WO1996018774A1

WO1996018774A1 - Steel moment resisting frame beam-to-column connections

Info

Publication number: WO1996018774A1
Application number: PCT/US1995/015686
Authority: WO
Inventors: David L. Houghton
Original assignee: Houghton David L
Priority date: 1994-12-13
Filing date: 1995-12-01
Publication date: 1996-06-20
Also published as: EP0797709A4; MX9704361A; EP0797709A1

Abstract

Steel moment resisting frame (SMRF) connections between vertical columns (14) and horizontal beams (19) are for both original and retrofit building construction. The SMRF connection is a column tree assembly (13) consisting of primary trunk assembly (17) engaging secondary branch assembly (18). Primary trunk assembly (17) has vertical parallel gusset plates (25, 26) secured to vertical column (14) with flanges (27) at each beam-to-column joint location, and base plates (28) at one end of the column and a splice (33) at the other end. Secondary branch assembly (18) is secured normal to primary trunk assembly (17) between parallel gusset plates (25, 26). Secondary branch assembly (18) includes stub beam section (30) fitted with shear transfer plates (32) secured to the web of stub beam section (30) and to parallel gusset plates (25, 26). Plate (28) is secured to each flange of the stub beam (30) and parallel gusset plates (25, 26) to bridge the gap (31). Vertical shear tab plate (32) is secured to the web of stub beam (30).

Description

STEEL MOMENT RESISTING FRAME BEAM-TO-COLUMN CONNECTIONS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of building construction, and more particularly to novel steel moment resisting frame (SMRF) connections and spliced joints joining structural steel vertical columns and horizontal beams, and more particularly to such connections and spliced joints which are used in the construction of both single and multi-story structures of either original or retrofit construction.

2. Brief Description of the Prior Art

The prior art contains many teachings for the construction of moment connections and other related structural steel joints. These teachings have either focused on connections that allegedly reduce construction costs and facilitate erection methods, or on improving the seismic energy absorption capability of isolated load transfer mechanisms in a given joint while ignoring other critical load transfer mechanisms that are required to complete the SMRF system. Quite importantly, given the severe lessons learned in recent major earthquake activity, prior art SMRF connections are not usable in seismically active areas. Examples reside in United States Letters Patents, 3,952,472, 4,094,111 and 4,993,095.

Prior to recently reported earthquake damage, the traditional beam-to-column SMRF connection used in most steel frame buildings consisted of a full- penetration single-bevel groove weld connecting both beam flanges of a horizontal beam to the vertical column flange to resist earthquake lateral forces in rigid joint/moment frame action. The gravity forces are resisted by a shear-resisting tab plate that is shop welded to the column flange and field bolted in single shear to the beam web using high strength bolts.

The design approach adopted by the structural engineering community for SMRF systems in seismic areas assumes that a significant level of system ductility can be developed. This ductility is potentially available in steel ductile frame if premature brittle failures are prevented. Testing to date of SMRF connections, following recent severe earthquake activity, suggests that the behavior of beam-to-column joints will depend on the strain rates imposed on the more brittle load transfer mechanisms along the load path. Observed recent earthquake damage to SMRF connections consists primarily of either a partial or complete failure of the full penetration single-bevel groove weld between the beam flange and the column flange, either in the weld itself or along the heat affected zone of the column flange, pulling with it a divot of parent column steel from the face of column flange. The origination of the crack is normally at the narrow root of the groove weld profile, which is inherently subject to slag inclusions during the field welding process due to its refined geometry. These inclusions act as stress risers that initiate cracking during the impactive load from an earthquake. Stress risers are also created by the backer bar used to bridge the root gap before making the weld. The backer box is commonly tack welded in place below each beam flange and not removed. In addition, these beam flange-to-column flange failures have resulted in shear failure of the high strength bolts connecting the beam web to the shear tab plate attached to the column flange for the support of gravity loads.

In other instances, the crack again originates at the root of the groove weld, but enters the column flange and propagates through the full thickness and width of the flange and into the column web. This particular cracking pattern appears to be more pronounced in the jumbo column sections, both rolled and built-up sections.

The effect of these SMRF connection failures in damaged buildings is three-fold; 1) the integrity of the seismic lateral load resistance of the connections has been seriously compromised, potentially leading to the loss of gravity support and partial collapse of the building during extended strong ground motion or aftershocks; 2) building owners and commercial property insurance carriers have lost confidence in the earthquake performance of steel buildings, and 3) the International Conference of Building Officials has issued an emergency code change that deletes the prequalified SMRF connection because of poor performance of steel moment frame beam-to-column connections in recent earthquakes and subsequent testing at the University of Texas-Austin.

