Why do bridges collapse – and how can we prevent it?

The Ponte Morandi bridge, Genoa, after its collapse, which has claimed dozens of lives. Image: Luca Zennaro/EPA.

As rescue workers look for survivors in the concrete rubble that used to be part of the Morandi bridge in Genoa, Italian authorities are starting their investigation into the possible causes behind this terrible tragedy.

It is too early to determine what may have caused the catastrophic collapse of more than 100 metres of the multi-span, cable-stayed suspension bridge, completed just over 50 years ago. But it’s important to understand that bridge engineering does not end when construction finishes and traffic starts to flow. In fact, properly looking after a bridge during its long life is as crucial as having a good design, using high-quality materials, and ensuring sound workmanship during construction.

Modern bridges are designed for a life of 100 years, though many centenarian bridges – such as the Forth Bridge in Scotland, which opened in 1890 – still provide sterling service, and of course there are smaller bridges built of stone to more ancient designs that have stood for many hundreds of years. Considering the number of bridges built in Europe during the expansion of the motorway networks from the late-1950s onwards, we should expect, and be prepared for, many to exceed their planned lifespan in coming decades. Facilitating this is ambitious but necessary, and made possible thanks only to regular inspection and maintenance that ensures that building materials have not degraded, and that structural elements are fit to bear the traffic and environmental loads they face.

The Forth Bridge outside Edinburgh, one of Britain’s iconic bridges, is more than 100 years old. Image: Andrew Shiva/The Conversation.

So what are the factors that affect the strength of a bridge and may compromise public safety?

Environment and climate

The climate in a bridge’s location, taken alongside atmospheric pollution common in cities, can have an adverse influence on the material of the bridge – for example, the corrosion of steel reinforcement or pre-stressed steel tendons embedded in concrete. Regular inspections are typically scheduled every six years for large bridges to identify any degradation, and to take appropriate measures to replace cracking concrete and corroded steel, or to introduce protective coatings.

In England, the Midlands Link motorway viaducts, comprising 13 miles of elevated motorway carrying the M5 and M6 motorways around Birmingham, suffered from chloride-induced steel corrosion early on in their life from exposure to salt used to de-ice the roads. This required an extensive application of corrosion protection measures in the early 1990s. More than 700 structures have benefited from this action, demonstrating the cost savings that can be made if appropriate action is taken at the right time.


Stress and fatigue

Fatigue caused by use is another factor, and inspectors will look out for tell-tale signs of failure often associated with the cyclical stress produced by passing vehicles, particularly heavy trucks. This type of failure is especially relevant for metal bridge decks and the cables of suspension and cable-stayed bridges. Traffic has increased ever since these bridges were built, which inevitably leads to the need for more maintenance and strengthening work, such as additional steel, glass or carbon fibre-reinforced plates on critical parts in order to restore or enhance their strength compared to what was deemed necessary during their design. For example, Network Rail in the UK used fibre-reinforced polymers to strengthen more than 20 bridges carrying highway or railway traffic between 2001 and 2010.

Consider how we all tend to react to a road sign bearing the words: “Essential Bridge Works – Expect Long Delays”. One such situation prompted this comment from a member of the public: “We are doomed. I am going to buy a tent and pitch it outside work for the three months while the misery goes on.” Perhaps knowing why this is necessary – and the consequences of not doing so – might persuade people to reconsider such views.

Money and willingness to spend it

Equally, we must understand that maintenance budgets need to be set at levels that far exceed those that would allow engineers only to “firefight” the most severe problems, as is becoming worryingly commonplace. Instead, budgets need to allow for planned interventions and necessary upgrades over many decades. That requires public and government support, as well as skilled engineers committed to ensuring the safety of an ageing structure.

There are challenges in devising improved methods to assess bridge strength, developing new repair techniques, and new ways of collecting and using inspection and monitoring data to provide advance warning of problems. These constantly push technological boundaries, making it possible to operate existing bridges safely during their long service lives. And the experience gained feeds into new designs that will become reality in years to come.

The ConversationThose investigating the collapse of the Morandi bridge will look at inspection and maintenance matters. Other lines of enquiry will no doubt include the unusual design of the multi-span bridge, with only a few cable stays to transfer deck loads to the towers, the ongoing work to shore up the foundations, and the heavy rainfall at the time of the collapse. In the shadow of this terrible loss of life, it is worth remembering that bridge inspection and maintenance may be annoying for commuters – but it is crucial.

