TECHNICAL FIELD
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The invention relates to the fields of structural engineering and materials engineering and can be used for the production and characterisation of multicomponent structural composites. More specifically, it discloses anchoring means for tie components.
BACKGROUND ART
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This invention covers different types and techniques of combining of composite elements. There are the manufacturing and testing applications for cement- and polymer-based elements comprising tie components (bars, strips, profiles, laminates, etc.) as an integral part of the structure. Another kind of application is related to reinforcement and testing techniques using pre-stressed Fibre-Reinforced Polymer (FRP) plates, sheets, and laminates. The latter technology is useful for strengthening the existing structures to secure the structural integrity and provide additional support to them. This invention also enables complex combinations of various reinforcing or strengthening systems.
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The group of reinforcing bars and reinforcement equipment are described in Fields & Bischoff (2004), Tension Stiffening and Cracking of High-Strength Reinforced Concrete Tension Members, ACI Structural Journal. This anchorage has two anchoring units (massive anchored concrete blocks) at the ends of the tensile element, in which the longitudinal groups of reinforcement bars of the test element are anchored, and the anchor rods. The anchor rods are pierced through each formed support block, where one end of the anchor rod is secured with plates resting on the inner plane of the concrete block and the other ends of the rods are fixed to a tensioning machine. Attaching the anchor rods to the test bench requires additional traverses that connect all anchor rods. The reinforced element can thus be connected to standard test equipment. The fastening equipment described does not guarantee the positioning of the reinforcement bars in the cross-section of the element. It is also impossible to position the reinforcement bars at a short distance from each other. Massive anchored concrete blocks at the ends of the element significantly increase the weight of the specimens. With this geometry of the specimen, it is difficult to interpret the cracking parameters of the element, as it is necessary to know the distance from the anchor block to the formation of a crack.
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Khorami et al. (2020) proposed an alternative setup enabling characterisation of structural elements reinforced with multiple bars. This apparatus, however, was developed for the application of steel reinforcement only.
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Reinforcing systems and techniques using Carbon Fibre-Reinforced Polymers (CFRP) are recently disclosed in some research papers, for example, Mohee et al. (2017), You et al. (2012), Correia et al. (2015), Hosseini et al. (2017), Michels et al. (2014), Hosseini et al. (2018). CFRP materials are employed in many applications due to their beneficial features such as strength, flexibility, etc. The techniques of CFRP stretching, employing pre-stretched CFRP ties, sheets and testing CFRP reinforcements typically comprise anchors with metal plates grasping and clamping a CFRP sheet. Further, this CFRP element with the anchoring equipment is employed in different applications such as reinforcing of old structures having cracks (Hosseini et al (2017), Hosseini et al (2018)), reinforcing concrete constructions and elements with pre-stretched CFRP bands providing stretch gradient to the element being reinforced (Michels et al (2014)), or testing properties of CFRP band stretching and reinforcing. However, in the listed prior art sources CFRP stretching is employed only on single CFRP bands or in Hosseini et al (2018) there is a stretched two CFRP bands in parallel, the anchors grasping two tapes simultaneously.
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The patent application
WO2018072589A1 discloses an automated and synchronized control system for bundled steel strand anchoring. The system is provided with a pre-tensioning device, an integrated tensioning device, a hydraulic pump station, and the main control center. Each part is organically connected via high-pressure hydraulic tubing, a data transmission cable, and a control component. The main control center issues a command and the hydraulic pump station then actuates the pre-tensioning device and integrated tensioning device to perform a tensioning operation under a pre-configured program. An integrated multi-piston, single-shaft pre-tensioning jack comprises a hydraulic cylinder and a piston. The hydraulic cylinder is provided with multiple piston openings. Each of the pistons is installed within a piston opening to form an integrated multi-piston structure. By using the pre-tensioning jack with a structure comprising a single hydraulic cylinder and multiple pistons a high degree of integration is achieved. The invention can realize simultaneous and automated pre-tensioning of multiple steel strands, automated inverse tensioning of an ultra-long steel strand with a jack, continuous pre-tensioning, faster operations, and lower labor costs. A single pumping station can achieve pre-tensioning and integrated tensioning. A single main control center can simultaneously control multiple pumping stations, realizing simultaneous pre-tensioning and integrated tensioning of multiple pre-stressed strands. This system allows to anchor strands of bundled steel in a synchronous way. The strands are attached individually and so on.
