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Creating Parametric Design Workflows for Rapid Conceptual Design and Optioneering

Authors:
  • Aurecon Group, Hong Kong

Abstract and Figures

p>Complex, large span structures including roofs and footbridges are functional structures and are often presented as works of art or sculpture to complement the surrounding landscape. The design process of architectural large span structures or footbridges require architects and engineers to collaborate closely to co-create visually appealing and structurally efficient forms that serve the aesthetic, functional and economical objectives. In the co-creation process, a rapid turnaround is often expected. However, a tool that links form exploration and engineering is lacking; a tool that allows exploration of parametric forms quickly with instantaneous engineering and physical feedback to assess feasibility of the concept. This paper presents a journey of exploration in developing workflows and associated tools in the digital virtual space that allows collaboration, co-creation between architects and engineers so as to work seamlessly in creating structurally efficient, functional yet architectural pleasing structures.</p
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IABSE Congress Resilient technologies for sustainable infrastructure
February 3-5, 2021, Christchurch, New Zealand
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Creating Parametric Design Workflows for Rapid Conceptual Design
and Optioneering
Dr Alecs Kak Tien Chong, Dr John Chen, Mike Tapley
Aurecon, Hong Kong
A/Prof. Dr. Ir. Arch. Kristof Crolla
University of Hong Kong
Contact: alecs.chong@aurecongroup.com
Abstract
Complex, large span structures including roofs and footbridges are functional structures and are
often presented as works of art or sculpture to complement the surrounding landscape. The design
process of architectural large span structures or footbridges require architects and engineers to
collaborate closely to co-create visually appealing and structurally efficient forms that serve the
aesthetic, functional and economical objectives. In the co-creation process, a rapid turnaround is
often expected. However, a tool that links form exploration and engineering is lacking; a tool that
allows exploration of parametric forms quickly with instantaneous engineering and physical
feedback to assess feasibility of the concept.
This paper presents a journey of exploration in developing workflows and associated tools in the
digital virtual space that allows collaboration, co-creation between architects and engineers so as
to work seamlessly in creating structurally efficient, functional yet architectural pleasing structures.
Keywords: parametric design; digital workflow; optioneering; automation; concept exploration.
1 Background
The idea of conducting this research project
originated from the first author’s experience and
observation of the engineering design industry of
conceptual design of bridges. In the competitive
construction and engineering consultancy market,
especially in the Asian environment, very short
timeframe is normally allowed for the
development of conceptual design.
It was the first author’s experience in working on
an architectural footbridge located in the Middle
East. The bridge was required to be a landmark
structure complementing the new development of
the surrounding areas. This footbridge was
required to have an elegant and slender
architectural form.
1.1 Conventional Approach
During the development of the concept of the
footbridge, the design team was given two weeks
by the client to produce a concept and a reference
design. A conventional linear design workflow
shown in Error! Reference source not found. had
been adopted to undertake the design. With this
workflow, the architect independently develops
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the conceptual form and geometry of the structure
which is subsequently passed on to the engineering
team to assess the structural feasibility and
produce the engineering design.
Figure 1. Conventional workflow for conceptual
design.
At the end of the conceptual design stage, the
footbridge was decided to adopt an elegant cable
stayed bridge form for further development in the
next phase. Figure 2 shows a rendering of the final
conceptual design of footbridge.
The footbridge is 300m long and the clear span
over water is 140m long. The footbridge features
an elegant and slender 80m high single inclined and
tapered pylon. The triangular bridge deck is
supported by a series of cables fanning out to pick
up the loads on the bridge.
Figure 2. Conceptual design of a cable stayed
footbridge.
Three years since the conceptual design had been
completed, the footbridge was in construction
under the design and build contract. The detailed
design was undertaken by another design team.
Potentially driven by cost and financial constraints,
the footbridge structural form was changed from
the elegant cable-stayed type to a box girder deck
spanning across the water with a shorter span
length. This is not unusual for the construction
industry.
1.2 “What-if” Scenarios
In hindsight, there was no time to carry out a true
collaboration between the architect and engineer
teams during the conceptual design stage. There
was no opportunity to properly optimise the
footbridge which can potentially lead to further
cost saving. There is also benefit of having more
flexibility to optimise at the start of the design
phase to achieve a more cost effective and efficient
structure. During the conceptual design stage, if
the inclination of the pylon could be finetuned (see
Figure 3), there would be opportunity to reduce the
bending moment in the pylon which could
potentially reduce the steel tonnage significantly
and hence construction cost.
