonry arch is tough to beat
It's simple yet it works so well
it is an engineering feat
and it's really strong as hell

Masonry arches made from block
can be quickly easily made
with cement and sand and rock
New bridges from new masonry laid.

Hay(na)ku epiphany

Block
can be
used for roofs.

Seismic support

Masonry built in seismic zones 

must be carefully designed

especially if it's used in homes

the strain must be confined.

For if it's allowed to move sideways

(and catenary thrust will go lateral)

not if but when, on somber days

and falling walls can shatter all.

We've learned it before, and yet again

the danger of inadequate wall

thoughts and prayers do begin

for the people of Nepal.

Clerihew #3

Saint Patrick crossed the border
into Ireland with some mortar
With religion he brought grace in
and became the right first mason.

The Block Not Taken

Two blocks replaced some rotting wood,
And sorry I could not lay them both
And be one mason, long I stood
And tamped down one as far as I could
To where it lay in the mortar bed;
Then took the other, as just as level,
And having perhaps the better aim,
Because it was glassy and wanted bevel;
Though as for that the grouting there
Had laid them really about the same,
And both that morning horizontally lay
In scaffold no step had trodden mud.
Oh, I kept the first for another day!
Yet knowing how lay course on the way,
I doubted if I should ever cut wood.
I shall be troweling this with a sigh
Somewhere ages and ages hence:
Two blocks replaced rotting wood, and eye-
saw the one less mortared by,
And that this mud all the difference.

Good help

Really good help is hard to find
but if you're involved and astute
you'll find a real peace of mind
in Workforce Development Institute.

They're there to help, they really are
They'll look you up and make a visit
just laugh as your dog greets their car
and ask "but what kind of dog is it?"

Friendly is -of course- very nice
yet work costs money, it is true
appropriate help for a quoted price
helps make jobs, for me and you.

Earth Day

By digging clay
locally found
On Earth Day
from the ground

It really should
be consciously fired
with local wood
not alive, but expired

No fossil fuels
no gas or petrol
break the rules
go carbon neutral

Play your part
in this scene
make some art
make it green.

Quoins

Striking joints
tucking points
mud anoints
the corner quoins.

Truths

A brick in the hand is worth two in the
Bush league masons don't stack
Up, up and away in my beautiful
Balloon frame construction is just a bunch of
Sticks, honey we live surrounded by
Rednecks make the best
Moonshine lights up my
Moonlit dome disdains All that man is,
All mere complexities,
The fury and the mire of human
Veins, so vain I bet you thought this poem's about you
you're so vain.

Landay

You dropped the block as you fumbled
I cried when it hit my toe and the sad block crumbled.

You said "don't worry, it's no trouble"
But tell that to my toe, and tell it to the rubble.

Alone now I lay block in a row
Just me without you, just me and my poor bloody toe.

Corrugations

An arch is made stronger  with corrugations
furrows and grooves that are parallel
repeated as regular reiterations
keep the arch braced, stiff as well.

Blocks which overlap and interlock
create the furrows and the grooves
herringbone pattern of stacking block
to create masonry arch roofs.

Two receiving grooves are placed
on each block to receive rebar
with these grooves equally spaced
like strings are spaced on a guitar.

The rebar's curved in the diameter
of the arch of the masonry span
to provide supporting parameter
and scaffolding for the masonry man.

Social Masonry

Through facebook, twitter, snapchat and such
I share with the world my news of block
the world just doesn't care too much
Of my instagram views of mud and rock.

Few 'thumbs up' and measured 'likes'
and fewer 'shares' and no re-tweets
this realm belongs to younger tykes
and music made of "massive beats."

But still someway I get the word out
Social media for masonry
To make foundation get the dirt out
and build upon it publicly.

Terrazo Terzanelle

Your floor may be marble or terrazo
polished smooth or tiled pattern
on which you eat hummus, even matzo.

You can revel in revelry, just like Saturn
In grandiloquence sprawled on travertine
having spit leisurely in your spat urn.

Living the life of a libertine
luxuriously having things DeLuxe
As featured in Martha Stewart's magazine.

(Ok, so Martha Stewart kinda sucks)
it shouldn't detract from your "Living"
turn on the light: Fiat Lux.

Just take masonry, I'll keep giving
my own opinion of good construction
quality of life concerns good living.

For these points need some reduction
A terzanelle about terrazo
marble needs no introduction
nor does the indulged American fatso.

Self conscious masonry limerick

There once was a masonry limerick
whose second line ended with "brick"
Twasn't Ginsburg's "Howl"
instead it used a trowel
To mortar in words I'd pick.