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The
Chinese utility model CN205630974U relates to pre-tensioning system precast beam pedestal, including rectangular shaped plate bottom plate and transmission column, transmission column-parallel arrangement is in the bottom plate both sides, and stiff end gooseneck and stretch-draw end gooseneck has been arranged respectively to the transmission column both ends, be connected with the tensioning equipment on the stretch-draw end gooseneck, arranged steel strand wires between stiff end gooseneck and the stretch-draw end gooseneck, when the tensioning equipment carries outstretch-draw to steel strand wires, steel strand wires and stretch-draw end gooseneck relative movement for the stiff end gooseneck is drawn to paste tightly in the transmission column tip, and simultaneous tension end gooseneck is overlaid tightly in transmission column's the other end. This pre-tensioning system precast beam pedestal has overcome the structure complicacy of traditional pedestal existence, extravagant material, and extravagant manual work and has made shortcoming long in time limit through the structural style of change pedestal, makes its simple structure, has practiced thrift the cost by a wide margin, has promoted the construction progress.
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The most relevant patent application
LT6275B discloses fastening equipment that can be used for producing and testing reinforced concrete elements. This equipment carries two symmetrical anchorage joints (3) of reinforcement bars (2) of a structural element (1). The anchorage joint embraces two plates (6) connected by central (7) and supplemental bars (8). Plates are used as permanent formwork for the casting of anchoring joints (3). The plates (6) have identically distributed holes for reinforcement bars (2) poured by concrete (9). The central bar (7) is connected to a tension device (4). A gap between the structural element (1) and anchorage joint (3) can be formed to measure the deformations of reinforcement bars (2). Element (1) and anchors (3) can be produced simultaneously and have the same or different filling (9). Supplemental equipment (10) can be used for shear restrain of anchorage joints (3).
However, this invention discloses reinforcement of composite elements still by internal bars or ties that are limited to a range of applications and constructions. -
In the present field of structural engineering and materials engineering, there is a need to manufacture pre-stressed composite systems with structural components produced from FRP materials having more complex geometry and shape of the cross-section than discussed above. The above prior art methods place a high demand on complicated production and testing equipment and require specific knowledge to operate it. Current techniques allow anchoring and aggregation of internal or external tie components, or each structural part separately in a bundle of ties. Thus, the present invention discloses an effective solution for a specific class of more complex constructions and applications.
SUMMARY OF THE INVENTION
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Special equipment and a new technique to distribute tie components in the cross-section of a structural element are the objects of the present invention. The proposed apparatus is useful for producing and testing of the composite members. Bars, sheets, laminates, strips, fibre strands, and profiles in various combinations can be used as structural components of structural elements made from cement-based or polymer-based composite materials. The equipment is also suitable for strengthening existing structures (including the application of near-surface mounted reinforcing systems). It can maintain the predefined position of the components, ensuring axial tension to the ties.
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A unique anchor assembly designed to fasten a complex set of the components is the specific feature of the invention. The anchoring joints ensure the design position of the tie assembly. The anchorage system enables to combine different materials varying the arrangement/distribution of the composite components within the cross-section. The filling of the anchorage blocks allows each part to deform differently in the anchoring zone, thereby equalising stresses of different composite components and, consequently, to reduce an eccentricity of the tie group. The choice of filler composition ensures the adaptive deformation of the anchor assembly as it allows control of the anchor strength and displacement of the components. That reduces the physical eccentricity of the composite structural member and allows the cast materials for producing the structural member to be varied.
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The equipment consists of two anchorage joints, each one comprising two spaced-apart plates and the central bar connected to the tensioning device. The two plates of each anchoring joint are perforated to ensure the design position of the tie components of the structural elements. The ties pass through the holes in the plates to fix them in the anchoring joints. The space between the plates of the anchor unit is filled with adhesive or other appropriate material. The anchorage blocks can be produced together with the element or separately to form a 3D cage enabling the application of pre-stressing technology. External tie components are either adhesively bonded to the newly formed lateral surfaces of the anchoring joints or fastened to the lateral surfaces by tailoring the external clamps shaped tightly around the filled anchoring joint.
