This is a project I created to improve my sketching skills, analyse historical, resilient buildings and engage with the history of London architecture..
Christopher Wren may be most famous for his design of the new St Paul’s Cathedral after the old one was destroyed in London’s Great Fire of 1666, but the architect and engineer was already an experienced church designer by the time he took that challenge on. Twenty two Wren-designed buildings still stand in London today, of which fifteen are churches located mostly in the Square Mile.
I wanted to capture Wren’s genius with an ongoing project to locate, observe and draw his buildings. Having stood the test of time, I believe they really showcase what good civil engineering should look like – robust, safe, human-scale and adapted to the needs of those who use it.
Wren lived and designed in a different century, but took pride in using what resources were available in his time. Today’s civil engineers may be pioneering low-carbon concrete and solar-energy-collecting windows instead of stone and glass, but we should emulate Wren’s approaches, because city dwellers still ultimately want their buildings to be fit-for-purpose, future-proof and beautiful.
I observed the testing of concrete intended for the headhouses of London Power Tunnels 2. This took place at the batching plant Capital Concrete in east London.
There are two types of concrete batching: wet mixes and dry mixes. The former can generally produce a higher quality concrete because it can be mixed using the industrial-scale mixers at the batching plant, rather than smaller mixers available on construction sites. Today, a wet mix is being prepared for the concrete slab. The intended strength is C40/50 (meaning a failure strength of 50MPa on a 5cm x 5cm x 5cm cube).
Note on sustainability. Concrete production is one of the world’s largest sources of CO2 pollution, meaning civil engineers need to come up with alternatives which are less polluting. In normal concrete, which is based on Portland cement, about 1000kg of CO2 is produced per tonne of concrete. A new technology called Earth Friendly Concrete (EFC) is capable of reducing this to about 200kg CO2 per tonne of concrete – a significant improvement – by replacing the Portland cement with Ground Granualted Blast Furnace Slag (GGBS) and waste fly ash from industry. The concept is in its infancy so its properties can be unpredictable – previous batches have not reached the required strength because of low-quality fly ash supplied from Dunkirk in France; now that the supplier has been changed, today’s mix should pass the required tests. If the rollout of EFC on this large project is successful, it could be a significant turning point for the construction industry to reduce its emmisions from concrete production.
The batch for testing is a sacrificial batch – it will not be sent directly to the project, but if test mix passes the strength tests, the same mix will be used on the project.
Huge industrial concrete mixer, with a ‘tap’ to transfer the mix straigh into mixing lorries for transport to site
^ The giant, industrial concrete mixer at the batching plant.
Testing the batch:
1) Slump test. This is done every half an hour for three hours. Concrete is filled into a conical mould and then the mould is removed so the mixture spreads into a heap. The change in height of the heap is the slump.
2) Bleed test. A cyclindrical container is filled with the concrete mix in five layers – between each layer a vibrating tool is used to ‘tamp’ the mixture and reduce air bubbles. In general, the way the concrete firms up is based on the water separating from the heavier particles over time until enough stiffness is achieved. The amount of water that forms at the top of the cylinder is the bleed; a lid prevents evaporated water from escaping from the test. The use of high proportions of GGBS results in a longer bleed time that conventional concrete but this can be reduced with fine aggregates (<50 micrometres). When bleed occurs on site, either the bleed water is remixed into the concrete (which may result in a weak top surface) or one can wait for the bleed water to evaporate. If the rate of evaporation is faster than the rate of bleed (e.g. on a very hot day), the concrete may experience plastic shrinkage, which is undesirable and should be avoided.
3) Cube tests. 5cm cubes are filled with the mix. They are tested, usually with a hydraulic machine, on days 1-7, day 14, 28, 56 and 96 for failure strength. Concrete gets stronger over time and the 28-day strength is usually the quoted value; the material must reach its target strength (here, 50 MPa) by that date to be acceptable.