In response to this building industry crisis, practicing structural engineers, together with university researchers, metallurgical and welding engineers, steel and welding electrode manufacturers, and steel fabricators and erectors individually and collectively appear to be largely focused on ways to dramatically improve and/or modify the traditional SMRF connection configuration. These improvements and/or modi ications to the traditional SMRF connection unfortunately still rely fundamentally on the post-yield straining of large highly-restrained full-penetration single-bevel groove welds (performed under hard-to- control field conditions which can dramatically affect weld toughness) or structural steel column shapes in a through-thickness direction (i.e., 90° to the longitudinal direction of the weld or normal to the rolled grain of the steel shape) , under the influence of impactive earthquake forces. As clearly demonstrated by the recently observed and reported widespread damage and subsequent testing, these joint configuration attributes do not provide a reliable mechanism for the dissipation of earthquake energy, and can lead to brittle fracture. Brittle fracture is in violation of the SMRF design philosophy as codified in the Uniform Building Code. Hence the need for a novel SMRF beam-to-column connection that altogether eliminates these negative attributes, which is the subject of this invention. SUMMARY OF THE INVENTION

Accordingly, the above problems and difficulties are obviated by the present invention which involves the novel SMRF connection configuration that joins vertical columns and horizontal beams using all shop fillet welds and all field bolted splices for new building construction. The novel SMRF connection is part of a column tree assembly which consists of a primary trunk assembly engaging a secondary branch assembly(ies) . The primary trunk assembly consists of a rolled column wide flange section or a built-up section that is fitted with two pairs of horizontal web stiffener plates at each beam-to-column joint location (i.e., one pair at the approximate location of each beam flange) and secured to two vertical parallel gusset plates along the exterior corner edge of each column flange tip, providing a horizontal gap between parallel gusset plates equal to the flange width of the column. Both the column web stiffener plates and parallel gusset plates are shop fillet welded to the column. The primary trunk assembly includes provisions for a base anchorage design (as applicable) at one end of the column and a column splice at the other end (either field bolted or welded) , including a column web tab plate to facilitate erection. A secondary assembly is secured normal to the primary trunk assembly between the parallel gusset plates. The secondary branch assembly consists of a rolled wide flange or built-up stub beam section that is fitted with a pair of vertical shear transfer plates (for transferring SMRF beam shear to the parallel gusset plates) that are secured to the web of the stub beam section and to the parallel extremity from the primary trunk assembly, and (for rolled beam sections only) a flange cover plate secured to each flange of the stub beam and to the parallel gusset plates to horizontally bridge the gap between parallel gusset plates, and includes at its extremity from the primary trunk assembly a vertical shear tab plate (to provide temporary shoring and final gravity support for the link beam that connects the juxtaposed column trees to one another in order to complete the inventive SMRF system) that is secured to the web of the stub beam and is prepared with bolt holes near its free edge. All plates to the stub beam section (i.e., shear transfer plates, flange cover plates (as applicable) and web shear tab plate) are shop fillet-welded to the stub beam section and to the parallel gusset plates. A net vertical gap is left between the end of the stub beam section closest to the face of column flange. The free end of each flange of the stub beam section is prepared with oversized bolt holes. A complete SMRF system is achieved by joining juxtaposed column tree assemblies at a given floor level with link beam. Assemblies that are bolted to the extremities of secondary branch assemblies using flange splice plates and the shear tab plate welded to the web of the stub beam section. The ends of the link beam are prepared with oversized bolt holes in each flange and with bolt holes in the web.

For retrofit construction, the existing SMRF connection is radically altered by removing the full penetration welds connecting horizontal beam flanges to vertical column flange by back-gouging and coping, and providing parallel gusset plates tailored with a smooth cut-out to allow weld access for attaching the parallel gusset plates to the existing column. If no continuity plates are provided in the existing column to stiffen the web panel zone, the column flanges are locally stiffened prior to securing the parallel gusset plates. In addition, a pair of flange cover plates are secured to the top and bottom beam flange to bridge the difference between the column flange width and the beam flange width. All plates (i.e., column web stiffener plates, parallel gusset plates and beam flange cover plates) are fillet-welded in the field to the existing column and beam. It is to be particularly noted that all flange splice connections at the extremities of the column tree assembly, including primary trunk assembly and the secondary branch assembly with associated tab plates, can be field bolted using high strength slip-critical bolts in double shear. All web tab plate connections are field bolted in either single or double shear using high strength bolts. Splice bolt connections are located at points of reduced flectural demand. Bolted splice plates utilize oversize holes to facilitate erection fit-up and accomplish fabrication/erection tolerances and to provide an energy dissipation mechanism through bolt slippage at high stress levels.

