EP0408597A1

EP0408597A1 - Joints for space frames in steel structural work.

Info

Publication number: EP0408597A1
Application number: EP89903203A
Authority: EP
Inventors: Biagio Carannante
Original assignee: METALMECCANICA CARANNANTE SpA; CARANNANTE METALMECC
Current assignee: METALMECCANICA CARANNANTE SpA; CARANNANTE METALMECC
Priority date: 1988-03-23
Filing date: 1989-03-09
Publication date: 1991-01-23
Anticipated expiration: 2009-03-09
Also published as: AU3351689A; EP0408597B1; DE68920430D1; OA09262A; BR8907334A; JPH0826585B2; AU628327B2; IT1226774B; WO1989009315A1; ATE116708T1; RU1838531C; IT8840410A0; JPH03505354A

Abstract

La présente invention se rapporte à trois types de joints pour poutres-piliers fixes ayant deux entretoises de contreventement horizontale et verticale (22, 24) qui peuvent être assemblées au moyen de boulons sur le chantier de construction pour: (1) des poutres (1) et des piliers (11) s'interrompant dans le joint; (2) un pilier (11) passant à travers le joint et des poutres interrompues; (3) un pilier en béton armé (11) avec coffrage portant l'échafaudage et l'acier-béton de poutre. Chaque type de joint se compose de deux parties caractéristiques (a) et (b) avec connexions à résistance pleine boulonnées. La ou les parties du joint (a) sont connectées à proximité du ou des piliers dans l'atelier et/ou peuvent être utilisées pour connecter un plus grand nombre de parties du joint (b), les parties des joints (b) étant soudées à proximité du joint.The present invention relates to three types of joints for fixed pillar beams having two horizontal and vertical bracing struts (22, 24) which can be bolted together at the construction site for: (1) beams (1) ) and pillars (11) interrupting in the joint; (2) a pillar (11) passing through the joint and interrupted beams; (3) a reinforced concrete pillar (11) with formwork supporting the scaffolding and steel-concrete beam. Each type of seal consists of two characteristic parts (a) and (b) with full strength bolted connections. The joint part (s) (a) are connected close to the pillar (s) in the workshop and / or can be used to connect a larger number of joint parts (b), with the joint parts (b) being welded near the joint.

Description

JOINTS FOR SPACE FRAMES IN STEEL STRUCTURAL.WORK

There are three types of fixed girder-pillar joints with -if nece^ sary- horizontal and vertical wind braces and joints that can be bolted in the yard for: 1) girders and pillars interrupted at the joint; 2) pillars passing through the joint; 3) r.s. pillars with mold supporting the scaffold and the pillars of steel-concrete. In the technical booklet n°ll "Braces in steel seismoresistant structures" by Prof. G. Ballio and F.M. Mazzolani, published by ITALSIDER, 1980, according to the analysis of static and dynamic tests, performed on building models with nine floors, scale 1:6, carried out by SHISHMELASHUILI and EDISHERASHUILI (URSS), at page 11 we read: "the comparison of the dynamic characteristics obtained from the aforesaid tests shows that the schema n°7 appears to be the most convenient one; the schema n°7 shows the frame with chequered braced meshes". And also "In broad lines, three classes of structures can be defined in respect of growing ductility:

1° - pendulous structures with set apart wind braces made either with reticular brackets, or with walls (or nucleus) of r.c; 2° - resistant frame structures connected with wind bracing elements of steel or of r.c; 3° _ structures with frames with ductile, rigid joints such as to allow the use of plastic hinges at the coupling between girders and columns.

