Category: Construction

Buildings vs. Water

Buildings vs. Water

Last week I wrote about what causes flooding and what we can do to help prevent it. For some communities, both in the UK and abroad living on water, or near water is a fact of life. To avoid being flooded these buildings might be built on stilts or float and adapt as water levels rise. Today’s blog explores these designs.

Floating buildings – Expanded polystyrene is a key component to ensure the house stays afloat. it can either be used to create a slab on the water: flexbase_01_02 or by creating a composite material with concrete:compositehull_001Presumably there are longevity issues with bare polystyrene and that the composite hull will be much longer wearing.

An alternative to polystyrene is to use a reinforced concrete hull: hercules_01 The hull is often left as a void, perhaps filled with polystyrene, with the house constructed above. It is possible though to use the hull as a basement though, as was shown on grand designs: formosa_the_amphibious_house_by_baca_dezeen_1_1000The building is connected to four columns, and can slide up and down these as required by the flood water. This ensures the house stays level as it rises and falls and it obviously means it doesn’t float off during a flood. Much of the design inspiration for these has come across from the Netherlands. In Amsterdam there are entire communities floating on the water, such as the IJburg estate: 14-floating-houses-east-amsterdam-6701All of the houses and walkways are connected to steel mooring poles to ensure they stay in place, floating up and down, as the water dictates.

Building on stilts – It may be very obvious how this design works in the floods, but let’s not knock the simplicity. Here are two UK build houses on stilts:uk-2 article-2031343-0d9eacad00000578-454_468x407Architecturally, building on stilts can be very effective. The top building appears to levitate above the ground due to the slender and dark columns. In contrast the bottom design emphasizes the columns locations with the glazing and wall panels breaking at these points, leaving clear vertical lines through the design. This is accentuated further by the horizontal lines at each floor level, and by the roof line.

All of the buildings featured in this blog have clear architectural / structural overlaps within the design work and must be the culmination of great collaborative working. As more developments creep onto existing floodplains I hope design strategies such as these are utilized and that rather than feeling threatened by more, unpredictable weather and the associated higher flood risks, we actually use it to inspire us. Perhaps we too will create floating communities like those in the Netherlands.

Engineering flooding

Engineering flooding

On Boxing Day massive areas of Yorkshire were flooded. Working on Kirkstall Road, Leeds, and having volunteered with many others to help clean up houses and businesses, I have seen first hand the devastation. Obviously we know that flooding is caused by heavy rainfall, but what is making the situation worse? And what can we do about it?

What might have caused this flood to be so much higher than previous records? 

Climate change is making our weather more unpredictable. Air holds water vapour. If this patch of air then meets a patch of colder air the water vapour condenses, creating rain. With global warming, the air is getting warmer, which means it can hold more water vapour, which means more water falls as rain. Flooding will increasingly occur as climate change affects us globally.

Lastly our own actions can cause flooding in the years to come. A large tree can absorb 100 gallons (450 litres) of water a day, so every time a tree is cut down large quantities of additional water is entering the streams and rivers. When a moor is managed for grouse shooting the ground is drained so that grouse can easily live there. Intensive farming can also mean large run offs into watercourses. Have a look at this article and this article for more information. Lastly, in Greater London, every year the area of Hyde Park, London is concreted over. This means there is no soil and plants to absorb the water, and it runs into the sewer systems instead.

Believe it or not but flood defences can also cause flooding! As a river meanders it has natural eddies, and currents as the water flow interacts with the river banks and river bed. This interaction means the water is slowed down by its surroundings. Flood defences are often built from concrete, so rather than having a soft, bumpy river bank, you get a vertical, flat, solid bank. The water doesn’t get slowed down by the concrete, in fact it speeds up. Flood defences don’t surround every stretch of water, so this style of flood defences simply moves the flooding elsewhere. This could mean onto planned farming flood plains, but can also be into towns and villages further downstream. I live in a village called Woodlesford where Leeds Council kindly built us a small flood defence last year. It protected our village from this winter’s flooding, however the next village downstream, Methley, had the worst flooding on record, with over 50% of the village under water. I expect our new defences had an impact.

So what can we do?

We could continue to build longer, taller, thicker flood defences to keep the water at bay, but knowing how this might cause flooding downstream, surely there’s got to be a better way?

Pickering, North Yorkshire, has a different way of managing the floods. The town was badly hit in the 2007 floods, but rather than build a large, and very expensive, flood defence (costing £3.2million) they looked at catchment measures that would slow down the water movement. Rather than all the water arriving at once, and causing a flood, the water would arrive over a longer time period, keeping the water level low. This article explains the situation in Pickering and this one details the catchment measures used. The measures were completed in 2015 at a cost of £2million. Not only were they cheaper, but planting trees has additional benefits of increased wildlife and CO2 absorbsion too. I should also add that the town didn’t get flooded on Boxing Day!

Obviously these strategies can only be completed in rural towns and villages, but can we mimic this in the city? Turns out we can… Sustainable Drainage Systems (SuDS) provide an urban alternative. SuDS effectively provides large, tanks underground where rainwater can be stored before it enters the city’s drainage system. In normal weather system works as it would in a traditional set-up. In heavy rain though, the water can be stored underground and released in a controlled manner. The city’s water levels are monitored so water is released when capacity allows and stored when it would otherwise cause flooding. Problem solved!

I hope this helps explain what exacerbates and alleviates flooding. Next week I thought I’d continue the theme, but focus on adapting building design in order to protect the property and our possessions when building on flood plains, or river banks.

Conference: CEMFree

logoAll civil engineers will be aware of CEM1 concrete. It’s a standard concrete mixture using cement to cure and harden. CEMFree has been created by the David Ball Group to entirely replace the cement requirement in concrete.

