TECHNICAL FIELD

The present disclosure is enclosed in the area of civil engineering, more particularly relating to modular and prefabricated structural systems.

PRIOR ART

The construction sector relies for several decades on old/conventional structural systems and erection techniques that are no longer suitable to address adequately existing challenges in terms of sustainability. Additionally, significant technological advancements are currently being introduced in the construction sector, for instance using addictive manufacturing and robotization. The robotization of the construction sector will shift a relevant portion of the construction works to a workshop, hence further enabling prefabrication and modular construction systems and overall quality and accuracy of the end-product.

Prefabrication and modular systems are emerging in the construction sector; however, only steel, timber or prefabricated reinforced concrete systems can be commonly found, and the existing solutions do not target ease of assembly and disassembly avoiding destructive disassembly operations. 2050 Circular and Zero Carbon Sustainable construction demands the adoption of new strategies and solutions that significantly change the consumption patterns of natural resources (consumption of 40% of the global materials), waste management and treatment. The need to reduce environmental impacts in the construction sector means that prefabricated solutions, combining sustainable and reusable materials (Design for Disassembly - DfD) have to be introduced in the market, directing the construction sector towards a future with more sustainable cities.

Significant developments have been attained in the past few years in the field of cold-formed steel (CFS) structures since it has been recognized that these products can be effectively used as primary structural elements, therefore representing a valuable and competitive structural solution. In fact, CFS sections present several important advantages when compared with more traditional hot-rolled and concrete solutions [1, 2], CFS sections also present versatility, ensuring that single sections may be combined to build compound cross-sections with two or more individual profile shapes, which can span more distance, present higher load-bearing capacity and torsional stiffness. This is also a big economical advantage since all the manufacturing process remains the same. However, the research on built-up elements, where several individual cross-section shapes are combined is still scarce, and specific design procedures do not exist even in design standards.

In terms of composite steel-concrete structural systems, the current practice is to use on-site concreting of elements and the fact that the existing structural elements are usually much heavier, limits prefabrication and excludes the use of composite systems for low to mid-rise buildings. Even in the situations where some developments were introduced in the field of steel-concrete composite systems demountable systems, the main achievement is related to the claim of the steel part where the concrete part is at least partially destroyed.

PROBLEM TO BE SOLVED

Relevant research has been undertaken in the field CFS structures, from material characterization to the overall behaviour of different structural solutions at both ambient temperature and accidental fire conditions, particularly on built-up CFS elements. To further expand the applicability and increase the competitiveness of CFS in the building construction industry new synergies must be established. Moreover, the number of hybrid structures in use increases every day since the use of different materials will provide significant advantages over the use of a single material. Seeking synergies is a trend that will lead to great benefits to the construction sector.

With that in mind, that is a need to develop prefabricated and modular construction systems capable of achieving the aforementioned synergy and having as key requirement the ease of assembly and disassembly of all its structural elements and where the destructive operations in the disassembly process are minimized.

The present disclosure is directed to a solution for the stated problem and describes a new prefabricated composite structural solution for a construction system, which is based on CFS profiles with lightweight concrete that may be combined with cross-laminated timber, presenting great structural performance ease of erection and possible reuse of pa rts/full structure in multiple life cycles.

SUMMARY

It is therefore the object of the present disclosure a prefabricated, modular, multi-material composite hybrid construction system.

In an advantageous configuration of this new construction system, it is comprised by a plurality of structural elements, floor modules and connection elements. The structural elements comprise a plurality of horizontal and vertical linear elements. The floor modules comprise a plurality a floor slabs, and the connection elements comprise a plurality of connector pieces adapted to provide connection between structural elements, floor modules and between a structural element and a floor module. Particularly, each structural element is comprised by a built-up hollow cold- formed steel structure that is at least partially filled with lightweight concrete, and the connector pieces are made of steel and are of a bolt and nut type connection.

The system now developed gathers several innovative characteristics, namely the combination of different structural materials to create new synergies to expand its applicability and targeting prefabrication, modularity and ease of assembly and disassembly, particularly minimizing destructive operations in the disassembly process. Additionally, being a hybrid system, that is, a multi-material system, it is possible to effectively explore the main characteristics of each material. It therefore provides an optimal functional performance in both ultimate limit state and accidental fire conditions due to the synergies obtained between the different structural members of the hybrid system developed. Moreover, being a prefabricated and modular system, it enables fast-track construction with high-quality products, optimizing on-site operations, reducing waste, improving safety, and ensuring efficient structural performance.

