50 Fun Facts About Structural Engineering

Which Washington state span, nicknamed Galloping Gertie, twisted itself apart in a gale four months after opening?

The Tacoma Narrows Bridge failed through aeroelastic flutter rather than simple resonance, and the only life lost was a cocker spaniel named Tubby, left in a car on the deck.

P. T. Barnum marched 21 elephants across which New York crossing in 1884 to show doubters that it was safe?

The Brooklyn Bridge was seen through to completion by Emily Warren Roebling, who relayed her bedridden husband's instructions to the engineers on site.

Which shape is the basic unit of a truss because it cannot be deformed without changing a side's length?

The triangle is the simplest figure that will not change shape while its side lengths stay fixed, which is why a bare rectangular frame needs a diagonal brace.

Which Babylonian king's law code put a builder to death if his house collapsed and killed its owner?

Hammurabi's code went further still: under the next law, if the collapse killed the owner's son, the builder's own son was to die.

Ming-dynasty builders strengthened the lime mortar of the Great Wall of China by mixing in which food?

Sticky rice, boiled to a thick soup, adds a starch called amylopectin that makes lime mortar stronger and more water-resistant.

Which American monument has an iron skeleton built by Gustave Eiffel, years before his Paris tower?

The Statue of Liberty is an early curtain wall: its thin copper skin carries no load and hangs from the inner frame, as glass does on a modern office block.

Which external arched support, used at Notre-Dame de Paris, let Gothic cathedral walls be thin and filled with glass?

The flying buttress carries the sideways thrust of a stone vault out to a separate pier, so the wall itself no longer has to be massive.

Which California span's roadway sagged flat in 1987 when 300,000 walkers packed it for a 50th anniversary?

The Golden Gate Bridge was so jammed by poor crowd control that the weight pulled its normally arched centre span level; up to a million people had turned out.

After marching soldiers brought down Broughton Suspension Bridge in 1831, the British Army ordered troops to do what?

Break step, meaning walk out of rhythm: the 74 men had felt the deck bounce in time with their feet and stepped harder for fun until a bolt gave way.

What struck the Empire State Building in thick fog in July 1945, yet left its steel frame structurally sound?

A military bomber, a B-25 Mitchell diverting in fog, hit the north face; the frame was not compromised and many floors were open for business less than 48 hours later.

What is the wedge-shaped stone at the very top of a masonry arch, set in place last, called?

The keystone locks an arch so that it can stand unaided, yet it carries the least stress of any stone in the ring.

What is a beam called when it is fixed at one end and free at the other, like the balconies of Fallingwater?

A cantilever sends all its load back to the one fixed support, and bridges are often built from pairs of them reaching out to hold up a central section.

Which Italian landmark was stabilised by 2001 after engineers dug soil from beneath its raised side?

The Leaning Tower of Pisa moved back 45 centimetres, to where it stood in 1838, once 38 cubic metres of earth had been drawn out, and was declared stable for 300 years.

Which skyscraper lets visitors view its 660-tonne steel ball, a pendulum that swings to steady the tower in high winds?

Taipei 101's ball is a tuned mass damper: made of 41 welded steel plates, it swings against the building's sway and can be seen from the 88th to the 92nd floor.

Which American inventor popularised the geodesic dome, patenting it in 1954 and building one for Montreal's Expo 67?

Buckminster Fuller did not invent the form: a German dome on the roof of the Zeiss works in Jena came some twenty years before he coined the word geodesic.

Which London footbridge shut days after opening because pedestrians' footsteps made it sway from side to side?

The Millennium Bridge taught engineers something new: people on a swaying deck unconsciously fall into time with it, and 37 fluid dampers had to be fitted to calm it.

Which Italian city's buildings stand on closely packed tree trunks driven through lagoon mud to a layer of hard clay?

Venice's builders chose alder, a wood noted for resisting water, and laid slabs of Istrian limestone over the pile heads to carry the walls.

Sydney Harbour Bridge is held together by about six million of which fasteners, each driven in red-hot by hand?

Rivets were the proven choice in 1932 because structural welding was not yet trusted for a job of that size; the largest one weighed 3.5 kg.

Steel, the backbone of modern structures, is an alloy of iron and a small amount of which element?

Carbon makes up no more than about 2% of steel by weight; add more than that and the metal becomes brittle cast iron instead.

Joseph Paxton's design for the 1851 Crystal Palace grew out of a glasshouse he built for which plant?

A giant water lily, Victoria amazonica, has leaves so strongly ribbed that Paxton floated his daughter Annie on one to test their strength.

Which kind of stress acts parallel to a cross-section, making internal layers of a material slide past one another?

Shear arises when forces push one part of a body one way and the neighbouring part the other, which is exactly what a pair of scissor blades does to paper.

Which term do engineers use for the permanent weight of a structure itself, as opposed to its occupants and furniture?

Dead load usually gets a smaller multiplier in design than the changing kind: a staircase might be checked for 1.2 times its own weight but 1.6 times the crowd on it.

Engineers measure stress in pascals, a unit that expresses force divided by which quantity?

Area is the divisor: one pascal is a single newton spread over a square metre, so small that structural stresses are normally quoted in millions of pascals.

Which Italian scientist's last book, Two New Sciences, set out an early theory of why beams snap under load?

Galileo Galilei showed in 1638 that a stick across the knee gives way most easily at its middle, and that the ideal beam held at one end tapers in a parabola.

Roman builders mixed lime with which material from Pozzuoli, near Naples, to make concrete that sets even under water?

Volcanic ash, called pozzolana, was shipped in enormous quantities to build the harbour at Caesarea, and it resists salt water better than modern concrete does.

