The invention relates the field of ducting utility fluids through a structure. In particular, but not exclusively, the invention relates to systems for circulating fluids through a building for purposes such as heating and cooling, or to systems for conveying fluids from one part of a structure to another for purposes such as ventilation, fire prevention and the like.

In the context of the present application, utility fluids are understood to mean any liquids or gases which are to be circulated through a structure, or conveyed from one part of the structure to another, for purposes related to the use of the structure. Utility fluids to be circulated through the structure might include heating fluids (usually air or water) or cooling or air conditioning (such as air, water or a refrigerant), or cleaning (vacuum supply, for example). Fluids to be delivered from one part of a structure to another include hot and cold water supplies, ventilation (air), or fire retarding fluids (water, foam, C0 ₂ ), for example. Fluids are generally transported through buildings and similar structures using a network of pipes or ducts, which can be fitted during the construction of the structure, or after completion of the structure. In many cases it is important that the pipework and ducting be hidden, or at least routed around certain spaces in the structure.

The structures which are referred to in this application may include any structure, which comprises parts maintained in compression using tensioning elements enclosed within ducts. Example include buildings or civil engineering structures such as walls, bridges, roads, tunnels, runways and power stations. Such structures frequently use pre-stressing or post-tensioning (PT) tendons or similar elements in tension to hold parts of the structure in compression, such as concrete beams, pillars or floor or wall slabs.

Pre-stressed concrete is commonly used for producing beams, floors, bridges and other structural elements which require a higher strength or a longer span than ordinary reinforced concrete. Pre-stressing tendons

(generally high-tensile steel cables or rods) are used to provide a clamping load which puts concrete under compression. The invention can be used with the types of pre-stressing, such as unbonded post-tensioning, in which the stressing tendons are free to move at least longitudinally relative to the structure they are stressing. In cases where tendons pass through a body of concrete, for example, unbonded tendons are commonly positioned in ducts or channels through the concrete. Alternatively, tendons may be coated with grease and encased in a plastic sheath before being cast in the concrete, in which case the tendon is relatively free to slide within the sheath. In other cases, tendons may pass through free space, in which case they will still normally be enclosed in a sheath, a duct or a coating of some kind to protect the tendons from corrosion.

Post-tensioning is conventionally used in addition to conventional reinforcement using rebar steel (bars or rods of reinforcing steel). Indeed rebar steel may be used to provide or reinforce anchor points for PT tendons.

Ducts suitable for containing tendons are often pre-formed tubes made of an impermeable substance such as plastics or metal, and these tubes may be positioned in a volume which is then filled with concrete. When the concrete has cured, the tendons are fed through the ducts, an anchor is attached to one end of each tendon and a hydraulic jack is attached to the other end. The jack puts the tendon under a predetermined amount of tension, taking into account the elastic behaviour of the tendon. Then another anchor is used to secure the jacked end of the tendon and the jack is then removed, leaving the tendon in tension and the concrete therefore under compression.

In order to protect tendons against corrosion, the ducts can be filled with a grease, wax or cement-based grout after the tendons have been tensioned. The ducts are then sealed to further protect the tendon against the ingress of any water or humidity. Grouting materials may be pumped in under pressure, either as compounds which then set solid, or as thixotropic

substances which remain in place once the ducts are filled. Such an

arrangement is disclosed, for example, in European patent application

EP0875636 (Freyssinet). It has hitherto been generally accepted that such filler materials should be solid or highly viscous - either to prevent water or air from reaching the tendon, or to help keep the filler in place, or to provide a

mechanical connection between the tendon and the duct.

It is usual for each individual tendon to be arranged to cover one span of the structure being tensioned. However, United States patent

US3579931 (Lang) discloses an arrangement in which a single tendon can be used to cover multiple spans of a structure.

Note that the term "concrete" shall be used throughout this application as an example of a structural material which is to be held in compression. The invention also applies to any other materials and structures to which tensioning elements can be added, and the term "concrete" should be understood to include such materials and structures when interpreting this text. Similarly, steel cables and rods are given as examples of tensioning tendons, but the terms "steel" and "tendon" should be understood to refer to any kind of material which can be tensioned to put a structure under compression.

References to a single tendon should also be understood to include groups or bundles of tendons. The term "fluid" is understood to mean a gas or a liquid. In the case of a liquid, the term is used to refer to substances which flow readily at the temperatures at which they are normally used.

