WO2009001388A1

WO2009001388A1 - Truss-like composite structural member

Info

Publication number: WO2009001388A1
Application number: PCT/IT2007/000468
Authority: WO
Inventors: Alessandro Ciocchetta
Original assignee: Alessandro Ciocchetta
Priority date: 2007-06-28
Filing date: 2007-06-28
Publication date: 2008-12-31

Abstract

A structural member (1) comprising one or more tension members (5) which connect the two ends (3, 4) of a beam (2), wherein at least one strut (6) is arranged between the beam (2) and the tension members (5), wherein the beam (2) comprises at least two sections (2a, 2b) which have a slope of a first angle (α) relative to a horizontal plane (P) passing through the ends (3, 4) and are located above the horizontal plane (P), said tension members (5) having a slope of a second angle (β) below the horizontal plane (2).

Description

TRUSS-LIKE COMPOSITE STRUCTURAL MEMBER

The present invention relates to a structural member for buildings, and in particular a horizontal prefabricated structural member which can be used as a beam or a floor slab for constructing buildings.

Horizontal structural members are already known for supporting a building roofing, which comprise two horizontal steel beams having the same length, being arranged parallel at a short distance to each other, which act as a sliding guide for a plurality of vertical struts laying on a chord arranged below the beams. The chord is connected to the beam supports which are constrained to the building walls in correspondence to the ends of the beams. Once loaded, said chord transmits a tensile force to said supports. The beams are constrained to each other, at a constant distance, in order to avoid buckling. The load arranged above the member directly lays on the struts supported by the chord, not directly on the beams, so that the latter only Have the function of a guide in order to prevent the struts from swerving laterally. In fact inside the two beams no compression force is applied. The slope of the horizontal beam is zero relative to a horizontal plane. This known structural member has the drawback of requiring at least one further member which is able to balance the horizontal and vertical tensile forces of the chord, such as for example the walls of a building, and thus it is not self-beating. Further, such a structural member is not able to resist to high loads, as the entire weight on the member is loaded on the chord.

Prefabricated structural members are known which comprise a reinforced concrete beam for providing spaces with a roofing. Said members have the drawback that, in order to cover wide spaces, they must have a very high thickness and thus they result to be very heavy.

Object of the present invention is thus to provide a structural member which is free from said drawbacks. Said object is achieved by a structural member whose main characteristics are specified in the first claim, while other characteristics are specified in the subsequent claims. The structural member according to the present invention is indeed self-balanced due to the peculiar sloped geometry of the beam and of the tension members. In loaded conditions, the beam exhibits small deformations which essentially consist of a lowering of the middle point of the beam and an increase in the distance between the two ends of . the beam, that is, the support points. The above-mentioned small deformations induce an increase in length of the tension members due to a tensile stress which translates into a compressive stress of the floor slab that tends to become shorter. A self-balanced suspension of the beam in correspondence to the middle point thereof where the strut is fixed results from said forces. In the same loading conditions, the bending internal stresses of the beam are remarkably reduced, and also the shear stresses result to be reduced. A further advantage of the structural member according to the present invention is that the beam and the strut can be made of reinforced concrete due to the fact of being subjected to a compressive stress, that is in optimal stress conditions for this material. This allows to achieve a remarkable saving and a higher lightness relative to the prior art structural members. Another advantage of the structural member according to the present invention is that it can be prefabricated, also with lateral protrusions and/or recesses for the mechanical connection to other structural members of the same type, so as to make a modular structure. The member is thus quickly ready to be applied with no need for a formwork or other forming structures. Still another advantage of the structural members according to the present invention is that it, as it is a zero horizontal force member, can be easily installed by being laid on suitable supports which are simply able to support vertical loads.

A further advantage of the structural member according to the present invention is that the encumbrance thereof is very small. Still a further advantage of the structural member according to the present invention is the possibility to arrange installations or the like between the beam and the tension members.

