“Structural engineers can make a big difference in terms of sustainability”

DGNB Blog all about sustainable building

written by Pia Hettinger

Buildings contain a lot of material. These in turn are valuable resources that are becoming increasingly scarce and are responsible for many CO2 emissions. Structural engineers can counteract this consumption of materials on a massive scale. At least that is how professor Patrick Teuffel sees it. We spoke with him about built heavyweights and the current state of research in the world of materials.

Pia Hettinger: Professor Teuffel, you are working as a structural engineer. What is your role in the construction process?

Professor Patrick Teuffel: Basically, we are responsible for ensuring that the building has a well-designed, economical and appropriate load-bearing structure and that it is sustainable in the end. We deal with everything that has a supporting function: walls, ceilings, pillars. In doing so, we are in exchange with the architects or even the building services planners. What role we take on in detail naturally depends on the construction task. A bridge requires different planning than an exhibition hall or a tower. In principle, however, we should be involved from the very beginning for an integrative and thus optimal planning, i.e. right from the interdisciplinary planning competition. Unfortunately, this is often not the case in reality.

Why should structural engineers in particular take their role as sustainability representative seriously?

For a long time, the debate about sustainability in construction was primarily about saving energy. But the big issue of today and tomorrow is the consumption of resources and the associated CO2 emissions as well. Since 80 to 90 percent of the resources are used in the shell of a building, i.e. in the foundations, ceilings, columns, walls, etc., the structural engineer has many opportunities to act in the interests of sustainability. The mass is in the supporting structure. With the necessary knowledge and appropriate advice we can reduce this on a big scale.

The relative share of CO2 emissions from grey energy is increasing compared to the emissions from energy consumption during operation. © DGNB

So this means that our buildings are absolute heavyweights.

The majority are. A few figures make it clear to us what kind of masses we are talking about in construction. Even today, most buildings in Germany consist mainly of reinforced concrete. Take a normal residential building with two floors. A 20-centimeter thick concrete ceiling weighs 500 kilograms per square meter. On top of that, it is estimated that about 50 percent is used for columns, walls and other building components. An ordinary residential building therefore already weighs several 100 tons. Now think about the enormous impact of saving a few centimeters per floor slab or wall. By the way, a study by the Institution of Structural Engineers: “How to calculate embodied carbon” showed that a structural engineer can save an average of 200,000 kg CO2e per year if the focus is on sustainable structural design.

So should we basically build as light as possible or is it sometimes worth another ton?

Lightweight construction is of course an obvious way to save resources. The Olympic Stadium Munich, for example, is symbolic of lightweight construction. These membrane and textile constructions work wonderfully as stadium roofing, but of course not for a floor slab in a ‘normal’ building. It has to carry a lot of weight and should not deform significantly. But here, too, we could certainly build lighter if we took advantage of the unused potential of optimisation to save materials. In practice, the utilisation of components often amounts to only 80 percent, even though 100 percent would be feasible. With simple optimisation studies, we could certainly achieve material savings of 10-20 percent without any problems. Structural engineers could do much more educational work in this area. But these studies naturally cost time and money and are not (yet) shown in the work phases of the “HOAI”. Too much caution and ignorance thus provide for unnecessary material consumption.

Which other possibilites are there besides weight reduction in order to protect our resources?

There is great potential in reuse at the material, component and building level. In terms of sustainability, wood is a promising building material at first sight: it is light, has a good CO2 balance compared to other building materials and is renewable. Various current projects show that wood also has great potential for skyscrapers. But wood is not infinitely available and also not completely cheap. Therefore we must also consider other alternatives and steer in the right direction. With conventional building materials, steel, for example, is easy to recycle. And when it comes to concrete, you can use recycled concrete, because the quality is in no way inferior to normal concrete. The problem here still lies in delivery and availability.

With regard to the reuse of components, there are already valuable research approaches. At Eindhoven University, for example, we are working on how to reassemble prefabricated reinforced concrete elements from empty office buildings into apartments. Looking at the building as a whole, the potential for conversion or even unmixed deconstruction should be taken into account during planning. The DGNB has developed its own DGNB certificate for this. At the university, we conducted a study on the conversion potential of existing buildings that can help owners make important decisions. After all, they are often faced with the question of what to do with their aging building. There is still a lot of catching up to do here.

You are teaching in the area of “Innovative Structural Design”. What is behind it and where do we stand in materials research?