Heating systems, cooling systems, ventilation, hot and cold water supply, fire-prevention, suction and other fluid systems which are installed in most buildings require the installation of pipework or ducting for conveying liquids or gases around the building. Other types of concrete structure may also require fluid circulation systems - roadways, bridges or runways may for example incorporate pipework for ground source heat extraction, or for low- temperature heating to remove ice or snow from the surface, or for delivery of fire-extinguishing fluids to fire-prevention access points. The circulation of fluids around a building is conventionally arranged by means of pipework or ducting which is fitted to the building once the structural work has been completed. Pipework for underfloor heating/cooling systems, also known as radiant hydronic systems, is conventionally embedded in a screed laid on top of structural concrete. It has also been proposed to embed pipework in the structural concrete itself, and even to use tubular instead of solid rebar steel in concrete, such that the rebar tubes can be used for heating or cooling.

Examples of such rebar tube proposals can be found in European patent application EP1512805 (Aicher), or French patent applications FR1309969 (lenciu) and FR00750875 (van Dooren).

One disadvantage with conventional PT structures is the need for grouting to inhibit corrosion of the PT tendons. Grouting requires an extra process step, and therefore extra construction time, as well as more materials. Furthermore, any deficiencies in the grouting can have consequences which can compromise the integrity of the structure over time. Air or water pockets in the grouting, for example, or small holes in the tendon ducting, can be virtually undetectable at the time of construction, yet can expose tendons to a long term risk of corrosion. A particular disadvantage of grout which sets solid is that the tendons cannot easily be removed for inspection or replacement. In the case of wax or grease-based grouting compounds, it is easier to remove the tendons, but they must still be cleaned of all the grouting compound in order to gauge their condition.

Another disadvantage of conventional prior art post-tensioned (PT) structures is the need for separate sets of pipes or ducts, as well as separate installation procedures, for each of the various fluid circulation systems in the structure. Whether embedded in structural concrete or installed separately, each extra set of pipework means an increase in the quantity of materials required for installation, an increase in the time and labour required, and the amount of space taken up by the pipework. Tubular rebar elements occupy a significantly extra volume of concrete when compared with the equivalent rebar steel rods, and can therefore reduce the strength in compression of the structure.

The object of the present invention is to provide a method and system for conveying utility liquids in a structure in which the overall amount of material used for fluid circulation elements, the total amount of space occupied by the fluid circulation elements, and/or the installation time are reduced. A further object of the invention is to provide a system for stressing a structure which avoids the need for a grouting process.

A further object of the invention is to provide a system for stressing a structure which facilitates a non-intrusive assessment of the state of the tendons and/or removal of the tendons for inspection.

A further object of the invention is to provide a system for stressing a structure which can incorporate embedded fluid circulation ducts without reducing the strength of the structure.

To fulfil these and other objects, the invention envisages a method of conveying a utility fluid through a structure, the structure comprising a tensioning element holding at least part of the structure in compression, and a duct enclosing the tensioning element, the method including conveying the utility fluid inside the duct.

The invention also envisages a system for conveying a utility fluid through a structure, the structure comprising a tensioning element holding at least part of the structure in compression, and a duct enclosing the tensioning element, the system comprising a first space inside the duct for accommodating the tensioning element, and a second space inside the duct for accommodating the utility fluid, a first connecting means for enabling the utility fluid to flow into the second space, and a second connecting means enabling the utility fluid to flow out of the second space, such that the utility fluid can flow from the first to the second connecting means through the second space.

According to a variant of the invention, the utility fluid is a thermal transfer fluid for heating or cooling the structure.

According to a further variant of the invention, the utility fluid is a fire- retardant or fire extinguishing fluid, and the second connecting means comprises a means of delivering the utility fluid to a region of the structure threatened by fire. According to another variant of the invention, the utility fluid comprises a corrosion inhibiting agent.

According to another variant of the invention, the utility fluid is a liquid.

According to another variant of the invention, the utility fluid contains a wetting agent.

According to another variant of the invention, the duct comprises thermal transfer promoting elements for promoting thermal transfer between the fluid and the duct and/or between the duct and the structure.

According to another variant of the invention, the structure comprises concrete, and in which the duct is at least partially embedded in the concrete.

According to another variant of the invention, the structure comprises a plurality of construction modules, each construction module comprising a section of duct, the sections of duct being provided with sealing connectors for sealably connecting the sections of duct of adjacent modules.

According to another variant of the invention, the system comprises means for monitoring physical parameters of the utility fluid inside the duct.

According to another variant of the invention, the duct is shaped such that it includes at least one bend.

The invention also envisages a tendon anchoring device for use of the above method or system, the tendon anchoring device being for securing a tensioning tendon at an anchoring point in the said structure, and for sealably capping an end of said duct, the tendon anchoring device comprising one or more inlet and/or outlet means for conveying fluid into or out of the said duct.

According to another variant of the tendon anchoring device of the invention, one or more connecting means may be provided for connecting the one or more inlet and/or outlet means to a heating, cooling or fire-prevention system.

The above variants of the method, system and device of the invention may also be combined as appropriate to fulfil one or more of the above objects of the invention.

Throughout the following description and the accompanying drawings, the same or similar components are referenced using the same reference numerals for the sake of clarity.