Further advantages and characteristics of the structural member according to the present invention will be evident to those skilled in the art from the following detailed and non-limiting description of some embodiments thereof with reference to the annexed drawings wherein: - Figure 1 is a top perspective view of a first embodiment of the structural member according to the present invention;

- Figure 2 is a bottom perspective view of the structural member of Figure 1 ;

- Figure 3 is a side view of the structural member of Figure 1 ; - Figure 4 is a longitudinal sectional view of the structural member of Figure 1 ;

- Figure 5 is a cross-sectional view of the structural member of Figure 1 in proximity to the strut;

- Figure 6 is a longitudinal sectional enlarged view of an end of the structural member of Figure 1; - Figures 7 and 8 are two perspective views of a second embodiment of the structural member according to the present invention;

- Figure 9 shows a cross-sectional view of the member of Figure 7 in proximity to the strut;

- Figures 10 and 11 are two perspective views of a third embodiment of the structural member according to the present invention;

- Figure 12 shows a cross-sectional view of the member of Figure 10 in proximity to the strut;

- Figures 13 and 14 are two perspective views of a fourth embodiment of the structural member according to the present invention; and - Figure 15 shows an enlarged sectional view of an end of the structural member of Figure 13.

Figures I₅ 2 and 3 show a first embodiment of the structural member 1 according to the present invention, which comprises in a known way a load-bearing beam 2 suitable to be supported in correspondence to ends 3 and 4 thereof, which are connected to each other by at least one tension member 5. At least one strut 6 is arranged between beam 2 and tension members 5.

According to the invention, beam 2 comprises at least two sections 2a, 2b which have a slope of a first angle α relative to a horizontal plane P passing through ends 3, 4.

The two sections 2a, 2b are located above horizontal plane P. On the contrary, lower end 7 of strut 6 is located below horizontal plane P and tension members 5 pass below said lower end 7 of strut 6 or cross it, thus forming a second angle β below horizontal - A -

plane P and being subjected to tensile loads, so as to urge strut 6 from the bottom and compressively stress beam 2.

In the present embodiment, strut 6 is arranged in the middle of beam 2 and structural member 1 comprises a plurality of tension members 5 which pass below lower end 7 of strut 6.

Beam 2 and strut 6 are manufactured in a single piece of reinforced concrete.

Figures 4 and 5 show a plurality of longitudinal steel bars 8, substantially parallel to each other, which are connected and stiffened by a plurality of stirrups 9a, 9b and 9c connecting said longitudinal bars 8 to each other. In order to optimize the mechanical behaviour of beam 2 in stressed conditions, first and second stirrups 9a and 9b, for example having a rectangular shape, are tilted at suitable angles relative to horizontal plane P, as it is shown in Figure 4. First stirrups 9a in proximity to ends 3, 4 of beam 2 and in proximity of strut 6 are tilted at an angle comprised between 40° and 50° relative to horizontal plane P, in particular 45°. Second stirrups 9b arranged in proximity to the middle points of first portion 2a of beam 2 and second portion 2b of beam 2 are tilted at an angle comprised between 22° and 32° relative to horizontal plane P, in particular 27°.

The substantially straight third stirrups 9c, whose sections are shown in Fig. 4, are connected transversally to longitudinal bars 8 in correspondence to the middle points of first portion 2a and second portion 2b, as illustrated in Figure 5. Also in strut 6 a plurality of fourth rectangular stirrups 9d can be incorporated, as illustrated in Figure 4.

As an alternative or in addition to the metallic reinforcement made up of bars 8 and stirrups 9a, 9b, 9c and 9d, a reinforcement of fibres or other suitable materials can be incorporated in beam 2 and in strut 6.