To the above classes the undersigned adds a third class, namely the structures with frames with ductile rigid joints, full resistance diagonal bars, and soft metal braces, that is braces with blocking elastic-plastic springs to be placed in any place allowed by the architectonic project, but so as to be more or less near the braced frames; this in order to obtain: the most convenient and ductile structure with reference to the dynamic characteristics. __,____,,__ PCT/TT89/00016 9/09315 '

- 2 - At the 10th C.T.A. meeting, 1985 ( C.T.A. Steel Technicians Board ), Piazzale Morandi, 2 - 20121 - Milan, Ing. Besio, Corbani, Cremonini and De Martino have illustrated a series of tests on the "Structural system of rigid joints for the girder-column by means of bolted brackets.

At page 3 of the report we read as follows: "In the general practice, untill recently, it seems that when no particular architectonic re¬ quirements must be fulfilled, the solution of re icular bracing, or bracings with nucleus in r.c. appears to be more convenient than the equivalent solution with rigid joints; this because the standard rigid connections, made by means of welded joints, or by means of flanged joints, with highly resistant bolts, are particularly ex - pensive, due to the low working productivity in the workshop and to the slow assembling operations in the yard". And "... the planning aspect has been developped which led to the definition of new types of joints ...". At the end of the report, the graph of the new joints is shown.

According to these premises, the specialized technical literature deems that the framed schema is the most convenient one for anti - seismic structures, however this schema is not employed for steel constructions as it implies too many difficulties during the pro - duction and in the assembling phases.

The joints which I am going to describe are rigid and, if correctly employed, they can be ductile. For these joints, vertical and hori¬ zontal bracings are foreseen; they can be mass producted in special¬ ized workshops, in that all the precision work is concentrated in one single composite piece; furthermore they allow a bolted assembling which can bu safely, easily and quickly carried out without waste of material.

The attached graphs show the three types of joints, which are similar but can be used for different applications. 9/09315

- 3 - Table 1 shows the joint for girders and pillars interrupted in the joint. This joint is suitable for buildings with a limited number of floors in that the standard stress is transmitted from one pillar to the other one through a bolted connection limited by the available room. This joint canttherefore be used for small buildings and, as all the bars are interrupted at the joint and are therefore short and light, it is suitable for manual assembling.

Table 2 shows the joint for pillars passing through the joint and interrupted girders. The prefabricated joints are introduced into the pillar which for instance is 12 m long, positioned at the desired height, (the axes of the joints must coincide with the axes of the pillar or not), in the case of bent scaffold and are blocked with by means of weldings carried out in the workshop. The usual error of centering and blocking the pillar in the joint does not cause dammage to the connection of the pillars in that the measur ment is carried out starting from the joint axes which are not effect ed by the eccentricity of the pillar in the joint; in fact, the eccentricity of a fraction of millimeter is practically neglectable in respect of the pillar height.

This kind of joint is suitable for any type of structure.

Table 3 shows the joint for r.c. pillars and metal girders which will collaborate with the concrete and with the additional bars, after the mix has hardened. When building the metal molds of the supporting pillars, having calculated them as bars of a casting supporting frame, this method allows to introduce the r.c. pillar into the joint. The metal cage of the r.c, consisting of longitudinal rods (7) and of molding boxet; (13), will involve one half of the lower floor and one half of the second floor, will be introduced in each scaffold,and will be blocked on the joint by the temporary connection. The metal mold which may have a square, circular, or octagonal section - A - can also represent the outside finish of the pillar and can be used as reinforcement for the pillar itself, while the metal cage of r.c. will have the task of connecting the lower and the upper pillar and that of reinforcing the blockage. Of course, when the piercing (23) on the upper plate (20) is smaller, the tapering of the pillars can be easily carried out.

It must be stressed that, according to the theory and contrarily to the technical practice of r.c, the superimposing of the reinforcements occurs at the center of the pillar and not at its foot, which enables to diminuish the number of the reinforcements when the distance from the joint increases.

The use of this joint allows a steel structural work in r.c. con - structions.

