Introduction:
Thesis project explores the redevelopments of the South Dock of Antwerp as the new fashion catwalk. The former industrial dock is split into three zone referencing the three former shipping bays. The first zone as a manufacturing platform for emerging designers to work from. The second zone at the other end of the south dock is a fashion school, serves as a platform to cultivate the young. Colliding at the centre stage is an event space, working in adjacent to the Museum of Modern Art to celebrate the Antwerp talents. Incorporation of the grid shell into building design as a lightweight structure. The structure provides opportunity to create dynamic canopy that references the fluidity of the Antwerp fashion industry. As the fashion design concentrates on hand crafted, custom made design. The grid shell structure of the fashion district uses natural material (mostly Glu-lam timber, that can cope with large spans). Although the grid shell structure flows according to the height required for each building program, as a nature of the dynamic roof, no two buildings are the same.
A usable, inviting covered public open spaces often is desirable to be permeability and flexible. In the current economic climate, cost-effective and efficient systems as desirable criteria for designing such structure. The use of lightweight structure considerably to be an advantage in terms of achieving the beneficial qualities for the spaces architecturally and economically. The choice to work with structural materials that are bendable during construction opened the door to the unique typology of bending-active structures. Bending-active structures are structural systems which base their geometry on the elastic deformation from an initially straight or planar configuration.[1] Bending-active shell structures can be defined as doubly curved structures built from bent members that together display a shell-like behaviour. They require minimal amounts of materials for making large spans. Trailblazing engineer Frei Otto spearheaded research in this domain in the 1960s and 1970s with buildings like the Mannheim Bundesgartenschau Multihalle (Germany, 1975) (figure 1). This project covers over 10,000m2 with a bent wooden grid shell structure. He developed a rapid and cost-effective construction method for this typology that involved prefabricating flat, regular, wooden grids with no shear rigidity that were then elastically deformed and braced into place. This shaping process saves construction costs and erection time, as the structural members do not need individual bending and the grid can be prefabricated flat on the ground (figure 2). Yet, few bending-active shell structures have been built since the Multihalle outside of academic research lab environments. This can be ascribed to two issues. Firstly, the related design-analysis processes are historically notoriously cumbersome and, secondly, there is a general lack of knowledge regarding the design solution space offered by the rather restrictive structural system. Recent design technological advancements are resolving both.
Until recently, only analogue form-finding methods were available to define a specific geometry’s appropriate boundary conditions, equilateral grid patterns and bearing positions.[2] Today, parametrically controllable digital design simulation tools absorb most of this heavy lifting in form-finding.[3] Since the end of the first decade of this millennium, easily accessible software became available that incorporates physics simulation engines, giving not only structural engineers but also non-specialist architects access to material behaviour simulations. These tools can be adapted for use in designing bending-active structures. Increases in computational power have recently allowed these simulations to take place in real-time, expanding their applicability to early-stage architectural concept design. This empowers architects to investigate options faster and focus their attention on other design criteria. The form-finding processes described by these simulations derive stable equilibrium states for a system under specific sets of loads for a specific boundary condition or starting point. By abstracting real-world material setups to networks of dynamic points and vector forces, these equilibrium states can be reached quickly and accurately in a digital environment. By breaking an object down into an interconnected network of points and subjecting these points to specific forces, such as gravity or spring forces, physical macroscale behaviour can be simulated (figure 3). Being in a digital environment allows for the possible automated extraction of data for real-world construction and implementation.
The two general construction method for creating the bending active grid shell are, the lay-up method and flatbed method. The Flatbed method is the construction of a flat, regular grid with no rigidity, elastically deformed and braced into place. The alternative lay-up method additively bends and joins individual members into the final shape onsite. Both types present important opportunities and restrictions. Two case studies are chosen to investigate each of the grid shell construction method, ZCB Bamboo Pavilion by Professor Kristof Crolla of The Chinese University of Hong Kong (lay-up method) and SheltAir Pavilion by Dr Geogory Quinn (Flatbed method).