Figure 6 shows that tension members 5 are steel cables, for example cables for mild reinforcement or spring steel strands, fixed to transversal plates 10 arranged at ends 3, 4 of beam 2. Plates 10 are suitable to distribute the tensile force of tension members 5 over the external surface of ends 3, 4 of beam 2. Tension members 5 are housed in through-cavities 11 formed inside ends 3, 4 of beam 2. Such cavities _.11 have a slope of the above-mentioned second angle β relative to horizontal plane P. -Tension members 5 can directly adhere to the walls of cavity 11 or can be inserted in suitable pipes (not shown) arranged inside these cavities. In an alternative embodiment, which is not illustrated, tension members 5 are thin plates.

In order to achieve an optimal suspension reaction in the middle of beam 2 together with a limited encumbrance of structural member 1, angle α between first and second portions 2a, 2b of beam 2 and horizontal plane P is preferably comprised between 0,5° and 3°, while angle β between tension members 5 and horizontal plane P is preferably comprised between 2° and 8°. Further, the ratio between length L of structural member 1 and height H is preferably comprised between 15 and 30. The ratio between length L of the structural member 1 and thickness T of beam 2 is preferably comprised between 20 and 80.

Figures 7, 8 and 9 show a second embodiment of structural member 1 according to the present invention, wherein the vertical edges of strut 6 can be provided with a protrusion 12 and/or a recess 13 suitable to overlap and match as several structural members 1 of the same type are arranged side by side and parallel to each other for forming a modular structure. In order to firmly join structural members 1 to each other, there is at least one through-hole 14 in protrusion 12 and there is at least one through- hole 15 in recess 13. Such through-holes 14, 15 are suitable to overlap and align, when several structural members are laid side by side, in order to receive at least one horizontally arranged fixing bolt (not shown). Figures 10, 11 and 12 show a third embodiment of structural member 1 according to the present invention, wherein protrusion 12' is suitable to overlap underneath recess 13' when several structural members 1 are arranged side by side parallel to each other thus forming a modular structure. In order to firmly join structural members 1 to each other, there is at least one through-hole 14' in protrusion 12' and there is at least one through-hole 15' in recess 13'. Such through-holes are suitable to overlap and align vertically, when several structural members are arranged side by side, in order to receive at least one fixing bolt 16 arranged vertically.

Figures 13, 14 and 15 show a fourth embodiment of structural member 1 according to the present invention, wherein each end 3, 4 of beam 2 is provided with a transversal rib 17 protruding below beam 2. Transversal rib 17 is generally laid in a seat formed on the support (not shown) of the beam and is preferably reinforced by means of a longitudinal rib 18 which is perpendicular thereto and arranged under beam 2. Longitudinal rib 18 may also extend along whole beam 2, so that the latter has a T- shaped cross-section, even without transversal rib 17.

Possible variations and/or additions may be made by those skilled in the art to the embodiments of the invention herein described and illustrated while remaining within the scope of the following claims. In particular, the width of beam 2 can be larger than length L thereof, so as to form a structural member functioning as a floor slab.

Claims

1. A structural member (1) comprising one or more tension members (5) which connect the two ends (3, 4) of a beam (2), wherein at least one strut (6) is arranged between the beam (2) and the tension members (5), characterized in that the beam (2) comprises at least two sections (2a, 2b) which have a slope of a first angle (α) relative to a horizontal plane (P) passing through the ends (3, 4) and are located above the horizontal plane (P), wherein the tension members (5) have a slope of a second angle (β) below the horizontal plane (P).

2. A structural member (1) according to the preceding claim, characterized in that the strut (6) is arranged in the middle of the beam (2).

3. A structural member (1) according to any of the preceding claims, characterized in- that the tension members (5) are subjected to tensile stresses, so as to urge the strut (6) from below and compressively stress the beam (2).

4. A structural member (1) according to any of the preceding claims, characterized in that the tension members (5) pass below the lower end (7) of the strut (6).

5. A structural member (1) according to any of claims 1 to 3, characterized in that the tension members (5) cross the strut (6).

6. A structural member (1) according to any of the preceding claims, characterized in that the beam (2) and the strut (6) are manufactured in a single piece.

