Structural Patterning and SMO Research

In response to interest in structural surface design for novel forms, CRAFT has been researching a two-pronged approach to its structural surface design—Section Modulus Optimization and Stress Patterning. After the initial steps of discretization and Finite Element Analysis, the goal is to use the data gathered as a parameter in the adjustment of surface properties. The two avenues explored in this study are local surface thicknesses and the patterning of structural reinforcement throughout the surface.

This was achieved in Grasshopper using Millipede and Karamba analysis engines. Illustrated here are Karamba’s Iso-Lines, paths between equal principal stresses across a shell structure. The contoured map tells a story similar to that of a topographical one, with increasing scalar values expressed in two dimensions. Below, a combination of Karamba’s Force Flow Lines, overlaid with a color-gradient Von Mises Stress map, illustrates multiple modes of stress representation. The Force Flow Lines, or load paths, map the distribution of loads over a shell, forming eddies in areas of ineffective force direction. Either of these line-mapping techniques could be implemented in the creation of a novel structural pattern.

CRAFT_15001_SK12.3dm

CRAFT_15001_SK12.3dm

By translating the scalar data from the Von Mises Stress map into vector data, the depth of the slab can be scaled using the local section modulus of each analysis element, in a process called Section Modulus Optimization (SMO). Holding the system stress at a uniform 3000 PSI and allowing the slab depth to vary from 6” to 24”, the solid result is calibrated to the architect’s formal ambition. 

CRAFT_15001_Modulus Optimization

Structural Patterning is nothing new. With the Pantheon, Apollodorus created one of the most enduring examples of structural expression — pictured here in partial section. Its ornamented coffers form a waffle slab which accents the enormous concrete dome, while decreasing weight. This language has remained untouched for almost 2000 years, while the lower sections have been remodeled with the fashions of the centuries that followed.

Pantheon Section
When building with concrete, or other plastic materials, the organization of the waffle slab ribs presents an exciting opportunity for novel Stress Patterning. Karamba and Millipede present beautiful options for mapping directions of principal stresses, load paths, and iso-lines of stress. The most structurally meaningful patterning utilized a scale field to adjust the density of ribs according to intensities of stress, yielding a field of expanding and contracting cells that could be expressed as concrete coffers.

15001_SD_012_72_5000

15001_SD_026_72_5000

Further development of stress-optimized structural patterning may combine Modulus Optimization and Stress Patterning to achieve an expressive and efficient system rendered in the most potentially plastic of construction materials.

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Inhabitable Skin

The Inhabitable Skin is an innovative exploration of materials and manufacturing processes that results in a three dimensional form that exists as an independent monocoque structural assembly. The formal expression of the skin is driven by the necessity of structure, environment and context, but ultimately it bends to the will of the designer who is capable of controlling it. The exciting prospect for a designer is the ability to explore form, but within a framework of definitive influences towards an architectural end. For the engineer, the Inhabitable Skin represents a revolution in structural morphology, an exploration of structural form not constrained by linear and planar elements but a combination of complex surfaces.

Inhabitableskin_casestudy

The concept of the Inhabitable Skin offers the potential to revitalize and re-energize densely populated urban centers. It focuses on existing masonry clad highrise buildings and takes advantage of the inherent strength of their structural systems. The Inhabitable Skin is a three dimensional lightweight composite cladding system that directly replaces the existing masonry veneer. The difference in self weight between the two systems represents the opportunity for inhabitation. In essence, the lightness of the composite skin allows for an extension of the floor plate to support additional live loading. The skin and floor extensions are fabricated with Polymer Matrix Composites and act together as an ultra efficient singular monocoque structure. The structural premise of the Inhabitable Skin relies on the reloading of the edges of the existing structural slabs in exactly the same manner as the masonry veneer that was removed. This allows the skin to act as a kind of cocoon that can be attached to the existing building’s exterior without relying on a separate supporting structure or adversely impacting the building’s existing gravity or lateral load resisting systems.

The opportunity for such an application in urban communities is surprisingly abundant. Each opportunity offers its unique set of influences to the visual character or language of the skin based on context, building orientation, materials, massing, etc. Some of the most evident opportunities exist on the facades of highrise buildings adjacent to much shorter buildings. In these cases, the existing building façade is limited by the potential of the shorter building to be replaced by much taller building. The façade is therefore unable to respond directly to its context but rather to its potential context. The Inhabitable Skin concept allows the building’s skin to operate on a shorter life cycle than the core of the building and therefore the building’s exterior can more dynamically react to its local conditions.

