WO2019025990A1

WO2019025990A1 - Connection node structure

Info

Publication number: WO2019025990A1
Application number: PCT/IB2018/055766
Authority: WO
Inventors: Luigi PALIZZOLO; Salvatore BENFRATELLO
Original assignee: Università Degli Studi Di Palermo
Priority date: 2017-08-01
Filing date: 2018-08-01
Publication date: 2019-02-07
Also published as: IT201700088597A1

Abstract

A connecting node structure (1), capable of acting as constraint to be arranged at the bottom of pillars and as connection between pillars and beams constituting a structure made of steel, that is a strut assembly or a frame, allows to obtain a frame made of steel with stiffness and resistance features independent therebetween and on this regard it comprises: a first flat connecting plate (2), apt to be connected to a connecting end of a first frame beam (121), and a second connecting plate (3), apt to be connected to a connecting end of a second frame beam (122), said flat connecting plates (2, 3) perpendicular like a L having a mutual spatial relation depending upon the shape and position of said connecting ends and one of their respective flat connecting backplates (125, 126) which is adhered to said first and second flat connecting plate (2, 3); and one or more stiff connecting elements (5, 8, 11) implemented by a L-like profile, interposed between said first and second flat connecting plate (2, 3), implementing a stiff connection therebetween and which have as a whole a stiff resistance limit, in terms of bending moment, lower than that of the beams (121, 122) which are connected, therebeyond said stiff connecting elements (5, 8, 11) deform plastically.

Description

connection node structure

The present invention relates to a connection node element, capable to act as constraint in frames constituted by beams, to be arranged at the bottom of pillars and as connection between pillars and beams constituting a spatial structure made of steel, or even other material, that is a strut assembly or a frame.

By pure way of example, referring to the case of a portal frame, it is constituted by two pillars connected at their top by a beam. In this simple frame, constraints are arranged at the bottom of the two pillars and two opposite connections are arranged between pillars and beam, acting as frame nodes. Usually, the above referred constraints and connections are implemented by connecting the pillars to the ground and to the beams by means of welded and/or bolted joints, so as to implement stiff continuity nodes. Once selected the profiles to be used, by imaging for simplicity's sake one single profile, the structural behaviour in terms of stiffness and strength depends exclusively upon the selected profiles, upon the structure geometry and upon the existing external constraints.

In practical engineering there are many spatial structures in which it would be very useful to gain stiffness and strength features independent therebetween, but this property apparently cannot be achieved by using the just described usual technology.

Two different methodologies for implementing structures in beams facing the problem of controlling the behaviour of pillar-beam nodes can be found in technical and scientific literature.

The first methodology is characterized by a procedure for reducing the end sections of the frame beams, implementing the so-called "dog-bone" profiles, by cutting portions of the wings of a H-beam profile. Such procedure substantially aims at guaranteeing to meet the required capacity design, that is it proposes to obtain, near the node, a beam with lower resistance features than those of the pillar.

This solution has been described in different publications, for example: Plumier A. "The Dogbone - Back to the future". AISC Engineering Journal - Second quarter 1997 - Volume 34, n° 2; Pachoumis DT, Galoussis EG, Kalfas CN, Efthimiou IZ. "Cyclic performance of steel moment-resisting connections with reduced beam sections - experimental analysis and finite element model simulation". Eng Struct 2010; 32:2683- 92; Plumier A, Doneux C, Castiglioni C, Brescianini J, Crespi A, Dell' Anna S, et al . "Two innovations for earthquake resistant design - the INERD project, final report". Research Programme of the Research Fund for Coal and Steel; 2004; Plumier A. "New idea for safe structures in seismic zones," IABSE Symposium, "Mixed structures including new materials", Brussels, 1990; e Montuori R, Piluso V. "Plastic design of steel frames with dog-bone beam-to-column joints", Third International Conference on Behaviour of Steel Structures in Seismic Areas, STESSA 2000, Montreal, Canada, 21-24 August 2000.

It is believed that such connection method, which improves the structural behaviour at the level of the beam-pillar node as far as the capacity design requirements are concerned, however highlights some limits and drawbacks, and moreover it does not face the problem of making independent the stiffness and strength features of a frame.

