A seismic retrofit for an adobe church in the Peruvian Andes

The Peruvian countryside is dotted with earthen buildings dating back to the Spanish conquest of the Americas. The Spanish adapted traditional European building typologies to the locally available construction material: earth.Many of these earthen buildings have stood the test of time and have become of great monumental value to local communities and visitors alike. Some of them, however, have suffered extensive damage, or even fatal collapse due to one of the threats in the new world not so critically shared by Spain: earthquakes. While buildings were soon adapted and retrofitted to resist seismic action, the combination of the low-strength adobe (mud-brick) and high regional seismicity has remained a concern for many – if not all – subsequent generations.

Remains of earth-cane barrel vault roof of a church near Ica, Peru that collapsed during the 2007 Pisco earthquake. (Image Tim Michiels, copyright The Getty Conservation Institute)

Today, relatively little attention is given within the academic community to the engineering and seismic design of earthen buildings. Despite the availability of advanced structural design codes, powerful calculation tools, and extensive material research labs, experts still struggle to characterize the behavior of masonry buildings, and especially earthen structures, during earthquakes. Thus, designing sensible and non-intrusive intervention techniques to preserve often languishing adobe monuments is a major ongoing challenge.

Front facade of the church of Kuño Tambo (Image Sara Lardinois, copyright The Getty Conservation Institute)

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How to describe the esthetics of structural surfaces? (2/2)

In an earlier post, I wrote about how and why we seem at loss for words when describing the esthetics of a structural surface. I continue that discussion here and analyse what vocabulary layman use and make suggestions for where we might seek additional jargon. I  build my argument upon the results of an experiment carried out by graduate student Rebecca Napolitano in Fall 2016 on the Princeton University Campus.  In the physical experiment, a membrane was installed on a highly frequented location on a central location next to a neo-gothic medium size building.The  membrane was shown in an existing built environment, which might have caused distraction from observing the pure membrane form, but allowed for a full 3D perception of the membrane deforming in the wind.  Randomly selected 138 undergraduate students who passed by the installation, were asked to describe the membrane structure with one word.  If their response coincided with an already recorded word, they were prompted for another defining word.

This physical experiment yielded a plenitude of words which can be catalogued according to formal analysis or subjective response classes. The first category, formal analysis, is grounded in the fine arts and Vitruvian architecture tradition. This type of analysis disassociates itself from reactions such as elation, fear and awe.  These words describe emotions or subjective responses and constitute the second category.  The subcategories in both classes were pre-established before the collection of data and are based on the ones discussed by [1].

Formal Analysis

We first investigated the vocabulary pertaining to the category of formal analysis. This category holds the subcategories of form, proportion, space and visual mass.

Observing the 3D form of the membrane is not a simple process. In the past, built form has been discussed as a hierarchy of simple forms combined according to rules, into an assembly of complex forms [2].  The words in the experiments refer either to the simple or the complex form or the rule.  Simple form descriptions in Rebecca’s experiment included words such as “round”, ”bulbous”.  Complex form descriptions included  “nurbs”, ”free form” and rules included “tangent continuity”, “cambered”, “periodic”, “smooth”, “logarithmic”, “interlacing”, “weaving”, “optimized” , ”linearly disruptive” and “bendy”.

Nurbs, non-uniform rational basis spline (image credit bluesmith.co.uk)

The subcategory proportion evaluates the geometric relationships between the different parts. Traditionally formal rules for proportioning have been defined buildings composed out of analytical forms including hemispheres and cylinders. Unfortunately, they are not that relevant for force-modeled systems such as the membranes in the experiments, because these membrane geometries are far more complex.  These geometries are generated by the laws of physics and are more difficult to proportion and steer than analytical ones.  A few words like “contrived complexity” hinting at these characteristics, showed up in the experiment.

A number of words in the experiments related to space.  The observers understood space as the Aristotelian idea that the membrane created both a positive space and a negative space or “embrace and grows space”. Words like “encompassing“ (positive space, the membrane itself) and, “limitless” and “unconstrained” (negative space, the space that co-exists separately alongside the space occupied by the membrane itself) exemplified the subcategory space.

