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Concrete Lego and the exploration of interlocking universal connection systems
AR30315 – Dissertation
Draft literature review
1.0 The problem
In the 2017/18 fiscal year, 144 people were injured at work in the United kingdom, 38 of those were on construction sites (Hse.gov.uk, 2018). This figure, over the last 5 years has flatlined asking the question how can it be decreased further. In the manufacturing sector the fatal injuries to the workforce in the same year was 15. A primary reason for this is the use of automation to aid speed of production in a safe manner. As much as these figures are surprisingly high considering the advancements in safety which we take for granted every day, it is worth pointing out across the European Union the average number of fatally injuries per 100,000 employees is 1.29 that drops to 0.51 in the UK (Hse.gov.uk, 2018). This leads to the reasoning that the impact of any safety measures will be felt to a greater extent in less economically developed countries.
Figure 1.0.1 A breakdown of the 144 fatally injured at work in 2017-18 (Hse.gov.uk, 2018).
1.1 Scope of the project
Technology has advanced significantly to allow for automated systems to be used on site as well as in prefabrication scenarios. The possibilities to improve safety measures by accelerating the speed of construction. In this dissertation, the focus is towards structural connections themselves. The part of the construction process which most requires human input presently is structural connections. Therefore, if connections were designed in such a way that a machine could do the same job as that of a construction worker, then people can be kept out of harms way as much as possible. The main constraint of connections in traditional building materials is the use of bolts, dowels and other rotational fixings. The use of such elements means human skill is needed on site as on a construction scale.
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In this project, across traditional building materials, the aim is to assess the feasibility of removing the need for elements such as bolts by exploring universal fixing techniques such as the interlocking nature of a Lego block. This project is being considered aims to purely assess feasibility, with the hope that in success there will be benefits such as minimising the environmental impact and cost reductions. Although it is hoped that the project will provide evidence for this style of construction, they are not considered in the development process.
The project hopes to create working prototypes on a smaller scale to show feasibility of what can be achieved. From these prototypes, dimensions will be scaled to assess whether the connections will work on a construction scale. This will be achieved by using design codes and simple hand calculations to show that the connection will not fail. Due to the nature of some of the connections proposed, it is conceivable they could be used for both temporary and permanent structures.
Prefabrication is an intriguing concept and solution to the same problem this dissertation addresses, this dissertation will not consider it. The reasoning being often prefabrication of bespoke elements is expensive and the trade off minimising on-site costs by speeding up construction. This project aims to reduce time on site (thus reducing cost and improving safety) by creating universal connection systems allowing for example, steel frames to be erected faster. By having a universal connection system, it reduces the skill needed in construction and opens the door for the use of automation.
1.3 Aims and objectives
The dissertation primarily focuses on the feasibility of using interlocking universal building elements to improve the speed of construction by reducing the reliance on standard connections which require bolts, welds and dowels. By taking a conceptual stance commercial drivers can be ignored to allow for a creative development process.
The main goals are as follows:
- Research what has been achieved previously in terms of innovative construction methods and the advancements subsequently made.
- Research the scaling of prototypes and the possible complications that can occur.
- The creation of desk scale prototypes across the traditional building materials of steel, timber and concrete.
- Validate the prototypes through the use of hand calculations leading to computational analysis of a structure.
- To assess the feasibility of what is created and comment on what the impact of what the end product could have on the industry.
“The connections used in any structural system play a significant role in defining the form, proportion, and overall aesthetic of a building” (Thomson A,2010)
- Lastly, if the previous goals are met, my final goal will be to have created something which will not only influence how buildings are designed and built, but provide a system which will allow boundaries to be pushed in terms of the form of structures.
2. Literature review
Concrete as a building material has been used for millennia. Recent advancements in manufacturing technology has allowed for more intricate shapes to be cast. Examples of precast concrete retaining walls with interlocking blocks are well explored worldwide. Companies such as LockBlock ltd., Tobermore and JP Concrete have a number of products that can be used for retaining structures and even small buildings.
Figure 2.0.1 JP concrete interlocking precast blocks are an example of a product already used in industry. (jp concrete,2018)
A significant advantage of this building method is the resistance to seismic forces compared to traditional masonry or concrete block construction. “during earthquake events, every interlocking block is allowed to move relative to each other. In a mortar-free interlocking block structure, earthquake energy input is mainly dissipated through friction between adjacent blocks, relative displacement and form micro-cracks of blocks rather than large cracks in bricks and failure in mortar bed joints in a conventional masonry structure.” (Tang, Ali and Chouw, 2018). Furthermore, as no grouting is required the speed of construction is increased leading to construction workers spending less time on site. The large weight of the blocks also leads towards them being positioned mechanically again getting construction workers out of harms way.
Figure 2.0.2 Shows an interlocking block retaining wall. Steel reinforcement is also used to stiffen the structure as the most likely method of failure is overturning at the boundary between courses of blocks. (Blockwalls, 2018)
Overall, the use of precast interlocking concrete elements in the construction industry is extensive. In infrastructural elements such as retaining walls near highways a cheap and quick to construct solution is on offer. However, for larger scale structures, it is far less efficient and the high dead load in taller buildings makes it inefficient as any qualitatively any financial gains due to speed of construction will be negated by the extensive foundations required which may have been avoidable.