Marios Chryssanthopoulos, Professor of Structural Systems, University of Surrey.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

What’s behind the rise of the ornamental restaurant toilet?

Toilets at Sketch restaurant, London. Image: Nik Stanbridge/Flickr.

A few weeks ago, I found myself in the toilets of a zeitgeisty new Italian restaurant in east London called Gloria. As with so many contemporary restaurant toilets, those in question were an aesthetic extension of the establishment’s soul. The inventive menu was matched by two-way mirrored toilet doors.

The setup was this: cubicle occupants could see out while the unisex crowd milling around the taps could check their outfits on the exterior mirrors. All fun and games, I thought. But then I found myself mid toilet with a guy peering into my door to change his contact lens. Either he had spectacularly bad manners or he was unaware of the two-way door thing. (Let’s hope it’s the latter.)

Gloria’s toilets aren’t unique in their attempt to be distinctive. The loos at nearby Mr Fogg’s Maritime Club & Distillery are adorned with specimen boards of dead spiders. Meanwhile, Edinburgh’s The Sun Inn invites patrons to pee in buckets, and trumpets double as urinals in The Bell Inn in East Sussex. Men can wee into the vista if they’re dining in the Shard. And Sketch’s ovum shaped loos are the stuff of urban legend.

Further afield, transparent doors become frosted only after they’re locked at Brussels’ Belga Queen. In Otto’s Bierhalle in Toronto, diners can press a button to activate their own private rave. And the toilets in Robot Restaurant in Tokyo have gold-plated interiors and dancing robots.

What’s behind this trend? Are quirky toilets just a bit of fun – or an unnecessary complication to the simple act of going for a wee and checking you don’t have tomato sauce on your chin?

Yotam Ottolenghi’s London flagship restaurant Nopi crops up often in conversations about restaurant bathrooms. A hall of mirrors glitters enticingly ahead of loo-bound diners. “The bathroom needs to be the nicest part [of] the whole place because that’s where you’re on your own,” says Alex Meitlis, the designer behind the space.

But no one is truly alone in 2019. If surveys are to be believed, nearly 65 per cent of millennials take their phone to the bathroom with them. Mike Gibson, who edits the London food and drink magazine Foodism agrees that the bathroom selfie – searches for which, incidentally, yield over 1.5m results on Instagram – is part of the reason that contemporary lavatory design is so attention seeking.


“Any new venue that's opening will be super aware that there's probably not an inch of their restaurant that won't be photographed or filmed at some point”, he says. But bathrooms like Nopi’s predate this trend. Indeed, Meitlis believes he has created a haven from the smartphone obsession; Nopi’s mirrors are angled in such a way that means you have to seek out your reflection. “You can choose whether to look for yourself in the mirror or not.”

Another driving force is the increasingly competitive restaurant landscape. “It’s almost like there’s some sort of ever-escalating competition going on amongst new openings, which makes every visit a faintly terrifying experience”, says food writer and New Statesman contributor Felicity Cloake. Gibson agrees. “Restaurants want an edge wherever possible, and design definitely comes into that.”

So novelty bathrooms get you noticed, promote social media engagement and entertain diners who are momentarily without the distraction of company. (Although, it must be said, quirky bathrooms tend to make the loo trip a more sociable experience; a Gloria spokesperson described the restaurant’s toilets as somewhere you can “have a good laugh and meet people along the way.”)

Nevertheless, I’m not the only one who finds bathroom surprises disconcerting.  One TripAdvisor user thought the Belga Queen loos were “scary”. And a friend reports that her wonderment at the Nopi bathroom was laced with mirror maze induced nausea – and mild panic when she realised she didn’t know the way out. Should restaurants save the thrills for the food?

“I think it's important not to be too snarky about these things – restaurants are meant to playful,” says Gibson. Cloake agrees that novelty is fine, but adds: “my favourite are places like Zelman Meats in Soho that have somewhere in the dining room where you can easily wash your hands before sitting down and tucking in.”

So perhaps we should leave toilets unadorned and instead ramp up the ornamentation elsewhere. Until then, I’ll be erecting a makeshift curtain in all mirrored toilets I encounter in future. An extreme reaction, you might say. But, as I wish I could have told the rogue contact lens inserter, it’s not nice to pry into someone else’s business.