Prefabrication experiments - 262 - Connectors - 03 - Charles Attwood, Unistrut and Moduspan

The successful application of steel in building structures has paralleled and entrenched standardization. The normalization of profiles, shapes, pieces and fittings was rigorously controlled from the factory to the field. Pre-established and calculated connections facilitated steel’s democratization by sharing validated models for engineering, architectural design and construction. The steel building construction sector developed an open exchange of fabrication, specifications and assembly standards. Further, this knowledge was certified in the factory and by academia supporting the use of published computations and theory. Industrialists imagined all manner of skeletal and reticulated building structures from the cataloguing of parts and assemblies. 

 

One of the most enduring systems, the Unistrut building component system was based on both standardized shapes and simple bolted joinery for securing pieces together in a plurality of directions and arrangements.  Charles Attwood created Unistrut in the early 1920s for mounting electrical components in equipment, racking or scaffolding applications. A spring-activated nut that is pushed and glided in a u-shaped profile is the central proprietary element. The nut is positioned along struts at any point and makes multiple arrangements possible. Expanded further, the Unistrut system went from a simple strut and tie structure to a reticulated 3d space frame with the addition and invention of a mulit-directional hub connector. 

 

Known as Moduspan, a subsidiary system of the Unistrut corporation, it employed a simple plate-based joining system for fastening a structural framework of upper, lower and diagonal chord members. The horizontal and vertical plates clipped together maintain an x,y,z coordinated system for coordinating anchor points. The standard Unistrut channels 40mm x 400mm could be bolted to the plates at different locations to vary length, angle and overall geometry. Applicable to floor and roof construction, as an open treillis, a type of three-dimensional truss, it was just one of many space frame prototypes (Mero, Triodetics, Abstracta) invented in the second half of the 20th century. Attwood marketed the no welding or drilling, flexible and adaptable business model from the early 1900s and it is still applied today. Moreover, the Unistrut and Moduspan design for assembly principle could today be reversed and speak to a design for disassembly model making all components part of systems with multiple service lives.

Moduspan connector

Prefabrication experiments - 261 - Connectors - 02 - Abstracta building system

 

Transferring know-how from object, product or commodity production to large-scale building construction has motivated a spectrum of potential building systems both in theory and in practice. Volumetric modular stacking as an approach to industrialized building has been compared to modular toy assembly sets. Toys, from Lego blocks to Lincoln Logs and the infamous Erector Set, were cited as procedural models for simplifying onsite assembly. Modular kits composed of controlled, standardized and compatible parts, still fairly marginal in building, have been successfully applied in furniture assembly. Elements are categorized, bundled and packaged according to predetermined formal or functional objectives. 

 

Scaling the modular kit from furniture to building was at the core of Poul Cadovius’ Abstracta reticulated structural frame system. The Danish born inventor, designer and producer conceived the system in the late 1950s and filed for a patent in 1964. The Abstracta system is composed of a formed cast steel connector joint with a varying number of specially profiled appendages ending in a spherical bulge that fits and locks into tubular struts of varying lengths. The connectors are designed on the same principle as Cadovius’ modular furniture kit with one key difference: the size and thickness of the tubular struts have a minimum diameter of 45mm and a wall thickness of 3mm. The straight member spokes are manufactured with an internal globular pocket for the connector spigot, lodging it in place and resisting compression and tension. The same connector and struts can be assembled into 3d structural matrices to make exhibit structures, scaffolding or even large scale dome and freeform structures.

 

The Abstracta system was awarded the Gold medal in 1961 at the International Inventor’s Congress in Brussels. Its application in building remained negligible. Casting a connector with varying limbs both in terms of spigot angles and a specific shape demands production processes and tolerances that have not been the norm in building construction. Further, the design of hub connectors in general architectural systems has not tackled requirements to coordinate systems other than structure and it is difficult to imagine one connector capable of attaining such universality. Cadovius’ Abstracta system’s ongoing application in furniture still inspires the longstanding intention of assembling architecture with the simplicity of a toy. 

