Achievement of structural stability

I presented a paper in the last Construction History congress in Paris, in July 2012. The paper was based on the work we have done with John Barber, Graeme Cavers and Andy Heald from AOC Archaeology.

For some, this works can fall in the experimental archaeology field. We tried to summarise the hypotheses about the configuration of brochs and link plan with elevation, structural performance and construction process – a tall order and more of the beginning of a research question. It started with what I perceive as a growing need in archaeological literature to focus more on the fabric and direct insight derived from field monuments, in the case of brochs, going beyond typological analysis or speculations about the purpose of certain features.

The study so far has attempts to discuss the complexity of this type of Atlantic roundhouse in the construction and planning processes, combined with their structural design and performance, and also to treat brochs like architectural structures (anothe strand of this research, where we have developed architectural models). Such focus is providing already further valuable information on how stability was achieved in dry stone built structures of this scale. It aims ultimately to augment what we learn about the technological culture and corresponding intellectual achievements of the period, something that is part of my broader teaching and research on construction history.

The proceedings have been published by Picard and I the paper and slides are here:


slides from ICCH12

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Global failure of brochs

The work of Iain Thew and Alastair Sutherland on brochs was just published in Structures & Buildings.

We studied the response of brochs to structural action by building two scale models and testing them in settlement, a possible source of failure. With the key features carefully reproduced and overall identical dimensions, the effect of variation of basal style between ground-galleried (Gurness type) and solid-based (Dun Telve type), the two main types, was examined. The tests indicated that solid-based brochs can withstand a horizontal displacement at the wall head of twice that of ground-galleried types. The discussion of these tests provides further insight into the effect of the form and features like restricted openings or the intramural void. The conoid drystone form showed substantial strength as large settlement was required to cause the failure of a scale model, suggesting that structural actions alone cannot cause collapse.

The collapse pattern of the Dun Telve model

The collapse patetrn of the Gurness model

The design works safely if full contact between blocks is ensured, continuous vertical joints are avoided and containment of thrusts is guaranteed. High strength reserves then are observed, as the extremely high settlement required to cause collapse. See the normalised change between the initial and final profiles (right) and the change in plan at wall-head of internal wall of solid based ‘Dun Telve’ model (left)

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Lost in the kindness of the anonymity of brochs

These are some thoughts I offered in a recent Pecha Kucha Night orgnised by Gordon Duffy and Tim Taylor: You can watch the video in YouTube and get the slides (20 slides x 20 seconds) here: Pecha_Kucha 2Dec11.

I hope you’ll find the following thoughts inspiring. I was inspired in my turn largely by the King of Asini (the void under the mask or the ruins of Asine) and other poems by Giorgos Seferis, created from nostalgia, memory and loss.


“Παμπάλαια υλικά κατάλοιπα που είχα την καλή τύχη να βρεθούν στον ανασκαφικό μου δρόμο, μια φορά στη λάσπη κι άλλοτε, συχνότερα, στο ξερό χώμα κάποια κρητικά καλοκαίρια, κάποτε και σε αραχνιασμένα μουσειακά υπόγεια. Και μόνο τυχερός; Γιατί να μη λογίζομαι πανευτυχής, τρισμάκαρ, όλβιος, αφού χάθηκα στην αγαθότητα της ανωνυμίας της προϊστορίας…» στον πρόλογο του βιβλίου του «Γεύση μιας προϊστορικής ελιάς» από τον Ικαρο, 2005

Ancient stuff that good luck brought them to my excavating path ….. And only lucky? Why wouldn’t I consider myself happy, blessed, joyful as I was lost in the kindness of the anonymity of prehistory. This is how G. Sakellarakis, a Greek archaeologist, described his experience with Minoan Crete.


Why happy to be immersed in a world without memory or history? because this is what we can usually say about prehistory. Maybe because we are in this strange threshold between our need to keep record of everything we do and move forward carefree from the layers of history above us.

Figure: my computer


I see this kindness from looking at peoples’ stories without any prejudice for what came before, after or around them, based only on the evidence of what they left behind, knowingly or not. Purity that in extremis could even re-invent civilisations, as A. Evans’ Minoan world that Sakellarakis often opposed in his work.

Figure: Knossos


Each country has an opportunity for such kindness in its prehistoric past and here are some thoughts I have from my work on this country where, to use the poet, “it was decreed by Athena that I should live”. I consider myself happy as I was lost in the anonymity of the Scottish Iron-age brochs.

Figure: Dun Troddan


Anonymity does no justice to the complexity of brochs: the galleries, the staircases, the height, the shape, the stones, the scale, the location. Their grand and conspicuous statements make us to want to know more but there is so little to read …

Figure: Dun Telve


But we can touch them like a mask and recognise the echoes from the voids underneath: was someone sleeping in these cells, were kids running up the stairs, would someone wake up in the middle of the night from the barking of the dogs at the guard cell, were the crops dry at the galleries?

Figure: inside Dun Troddan


And who build them? Who planned? Who cut or gathered the stone? Who corbelled the cells? Who celebrated watching it grow? Who dared to thatch the roof when it finished or repair it when it was blown away? This is my happy friend John Barber who introduced me to brochs.

Figure: Spittal broch


And who saw them crumbling slowly or being attacked and then repaired them, taking gradually down parts of the height as its inhabitants didn’t use them or didn’t believe any more in them. And who were the last who decided to abandon the fight with men and elements and leave them?

Figure: Yarrows broch


We are in prehistory: their names are not everywhere with us, their children did not become statues, only a passing Viking would sing the story of a princess in a tower, their desires would become the fluttering of the birds. They left their empty shells.

