EP0408597B1

EP0408597B1 - Joints for space frames in steel structural work

Info

Publication number: EP0408597B1
Application number: EP89903203A
Authority: EP
Inventors: Biagio Carannante
Original assignee: METALMECCANICA CARANNANTE SpA
Current assignee: METALMECCANICA CARANNANTE SpA
Priority date: 1988-03-23
Filing date: 1989-03-09
Publication date: 1995-01-04
Anticipated expiration: 2009-03-09
Also published as: IT8840410A0; WO1989009315A1; JPH03505354A; BR8907334A; ATE116708T1; DE68920430D1; AU628327B2; EP0408597A1; RU1838531C; IT1226774B; JPH0826585B2; AU3351689A; OA09262A

Abstract

Three types of fixed girder-pillar joints with two horizontal and vertical wind braces (22, 24) that can be assembled by means of bolts in the building yard for: 1) girders (1) and pillars (11) interrupted in the joint; 2) pillar (11) passing through the joint and interrupted girders; 3) pillar of reinforced concrete (11) with molds bearing the scaffolding and girder steel-concrete. Each type of joint consists of two characteristic parts (a) and (b) with bolted full resistance connections. The part (parts) of the joint (a) are connected near the pillar (pillars) in the workshop, and/or can be used to connect more parts of the joint (b); the parts of the joints (b) are to be welded near the joint.

Description

The present invention relates to structural elements for building constructions, and particularly to joints for lattice metallic frames formed from pillars and girders, optionally stiffened by diagonal braces.
In general, all current methods of building contructions make use of three types of joints, namely joints connecting interrupted metallic girders and pillars, joints connecting monolithic metallic pillars passing through the joints to interrupted girders joints connecting conventional girders to composite pillars made of reinforced concrete and supporting scaffolds.
Comparative tests carried out on models of multifloored buildings have shown that framed structures with chequered braced latticeworks are highly effective in resisting seismic energy as they exhibit significant structural ductility.
In respect of growing ductility, the following classes of structures can be defined:

hinged structures locally braced either by diagonal bars or by reinforced concrete walled cores;
full resistant framed structures stiffened by steel or reinforced concrete braces;
lattice framed structures with ductile joints using plastic hinges at the pillar-girders connections.

Optionally, these latter structes can be further reinforced by full resistance diagonal bars and soft reinforcing braces, so as to further enhance overall ductility and economy in assembly.
Hinged structures with braces of steel or reinforced concrete are known to be more economical and simple to effect than structures with rigid joints. In fact, the welded joints or high strength bolted connections of rigid structures have to be carried in the yard with evident low productivity. Further, the bolted connections involve piercing the pillars, which are the most critical components of the structure, in positions proximate to the maximum concentration point of bending moment, thus resulting in weakening of the structure.
FR-A-2 457 349 discloses a modular joint comprising a unitary cylindrical body adapted to receive vertical columns and having a peripheral radial extension formed at one end thereof to interconnect the columns with horizontal girders. The cylindrical body is directly attached to columns and girders by bolts inserted in holes formed in the walls of the same, which are therefore weakened at the most critical area. Further, in this prior joint transmission of moment is rather poor as the girders are substantially hinged to each cylindrical body by bolted connections. These modular bodies are unitary formed by a casting process, which are known to be expensive techniques and involve critical non destructive testing to screen acceptable quality.
FR-A-2 226 516 described a joint for structural frames according to the preamble of claim 1.
It is an object of the present invention to remedy the foregoing drawbacks by providing a joint for structural lattice frames exhibiting characteristics of rigidity combined with significant ductility so as to improve overall resistance to seismic energy.
Another object of the present invention is to provide a joint preventing weakening of critical components of the structures.
It is another object of the present invention to provide a composite joint which is simple in structure, can be readily and mass produced from conventional material in specialized workshops and is economical to manufacture.
It is a further object of the present invention to provide a structural joint which is adapted to be quickly and safely assembled with simple procedures involving no time consuming and waste of material.
These and other objects are obtained by joint for structural frames for connecting girders to a pillar comprising
a first part or member which is connectable to a pillar and by hinged connection to horizontal and vertical braces eventually provided in the frames;
at least one second part or member connectable to a respective girder;
said first and at least one second members being provided with holes and corresponding bolts, in order to mutually couple them by a full resistance welded connection upon final assembly of the structural frames;
said first and at least one second members being connectable respectively at the pillar and at the girders with a variable predetermined inclination each other, said joint being, characterized in that said second member is made up of four plates, and particularly two substantially horizontal longitudinal plates for transmitting the bending moments, a vertical longitudinal plate for transmitting the shear stresses and a transverse vertical plate for transmitting the torque; said plates being connectable by said bolts and piercings connections to said first member; and said second member having a structural strength higher than the structural strength of the girder connected to it.
The advantages offered by the invention are mainly that the proposed joint provided full transmission of stresses to the pillars while permitting local formation of plastic hinges during earth-quakes.
Another advantage of the proposed joint is that it make it possible a bolted assembly of the frames in the girders and starting from the top.
Further features and advantages of the invention will be more readily apparent from the following detailed description of three embodiments given by way of illustrative but not limitative examples, in conjunction with the accompanying drawings, wherein:

