Bridging The Expanse - First Season

Bridges have always been part of our narrative.

Part of the very fabric of society.

It's always been important for people

and places to connect and bridges do that, literally.

Few other structures represent

our ability to solve problems.

I think a great bridge provides both form and function.

Transforming our everyday lives.

It provides an incredibly important way

of bringing the world together.

Learning from the masters and their disasters,

we continue to innovate and progress.

The conquest of nature, the conquest of gravity,

there's something spiritual about them.

Wherever we build incidental,

ornamental, or monumental spans,

we succeed in Bridging The Expanse.

Throughout history, our destinies have been shaped

by our ancestors insatiable need

to hunt, to explore, to subdue.

And for better or worse,

these pursuits would never have been possible

if it weren't for the wonder of bridges.

Throughout history,

they were very well advanced

and well thought out structural solutions to bridges

and people have always been pushing the boundaries

of spanning further or going across wider rivers.

So they've always been a technical challenge.

Even in their most basic form,

bridges speak to our ingenuity.

One of the interesting things about a bridge

is it's potential.

Even in simpler times,

there were technological innovations,

as far as bridges were concerned,

that were extraordinary.

The earlier bridge builders had a limited array

of materials and a limited array of tools.

And the tools and the materials you have available

control what you can do.

Really primitive bridges could just be stones in a river,

a log across the river, group of logs across the river

starts to get a little bit more sophisticated.

We can call them log bridges, they're simply beam bridge.

It's the simplest beam type bridge that there is.

The word beam is an old English word that means tree.

And whether it was a timber log

or a stone plank across the stream,

beam bridges have always been around.

While some of our forebears

made timber beam bridges,

others prefer to build structures from stone.

Clapper bridges were river crossings

constructed in Southwest England from the early bronze age.

Their megalithic character reminiscent of Stonehenge.

Along this beauty point among historians,

how on earth did the early Britons

get those enormous stones to Stonehenge?

Those that remain in the landscape today

are reconstructions of their originals

washed away and rebuilt time and time again.

The most impressive, is the Tarr Steps

spanning the river bale.

17 two ton slabs sit above the water on stone piers

held in place by their own weight,

rather than any form of mortar.

There are many different types of bridges,

but essentially there are only really three types.

The arch, the suspension bridge, and the beam.

Beam's provide the vast majority of bridges.

And they are a subtle combination of an arch

and a suspension bridge.

The catenary profile of a suspension bridge

is a very natural shape.

It's what nature would give you

if you asked it to build a bridge.

Regardless of the size or antiquity

of a simple suspension bridge,

it's catenaries or main cables

are always anchored in the ground.

So the forces are mainly carried by

the main cable and the main cable is a tension element.

It's the most efficient way of transferring forces.

The deck hangs from small suspenders

that are attached to the main cables.

Thinking about a suspension bridge like a clothes line,

like the load of our clothes,

we are carrying the load of the deck of the bridge

into that cable,

and then into the ground.

Suspension bridges historically have been made from

very primitive materials.

From ropes and vines to chain and wood.

And it really served the purpose of the local community

to use whatever was at hand to overcome an obstacle

that they were faced with.

If all you've got is vines,

pull them across, weave them together, let them grow.

The bridge is really a triumph over nature.

And in that sense, it learns from nature.

While living root bridges,

gain strength over time,

fiber spans need to be regularly replaced.

And in the deepest canyons of the Andes,

this requires a great deal of communal effort.

The tradition of replacing the Q'eswachaka

across the Apurimac River

has taken place annually since the 15th century.

The basic concept of suspending things

between two points with a draping cable

is very intuitive,

but the brilliance of what they did

was the ability to make a cable of the length needed

with the materials they had available to them.

That's just brilliance.

The Q'eswachaka is the last

of the Incan rope bridges.

An invention that coincided

with the rise of the Incan Empire

and the rapid expansion of their territory

through the creation of the great Incan road.

A 40,000 kilometer system of pathways

constructed by hand in little more than a century.

Bridges were an integral part

of that ancient pedestrian network,

many making use of the grasses to hand.

The technology that the Incans used

was to take individual blades of grass,

and they would braid those into small cables

and they would weave those together

to create a bigger cable.

And then that fiber would be woven into bridge structures.

This traditional technique

had passed from father to son for five centuries.

Ensuring the rebuilding of as many as 200

throughout the empire.

Now only one remains

providing a physical link between four communities

and a spiritual tie to the past.

When you weave things together you make them stronger.

Today we weave reinforcing with concrete.

We weave the individual strands of steel

to create a piece of steel rope that is tighter

and stronger.

The concept of the braided cables from historical times

certainly was a building block for the more modern cables.

It really was the origins of community efforts

for bridge building.

They still do that even today.

While the Incans

were the only ancient civilization in the Americas

to develop suspension bridges,

their use was widespread in the Himalaya.

Suspension bridges in developing countries

are used often just because we want to be able

to construct foundations on land

and not out in the water.

The bridge form itself has been known

since ancient times,

but the material that would allow it to span

present obstacles was not available

until very much later in history.

The Lakshman Jhula suspension bridge

near Rishkesh in Northern India

crosses the mighty Ganges.

It was completed in 1929 where Lakshmana,

an avatar of Lord Vishnu,

is said to have crossed the holy river

on ropes made of jute,

a fiber that grows naturally in India.

More commonly used to make Hessian bags.

The 137 meter steel cable and timber decked span

was built to provide a far safer crossing

for two and four legged pedestrians.

Plus the occasional motor bike.

When we design a bridge,

we think about the effect of impulse load.

So those are forces that are applied to a structure.

Every bridge, regardless of its age or typology

is designed to take advantage of the properties

within its materials to resist or exploit

the forces applied to it.

A bridge has to carry a variety of different loads.

And as a designer, I need to take all of those into account.

First and foremost, of course, is its own weight.

Which in many cases is the dominant factor.

So we might call them permanent loads

or we used to call them deck loads.

And then we also have live loads or variable loads.

Those are things like the weight of people on the bridge

or the weight of vehicles crossing it

or a train crossing it.

But we also get other environmental loads

that fluctuate like thermal effects or wind loads.

All of these types of loads influence the bridge

and its functionality.

Ultimately that's the hardcore engineering

is to make sure that the bridge can be resilient

to those loads and to last a very, very long time.