This current evolution of the concept focuses on masonry clad highrise buildings in Manhattan and suggests a formal response through a case study of an existing building located in midtown. This specific building was chosen because of its prominence in the midtown Manhattan skyline as well as the amount of masonry on its façade with a clear southern exposure. This coupled with the fact that it is a residential highrise building, offered a compelling scenario for intervention with some clear design influences and constraints. Below is a set of before and after images of the conceptual design for an Inhabitable Skin.

inhabitableskin_conceptualdesign

The form of the Inhabitable Skin in this case study is driven by the necessity to create a structurally cohesive form influenced by its environment. The direct southern exposure of the façade challenges the skin to respond as a passive solar shading device to reduce the thermal heat gain potential of direct sunlight into the interior spaces. Therefore, the symmetric forms of the skin on either side of the existing windows blocks early and late day sun and the rippling in the surface creates passive shading at each floor level for direct midday summer sun. The form of the Inhabitable Skin is constrained by the extents of brick masonry on the façade as well as the location of program on the interior of the building. The effectiveness of the solar shading as well as the creative freedom enabled by composite materials is evident in the rendering below. This specific skin design solution extends the floor plates up to 10 feet from the existing face of the building and adds more than 11,600 square feet of rentable floor area to 36 stories of an apartment building.

Polymer Matrix Composite materials have been around for many decades but concerns regarding their UV stability, fire resistance and sustainability have limited their impact on the building industry. This case study specifically addresses these issues through an innovative layering of materials. The composite structure of the panel is fabricated with a protective exterior coating of high density ceramic concrete as well as a lightweight fire resistant ceramic concrete interior coating. The layering of these materials to perform their individual but complementary tasks creates a highly efficient and lightweight system which reduces the overall energy footprint in fabrication, delivery and on site construction when compared to traditional methods of façade replacement.

This concept will be presented for the first time at the Innovate: Integrate – Building Better Together exhibition at the New York Center for Architecture. The exhibit opened on October 6th and runs until mid-January.

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The Dynamic Intersection of Structural Engineering and Architecture

Structural engineering is transforming.

The structural engineer of this century will be very different from that of the last century. Maybe not all of the structural engineering community, but at least a very exciting subset. The practice of engineering has traditionally been slow to adapt to new technologies and new ideas, but in order to keep pace with the formal experimentation that is occurring now in architecture, it has to evolve.

TD Center, Mies Van Der Rohe

TD Center, Mies Van Der Rohe

The International Style beginning in the early 1900’s and leading into the Modernist movement in Architecture set the stage for a kind of reductionism in architectural expression, but it also represented the consolidation of structural theory into the practice of modern structural engineering. The leading theorists of the architectural movement sought to create a kind of formal expression that was devoid of ornament and represented a re-thinking of geometry right to its core elements of line and plane.  These geometrical typologies became the expression of this new style as seen in the work of Mies Van Der Rohe, Philip Johnson, and Le Corbusier, but they also represented the dominant elements of engineering calculation.

Glass House, Philip Johnson

Glass House, Philip Johnson

The industrial nature of the movement, summarized by Le Corbusier’s description of buildings as “machines for living” was inspired in part by the technological advances in material and manufacturing rising from the Industrial Revolution. The movement latched on to the evolution of steel, concrete and glass as its core materials and sought to express the character of these materials and their manufacturing processes in this new style. Steel therefore took on the character of the line or curve, geometrically the extrusion of a point along a path. Glass became the simple expression of a plane and concrete offered the potential to merge the two typologies together as a slab-beam hybrid.

Villa Savoye, Le Corbusier

Villa Savoye, Le Corbusier

As a result, most building structures today are reduced to a language of line and plane, or in engineering terminology, beam or column and diaphragm or shear wall. This is the basis of modern structural engineering. Even complex forms are described using these most elemental terms.  The notion that structural engineering today is transforming stems from the fact that architecture at some level can no longer be simplified in this way, or at least it does a disservice to architecture to reduce it to these terms.  Architects today are exploring the definitions of geometry and its expression in a similar manner to the International Style but with a much more sophisticated set of geometrical typologies and much more sophisticated methods to manipulate them and to manufacture the resulting forms.

Structural engineers today need to evolve our methods and adopt new skills in order to play a constructive role in the evolution of architecture. This is the intersection of structural engineering and architecture. It is the new role of the structural engineer, one in which he contributes to the development and definition of form, one in which he is an active participant in the conversation. In order to do so, the structural engineer of today needs to augment his traditional education with studies in geometry, modeling, meshing, computation and methods of analysis beyond the line and plane. A kind of discovering of the tenants of the Bauhaus concerned with craftsmanship and industrial technologies but in a computationally more sophisticated design environment.

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