The accompanying drawings are included to provide a further understanding of the invention. The drawings serve to illustrate embodiments and examples of the present invention and, taken together with the description, serve to explain the principles of the invention. However they are not intended to limit the scope of the invention, which is defined in the accompanying claims

Figure 1 illustrates a prior art post-tensioning (PT) arrangement.

Figure 2 illustrates a post-tensioning arrangement fluid circulation system according to the invention.

Figures 3 and 4 illustrate examples of tendon anchors according to the invention.

Figure 5 illustrates a variant of the fluid circulation paths in the invention.

Figure 6 illustrates a modular construction using the invention.

Figure 7 illustrates a multi-pass tendon arrangement using the invention.

Figure 8 illustrates a fire prevention arrangement using the invention With reference to figure 1 , a simplified depiction of a standard post- tensioning (PT) arrangement is shown. A block (1 ) to be put under

compression, such as a concrete beam or slab, has been cast with PT ducts (2) embedded in the concrete. Once the concrete is sufficiently cured, a steel tendon (3) is then fed through each PT duct (2). An anchor (5) is attached to one end of the tendon (3), and a hydraulic jack (not shown) is used to exert a predetermined pulling force on the other end of the tendon (3). While the tendon (3) is under tension, a second anchor (5) is used to anchor the tendon to the block (1 ) such that the tendon (3) is anchored at both ends and under considerable tension. With the tension now established in the tendon (3), the hydraulic jack is then removed, leaving the tendon (3) in position and the block (1 ) under compression. A grout such as a wax, a grease, an epoxy resin or a cement-based compound is then pumped into the space (4) in the ducts (2) and, if appropriate, allowed to cure.

Figure 2 shows in simplified schematic form, the PT tendon and anchor arrangement of the present invention. The structure to be placed under compression, in this case a block (1 ) of concrete, is constructed, as in the prior art, with ducts (2) for PT tendons (3) anchored by tendon anchors (5) at each end. Instead of filling the spaces (4) inside the ducts with grout, however, the ducts (2) are connected to pipework (7) which is then connected to a fluid circulation system (not shown), but which uses the ducts (2) as ducts for circulating the fluid around the structure.

The invention can be applied to all fluid circulation systems which require fluid to be circulated around a post-tensioned structure. Examples include radiant hydronic heating systems, cooling and refrigeration systems, ground source or similar heat collection systems, air conditioning, hot and cold water supply, sprinkler systems, delivery of fire-combating liquids or gases, drainage systems, suction or vacuum systems. It may be that the fluid circulation is only intended to be used rarely (as in a fire-prevention system), or only for a short time - as in the case where the fluid-filled PT ducts are used to heat or cool a concrete structure while it is being cast, to influence the rate of curing of the concrete or to protect it against extremes of temperature. Each tendon (3) is anchored at both ends using a tendon anchor (5). As shown schematically in figures 3 and 4, fluid flow connections to the duct (2) can be arranged as channels (1 1 ) through the tendon anchors (5). Alternatively channels can be provided separately from the tendon anchors (5). This latter arrangement is not illustrated.

Figures 3 and 4 show alternative tendon anchors with channel and connector arrangements for carrying out the present invention. In both cases the channels are formed in the anchor, and connectors are provided on the outer side of the tendon anchor for connecting pipework to the duct (2). The tendon anchors (5) are positioned over the open end of the duct (2) with a seal or gasket (1 6) to prevent the escape or entry of fluid once the anchor (5) is in place, once the tendon (3) is under tension and once the space (4) is

connected to a fluid circulation system (not shown) via channels (1 1 ). In the examples illustrated, the connections are secured using screw-on connectors (12) or a bolted flange arrangement (13) with gasket (1 6).

It will be appreciated that the anchors illustrated are greatly simplified representations of tendon anchors, and that tendon anchors can take many and complex forms. The tendon retaining elements are schematically illustrated as a tapered conical ring (10) which fits into the body (9) of the anchor (5), however this is for illustrative purposes only, and it will be understood that modern tendon anchors are significantly more sophisticated than this.

Connection to such a fluid system will normally mean that the pressure inside the duct (2) is different from atmospheric pressure. Hence the need for seals or gaskets (16) to prevent escape or entry of fluid into or out of the duct (2), except via the intended channels (1 1 ).

Figure 5 shows in schematic form an alternative example of a post- tensioning arrangement using the present invention. The duct (2) in this case is linked, instead of by external pipework (7) shown in figure 2, by sections of internal connecting duct (14) which is assembled with the ducting prior to casting the concrete block (1 ). In this example, only two of the tendon anchors (5) are provided with channels for fluid, but the fluid is able to flow through the structure, following the path determined by the ducting (2 and 14).