Therefore, it is among the primary objects of the present invention to provide a novel SMRF beam-to- column connection configuration and fabrication which eliminates altogether the post-yield straining of large highly-restrained full-penetration single-bevel groove welds and/or structural steel column shapes in the through-thickness direction and replaces these negative attributes with simple unrestrained fillet-weld group configurations and bolted splice configurations which are recognized to be inherently ductile fabrication and erection practices that perform particularly well under the influence of i pactive earthquake forces and which are not subject to variable field conditions.

Another object of the present invention is to provide a novel SMRF beam-to-column connection that is readily adaptable for new construction as well as retrofit construction.

Another object of the present invention is to provide a novel joint configuration for use in beam-to- column moment connections in steel moment resisting single or multi-story frame buildings that fully complies with the emergency code provisions recently issued by the International Conference of Building Officials.

Another object of the present invention is to provide a novel SMRF beam-to-column connection that is totally fabricated off-site at a shop location for new construction and transported to a building site for bolted securement to complete the SMRF system.

Another object of the present invention is to provide a novel SMRF beam-to-column connection that is partially fabricated off-site at a shop location for retrofit construction and transported to the building site for simple fillet-welded securement to complete the SMRF system.

Yet a further object resides in providing for new construction a combination of fillet-welded and bolted securement between a vertical SMRF column and the end of a SMRF horizontal beam which is capable of transferring and dissipating seismic lateral impactive forces while providing positive gravity support during and after a major earthquake.

Another object resides in employing oversize bolt holes in securement of the link beam assembly in new construction to facilitate erection fit-up, accommodate fabrication and erection tolerances and to provide an energy dissipation mechanism through bolt slippage at high stress levels.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood with reference to the following description, taken in connection with the accompanying drawings in which:

FIGURE l is a diagrammatic view, partly in section, of a multi-story SMRF building employing the novel SMRF beam-to-column connections embodying the present invention;

FIGURE 2 is a top plan view of the structure shown in FIGURE 1 as taken in the direction of arrows 2-2 thereof;

FIGURE 3 is an enlarged elevational view of the SMRF connection configuration between a vertical column and a horizontal beam employing the inventive concepts;

FIGURE 4 is a section through the stub beam as taken in the direction of arrows 4-4 of FIGURE 3;

FIGURE 5 is an enlarged top plan view of the SMRF connection configuration shown in FIGURE 3 with portions broken away to show underlying joints;

FIGURE 6 is an exploded isometric view of the SMRF connection configuration shown in FIGURES 3, 4 and 5 illustrating the relative relationship of all components;

FIGURE 7 is a view similar to the view of FIGURE 3 showing the SMRF connection configuration adapted for us in retrofit construction;

FIGURE 8 is an end view of the SMRF connection configuration shown in FIGURE 7;

FIGURE 9 is a top plan view of the SMRF connection configuration shown in FIGURES 7 and 8;

FIGURE 10 is a partially exploded isometric view of the SMRF connection configuration shown in FIGURE 7; and

FIGURE 11 is an enlarged cross-sectional view of the bolted flange between the extremity of the secondary branch assembly stub beam section and the link beam assembly, illustrating the oversize hole through which a high strength slip-critical bolt is disposed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGURE 1, a steel moment resisting frame (SMRF) building is indicated in the general direction of arrow 10 which includes an exterior curtain wall system 11 which includes suitable windows adjacent to different floors and suitable doors for ingress and egress to and from the building. Inside the exterior curtain wall system, the complete SMRF system is provided for resisting earthquake lateral forces and for gravity forces acting on the building, on a foundation 12. The novel SMRF system consists of a plurality of juxtaposed column tree assemblies 13 connected laterally by link beam assemblies 16 at each floor level, and connected vertically (as applicable) by column splices 15. The column tree assembly 13 includes a vertical column 14 which may include splice 15 so that a plurality of column tree assemblies may be connected together as the building frame is erected. The novel column tree assembly 13 incorporating the present invention consists of a primary trunk assembly 17 which couples a secondary branch assembly(ies) 18. It is noted that the link beam assembly 16 is oriented in a horizontal manner so that each end of the link beam 19 resides adjacent to the free end of the secondary branch assembly for splicing purposes, to complete the SMRF system.