Joseph Aspdin patented which building material in 1824, naming it after a pale limestone quarried in Dorset?

Portland cement, the binder in almost all modern concrete, got its name because once hardened it resembled the prized stone used for St Paul's Cathedral.

Which 1850s steelmaking method, blowing air through molten iron, first made steel cheap enough to build with?

The Bessemer process burned the impurities out of molten pig iron in a blast lasting about 20 minutes, the first inexpensive way to make steel in bulk.

Which goldsmith won the contest to build Florence Cathedral's dome, then raised it without a timber frame to hold it up?

Filippo Brunelleschi laid the bricks in a herringbone pattern that tied each fresh course to the ribs, since Tuscany did not have enough timber for conventional supports.

Greek temples and Stonehenge both use which ancient building system of horizontal beams resting on upright supports?

Post and lintel suits stone badly over wide gaps, because a beam sags in the middle and its underside is pulled apart, the one thing stone resists poorly.

Which Chicago skyscraper, the world's tallest when it opened in 1973, is built as nine square tubes bundled together?

Willis Tower, known as the Sears Tower until 2009, is said to have been worked out with nine cigarettes held in a cluster at staggered heights.

Which American monument, 630 feet high, is exactly as wide at its base as it is tall?

The Gateway Arch has no hidden frame: its steel skin is also its structure, and Eero Saarinen raised the design from 580 to 630 feet before it was built.

The Millau Viaduct, which carries a French motorway high above the Tarn gorge, is which type of bridge?

Cable-stayed was the jury's choice in 1996, a multi-span design by engineer Michel Virlogeux and architect Norman Foster with a structural height of 343 metres.

Which Scottish railway crossing, opened in 1890, gave English an expression for a task that never ends?

The Forth Bridge took its present form because an earlier design was scrapped when the same engineer's Tay Bridge collapsed in 1879; the saying is about painting it.

The Morandi Bridge, a motorway viaduct that partly collapsed in a 2018 rainstorm, stood in which Italian city?

Genoa lost 43 people when a 210-metre section fell; what was left was demolished in 2019 and a new crossing named after Saint George took its place.

In which country did a 1995 earthquake push a half-built bridge's towers apart, adding a metre to its main span?

Japan's Akashi Kaikyō Bridge was nothing but two towers at the time; the Kobe quake moved them apart and the central span had to grow from 1,990 to 1,991 metres.

Which East Asian tower has a central pillar, the shinbashira, long credited with helping it survive earthquakes?

A pagoda's central pillar runs its whole height and pokes out of the top storey to carry the finial, and pagodas have stood through quakes that felled newer concrete buildings.

Which English scientist first stated his law of elasticity in 1676 as a Latin anagram, solved two years later?

Robert Hooke's unscrambled anagram says that extension is proportional to force, and he claimed to have known the rule since 1660.

Young's modulus, the ratio of stress to strain in a solid material, is a measure of which property?

Stiffness is not strength: the modulus says how far a material stretches under a given pull, not when it breaks, and it is named after the British scientist Thomas Young.

Which property lets structural steel stretch and deform permanently before it fractures, unlike brittle cast iron?

Ductility gives a warning: a steel member bends and stretches visibly before it fails, where a brittle material simply breaks.

What do engineers call the turning effect of a force, found by multiplying the force by its distance from a point?

Moment is the quantity usually called torque elsewhere; doubling the distance doubles it, which is why a long spanner shifts a nut that a short one cannot.

Which Swiss mathematician derived the formula for the load at which a slender column suddenly bows sideways?

Leonhard Euler's formula shows that doubling the length of a column cuts the load it can carry to a quarter, which is why slender struts are braced along their height.

Which engineer, known as the father of tubular designs for high-rises, engineered Chicago's John Hancock Center?

Fazlur Rahman Khan made a high-rise act like a hollow tube with its strength in the outer walls, and has been called the Einstein of structural engineering.

Which Scottish engineer, nicknamed the Colossus of Roads, built the Menai Suspension Bridge in the 1820s?

Thomas Telford earned the pun on the Colossus of Rhodes through sheer output, and served as first president of the Institution of Civil Engineers until his death.

Which Canadian crossing of the St. Lawrence collapsed twice while being built, in 1907 and 1916, killing 88 workers?

The Quebec Bridge's first collapse killed 75 of the 86 men on it; the steelwork had turned out far too heavy for its own members to carry.

What caused one corner of London's 22-storey Ronan Point tower block to collapse in May 1968?

A gas explosion on the 18th floor, set off when a resident lit her stove to make tea, blew out load-bearing walls; the failure led to major changes in building regulations.

Which Manhattan tower, perched on four stilts above a church, was quietly reinforced in 1978 after a student's query?

Citicorp Center's wind braces had been bolted rather than welded to save money, and the repairs were carried out at night and kept secret until 1995.

A chain hanging freely from two points takes which curve, the ideal line for an arch when turned upside down?

Catenary comes from the Latin word for chain, and turning the curve over swaps its pull for pure push, so every stone of the arch is simply squeezed.

Which earthquake-protection method rests a building on rubber or sliding bearings so the ground can shake beneath it?

Base isolation decouples the structure above from the foundations below, so the bearings take up the motion instead of the frame.

Which term expresses how much stronger a structure is built than it needs to be for its maximum expected load?

A factor of safety of 2 means a part should fail only at twice its intended load, and building codes usually fix the minimum margin in advance.

Which curved masonry supports, perfected at Hagia Sophia, let a round dome sit on top of a square room?

Pendentives were tried by Roman builders in the 2nd and 3rd centuries but reached full development only in the 6th-century cathedral at Constantinople.