Patent drawing for the connector

Prefabrication experiments - 260 - Connectors - 01 - The Universal Building Joint

Architecture and construction in their basic essence are related to joining. Connecting, linking, aligning and fitting materials together require knowledge of both crafting and detailing. Joinery reveals how architecture is made. The modern architect streamlined design and construction through systematized thinking translated into translatable and intelligible building assemblies. Factory production made detailing into a language for the architect to showcase how to build through drawings and specifications. The search for the universal connector was an underlying theme of the modern architect’s new role of detailing construction.

 

The most cited and prominent example of this ideological vision of a multifunctional building joint leveraged toward multiple patterns is the General Panel House connector created by Walter Gropius and Konrad Wachsmann in 1941. The heart of the modular panel house system, the pluri-directional surface connector, was developed to join panel edges horizontally and vertically to arrange an infinite number of dimensionally coordinated variations. Inspired by his training as a cabinetmaker and as chief designer for the Christof and Unmack timber house producer, Wachsmann devised a steel biscuit joint precisely shaped and connected through a plate and wedge system. The plates were cut and shaped to match-up with the precision of a lock mechanism.  The hook-type metal clips would be kept in a latched and locked position by a compression steel plate wedge inserted through the panel’s thickness attaching panel and joint. Modular stressed skin panels and planning modules were outlined by what at the time had become the standard for material coordination: 4-inch module and 40-inch grid. The connectors were positioned according to the grid creating a repeated stitch pattern. 

 

The General Panel Corporation set up in a repurposed aircraft factory was to be highly automated and influenced by the era’s highest production standards. In 1984 Gilbert Herbert recounted the story of the General Panel Corporation in his book The Dream of the Factory Made House and cited many reasons for the company’s failure to attain what Wachsmann had promised. 

 

Architecture’s and architects’ fascination with joinery is still an obsession throughout the discipline and the quest for a universal connector is the theme of the next 10 blog posts which will present a number of connectors designed to attain a universally applicable joint.

The universal connector

Prefabrication experiments - 259 - Operation Breakthrough - 10 - Descon-Concordia's forward looking platform architecture

Design for manufacturing and assembly (DfMA) or the concept of product architecture, already applied in various industries, have been put forward as strategies for applying the same methodologies to building production. Kieran and Timberlake’s manifesto (Refabricating architecture, 2004) and an abundance of literature since the publication seem to point to modularization, design platforms, and offsite fabrication as outlets for lean production.  A recent example of this ideology explored by Bryden Wood, Platforms Bridging the Gap Between Construction and Manufacturing, develops similar notions including virtual modeling and prototyping and data harvesting to streamline the building process. 

 

Even as platforms are being identified as ground-breaking, theories for increasing productivity and product architectures are not new concepts. Perhaps terminology has evolved but the type of systemic breakdown of a project’s components and logistics were central to Operation Breakthrough. Proposals were truly innovative in this regard as many were based on comprehensive logistical frameworks similar to what has been recently titled a building platform approach to DfMA (pDfMA). 

 

One specific example and the only foreign project approved for US construction was the Descon-Concordia panel system. The sophisticated management plan included an open structural system of reinforced concrete factory-produced prestressed modular panels. From two storey to twenty-two storey high collective dwelling units, panels would be prepared in accordance to specific structural criteria while all other elements were to be shared between different designs and scales. Large reinforced concrete panels, off-the shelf components and mechanical sub-assemblies were part of the overall modular ideology shared between collaborating partners. This collective modular and dimensional coordination created an environment for manufacturers to produce all required elements concurrently for different sites, increasing production and productivity. Five modular panels for walls and four panels for ceilings made up the essential building blocks for a large number of designs. The proposer defined their system as a flexible management system and building kit : a type of product platform for reforming construction’s lagging challenges. Descon-Concordia, a consortium from Montréal, Canada was arguably the most advanced, forward-looking system in Operation Breakthrough and would certainly still be considered as a great innovation today in matters of applying factory production to building construction. 

Descon-Concordia building components and management system

Prefabrication experiments - 258 - Operation Breakthrough - 09 - Pemtom's three-dimensional housing matrix

 

Mat modular housing is a longstanding idealized experiment in planning spatial and geometric relationships for dwellings. The regulating grid unites housing dimensions, criteria and collective dynamics with standardized production parameters. A dwelling field, clusters expanded horizontally and vertically could be programmed for low, mid and high-density patterns. Further, the volumetric tessellation could be mapped over any topography and setting as each unit is a type of generic kernel.  