Consequently, it is envisaged that the developed solution will be able to compete with more traditional prefabricated reinforced concrete and light steel framing solutions.

DESCRIPTION OF FIGURES

Figure 1 - representation of a plurality of embodiments of the structural elements; the numerical references represent:

1 - structural element;

1.1 - horizontal linear element;

1.2 - vertical linear element;

1.3 - cross section shape;

1.4 - steel shape;

1.5 - self-drilling screw;

1.6 - lightweight concrete.

Figure 2 - representation of a structural element; the numerical references represent: 1 - structural element;

4 - transverse inner hollow cylinder.

Figure 3 - representation of an embodiment of the system; the numerical references represent:

1 - structural elements;

2 - floor module;

3 - connection elements.

Figure 4 - representation of a connection between a floor module and a structural element; the numerical references represent: 1.1 - horizontal linear element;

2.1 - floor slab;

2.2 - composite lightweight concrete slab;

2.3 - steel deck;

2.4 - pocket holes;

3.1 - bolt;

3.2 - rivet nut.

Figure 5 - schematic representation of a configuration developed for the connection of vertical linear elements and floor modules; the numerical references represent:

1.2 - vertical linear element;

3 - connection element;

3.4 - anchor bolt;

3.5 - stiffener element;

4 - transceiver inner hollow cylinder.

Figure 6 - schematic representation of a configuration developed for the connection of vertical and horizontal linear elements; the numerical references represent:

1.1 - horizontal linear element;

1.2 - vertical linear element;

3.1 - self-drilling screws;

3.4 - housing structure;

3.5 - stiffener element;

3.6 - end-plate.

DETAILED DESCRIPTION

The more general and advantageous configurations of the system are described in the Summary. Such configurations are detailed below in accordance with other advantageous and/or preferred embodiments of implementation of the system. The construction system aims to explore the versatility of cold-formed steel products, combining efficiently different individual configurations to fabricate built-up structural elements that can be combined with lightweight concrete (cold- formed steel lightweight concrete, CFS-LWC). In connection to that, the connector pieces target ease of assembly and disassembly (design for disassembly) ensuring future reuse or relocation of the structural elements.

For the floor modules, both composite slabs with lightweight concrete and Cross-Laminated Timber (CLT) panels may be used depending on the desired level of prefabrication. The use of composite slabs with lightweight concrete and profiled steel decking may require on-site concreting, whereas the CLT panel ensures an easy and fast assembly. For both scenarios, the proposed tailored connecting solutions/devices ensure adequate composite action between the structural elements and the floor modules.

This type of strategy can be extensively used to fabricate tailored and optimized structural elements, such as columns and beams. Composite CFS-LWC structural elements are innovative solutions for prefabricated structural systems expanding the field of applicability of existing products that can be effectively combined. The developed structural elements are then connected using tailored connector pieces, that may be fabricated with hot-rolled steel plates. The structural elements will also have pre-drilled holes and passing self-drilling screws to ensure efficient and easy assembly. A similar approach was considered for the connections between the horizontal elements and floors modules, enabling efficient composite action but still fulfilling the established requirements in terms of ease of assembly and disassembly. To achieve this, bolts are extensively used as well as self-drilling screws and rivet nuts.

The developed construction system aims to optimize the on-site construction process, enhancing the industrialization of the construction sector, promoting prefabrication, delivering high-quality products, and reducing construction waste. Preferentially, the solution is targeted for low to mid-rise residential and office buildings, directly competing with more traditional reinforced concrete solutions, light steel framing, and prefabricated reinforced concrete solutions. The construction system will now be described in reference to the drawings. As illustrated in figure 3, the system is comprised by three component groups: structural elements (1), floor modules (2) and connection elements (3).

Structural elements:

The structural elements (1) comprise horizontal linear elements (1.1), such as beams, and vertical linear elements (1.2), such as columns.