4) Weight test. This is just a way of obtaining the concrete density, which is a vital parameter to consider for safe structural concrete design.
5) Beam test. A 3-point test (simple supports at the ends, and a point force applied at the middle) is taken on an unreinforced beam of concrete at 28 days. This tests the bending strength of the mix.
This church was rebuilt after the Great Fire of London when it was severely damaged. For Wren, the Gothic style makes this one of his more unique designs. I was particularly intrigued by the tower, which retains the blockiness of many of Wren’s churches yet is mellowed out by the classic Gothic arches of the windows and octagonal turrets. I’ve chosen to sketch that here.
Exquisite stained glass is the centrepiece on entering. I appreciate the little circular windows towards the top of the facade; they make you feel like you’re on a ship. They let light in, but their height makes it impossible to see out – reminding worshippers of their smallness. In religious terms, this perhaps indicates the almighty power of God, and to non-religious observers like me, the power of the planet and the hugeness of the universe.
From a construction perspective, the main advantage of such a window placement is that the glass does not have to hold any weight – this structure would hold up just fine even if the glass were damaged – the stone walls and arched ceiling form the essential structural elements. Modern glass-facaded buildings use a ‘curtain wall technique’, where again the glass doesn’t hold any weight, but instead of a massive stone outer structure, the building is supported by internal columns, beams and braces made of steel and reinforced concrete. The disadvantage being, of course, the loss of an unbroken internal space, a key component in many of Wren’s churches.
^ stained glass visible on entry^ high-up window placement^ the tower from the outside; on the right, the facade with the little circular windows
Missable from the street – you’d easily wander past this one. But tucked away behind the buzz of the City, the people and their pints and their suits, stands a huge expanse of courtyard. Empty and flat, the pale stone transports us to southern Europe; it feels almost Milanese. Yet the roughness of the church bricks brings in that earthy British tone. There the church stands, spire up into the sky on this strange island of peace in inner London.
St Lawrence Jewry has a very familiar style – very much a main block with a sloping roof, with a tower about double the height, also rectangular, on one end. Unfortunately I was unable to go inside this church to examine the structure in more detail.
The church was actually rebuilt after extensive damage during the Blitz, but the architect Cecil Brown stuck to Wren’s initial design.
^ the view into the courtyard; the facade of St Lawrence Jewry is the building on the very right and in the centre is Guildhall^ quick sketch-up showing familiar Wren style
On the other side of the courtyard stands another church-like building, which is actually Guildhall, the HQ for the City of London Corporation.
Today, this complex acts as a retirement and care home, but it has housed a range of other groups including ware veterans in the past. It is generally regarded as a luxury home for the mostly upper classes, and only admitted women in 2009.
The courtyard reminded me most of an Oxford college – in particular the Queen’s college – with its distinctive symetrical windows and neatly kept grass.
I decided to use two-point perspective as a sketching technique for this because it felt appropriate to the building scale and shape.
^ Chelsea Royal Hospital in two-point perspective^ Queen’s College, Oxford, for reference^ Queen’s College, Oxford, for reference
In more detail, I did a close-up sketch of the entrance in the middle of the courtyard. The neoclassical influence is very distinctive here.
Rhodes House is a university building in the centre of Oxford, home to postgraduates on a type of scholarship. It contains residential areas as well as conference and teaching and learning spaces. Despite the building being less than 100 years old, its style is more historic, with a design by Sir Herbert Baker which is reminiscent of 1600s Europe – to match much of the city’s university architecture.
As a listed building, it’s vital that the architecture is well-preserved. The idea of the project was, as a lead engineer described, to make it appear as if nothing had changed once the project is complete: most of the updates will be made underground, including a new conference room and new accessible lifts.