Each of the three types of joints can be divided into two character¬ istic parts with a bolted joint between them. When subdivided into its main parts, the part (parts) of the joint (a) are connected near the pillar (_ pillars) and can be used to connect more parts of a joint (b); the parts of joint (b) must be welded near the pillars. The part of joint (a) is made of a lower plate (4) with the piercing (21) and of an upper plate (20) with the piercing (29), suitable to receive the bolted joint of the parts of the joint (b) and with the optional piercing (17) suitable to receive by means of a hinged joint, the connections (c) of the horizontal diagonals (22) and with the optional piercing (32) for the permeability of the installations. In the hypothesis of the pillar passing through the joint made of steel or of r.c (11), on the lower plate (4) and on the upper plate (20), a central piercing (23) must be carried out for the introduction of the pillar. The anchorage of the part of joint (a) to the pillar (15) will be made in the workshop by means of welding and, in the case that the pillar is subject to rolling tolerances, it is possible to vary the positioning clearance and the width of the reinforcement plates (16) if any, at the pillar with the joint.

The anchorage of the part of joint (a) with the pillar (11) will take place by means of the mix and of the additional rods which pass through the joint. The pillar (11) of r.c.. will be cast together with the upper scaffold which will be supported by the steel girders, by the supporting molds (8) and by the lower wind braces (24). The casting of the scaffold will be supported by the molds, if any, and by the prefabricated slabs. The connection of the part of the joint (a), with the bearing molds (8), is achieved with the bolted connection (12) through the plates (25) welded northogonally to the plates (4) and (20). The plates (25) and the molds (8) will delimit the section of the r.c. pillar (11). Again in the hypothesis of the pillar passing through the joint, the plates (4) and (20), in order to form the part of the joint (a) are connected together by means of plates (5) with the optional piercing (32) for the permeability of the installations, and by means of the plates (26) which contain the piercing (31) for the transmission of the cutting stress from the girders to the pillar. In the hypothesis of girders subject to torsion, it is convenient to reinforce the plates (4) and (20) with a further connection, in the inside part of the joint, so as to transform the torque, discharged into the joint, in a bending moment for the other bars which meet in the joint, without having to bend the plates (4) and (20). In the hypothesis of interrupted pillar, the plates (4) and (20) are not connected. They will be connected in the yard, with a bolted con¬ nection which will take place by means of two couples of profiles (19) angular or not, bearing a piercing (31) and welded on the plates (4) and (20). The assembling of the profiles (19) of the plates (4) and (20) in the yard will allow of the pressure flexion stress to pass from the upper pillar to the lower one; furthermore, as this bolted joint connects PC_7_T89/00016 /09315

_ 6 - also the plate (3) of the part of the joint (b), it allows also the transmission of the cutting stress from the girder (4) to the pillar (15).

In the hypothesis of pillar passing through the joint, the upper plate (20) is smaller than the lower plate (4), this in order to allow the threefold, bolted connection of the part of the joint (b) with the pillars which will be assembled from the top.

In order to complete the part of the joint (a) on the symmetry axis of the girders meeting in the joint, on the plates (4) and (20) and at level with the future position of the pillar on its outside side, the joint will be equipped with the connections (6) and with the piercing (27) for the vertical wind braces. Said connections will be assembled on the joint, or supplied separately. If supplied separately, they may have a variable piercing and/or become further parts of the joint (a). The part of the joint (b) is made of three plates.

The lower plate (2) with the piercing (21) and the upper plate (28) with the piercing (29) transmit the bending moment, induced by the girder, connected to the part of the joint (b) to the frame. The plates (2) and (28) will have an increased resistance as compared to the wings of the girder connected in order to resist to the larger moment at the fixed end, a length calculated in function of the possi¬ bility of welding the girder (1) to the part of the joint (b) and in function of the point where the plastic hinges must be made to face the increase of the stresses; a width in function of the bolted connection, and a thickness (taking into account also the thickness of the bar which reaches the joint) in function of the piercing upsetting which, in order to simplify the assembling operations, should be possi¬ bly carried out with few bolts, having a large diameter, in piercings that do not vreaken the girders and which, for lack of room, could not be carried out on the girder.