Precedent 1 – ZCB Pavilion:
The ZCB Bamboo Pavilion is an incredibly light-weight public event space, consisting of a thirty-seven metre span bamboo grid shell – the biggest of its kind constructed to date. It is built from natural bamboo culms, connected with steel wire by hand using centuries-old Cantonese bamboo scaffolding knots (figure 5, 6). The design represents how the vastly adaptable design models and computation-driven scripts, seen as an all-inclusive process engineering tool that also accounts for craftmanship, allows the project to account for unavoidable deviation.
To install the main bamboo structure, the continuous axis lines of bamboo from the digital model had been unrolled into long straight lines with their intersection points, each with an identification number (figure 7, 8, 9, 10). Each member and intersection point received a digitally generated identification label which contained all necessary information, like the intersection points and curve location. Appropriate bamboo poles were selected for trimming to the correct length and labelled. The poles were tied together using the traditional technique using stainless steel wires. Temporary bamboo scaffolding was built on the wooden decking while the labelling was being carried out and first members could be hoisted up (figure 11, 12). Although an individual pole can easily be lifted by one person, they are almost impossible to manually bend. A fully interconnected long member, however, behaved like a flexible reed and could easily be shaped. As they were hoisted up, their endpoints were slid over the foundation starter bars (figure 13). Bringing corresponding labels together was easy at first as the overall structure, with few connection nodes locked in place, allowed for a lot of movement and flexibility. Over time, however, as the structure became stiffer, it became trickier to have labels meet precisely. Natural dimensional variations of the bamboo and tolerances in the knots made it impossible to perfectly match each label in all places as accumulative slippage occasionally developed. Because of this, the interconnected members often became too short or too long at the foundation’s anchor points. The absolute intersection coordinates in the digital simulation model eventually materialised into nodes measuring up to 20cm in diameter. Yet, these occurred without any problem to the overall structure and could be tolerated with the applied detailing methods. As construction progressed, and the cut bamboo poles water content evaporated in Hong Kong’s tropical summer has decreased their flexibility. Unfortunately, the last poles to be installed were the ones with the tightest bending radii (figure 14), would buckle when bent onsite. A bamboo furniture technique was used to overcome the issue (figure 15)[4]. The inside is reinforced with rebar and grout for strength. Two minuscule holes at the end of the pole allows expanding foam plugs to be injected to seal off the inside of poles. Then, a sequence of holes drilled on to the poles, non-shrink grout was poured inside the pole cavity. The holes used to insert grout were used to pull the rebar into a central position inside the pole. Using hammering as a vibrator, the grout was spread throughout the cavity until completely full[5]. The primary frame creates an overall form, however because of its lightness, the structure itself would not be enough to be resilient to external forces.
The bamboo (6.35 tonnes) and fabric (0.45 tonnes) only weighed approximately 6.80 tonnes. This was only 70% more than the weight of the 4.00 tonnes of air the pavilion contained. The total fabric area of the pavilion was 910m2, with the biggest span measuring 37m. A concrete footing slab of 5.4m diameter and half a metre thick was cast on top of the grass for each of the connection point to the ground. Their combined weight was over 100 tonnes – roughly sixteen times the weight of the entire structure above, the slab helps to stabilise the structure by pulling the bamboo structure without visibly adding the weigh on top. An underground concrete cross bracing fin was added underneath the slab geometry to prevent the legs from sliding open (figure 16). The bamboo using rebar starter bars, protruding from the concrete slabs, cast into bamboo culms using non-shrink grout (figure 17). The interior profile of the bamboo culm provided a similar friction bond to the concrete as the ribs on the steel rebar to the grout and concrete slab. A little plinth was required underneath each pole base through which the starter bars would protrude to avoid water contact. The top surface of these plinths needed to be perpendicular to the axis of the culms to avoid varying load distribution along the contact edge with the pole. This meant that every plinth needed to be unique, tailor-made to integrate the varying angles for each of the 54 bamboo poles ends. Each of the starter bars also needed to be bent accordingly. Basic methods were used to bend them to the appropriate angles (figure 18, 19)[6].