Dialogue between block and mortar

I am block, concrete all through
I am so strong and inexpensive
mortar, why do I really need you?
with your presence so extensive?

Block my friend and my old companion,
You'd be lost without my bonding
Colorado River without Grand Canyon
Or a bloody steak served to Gandhi.

Mortar my old and true acquaintance,
this block is rather disgusted
I almost puked at your reference
To Mahatma's diet entrusted

To mortar's odd whims and all
But together, we should stay
and just keep the solid wall
"block and mortar" for every day.

For ours is an ambivalent art
the question asked is if whether
the mortar keeps the blocks apart
or if it keeps 'em together.

Production

Incessantly filling and leveling action
the mold receives mix from the hopper
then down comes the shoe with compaction
there's just no way to possibly stop her.

Six blocks are made every ten second
the pallets are full of new block
they slide along, and hardly need checking
they move in good time with the clock.

More than a wise man or even an oracle
It takes a good team to make it all work
the ballet of production is no small miracle
with a sharp action, a heave and a jerk.

The beautiful block just slide off the line
the pallets get ordered and stacked
and mechanically handled with a touch fine
and placed gently upon the rack.

The forklift picks up the whole big load
and carries to the kiln for curing
the block spend a night, tucked in their abode
while the block machine keeps whirring.

Under the arch

Even the dark is lighter and the sounds are cleaner
the solid thing has always been, so it seems
all encompassing surrounded by green so greener
the twilight of my once blurry waking dreams.

The weight is lighter and the touch is distinct
the massive sense of surrounding all
the integral speaks from a paper inked
in my mind it begins with a solid wall.

The vertical preamble for what's yet to come
the arch turns in at the top of what's known
knowledge forgotten, from an echoing drum
unconsciously there and subconsciously shown.

In the marrow of my bones, a sense of it
the knowledge wiped clean and rules all broken
The airy arch came from some deep unknown pit
from the wish of my ancestors long unspoken.

An arch begins

I got there soon, as a matter of fact
they told me "come see these newest block Pete!"
Not only do they work well - in the abstract
but they also worked well in the concrete.

New Block

Brand new mold to the world of masonry
brand new block, but must not hasten we
wait and fine tune it - to dial it in
and then on Monday we'll do it again.

Calligram

At

the 

top

is a

cupola

then the

keystone

and then the crest

of the arch at the top of the

dome,  spreading,  elegantly  into  the

haunch of  the  arch - where  thrusting  forces 

begin to push out, fighting gravity by using gravity:

depending on the weight of all the masonry to force the

voussoirs together into a consolidated whole relying on the

weight above it, but with all that weight the walls begin to get

thicker toward the bottom, in order to prevent any cracks from

developing near the bottom of the dome the thickness acts as a 

restraining force, with more thick walls at the base total restraint.

Palinode

The last poem made financial projections
based upon rates of production
These estimates are now facing rejections
disregarding the cost of corruption.

Kickbacks and bribes, conflicts of interest
You know how greasy it feels
so your friends will facebook 'like' and pinterest
Gotta grease those squeaky wheels.

The vigilant never quite fully relaxes
adamantly checking financial inspection
any profit is gone to pay taxes
Gotta revise the financial projection.

Did you hear what I said?  Must I re-state?
Over thirty million per year?
I cannot even begin to relate
so clean the wax out from your ear:

Stop the starry-eyed wishful dreamin'
the financial prophets prophesied;
You'll be lucky to just break even
financial projections are set aside.

Masonry Accounting

The patent filing cost eight grand
the new mold: thirty-five thou
production, 14K in hand
13 hundred for half block (wow).

It's expensive to make new block!
These costs bring compunction-
money's time, so check the clock
how does this financially function?

The numbers help confirm my loyalties
'cuz rates of production do confirm
the key to the model is found in royalties
if we look at how much it can earn

Twenty one thousand block are made
In one single eight-hour shift
Fity-cent per each block is paid
as a royalty-paying constant gift

One mold working one third of the time
(8 hours out of the day's twenty four)
Creates an income which serves just fine
Hopefully keeping the wolf at the door.

One mold working 48 weeks per year,
working just those 8 hours per day
And soon it becomes abundantly clear
One mold makes over $3 million in pay.

Ten molds rotated, on a global basis
to serve the globe's seven billion
are set to keep the financial pace is
annual income over thirty million.

Aubade

Dreams of rocks and blocks and bricks
are broken by my aching back
but using some gymnastic tricks
out of bed with a creak, a crack.

Fingers' numbness is replaced
with sharpened pains of flexing them
the cement stings from skin's waste
it's time to do it all again.