FIGURE 1 is an elevation view, partly broken away of a first embodiment of joint structure according to the invention;
FIGURE 2 is a plan view of the joint structure of fig. 1, partly broken away along line II-II;
FIGURE 3 is a plan view of the joint structure of fig. 1, partly broken away along line III-III of fig. 1;
FIGURE 4 is a fragmentary sectional view of a particular of fig. 3 taken along line IV-IV;
FIGURE 5 is an elevation view, partly broken away of a second embodiment of joint structure according to the invention;
FIGURE 6 is a plan view of the joint structure of fig. 5, partly broken away along line VI-VI;
FIGURE 7 is an elevation view, partly broken away of a third embodiment of joint structure according to the invention;
FIGURE 8 is a plan view of the joint structure of fig. 7, partly broken away along line VIII-VIII.
FIGURE 9 is a fragmentary, sectional view of fig. 7 taken along line IX-IX.

The lattice framed structure incorporating the joint in accordance with the invention is generally formed from superimposed substantially vertical pillars 11, 15 connected to substantially horizontal girders 1 preferably made of steel.
With reference to fig. 1 to 4 there is illustrated a first embodiment of joint for girders and interrupted pillars. This type of joint is suitable for buildings with a limited number of floors in which mechanical stress as are transmitted from one pillar to the other through bolted connection having reduced bulkiness due to the limited available space. This type of joint is therefore adapted for use in construction of small buildings and, as all the braces are interrupted at the joint and have reduced dimensions and weight, it is suitable for manual assembling. With reference to Fig. 5 to 7, there is illustrated a second type of joint in accordance with the invention and specifically adapted for connecting monolithic pillars to interrupted girders. These joints can be positioned around the pillar which is for example 12 meter long, they can further be adjusted at the desired level preferably in alignement with the axis of the pillar. In case of use of bent scaffolds, these may be attached to the joint by means of preliminarly weldings effected in a workshop. This kind of joint is suitable for any type of structure including multi-floored buildings.
With reference to Fig. 8 to 9, there is illustrated a third embodiment of joint adapted for use with reinforced concrete pillars and metal girders which collaborate with the concrete as well as with the additional bars, once the concrete has hardened. If the metallic formwork of the pillars have been calculated as bars in a casting supporting frame, the r.c. of the pillar can be considered as part of the joint. This kind of joint is highly effective in steel frames for r.c. constructions in large and multi-floored buildings.
In general, all the above mentioned structures of joints appear to formed from two main portions or member referenced A and B which are adapted to be mutually attached by bolted connections.
More specifically, member A is adapted to be secured to the pillar 11, 15 while member B is adapted to be connected to a respective girder 1. The member A consists of a pair of superimposed anchor plates, respectively a lower plate 4 provided with piercings 21, and an upper plate 20 provided with holes 29. Corresponding holes 21′ and 29′ are effected on the member B in such a manner to provide a full strength connection using bolts of relatively large diameter which induce no weakening in the corresponding attachement portions. Optional hole 17 may be formed on plates 4, 20 to receive hinged connections to horizontal diagonals 22. Members A and B may have apertures 32 for the passage of building installations.
In the second and third types of the joint structures shown in fig. 5 to 9 and emboding uninterrupted the pillars passing through the joint made of steel or of r.c. the upper and lower anchor plates 4, 20 have central openings 23 axially aligned for the insertion of the pillar. Anchorage of the component parts of member A to the pillar 15 will be made in the workshop by means of welding process or the like. In case that the pillars exhibit significant rolling tolerances, it is possible to vary the positioning clearance and the width of suitable coupling plates 16.
In case of pillar made of r.c., member A will be embedded in the composite structure of the pillar 11. The pillar 11 of r.c. will be cast unitarily with the upper scaffold, which will be supported by either steel girders 1, prefabricated slabs, not illustrated in the drawings, supporting formwork 8 and optionally by the lower diagonal braces 24. The formwork 8 may be bolted at 12 to plates 25 which are vertically welded to plates 4 and 20. Bu this arrangement, the plates 25 and the molds 8 will delimit the section of the r.c. pillar 11 defining a not dismantlable forming box.
In case of joints adapted for use with pillars passing through the joint, the anchor plates 4 and 20 are maintained in substantially parallel, spaced relation and are rigidly joined to each other by means of spacing plates 5, having top and bottom ends welded to the anchor plates to form a unitary structure. Such spacing plates 5 may have apertures 32 for the passage of the installations, and may be connected to member B by means of interlocking plates 26 having piercings 31 for transmitting shear stress between girders and pillar.
The anchor plates 4 and 20 may be further rigidified to avoid bending thereofby additional reinforcing parts not shown in the drawings, disposed centrally and adapted to resist torque moment, partially transforming it into bending moment transmitted to diagonal braces intersecting the joint.
In case of interrupted pillar, depicted in fig. 1 to 4, the anchor plates 4 and 20 are not welded to each other in a workshop before assembly of the frame, but they will be attached in the yard by means of bolted connnections. To this end, the anchor plates 4, 20 are spaced apart by means of two couples of spacing elements 19 consisting of angled or similar cross sectioned profiles, which are welded at one end to plates 4 and 20 and are provided with holes 31.
Attachment of the two spacing elements 19 is made during assembly of the frame in the yard will allow transmission of flexural pression from the upper portion of the pillar to the lower one. Further, as this bolted joint connects also the plate 3 pertaining to the joint B, it allows also transmission of the shear stress from the girder 4 to the pillar 15.
Turning to the joint adapted for use with monolithic pillars passing through the joint, the upper plate 20 is advantageously smaller than the lower plate 4 in the sense that the former has a smaller radial extension than the latter, in order to allow the positioning of girder relative to the pillar from above. The member A may be equipped with upper and lower connecting fins 6 and with peripheral holes 27 for hingedly connecting vertical braces to the joint. These additional hinged means will be welded to the joint or supplied separately for subsequent welding, in which case they may be suitably adjusted.