Visual mass as opposed to actual mass can be achieved by the perceptions of light, color and texture. The untrained observer tends to make a connection between visual and gravitational mass.  Previous studies show how white surfaces, such as the one in the physical experiment, and the smoothness of the membrane in the experiment helped the structure as being perceived as lightweight [1] . These perceptions were captured in the experiments in the words “sinuous” and “slim”.

Subjective Responses

Besides the words that fall in the category of formal analysis, we closely examined the second category, called subjective responses. The results showed that the observers felt that the membrane has a certain character that spoke to them.  The words were distributed over the subcategories anthropomorphism, sensuality allusion, physical security and empathy.

Some observers saw the membrane as a living creature (eg. “sting ray”, “cocoon”) and endowed it with personality and intent. This association is called anthropomorphism.  The membranes were also perceived as “pregnant in the breeze”, “in bloom” and “about to take flight”.

Many observers found that these surfaces had a sensuous quality and captured those impressions in words like “sensual”, “voluptuous” and “calliphygian”. These words refer to the movement of the membrane as it progresses to a visual climax, followed by a relief of tension. In particular the inward and outward curving membrane surfaces have a particular sensual quality, which is missed by forms with single curvature.

Some spectators covertly or indirectly referred to an object from an external context.  The membranes evoked allusions with words such as “Rubenesque”. This word for example refers to the works of the Baroque painter Pieter-Paul Rubens (1577-1640) and means plump or rounded in an attractive way.  Other images included poetic metaphors such as “symphonic”, “motion frozen in time”, “essence of motion”, “natural choreography”.  Other allusions included scientific, artificial natural associations such as “meniscus”, “satin/silk, “hilly” and “motion of water”. These references to physical objects, although they are not grounded in the innate perception of the observer, contributed to aesthetic experiences while viewing the membrane.

Anthropomorphism, an association to a sting ray (left ), allusions to Ruben’s works (right), ,silk (bottom right) and hilly (bottom left) call the membrane in the wind to mind without mentioning it explicitly. (image courtesy Flickr the Commons)

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How do gridshells and longspan roofs perform in earthquakes?

The 500km rupture of the 2011 M9 Great East Japan Earthquake resulted in extensive damage in over a half dozen prefectures from Tokyo to Iwate.  Several lessons can be drawn from the response of spatial structures, particularly long span roofs. While the global behavior was generally excellent, nonstructural element damage and local failure modes were widely observed. This is unfortunate, as such structures play a vital role in post-disaster recover as shelters (e.g. Shigeru Ban) and minor design changes could have prevented much of the damage. In the aftermath, the Architectural Institute of Japan [1] conducted a detailed reconnaissance of dozens of gymnasiums, sports stadia and halls and found several reoccurring damage patterns:


Miki Disaster Management Park Beans Dome, Sport Stadium and Emergency Staging Area in Hyogo Prefecture (photo credit penccil::Slowtechture)

Shear failure of baseplate anchors

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Constructing Ice Structures

Since it has been snowing in Princeton this week, there is really no better time to write about how to construct structures out of ice. The motivation of building with ice – as opposed to another construction materials such as concrete-  is that it makes experimenting much more economic and zero-carbon.  Structural ice experiments also allow for the ability to discover a new medium that could fill the demand for a building material that will not see a dramatic decrease in its strength after being subject to several extreme freeze-thaw cycles [1].  In many extreme cold environments, it would be desirable to have an inexpensive and safe way to reconstruct infrastructure or buildings out of ice to address annual need for shelters and roads rather than rebuilding or repairing these possibly concrete structures that will ultimately be damaged by the weather each year. In the following sections we provide a historic glimpse of key ice structures and how they were built.

Throughout history, ice has been used as an inexpensive and naturally available building material. The oldest known ice structures are igloos that were made from snow blocks [2]. The igloos date from prehistory and have developed a form in which the structure takes exclusively compressive stresses and experiences zero bending moment everywhere in the shell. This form, called a catenoid evolves from the revolution of a parabolic cross-section into a dome. The igloos are constructed into this form using compacted ice blocks.  The gaps between the blocks are filled with snow.  Heating in the igloo then melts the inner surface of the igloo which then refreezes as a layer of ice that contributes to the overall strength of the igloo [2].