In the hypothesis of pillar passing through the joint, the lower plate (2) will be shorter than the upper plate (28) so as to allow the bolted connection with the girders coming from the top. The plate (3) with the piercing (31) for the transmission of the cutting stress from the girder (1) to the part of the joint (a), is positioned along the axis of the bolted connection of the plate (2) and (28) until it meets the plate (30). It can also contain the optional piercing (32) for the permeability of the installments. The plate (30) is used as a measure for. the bars (1) and for transmitting the torque to the part of the joint (a). After the assemblage, when bolted joints are used, the steel structure of the building will be a space structure made of several flat vertical frames with or without wind braces and of several flat horizontal and/or bent, and/or curved frames with or without wind braces.

The production and the introduction in the market of a series of this new element, namely the bolted joint (to be reported in the hand books as it is done for all the steel industry production) offers the following advantages:

1) Even the smallest workshops will be encouraged to build their own structures using the prefabricated joint and they will be led to choose the wind braced framed scheme, the most convenient for steel structures, because the only operation to be carried out is that of unscrewing the bolts, subdividing the composite piece into its single parts and welding in the workshop the part (a) near the pillar (or pillars) and the parts (b) near the end of the girders. The only operation required for the bars is that of cutting them, according to the required size. In this way, all construction de¬ fects are removed, starting from the theoretic calculation scheme, enabling to obtain structures with regular shapes, which is the first rule for antiseismic constructions. Also the welding of the bars to the joint in the workshop is prearranged, in that the girders enter into the joint for a good part and the full re - sistance welded connection is foreseen even if the welding is not 09315 '

- 8 - of the best quality as it can be checked in the workshop before being used. Furthermore, the workshop can be placed near the yard so as to avoid the transportation of the structure elements from the workshop to the yard. 2) The advantage of availing of prefabricated joints is that any stru cture can be designed, calculated, and built in a very short time, in that it can be programmed by computer. 3) The process is indipendent from the rolling tolerances in that the bar is rolled and introduced into the joint, the pillar passing through the joint or into the end of the girder and connected by welding, with the possibility of introducing, if necessary, suit¬ able adapters. The assembling precision will be ensured by the prefabricated bolted connection, carried out by specialized workers and by the axis/axis positioning of the joints. 4) Jetties can be easily made.

5) As to frame bars, not only the maximum size which can be received by the joint can be employed, but it is possible to use all other small profiles simply adapting the joint to them.

6) If the part of joint (a) is reached by a lower number of rods, the part of joint which is not necessary can be easily cut away.

7) Varying the size of the joint, it is possible to employ more rigid profiles in the lower floors and less rigid ones in the higher floors with the result of better materials and consistently with the theoretical calculation. 8) It may be that the use of these joints will render the steel stru¬ cture competitive in respect of the one of r;c. in that contrarily to r.c. it is possible to make wind braces with diagonal tension bars at a low cost. Furthermore, these types of wind braces, as they absorb the stresses caused by the seismic action, relieve the rest of the structure from them.

9) The use of the joint will increase the number of buildings with steel structure. This will be an advantage for the steel industry and for the people who will have safer structures to protect them from the seisms. 10) The use of the joint will reduce the weight of the structures and will ensure the uniformity of the girder heights with a consequent ^r higher productivity; there will be not set apart wind braces and therefore, no concentration of stresses with the result of lower costs concerning the foundations and the wind braces; the assembl¬ ing operations will furthermore require less time and the structure will appear more elegant. _l)The boring phase of the calculation for the connection of the frame bars will be eliminated with the result of avoiding possible errors in that the calculation which will be carried out during the planning of the prototype of each joint to be carried out in mass production.