The member B is generally formed from a plurality of stress transmitting plates, preferably four plates, adapted to be attached by welding or similar process to the ends of each girder 1. The first pair of these plates are substantially parallel and vertically spaced plates 2, 28 and are attacheable to the upper and lower wings of the associated girder and are provided respectively with hole 21′ and 29′. The plates 2 and 28 are so sized to have: an increased resistance in comparison with the wings of the girder connected thereto in order to resist the larger moment at the fixed joind; a suitable length to permit welding of the girder 1 to the parts of member B; a width allowing positioning of the bolted connections 21′, 29′; and a thickness sized to provide a full strength connection, also taking into account the strength of the braces connected to the joint. In order to semplify the assembling operations, the bolted connections make use of few bolts, having a large diameter, thus avoiding weakening effect on the girders. These holes of relatively large diameter could not be carried out during assembly the girder, due to lack of room in the joint, and therefore it is evident the advantage of being carried out in a workshop before assembly.
To permit positioning of the girder from above, the lower plate 2 will be shorter than the upper plate 28 in accordance with the deferent radial extension of the anchor plates 20 of member A. The member B comprises a third plate 3 with the hole 31 adapted to transmit the shearing stress from the girder 1 to the part of the member A. The plate 3 is welded to the web of the girder along the axis of the bolted connection of the plate 2 and 28 and can further include the optional hole 32 for the passage of the building installations. A fourth plate 30 is connected to plates 2 and 28 for transmitting to the member A the torque induced by the girder 1.
The above described structures of joint can offer the following advantages.
Even the smallest workshops will be encouraged to build their own structures using prefabricated joint and they will be led to employ the wind braced framed scheme, the most appropriate for steel structures, because the only operation to be carried out is that of unscrewing the bolts, preparing the components of its members and welding them in the workshop the member A to the pillar, or pillars, and the member B to one end of the girders. The only operation required for the braces is that of cutting them, according to the required size. In this way, all defects of construction can be avoided starting from the theoretical calculation scheme, making it possible to obtain structures with regular shapes, which is the first requirement for antiseismic constructions.
A further advantage is that any structure can be designed, calculated and built in a very limited time, and can also be computer programmed.
The construction method using the present joints is independent from the rolling tolerances in so far as the it is possible to make use of suitable adapters and spacers at the connection points. The desired accuracy of assembly can be ensured by the prefabricated bolted connection, carried out by specialized workers and by the alignment of the joints.
Concerning the braces for the latticeworks, they cannot have necessarily the maximum size but it is also possible to use all other small sections simply adapting them to the joint. If the parts of member A are to be connected to a limited number of braces, the part of joint which is not necessary can be easily cut away.
Varying the size of the joint, it is possible to employ higher strength sections in the lower floors and less rigid ones in the higher floors this resulting in a better material distribution in accordance with theoretical calculations. The use of these joints could render the construction of full metallic structure more competitive with respect to the composite ones in reinforced concrete, as unlike to r.c. it is possible to make reinforcing braces with diagonal tension bars at relatively low cost.
In general, the use application of these joint will reduce the overall weight of the structures and will ensure uniformity in girder height with more economical investments; local wind braces are no more necessary thus reducing concentration of stresses with the result of lowering costs for foundations.
The proposed structure of joint allows dissipation of seismic energy due to non elastic deformation in the bolted connections caused by ovality of the holes in member A and B as well as by plastic deformation of the girder in correspondence of the connection thereof to the member B.
In fact, it is know that the behaviour of the bolted joints depends on sliding involving the connected parts, which effect is known to be not completely random and has a positive effect on strength. Moreover, the ductility of a structure incorporating bolted joint is at least equal to that of an entirely welded structure,
Finally, the use of bolts having a relatively large diameter generally improves mechanical strength with no reduction in ductility. Also, the dissipation of energy in the hysteris cycle is considerably increased.
In conclusion, the proposed joints provide a formation of plastic hinges, specifically where the passage between the cross section ot the girder profile and of the joint takes place. In fact, in that point where the girder must be dimensioned to resist a moment which is almost equal to the center line moment but lower than the maximum fixed joint to which the same dimensioning of the girder with flanged joint is subject, and abrupt decrease of the cross section is made.
It is observed that the proposed joint makes it possible to assemble the pillar from the top. The pillar is lowered by a crane and guided into its site so that it is positioned automatically and cannot fall down because it leans against the joint and the member B of the joint cannot shift horizontally.
In an exemplary arrangement of the joint, there can be provided a vertically extending pillar and four girders arranged perpendicular to each other, four or eight horizontal braces and eight vertical wind braces. With the same type of assembling, however, it is possible to realize a joint with a different number of girders and braces with a different angle as well as of girders with different height.
The different angle of the tie sleepers can be obtained by introducing them with substantially aligned with the plates 2, 28 of the member B and bending these plates in correspondence of the plate 30.