As illustrated in figure 1, said elements (1.1, 1.2) are built-up CFS elements that may be fabricated using individual cross-section shapes (1.3) such as C, U and 2. The individual cross-section shapes (1.3) are arranged and connected using selfdrilling screws (1.5). Two situations may be considered: either fabricate closed built-up CFS sections comprising two or more individual shapes (1.3) or fabricated open built-up sections comprising two individual shapes (1.3). Preferentially, the elements (1) are based on closed built-up CFS sections comprising 4 individual members, that is two cross-section shapes (1.3) and two steel shapes (1.4) acting as formworks, which provides significant advantages in terms of fabrication, transportation and erection. The hollow part is then filled with lightweight concrete (1.6) to fabricate a CFS-LWC composite body. In one embodiment, square CFS-LWC bodies are used as vertical linear elements (1.2), such columns, whereas rectangular CFS-LWC bodies are used as horizontal linear elements (1.1), such as beams.

In both composite CFS-LWC horizontal and vertical elements (1.1, 1.2), transverse inner hollow cylinders (4) are positioned where suitable (see figure 2), to allow the easy assembly of the connection elements (3), responsible for establishing the connection between structural elements (1) and floor modules (2). The hollow cylinders (4) are embedded on the concrete (1.6) infill, hence contributing to mobilizing the composite action between LWC and CFS. This requires high levels of precision, hence the operations shall preferably be performed in an automatized assembly line. Floor modules:

For the floor modules (2) different alternatives are considered and may be adopted using the proposed "structural skeleton" developed and described. The existing alternatives for the floor slabs (2.1) are the composite slabs with profiled steel decking and lightweight concrete (1.6) panels or the cross-laminated timber (CLT) panels. In case of composite slabs with profiled steel deck, the reuse of that specific element in multiple life cycles is limited, however it is worth mentioning that the composite action between the horizontal element (1.1) and floor module (2) is achieved by using demountable connection elements (3), such as bolts (3.1), hence allowing, with limited destructive operations to separate the composite floor slabs (2.1) from the horizontal elements (1.1). The other alternative is the use of CLT panels, which also provides the necessary load-bearing capacity and stiffness to the structure, acting efficiently as horizontal diaphragms, since the composite action between the floor slab

(2.1) and the horizontal element (1.1) may be ensured by the use of demountable shear connectors.

As illustrated in figure 4, the connection between a horizontal element

(1.1) and a floor slab (2.1) formed by a composite LWC slab (2.2) and a steel deck (2.3), is established by the use of large threaded rivet nuts (3.2) used simultaneously to connect the individual CFS section shapes and allow the easy fastening of the floor slabs

(2.1) to the horizontal elements (1.1) by means of the bolts (3.1). Exploring the benefits of prefabrication and the possibility of fabrication in an assembly line, pockets (slab holes, 2.4) and coupling devices may be embedded on the floor slab (2.1), ensuring that only the use of a bolt (3.1) is needed to connect the slab (2.1) to the concrete filled CFS- LWC element (1.1).

In one embodiment, considering a main horizontal element (1.1), such as a main beam, a concrete-filled closed built-up CFS beam with composite floor slab (2.2) with profiled steel deck (2.3) is used, whereas for the secondary beams connected to the main beams simple open built-up CFS beams can be used. Connection elements:

Connection elements (3) are used to provide connection between structural elements (1), floor modules (2) and between a structural element (1) and a floor module (2). The connection elements (3) may be seen as joints that use tailored steel connectors that may be fabricated with hot-rolled steel plates. One of the key aspects governing the structural performance and assembly and disassembly efficiency of the innovative construction system concerns the connections between the main elements (1, 2). Since such elements, particularly the structural elements (1), are built- up CFS-LWC filled members, to easily connect and disconnect composite members is complex. There is simultaneously the need to mobilize the composite action between the materials and to ensure the efficient connection between the two types of members (horizontal and vertical elements). The connectors (3), being made of steel, provide great structural performance with ease of erection.

Additionally, only bolted joints are considered in this structural system, enabling ease of assembly and disassembly without the use of destructive operations. All components of the composite joints can be easily disassembled and reused in multiple life cycles.

A more detailed description is provided below:

Vertical element to floor module connector - see figure 4: as previously detailed the basic concept consists of using tailored steel connectors, that may be manufactured with hot-rolled steel plates, and transverse inner hollow cylinders (4) passing through the entire cross-section of the element (1.2). The cylinders (4) are embedded on the concrete (1.6) infill, mobilizing the composite action between CFS and LWC and allowing the positioning of bolts (3.1) that are used for the connection. The anchor bolts (3.3) may be used, being connected to the reinforced concrete footings.