The anchoring of the bamboo structure to the concrete foundation adds further stability to the structure to fight against high wind uplift, by injecting grout into the culms placed over the starter bars. Cumulative tolerance throughout the structure had made several members too long – these were simply trimmed – and others too short (figure 20). A simple solution was proposed (see figure 21); cut standard PVC tubes were again used as a mould to bridge the gap between the plinths and the members that were too short. Then, holes were drilled in each member above the top of the starter bar to insert the grout. These holes were placed at the bottom side of the pole, so that potential rainwater running down the poles would not find its way inside. Using a funnel and an old cut-up fire hose, the grout was manually squeezed through the opening while hammering the culms to make sure the grout would find its way to the base. Once the rebar as fully covered, the holes were sealed again using the round bamboo plugs that were drilled out. Stainless steel hose clamps were added around the bamboo pole base as a precaution to prevent the bamboo from sliding off the concrete in case of splitting. In addition to the solid anchoring of the structure to the foundations, a typhoon contingency plan was put in place that would weigh the structure down in times of need by anchoring it to the several existing concrete tree planters on the wooden deck. Each planter weighed roughly two tonnes. Six points in bamboo culms around the belly line and ten points higher up in the structure were internally reinforced and provided with anchoring points. In the event of a typhoon, large stainless-steel cables could be quickly hooked onto the structure and anchored to the planters (figure 22, 23). Together with the heavy concrete footings, significant ballast could thus be fixed to the structure to hold it down. The reinforcement of the bamboo necessary to avoid crumpling or flattening of the individual poles under the tension force of the anchor cables. This was done in a way like the reinforcement of the notched poles. Foam plugs were placed a metre in each direction from the anchor points and non-shrink grout was inserted through a plughole on top. Six additional anchor points were installed in the upper shell from which the belly line was suspended to combat with the deformation from the digital model. These were to prevent progressive creep and slumping of the lower parts of the pavilion.
The final steps involved the connection of the membrane at each of the node points (see Fig. 24, 25). The same stainless-steel wire used to tie the bamboo together was used to install fabric flaps that had been fused into the sleeve to the bamboo structure underneath. Standard turnbuckles were used to tighten up the fabric at the bottom edges and at the seams inside each leg. The membrane cover and bamboo treatment ensure the structural contact with rainfall to the minimum and prevent any cumulation of water that would rot or corrode the materials.
Precedent 2 – SheltAir Pavilion:
SheltAir Pavilion were assembled using aluminium poles that form quadrilateral grid in as a two-dimensional flat sheet. It is then spatially deformed to take the shape of a doubly curved, edge supported grid shell. The connection nodes of the grid feature one degree of rotational freedom such than the system effectively. The capability to pre-assemble a flat grid means that only a vertical repositioning of the grid into its final shape is necessary on site. Erection methods for elastic grid shells can be grouped into four categories: ‘lift up’, ‘push up’, ‘ease down’ and ‘inflate’ (figure 26)[7]. The erection phase is usually the most important and risky, due to high bending stresses applied onto the structure by tight curves and twists. Such stresses are highly dependent on the method of erection and on the shape and size of the shell. The primary motivation for minimizing bending related stresses to avoid fractures of the poles during erection. And, to ensure that enough tolerances are reserved for the poles in the final form. Inflation method were used in this project (figure 27). The preassembled grid was placed on top of the inflatable pad before it was erected. The inflatable applies gentle forces throughout the grid to minimise breakage (figure 28)[8]. The poles were connected to the ground planks at the peak inflated state, along with structure frame applied to the entrance and exit gap. The inflatable pad is only deflated and removed once the assembly once the structural integrity is complete (figure 29)[9].