The limits derive from the need of using H-beam sections. For example, should box-like sections be used, as it often happens, this kind of solution would not be possible. Moreover, the flange reduction involves a reduction not only in stiffness but even in strength of the treated element. Still, when the reduced portion is damaged, for example due to possible plasticizations, the whole beam element would result to be irremediably jeopardized.

The second approach is characterized by the implementation of a connection with welded or bolted steel plates of two end tracts of beams made of steel in proximity of the beam- pillar node. The main aim of this method is to define a section wherein plastic deformation have to be concentrated and therefore, basically, capable of dissipating plastic deformation energy, leaving the main structure in linear elasticity .

This solution has been described in several publications, for example: Castiglioni CA, Kanyilmaz A, Calado L. "Experimental analysis of seismic resistant composite steel frames with dissipative devices". J Constr Steel Res, 76:1- 12, 2012; Calado L, Proenga JM, Espinha M, Castiglioni CA. "Hysteretic behavior of dissipative bolted fuses for earthquake resistant steel frames". J Constr Steel Res, 85:151-62, 2013; Calado L, Proenga JM, Espinha M, Castiglioni CA. "Hysteretic behavior of dissipative welded fuses for earthquake resistant composite steel and concrete frames" Steel Compos Struct, 14 ( 6) : 547-69, 2013; Valenti M, Castiglioni CA, Kanyilmaz A. "Welded fuses for dissipative beam-to-column connections of composite steel frames: Numerical analyses". Journal of Constructional Steel Research 128, 498-511, 2017; e Valenti M, Castiglioni CA, Kanyilmaz A. "Numerical investigations of repairable dissipative bolted fuses for earthquake resistant composite steel frames". Engineering Structures 131, 275-292, 2017.

However this solution, with which it is possible to obtain the section wherein plastic deformations have to be concentrated, does not face the problem of making independent strength and stiffness features of the frame. Moreover, even in this case the use of this solution is substantially limited to the presence of H-beams.

The International patent application N. WO 2016/086,283 Al describes a pliable structural connection with two fastening plates opposed and parallel therebetween and an intermediate portion with variable section.

The German patent application N. DE 197 58 122 Al too describes a structural connection with two separated connection plates, which can be rotated with respect to one another, and with a box-like intermediate portion.

The US patent application N. US 2015/0,167,299 Al describes a structural connection including, in an intermediate portion thereof, pairs of sliding surfaces arranged obliquely with respect to the development of the intermediate portion between parallel connection plates.

The US patent N. 6,073,405 A and the Japanese patent application N. JP 2002 256,709 A describe angular connection elements with two different types of intermediate portions with respect to the respective connection plates.

The technical problem underlying the present invention is to provide a structural connection node element for structures in beams, for example made of steel or metal, allowing to obviate the drawback mentioned with reference to the known art . Such problem is solved by a connection node element as defined in the enclosed claim 1; additional details of the invention are reported in the enclosed depending claims.

It is meant that the node element, which will be described hereinafter in different embodiments, could be implemented by modifying conveniently the ends of the beams to be connected, that is the end of a pillar and the end of a beam.

Otherwise, it is also possible that the node element is constituted by a real independent node, to be put between the existing ends of two beams in a frame.

The main object of the present invention is then to provide a hinge connection device having a limited resistance and which is capable of deform plastically once having overcome said resistance limit, and which is capable of connecting the ends of two beams, in particular two beams made of steel, in a frame.

The connection which is then implemented can be designed so as to have two fundamental features. On one side it has a bending moment representing a structural failure limit and, on the other side, it does not vary the overall stiffness of the frame.

Moreover, further details of the connection shape make independent its elastic behaviour, in terms of stiffness, from its limit behaviour in terms of bending moment.

Such connection node element then fulfils many functions: for example, when it is suitably sized and placed at the end of a beam, in proximity of the node it reduces arbitrarily the beam limit moment by allowing to meet wholly the beam- pillar capacity design requirements. This node element can be used for any (H-beam, box-like, etc.) beam section, and its damage does not compromise the integrity of the main element, that is the beam itself.

Moreover, when it is suitably sized and it is placed at the end of a beam, in proximity of the node, it allows to use a portion of reduced sizes arbitrarily, wherein plastic deformations are concentrated. Even in this case, it can be used for any (H-beam, box-like, etc.) beam section.