What’s wrong with using cement?

Portland cement (OPC) is a mined material. It is therefore a finite resource, and has an environmental impact in its creation. During the curing process of cement / concrete large quantities of carbon dioxide is released into the atmosphere (0.95 tonnes / tonne concrete) which has a knock on effect on global warming and climate change.

What is CEMFree?

CEMFree is high performing cementicious binder that can entirely replace the need for cement. It consists of ground granulated blast-furnace slag (GGBS) and pulverised fuel ash (PFA) plus an admixture (kept very secret!?) so uses a large quantity of waste products in its creation.

CEMFree technical comparison to CEM1

  • Better chloride protection
  • 0% permeability
  • Lower embodied energy (<1.5GJ/tonne vs. 5GJ/tonne)
  • 95% less CO2 emissions (0.09tonne/tonne vs. 0.95 tonne/tonne)
  • Reduction in thermal expansion so no expansion gap requirements
  • No requirement for crack control so reduction in steel usage
  • Equal strength at 28 days with a greater strength from then onwards

Publicly available specification is available: PAS 8820:2016

All in all it seems to be a miracle product to help revolutionise the industry into a climate friendly industry. This could presumably also use recycled aggregate to further reduce its environmental impact. It does make you wonder what the admixture is though?

Conference: Passivhaus

ph_logo-strapline_blue_1I had heard of Passivhaus prior to attending the conference, but not many details in what it was and how it affected structural engineering. Put simply Passivhaus is design focussed on minimising energy use during it’s lifetime. (This links quite nicely with Peter Head’s talk focussing on performance focussed, rather than financially focussed tenders written about here.) Passivhaus, as a basis, tends to ensure the following in its design:

  • good levels of insulation with minimal thermal bridges
  • passive solar gains and internal heat sources
  • excellent level of airtightness
  • good indoor air quality, provided by a whole house mechanical ventilation system with highly efficient heat recovery (more info)

There is also a very similar set of standards for retrofitting properties called EnerPHit, since we obviously can’t solve poor building design by simply starting again. The EnerPHit standard is a slightly more relaxed version to Passivhaus due to the difficulties in renovating properties and because there needs to be an element of value for money. I live in a draughty, Victorian terrace, solid wall construction. Making it anywhere close to Passivhaus standards would be incredibly difficult.

Why follow Passivhaus design?

In an average building there is a 60-80% increase on heating costs compared to its design expectations.

78% of homes do not achieve the required air change rate rising high humidity levels, condensation, mould growth and associated health issues.

How does it affect structural engineering?

Thermal bridging: Make sure the structural framework of a building is enveloped within a thermal, insulating layer (and preferably a thick one). In professional work ensure a masonry column supporting a steel beam doesn’t penetrate through the cavity, ensure appropriate construction notes ensure all displace insulation is re-inserted.

Airtightness: During construction a building should have continuous plastic sheeting within the external structure. How do you fix this without using nails or staples? How do you ensure a building’s structure doesn’t penetrate through this?

Communication: Both of the above topics cannot be resolved without considerable communication between architects and engineers. Personally I have a great interest in sustainable design. Unusually I also have a degree in Architecture, as well as currently studying in Civil / Structural engineering. I hope in the future I am able to work on projects that combine both my personal interests, and also combine my skill sets.

Literally Green Buildings

Literally Green Buildings

The Bosco Verticale in Milan are literally green tower blocks. The two tower blocks are home to over 700 trees, of which there are 90 species of plant! There are sooo many benefits to this, but these are the key ones:

Passive solar / thermal design – A deciduous tree during the summer has thick foliage, providing shading. If designed well, and integrated into the overall building’s design the trees could reduce strong glare and overheating during the summer months. Equally during the winter months, when the weather tends to be more overcast the lack of leaves allows much more light and heat to enter a building. This ultimately reduces the need for lighting and air conditioning / heating.siting10

Water use – If there is a cohesive building wide strategy for water use, including biodegradable shower and cleaning products then…

So much more to read about…

Temporary Shelter

Temporary Shelter

I recently came across the IKEA refugee housing solution that appears to have been around for a couple of years. It got me thinking…

I have a great belief in social justice and in everyone taking part in helping to alleviate someone else’s suffering, in whatever way interests you. As a structural engineer I’d wondered if I could ever be involved in designing products such as these, so I thought I’d find out more about what other products are currently available. Below are those that I’ve so far come across.

SpaceMax modules start off the size of a steel carrier, however with clever design each side opens up creating a ceiling, floor and walls, tripling the internal space. Hard to explain, but they have a useful video on the webpage. The space within can then have bathroom, bedroom, kitchenette modules inserted (presumably these are transported within the remaining space in the container shape?).

Continue reading…

Old plastic bottles = new brick

Old plastic bottles = new brick

“Argentinian researcher Rosana Gaggino from the National Council of Scientific and Technological Research (CONICET) and her team designed a process that recycles discarded plastic bottles turning them into construction “ecological bricks” (ladrillos ecológicos).” Interest Engineering link

Traditional concrete blocks use sand and cement as the main constituent parts. These blocks are simply created by replacing the sand with plastic particles from ground up bottles. Approximately 20 bottles are used for each brick.

Not only does the brick help reduce landfill, it’s insulation properties are 5 times better than those of conventional bricks, helping to also reduce the consumption of insulation materials. It is also lighter, weighing 1.4 kg per brick, rather than 2.4 kg per conventional brick. Lighter buildings means smaller foundations, which again saves material. Also, could this material mean we can build in sandier soils more easily?

PET is recycled in many areas within the UK (I know Leeds city council accepts it). It would be great to see if the UK will take up the production of this item.

I wonder what it’s structural properties are? Could this become a leading alternative construction material, competing alongside concrete blocks?

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