Although a completed construction is shown, it is to be understood that the primary trunk assembly and the secondary branch assembly, including the link beam, may be shop fabricated as separate components, with the primary trunk assembly and the secondary branch assembly joined in the shop into a column tree assembly, prior to transport to the erection site. In this manner, all welding procedures can be done under controlled conditions within the shop, while splice connection 20 of the link beam to the juxtaposed column tree assemblies can be done by field bolting at the job site. Shop fillet welding of the SMRF connection can be done for assembling the primary trunk assembly 17 at the shop while the energy dissipation mechanism 20 using bolted connections with oversized bolt holes can be constructed at the job site.

Referring to FIGURE 2, a typical metal decking with concrete fill or other suitable floor system is indicated by numeral 21 and a floor covering is indicated by numeral 22. The flooring is supported by typical floor beams 23.

The primary trunk assembly and the secondary branch assembly, as well as the link beam assembly, will now be described. In general, the column tree assembly consists of all fillet-welded component construction, and joins together the primary trunk assembly with secondary branch assembly(ies) . The attachment of the free end of the secondary branch assembly to the link beam assembly is a field bolted procedure which includes the energy dissipation mechanism.

The inventive SMRF beam-to-column connection configuration for new building construction is illustrated in FIGURES 3-6, inclusive. The link beam and stub beam section column may take the form of a rolled wide flange steel shape or it may be a built-up section constructed of steel plate. The primary trunk assembly 17 consists of a column section 14 that is stiffened with two pairs of web stiffener plates 27 at each beam-to-column location (i.e., near the vertical location of each beam flange) and secured to the two vertical parallel gusset plates 25 and 26 along the exterior corner edge of each column flange tip. The parallel gusset plates and column web stiffener plates are fillet welded to the column section. A secondary branch assembly 18 is secured normal to the primary trunk assembly 17 between the gap provided by the parallel gusset plates 25 and 26. The secondary branch 96/18774 PCMJS95/15686

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assembly 18 consists of a stub beam section 30 that is fitted with a pair of vertical shear transfer plates 32 and to the parallel gusset plates 25 and 26. A gap 31 is provided between the terminating end of the stub beam section 30 and the opposing flange surface of vertical column 15. When the stub beam section 30 is a rolled structural stub, a flange cover plate 28 is provided and secured to each flange of the stub beam and to the parallel gusset plates 25 and 26 to horizontally bridge the gap between parallel gusset plates. When the stub beam section is a built-up section using steel plate, the flange width of the built-up section is cut to bridge the gap, eliminating the need for flange cover plates. The secondary branch assembly is also fitted with a vertical shear tab plate 38 at its extremity from the primary trunk assembly that is secured to the web of the stub beam and is prepared with bolt holes near its free edge to receive the spliced field-bolted web connection of the link beam assembly 16. All plates secured to the stub beam section (i.e., 32, 28 and 38) are shop fillet-welded to the stub beam section 30 and to the parallel gusset plates 25 and 26. The free end of each flange of the stub beam section is prepared with oversized bolt holes 39 to receive the spliced field bolted flange connection plates 33 connecting the link beam assembly 16. The ends of link beam 16 flanges are also prepared with oversized holes to receive splice connection plates 33.

Attachment of the splice plates to the flanges of the respective beams is achieved by a plurality of bolts, such as bolt 37. All bolted splice connections of the completed SMRF system, including the primary trunk assembly, secondary branch assembly, and link beam assembly, are field bolted using high-strength slip- critical bolts in double shear. All web tab plate connections are field bolted in either single or double shear, as necessary, using high-strength bolts. Splice connections are located at frame points of reduced flexural demand. The bolted flange splices utilize over-size holes in the parent beam sections, such as shown in FIGURE 11, wherein bolt 37, as an example, is shown having a shank which passes through over-size hole 39 in the flange of beam 30, as an example, between flange splice plates 35 and 36. The over-size holes, whether they be in the web or flanges of the respective beams, facilitate erection fit-up and accommodate fabrication/erection tolerances and provide an energy dissipation mechanism through bolt slippage at high stress levels. Therefore, in summary with respect to the novel SMRF beam-to-column connection shown in FIGURES 3-6, inclusive, it can be seen that the entire SMRF column tree assembly is for new construction shop fabrication.