Substantially, such node element meets the requirements of both previously mentioned methods, but in a broader way and with a greater number of possible applications. Still, main feature stimulating interest for its applications, the structural connection node element according to the invention allows to obtain a frame made of steel with the stiffness and strength features independent therebetween.

For these reasons, such connection node element has many chances to be put and widespread in the market. In particular in the field of the metallic carpentry for civil and industrial constructions. In fact, such node, considering its features, could be widely used especially in the restoration works and seismic improvement of existing buildings and not only made of masonry, but other useful applications can be provided even for the new constructions, both made of reinforced concrete and of steel.

The present invention will be described hereinafter according to a preferred embodiment example, provided by way of example and not for limiting purposes with reference to the enclosed drawings wherein:

* figure 1 shows a top perspective view of an end of a beam apt to constitute a first embodiment of structural connection node element according to the present invention:

* figure 2 shows a side perspective view of the node beam end of figure 1 ;

* figure 3 shows a perspective view of a frame portion, with a beam and a pillar assembled at the respective ends implementing a connection according to said first embodiment, one thereof is the end of figure 2 ;

* figure 4 is a front view of the node beam end of figure 1 ;

* figure 4A is a section view of the node beam end of figure 1, taken along the plane A-A shown in figure 4 ;

* figure 5 shows a side view of a structural connection node element of a second embodiment of the present invention;

* figure 6 shows a plan view of the connection node element of figure 5;

* figure 7 shows a side perspective view of the structural connection node element of figure 5; and

* figure 8 shows a perspective view of an application example of the connection of figure 5 to two ends of a pillar and a beam. With reference to the figures 1 to 4A, a connection is designated as a whole with 1. It comprises a first beam end 100 constituting the node element which will be described hereinafter .

In this example, the beams which will be described are H- beams, with a central core and two side secondary beams, but it is meant that any other type of beam could be used, such as T-beam, box-like beam, solid beam and so on.

The beam end 100 comprises a first flat connecting plate 102, having a connecting face 101 exposed outside the end 100, apt to be connected to a first flat backplate 125 belonging to a connection end of a beam 122.

Moreover, the end comprises a second flat connecting plate 103, having a respective connecting face exposed outside the end 100, apt to be connected in the present example to the wing 126, acting as connecting backplate, of the pillar 121.

As it can be noted from figures, the flat connecting plates 102, 103 have a mutual spatial relation depending upon the shape and the position of said connecting ends and one of their respective connecting flat backplates 125, 126, which is adhered to said first and second flat connecting plate 102, 103.

In the embodiment of figures 1 to 4A, the two flat connecting plates 102, 103, as well as their respective backplates 125, 126, are parallel therebetween and their respective flat faces adhering in contact to one another are parallel therebetween too.

The pillar 121 in turn has an additional box-like shaped end 110, having four plates arranged to form a parallelepiped at the beam end. One of these plates connects the additional end 110 to the pillar, the other three plates are positioned so as to be able to act as flat connecting backplate. They are fastened therebetween to the edges and by means of the beam core. Said plates are constituted by four flanges, with adequate thickness, for the node stiffening, aligned with intrados and extrados of the beam 122.

The two ends, as a whole, constitute a node structure 1 according to a first embodiment of the invention.

In the above-described end 100, the two connecting plates 102, 103 are connected by means of one or more connecting elements 104 interposed therebetween. In the present example, the connecting elements 104 are a pair and they are symmetrical to one another with respect to a median plane perpendicular to the connecting plates 102, 103.

Each stiff connecting element is constituted by a metal plate which is substantially divided into two opposite end portions 105, connected rigidly to the connecting plates 102, 103, and an intermediate portion 106 joining the two end portions 105.

In the present example, the intermediate portion has a smaller thickness than the thickness of the end portions 105. In this way, it is possible to determine the thickness of the intermediate portion 106 with respect to that of the end portions 105, so that, as a whole, they implement a strength limit, in terms of bending moment, lower than that of the beams which are connected, therebeyond said stiff connecting elements 104 deform plastically.

From the flat connecting plates 102, 103 screw rods 107 project perpendicularly, intended to engage through-holes implemented in the backplates 125, 126, to be then clamped with suitable nuts so that a bolted stiff connection 23 is formed .