As we have already mentioned, at present the state of the technique foresees framed steel structures only when it is strictly necessary to fulfill architectonic or structural requirements, as for instance in the case of skyscrapers; in these cases the joint is usually entirely welded at the building yard, because the now available bolt¬ ed connections are not easy to be realized and they only seldom can achieve a full resistance welded connection of the weakest element in the structure. For instance, the joint with flanged fixing - the most used in the practice is considered the "most efficient one from a static point of view", as reported in the Italsider issue, reprinting 1979, "The connections in the steel structural work" - at page 58 has the disadvantage of piercing the column with the result of rendering it weak in the point of the maximum moment, namely at the point where instead a reinforcement is required. On the contrary, the joint in subject foresees a joint with reinforc¬ ed column welded in the workshop. It must be stressed that the re¬ inforcement of the standard steel profiles is convenient in that in

- 10 - the framed structures, the moment has a null point in the center line of the pillar and a maximum value in joint, and also because usually, each pillar belongs to two plane frames, positioned at right angle so that it is necessary to confer the pillar a good flexion resistance also in the weaker direction. This reinforcement must be such that , after the seismic forces have caused the yielding of the vertical di¬ agonals and therefore the shifting of the scaffolds with the result that the produced moments start to become significant, the plastic hing≡s are formed at the end of the girders and not at the end of the pillar, because this would led to the collapse of the whole structure. The re¬ inforcement of the pillar in the joint is useful not only for the cal_ culation of the structure, but also for the connection of rolling defects of the pillar passing through the joint which, as a rule, must pass through the piercing (23) and must be along its outline. The piercing can be exactly calculated for each profile; in fact, by changing the clearance between the plates (16) and the pillar ( for instance, according to the Italian rules, the clearance must range between 0 and 3 mm for plates larger than or equal to 10 mm) , it is possible to contain a rolling clearance for pillars of 3 mm x 4 weld- ings = 12 mm; namely, it is possible to overcome the rolling tolerance for all HE pillars except HEM 500. In this case, it will be necessary to change also the thickness of the reinforcement plates. This is al. lowed in that, if the rolled profile is smaller than the theoretical one, it is convenient to reinforce the section with thicker plates and if the profile is larger with less thick plates.

The plast deformation of the vertical diagonals before, and of the girder ends afterwards, must dissipate the kinetic energy transmitted from the seismic event to the building, hindering it to collapse or, in the worst case, allowing the evacuation of the building before it collapses.

Another defect of the flanged joint is that the connection bolts are placed at growing distances from the point where the tensile stress 9/09315

- 11 - is transmitted from the girder to the pillar and as the bolts are not engaged in the same measure, the breakage of a series of bolts is followed by the breakage of another series of bolts can occur. The bolt deformation before breakage occurs has a positive effect in respect of the ductility of the joint, however it does not form ductile rigid joints, because the dissipation of energy in the bolts before the collapse is very low.

The proposed joint instead allows non elastic deformation in the bolted joint with the ovalization of the piercings (plastic defor - mations in the connected plates) as well as the formation of actual plastic hinges.

Contrarily to the flanged solution, with ovalization of the piercings, the bolts are all engaged at the same time and in the same way so that the dissipation of energy occurs in the plates and not in the bolts. It is worthwhile to report the following sentences taken from the monography n°5 "Experimental research on the resistance and ductility of the structure connections" by Italsider - European Community - July 1981, Genoa. At page 42/43 at the end of the tests on the St. Andrew's cross shaped vertical frame work wind-brace joint, we read: "The behaviour of the bolted joint is ruled by the slidings which however do not seem to be casual and which anyway have a posi¬ tive effect; in fact, they contribute significantly to render the joint ductile, with the result of improving the dynamic answer of the system" and: "The ductility of the structure of the bolted joint is in these conditions, not less than that of the entirely welded so¬ lution." Speaking of the welded solution: "However together with the relevant difficulties connected with the necessity of carrying out the welding in the yard, this solution shows less dissipation of energy, furthermore there is no significant Eontribution to the ductility of the joint and the answer to seismic actions appears less progressive as compared to the bolted joint." And finally: "The test with bolts with larger diameter, M20, shows, in general, that an /09315

- 12 - increased size of the bolts offers positive aspects as to resistance without however reducing the ductility characteristics; actually, there are moments of more than 10% than those observed with bolts M14 with significantly higher rotation to breakage. Obviously, also the dissipation of energy in the hysteris cycle results to be con - siderably increased."

