Patent Application
20250129558
The present invention relates to the field of civil engineering involving structural elements or tensioning elements e.g. tendons, which are to be detensioned, demounted or replaced. In addition, the detensioning system and method according to the present invention are suitable to detension structural elements and/or tensioning elements that are being pre-tensioned at a stressing force of for instance 4000 kN or 8000 kN or more.
Structural elements or tensioning elements of civil engineering structures such as bridges or columns need to be maintained or replaced from time to time in order to ensure their safety. These pre-tensioned structural elements or tensioning elements needs to be detensioned in a controlled manner before being demounted and replaced completely.
Patent document DE102017201907 A1 discloses a method for replacing a tensioning element of a large civil structure such as a suspension bridge with towers in the structure thereof. A number of mobile temporary hangers are placed on the upper cable to be replaced, the cable to be replaced is located in the lower portion of these hangers and the cable is removed from the anchors thanks to the mobile temporary hangers that are connected to upper cable. These hangers can be moved towards the deck of the bridge in order to remove the cable to be replaced. This solution is complicated to set up. Moreover, it is only suitable to detension to certain types of structural elements or tensioning elements such as the one described therein.
A “window cutting method” is also known in the art for the detensioning of structural elements or tensioning elements of a civil structural. This de-tensioning method consists of providing several windows along the tendon (tension element), where the protecting sheathing and grout surrounding the strands is removed. The tendon (tension element) is then cut by gas torch or remote-controlled diamond wire strand by strand in one or two windows. As the strands are cut, the force in the remaining strands increases and eventually rupture due to overstress. The sudden rupture of the remaining strands leads to a high residual force release which cannot be fully controlled and might in the process of sudden release cause an impact to the surrounding structure. The impact of the sudden residual force release may be reduced by providing additional damping; however, the force release is not fully controlled and there remains a degree of uncertainty to the implications to the surrounding structure. The above description covers the usual case of a tendon (tension member) formed by a set of individual strands, but it is also applicable to other types of tendon (tension member), e. g. tendon composed of wires or ropes
Therefore, there remains a need to find an improved system and improved method for a fully controlled de-tensioning method and complete force release of the tension element to enable the replacement of structural elements and/or tensioning elements that are being pre-tensioned or pre-stressed.
In the present invention, it is proposed that the tendon force of the structural element or the tensioning element is transferred to the stressbars of a bracket system (e.g. presently described detensioning system) clamped to the structural element or tensioning element (e.g. tendon) which are being pre-stressed, with the objective to reduce the tendon force in at least a portion of a structural element or tensioning element. The tendon is then cut in said portion which has been detensioned, for example in between two activated clamping devices. Once the tendon has been cut, the restrained stressbars of the detensioning system can be released in a controlled manner by de-tensioning the stressbars for instance through hydraulic cylinders, which in turn will release the tendon force over the full tendon length.
The detensioning system according to the present invention can be realised through at least one clamping device. Nevertheless, it is also foreseeable that the clamping device is provided on both sides of the portion of the structural element or the tensioning element to be detensioned. Thanks to the detensioning system which comprises at least one clamping device, wherein the clamping device provides a substantially elongated, annular cavity comprising a gradually declining diameter along a longitudinal axis of the elongated annular cavity shaped by at least one peak and one groove on the internal surface profile of the clamping device, the detensioning system and particularly the clamping device according to the present invention can be built more compact compared to other clamping system, for instance a clamping system comprising a cylindrical annular cavity, as the clamping device according to the present invention allows higher gripping force to the tendon.