Referring to FIGURES 7-10, inclusive, the SMRF beam-to-column connection is disclosed to achieve retrofit or rehabilitation to existing traditional seismic moment resisting frame joint connections in steel buildings. The retrofit SMRF connection is illustrated in the general direction of arrow 41 and is employed to connect one end of existing SMRF horizontal beam(s) 42 framing into a beam-to-column joint with an existing SMRF vertical column 46. The retrofit SMRF connection includes a pair of parallel gusset plates 43 and 44 which are deposed on opposite sides of the existing column 46 and are joined therewith by fillet welds and by a pair of upper and lower column stiffener plates 47. These plates, as well as the parallel gusset plates, are similar to those previously described for original (new) construction. It is noted that in this adaptation of the novel SMRF beam-to-column connection, a tailored smooth cut-out, indicated by numerals 50 and 51, are required in each companion gusset plate to allow field weld access to provide the fillet-welded vertical attachment along the tips of the column flanges. Prior to attaching the companion gusset plates, the existing restrained full-penetration, single-bevel groove welds at each beam flange are removed by back-gouging and coping out the flange material at the location of existing weld web-access holes, as indicated by numeral 52, and grinding back the balance of flange weld material to the face of the column to a smooth competent surface. In addition, two new beam flange cover plates, as indicated by numerals 53 and 54, are required to be welded to both the top and bottom beam flange to bridge the difference between the column flange and the beam flange width. If no continuity plates are provided in the existing column panel zone, the column is locally stiffened with two pairs of web stiffener plates 46 and 47 near the vertical location of each beam flange, prior to attaching the companion gusset plates. The existing beam shear tab plate connection, as indicated by numeral 55, is left unaltered or, as may be deemed necessary, appropriate strengthening by fillet welding around perimeter of the free edges of the tab plate may be performed.

In summary, the structural engineering community, together with steel frame building owners and material/welding experts, remain stunned by the significant and widespread damage suffered during recent earthquake activity by the heretofore traditional conventional steel moment resisting frame (SMRF) beam- to-column joint connections employed in steel buildings.

The reported SMRF connection failures attributed to earthquake occurrence are particularly treacherous because of their subtlety in being detected. In many instances, the structural damage is accompanied by only relatively minor stress to architectural finishes and virtually no global structural out-of- plumbness is experienced. Because the structural damage is generally not readily detectable on the basis of distress to architectural finishes, there is reason to believe that similar damage to steel frame buildings with SMRF connections may already exist and remain undetected in other seismically active areas.

In view of the foregoing, it can be seen that the inventive SMRF beam-to-column connection configuration and fabrication provides a complete departure from the heretofore traditional SMRF beam-to- column joint configuration and fabrication approach (including modifications and/or adaptations of same) by eliminating altogether the unseemly welded connection between the seismic moment resisting frame beam flanges and the face of column flange that relies fundamentally on the post-yield straining of either 1) large highly- restrained full-penetration single-level groove welds performed under hard-to-control field conditions which can dramatically affect weld toughness) and/or 2) structural steel column shapes in a through-thickness direction (i.e., 90° to the longitudinal direction of the weld or normal to the rolled grain of the steel shape to resist impactive earthquake forces. The novel SMRF beam-to-column connection configuration and fabrication approach disclosed in this invention replaces it with simple unrestrained inherently-ductile fabrication and erection practices that have performed well during past earthquakes without serious incident and are not subject to variable field conditions. The inventive SMRF beam-to-column connections for new construction consist of all shop fillet-welded construction and all field bolted splice connections. The adaptation of this inventive SMRF beam-to-column connection for retrofit of existing traditional SMRF connections is all field fillet-welded construction. The load transfer mechanisms involved in the novel SMRF connection configuration do not impose post-yield straining of either the fillet welds or the structural steel column shapes in the through-thickness direction. In addition, the size of the fillet welds is relatively small because of the ample dimensions provided by the parallel gusset plates in proportioning the joint configuration. In addition, the problem of cracks being initiated during an earthquake because of stress risers created by slag inclusions at the root of the single- level groove weld and/or by tack welded backer bars that are left in place is totally eliminated with the use of all fillet-welded construction. The integrity of fillet weld construction in the inventive SMRF beam-to-column connection is further enhanced for new construction since it is all performed in the shop where controls on quality are easier to enforce and variable field conditions ar mitigated. Accordingly, the present invention is a radical departure from what has normally been done in designing and fabricating seismic moment resisting frame systems to date. All joint connections of the present invention can be designed to develop as required in excess of l.5x plastic moment capacity (M_p) of the required beam capacity.