Pulling the end of the poles to their support points immediately after inflation is an essential step in the proposed erection method (figure 30, 31). The end connectors for the structure need to transfer any compression or tension loads from the grid shell. It needs to facilitate repositioning from a cantilevered position directly after inflation to pin-supported at the perimeter in the end-state. As the angle of the structure touching the ground is not perfectly perpendicular to the rod and so a certain amount of rotational freedom must be permissible in the guiding path as it shortens. Simulation was used to ensure that the structural system is stable under the sustained wind load (figure 32, 33). The bolted nodes are pliant and so the stress peaks were less prominent at the support points. The use of bracing cable helps to retain the structure whilst under load. The grid shell’s ability to accommodate such significant point loads and deformations despite its low weight and slender elements is a testament to its toughness and structural capability (figure 34, 35)[10].
The details developed for the SheltAir pavilions were designed mainly to be efficient, fast to assemble and architecturally refined. The use of poles was desirable due to the easiness to carry and construct (figure 36). As the pole section diameter was only 15 mm, jointing proved a challenge. All poles connections (crossover, in-line and beam end) were achieved by means of steel pins or screws which pierce the section completely. Altered garden trellis connectors made from cast-steel were used for the connections between steel cables and the poles. Cut steel tube details were developed for the pole end connection which dock into vertical openings in the steel foundation plates (figure 37)[11]. The steel foundation plates were designed to be heavy to act as a ballast against uplift. A clamping strip on the inner edge of the foundation plates served to clamp the cushion upper and lower parts to achieve an adequate air-tight seal. The foundation plates interlock into their neighbours to define the perimeter without the need of on-site measuring or marking. The foundation plates are anchored to the ground via rammed earth screws which not only secure the foundation against lateral and vertical movement but also operate as an anchor point for securing and pre-tensioning the outer architectural membrane. The use of multi-layered grid has been effective overall (figure 38). The primary grid shell proved structural integrity whilst the additional layer of bracing cables has helped to with stand wind load. Along with the membrane restraint (figure 39) that keeps the structures compact and functionable as whole. The outer membrane also works as water and wind proof layer to separate the inner microclimate from the outside weather.
Investigation:
Which materials are best suited to construct a grid shell structure that?
The most difficult issues of a riverside location are wind, rain and moisture content. Despite the necessary tolerance from the natural material variations and human errors that the connection nodes needed to account for, a multi-layer system is necessary for being resilient grid shell structure in an exposed riverside urban location. The larger the bending active grid shell is, the heavier the foundation connection needs to be for countering the uplift that create from the wind flow. As grid shell structure is designed to be as light as possible, the foundation would be the only part of the construction system that provides the grid shell with stability. Even With the use of heavy foundation, the use of steel cable truss joint onto the primary structure helps to counter sheering. However as low pressure above open grid shell like the ZCB Pavilion suffers severely from uplift, just the heavy foundation is not adequate to hold on to the structure. Anchoring technique would be an efficient approach to counter the major force load issue. Furthermore, an outer skin would act as a water prove or a vaper barrier, is essential to ensure rainwater would not cumulate and affect any structural materials. However as riverside location has high moisture content, natural material is particularly vulnerable that special treatment is required against infestation and decomposition.
Bamboo was the initial consideration for the grid shell structure. Although Bamboo can achieve the original intention to create a minimal structure that flows effortlessly and lightly, due to the required wide span on the site, bamboo would not be possible to achieve such large-scale structure. The lack of skilled workers in Antwerp that are familiar with bamboo is another problem, Reliant on such a manual craftsmanship construction technique like the ZCB Pavilion is problematic for such location.
Timber on the other hand is a better choice than bamboo, as it can span a larger distance, however the imperfections of such a natural material might be risky for achieving such demanding design of mine. Additionally, timber is not able to achieve the high degree of curvature that I intend to adapt into my design (figure 40). However, as contemporary technology develops, Glulam timber has been able to withstand both structural requirements and environmental challenges.