Moreover, the clamping device according to the present invention may comprise for instance one, or more preferably with two half conical clamps (e.g. machined high-strength steel sections), which may then be bolted together to form a conical stressing clamp, comprising at least one substantially annular cavity. Apart from the two halve (or “U-shape”) conical clamps, the clamping device may also comprise other mechanical components such as sealing plates, bolts, gasket seals, hydraulic cylinders and etc. to form a functioning clamping system. The detensioning system further comprises stressbars to allow a portion (e.g. between two clamping devices) of the tendon force to be transferred thereto before detensioning of the remaining length of the tendon is taken place. Prior to the installation of the detensioning system such as the clamping device, the sheath and/or grout around the surface of the tendon may be chiselled away partially or completely so as to increase the friction (or the grip) of the clamping device to the tendon (when the inner element is introduced to the annular cavity). One or more inner elements can be introduced to the substantially elongated, annular cavity provided by the conical clamping device. The inner element can be a preform element or can be formed by a filler hardening material such as a grout.
A first aspect of the invention is to provide a detensioning system for detensioning a portion of a structural element or a tensioning element, comprising
A second aspect of the invention is to provide a detensioning method for detensioning a portion of the structural element or a tensioning element, comprising the following steps:
According to a third aspect of the invention, it relates to a use of the detensioning system according to present invention in detensioning a portion of a structural element or a tensioning element.
According to some embodiments, each of the clamping device is formed by at least two half clamps, wherein the two half clamps are joined together by mechanical fixing means, wherein one or two clamping devices are provided to each side of the portion of the structural element or the tensioning element to be detensioned. This allows the clamping device to be installed and de-installed easily.
According to some embodiments, the clamping device comprises a surface profile, arranged to form a substantially elongated, annular cavity having multiple segments, defined by multiple grooves and peaks, wherein each of the segment of the annular cavity comprises a gradually declining diameter along the longitudinal axis of the elongated, annular cavity. This allows an even higher gripping force to the tendon.
According to some embodiments, the substantially elongated, annular cavity comprises one or more segments, wherein each segment of the annular cavity comprises at least one channel for introducing of the filler hardening material and at least one channel for venting of the filler hardening material, wherein the filler hardening material is introduced through the channel into the substantially elongated, annular cavity formed by the clamping device, such that the one or more inner elements that is hardened comprises a reversed impression of the internal surface profile of the clamping device, or comprises a similar impression as the surface profile of the annular cavity. This allows the filler hardening material to be introduced into the cavity.
According to some embodiments, the substantially elongated, annular cavity comprises one or more segments, wherein the segments are provided in a trapezoidal or a conical form, or a wedge when viewed from a longitudinal section, so as to increase the longitudinal force transferred between the structural element or the tensioning element to be detensioned and the clamping device, through the one or more inner elements. The different forms of the segment can be chosen based on the actual need and depends on the situation.
According to some embodiments, the substantially elongated, annular cavity comprises one or more segments, wherein each segment of the annular cavity is provided with same or different volumetric capacity for accepting the filler hardening material for the formation of the one or more inner elements such that each segment of the one or more inner elements comprises the same or different amount of filler hardening material.
According to some embodiments, the substantially elongated, annular cavity comprises a periphery with edges and/or a substantially linear periphery. In other words, the annular cavity formed by the clamping device may not have corners (round) or may have one or more edges and corners.
According to some embodiments, the substantially elongated, annular cavity comprises one or more segments, comprising a surface profile defining between two and ten segments or at least two, three, four, five, six, seven, eight or more segments, defined by multiple grooves and peaks, wherein each of the segment is provided in a conical shape, or a wedge when viewed from a longitudinal section. It has been found that generally the more the number of segments, the higher the gripping force to the tendon.
According to some embodiments, the substantially elongated, annular cavity comprises one or more segments, wherein each segment of the annular cavity is provided in form of a trapezoid or a cone, or a wedge when viewed from a longitudinal section, wherein the wedge angle is provided in between 5° and 65°, preferably between 10° and 60°, between 15° and 55°, between 20° and 50°, between 25° and 45°, between 30° and 40° or preferably at around 30°.
