In many structures, space frames are used as the main load-bearing system. Especially for structures that are designed to have large spans or free-form in design. The reason is that space frames have a very high structural performance. Besides, they are also material and cost-efficient. Challenges for space frames are that they often require complex designs and the elements used are unique. Joint design is also difficult for these irregular constructions. This thesis explores the possibility of structurally optimising space frame design by using topologically reconfigurable modules, taking into account circularity. The focus lies on planar, square on square double-layered grids. The research question to be answered is the following:

”What kind of topologically reconfigurable modular system enables the generation of efficient space frames that are suitable for circular construction?”

The first design step is the initial topological design of steel cubic modules. This forms the basis of the catalog. With Grasshopper and Karamba3D (parametric FEM software) single-span trusses are then designed to determine the required cross-sections of the elements. The beams and columns are given SHS cross-sections for different spans and the diagonals are given various CHS cross-sections. With the software IDEA StatiCa various intra- and intermodular joints are designed and the rotational and translational stifffnesses analysed for
the different modules.

The former Grasshopper model is extended with a GA called Galapagos which is a plugin just like Karamba3D. This is used for topological optimisation of a given space frame structure. A GA is an evolutionary algorithm that is inspired by the natural selection process that Darwin described. The fittest genes in every population of solutions are used in further iterations. This process continues until the total number of iterations is reached or a threshold is met [1]. The algorithm reconfigures the different modules and minimises the weight of the structure
while staying within the constraints of maximum deflection, maximum material utilisation, and avoiding buckling. Logarithmic barrier functions are used for these constraints and together with the minimisation of the weight a fitness function is made. The lower the value of the fitness function, the better the solution is. The joint stiffness for each of the joint types for different |M|/N ratios is known. In the model, an initial stiffness is assigned to the joints. Then, depending on the moments and forces found in the joints, a new stiffness is assigned corresponding with the relations found in the stiffness analysis. The resulting stiffness loop describes non-linear behavior.

A verification is performed for the joints in the model. It was observed that the model was sensitive to small differences in stiffness within the joints of a standard truss. There were torsional moments observed that also resulted in an uneven distribution of the forces in the truss. To overcome this problem the stiffness of all joint groups is changed at once instead of individually. This resulted in more logical results where the support reactions were symmetric again. The model is then verified with a simple structure to see if the performance of the algorithm matches the expectations. A simple 2 x 2 grid is constructed and the model is tested. The simulation could not be performed until 50 generations because the stiffness loop led to a large accumulation of memory on the computer. It was concluded that the loop was not needed and therefore omitted because mostly only 1 iteration was needed. The model then was tested again on the small-scale model and compared to a couple of intuitively good-performing structures. This resulted in the conclusion that the model performed well and converged towards a final solution. However, since there were 106 different configurations possible the best solution was not reached in the end. It is recommended to always perform a couple of simulations to get a good solution.

After verification, the model is validated with a different FEM software called RFEM 5. Single grasshopper modules are structurally analysed in Karamba3D and imported in RFEM as well. The results show similarity in the order of magnitude of the stresses and the way the stresses are distributed. Furthermore, the reaction forces are also similar. The percentual differences between both models for the minimum and maximum stress are all below 5% except for module type 4. The absolute differences are in the order of 0.01 kN/cm2. Besides, a small frame is analysed in Karamba3D and RFEM as well to check if the deflection is in the right order of magnitude which is also the case. The percentual differences for the maximum and minimum stress are 6.40% and 7.85%, and for the deflection 12.15% and thus slightly larger than for the modules. However, for the deflection, the difference is just 1.5 mm for a structure with a span of 16 m which is a small difference. The Karamba3D model is valid and also conservative because the observed stresses are larger than in the RFEM model for the same
load condition.

A literature case study is performed on a space frame located in India. It is compared to the topologically reconfigurable model to check if the order of magnitude of the deflections and stresses is normal for this type of truss. First, a standard Pratt truss is modelled in Grasshopper to see if it is possible to design a feasible structure. This structure stayed within the limits of the constraints for the applied load which meant it worked. The case study truss is of a different size than the small structure used in the verification. With the catalog of 6 different modules and 66 possible locations for the modules as many as 10101 configurations would be possible. For this reason, the simulations are performed with 1 module type first (module type 6) and then with 2 (module types 3 and 4), greatly reducing the amount of possible
configurations. These are respectively 10^71 and 10^19. There are more solutions for the simulation with 1 module type because this module has a larger number of orientations than the other two modules combined. The outcome of the case study was that the algorithm did
not find better or equal solutions than the truss structure. This was because the convergence of the model was very slow, even for a simulation of more than 200 generations (10050 solutions) the best solution had a fitness value much larger than the truss structures. The issue was mainly that the extreme utilisation of some of the members was too large which made them fail. The BLF and displacement were within the boundaries. Comparing it with the case study the maximum stresses were indeed larger but the deflection was in the same
order of magnitude. The Pratt truss with reconfigurable members which resembled a regular truss was in the right order of magnitude for deflection as well. This truss does not have extra parallel beams since not entire cubes are joined together but single beams and columns.

An application is analysed to see how the model acts when the supports are irregular. From this setup, it was unclear what would be an optimal solution. The selected modules for this problem did not give the option to create a regular truss-like structure. The model found a slightly better solution than the one initially found using intuition and expert judgment. The value of the fitness function decreased from 0.84 to 0.80, which is a 5.5% decrease. The conclusion from this case study is that when the optimal solution is unclear and the design
space is large the model can find a relatively good solution. Combining this expert judgment and computational design can improve a model even more.