To this end, there must be a better way to facilitate
better collaboration between the architect and the
engineer to rapidly test ideas of conceptual design.
Imagine if there is a tool which allows the engineer
and the architect to sculpt a structure in 3D virtual
space with immediate feedback of the physical
structural response. It would be very beneficial to a
project similar to the footbridge presented earlier.
Figure 3. Hypothetical concept of the cable stayed
bridge.
2 Objective
The primary objective of this research is to address
the problem statement described in the previous
section. The solutions are explored through
blending digital technologies with engineering to
achieve the following objective:
Creating a digital design environment to
explore architectural geometries, forms and
shapes while ensuring a physical efficiency of
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the structures from the engineering
perspectives.
Digital workflows using parametric computational
design are adopted to achieve the above objective.
To elaborate this further, a designer would start
with a simple initial concept of a structure, imagine
that the designer can enter a virtual environment
in which the designer can sculpt and alter the shape
and form of the initial concepts. The physical
behaviour and structural performance of the
altered structure can be reflected in real time. In
doing this, the possibility of creating interesting
structural form and shape would be endless.
This concept is further elaborated through the
depiction of Figure 4 for the case of a vierendeel
truss footbridge. The truss starts from an ordinary
form and is then morphed and twisted into
interesting final forms.
Figure 4. Possibilities of digital sculpting of a
footbridge.
3 Development of Logic Workflows
3.1 Parametric Design
Parametric design or computational design is a
parameter-based modelling technique used to
define shapes and geometries. Parameter-based
modelling is achieved through setting up workflows
within a visual scripting environment. The use of
computational design has made exploration of
geometry into territories that have never been
possible before. Beyond the realm of exploration,
many full-scale projects based on concepts of
parametric computational design have been
completed around the world in recent years.
In this study, visual scripting tools are used to
define workflow for creation of parametric
geometries are as well as driving structural analysis
within the common environment. Combining the
parametric geometry creation with the structural
analysis is the key objective of this research.
3.2 Parametric Scripting Tools
The two most commonly used parametric scripting
tools are “Grasshopper” and “Dynamo”.
Grasshopper is the visual scripting plug-in for
“Rhinoceros”, a 3D computer graphics and
computer aided design software widely used by the
architect community. Dynamo is the visual
scripting tool for Autodesk products, for example,
Revit.
To create a common workflow between geometry
creation and structural behaviour simulation, the
visual scripting tools such as Grasshopper and
Dynamo would need to be linked with engineering
analysis software packages or plugins. Three
software packages were identified:
a) Robot Structural Analysis with Dynamo
b) Karamba3D with Grasshopper/Rhinoceros
Both Grasshopper and Dynamo adopts the visual
scripting as their core for workflow logic
development.
3.3 Robot Structural Analysis with Dynamo
Robot Structural Analysis is a structural analysis
program owned by Autodesk. A Dynamo visual
scripting “package” was released by Autodesk in
2015 to link Dynamo with Robot Structural Analysis
using Application Program Interface (API). With this
Dynamo package, structural analysis can be
combined with geometry generation and through
which optimise the conventional structural analysis
workflows.
The shortcoming of using this particular Dynamo
package is its limitation of the available analysis
functionalities. Despite the shortcoming, having
the workflows in Dynamo and within the Autodesk
environment opens the possibility of combining
other Autodesk software such as Revit, Infraworks,
Civil3D, in the workflows, as such allowing the
design process e.g. geometry creation, analysis and
design, and BIM model production, to be
streamlined.
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3.4 Karamba3D with Grasshopper
Karamba3D is a parametric structural engineering
tool developed by Dr Clemens Preisinger and team
[1] [2] for the analysis of various types of structural
problems, including spatial trusses, frames and
shells. It is fully embedded in the parametric design
environment of Grasshopper. This enables
combining the parameterised geometric models,
finite element computations and optimisation
algorithm such as the “Galapagos” engine within
Grasshopper. Setting up the geometry and physics-
simulation within Grasshopper using Karamba3D
effectively provides a real-time update mechanism
of geometry and physics representation of the
behaviour of the structure.
4 Parametric Design Workflow
The workflow for setting up a parametric design
can be broadly defined in four key steps i.e.
Step 1 Creation of parametric geometry;
Step 2 Definition of engineering parameters;
Step 3 Analysis and processing result output; and
Step 4 Communication of analysis results with
other parts of workflow
For the purpose of presenting a typical workflow
development, the Grasshopper-Karamba3D scripts
are presented in the following sections.