Iglulik Snowhouse (photo by Albert Low, 1903, image credit Library and Archives Canada/C-24522).


In 1739, Russian empress Anna Ivanovna order the first ice palace to be built [2].  These impressive structures were made of blocks from rivers and lakes that were trimmed and stacked to form a masonry wall [2].  This marked the beginning of functional ice structures that did not take the traditional catenoid shape.The form was imitated in the 1980’s using cast snow in which wooden molds were used to create compact snow walls to be sculpted.

Ice palace (left) for Russian empress Anna Ivanovna (right Louis Caravaque, 1730)  (image credit wikimedia)

More practically, recent construction of ice hotels has seen the use of special wet snow being sprayed onto steel molds with heights up to 5m and spans up to 6m.  In this process the snow is allowed a two day freezing period before the molds are removed.  These structures get stronger as the snow melts and refreezes over time.  This occurs on a diurnal cycle as the top layer of snow melts slightly each day and then freezes to solid ice during the night [2].

Ice Hotel Sweden constructed of wet snow sprayed onto steel molds (image credit holidayguru.ie)

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“Thinking by Modeling”- Frei Otto Exhibition

In November 2016, the ZKM – Zentrum fuer Kunst und Medien – Centre for Arts and Media – in Karlsruhe, Germany, inaugurated its exhibition on the works of Frei Otto entitled “Frei Otto – Thinking by Modeling” (November 05, 2016 – March 12, 2017): an exhibition unprecedented in terms of conception and extent, curated by Prof. Georg Vrachliotis. In the year before, Frei Otto had passed away, while in the same year he had been awarded the prestigious Pritzker Prize for architecture. As a result, the attention  of architects, engineers and designers worldwide has been refocused on the  personality, the works and the achievements of Frei Otto. The opening of the exhibition was widely picked up, attracted a lot of visitors and comes along with several “special events”, one of them being a symposium which will be held on January 26-27, 2017.

© ZKM Zentrum für Kunst und Medien, Foto: Grünschloss

The works of Frei Otto and his research teams play an active role in current design of architecture and engineering. They are often referred to when lightweight structures or bionically inspired designs are discussed. The current attention on Frei Otto,his insights and merits should be interpreted as contributions to our heritage, prospect and responsibility. His exclamation “Stop building the way you build!“, formulated during a lecture in 1977 [1], is still reverberating. This outcry can be taken as an inspiration for many disciplines, be it architecture, engineering, biology or social sciences.

Frei Otto and the Institute of Lightweight Structures in Stuttgart

The establishment of the “Institute of Lightweight Structures” at the University of Stuttgart, Germany, was a starting point to a “time line” of lightweight structures at this location. Fritz Leonhardt called Frei Otto, who was at that time living and working in Berlin, to Stuttgart University. Fritz Leonhardt (1909 – 1999) was the designer of the Stuttgart television tower which was the first of its kind being constructed in reinforced concrete, the author of books dealing with “aesthetics” of bridges, and pioneer in the field of designing structures in reinforced concrete. Leonhardt had published his thoughts about lightweight structures as a “demand of our times” in 1940 [2], a time facing material scarcity during a devastating war which had been triggered by Nazi-influenced Germany. The lack of material, or the restriction to a certain kind of material, can be taken as a source of inspiration for lightweight construction: Eladio Dieste, Felix Candela and Robert Maillart developed their unique aesthetics by this kind of limitation. Fritz Leonhardt was aware of this special quality and in that spirit he called Frei Otto to be Professor at the the Institute of Lighweight Structures IL at Stuttgart University.

During this time, Frei Otto was dealing with the detailed design of the German pavilion for the Expo Montreal in 1967, a piece of architecture which was path breaking in many ways. A test building of the Expo roof, prototype of a cable net structure, was to become the place of location of the IL.