 

The Pemtom group’s proposal for Operation Breakthrough represents still another view of this highly peddled architectural experiment. Each factory-produced volume would be composed of walls, roofs, and floors, outlined by a rigorous grid module, 13’ (3.9meters) x 13’ (3.9meters) x 9’ (2.7 meters) and constructed from stressed-skin panels. The structural insulated panels (SIPs) of stressed skin construction employed the same composite structure, a laminate of plywood layers and an insulating urethane core, as the panels that had been previously been studied by the US Forest Service as far back as 1937. Pemtom’s proposal references USFS research.

 

Nine juxtaposed, stacked and aligned building blocks would be required to organize a 1500 square-foot three-bedroom dwelling. Each volume was programmed for particular dwelling functions, rooms and living spaces, while more mechanically complex designs could be used for bathrooms, kitchens or service cores. 12 spatial units were provided in the proposal as a catalogue of composing parts.  The sections attached to one another formed a uniform structure with a few composing parts. The clustered volumes or boxes would be mass-produced and their on-site juxtaposition streamlined up to fifteen stories high within a concrete or steel cradle or mega-structure. As described and illustrated, the three-dimensional grid regulates of every part of the building system without any evident hierarchy or separation of the public, private or common areas.

 

Pushed in many forms, this type of normalized housing has been largely opposed by market forces perhaps because architects and manufactures never provided for the conceptual interfaces between architecture, production and individual habitability. Pemtom’s proposal foreshadowed current information based experiments and DfMA approaches where building platforms are delineated by and limited to a controllable quantity of customizable options in a scalable housing system.

Pemtom's catalogue of parts

Prefabrication experiments - 257 - Operation Breakthrough - 08 - Birdair and Poly Petro Chem - inflatable forms

The most noteworthy aspect of Operation Breakthrough is the amount of partnerships formed to respond to the challenges of construction’s lacking productivity and reinvent industrialized building. This reinforced George Romney’s affection for cooperative capitalism and cross-pollinating stakeholders. The result, leveraging the construction industry and its composing partners toward an open source sharing of strategies - a catalogue of construction techniques - could be an example to today’s still lagging construction industry. Expressly within the framework of identifying affordable housing systems, Operation Breakthrough provided a space and platform for presenting well-known as well as more marginal systems, materials and methods. A prime example of an inventive industrial partnership was provided by the consortium identified as Housing Advocates composed of Birdair (a tensile structure producer) and Poly Petro chem (a plastic producer). Both companies came together to imagine a building system and process articulated to their specific areas of expertise. 

 

Birdair is well known for their tensile structures.  The company’s foray into inflatable and reusable concrete formwork leading to the publication of a patent (US723751A) was the main element of their proposal. The idea is to employ Birdair’s knowledge of inflatable tensile structures to produce an inflatable, fill it with enough pressured air to shape a compressive geometry and its structural formwork. Fluid material could then be poured or cast onto the inflatable and left to set and cure. Once cured the reusable formwork could be deflated, removed and set-up to cast other structures. For Operation Breakthrough, the on-site concrete was replaced by a material identified as Carbalon; a two-part urethane compound sprayed, or cast onto any mold. This material would be hardened over Birdair’s reusable and inflated forms to shape exterior walls, and interior walls, while service cores and other required components would be produced by third party partnering manufacturers. 

 

The inflatable forms would be anchored in place by strapping the tensile structure over a foundation. Door and window openings, part of the casting mold, would also be positioned in place while casting the material and allowing it to cure into a monolithic structure, which could then be finished in a variety of ways from traditional siding to stuccoing. Along with the casting controlled on-site with portable equipment, the pneumatic formwork creates a site intensive industrialized construction process. 