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The shape of anchoring joint plates and external clamps can be tailored to fit the geometry shape of the external components (e.g., sheets, laminates, strips) having different cross-section, for example, zig-zag shaped profiles.
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According to the producing and testing layout, employing the above means of reinforcing and anchoring the structural cast member, further, the tensile load is transmitted from a standard tensioning machine to the reinforcing assembly of the structural member.
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According to the technique, the cast structural element and its anchoring joints can be made at the same production stage with the same composite filler (e.g., polymer- or cement-based composite), or the anchoring joints with the tie assembly can be made before the cast element is produced. Such flexibility of production steps allows preparing a specimen (structure member/construction element) by a single or few different stages and manufacturing pre-stressed construction elements. The latter procedure is also applicable for the strengthening of existing structures.
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There are gaps between the edges of the cast structure member and the anchorage joints. These gaps allow the measuring of displacements and control of deformations of tensioned internal and external tie components.
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Practical applications are focused on structural engineering and materials engineering as well as characterisation (testing) of the composite systems containing longitudinal tie components. The next chapter provides several embodiments of the invention.
DESCRIPTION OF DRAWINGS
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To understand a fixture for a group of reinforcing bars and reinforcing sheets for a structural member, and appreciate its applications, the following pictures are provided and referenced hereafter. Figures are given as examples only and in no way should limit the scope of the invention. The invention is explained in the drawings, wherein:
- FIG. 1
- depicts a schematic diagram of a fixture for a group of reinforcing ties for a structural cast member (Note: reinforcing strips or profiles with a more complex geometry of the cross-section can be positioned in the composite element in the same manner);
- FIG. 2 a-c
- depicts the construction of the anchorage block and fixture of an external reinforcing laminate plate by using the external clamping equipment: (a) the assembled anchorage block with fixing plates and connecting bolts; (b) anchorage block filled with the filling material between the fixing plates; (c) anchorage block clamped by an external clamp and fixing the external reinforcing lamination sheet to the anchorage block;
- FIG. 3
- shows an application example of equipment for the characterisation of tensile reinforced concrete elements. Three different composite tie groups are used: internal fiberglass-reinforced polymer rods, external carbon fibre reinforced polymer laminates, and carbon fibre reinforced polymer strips mounted near the surface of the element;
- FIG. 4
- shows an application of equipment for manufacturing pre-stressed reinforced concrete beams. The equipment is used for pre-stressing glass fibre reinforced polymer rods;
- FIG. 5
- shows an application of equipment for the strengthening of flexural members. The equipment is used to pre-stress carbon fibres laminate attached to the outside of the beam.
DRAWINGS - Reference numerals
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- 1 a structural element (or member) reinforced by internal and external ties anchored at both ends of the structural element;
- 2 Internal tie components, e.g. steel bars, basalt, aramid, glass or carbon fibre reinforced polymer strips, bars or profiles;
- 3 Anchorage block (or joint, or unit);
- 4 Standard connections (or terminals) of a standard tensioning machine;
- 5 Spherical hinges attached to the connections of the tensioning machine;
- 6 Fixing plate of the anchorage block;
- 7 The central bar of the anchorage block, connected to the tensioning machine through the spherical hinges;
- 8 Connecting bolts of the anchorage block;
- 9 Filing material (or filler) of the anchorage block (concrete, polymer, or other);
- 10 The external clamp of the anchorage block;
- 11 External reinforcing laminate plate, for example, made of CFRP and used for external reinforcement;
- 12 Fibre reinforced polymer bars (internal reinforcement);
- 13 Fibre reinforced polymer strips (near-surface mounted reinforcement);
- 14 Fibre reinforced polymer laminate (external reinforcement);
- 15 The gap between the anchorage block and the structural element being tensioned;
- 16 Displacement/deformation measurement equipment arranged in the gap between the anchorage block and the structural element.
DETAILED DESCRIPTION
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This chapter describes the anchoring equipment, producing method and characterisation technique in different applications.