It is meant that flat connecting plates 102, 103 and stiff connecting elements 104 are implemented as one single piece with adequate thicknesses, for example made of steel, and they are welded therebetween.

With reference to figures 5 to 8, a second example of structural connection node element is designated as a whole with 1, this time independent from the ends of the beams. It comprises a pair of flat connecting plates 2, 3 arranged perpendicularly to one another, with a respective overlapped corner 4 to form a L-like structure.

In this example, the two flat connecting plates are made of steel with adequate thickness, they have substantially square or rectangular shape and they are welded therebetween at said corner 4, thus forming an intrados of the node 1, with an angle of 90°, and an extrados complementary to the intrados .

At the extrados, the so-united two plates 2, 3 exhibit respective connecting surfaces at the ends of beams of a stiff structure, that is a strut assembly or frame (figure 8) .

Such beams, connected with an angle of 90°, constitute a pillar 121 and a beam 122 of the structure.

As it can be noted from figures, the flat connecting plates 2, 3 have a mutual spatial relation depending upon the shape and the position of said connecting ends and a respective flat connecting backplate thereof 125, 126 which is adhered to said first and second flat connecting plate 2, 3.

In the embodiment of figures 5 to 8, the two flat connecting plates 2, 3, as well as the respective backplates 125, 126, are perpendicular therebetween, so as the respective flat faces adhering in contact to one another.

At the intrados, to the node element 1 a first profile 5 is connected, preferably by welding, which connects the inner surface of the two plates in proximity of the connecting corner thereof.

In the present example, such first profile 5 is a L-like profile, implemented by welding two flat plates or by bending one single plate, or still by extrusion, which has bent ends 6 arranged inside the node element 1, that is without their projecting from the side edges of the plates 2, 3. Moreover, the first profile 5 has first smooth edges 7 connected, preferably by welding, to the inner surfaces of the plates 2, 3.

Moreover, the node element 1 comprises a second profile 8 which is connected, preferably by welding, to the inner surfaces of the two plates 2, 3 in proximity of their edge opposite to the connecting corner 4.

In the present example, such second profile 8 has a shape analogous to that of the first profile, that is a L-like profile, implemented by welding two flat plates or by bending one single plate, or still by extrusion, which has bent ends 9 arranged inside the node element 1, that is without their projecting from the side edges of the plates 2, 3; and second smooth edges 10 connected, preferably by welding, to the inner surfaces of the plates 2, 3.

Due to the effect of this geometry, the first profile 5 is included in the second profile 8. In this embodiment, the two sides of the two profiles are equal therebetween so that they have a squared section with different sizes.

Moreover, the node element 1 comprises a flat septum 11 arranged in the intrados perpendicular to both plates 2, 3, in the centre of each one, which connects them and obstructs completely the space included between said profiles 5, 8.

Preferably, the flat septum 11 is welded both to the plates 2, 3 and to the profiles 5, 8, that is to the respective extrados, by dividing the node into two substantially specular halves.

In this second example, the profiles 5, 8, together with said septum 11, constitute stiff connecting elements interposed between said first and second flat connecting plate 2, 3 and they implement a stiff connection therebetween .

Lastly, each plate 2, 3 has connecting through-holes 12, for fastening the beams 121, 122. In the present example, each plate 2, 3 has respective four holes arranged at the vertexes of a square, two on one side of the flat septum 11 and two on the other side. Preferably, the four holes 12 are arranged in a position comprised between the two profiles 5, 8 ( figure 7 ) .

The connecting through-holes 12 then can be coupled to corresponding holes existing at the ends of beams intended to be connected to the node element 1, so as to be able to bolt beams and node with suitable bolts 23 (figure 8) . It is meant that node elements and beams can also be fastened in a different way, for example they can be welded therebetween. The suitable size of the profiles 5, 8 constituting the node 1 allows to pre-establish the strength limit of the node element 1, that is the plastic limit moment of its section, which has to be lower than that of the sections of the pillar 121 and of the beam 122.

Therefore, based upon their thickness and their shape, the profiles 5, 8 and the septum 11 as a whole have a strength limit, in terms of bending moment, lower than that of the beams which are connected, therebeyond said stiff connecting elements deform plastically.