Horizontal element to vertical element connector - see figure 5: tailored steel connectors (3) and the anchor mechanism are explored to propose different configurations of innovative composite CFS-LWC joints, namely semi-rigid and simple joints. Transferring forces between two concrete filled elements (1.1, 1.2) is a complex task, especially when ease of assembly and disassembly is a key performance target. To address the existing challenge and exploring prefabrication, passing through hollow cylinders (4) are positioned where appropriate, enabling the positioning of the bolts (3.1) used to fix the different members and to mobilize composite action by acting as shear connectors. The passing through bolts (3.1) are then used to provide a structurally efficient joint that is easy to assemble on-site. Tight tolerances are considered for such joints since all pieces are manufactured in a workshop. The steel connectors (3) developed may be characterized by a set of steel plates welded and prepared in a workshop. Similarly, the elements (1.1) and (1.2) are previously manufactured in an industrial facility where passing through holes are prepared using adequate steel tubes (equivalent diameter to the bolts).

The developed connectors (3) may be used in corner, external and internal joints. The connectors (3) comprise L-shaped plates welded to an extended endplate (3.6), forming a housing structure (3.4), where triangular stiffeners (3.5) may be added to increase the overall resistance of the joint. The steel connectors (3) are bolted to the vertical elements (1.2) using the passing through bolts (3.1). Similar approach is used to connect the composite built-up CFS-LWC horizontal element (1.1). Governing the behaviour of the joint and its overall stiffness and resistance, is the thickness of the steel plates used in the housing structure (3.5) and the distance between the passing through bolts (3.1). With the proposed system the steel connector (3) may be positioned in the CFS-LWC vertical element (1.2) and with a single movement the horizontal element (1.1) can be positioned and bolted to the steel connector (3).

EMBODIMENTS

The present disclosure relates to a prefabricated, modular, multi-material composite hybrid construction system. In a preferred embodiment of the system, it is comprised by:

- structural elements (1) comprising:

- a plurality of horizontal linear elements (1.1);

- a plurality of vertical linear elements (1.2);

- floor modules (2) comprising: - a plurality of floor slabs (2.1);

- connection elements (3) comprising:

- a plurality of connector pieces, adapted to provide connection between structural elements (1), floor modules (2) and between a structural element (1) and a floor module (2); wherein, each structural element (1) comprises a built-up hollow cold-formed steel structure that is at least partially filled with lightweight concrete (1.6); and the connector pieces are made of steel and are of a bolt and nut type connection.

In another embodiment of the system, the horizontal linear elements

(1.1) have a built-up rectangular cross-section, and the vertical linear elements (1.2) have a built-up squared cross-section. The versatility in the forms that the cross sections of these elements (1) may have is favourable to optimize the prescribed structural system actively contributing to reduce the consumption of natural resources. Alternatively, both the horizontal linear elements (1.1) and the vertical linear elements

(1.2) have a cross-section of a same, that is equal, shape. This particular configuration is appropriate to increase the resistance of the structural members.

In another embodiment of the system, the cold-formed steel structure of a structural element (1) is formed by a plurality of individual cross-section shapes (1.3) and a plurality of steel shapes (1.4); the steel shapes (1.4) being adapted to provide a framework defining the cross-section shape of the structural element (1); and, the steel shapes (1.4) being connected to the cross-section shapes (1.3) by means of self-drilling screws (1.5). Built-up members, formed through the combination between steel shapes (1.4) and the cross-section shapes (1.3), are symmetric and the combination of multiple individual profiles allows to reduce the global slenderness, increasing the strength of the individual elements, thus, overcoming load-bearing capacity and stability limitations. In another embodiment of the system, each structural element (1) comprises: a plurality of transverse inner hollow cylinders (4), throughout the entire cross-section of the structural element (1); the cylinders (4) being embedded on the lightweight infill concrete (1.6) defining a position for the connector pieces used to connect the different structural elements (1); preferably the cylinders (4) are made of steel; and a plurality of bolts (3.1) adapted to fit in the embedded hollow cylinders (4).

The use of these cylinders (4), embedded on the concrete (1.6) infill, allows to mobilize the composite action between the CFS and the LWC and also allows the positioning of the bolts used to connect the structural elements and the connector pieces.