Taking advantage of the fact that the entire
analysis workflow is within one parametric
scripting environment, the output from the
workflow can be utilised back within the workflow
to enhance the structural design.
Figure 5. Overall Karamba logic to create a
structural analysis model and result output.
The results computed through the analysis
algorithm, e.g. in Karamba3D, can be fed back to
update the initial parameters defining the
structural geometry. For example, the location of
supports can be varied to achieve a minimum
deflection of a specific location of the structure.
This is depicted in Figure 6 where the “Galapagos”
optimisation engine is used to optimise the
behaviour of a structure.
Figure 6. Analysis results are looped back within the
workflow to facilitate optimisation of structures.
Step 1 requires the most effort for creating the
parametric features of a structure. Step 2 and Step
3 are relatively more straightforward. As soon as
the computational designer is familiar with, e.g. the
Karamba3D components and their functionalities,
the setting up of the engineering parameters and
analysis setting would be similar for all types of
structural analysis. The parametric model is
essentially completed as soon as Step 1 through
Step 3 are completed. Structural form exploration
can be performed through manual alteration of the
parameters set up upfront in Step 1. Step 4 is an
optional step for automating process to achieve a
targeted outcome. For example, optimisation to
formfind the optimum shape or determine the
optimum structural member sizes.
Figure 7 summarises the proposed enhanced
workflow for exploration of forms and shapes,
Comparing with the conventional workflow shown
in Figure 1, instead of taking up to two weeks to
iterate a design option, with the enhanced
workflow, once the architect and engineer
collaboratively have set up the initial digital
workflow or scripts for defining the geometric
features, engineering parameters and analysis
requirements, each iteration will take essentially
only several minutes to complete.
5 Case Studies
The methodology of the parametric design
workflows presented in Section 4 are applied to the
parametric design for several case studies. These
Update
geometry
paramet er
s
Optimisation
Geometry
Material & Cross Section
Loading &
Boundary
FE Discretisation
&
Results Output
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structures are “sculpted” in the parametric virtual
space and their physical behaviour are analysed
instantaneously. Three case studies are presented:
i) Arch Cable Bridge; ii) Cable-Stayed Bridge; and iii)
Bending Active ZCB Bamboo Pavilion.
Figure 7. Proposed enhanced workflow for
conceptual design.
6 Case Studies
The methodology of the parametric design
workflows presented in Section 4 are applied to the
parametric design for several case studies. These
structures are “sculpted” in the parametric virtual
space and their physical behaviour are analysed
instantaneously. Three case studies are presented:
i) Arch Cable Bridge; ii) Cable-Stayed Bridge; and iii)
Bending Active ZCB Bamboo Pavilion.
6.1 Case Study 1 – Arch Cable Bridge
This case study is on a multimodal twin arch bridge
spanning across a creek. The overall length of the
bridge is 190m, of which the main span is 140m
supported off the steel parabolic arches via vertical
cable stays. The twin arches are two independent
structures supporting two set of bridge decks. This
arch bridge has been used as a case study for the
parametric modelling workflow to conduct a study
on the structural efficiency. Figure 8 shows a 3D
model of the arch bridge.
Each of the arches support a vehicular deck and a
pedestrian deck via two sets of parallel cables as
shown in Figure 9, which shows the structural load
path and the deck balancing nature of the bridge.
The efficiency of the arch would partly depend on
the ability of the structure to achieve a balanced
condition under its own gravity load.
Figure 8. Elevation and section of the Arch Bridge.
Figure 9. Left: Structural load path and behaviour of
one arch. Right: Cross section of one of the arches
and decks it supports.
This case study was conducted using Dynamo
scripts and the application of the “Structural
Analysis for Dynamo” Dynamo package that links
the scripts to Robot Structural Analysis software.
Figure 10 shows a screenshot of the Dynamo script
window and the model of one of the arch bridges.
Figure 10. One of arches and the bridge deck
modelled and analysed using Dynamo scripts.
In this case study, the focus was primarily on
studying the factors affecting the verticality of the
arch. This case study was carried out through
investigating the parameters defining the features
of the bridge as follows
Height-to-span ratio
Number of cables
Offset of pedestrian deck from arch
Of the three parameters that were studied, it is
determined that the horizontal offset of the
pedestrian deck is the most effective parameter to
control verticality of the arch. The outcome of the
parametric study is shown Figure 11.