Figure 6 shows a further embodiment of the invention, in which the structure (1 ) to be put in compression is a modular or segmental structure, comprising a number of modules or segments (1 '). Note that the terms module and segment are used interchangeably in this text. Each module is provided with a section of duct (2'), and the sections of duct (2') are sealably joined by a connector (6). This variant may be constructed with external joining pipework

(7) or internal ducting (14) as shown in figure 5.

In the foregoing examples, PT tendon arrangements have been described in which one PT tendon is used for each tensioning span. Figure 7 shows an embodiment of the invention in which PT tendons are used in a multi- span arrangement, where one tendon can provide compression for multiple spans. Using multi-span tendons means that larger volumes of a structure (1 ) can be placed in compression more quickly, and using fewer tensioning tendons (3) and anchors (5).

In such multi-span cases it is advisable to tension the tendon from both ends, since, even if the tendon and the ducting are well lubricated, the tension losses to due friction (Euler contact angle theory) at each bend can be significant. In the example illustrated in figure 7, the concrete block (1 ) might form, for example, a floor in a building, with radiant hydronic heating fluid flowing through the ducts (2).

Figure 8 shows how the invention can be used, for example, in fire- prevention systems. In this case, the slab (1 ) could form part of the ceiling of a building, and fire-inhibiting liquids or gases can be pumped under pressure through the ducts (2) and be forced out through, for example, sprinkler valves

(8) .

In addition to its use for thermal transfer or for fluid conveyance as already discussed, the presence of a fluid inside the duct instead of a solid or viscous grouting material has other advantages: a water-based liquid containing a corrosion inhibitor may be used, for example, thereby reducing the corrosive effect of any water ingress into the duct. Moisture entering the duct will merely dilute the corrosion inhibition solution locally and insignificantly. A liquid surrounding the tendon also provides better wetting of the tendon surface than a solid or viscous grout (particularly if the liquid contains a wetting agent), and the improved wetting would lead to better surface contact between the tendon and corrosion inhibiting agents in the liquid, which in turn leads to better corrosion protection of the tendon.

Under normal circumstances the tendons are permanently in contact with the fluid to be circulated through the tendon ducts in the present invention. If the fluid is a liquid, a corrosion inhibiting agent can be added to the liquid in order to protect the tendons against corrosion due to chemical or electrolytic effects. Such corrosion inhibitors may include volatile components which are adsorbed on to the steel of the tendon, for example, giving the surface of the metal an extra means of corrosion prevention, even if small pockets or bubbles of air remain trapped in the liquid.

The liquid in the duct can be inspected and treated or replaced easily, as can the tendons themselves. Corrosion prevention is also not compromised by movement in the structure which might otherwise cause small voids between a tendon and a solid grout. Such voids are undesirable because moisture may find its way into them and remain in the voids long enough to cause corrosion.

Another method of inhibiting corrosion in the system of the present invention is to applying a potential difference across the liquid in the duct, with the tendon acting as one electrode, and using a second electrode in contact with the liquid. Such a potential difference can be used either to counter corrosive electrolytic effects or to deposit and maintain a corrosion-inhibiting coating on the tendon.

Bleed valves can be positioned at appropriate points along the ducting, so that any gases trapped in the liquid can be bled off easily, thereby improving the thermal efficiency of the fluid circulation system and also reducing the likelihood of corrosion of the tendons.

Any chemical or electrolytic change, such as corrosion, of the tendons is also likely to be detectable from a chemical analysis of the fluids circulated, particularly if the fluid is a liquid. This provides an easy way of monitoring the tendons for corrosion without the need to remove the tendons or even to drain the system. Additives may be added to the liquid, either continuously or at predetermined monitoring periods, to enhance the sensitivity of the analysis for detecting substances in the liquid whose presence could indicate corrosion in the system or to replace corrosion inhibitors used or lost over time.

The chemical composition of the fluid to be circulated can be selected depending on the function which the fluid is expected to perform.

Refrigerants can be used for cooling systems, for example. Water, a foaming agent, or carbon dioxide could be used for fire-prevention. Other substances may also be necessary, such as anti-freeze or corrosion inhibitors.

Sensors can be used to monitor the level, or the pressure, or the chemical composition, or other physical or chemical parameters of the fluid inside the ducts. Such sensors can in turn be used to signal out-of-tolerance conditions such as a drop in fluid level or pressure (due, for example, to a leak), or an unexpectedly high or low temperature (caused by fire or frost), or a change in flow-rate (caused by a blockage, for example).

The ducts used in for the present invention can be made of any suitable material, such as metal or plastics. Exceptionally, it is also possible to implement the ducts from the concrete itself, without using a separate material, by for example using a moulding form during casting and subsequently removing the moulding form. The concrete in this case should be of sufficient density and composition to be impermeable to the fluid it should contain, unless it is desired to use the duct to convey a fluid which is intended to permeate the concrete.