According to some embodiments, the one or more inner elements is made by a filler hardening material, which is a grout such as an epoxy-based or a concrete-based grout. Filler hardening material is advantageous over such as pre-forms as the shape is only formed upon the hardening of the hardening material.
According to some embodiments, one or more displacement sensors are provided either in between the clamping devices located on at least one side of the portion of the structural element or the tensioning element to be detensioned, or to the far end of the clamping devices to a fixed reference.
According to some embodiments, strain gauges are provided to the detensioning system, for instance the strain gauges are mounted on the surface of the portion of the structural element or tensioning element to be detensioned, in the filler material and/or at fixings between two half clamps.
According to some embodiments, a cutting machine such as a diamond wire cutting machine is provided and set up before stressing operation begins.
According to some embodiments, the clamping device configured to form one or more annular cavities comprises two half clamps, mechanical fixing means such as high strength bolts, debonding agent, sealing plates, sealant, stressbars and/or instrumentation for monitoring purposes such as through strain gauges, displacement sensors and/or video camera.
According to some embodiments, the detensioning method according to the present invention further comprising one or more steps of
By “about” or “approximately” in relation to a given numerical value, it is meant to include numerical values within 10% of the specified value. All values given in the present disclosure are to be understood to be complemented by the word “about”, unless it is clear to the contrary from the context.
The indefinite article “a” or “an” does not exclude a plurality, thus should be treated broadly.
To this end, it is disclosed that the stressbar can be replaceable with other similar component or element having similar function. For instance, instead of stressbar, one or more strands or ropes can be used instead of the stressbars.
The term “structural element” as used herein refers to a basic component of a building structure which forms a structural frame building structure such as beams, pillars, roof terraces, slabs, columns, girders and/or other structural members and connections.
The term “tensioning element” as used herein refers to an element which carries tension and no compression. The tensioning element may be provided to such as bridge cable in order to support the main deck where the traffics flow. The tensioning element described herein may be for instance a tendon.
The inventors of the present invention propose a detensioning system and a method for a controlled de-tensioning of the structural elements or tensioning elements (e.g. tendons) which have previously been pre-tensioned, involving one or more clamping devices of the detensioning system espoused herein. The clamping devices are mounted for example in between the cutting location, and both the clamping devices are stressed via stressbars against one another for instance to 90% of the tendon force before cutting the tendon. The detensioned tendon section (in between the clamping devices) can then be cut by for instance a diamond wire cutting machine, and subsequently the tendon can be de-tensioned in a controlled manner by de-tensioning the stressbars with hydraulic cylinders (e.g. jacks) until the entire tendon force of the tendon is released.
The structural elements or the tensioning elements to be repaired or replaced e.g. tendon, in the present context are usually pre-tensioned at a very high tension. For instance, the tendons can be stressed to at least 4000 kN or more. Before cutting the aged or damaged tendon, the tendon force has to be transferred so that the tension of the tendon can be detensioned in a controlled manner before the tendon can be safely cut. In doing so, at least one clamping devices is arranged on each side of the structural element or the tensioning element to be detensioned.
In case a detensioning system comprising one or more clamping devices are used to detension the tendon, annular cavity which is generally a cylindrical in shape formed by the clamping device may be suitable to be used in the detensioning operation. However, the cylindrical annual cavity has lower gripping force compared to the clamping device in the present invention, wherein the substantially elongated, annular cavity comprises a gradually declining diameter along the longitudinal axis of the annular cavity. This in turn allows a smaller and more compact clamping device as well as detensioning system. This is advantageous when limited space is available for the replacement work to be carried out.
According to the gist of the present invention, the detensioning system comprises at least one clamping device 120 arranged on at least one side of the portion 20a of the structural element or the tensioning element to be detensioned, wherein the clamping device 120 having an internal surface profile, arranged to form a substantially elongated, annular cavity 55c surrounding the structural element or the tensioning element to be detensioned, comprising an empty space for receiving one or more inner elements 55 to be introduced therein, wherein the substantially elongated, annular cavity comprises a gradually declining diameter along the longitudinal axis of the elongated annular cavity 55c shaped by at least one peak and one groove of the internal surface profile of the clamping device 120.