Steel frames are an incredibly popular structure in the construction industry due to the versatility they offer in terms of the scale they can be used at. Generally, the limiting factors in design of the frames is deflection criteria of beams and the moment resistance of the beams. And in terms of shear resistance connections are often over designed due to the geometry of the beams required to pass the previously mentioned criteria. All proprietary products widely available rely on rotational fixings.
Figure 2.1.1 Shows the girder clamp product offered by Lindapter. As much as it is step towards the possibilty of automated construction, it still relies on rotational fixings. (Lindapter, 2018)
On site welding is an example of a process which requires human intervention directly to produce a structural connection. This has largely been phased out due to most steel fabrication occurring in a factory.
In terms of innovation, one company who have deviated from traditional methods are Lindapter. The range of products they offer mean that on site drilling and welding is not necessary. “The Girder Clamp is capable of being used in many loading situations including tensile, friction or a combination of the two as well as on horizontal or vertical sections. Capacities range up to 250kN for a four bolt configuration,” (Lindapter,2018). The main drawbacks to the product are that each piece is bespoke for each connection. “This flexibility means the Girder Clamp is not an ‘off the shelf’ item, but a bespoke steelwork connection solution,” (Lindapter,2018) shows that the company acknowledge this but do not offer a product which is readily available. The drawback of this is despite it’s usefulness in construction, it still requires human input and judgement. As much, to some degree, the construction process requires this it is not efficient for automated design as each connection is still slightly different. The main gap in terms of steel construction is there is not an “off the shelf” universal building system.
The other principle drawback to the product is the reliance on rotational fixings and small connecting parts. Again, this does not lend itself to automated construction and relies heavily on human input on site.
Modular construction of steel frames is widely used in “structures with repetitive units, e.g., apartments, schools, offices, dormitories, hotels and hospitals” (Deng et al., 2017). As of yet, the modularity of construction has not been scaled down to the individual members. It reasons, if modular repeating systems are beneficial from a cost point of view, then if all the connections were universal then construction could be even quicker. Further more other benefits include: A smaller environmental impact as noise and any pollution such as dust or fumes, A better construction quality as elements are fabricated in more controlled factory conditions and the ability to dismantle and reuse elements as they all have the same connection interface they can be used again in other projects or simply replaced from a maintenance point of view (Deng et al., 2017).
Figure 2.1.2 (Deng et al., 2017)
The concept of having universal connections at nodes has yet to be fully explored. And this dissertation should tackle this head-on, even if at the end it surpasses that there is a reason why it has not been used in industry.
The main types of timber connection used in industry are as follows: traditional carpentry ,the use of dowels or bolts and the use of adhesives.
In Eurocode 5, guidance is still only offered for bolted metallic connections (Thomson A, 2010). Bolted connections firstly offer potential issues from a fire-resistant point of view. This is because of the thermal conductivity of the metal, which allows further thermal penetration into the timber member meaning in terms of volume more timber will be exposed to the fire and higher temperatures. The other factor that this dissertation aims to minimise the need for on site human labour, which is required for bolted connections. The one significant advantage held with bolted connections is the extensive research which has been done into failure methods between metal and timber. As much as on-site intervention is required, they can be designed closer to the ultimate limit state of the connection.
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Dowel connections in timber construction is a topic of research which has expanded considerably over the last decade. Materials such as Glass fibre reinforced pultruded rod (GFRP) and increasingly timber dowels have been tested and have benefits from fire engineering and cold bridging perspectives (Thomson A,2010).
Adhesives have been researched thoroughly of late and a wide range of adhesives are available and tailored to specific materials and types of connection. Extensive testing has been undertaken and published in relation to both manufacture of connections in terms of how the effects of clamping impact the glue line and how this affects materials properties (Aicher S, 2016).
In relation to this dissertation, it appears that research towards timber joints without adhesives or connecting members such as dowels is being conducted. Research has also been recently conducted by looking at traditional timber construction methods such as wooden pegs in restoration of structures (Ceraldi et al., 2017).
The significant gap in research appears to be the analysis of traditional carpentry methods. The general methods used to day are passed down “rule of thumb” rules which have been identified through centuries of knowledge passed down. To use the analogy of boat building, this makes a lot of sense as the risk of changing something known to work could have disastrous consequences when there isn’t a safety net. However, with advances in technology from inception of these building methods it is likely that refinements could be made to improve the quality of connections and take steps towards more efficient less labour-intensive connection design.
In summary, concrete as a material for the use of modular interlocking elements is a well-researched field. Products are used worldwide and any significant improvements to the systems in place are likely to be well beyond the scope of this dissertation. Steel framed structures have been realised to have potential for modular design. At present, this is limited to modular units the size of rooms. This offers cheaper construction costs, the opportunity to recycle elements and easy maintenance. However, no research has been conducted into a more fluid method of modular construction from the compatibility of each beam or column. Research into exploring this is planned for this dissertation. Removing the need initially to conform to the constraints of commercial pressures, allows for the chance to purely establish a system that works before validating it for real world use.
Research into non-metallic timber connections seems to be a growing field. As of yet, most if not all research focuses on the use of dowels and other small connecting members. The main disadvantage of these types of connections is that it requires skilled labour on site which in relation to this dissertation is something to challenge the relevancy of modern construction. Taking precedence from traditional carpentry methods is certainly a route worth exploring. If carpentry connections could be fabricated off site reliably this could enable construction to be quicker in a risk averse manner and consequently safer as less hours are spent on site.
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