The proposed joint helps to form plastic hinges; there where the passage between the girder profile and the joint takes place. In fact, in this point (where the girder must be dimensioned for a moment which is almost equal to the center line moment and rather lower than the maximum fixed joint to which the same dimensioning of the girder with flanged joint is subject to a continuous charge of the stress), an abrupt decrease of the resistance takes place.

Another advantage of the proposed joint is that it makes 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 part of the joint (b) cannot shift horizontally.

A last advantage in respect of the flanged solution is that it is not necessary to weld the plates in the inside of the pillar in order to restore the continuity of the girder which passes through the joint because this continuity is given by the joint itself on the outside of the pillar.

The types of joints attached to the report of Ing. Besio, Corbani, Cremonini and De Martino, foresee brackets to be bolted near the pillars, the profiles of the not reinforced girders to be bolted near the brackets, and the connections with joint coverings. In this kind of assembling, the pillars must be pierced and furthermore no rein¬ forcement of the girders and of the pillars in the joint, no wind braces are foreseen and, finally, it consists of too many pieces. ith the proposed joint, during the assembling in the yard, the worker must only avail of bolts, nuts, washers and an equipment for the centering of the piercings and besides it is necessary to fix only the bolts and not also the braces, the plates and joint coverings, which are heavy and bulky.

For best employment, the' configuration of the joint foresees the lower and the upper pillar four girders orthogonal to each other,four or eight plane wind braces and eight vertical wind braces meet in it. With the same type of assembling, however, it is possible to realize joints which foresee the confluence in it of a different number of rods or rods with a different angle as well as girders of different height. The different angle of the tie sleepers can be carried out introducing them with a non different axis in respect of the part of the joint(b) and bending the plates (2) and (28) in correspondence of the plate (30). It is worthwhile to stress that the three wind braces are useful also when they are not required in the project, in that they are convenient for the assembling of the structure.

SUBSTITUTE SHEET

Claims

PATENT CLAIMS

1 . New steel structural elements: joints for space frames with or without wind brackets characterized by the fact that they consist of two characteristic parts (a) and (b) with ^"piercings that can be bolted in the yard. The parts of the joint (a) are prearranged to receive by means of a full resistance welded connection, the parts of the joint (b) and by hinged connection the horizontal and vertical wind braces, if any. The parts of the joint (a) and the parts of the joint (b) will be connected in the workshop with an inclination that can vary respectively at the pillars and at the girders. The girders and pillars assembled in the yard with a bolted connection will form a space structure with rigid joints with or without wind braces. The parts of the joint (a) can connect also only more parts of the joint (b) without being connected to the pillars.

2 . The part of the joint (b) referred to in the claim 1., character¬ ized by the fact that it consists of four plates, having the function of transmitting, by means of bolted connection, the stresses coming from the girder, which is connected to it, to the part of the joint (a).

In detail, the plates (2) and (28) transmit the bending moment, the plate (3) the cutting stress and the plate (30) transmit the torque. In order to simplify the assembling in the yard, the size of the plates can be such as to allow bolted connections (21), (29) and (31), by means of large bolts with large diameter in piercings which could not be carried out on the girders due to lack of room. This would also avoid to weaken the girders with the piercings. Furthermore, the resistance of the part of the joint (b), taking also into account the piercing, can be calculated to be stronger than the resistance of the girder connected to it, this in order to take into account of the greater value of the characteristics of the stresses at the fixing point.