The inner element may be a preform element which is placed within the annular cavity of the clamping device (e.g. clamped by the clamping device), or may be a grout or a filler material to be introduced into the space within the annular cavity formed by the clamping device such that a filler hardening material having a reverse impression of the formwork can be formed encircling the structural element or the tensioning element to be detensioned.
In the above exemplified embodiments, once the set-up of the detensioning system 100 is in place, the tendon force (of the tendon to be replaced 20) in the portion 20a can be transferred to the detensioning system 100 such to the stressbars 140 with the help of for instance hydraulic cylinders 160 (e.g. centre hole jacks) mounted on one or both sides of the clamping devices 120.
Thanks to the conical clamping device 120 which comprises an elongated and annular cavity 55c, wherein the cavity 55c comprises a gradually declining diameter along a longitudinal axis X of the annular cavity (
As the clamping devices 120 are designed to comprise an annular cavity 55c comprising a gradually declining diameter along a longitudinal axis X of the annular cavity, the gripping force of such a clamping device 120 having a unique internal surface profile (e.g. wedge shape profile when viewed from a longitudinal section) is higher, therefore tendon force in the portion 20a can thus be effectively reduced to a nominal force through the smaller size clamping device 120, as shown in the examples demonstrated in the
A number of bolts may be used to serve as a mechanical fixing means 128 to tighten the two half clamps 120a, 120b when the two half clamps 120a, 120b are aligned. In this connection, it is disclosed herein that each of the segment 135 may comprise at least one channel 182 for injecting of the filler hardening material 50 (not shown in
It is disclosed herein that the inner element 55 may be a preform which has a pre-determined shape, wherein the one or more inner elements 55 is first provided to surround the tendon 20, subsequently surrounded by the two half clamps 120a, 120b. Alternatively, the inner element 55 may be formed by injecting a filler hardening material 50 or a grout through the one or more injecting channels 182. The inner elements 55 formed by the filler hardening material generally comprises a reverse impression of the internal surface profile of the clamping device 120.
The inner element 55, which are inter-connected longitudinally, when viewed from a longitudinal view, resembles a six wedged shape “teeth” as illustrated in the
The filler hardening material 50 or grout for forming the one or more inner elements 55 may be a high strength epoxy grout (e.g. Sikadur) or a high strength cement-based grout (e.g. Ductal).
For instance, an epoxy-based (e.g. Sikadur) may be used as a filler material 50 for the mould 55 formation. Such filler material 50 are particular suitable to be used for certain applications as it achieves the following properties:
Alternatively, Ductal or ultra-high-performance cement-based grout with early strength development may be used to form the inner element 55. The ductal or ultra-high-performance cement-based grout is based on the following properties:
The de-tensioning system 100 according to the present invention comprises clamping devices 120 as well as stressbars 140. Suitable stressbars are for instance high strength bars (Grade 1030 diameter 56) as they comprise good properties as follows:
Type VSL CT Stressbar (Bar Grade 1030), nominal tensile strength 1,030 MPa; Alternatively, SAS Stressbar (Bar Grade Y 1050/1035, nominal tensile strength 1,050 MPa)
A number of hydraulic cylinders 160 (or bar jacks) may be used in the present invention and not limited to certain jacks. For instance, double-acting hollow core bar jacks (also called centre hole bar jacks) are mounted on top of a stressing chair 165, which in turn is bearing against the back of the clamping devices. The bar jacks are used to stress as well as to de-tension the stressbars 140 after cutting of the tendon 20a. Ideally, the bar jacks should be calibrated before use. Suitable bar jacks may have properties as follows:
As explained, the tendon force is able to be transferred temporarily to the stressbars 140 of the detensioning system 100, through the clamping devices 120 which is clamped to the tendon 20, as it allows the tendon force in between the clamping devices 120 (the portion 20a) to be reduced to a nominal force before the portion 20a can be cut. After cutting the tendon 20, the stressbars 140 of the detensioning system 100 are released and detensioned in a controlled manner through the hydraulic cylinders 160, which in turn will release the tendon force over the full tendon length.