Joerg Schlaich was the successor of Fritz Leonhardt as Professor at the University of Stuttgart. Werner Sobek assumed the chair of Frei Otto at the Institute of Lightweight Structures in 1994. In 2001, he was additionally appointed as successor to Joerg Schlaich’s Chair. The two chairs were merged to become the “Institute of Lightweight Structures and Conceptual Design” ILEK. In 2015, Werner Sobek was awarded the “Fritz Leonhardt Prize”, a distinction awarded every three years to an engineer in recognition of outstanding contributions to the area of structural engineering. In a very emotional speech, Sobek stated his view of the necessity of lightweight structures, based on very descriptive and startling numbers [3].

The circle is closing: the need for lightweight structures, be they named material-efficient or low-carbon-footprint, is even more relevant in the beginning of the 21st century. Frei Otto initiated a center of knowledge which reached out to the world.

“Thinking by Modeling” – the exhibition

The exhibition is set up in two large-scaled rooms of the “ZKM” (Zentrum fuer Kunst und Medien – Center for Arts and Media) museum in Karlsruhe. The building itself was originally built as a munition factory and is a protected monument with classical elements of industrial architecture. It hosts the ZKM since 1997.

The city of Karlsruhe is also the location of the “saai” (Suedwestdeutsches Archiv für Architektur und Ingenieurbau – Southwest German Archive of Architecture and Engineering), where Frei Otto’s works have been archived after his passing away.

Due to the initiative of Prof. Georg Vrachliotis, Professor at the KIT Karlsruhe, this impressive exhibition has been realized.

The exhibition is constituted by four elements: model landscape, open archive, cosmos, and projection.

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How to describe the esthetics of structural surfaces? (1/2)

It has been said that the work of Frei Otto (Germany, 1912-2015) has a sculptural quality to it [1]. Although Frei Otto’s parents were sculptors, he insisted that the shapes he produced were rigidly grounded in the laws of physics [1], and was very reluctant to describe their aesthetic value. This observation hints at the questions that this paper starts to address, namely how can one describe the aesthetics of a curved structural surface?

Structural Membrane Form Finding Study – Image Credit Frei Otto

It is observed that structural aesthetic critique is a little practiced discipline. In engineering education, students generally are not encouraged to express their emotions about the built environment, and are not frequently encouraged to develop an enthusiasm for visual experiences [2]. Beauty seems to engineers such a vague concept, hard to define accurately to others.

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Our ultimate top 20 book list for 2016

As the holidays are approaching and as your loved ones – yet again – run out of inspiration for your holiday gift… the Form Finding Lab comes to the rescue. We present you a list of our favorite books on engineering, architecture and anything in between.

Happy holidays,

The Form Finding Lab.


Compiled by Tim Michiels, with contributions of Sigrid Adriaenssens, Victor Charpentier, Demi Fang, Andrew Rock and Olek Niewiarowski

What I am thinking: the engineer and architect Marc Mimram

Marc Mimram is a celebrated French engineer and architect with projects in France and around the globe. He generously shares with us his ideas on bridge design in conversation with PhD candidate Victor Charpentier.

Victor Charpentier (VC): Marc Mimram, you are both an architect and engineer. Yet you have said that when you are given a project, the greater part of the inspiration for the initial spark comes from a third field, which is study of the landscape and geography. Can you explain why this is so important to you and how this affects your designs?

Marc Mimram (MM): Each project should be specific. It has to be depending of the situation where it take place.

To become a coherent project, it has to be related to the geography, the horizon. It should express the relation to the ground, to the sky, to the landscape considered as a geography informed by history.

In that case the structural project can take roots in the reality and forget the abstract equation of strength of materials to express gravity, the movement of forces, the movement of light; being part of the situation, part of the world, belonging to the site.

Whong Sheng Da Dao Bridge in Sino Singapour, Tainjin Eco-City (China). (Image provided by Marc Mimram)

Advanced technologies have allowed structural form finding to become an integral part of many recent design projects. How do you add your personal, creative touch to a process that can become largely computational? What are your thoughts on the role of this method for the future of engineering design?

MM: The process of computational form finding is a method of optimization and as such, it follows the development of the project. It is obviously important to develop the project with frugality but the rational process of development can be plural and the choice has to be related to the specific situation, taking into account the landscape, the topography but also the economical situation, the knowledge, the development of local craftsmanship, the local materials.