Examples of such adaptations and modifications include the ability to provide moment resisting capability for a given SMRF column in each principle building direction, i.e., about both the strong and weak axis of the column, using a pair of secondary parallel gusset plates (for resisting weak column axis moment) fillet welded to a pair of primary parallel gusset plates (for resisting strong column axis moment) to engage an orthogroove secondary branch assembly(ies) oriented perpendicular to the weak axis of the column. Additionally, adaptations include the ability to provide moment resisting capability for a given box column in each principle building direction, i.e., about both axes of the box column, using a pair of secondary parallel gusset plates disposed as described in the example.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that adaptations and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

Claims

WHAT IS CLAIMED IS :

1. A steel moment resisting framed connection for joining a horizontal link beam with a vertical column, the combination which comprises:

a secondary branch assembly having opposite ends disposed between said column and said link beam;

a primary trunk assembly securing one end of said secondary branch assembly with said column;

an energy dissipation mechanism securing the other end of said secondary assembly with said horizontal link beam;

fillet weld securement attaching said primary trunk assembly with said column and securing said primary trunk assembly to said secondary branch assembly to provide an unrestrained, inherently ductile construction joint that eliminates the post-yield straining of restrained full-penetration single-level groove welds and structural steel column shapes in the through-thickness direction.

2. The invention as defined in Claim 1 wherein:

said energy dissipation mechanism includes a shear tab secured to said secondary branch assembly by a fillet weld and secured to said link beam by shear tab bolt fasteners.

3. The invention as defined in Claim 2 wherein:

said energy dissipation mechanism further includes a plurality of flange splice plates secured between said secondary branch assembly and said link beam;

said flange splice plates spaced apart from and separated by said shear tab; and

said flange splice plates having over¬ sized holes for receiving plate bolt fasteners.

4. The invention as defined in Claim 3 including:

a shear transfer plate means joining said one end of said secondary branch assembly to said primary trunk assembly; and

filet weld securement of said shear transfer plate means to said primary trunk assembly.

5. The invention as defined in Claim 4 wherein:

said primary trunk assembly includes column web stiffening plates joined by a plurality of fillet welds to said column and to said primary trunk assembly.

6. The invention as defined in Claim 5 wherein:

said primary trunk assembly includes a pair of parallel gusset plates having opposite ends secured to said column, said one end of said secondary branch assembly, said column web stiffener plates and said shear transfer plate by said fillet weldments.

7. The invention as defined in Claim 1 wherein: said primary trunk assembly includes a pair of spaced-apart parallel gusset plates having opposite ends;

a selected end of said parallel gusset plates defining a yoke having a space between opposing gusset plates of said pair occupied by said column;

said other end of said gusset plates secured to and separated by said secondary branch assembly; and

said fillet weldments securing said gusset plates to said column and said secondary branch assembly.

8. The invention as defined in Claim 7 wherein:

said secondary branch assembly includes a stub beam having opposite ends with a selected end secured to said gusset plates and the other end secured to said link beam by said energy dissipation mechanism;

said energy dissipation mechanism includes a plurality of flange splice plates interconnecting said stub beam with said link beam; and

said stub beam and link beam members having over-sized holes with respect to bolt fasteners attaching said stub beam to said link beam.

9. In an existing structural steel moment connection between a flanged vertical column and a flanged horizontal beam, the improvement which comprises:

a pair of parallel gusset plates separated by said column and said beam;

a plurality of flange splice plates joining said gusset plates with said beam;

said parallel gusset plates having rear cut-outs adjacent to said beam allowing welding access to said beam and said gusset plates;

column web stiffener plates disposed on said flanged column adjacent to said parallel gusset plates; and

fillet weldments securing said parallel gusset plates to said column and said beam, securing said flange splice plates to said parallel gusset plates and said beam and securing said column web stiffener plates to said column and said parallel gusset plates to provide an unrestrained, inherently ductile construction joint that eliminates the post-yield straining of restrained full-penetration single-level groove welds and structural steel column shapes in the through- thickness direction.