The morning sun shows yesterday's
block still freshly placed and struck
Inspection of the joints and ways,
the arch is rising from the muck.

That first bag of mortar ripped
and dumped into the mixer
that first bucket of water tipped
and mixed is my elixir.

To overcome my whole inertia
and pick up block, and set 'em straight
will the paycheck reimburse ya?
When passion for building is my fate?

The work itself is not just all
that is its own just reward
it is, alas - just a wall
built by me, my just accord.

The blocks are better than they were

The blocks are better than they were the snow is getting brown 

The mason's waist is plumper the ice is out of town.

The tender wears one less sweater the scaffold less forlorn 

Lest I sh'd be more chastened I’ll put a tool belt on. 

i carry your trowel with me

i carry your trowel with me(i carry it in
my hand)i am never without it(anywhere
i go you go,my block; and whatever is laid
by only me is your doing,my block)
i fear
no wall(for you are my wall,my block)i want
no wood(for rickety you are my wood,my rot)
and it's you are whatever a lunar base always cement
and whatever a solar wind will always fire this block

here is the deepest mortar nobody sees
(deep in the wall of the mall and the wall of Wal-mart
and the rows of the Lowe's of an aisle called block;which builds
higher than the code can hope or mine can hod)
and this is the mortar that's keeping the blocks apart

i carry your trowel(i carry it in my hand)

 

Alone in my pursuit

It is hard for me to believe, I still don't quite get it
I work in a field thousands years old, you can bet it.
Masonry arches have been made by man forever
and the ubiquitous concrete block is found wherever.

But somehow, some way, nobody has ever attempted:
to make an arch with concrete block, mortar all cemented.
It is so obvious! I'm not just a parroting fool!
An arch made of concrete block is so strong, and cheap and cool.

I have scoured the country and searched this whole planet,
looked into concrete from cinders, limestone and granite.
But nobody, no one, no single person anywhere,
has dared use concrete block to build arches in the air.

It's a conservative industry, and works well enough
there is no need to contemplate your newfangled stuff
We've done well without any arches, without any art
without any soul, without beauty too, without your part.

And still I pursue it, I can't help but do it, arch block
an unfulfilled, undiscovered unknown way with rock
Yet known too well, for millenia, masonry arch roof:
that I should be the first (and only!) is a humbling truth.

Anisotropy

Concrete is made of rocks and sand
glued together with cement
the aggregate you understand
is irregular, with intent.

The intention of irregular shape
is tip-to-face contact all throughout
aggregate packed to reduce the gape
of free space between the grout.

Concrete made into block
has aggregate pressed and jostled
irregular aggregate interlock
frozen into position, fossiled.

The axis of this huge compaction
is the one of greatest strength
energy of vibrating action
aligns the rocks along their length.

When measured strength is the same
in all the measured block directions
"Isotropic" is the name
for equally strong strength detections.

When manufactured block's the topic
It's not so strong in sideways view.
It's known to be anisotropic
and highest strength is vertical too.

New Blocks on the Kid

Five years ago today, my friend Jennifer L. Knox double-dog-dared me to write a poem every day for the month of April about masonry, for National Poetry Writing Month, or NaPoWriMo.  This will be my fifth year of participating in NaPoWriMo.  It's tricky to come up with poems every day for a month, and especially so when they are all about a specific topic: masonry.  I beg the reader's indulgence while I try this again.

New Blocks on the Kid
March has left like a lion
April is on the lam
But soon I will be tryin'
To make the best blocks I can

I will because I must
I must because it's there
It's there because I trust
in warming of the air.

With warmth I'll mount the mold
upon the block machine
In with new, out with old
new block never seen.

With contempt we leave you, March
and hope for a new beginning
A new block to make an arch
and April will be winning

All the cold dark winter long
patents filed, mold was made
nothing should really go wrong
as winter too soon shall fade.

As the earth will soon awaken
and I make this new design
the doubts of winter are forsaken
This new block will align

And stack upon itself with ease
into an arch with lovely lines
with facility sure to please
questions in the mason's minds.

R&D in Concrete Block Masonry

Manufactured concrete block represents a great success story of the 20^th century.  An entire global industry has developed and evolved into a high state of efficiency and economy, all based on manufactured concrete block.  This technology thrives in virtually every country on earth: the traditional, rectangular concrete masonry unit (CMU) is produced inexpensively and with an engineering knowledge which is well understood and successfully put into practice by block producers globally.  The result is something we all tend to take for granted: high-strength, consistently dimensioned, inexpensive, rapidly produced CMU’s which are suitable for vertical walls in virtually any type of building, including residential, commercial, public buildings and infrastructure.  With such a successful model of production, distribution, assembly and availability already well established and in place, what –if any- new developments can research and development (R&D) add to this existing industry and practice?