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Anchorage equipment. The internal ties 2 of the structural element 1 are fixed into the anchorage blocks 3 that further are connected to the standard tensioning machine joints 4 using spherical hinges 5. The anchorage block 3 consists of two perforated fixing plates 6 having identical holes where the tie components 2 are inserted, the centre rods 7 connected to the standard tensioning equipment joints 4, and additional bolts 8 connecting two fixing plates 6 (FIG. 2 a). The spaces between the fixing plates 6 are filled with an adhesive material 9 (FIG. 2 b). Cement- and polymer-based concrete can be used for that purpose. The anchorage joint 3 assemblies may have additional clamping equipment 10 to increase the anchoring confinement (FIG. 2 c). When connecting the centre rods 7 to the tensioning machine (e. g. UMM-200), additional spherical hinges 5 can be used to provide central tensioning. There is a gap 15 between the anchorage joint assembly 3 and the structural member 1 to allow displacement/deformation sensors 16 to be mounted to the ties 2 and/or external plates 11.
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The proposed anchorage equipment (comprising two anchorage joints 3) allows manufacturing/preparing the structural element 1 in different ways:
- In the first case, the entire composite system comprising the two anchorage joints 3 and the structural element 1 is manufactured simultaneously using the same filler 9.
- In the second case, the anchorage blocks 3 and the structural element 1 can be manufactured by more than one stage: fixing plates 6 assembled with connecting bolts 8 and reinforcing bars 2 are pierced through the design holes of the fixing plates 6. Further, the space between the fixing plates 6 is filled with the filling material 9 before the production of the structural element 1. After the filling material 9 hardened and anchorage blocks 3 formed, in the next step the reinforcement bars 2 can be tensioned thus forming the pre-stressed structural element 1 or the pre-stressed design of reinforcement element 2 and 11 groups.
- Alternatively, the anchorage blocks 3 can be tailored to fit the shape of an existing structure (not shown). After the filling material 9 is hardened, the external tie components 11 and near-surface mounted strips 13 are fixed using an adhesive and the gripping system 10. A tensile machine enables to pre-stress these ties. The application of such setup allows for strengthening the existing structure.
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In any way, the structural element 1 with the prepared anchorage blocks 3 is attached via the central rods 7 from the fixing plates 6 to the tensioning machine connections 4. The tensioning machine can be employed without integrated hinges (not shown), or with spherical hinges 5, or with pin hinges (not shown), thus additionally fixing the structural element 1. The tensile load is transmitted through the anchorage block 3 to the tie components 2 of the member 1. A gap 15 is provided between the anchorage joints 3 and the structural element 1, thus allowing the measuring sensors 16 to be directly attached to the ties 2 for monitoring the deformations.
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The deformation sensors 16 measure the deformations of the internal and external tie components 2 and 11, as shown in FIG. 1.
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The invented anchorage system is compatible with reinforcing ties of various materials and geometries and can be used for the production of pre-stressed structural composite members and characterisation (testing) of the tensile elements having longitudinal tie components.
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Anchoring method. The anchoring method for pre-stressing and testing of a group of different reinforcing elements comprises steps at least of:
- 1) Preparing the fixing plates 6 of the anchoring blocks 3 with the desired configuration for a design of groups of internal tie components 2. The fixing plates 6 have holes corresponding to the ties 2 and the near-surface mounted strips 13 inserted through the plate 6 that secures the design position of the tie components.
- 2) Assembling the anchorage blocks 3 each one of two plates 6 and connecting with sets of bolts 8, mounting central tensile bars 7, inserting into the plate 6 holes the internal ties such as internal bars 2 and/or internal near-surface strips 13 that are required by the design.
- 3) Filling the two anchorage blocks 3 with the filling material 9 that can be a type of concrete, polymer or other applicable cast material. Further, the filling material 9 is allowed to harden.
- 4) Preparing side surfaces of the anchoring blocks 3 for attaching and clamping the external tie components, for example, laminate plates 11 made of a carbon fiber-reinforced polymer (CFRP).