Prior to the installation of the clamping devices 120, the sheath and/or grout of the tendon may be chiselled away to increase the friction. After installation of the clamping devices 120, the space between the tendon 20 and clamping device 120 (which is the annular cavity 55c) is filled with the inner element 55 (e.g. filler hardening material 50). The internal surface profile of the clamping device 120 comprises at least one groove 133 and peak 134, forming at least a segment 135, wherein the segment 135 comprises a gradually declining diameter along the longitudinal axis X. Such conical annular cavity is advantageous compared to cylindrical annular cavity as it not only enhances the gripping force of the clamping device, it also prevent the displacement of the inner element in the longitudinal axis direction.
According to a most preferred embodiment, the annular cavity 55c comprises six segments 135 connected longitudinally, wherein each of the segment 135 are provided in a conical shape (but without the vertex or the tip region). The wedge angle α can be provided in between 10° and 45°, while 30° being the preferred wedge angle.
Once the defect or aged tendon is identified, the HDPE around the surface of the tendon 20 where the clamping devices is to be placed may be firstly removed, followed by chiselling away the grout in order to expose the core of the strands E (
Approximately three strain gauges 129 may then be installed at the lower half of the inside of the clamping device 120a (cf: 129i of
Once the preparation works of the lower half of the clamping device 120a is completed, similar preparation works can be repeated to the upper half of the clamping device 120b, for instance by applying the debonding agent 127 and the strain gauge 129 as explained (
The filler material 50 such as grout can be prepared and introduced through a lower grout vent channel 182 while another channel 184 can be seen in the
Once the injection of the filler material 50 is completed, stressbars 140 (diameter 56) are installed from one end to the other end of the clamping device 120 (in case one clamping device 120 is provided on each side of the tendon 20 to be cut as shown in
The tendon may then be cut by a diamond wire cutting machine 150 for instance, as illustrated in
Under such set up, the tendon 20 can be cut remotely with the diamond wire cutting machine 150. After the tendon 20 is cut, the force is fully transferred to the stressbars 140 and the clamping devices of the detensioning system 100. Subsequently, the stressbars 140 are released by retracting the centre hole bar jacks. The centre hole bar jacks can be remotely operated. For instance, a retracting of 150 mm of the bar jacks allows the tendon to be fully de-tensioned.
To this end, it is disclosed that for example two type of instrumentations can be installed for monitoring purposes. The first type of the instrumentation is the strain gauges 129 where they are being installed to monitor the stresses of the clamping devices 120. As an example, three strain gauges 129, each may be installed at the lower and the upper half of each clamping device 120a, 120b. The strain gauges 129 are mounted on the inside of the clamp and are connected with a wire through the grout vent 182.
The second type of the instrumentation is the displacement sensors where they are installed to monitor the movement of the clamping devices during the stressing and de-tensioning operation. In this case, the position of the clamping devices 120 to a fixed reference and the gap between the two clamping devices 120 can be monitored with displacement sensors.
To this end, it is disclosed that several video cameras can furthermore be installed to allow remote controlled monitoring of the critical operation steps without having to go near to the tendon. This enables operations like stressing the stressbars with the bar jacks, monitoring the displacement, cutting and de-tensioning of the tendon to be carried out remote controlled without human intervention. To confirm the tendon has been fully cut, a suitably placed LED strip can be mounted at the cutting location of the tendon, providing a signal at the monitoring station when the tendon is fully disconnected.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/076418 | 9/24/2021 | WO |
