Static structures (e.g. – buildings) – Openwork; e.g. – truss – trellis – grille – screen – frame – or... – Embedded-type free – discrete elements; e.g. – set or rings
Reexamination Certificate
1999-06-25
2001-09-25
Stephan, Beth A. (Department: 3635)
Static structures (e.g., buildings)
Openwork; e.g., truss, trellis, grille, screen, frame, or...
Embedded-type free, discrete elements; e.g., set or rings
C052S660000, C052S745170
Reexamination Certificate
active
06293071
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is the national phase of International Application No. PCT/GR97/00043 filed on Dec. 31, 1997 and designating, inter atia, the United States. International Application No. PCT/GR97/00043 claims priority from Greek Patent Application No. 970100003 filed on Jan. 3, 1997.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention refers to stirrups for reinforcement of load bearing structural elements, and in particular for reinforcing concrete load bearing building elements, such as columns, shear walls, beams, slabs, footings, lintels, piles. The invention refers also to a method for reinforcing structural elements as well as to these elements.
2. Description of the Prior Art
Stirrups and ties constitute one of the most critical factors of quality and antiseismic strength of buildings. Essential factors for the liability of stirrups are the proper hooks at their ends and the bend diameter at corners. The hooks at the end of the conventional stirrups are absolutely necessary for ensuring the proper functioning of the stirrup or tie in case of a very strong earthquake, when the spalling of the concrete occurs and when the hooks is the only remaining anchorage mechanism.
The following stirrups are used in building industry today:
i) Individual stirrups
8
, which may be of various forms, such as described in FIG.
1
. For individual stirrups it is essential to be fastened in a plurality of points to the principal reinforcement rods
1
of the reinforcement as well as to the woodform. Thus their assembly is complicated and has a high cost. The individual stirrups
8
comprise hooks
6
, for anchoring the stirrups to the load-bearing element of the structure.
ii) “Mantles”, i.e. stirrup cages made of prefabricate welded meshes (see FIG.
2
). These are made of standardised welded meshes in suitable machines. The partial replacement of common stirrups by the “mantles” or “stirrup cages” was the first attempt to transform the painful task of reinforcing the load bearing elements of the structure into an industrial process. However the manufacture of the mantles is done in two phases, and only part of the process may become an industrial one: The first phase is an industrial process aiming in the production of plane meshes, such as shown in
FIG. 3
, from steel rolls using huge machines. During the second phase the meshes are almost manually assembled to form stirrup cages. The production of “mantles” have the following limitations: a) it is difficult to manufacture compound stirrup shapes by analysing them in simple rectangular shapes, b) it is impossible to increase or decrease the spacing of the stirrups resulting in superfluous weight of the reinforcement, c) it is expensive to transport them due to the size of the cages, d) it is difficult to manufacture double hooks, which is a necessity in antiseismic structures, and e) there is a danger of buckling of the vertical binding bars in case of an earthquake.
iii) Circular or orthogonal spiral stirrups such as disclosed in EP-A-0152397. Numerous experiments have been executed with circular spirals, which proved that if the spacing of the windings, i.e. the pitch, is kept below a minimum distance, the spirals are actually functioning like steel closed mantles, whose strength is increased due to the presence of triaxial stress system. The spiral stirrups currently known are appropriate only for reinforcing columns with rectangular cross-section. Further they are uneconomical because of the constant spacing between windings, which is determined by the shear level at the most critical region of the member. They also present problems in manufacturing and difficulties in placing them by the skilled workmen, because of the excessive weight in cases of strongly reinforced columns with many sides.
SUMMARY OF THE INVENTION
An object of the present invention is a stirrup overcoming the problems of the known stirrups. A further object of the invention is a stirrup which may be used for reinforcing load bearing elements of various cross-sections such as columns, shear walls, beams, slabs, footings, lintels, piles.
An object of the invention is also a method for reinforcing the load bearing elements of a structure as well as such an element.
The stirrup for reinforcing load bearing elements, in accordance with the invention, comprises a plurality of consecutive windings disposed along the longitudinal direction of the stirrup and has a continuous cross-section, so that the stirrup has a spiral form, whereby the windings of the stirrup form a plurality of discrete cages for housing the main reinforcement rods of the load bearing element.
The method of reinforcing a load bearing element, according to the invention, comprising at least two sets of reinforcement rod elements, includes the step of providing a spiral shaped stirrup with a continuous cross-section and a plurality of consecutive windings, which windings form a plurality of cages, with each cage tightening a different set of reinforcement rod elements.
A load bearing element, according to the invention, comprises at least two sets of reinforcement rod elements and a spiral shaped stirrup with a continuous cross-section and a plurality of consecutive windings, which windings form a plurality of cages, with each cage tightening a different set of principal rod elements.
Stirrups in accordance with the invention have a spiral form, so that the axial load carried by the stirrup may continuously transmitted with no interruption along its length. The windings of the stirrups of the invention form more than one cages for the principal reinforcement rods, so that they may be used for the reinforcement of load bearing elements of various cross sections such as orthogonal, T-shaped, L-shaped, Z-shaped etc. The stirrup may be brought in site compressed, and stretched during its positioning around the principle reinforcement rods. Its attachment to the reinforcement rods requires a relatively low number of fastenings—it is enough to fasten each winding to four or even three principle reinforcement rods—and involves relatively a low cost. The use of the stirrups of the invention allows the manufacture of the transverse reinforcement, which is essential for antiseismic and other reasons, to become an industrial process with low manufacturing cost and high quality of the product.
Stirrups according to the invention may be manufactured from a steel grade with very high strength, for example S1200 (1200 MPa), because there is no need to use hooks for anchoring, which are usually the weak points of the known stirrups. A further advantage of the stirrups of the invention is that their production and the stirrups themselves, may be standardised so that they may be of high quality and they could be used for reinforcing standard types of load bearing elements.
The features of the invention described in the dependent claims offer further advantages.
REFERENCES:
patent: 3882905 (1975-05-01), James
patent: 4150475 (1979-04-01), Bondpers
LandOfFree
Antiseismic spiral stirrups for reinforcement of load... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Antiseismic spiral stirrups for reinforcement of load..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Antiseismic spiral stirrups for reinforcement of load... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2530337