Sketch of the Housing Advocates proposal

Prefabrication experiments - 256 - Operation Breakthrough - 07 - Christian Frey's Universal Building Rib

Architect, inventor and founder of Suspended Structures inc, Christian Frey represents a particular type of industrialist, that from generation to generation sees industrialisation as the way out of lagging productivity issues for construction and for developing affordable housing. Involved in research and in expanding his own visions and building systems, Frey’s most ambitious project is arguably his patent for modular dwellings suspended from a central core. Published in 1967, Frey’s patent, Suspended Module Buildings(US52323465A) proposed a central mast from which cables carried gallow-like cantilevered beams onto which any dwelling unit could be assembled. This class of open systems has been studied and explored in various formats and share the idea of a collective infrastructure with unrestricted floor areas for individualized housing. 

 

For Operation Breakthrough, Frey’s proposal is a toned down version of the patent; what remains is the idea of a sequence of suspended platforms. The rectangular floor surfaces attached to the structural core organize the open framework. Each floor panel structure would be assembled from open web joists to form lightweight slabs cantilevered from and attached to vertical columns. The floor panel loads are carried to transverse rib beams connected to vertical columns. Together, the horizontal frames, rib beams and vertical columns form what the inventor identified as an «URB» Universal Building Rib. The «URB» planning module could be aligned, juxtaposed, stacked to create a spatial variety acquiescing any individualized interior arrangement. 

 

The floor pallets and their open webs and grids connect to vertical ducts for distributing wiring, pipes and ductwork. The unobstructed vertical and horizontal network idealize a dynamic framework expandable in every direction and planned for large scale and small-scale dwelling aggregations. Separating and layering structure and interior organization follows the «open building» tenets. This essence of open systems continues to illustrate the conceptual distance between architectural designed industrialisation and the requirements of manufactured building. This archetype of fixed infrastructure and variable infill does not respond to manufacturing constraints of modular building, it is merely a structural concept. Further it doesn’t address the architectural singularity sought by many architects. Like many of its contemporary open systems, this architect’s dream and obsession gained little traction in industry and in architecture. 

Universal Building Rib and patent section (extreme right)

Prefabrication experiments - 255 - Operation Breakthrough - 06 - Optor Corporation

Organized in the late 1960s, it is unclear how much influence, if any, the building experiments undertaken in the Man and his World (Expo 67, Montreal, Canada in 1967) universal exhibition had on Operation Breakthrough’s proposals and processes. Moshe Safdie and August Komendant, architect and designer of Habitat 67 surely inspired a generation of architects through their vision of housing and construction’s industrialization. Many proposals conceived for Operation Breakthrough argued for similar concepts, pushing the idea of modular boxes, stacked, amassed, clustered or juxtaposed to breed new housing patterns. 

 

Exhibition pavilions have long informed and guided architectural advancements and Expo 67 included many accounts of formidable structural units deployed in multiform varieties. The lineage from exhibit structure to inhabitable space frame was also displayed in metabolism experiments. This theme is also evident in one particular proposal for Operation Breakthrough.  The Optor Corporation project, designed and developed in Montréal, offers a glimpse into potential cross contamination between exhibit structures and housing. The space frame structure of inhabitable tetrahedrons assembled from tubes and hubs defined an open structural concept divided or enclosed by stressed skin panels, service walls or functional units. The support and infill strategy would be easily assembled and as simply disassembled stacked, packed and redeployed for other sites. 

 

The slotted aluminum hub fasteners secured flattened tubular ends slipped into the cylindrical hub’s grooves in a similar fashion to the already well-known Triodetic connector used for many exhibit buildings (see blog post 149). The exact source of Optor Corporation’s design is an architectural mystery. A clue for further investigation may be found in an article that appeared in the ABC journal (Architecture Bâtiment Construction) in may 1968. Author and architect Étienne Dusart described a space frame building system that in all respects seems to be the ideological basis for the Optor system. The author describes the same basic framework and stressed skin fiberglass panels. Sprawling horizontally and vertically the space structure would shape a new type of urban structure that could theoretically grow in every direction as a structured geometric trellis.  Both systems also share the basic triangulated support system and functional units delineating a multiplicity of infilled dwelling patterns. 