3 . The plates referred to in the patent claim 2;, are characterized by the fact that the bolted connections (21), (29) and (31) can be carried out indipendently from each other so as to simplify the assembling of the girders in the yard.

4 . The section variations in the cross point between the girder and the part of the joint (b) is characterized by the fact that the variation does not occur gradually; it is abrupt so as to facili tate in this point the formation of the plastic hinges when the stresses are increasing.

5 . The part of the joint (a) referred to in the patent claim 1., characterized by the fact that it is possible to receive one, or more parts of the joint (b) by means of the piercings (21), (29) and (31). It can be equipped with the connections at the top and at the bottom with the piercing (22) apt to receive the vertical wind braces, with the piercing (17) apt to receive the horizonta wind braces and with the piercing (32) for the permeability of the installations.

The lower and upper connections (c) can be, if necessary, furthe parts of the joint (a). It is furthermore characterized by the fact that as it receives more parts of the joint (b) it will automatically have a greater resistance, useful to bear the increase of the stresses in the joint.

6 . The part of the joint (a) referred to in the patent claim 5., fo steel pillars passing through the joint (table 2), characterized by the fact that the plates (5) and (26) for the transmission of

SUBSTITUTE SHEET the cutting stress connect the plates (4) and (20) so realizing one single element. This part of the joint is furthermore chara¬ cterized by the fact that on the plates (4) and (20) the piercing (23) is carried out for the pillar to pass through and by the fact that the plate (20) is smaller than the plate (4) in order to simplify the bolted assembling of the frame bars in the yard. In fact, the girders put in the parts of the joint (a), centered and fixed by the lower wind braces in the yard cannot fall down because the parts of the joint (b) cannot shift horizontally. if the joint is at the end of the piece, it may be not necessary to carry out the piercing (23) or in case to make it on one single plate.

Part of the joint (a) referred to in the patent claim 6., for mixed structure of steel-concrete (table 3), characterized by the fact that the plates (25) with the piercing (12) are positioned on the plates (4) and (20) for the bolted connection of the part of the joint (a) by means of molds characterized by the fact that they must support the scaffolds. This method confers to the r.c structure the precision of the steel structural work.

And it also allows to cast the pillar together with the upper scaffold in that the scaffold weight can be supported by a tempo¬ rary frame whose bars consist of the supporting molds that can be later removed or not, the girders which collaborate with the casting when the mix has hardened and the lower wind braces. In this way, it is possible to position and connect the steel cage for r.c. in the joint to each scaffold. The reinforcement will involve one half of the lower floor and one half of the upper floor with the superimposing of the reinforcements at the pillar center. The part of the joint (a) referred to in the patent claim 5., fo the pillar interrupted at the joint (table 1) characterized by the fact that it consists of two parts which will be connected during the construction using also the parts^' of the joint (b) by the bolted connections (31), (21) and (29). On the plates (4) an (20) as well as plates (2) and (28) of the part of the joint (b) which in this case may be similar, two profiles (19) with the piercing (31) are arranged in alternative way so that when they are approached for allowing the corrispondent piercing (31) to coincide, there will be room left for placing between them the plate (3) of the part of the joint (b) equipped with the piercin (31). This type of joint, being all the bars interrupted in the joint, and therefore lighter and shorter, is suitable for manual assembling. In fact, placing a pillar passing through the joint the top on a pillar vertical line, the girder is lowered looked a piercing of a part of the joint (b). Forming a hinge in the upper hole of the piercing (31) of the profile (19) and with the other part of the joint (b), the part of the joint (b) hooked to the pulley is placed on another pillar. At this point, the plate (2) of the parts of the joint (b) are bolted in the plates (4) o the parts of the joint (a). After having lowered the upper pilla and the pillar passing through the joint, the bolts of the pierci (31) allow the pressure-flexion stress to be transferred from on pillar to the other one and the discharge in the joint of the scaffold weight which rests on the joint.

SUBSTITUTE SHEET