- 5) Attaching the external reinforcement elements 11 to the prepared lateral surfaces of the anchorage blocks 3, for example, bonding with adhesives, grasping with special friction plates and clamping tightly with the external clamp 10 to the block 3.
- 6) Providing tension force from the tensile machine to the anchorage joint 3, to the anchored groups of internal ties 2 and external ties 11 and to the structural element 1, correspondingly.
- 7) The deformations of the reinforcement is measured in the pre-defined gaps between the anchorage blocks 3 and the structural element 1 being tensioned between the two anchorage brocks 3.
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The same method and anchorage steps are applicable for various combinations of composite tie components. A single reinforcing type can also be used. For example, the set of internal bars 2 can be used as a single reinforcing group. In this case, all anchorage steps are remaining the same, i.e. the clamping 10 is also recommended for ensuring the additional confinement of the anchorage blocks 3. Alternatively, the external plates 11 (with or without the pre-stressing) can be used for the strengthening of existing structures.
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Embodiments of the anchoring apparatus. The preferred embodiment of the present invention is presented in FIG. 3. It depicts the general application of the anchoring system for characterisation of tensile composite elements 1. There are three tie components used for the composition of the structural member 1: the inner steel or various fibre-reinforced polymer rods 12, the external fibre reinforced polymer laminate plates 14 and the near-surface fibre reinforced polymer strips 13.
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FIG. 4 demonstrates an alternative embodiment of the invention equipment. The anchorage blocks (3) are used to pre-stress fibre reinforced polymer rods 12 for producing pre-stressed composite beams.
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FIG. 5 shows the application of the proposed equipment for reinforcing flexural composite members. The apparatus is used to tension ties attached to the tensile surface of the beam. For this application the size of the anchorage blocks (3) depends on the flexural stiffness of the ties (14). For low flexural stiffness ties (14) size of the perforated plates (6) can be diminished and the number of the connecting bolts (8) can be reduced. This application is typical for the strengthening of the existing structures.
CITATION LIST
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Correia, L., Teixeira, T., Michels, J., Almeida, J. A., & Sena-Cruz, J. (2015). Flexural behaviour of RC slabs strengthened with prestressed CFRP strips using different anchorage systems. Composites Part B: Engineering, 81, 158-170. https://doi.org/10.1016/j.compositesb.2015.07.011
- Fields, K., & Bischoff, P. H. (2004). Tension stiffening and cracking of high-strength reinforced concrete tension members. Structural Journal, 101(4), 447-456.Hosseini, A., Ghafoori, E., Motavalli, M., Nussbaumer, A., & Zhao, X. L. (2017). Mode I fatigue crack arrest in tensile steel members using prestressed CFRP plates. Composite Structures, 178, 119-134. https://doi.org/10.1016/j.comp-struct.2017.06.056
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Hosseini, A., Ghafoori, E., Motavalli, M., Nussbaumer, A., Zhao, X. L., & Koller, R. (2018). Prestressed unbonded reinforcement system with multiple CFRP plates for fatigue strengthening of steel members. Polymers, 10(3), 264. https://doi.org/10.3390/polym10030264
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Khorami, M., Navarro-Gregori, J., & Serna, P. (2020). Experimental methodology on the serviceability behaviour of reinforced ultra-high performance fibre reinforced concrete tensile elements. Strain, e12361. https://doi.org/10.1111/str.12361
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Michels, J., Martinelli, E., Czaderski, C., & Motavalli, M. (2014). Prestressed CFRP strips with gradient anchorage for structural concrete retrofitting: Experiments and numerical modeling. Polymers, 6(1), 114-131. https://doi.org/10.3390/polym6010114
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Mohee, F. M., Al-Mayah, A., & Plumtree, A. (2017). Development of a novel pre-stressing anchor for CFRP plates: Experimental investigations. Composite Structures, 176, 20-32. https://doi.org/10.1016/j.compstruct.2017.05.011
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You, Y. C., Choi, K. S., & Kim, J. (2012). An experimental investigation on flexural behavior of RC beams strengthened with prestressed CFRP strips using a durable anchorage system. Composites Part B: Engineering, 43(8), 3026-3036. https://doi.org/10.1016/j.compositesb.2012.05.030