My own work as a masonry designer has addressed this question for 25 years now.  I will attempt to summarize the areas of potential future growth, development and design which this robust industry has left essentially unfulfilled.  A look at current areas of research conducted by various segments of the scientific and engineering world indicate areas which stand to benefit and develop rapidly from the existing engineering practices of the concrete block industry.  The research and development proposed here hold the potential to transform the concrete block industry’s offerings into an entirely new realm of products which will provide better building systems at a lower cost on a global basis.  A modest effort in research and development will reap huge benefits for humanity; it will grow the concrete block industry and make superior, affordable, beautiful and holistic construction available for all.

One specific area of current research which has garnered significant attention from scientists, engineers, designers and practitioners is the idea of topological interlocking structures.  “Topological” refers to “Topology (from the Greek τόπος, "place", and λόγος, "study") [which] is the mathematical study of shapes and topological spaces. It is an area of mathematics concerned with the properties of space that are preserved under continuous deformations including stretching and bending, but not tearing or gluing. This includes such properties as connectedness continuity and boundary.  Topology developed as a field of study out of geometry and set theory, through analysis of such concepts as space, dimension, and transformation. Such ideas go back to Leibniz, who in the 17th century envisioned the geometria situs (Greek-Latin for "geometry of place") and analysis situs (Greek-Latin for "picking apart of place"). The term topology was introduced by Johann Benedict Listing in the 19th century, although it was not until the first decades of the 20th century that the idea of a topological Space was developed. By the middle of the 20th century, topology had become a major branch of mathematics” (taken from Wikipedia).

Currently, concrete block design and practice do not provide for topological construction.  The standard rectangular concrete block designs (with which we are so familiar) can only be used to create straight vertical walls and square corners.  A few designs allow for a slightly curving wall, which have found use mainly in retaining walls and landscaping applications.  Other novel designs allow for slight variations to the basic idea of a vertical wall, including corners which occur at 45 degrees and so on.  Current concrete block designs are far from providing a full expression of topology.  Curving walls –such as those provided by landscaping applications- only curve in one dimension, like a cylindrical surface, and do not allow curvature in two dimensions, like a spherical surface.  A form of concrete block known as “articulated block” (shown above and below) does some interesting work as an erosion-arresting embankment material.  Articulated block do not interlock in the plane being assembled; blocks can slide in and out of the assembly.   There are some great articulated block designs being developed though.

The design of CMU’s which allow for full topological expression provides the ability to use block to make roofs and complete curved structures (e.g. complete spheres, ovals, elliptical, catenary and other designs).  The design ability which can create a full expression of topology allows the use of high strength, affordable, rapidly produced building components which provide all the benefits of concrete block, including: fire resistance, termite resistance, rot resistance, building longevity, resale value, solidity, appearance, and the ability to withstand extreme weather events (hurricanes, tornadoes, typhoons, storm surges, tsunamis, etc.).    The creation of CMU designs which allow for full topological expression will create an entirely new architectural vocabulary for building with concrete block, and will create entirely new markets for concrete block.

If an interlocking aspect is included in the masonry unit then the topology in masonry is made particularly more effective.  One striking example (which has fueled much of the current research) is the failure of thermal tiles on the space shuttle Columbia.  Because they did not interlock, these topological tiles (designed to wrap around the shuttle: topologically) were free to move and dislodge themselves from their protective positions since they were held in place only by adhesive, leaving the shuttle vulnerable to catastrophic reentry into the earth’s atmosphere.  Researchers were quick to realize that if an interlocking aspect of each masonry unit (or tile) were incorporated, then the geometry of the individual masonry units would have helped keep them in their proper location (anchored by adjacent masonry units) and prevented them from being removed.  Furthermore, researchers have realized that topological interlocking masonry units (or tiles) would not suffer complete, systemic failure if one of these masonry units were damaged: the other adjacent and surrounding tiles would stay in place, even if one tile broke or was removed.  By including the interlocking feature into the masonry unit itself, a separate independent connector is not required.

While this idea of the beneficial nature of interlocking masonry units is illustrated by the Columbia tragedy, it holds great significance for the less exotic application of buildings here on terra firma.  To fully understand this, we will look at the current state-of-the-art for masonry engineering analysis.  Examining a masonry arch, the current engineering model makes 3 assumptions: 1. Masonry units have infinite compressive strength; 2. Masonry units have no tensile strength; 3. Masonry units never slide against each other (they remain in their fixed position).  We will concern ourselves here with the third assumption, the idea that masonry units in an arch (known as voussoirs) never move relative to one another.