What’s special about our department is that, unlike chairs such as solid construction, steel construction, timber construction and aluminum, it’s not limited to one material. Instead, we research innovative materials. One focus is the application of smart materials. This is illustrated by a prototype that we are currently testing in our laboratory: We simulate earthquakes on a three-story building and vary the stiffness of materials and thus the dynamic behavior of the structure. Smart Materials can change these and thus react adaptively to the earthquake. This allows for less material to be used.

Endures day and night: The bio-based pedestrian bridge at the TU Eindhoven is in brisk use. ©Tom Veeger

The 14-meter-long bridge in Eindhoven is made of renewable materials. Here you can get more background information on the design, production and ongoing in situ monitoring: ©TU/e

Another key area for our future lies in the use of bio-based materials such as hemp, flax fibers or bio-based resins. In the laboratory, we research the mechanical properties and how the materials perform during the life cycle using. Therefore we use real bridge structures. In 2016 we designed and realised a pedestrian bridge made of bio-based fiber composite material in Eindhoven. We are currently working on the European Interreg research project “Smart Circular Bridge for a circular built environment” with 14 partners, in which we will build a total of three bridges made of bio-based fiber composite materials with integrated sensors that monitor the structural condition in real time by 2023. These materials definitely have the potential to transform the construction industry in terms of climate protection and resource conservation and can gradually reduce the use of concrete.

The world in a grain – or when we run out of sand?

Howard Mc Allister, a researcher at the University of Hawaii, estimated that the number of sand grains at all the world’s beaches count to around 7.5 quintillions or 7.5 billion billions. I have no idea if this number is correct and even if it sounds a lot, sand is a resource, which is an essential part of everybodies life. In his book “The world in a grain” the author Vince Beiser explains the importance of sand for our modern industry and society.

The book describes the increasing dependence on sand in (nearly) all of our areas of life, although the start of this “success” story was slow.
At the end of the 19th century, concrete (enormous amounts of sand are required to produce it) started its journey from England via France to America. After a laborious start, his successful story started in 1906 right after the earthquake in San Francisco. A single concrete building, that survived this quake undamaged, became the unrestricted advertising symbol for this material, despite the fact that some brick houses also survived. This earthquake made it possible for concrete becoming the number one material of modern architecture. To be mentioned: the Panama Canal, the Hoover Dam, the Guggenheim Museum in New York and countless Bauhaus buildings.

Further on, one of the first sand demanding projects was the Interstate project in the United States, which was at that time the biggest public project in US history. In 1904 the United States had a grand total of 141 miles of paved roads (not counting city streets). If you wanted to move lots of people or large quantities of goods any significant distance, you did it via water or railroads. That could not last in a country where everyone suddenly wanted a car. But a car without pavement is like a pair of skis without snow. The ascent and ultimate dominance of the auto required the deployment of vast legions of sand. Dwight D. Eisenhower, who in 1919 joined a disastrous military truck convoy, crossing the country from coast to coast on poor or non-existent roads, was elected president in 1952. Driven by this frustrating experience he did everything to realize the Interstate Highway system. Today we are talking about 2.7 million miles of paved routes in the U.S. (runways, parking-places, swimming-pools ….)

Obviously concrete is not the only driver for the increasing demand for sand. Modern architecture as well as many other industrial branches are big consumers of glass, which basically is also produced from sand. On top of that, the high-tech industry uses a lot of silicium, which is also – surprisingly – based on sand.

The following chapter focuses on the development of artificial islands, where the various projects in Dubai are well-known, but actually they are not the only activities in that field. According to a study by Deltares, a Dutch research group, since 1985 human beings created more than 15000 square kilometres.

In many of the described examples it is not only about serious business, but also about crime, where people were killed for …
So, whoever is interested to read more details and to learn more about this very important resource is welcome to read Vince Beiser’s book.

PS: Here you can find another interesting article about this topic: Demand for Sand: the largest mining industry no one talks about

PPS: And just to be clear: I don’t get any commission from Amazon or anybody else for this review.

Traditional Japanese wooden techniques – Introduction of a practical usage and a basic interlocking joint system.

Ways to recognize the Nature

” Remarkably, there is evidence that modern Asians also tend to see the world as consisting of continuous substances, whereas modern Westerner are more prone to see objects.”

This is one of a sentence extracted from [1]. The book also mentions the difference in the way Americans and Japanese recognize objects and says that, through certain experiments, Japanese are more likely to identify objects through “substances”(material) and their relations to their surroundings.