140m
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Figure 11. Effect of horizontal offset of pedestrian
deck on lateral displacement at crown of arch.
The original horizontal offset of the pedestrian
deck is about 17m, the optimisation algorithm of
the workflow scripts determined that when the
deck is offset by 30m from the centreline of the
vehicular deck, under self-weight loading
condition, the arch is vertical. If such geometry is
provided as the base structure, the unbalanced
loads will only be resulted from the difference in
live loading on the two decks. By this way, the arch
can be designed to resist a lower level of
unbalanced out-of-plane bending moment which
can possibly lead to significant saving in material.
This case study demonstrated an early stage
collaboration between the engineer and the
architect would be beneficial structurally and
economically for a project. With the parametric
design tool, various parameters can be rapidly
assessed, and decision made effectively between
architects and engineers.
6.2 Case Study 2 Cable Stayed Bridge
The cable-stayed bridge type is an efficient
structural form for long spanning bridges. The most
conventional form is based on the concept that the
bridge deck located on two side of the pylon is
supported by cables fanning out from the pylon. It
is an efficient self-balancing system suitable for
long spanning structures. Figure 12 shows the
classical cable-stayed bridge system.
Figure 12. Classical cable-stayed bridge system [3].
The variations made on the classical cable-stayed
system include curving horizontal alignment of
deck, inclining pylons, curving pylons, varying pylon
heights, cable patterns. See Figure 13 for some
famous variants. In this case study, these features
were set up and by changing these parameters
allows the modeller to “sculpt” interesting
structural geometry of cable-stayed bridge.
Figure 13. Variants of cable-stayed bridges
(courtesy of Dillinger Hutte GTS, Flickr user “The
Dilly Lama”, Wilkinson Eyre and Resolve Group).
Figure 14 shows the Dynamo scripts of the
parametric workflow for creating the cable-stayed
bridge model. The model shown in Figure 14 is a
bridge with horizontally curved deck and inclined
pylons. The curvature of the deck and the
inclination of the pylons are adjustable to produce
the classical cable-stayed bridge with straight deck
and vertical pylons.
Figure 14. Cable-stayed bridge modelled and
analysed using Dynamo scripts.
For this case study, the lateral displacement of the
top of the inclined pylons was taken as the
structural performance to be investigated. The
lateral displacement is a good indication of the
Samuel Bec kett Bridge
South Quay Bridg e
Langkawi Sky Bridge
Ormiston Road Bridg e
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level of transverse bending in the pylon, which is an
undesired effect to be avoided as much as possible
in design planning.
The parameters below were tested to determine
which are critical parameters governing the top
displacement of the pylons.
Number of cables
Horizontal radius of deck
Horizontal offset of deck from pylon base
Based on the study of the parameters above, it is
determined that adjusting the offset of the deck
from the pylon is the most effective method to
minimise the lateral displacement at the top of the
pylons. The result is shown in Figure 15. New
conditional coding scripts were subsequently
added to the workflow to extract the pylon tip
displacement, feed into a conditional testing
criterion and iterate to achieve the pre-set
criterion. Figure 16 shows the optimisation code
block added to the workflow.
Figure 15. Effect of horizontal offset of deck from
pylon base on lateral displacement at top of pylon.
Figure 16. Optimisation code block added in
Dynamo scripts to formfind optimum geometry.
Convergence was achieved after the two iterations.
The deck offset required was determined to be
5.7m and the corresponding pylon tip lateral
displacement is 42mm.
This case study demonstrated the benefit of a
parametric driven geometry and analysis workflow
system which facilitates optimisation of efficiency
of structures.
6.3 Case Study 3 – Bending-Active ZCB
Bamboo Pavilion
This case study is part of an ongoing collaboration
research project with Professor Kristof Crolla of
Chinese University of Hong Kong (CUHK), who one
of the co-authors of this paper and Dr Clemens
Preisinger, the founder of Karamba3D. This
research project is related to designing and
constructing of lightweight bamboo hybrid shell
structures using parametric design tools for
conceptual architectural design and structural
performance evaluation.
The parametric design workflow tool developed in
this research collaboration [2] adopts the
Grasshopper scripting environment with the
Karambo3D parametric structural analysis module
which is fully embedded in Grasshopper.
This digital workflow tool has been applied to
analyse the “ZCB Bamboo Pavilion” shown in Figure
17, an award winning full-scale bamboo pavilion
previously built by Professor Crolla and his team [4]
at the Hong Kong Construction Industry Council’s
(CIC) Zero Carbon Building (ZCB) public event
space. The pavilion was a 4-storey high bending-
active gridshell structure with a footprint of about
350m2 and a seating capacity of 200 people.