Figure: Gurness (Monuments Record)


We can’t imagine “their large eyes, the curved lips, the curls”, only their shape if you like. Sometimes we can find behind them their clothes, their shoes, their tents. We imagine what they eat but it’s so frustrating we can’t tell how they died or where they are buried …

Figure: the hood from the National Museum of Scotland


Sometimes we get the fragments of what they touched, what made them happy. Funny enough we are excited from their leftovers, they only thing we can find for sure, rather than what was really precious for them. This science is about their piles of rubbish?

Figure: Their artefacts


Where are they??? Where are their tombs??? Does there really exist among these ruined lines, edges, points, hollows and curves; does there really exist here where one meets the path of rain, wind and ruin does there exist the movement of the face, shape of the tenderness ….

Figure: Edin’s Hall


of those who’ve waned so strangely in our lives, those who remained the shadow of waves and thoughts. Or perhaps no, nothing is left but the nostalgia for the weight of a living existence there where we now remain unsubstantial, image of a form that the sentence to everlasting bitterness has turned to stone:

Figure: a gate


Figure: the cult statue of Apollo Oplitis


Is archaeology the modern cult of the ancestors? Or the anonymity of prehistory is a kind offer to remember of things past in silence, respect and self-awareness? But like art, is memory useless? What can we do with memory? Do we practice a “modern cult of monuments”?

Figure: Neuesmuseum, Berlin –  restoration


And how anonymous memory can be recollected? It’s become a science, archaeology, which previously under the pretexts of antiquarianism unearthed and even re-created the story of brochs – but maybe not their history, this is the confusion at Nybster…

Figure: the archaeological survey at Nybster (Graeme Cavers, AOC Archaeology)


And what a moment is archaeology when order emerges from the ground… The anonymous fabric crops out of the anonymous earth, only to confirm that it will stay anonymous, for ever, as there are no names to read …

Figure: excavation by AOC Archaeology


What is to remember, what is to forget and what is in between them? I’ve realised that even where we know the history, the stories are endless and we are all entitled to them

Figure: Koldinghus Castle, Denmark (Johannes and Inger Exner)


Can a broch be restored or is it simply strengthened – which makes my life as an engineer much easier? Are their values there or it is upon scientists like myself to find them for all of you? Is this the frontline of science to set the cultural agenda?

Figure: Clachtoll


But they are impressive iconic structures on their own – even if only few – and maybe this together with science is a new cultural value rather than the historic or artistic ones that we often seek in conservation. Maybe we should not be so sad after all about the void behind the mask.

Figure:  A take on Becher – this is for you Tim


If you want to thank someone now, rather thank these two people, Giorgos Seferis and Yiannis Sakellarakis.

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Edin’s Hall 14 November 2011

I visited this broch outside Edinburgh (almost Berwick) last Monday and although it took me some time to find it it was really worth while. Not only a big part of the masonry is intact (ok, largely restored) but it is also located in a (probably later) Iron Age hillfort – the first I saw anyway.

Factual information about the broch, bibliography and how to reach it can be found as usually at the Canmore database and the monument, its geometry and archaeology are extensively discussed in this paper by A. Dunwell.

What impressed me firstly was the quality of the stonework. Although extensively restored and without a record, the masonry showed this confident almost arrangement of large, locally sourced blocks, inserted in a cuneiform/ wedged fashion, and carefully filled with smaller blocks often in triplets. No overlaps or “stretcher” bonds were attempted here and the pattern reminds me of something similar you can see in Dun Telve.

The masonry of the inner wall

The cells have also had a unique geometry (I don’t know how original it is) where all apart from the guard cells split into two from the entrance, divided by a return. The guard cells also show a sophistication in the corbelling that possibly roofed them, as the blocks are slanted inwards aiming to create a gentle curve instead of plain corbelling. I believe it can be seen in this video from the North guard cell

The overall dimensions are substantial (17-18m diameter) as can be seen in this overall view. The wall is 5-6m thick with a rubble infill and is preserved to 1.55 m in the internal face.

The thickness of the wall on the S side

It is possible the stone from upper parts of the broch was robbed to form parts of the huts of the hillfort and/ or the broch was at the same transformed into a lower dun. The extensive restoration could not have reached the lower courses and foundation so I believe we have evidence of a very well built Lowlands broch.

I could see no major damage during my brief survey in the (restored) fabric apart from a compressive, vertical crack on the internal return at the entrance (N side). This is a delicate area due to the complex geometries combined there originally (the stacked opening along the broch’s height, the change in the roof of the entrance, the guard cells weakening the fabric etc). Dun Telve shows similar damage around the openings at this area and it is probable significant collapse occurred in the area, with eccentric loads from the failing masonry shedding disproportionate loads to the interior.

Crack at the internal return of the entrance (N side)

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Sharing some more thoughts on brochs

I thought of setting up a blog on brochs following my work on these incredible structures the last few years. My involvement started with AOC Archaeology and especially their chairman John Barber and since then we have produced a lot of new insight into the fabric, structural stability and lately architectural performance of these enigmatic and sophisticated buildings.

Some of the work so far has been published in AOC website and their Special Interest Group site, as also in my own dedicated site and a forthcoming paper in ICE Structures & Buildings. A lot of thoughts have been tested by my students in the Schools of Architecture and Engineering of the university in their dissertations or placement projects and as we develop further things some new thoughts that may or not find place always in these works will be shared in these pages. We will all look forward to your comments.

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