In reality and in practice, voussoirs are known to move against each other in a masonry arch.  When this occurs, the arch can be significantly weakened and this movement of voussoirs can result in failure and collapse of the arch.  A catenary thrust line is an imaginary line of force which exists in the wall thickness of the arch.  Catenary (from Latin “catena” or chain) is the shape of a hanging chain or cable under gravity; if this shape of a hanging chain is inverted, then a catenary thrust line is generated.  As long as this imaginary thrust line does not touch or exit the arch wall thickness, the arch will remain standing and stable.  If the imaginary catenary thrust line touches or exits either the inner surface (intrados) or the outer surface (extrados) of the arch, then a hinge will form at that location.  Several hinges allow a mechanism for movement of the arch, resulting in a buckling or folding of the arch about these hinge locations, leading to failure and collapse of the arch.  However, if voussoirs possess an interlocking feature such that they are not free to move relative to any adjacent (interconnected) voussoirs, then the catenary thrust line will not touch or exit either the intrados or extrados of the arch due to movement.  Thus interlocking masonry units in an arch are fundamentally much stronger, more robust and more stable than masonry units which do not interlock.

The creation of an effective interlocking feature on a topological masonry unit produced on a standard conventional block machine is a very real challenge for the masonry designer.  Interlocking features are actually commonplace in standard (non-topological) blocks: the ‘top’ and ‘bottom’ of the concrete masonry unit can readily incorporate interlocking features.  A wide variety of designs is possible if the interlocking feature does not include topological arrangements, but the designer is still limited to building straight vertical walls.  In order to provide an interlocking feature for a topological masonry unit, the sides of the block must be used (not just the ‘top’ and ‘bottom’ of the block) as sites of interlock.  The difficulty here is that a block mold must be readily stripped from the block without any undercut, or draft, or negative angle.  In other words, an interlocking feature on a topological block will create undercuts: an interlocking topological block simply will not release from a mold.  This contradiction can be overcome by symmetry and design.

Another difficulty in creating an interlocking topological block on a block machine is the ability of the mold cavity to be filled completely, evenly and homogeneously.  If a section of the mold near the ‘bottom’ of the block has an overhanging feature (steel mold above it) then it will not fill as readily as an open cavity which allows the concrete mix to flow into it, unimpeded.  A section of mold cavity which has an overhanging feature will impede the flow of concrete into the cavity, resulting in segregation of aggregate.  This segregation of aggregate will typically result in a weakened section of the block where larger aggregate is prevented from filling as easily as in an open mold cavity.  Lack of larger aggregate in a filled mold section creates a weaker section of concrete as a result.

In addition to sections of mold being less than ideally filled due to overhanging mold parts, there is another problem where a section of mold cavity at the ‘top’ of the mold has an open space below it (at the ‘bottom’).  This will create an overhanging projection of block, which is unsupported from underneath (at the ‘bottom’).  These cantilevered features of block are prone to cracking and breaking, especially upon handling as the un-cured block leaves the block-making machine. 

How can a topological interlocking masonry unit be created in a manner that provides adequately filled mold cavities at the ‘bottom’ of the mold, while also not creating weak cantilevered sections at the ‘top’ of the mold?  This is a very interesting design challenge; one which I hope will attract the efforts and solutions of other designers.

Catenary thrust line analysis of masonry domes is another area of current research.  Computer models which digitally process the applied stress and the resulting strain as hinge mechanisms are used to develop visual models.  Catenary thrust line analysis is also used to digitally analyze a computer 3D model as a tool for designing buildings.

Biomimicry/Biological Design as a source of masonry design is ripe with potential.  “Nature’s masons” include single-celled radiolarian and foraminifera, coral, sea anemones, sea horses, turtles and tortoises, Thor’shero shrew, and an endless array of life’s other innovative design solutions.

Anisotropy in manufactured concrete block has not been fully utilized with current block designs.  Vertical block walls are made with the weaker axis of the block facing horizontally, to the outside.  It is possible to orient the block so that the high strength axis faces outside, resulting in a significantly stronger building.

Robotic assembly is still in its early stages regarding masonry, but real progress continues in this field.  Robots may play an important role in the future of masonry.  Robotic assembly may have an early adaptation for situations that might endanger a human mason, such as radiation or other hazardous materials.  Construction Robotics is one company that is currently successfully developing robotic masonry.

3D Printing is also in its early stages, but is expected to develop with time.  3D printing should find early use in masonry applications which require a unique masonry piece, such as at the intersection of two arches, or to allow conduit or openings, etc.   In this role it will be cost effective fairly soon.