The tasks:
1. Install a spiral staircase into the rotunda
This is the rotunda from the basement. The celing must be drilled to form a hole leading to the ground floor, in which the staircase will be installed. The other challenge is the removal of the support columns – the weight they are currently carrying is minimal but the remaining concrete must be strong enough to hold as a kind of cantilever from the outer walls. Calculations predict that reinforcements will not be required, but this could change as the project progresses.
2. Preserve the strong masonry columns in the basement as a structural component, and line them up with those on the floors above
The original columns are extremely robust and strong so will continue to be used to hold the basement structure up. They will be refined and re-covered for aesthetic appeal.
3. Extend the basement: to create a large conference space and fire exits
The basement extension from outsideThe basement extension from inside
The basement is extended using exposed reinforced concrete. There has been specially selected insulation installed for heat regulation; the holes you can see link to the ventilation and air conditioning system. The arch is an effective support structure; it also provides natural lighting for the conference space.
4. Construct sixteen new residential rooms in an excavated space, whilst allowing natural light in.
The rooms are dug underground. As well as being a space-saving solution, this is excellent for energy efficiency because the earth covering the rooms is a thick insulator, keeping rooms cool in the summer and warm in the winter. Spaces are fronted with solid oak doors and triple-glazed, full length windows; the walkway will be lined with trees down the middle to provide privacy.
5. Create a new outdoor social area
Above is the space where the social area will be – clearly, there is still work to do! On the left is a diagram of the small cafe structure, which will be used during events and conferences. I drew it out to try and visualise what had been explained by the lead engineer. Essentially a process called steam-bending will form timber into the right shape. This material takes the weight of the structure, which will be about four metres high. Weatherproof structural glass will be arranged in a facade around the edge, taking no weight but providing shelter from the weather on rainy, windy or cold days.
City Hall is an understated yet impactful building on the riverside in London. It is the headquarters of the Mayor of London and Greater London Authority – where decisions are made with regards to transport and other issues in the city. It was completed in 2002 and its ten stories each offer views towards the river.
This has always been one of my favourite modern buildings in London, because its shape is understated; it’s not overwhelming yet the building’s presence is somehow fitting to its location and function.
Although my sketch can’t depict it, the inside features a spiralling ramp that circles the building, framing the main assembly hall on the ground floor. Light pours in through the river-facing glass panelling providing a professional yet inviting atmosphere. Somehow, I just find this building intriguing!
Munich’s 291m Fernsehturm, or TV Tower, is an iconic part of its skyline. Being lucky enough to visit, I sketched its shape to show its structure and how each section is used.
A year ago, I also visited Berlin, the largest city in Germany and also home to an iconic TV Tower. Well I was interested in comparing these two structures, which have similar functions yet differing shapes and histories.
the Munich Fernsehturm
the Berlin Fernsehturm, for comparison
The Berlin tower is the tallest structure in Germany, at 318m (compared to the 291m of Munich’s tower). Much of each tower’s total height is made from its top aerial, coloured red and white. Berlin’s is tapered; Munich’s is a straight cylinder. Also, a lightly tapered concrete base contains the lifts in each tower.
Both contain two public floors: one for views and the other a revolving restaurant. Munich’s restaurant is at 182m and viewing floor at 190m; Berlin’s restaurant is at 207m and viewing floor at 203m, towards the bottom of the iconic 32m diameter sphere. Its triangular embossed facade also adds to the impact of the panoramic views of the city.
The Munich tower was completed in 1968, the Berlin tower in 1969. Incredibly, at the time, they were in different countries, the BRD (West Germany) and the GDR (East Germany).
BMW Welt, or BMW World, is a centre and museum in Munich showcases the history and future of the automobile industry. The building is modern and futuristic. To access it, you walk over a bridge over the main road, leading you straight through the entrance to the first floor.
It was from the bridge I sketched; facing the geometric hourglass shape that is the centrepiece of the building’s design.
My close up photo of the steel truss frame my sketch also conveys. It’s clear the truss is useful to increase the twisted structure’s rigidity.