Claims

Joint for structural frames for connecting girders to a pillar comprising
a first part or member (A) which is connectable to a pillar and by hinged connection to horizontal and vertical braces eventually provided in the frames;
at least one second part or member (B) connectable to a respective girder;
said first (A) and at least one second (B) members being provided with holes and corresponding bolts, in order to mutually couple them by a full resistance welded connection upon final assembly of the structural frames;
said first (A) and at least one second (B) members being connectable respectively at the pillar and at the girders with a variable predetermined inclination each other, said joint being characterized in that said second member (B) is made up of four plates (2, 3, 28 and 30), and particularly two substantially horizontal longitudinal plates (2, 28) for transmitting the bending moments, a vertical longitudinal plate (3) for transmitting the shear stresses and a transverse vertical plate (30) for transmitting the torque; said plates being connectable by said bolts and piercings connections to said first member (A); and said second member (B) having a structural strength higher than the structural strength of the girder connected to it.
Joint according to claim 1, characterized in that said bolted connections (21, 29, 31) are independent each other.
Joint according to one of the preceding claims, characterized in that said second member (B) has a varying section at the point of coupling with said girder, said variation being abrupt in order to allow the realization of plastic hinges at this point.
Joint according to claim 1, characterized in that said first member (A) receives one or more of said second member (B) and is provided with upper and lower connections (21, 29, 31); said first member (A) having a higher structural strength with respect to said member (B).
Joint according to claim 4, characterized in that said first member (A) is provided with a central hole (23) for the passing through of the pillar, in that it comprises plates (5, 26) for the transmission of the shear stresses connected to further plates (4, 20) in order to realize a single structure; and in that one plate (20) is smaller than the other (4).
Joint according to claim 5, characterized in that said first member (A) comprises plates (25) provided with a hole (12) placed on said plates (4, 20) to connect the first member (A) by bolts, said plates (25) supporting formwork (8).
Joint according to claim 4, characterized in that said first member (A) is made up of two separate parts connected each other by bolted connections (31, 21, 29) and by said at least one second member (B); said plates (4, 20) and said plates (2, 28) of the second member being provided with two profiles (19) having holes corresponding to said hole (31) in such a way to obtain an interspace.