In this way, the main elements of the frame remain in elastic range even when the node plasticizes. The possibility to control the resistance, and therefore to impose a suitable limit value at time of plasticizing, allows to design a frame with prefixed stiffness and resistance, independent therebetween.

Such possibility first of all allows to solve the problem typical of the auto-frettage made of steel which are implemented in masonry walls after opening new compartments. In fact, in such case it is usual to design frames restoring the stiffness of the masonry wall, but by using current connecting techniques, generally such frames involve an increase in the resistance of the same panel.

Such case is not always positive from the structural point of view, as it causes a modification of the overall structural behaviour and, consequently, new and not foreseeable paths for the collapse mechanisms. Therefore, considering the masonry wall wherein a new opening has to be made, the possibility of designing frames with independent stiffness and resistance results to be fundamental to restore accurately the mechanical features of the panel itself by leaving unaltered the structural overall behaviour .

Such elasticity in optimum design can be obtained by using the proposed device. Clearly, the use of the limited resistance node can have even other applications such as, for example, the adjustment in terms of stiffness and resistance of an existing masonry building, by integrating stiffness whenever required and controlling resistances so as to determine collapse modes involving a minimum risk.

The above-described connection node element carries out the function of collecting monodimensional elements made of steel by implementing a weakened "section" thereat the possible plasticizations are concentrated due to overcoming the intensity thresholds of expected actions.

The suitable arrangement of such node element inside a complex structure allows to impose a limit resistance of the structure independently from their structural elements' own stiffness. Therefore, considering the structure subjected to increasing loads, the response of the same in kinematic terms will be controlled by the dimensional features constituting the main structural elements, whereas its response in terms of resistance will be conditioned by the limit mechanical features of the proposed device. Consequently, under expected limit conditions, the main structural elements will always show an elastic behaviour, that it the possible damage of the material will be avoided, whereas the proposed devices will show an elastoplastic behaviour, by determining the mechanical limit condition for the structure.

Once plasticization has taken place, when the phase characterized by exceptional loading conditions has finished (that is rare and limited-in-time conditions), the node element could be then wholly restored by only replacing the proposed nodes.

To the above-described structural connection node element a person skilled in the art, with the purpose of satisfying additional and contingent needs, could introduce several modifications and variants, however all within the protective scope of the present invention, as defined by the enclosed claims.

Claims

1. A connection node structure (1), comprising:

• a first flat connecting plate (2), apt to be connected to a connecting end of a first frame beam (121), and a second connecting plate (3), apt to be connected to a connecting end of a second frame beam (122), said flat connecting plates (2, 3) being perpendicular therebetween and having a mutual spatial relation depending upon the shape and the position of said connecting end and one of their respective flat connecting backplates (125, 126) which is adhered to said first and second flat connecting plate (2, 3) ; and

• one or more stiff connecting elements (5, 8, 11) interposed between said first and second flat connecting plate (2, 3), implementing a stiff connection therebetween and having as a whole a resistance limit, in terms of bending moment, lower than that of the beams (121, 122) thereto they are connected, therebeyond said stiff connecting elements (5, 8, 11) deform plastically,

characterized in that

• said first and second flat connecting plates (2, 3) are arranged, with a respective overlapped corner (4) to form a L-like structure, thus forming an intrados, and having at the extrados respective connecting surfaces at ends of beams (121, 122) of a frame; and

• the stiff connecting elements include at least a L-like profile (5, 8) connecting the inner surface of the two plates (2, 3), having smooth edges (7, 9) connected to the inner surfaces of the plate (2, 3),

the size of said at least one profile (5, 8) determining the plastic limit moment of the section of the connecting node (1) .

2. The node (1) according to claim 1, wherein the two sides of said at least a profile (5, 8) are substantially equal and perpendicular therebetween, so that it has a squared section .

3. The node (1) according to claim 1, having a first L-like profile (5) connecting the inner surface of the two plates (2, 3) in proximity of their connecting corner (4), and a second L-like profile (8) connecting the inner surface of the two plates (2, 3) in proximity of their respective edge opposite to the connecting corner (4), the first profile (5) being included in the second profile (8) .

4. The node (1) according to claim 3, comprising a flat septum (11) arranged in the intrados perpendicularly to both plates (2, 3), in the centre of each one, so as to wholly obstruct the space included between said profiles (5, 8), by dividing the node into two substantially specular halves.