GB2062055A

GB2062055A - Prestressed beam

Info

Publication number: GB2062055A
Application number: GB8024947A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-10-03
Filing date: 1980-07-30
Publication date: 1981-05-20
Also published as: FR2466589A1; DE3034073A1

Abstract

A prestressed beam (10) which is compressively preloaded along its length and transversely thereto by means of one or more cables (14, 16) which are engaged in tension with the beam. The cables are arranged in suitable configurations, e.g. zig-zag, which may oppose and overlap each other. The cables may be on one or both sides of the beam, or centrally of the longitudinal axis of the beam. The beam may be latticework or concrete. <IMAGE>

Description

SPECIFICATION Prestressed beam This invention relates to a prestressed beam for use in load supporting structures and to a method of prestressing the beam.

The invention provides a method of prestressing a beam which includes the step of engaging means in tension with the beam to produce substantially oppositely directed bending forces in the beam.

Further according to the invention the method includes the step of engaging the tension means with the beam is a first configuration which extends along at least part of the beam in a first direction and transversely to the first direction.

The invention may include the further step of engaging the tension means in tension with the beam in a second configuration which extends along at least the said part of the beam and which is substantially an image of the first configuration.

In a particular application the beam includes at least two beam members and spacer members which hold the beam members in a spaced relationship to one another, the method including the step of arranging the tension means so that the first and second configurations respectively extend between opposing ends of selected spacer members.

The invention also provides a prestressed beam which includes means engaged in tension with the beam at least in a first configuration which extends along at least part of the beam in a first direction and transversely to the first direction and which produces substantially oppositely directed bending forces in the beam.

The first configuration may be a zig-zag or any other suitable configuration which through the oppositely directed bending forces compressively preloads the beam.

The tension means may be engaged in tension with the beam in a second configuration which extends along at least said part of the beam in the first direction and transversely to the first direction and which is substantially an image of the first configuration.

The beam may be of cementitious material.

Alternatively the beam includes at least two beam members and spacer members which hold the beam members in a spaced relationship to one another, the first and second configurations respectively extending between opposing ends of - selected spacer members.

The tension means may consist of a plurality of rods, turnbuckles or the like but preferably comprises at least one flexible tensioning element such as a cable or chain.

The invention is further described by way of examples with reference to Figures 1 and 2 of the accompanying drawings which respectively are side elevations of prestressed beams of the invention.

Figure 1 illustrates a beam according to the invention which consists of two beam members 10 which extend over the length of the beam, a plurality of posts 12 which are fixed to and space the members 10 and two high tensile steel prestressing cables 14 and 1 6.

Cable guides 18 are located on and extend outwardly from the beam members 10 at the ends of the posts 12 intermediate the end posts of the beam. Suitable cable anchors 20 are located on the beam members at the ends of the terminal posts of the beam.

In use, the cables 14 and 1 6 are anchored at one or the other end of the beam to a cable anchor 20; The cables are then each loosely and slidably located over the guides 1 8 in a zig-zag configuration as shown in the drawing with one cable passing over a guide at one end of a post 1 2 and the remaining cable over the guide at the other end of the post. With the cables in position on the beam the free end of each of the cables is jacked against the end of the beam at which it located to tension it. When jacked to a predetermined tension the free ends of the cables are locked to the beam under the predetermined tension by the cable anchors 20. The lengths of the cable extending from each guide 18 are under tension and so induce bending forces in the beam.

The bending forces generated in this way by the cables extending from each pair of opposing guides 18 are oppositely directed and centered on the respective post 12 between the guides. Thus the post is compressively prestressed. The beam members 10 are also compressively prestressed by the tensioned cables.

In the embodiment of Figure 1 the beam members need not necessarily be parallel to each other. Additionally, to balance the prestressing loads on the beam if the cables 14 and 16 are to one side of the plane of the beam as described above a second pair of prestressing cables may be arranged and tension identically to the pair 14 and 16 on the opposite side of the beam. Alternatively, to avoid the use of four cables a single pair of cables could be used to provide the required prestressing provided that the cables are located in the plane of the beam. This could be accomplished by passing the cable through the posts 12 over suitable guides located in the posts.

In the beam described thusfar the cables compressively load each of the posts 12.

This need not necessarily be so and only selected posts may be loaded depending on the design requirements of the beam. Also, in some applications, for example where the beam is supported by other structure intermediate its ends, some of the posts need only be loaded in one direction from only one of their ends.

Figure 2 illustrates a concrete beam 30 prestressed in accordance with the invention. A number of guides 32 are cast into the beam and two cables 34 and 36 are engaged with the guides in opposing zig-zag configurations, i.e.

each configuration being substantially an image of the other. The cables are tensioned and anchored to the beam. As before the opposing divergent cable lengths set up opposing bending forces in the beam. The intervening portions of the beam are compressively preloaded and the beam is, in addition, compressively preloaded along its length.

It should be noted that oppositely directed bending forces are also induced in a beam if the tension means is arranged in only one zig-zag configuration. The bending forces do not then directly oppose one another but alternate along the length of the beam. An application of this type is also extended to fall within the scope of the invention.

Claims

1. A method of prestressing a beam which includes the step of engaging means in tension with the beam to produce substantially oppositely directed bending forces in the beam.

2. A method according to claim 1 which includes the step of engaging the tension means with the beam in a first configuration which extends along at least part of the beam in a first direction and transversely to the first direction.

3. A method according to claim 2 which includes the step of engaging the tension means in tension with the beam in a second configuration which extends along at least the said part of the beam and which is substantially an image of the first configuration.

4. A method according to claim 3 wherein the beam includes at least two beam members and spacer members which hold the beam members in a spaced relationship to one another, the method including the step of arranging the tension means so that the first and second configurations respectively extend between opposing ends of selected spacer members.

5. A method according to any one of claims 1 to 4 wherein the tension means comprises at least one flexible tensioning element, the method including the steps of anchoring a first end of the tensioning element to the beam, engaging the tensioning element with the beam, tensioning the element and anchoring a second end of the tensioning element to the beam.

6. A prestressed beam which includes means engaged in tension with the beam at least in a first configuration which extends along at least part of the beam in a first direction and transversely to the first direction and which produces substantially oppositely directed bending forces in the beam.

7. A prestressed beam according to claim 6 wherein the tension means is engaged in tension with the beam in a second configuration which extends along at least said part of the beam in the first direction and transversely to the first direction and which is substantially an image of the first configuration.

8. A prestressed beam according to claim 6 or 7 which is made principally from a cementitious material.

9. A prestressed beam according to claim 7 which includes at least two beam members and spacer members which hold the beam members in a spaced relationship to one another, the first and second configurations respectively extending between opposing ends of selected spacer members.

10. A prestressed beam according to any one of claims 6 to 9 wherein the tension means comprises at least one flexible tensioning element.

11. A prestressed beam which includes means engaged in tension with the beam in at least two overlapping configurations whereby the beam is compressively loaded in at least two directions.

12. A method of prestressing a beam substantially as herein described with reference to either of the accompanying drawings.

13. A prestressed beam substantially as herein described with reference to either of the accompanying drawings.