Liu Shu footbrigde in the City of Yangzhou with a variable width of 3 to 5.7 m (Image provided by  Marc Mimram)

In the past decade, many of your larger bridge projects have been built in Asia or in North Africa in part because of more local design freedom. In your opinion, are there too many inhibitions in the field of construction in western countries? What could be improved to bring creativity and exploration back to construction while at the same time maintaining the high standards of safety?

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Keeping Sharks and Rocks Away: A few of the countless applications of nets



Some of Frei Otto’s sketches from the Institute for Lightweight Structure’s “Netze in Natur und Technik” (1975)


Nets have been a perennial source of fascination in fields as diverse as engineering, architecture, art, and mathematics. As such, thinkers in these fields have come up with a dazzling array of applications and uses for nets, which force us to expand upon our preconceptions of what nets are and what they can be used for.

Pause for a moment – how many applications of nets can you think of? The late Frei Otto had a well-known interest in nets and their applications to structural engineering. A flip through a 1975 publication from the University of Stuttgart’s Institute of Lightweight Structures (of which Frei Otto was a director) reveals pages of sketches (see above and below) on net elements, forms, typologies, and applications. The applications range from the prosaic (tennis racquet, hammock) to the extraordinary (stadium roofs, bridges), to the bizarre (airplane barrier, anti-U-boat net).

Personally, my research concerns underwater cable nets, and I’m currently assisting with the design of a net with a very unique application: preventing shark attacks.

La Reunion, a French island in the southern Indian Ocean, is renowned for its surfing and beautiful beaches. However, this paradise has been suffering from a surge in shark attacks in recent years. Since 2011, there have been nineteen attacks, of which seven were fatal. The attacks peaked in 2013, which forced authorities to temporarily ban aquatic activities. As a result, the island’s economy has been strained, with beach-front businesses bearing the heaviest losses.

“Net Out Of Order,” reads a sign on the empty Boucan Canot beach.

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Grow strong and live beautifully: Colombian bamboo structures

While the new group of senior students are getting up to speed with their senior theses, we look back in this weeks blog post on the work of Russell and Lu Lu in Colombia.

In March 2016 Russell Archer (’16) and Lu Lu (‘16) traveled to the city of Cali, Colombia and the coffee region (Spanish: Eje Cafetero) north of Cali where they visited a variety of structures made of south American bamboo species Guadua angustifolia, known as the “vegetable steel” for its impressive strength. These structures range from traditional vernacular houses, roofs and bridges designed by Simón Vélez, to classrooms designed by Andres Bappler. Russell and Lu were inspired by both the abundance and the level of sophistication found in these bamboo buildings.

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Left Image: Russell (right) and Lu (left) standing in front of a huge bamboo forest near a school building construction site at UTP campus in Pereira, Colombia. Right Image: A vernacular bamboo chair in a local bar.

Visiting Cali, Colombia and the surrounding regions showed us how bamboo is deeply ingrained as a part of daily life in Colombia, from chairs and fences to larger scale bridges and buildings. Much of bamboo design is driven by designer’s and builder’s knowledge of the material properties. This knowledge has expanded over generations and has added to the scale of the structures that can now be achieved. At the Universidad Technolόgica de Pereira (UTP), an arch bridge designed by Simón Vélez (http://www.simonvelez.net/) traverses a roadway connecting two parts of the campus. He also designed the CARDER regional office. These bamboo structures are representative of emerging efforts to locally enhance the perception of bamboo as a building material. The efficient joinery techniques that incorporate mortar inserted into the poles and steel bolts, are indicative of the sophistication involved in the bamboo design.

3 View looking across the bridge deck at the Universidad Technolόgica de Pereira by Simón Vélez. The bamboo poles are covered with dark coating that protect them from sun and rain.

4 Russell (left) discussing the structural system of the arch bridge with DAGMA architect Daniel (right)


Interior Corporaciόn Autόnoma Regional de Risaralda(CARDER) where inclined bamboo poles support the roof Exterior of Corporaciόn Autόnoma Regional de Risaralda (CARDER) with structural timber and bamboo poles

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