From ancient times, Japan has had a belief that all beings have been given a sense of life. They have not placed a hierarchy between nature and have set themselves down in the same part of the world. In other words, more than interpreting nature objectively, they were used to capture the “substances”. This integrated perspective, in which to have no hierarchy between nature, tends to remain when they treat timbers in architecture and even in nowadays has evolved in various forms as unique skills.

Principles of Traditional Joints

Traditional Japanese wooden technology is well known for the details of joints and fittings, so-called “Tsugite” and “Shiguchi” Tsugite is the name of joints for beams and Schiguchi for Column. At the end of the 1980s, a book of joints and fittings was published by Gengo Matsui entitled “Wood Joints in Classical Japanese Architecture”. These systems are well known to create an ” interlocking joinery” with successfully combining physical properties such as ” Bearing Force” (1. Parallel to fiber 2. Perpendicular to the grain) and “Shear force”. The Geometry is carefully controlled to achieve adequate performance on each joint. For example, by taking advantage of the anisotropic character of wood, joints which are based on the ” Bearing Force perpendicular to grain” works to resist seismic loading (see below). Joints between column-beam are called crosspiece joint (Nuki-joint, Fig.1-1) and joints between column-foundation are called embedded-column base joint (Hottate-Bashira, Fig.1-2).

Fig 1 Nuki-Joint Fig 2 Hottate-Bashira

However, due to the slippage on the contact surface, there is a time lag before the mechanism of embedding occurs, and this can cause a decrease of initial stiffness, which might not be accepted to satisfy the clearance required for facades. Therefore, it is normally desired to be integrated with a highly rigid element such as “tilt stability of columns” or “mud walls” to compensate for the initial stiffness. It could, however, be designed without these reinforcements when those risks have been removed in advance. For instance, in GIFU ACADEMY OF FOREST SCIENCE AND CULTURE abundance of this “Nuki” mechanism (Fig.2) has been utilized. The structural joinery system not only works effectively against seismic load but also matches perfectly with the concept of the design.
Bearing system at GIFU
Another good example is MINAMI OGUNI TOWN HALL (structural design by YSD) which the “embedded column-base” has been utilized.

Fig 3-1.

Fig. 3-2. Embedded Column Base during the construction

Fig 3-3.Nuki-Joints

Fig 3-4. Carpenter chiseling column head

Fig 3-5. YSD Yamada Noriaki Structural Design Office

lso, there are the Daimochi joint, the Okkake-Daisen joint which is applied mainly in a part to carry shear forces and bending moment, respectively.

“Daimochi Tsugi (Shear resisting joint)”

A joint applied in an area mainly to resist shear forces. The cross-section of the shear-forced area can be almost fully utilized. This is an effective geometry since the end shear strength of the wooden beam is well known to be significantly reduced by a notch

“Wedged and halved scarfed joint, Okkake-daisen-Tsugi”

A joint mostly utilized in a part to carry the bending moment. Resist to bending with a Bearing force parallel to the grin in each nailed area.

Introduction of practical utilization

In follow would be introduced a project, which are designed with the utilization of traditional Japanese joints.

AWA HIGH SCHOOL MARTIAL ART HALL

AWA High School Martial Art Hall

YSD Yamada Noriaki Structural Design Office

Coexisting than Dominating

Why use such a complicated joint that requires complex machining in the first place? It sits on the idea of regarding nature as something alive, in this case, the idea is to understand the substances of wood. Wood is a material that cracks and deforms due to drying shrinkage and creep, so it moves over time. The feature of this joint system is to assume that “movement” naturally comes up and to accept it in a certain level. We use interlocking joinery since the woods comply in harmony with each other and therefore try to confine the amount of foreign material, like steel. It’s more the idea of “coexisting” or “accompanying” than “controlling” or “dominating.

This idea of coexistence is not limited to the joint. In all of the aforementioned cases, sufficient workshops were held in advance at the site to figure out and understand standard length of locally sourced trees , sizes, species and any other characteristics which the tree possess. And also the performance of the CNC processing machine. The structural plan is built based on this research. It’s a passive approach, but it enables it to design under local circumstances. Traditional joining can be adopted for buildings up to a certain scale as long as the wood processing is accurate.

Encouraging locals to participate and designing with locally sourced materials will not only promote the circulation of forests in the area, but will also enable the architecture to be loved and carefully maintained.

[1] The Geography of Thought: How Asians and Westerners Think Differently…and Why, Richard Nisbett Ph.D. | 1. April 2004

[2] 日本人にとって自然とはなにか,宇根豊 ,筑摩書房, 2019/7/10

[3] Design Manual for Engineered Timber Joints, Architectural Institute of Japan, 2009