Which construction details are necessary to create a resilient grid shell structure in an exposed riverside urban location?
As the Glue laminated timber grid shell is used to shade the main building underneath, the grids require infill such as ETFE panel that provide enough insulation against the natural environment (figure 41). Wind is a significant element on the site close to the harbour, due to the sheer size of the structure I need to create, using tension cable simply would be too much to handle. To withstand against the wind load, the grid shell canopy would need to flow towards a series of columns to create more stable structure (figure 42).
With the help of contemporary computational software, the use of thick Glued laminated timber structure, like waffle slab, would be incredibly stable and able to create fluid, dynamic structure that would not be possible otherwise. The unique typology required specialise solution and design approach to create compliant structural detail that would withstand the harsh seaside environment. The use of heavy, stable foundation that has shown in the ZCB Bamboo Pavilion is an essential part for designing any grid shell buildings in a large scale. Not only the foundation but using the floor slabs of the different buildings as a stability element, would become part of the important connection.
The use of traditional craftsmanship has always been an essential part of natural material construction. However, that also represents possibility for large deviation from original design. The use of Glued laminated timber would provide the accuracy of prefabricated computational design, while respecting the local craftsmanship in the joints.
The amount of detail in creating the details needed to create such complex design system is very complex and consuming. However, with construction method would provide mesmerising outcome that would not be achievable other than by using bending active grid shell.
Conclusion:
[1] Lienhard, Julian (2014) Bending-Active Structures Form-finding strategies using elastic deformation in static and kinetic systems and the structural potentials therein, Stuttgart: University of Stuttgart, pp 13
[2] Max Bächer, Berthold Burkhardt and Frei Otto (1978), IL13 – Mannheim Multihalle, Stuttgart: Institut für Leichte Flächentragwerke
[3] Martin Tamke and Paul Nicholas (2013) “Computational Strategies for the Architectural Design of Bending Active Structures,” International Journal of Space Structures, 28(3-4), pp. 215-228,
[4] Crolla, Kristof (2017) ‘Building indeterminacy modelling – the ‘ZCB Bamboo Pavilion’ as a case study on nonstandard construction from natural materials’, Visualisation in Engineering, 5(15), pp. 6-12 [Online]. Available at: https://viejournal.springeropen.com/track/pdf/10.1186/s40327-017-0051-4 (Accessed: 12th December 2019)
[5] Crolla, Kristof, and Ip Tsz Man Vincent. “Indeterminacy in designing large-scale bending-active bamboo grid-shells – a Hong Kong case study”, Proceedings of 7th annual Symposium on Simulation for Architecture and Urban Design (SimAUD), London, 2016, pp. 257- 264.
[6] Crolla, Kristof (2018) ‘The Vibrant Objectile’, in (ed.) Building Simplexity – The ‘More or Less’ of Post-Digital Architecture Practice. Melbourne: RMIT University, pp. 156-271.
[7] Gregory Quinn (2018) ‘Erection Methods for Elastic Gridshell’, in (ed.) Pneumatic Erection of Elastic Gridshells, Berlin: Berlin University of the Arts, pp. 13-17.
[8] Gregory Quinn (2018) ‘Full Scale Demonstrators’, in (ed.) Pneumatic Erection of Elastic Gridshells, Berlin: Berlin University of the Arts, pp. 121-1306.
[9] Gregory Quinn (2018) ‘Elastic Gridshell’, in (ed.) Pneumatic Erection of Elastic Gridshells, Berlin: Berlin University of the Arts, pp. 5-12.
[10] Gregory Quinn (2018) ‘Full Scale Demonstrators’, in (ed.) Pneumatic Erection of Elastic Gridshells, Berlin: Berlin University of the Arts, pp. 131-132.
[11] Gregory Quinn (2018) ‘Full Scale Demonstrators’, in (ed.) Pneumatic Erection of Elastic Gridshells, Berlin: Berlin University of the Arts, pp. 127-128.