Overall the model can be used to design planar steel space frames with varying support conditions. These space frames are circular in design because their parts can easily be deconstructed and reused in similar structures. This is a huge advantage because it can save a lot of material and construction time as well. The modules themselves have the extra advantage that they can also easily be changed to a different type by varying the diagonals. This makes the system flexible in design. However, the optimisation efficiency is not very good.
The algorithm does not find optimal solutions that can be used in practice for a large design space. The type of structure is also much heavier in general compared to conventional space frames. This is because joining entire modular cubes together requires more steel. There are numerous parallel members that do not appear in regular space frames where beams, columns, and diagonals are individually placed in the structure. This makes stress on the members relatively high and therefore unfeasible. To use the system is therefore a consideration for the designer. When focussing on modular and circular construction this system is very useful but it is less structurally efficient. The model with ”modular elements” could potentially be used for a more structurally efficient system if the convergence towards a solution can be improved (with a different algorithm) and the speed at which solutions are calculated as well.

The Mekong Delta in Vietnam is facing several challenges as a result of climate change. Among others, the effects include an increase in river discharge during the wet season, leading to river floods, and a decrease in river discharge during the dry season. The decrease in discharge results in a shortage of fresh water required for irrigation and drinking water. Besides that, the combination of sea-level rise, land subsidence, and decreased river discharge during the dry season results in saltwater intrusion. This threatens freshwater supply even more. Furthermore, there is an increasing risk of floods from the sea due to low land elevation and the rising sea level in combination with the occurrence of storm surges. The scope of this research is the area around the Ham Luong estuary, which is a branch of the Mekong River. The partial closure of this river branch is considered by the Vietnamese government as a measure to reduce the effect of the above-mentioned effects of climate change. However, not enough research has been conducted yet on the impact of a partial closure on the Ham Luong estuary. This has lead to the following research question: “What is the impact of various closure scenarios on the hydraulic characteristics and social activities in the Ham Luong estuary, considering a 75-year forecast?” The region of the Ham Luong estuary is characterised by its intensive agri- and aquaculture. More than 60% of the inhabitants is directly active within the agri- or aquaculture. As these activities are strongly dependent on the salinity of the estuary, they are highly affected by the effects of climate change. The region is densely populated with more than 125,000 inhabitants living near the Ham Luong estuary. It is clear that the effects of climate change are threatening the region in hydraulic aspects, as well as socio-economic aspects. A partial closure could reduce these effects, but will influence the region in several ways. In order to estimate the impact, a combination of hydraulic and socio-economic aspects is assessed based on a criteria set. This criteria set contains the criteria of freshwater supply, agricultural and aquaculture adaptation, biodiversity, stable riverbanks, and navigability. These criteria will be tested on a total of four alternative interventions in the Ham Luong estuary. Three alternatives with a storm surge barrier and one alternative without a storm surge barrier. All alternatives include heightening of the existing dyke system, as this seems to be inevitable when aiming for long-term development in the region. The extend of dyke heightening is subject to the choice of alternative. As a part of the impact analysis, a Delft3D model was built to analyse the hydrodynamic and morphodynamic processes in the Ham Luong estuary. The model was restricted to the chosen spatial scope, which only covers the Ham Luong estuary, without any upstream bifurcations. The model gave insights in processes like salt intrusion, sedimentation rates, and water levels. However, due to model simplifications and assumptions, the outcomes of the model where not useful for quantitative assessments. Still, the results are used to compare the impact of the different alternatives to each other. As expected, the alternatives that include a storm surge barrier will provide more possibilities to retain fresh water than the alternative without a barrier. From the results, it followed that the limited spatial scope excludes the redistribution of upstream discharge. It is recommended to look at a larger scale of the Mekong Delta when assessing hydro- and morphodynamic processes. Forming a flood protection system, the structural design of such a storm surge barrier, together with a quick estimation of a dyke system. The dyke system is different for each alternative, depending on the presence and the location of a barrier. The barrier design includes a thorough analysis on feasibility of gate types, technical requirements, load combinations, design of dimensions, and the operation. The load combinations take hydrostatic, hydrodynamic, wind, and soil loads into account. The design of the dimensions is done for the gates, sill, lifting structure, pier, foundation, and the bed protection. By assessing the above-mentioned criteria, a preferred solution is identified. This preference is based on a Multi-Criteria Analysis, which includes weighted scores for all alternatives. The outcome of the Multi-Criteria Analysis appears to be very sensitive to the rating and weights of the criteria, which makes it difficult to identify one of the alternatives as the preferred solution based on only the score on the different criteria. For this reason more research is needed. However, when including a cost estimation of the four alternatives, it can be stated that the alternative of no storm surge barrier and only the corresponding extensive dyke heightening could be considered as most cost-beneficial alternative and therefore as the preferred solution. It is expected that with or without closure of the Ham Luong estuary the system will change. The availability of fresh water will be improved by the presence of a closure, although more research is needed to specify this further. The increasing salt intrusion, as a result of Relative Sea-Level Rise (RSLR) will lead to agricultural and aquaculture adaptation in all alternatives. Either due to the construction of the barrier, or due to the gradual RSLR. A closure also has effect on the biodiversity, stability of the river banks, and navigability in the river. When implementing a closure these effects should be further investigated to assess the effect quantitatively.