In another embodiment of the system, the structural element (1) is a vertical linear element (1.2) and the connector piece, adapted to connect a vertical linear element (1.2) to a floor module (2), comprises: a single piece connector (3), formed by a first section, parallel to the floor module (2) and comprising a plurality of through-holes; and by a second section, perpendicular to the first section and parallel to the vertical linear element (1.2), and comprising a plurality of through-holes adapted to fit the bolts (3.1) of the vertical linear element (1.2); a plurality of nut-type connectors adapted to fix the second section of the connector piece to the vertical linear element (1.2) by engaging the bolts (3.1) of said vertical linear element (1.2); and a plurality of anchor bolt (3.3) type connectors adapted to pass through the through-holes of the first section in order to fix said first section of the connector piece to the floor module (2). The single piece connector (3) may further comprise stiffener elements

(3.5), preferably of a triangular shape. These elements (3.5) allow to increase the overall resistance of the connector (3).

In another embodiment of the system, the floor module (2) further comprises reinforced concrete footings; said footings being adapted to fix the anchor bolt (3.3) type connectors.

In another embodiment of the system, a connector piece adapted to connect a first structural element (1) to a second structural element (1), the structural elements (1) being of a different type, comprises: a housing structure (3.4), being fixed to a longitudinal section of a first structural element (1), and configured to receive an end section of a second structural element (1); the housing (3.4) comprising a plurality of through-holes adapted to: fix the housing (3.4) to the first and the second structural element (1) by means of a plurality of bolts (3.1) installed through the transverse inner hollow cylinders (4) of the respective structural elements (1) and the through holes of the housing (3.4).

This particular configuration of the housing structure (3.4) allows to easily install the beam and still ensuring great versatility to obtain multiple performance levels by simply modify the plate thickness and the stiffeners.

In another embodiment of the system, the housing structure (3.4) comprises stiffener elements (3.5), preferably of a triangular shape. These elements

(3.5) allow to increase the overall resistance of the housing structure (3.4).

In another embodiment of the system, the first structural element is a vertical linear element (1.2) and the second structural element is a horizontal linear element (1.1); the vertical linear element (1.2) being a column and the horizontal linear element (1.1) being a beam.

In another embodiment of the system, the connector piece used to connect a first structural element (1) to a second structural element (1), the structural elements (1) being of a different type, further comprises an end-plate (3.6) made of steel. Particularly, the housing structure (3.4) being fixed to the longitudinal section of a first structural element (1) through the end-plate (3.6). Such end-plate (3.6) contributes to distribute uniformly the acting forces through a large surface area.

In another embodiment of the system, the connector piece adapted to connect a horizontal linear element to a floor slab is of a threaded rivet type (3.2). The use of such type of connector piece allows to simultaneously connect the individual cold- formed steel cross-section shapes and allow the fast connection between the selected floor system and the beam. Such solution also enables the easy disassembly of the system.

Particularly, in another embodiment, the connector piece is a threaded rivet nut (3.2), and the connection between a floor slab (2.1) and a horizontal linear element (1.1) is provided by means of a bolt type connection adapted to pass through the floor slab (2.1) in order to engage the threaded rivet nut (3.2) placed on the horizontal linear element (1.1). Additionally, the floor slab (2.1) may further comprise pocket holes (2.4) and coupling devices through which the self-drilling screws (3.1) are inserted into the slab (2.1). The use of pocket holes (2.4) and coupling devices allows to easily assemble and disassemble the entire composite beam by tightening or untighten the connecting bolts passing through the pocket holes and coupling devices.

In another embodiment of the system, the floor slabs (2.1) are made of a mixture comprising at least lightweight concrete (1.6); preferably, a floor slab (2.1) comprises composite lightweight concrete slab (2.2) and a profiled steel deck (2.3).

Alternatively, the floor slabs (2.1) are made of CLT.

In another embodiment, the system further comprises light steel wall frames; said wall frames being assembled to the structural elements (1) by means of rivet nut type connectors (3.2). The light steel wall frame assembly is used to increase the lateral stiffness of the system.

As will be clear to one skilled in the art, the present invention should not be limited to the embodiments described herein, and a number of changes are possible which remain within the scope of the present invention.

Of course, the preferred embodiments shown above are combinable, in the different possible forms, being herein avoided the repetition all such combinations.

REFERENCES

[1] Yu, W.-W. and Laboube, R. (2010), Cold-Formed Steel Design - Fourth Edition, John Wiley & Sons, Inc., USA, 767 p.

[2] Dubina, D., Ungureanu, V., Landolfo, R. (2012), Design of cold-formed steel structures. Eurocode 3: Design of steel structures. Part 1-3: Design of cold-formed steel structures, ECCS - European Convention for Constructional Steelwork, Wiley-Blackwell, 676 p.