7. A structural member (1) according to any of the preceding claims, characterized in that the beam (2) and the strut (6) are made of reinforced concrete.

8. A structural member (1) according to the preceding claim, characterized in that the beam (2) comprises a plurality of longitudinal bars (8) which are connected by a plurality of stirrups (9a, 9b, 9c).

9. A structural member (1) according to the preceding claim, characterized in that first substantially rectangular stirrups (9a) are arranged in proximity to the ends (3, 4) of the beam (2) and in proximity to the strut (6) and are tilted at an angle comprised between 40° and 50° relative to the horizontal plane (P).

10. A structural member (1) according to the preceding claim, characterized in that second substantially rectangular stirrups (9b) are arranged between said first stirrups (9a) and are tilted at an angle comprised between 22° and 32° relative to the horizontal plane (P).

11. A structural member (1) according to the preceding claim, characterized in that third straight stirrups (9c) are arranged between said second stirrups (9b).

12. A structural member (1) according to any of claims 7 to 11, characterized in that the strut (6) includes a plurality of fourth stirrups (9d).

13. A structural member (1) according to any of claims 7 to 12, characterized in that a fibre reinforcement is incorporated in the beam (2) and/or in the strut (6).

14. A structural member (1) according to any of the preceding claims, characterized in that the tension members (5) are steel cables.

15. A structural member (1) according to any of the preceding claims, characterized in that the tension members (5) are plates.

16. A structural member (1) according to any of the preceding claims, characterized in that the tension members (5) are fixed to transversal plates (10) arranged at the ends (3, 4) of the beam (2) in order to distribute the tensile force of the tension members (5) over the external surface of the ends (3, 4) of the beam (2).

17. A structural member (1) according to any of the preceding claims, characterized in that the tension members (5) are housed in through-cavities (11) formed inside the ends (3, 4) of the beam (2), said cavities (11) having a slope of the second angle (β) relative to the horizontal plane (P).

18. A structural member (1) according to the preceding claim, characterized in that the tension members (5) adhere to the walls of the cavities (11).

19. A structural member (1) according to claim 17, characterized in that the tension members (5) are inserted in pipes arranged inside the cavities (11).

20. A^' structural member (1) according to any of the preceding claims, characterized in that said first angle (α) is comprised between 0,5° and 3°.

21. A structural member (1) according to any of the preceding claims, characterized in that said second angle (β) is comprised between 2° and 8°.

22. A structural member (1) according to any of the preceding claims, characterized in that the ratio between its length (L) and its height (H) is comprised between 15 and 30.

23. A structural member (1) according to any of the preceding claims, characterized in that the ratio between its length (L) and the thickness (T) of the beam (2) is comprised between 20 and 80.

24. A structural member (1) according to any of the preceding claims, characterized in that the vertical edges of the strut (6) are respectively provided with a protrusion (12, 12') and/or a recess (13, 13') suitable to overlap and match recesses (13, 13') and/or protrusions (12, 12'), respectively, of other structural members (1) of the same type arranged side by side parallel to each other thus forming a modular structure.

25. A structural member (1) according to the preceding claim, characterized in that there is at least one first through-hole (14, 14') in the protrusion (12, 12') and/or there is at least one second through-hole (15, 15') in the recess (13, 13'), said holes (14, 14', 15, 15') being suitable to overlap and align with second holes (15, 15') and/or first holes (14, 14'), respectively, of other structural members (1) of the same type arranged side by side parallel to each other thus forming a modular structure and being suitable to receive at least one fixing bolt (16).

26. A structural member (1) according to any of the preceding claims, characterized in that one or both ends (3, 4) of the beam (2) are provided with a transversal rib (17) protruding below the beam (2) .

27. A structural member (1) according to any of the preceding claims, characterized in that a longitudinal rib (18) is arranged below the beam (2).

28. A structural member (1) according to the preceding claim, characterized in that the longitudinal rib (18) extends along the whole beam (2), so that the latter has a T-shaped cross-section.