Images above : Article from ABC journal ; Image below : Optor proposal

Prefabrication experiments - 254 - Operation Breakthrough - 05 - Commodore Corporation and stacking mobile homes

A mainstream example of the modular, manufactured or mobile home builder’s business model, the Commodore Corporation along with its subsidiaries and partners has been manufacturing affordable housing since the early 1950s. Their segment, the mobile home, although somewhat marginal, represents the successful application of industrialisation to construction. The integrated process harmonizes design, manufacturing and procurement supply chains adjusted to assemble a number of predetermined housing patterns. This combined design and delivery process applied to single-family dwellings relies on a standardized pattern book of models to circumscribe supply chain management, regulatory approvals, quality control, timeline and cost structure while reducing onsite construction risks.

 

This straightforward business model was tweaked in Commodore Corporation’s proposal for Operation Breakthrough. Along with a number of design firms, manufacturers, research and code specialists the company proposed a reinforced concrete megastructure assembled from «precast» or «prestressed» components for high-density frameworks, steel components for medium-density frameworks, and timber for low-density frameworks. These structural skeletons would carry stacked modular volumetric boxes using Commodore’s established process. Idealized as a simple switch from individualized dwellings to collective dwellings the company would mass-produce up to 30 000 units per year. 

 

The superstructure grid, defined by a 14-foot square horizontal module and a 11-foot vertical module, was dimensioned for fitting normalized 12’ wide, 10’ high and from 44’ to 60’ long modular units. The simplicity with which the system was illustrated displays the long-standing disconnect between dwelling manufacturing and collective housing construction. Interfaces between units were simply omitted or neglected. This simple stacking rhetoric avoided the necessary on site joinery and stitching, which must be detailed and optimized with the same quality control rigor associated with the factory to circumvent onsite entanglements. 

 

The Commodore Corporation would oversee marketing, design, procurement, construction management, module delivery and assembly. This comprehensive building model seems ideal. However the necessary parameters and criteria that come along with collective housing, the correct and robust detailing of sound control or fire control, have been replaced by simple stacking. Omitting interfaces and promoting one-dimensional stacking continues to haunt modular construction. Holistic systemic criteria must be included in project design. If not any real advantages of off site construction are quickly lost. 

Proposal rendering - modules inserted into a load-bearing framework

Prefabrication experiments - 253 - Operation Breakthrough - 04 - Spun Plastic Domes

The vast majority of Operation Breakthrough proposals identified some category of modular construction to solve construction’s lagging productivity. Boxes or panels assembled into clusters of medium to high-density housing organizations would offer affordable solutions. The manufactured systems would arrive on site and simply be assembled reforming traditional construction processes. Less prominent, but equally important proposals offered unfamiliar materials, models or strategies detached form conventional prefabrication approaches. One of the more intriguing and eccentric proposals from DOW Corporation, the Spun Plastic Domes, calls to mind the singular dwelling visions associated with Buckminster Fuller’s Wichita house patented some years earlier. 

 

Dow’s polygonal dwelling unit would be assembled from vertical panel service walls that formed a lightweight but deep exterior wall. The wall’s depth included integrated built-in furniture or storage. This useful thickness circumscribed interior space in a served versus service space configuration. The segmented deep structural skin, one to two stories high, supported a half-sphere dome cap. A thin shell cupola rested on panels built from conventional wood stud framing. The dome’s composition was shaped on site. An extruded polystyrene insulating core was sprayed over a metallic framework grid attached to the fiberglass reinforced exterior shell’s intrados. The dome’s interior would then be sprayed with a decorative plastic coating to produce a harmonized interior surface. Each dome covering included a central oculus for lighting and ventilation further rendering its lineage to Fuller’s Dymaxion Unit.

 

Although the dome was the proposal’s flagship element, the envelope service pieces were the innovative idea as they argued for a multi-functional exterior wall. Designed as modular segments, the rounded plan could be individually planned, mixed and matched according to varying uses and compositions. Housing clusters included multiple configurations all articulated to a grid of service distribution points radiating in multiple directions. This service matrix was designed as a field over which the circular dwellings were moored. Anchored by earthwork and foundations to the collective infrastructure and service matrix, the center of each unit was positioned over the service point by a vertical circulation stack that connects lower spaces with upper living spaces. The panel service core would be customized in the factory to include plumbing, electrical systems or any other mechanical device.

Dome dwellings rendering