Figure 17. ZCB Bamboo Pavilion [4].
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For the construction of bamboo gridshell, bamboo
is required to be bent into the desired shape. This
construction technique is called “bending-active
construction. It is a deliberate elastic deformation
process to form curvatures in structural elements
into the desired shape. Unlike conventionally used
materials such as structural steel and concrete
which are constructed to the desired shape stress-
free prior to imposing loading, bending-active
structures are pre-bent and stressed to form their
shapes. In physical simulation, the pre-bending
stresses or strains cannot be omitted.
One of the features of the workflow tool developed
in this research is the incorporation of initial strain
resulting from the bending-active process based on
their curvatures. This concept is shown in Figure 18.
Figure 18. Formulation for including bending-
active-induced initial strain in analysis.
From the analysis results, it is noticed that bamboo
elements with tight radius are highly stressed and
some exceed allowable stress limits. This correlates
well with the observation made during the
construction of the ZCB Bamboo Pavilion where
site stiffening with steel reinforcement and
grouting were required for some bamboo elements
at tight radius as shown in Figure 19 and Figure 20.
Figure 19. Analysis results showing highly stressed
elements.
More detailed findings related to this research
project can be found elsewhere e.g. [2]. It is
demonstrated that the tool can effectively and
rapidly simulate the physical behaviour of bending-
active bamboo structures and be adopted to design
other types of bending-active structures.
Figure 20. Stiffening for bamboo at tight radius.
7 Conclusions
This paper demonstrates that application of
parametric visual scripting can be used to
effectively enhance workflow for rapid exploration
of conceptual design and exploration of forms and
shapes of complex structures. Using the proposed
enhanced parametric design workflow can
considerably shorten the duration taken to iterate
and test design options and, as a result, promoting
a close collaboration between architects and
engineers.
8 References
[1] Aksoez, Z. and Preisinger, C. An Interactive
Structural Optimization of Space Frame
Structures Using Machine Learning.
Proceedings of the Design Modelling
Symposium, 2019; Berlin, Germany.
[2] Crolla, K., Preisinger, C and Chong A. K. T.
Parametric structural evaluation of bending-
active bamboo shell structures: Tools for
conceptual architectural design performance
evaluation. IASS Annual Symposium, 2019;
Barcelona, Spain.
[3] Gimsing, N. J. and Georgakis, C. T. Cable
Supported Bridges: Concept and Design, 3rd
Edition, John Wiley & Sons; 2012.
[4] Crolla, K. Building indeterminacy modelling
the ‘ZCB Bamboo Pavilion’ as a case study on
nonstandard construction from natural
materials. Visualization in Engineering. 2017;
5(15).
ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
If unprocessed natural materials are the most environmentally friendly construction materials available, how do we develop and communicate design model and construction information that allows dealing with their volatile indeterminacies? This paper discusses the design and development of the ‘ZCB Bamboo Pavilion’, a 30-metres-spanning, light-weight, bending-active gridshell from hand-tied bamboo poles, as a case study for the computational design and building information modelling of nonstandard architecture where both applied materials and employed craftsmanship are highly unpredictable in terms of accuracy and precision. Reflective practice and participatory action research are used to extract knowledge on and challenge the environment of practice, and improve design and construction strategies. The project is used to discuss how traditional construction can be augmented through the strategic injection of computation in the design and construction process, how computation allows for a different mode of collaboration with increased impact for the designer, and how bespoke building information models enable an expanded architectural design solution space. The paper concludes by arguing for a mode of digital design practice that more proactively operates within a field of real-world indeterminacy. The risk and ambiguity of working with indeterminacies are to be strategically balanced out against idealised digital set-ups and onsite opportunities.
Chapter
The conventional methods used for structural optimization are handled by iterative simulation and evaluation runs, that are developed specifically for each problem, these processes can become computationally expensive very quickly. This work describes an approach to optimization of free form space structures, using Finite Element Analysis and Machine Learning, to overcome long computation periods.
Parametric structural evaluation of bending-active bamboo shell structures: Tools for conceptual architectural design performance evaluation
  • K Crolla
  • Chong A K T Preisinger
Crolla, K., Preisinger, C and Chong A. K. T. Parametric structural evaluation of bendingactive bamboo shell structures: Tools for conceptual architectural design performance evaluation. IASS Annual Symposium, 2019;