10. The invention as defined in Claim 9 including:

an existing shear tab secured between said beam and said column in spaced relationship with respect to said parallel gusset plates.

11. The invention as defined in Claim 10 wherein:

said column and said beam provide a shop- fabricated pre-constructed framing system.

12. The invention as defined in Claims 1 and 9 wherein: said column and said beam having a continuous web separating upper and lower flanges; and

said parallel gusset plates secured to and separated by opposite exterior sides of said column flanges and said beam flanges.

13. A structural joint connection for connecting a horizontal beam having top and bottom flanges to a vertical column having left and right flanges, said joint connection comprising two vertical plates adapted to be disposed in parallel relationship on opposite sides of said column and adapted to be attached to said column and adapted to extend horizontally from said column, means disposed against said horizontal beam flanges and attached to said flanges by horizontal fillet welds, said means further attached to said vertical plates by horizontal fillet welds, said horizontal fillet welds directed longitudinally in the direction of said beam.

14. The joint connection of Claim 13 wherein:

said horizontal beam is a stub beam and wherein is included a second beam having top and bottom flanges and wherein is included means for bolting said stub beam to said second beam.

15. The joint connection of Claim 14 wherein:

said means for bolting said stub beam to said second beam comprises one or more flange connection plates adapted to be connected by bolts to said top and bottom flanges of said stub beam and said second beam.

16. The joint connection of Claim 15 wherein:

said stub beam is comprised of a web connected intermediate said top and bottom flanges of said stub beam and wherein said second beam is comprised of a web connected intermediate said top and bottom flanges of said second beam and wherein said means for bolting further comprises a vertical shear transfer plate welded to said web of said stub beam by a vertical fillet weld and wherein said vertical shear transfer plate has bolt holes for connecting to said web of said second beam.

17. The joint connection of Claim 14 wherein:

said stub beam comprises a web connected intermediate said top and bottom flanges and wherein is included two vertical shear transfer plates, disposed on opposite sides of said stub beam and each of said vertical shear transfer plates having a vertical fillet weld to said web of said stub beam and a vertical fillet weld to a respective vertical plate.

18. The joint connection of Claim 17 wherein:

each said vertical shear transfer plate is further connected to said stub beam flanges by fillet welds at each end of said shear transfer plate.

19. The joint connection of Claim 13 wherein:

said horizontal beam comprises a web connected intermediate said top and bottom flanges and wherein is included one or more vertical shear transfer plates connected between said web of said horizontal beam and said column, and wherein said one or more vertical shear transfer plates is connected to said column by vertical fillet weld.

20. The joint connection of Claim 13 wherein:

said beam comprises a web connected intermediate said top and bottom flanges and wherein is included one or more vertical shear transfer plates, each vertical shear transfer plate being connected to said web of said beam and one of said parallel vertical plates by vertical fillet welds.

21. The joint connection of Claim 20 wherein:

each said vertical shear transfer plate has opposing ends and wherein each said vertical shear transfer plate is further connected to the flanges of said beam by fillet welds at opposing ends of each said vertical shear transfer plate.

22. The joint connection of Claim 13 wherein:

said vertical parallel plates are connected to said column by vertical fillet welds.

23. The joint connection of Claim 22 wherein:

each said vertical parallel plate is connected to both said left and right flanges.

24. The joint connection of Claim 13 wherein: all of said welds are first accomplished under shop conditions, leaving only bolt connections to be made under field conditions.

25. The joint connection of Claim 13 wherein:

all of said welds are first accomplished under shop conditions and, subsequently, only bolt connections are made under field conditions.

26. A structural joint connection for connecting a horizontal beam to a vertical column, said joint connection comprising two vertical plates disposed on opposite sides of said column and wherein is included means attaching said vertical plates to said column and wherein said vertical plates are disposed to extend from said column along the sides of said beam and wherein is included means attaching said vertical plates to said beam.

27. The structural joint connection of Claim 26 wherein:

said means attaching said vertical plates to said column comprise welds between said column and said vertical plates.

28. The structural joint connection of Claim 26 wherein:

said means attached said vertical plates to said column comprise plates welded to said column and welded to said vertical plates.

29. The structural joint connection of Claim 26 wherein:

said means attaching said vertical plates to said horizontal beam comprise welds between said vertical plates and said horizontal beam.

30. The structural joint connection of Claim 26 wherein:

said beam comprises top and bottom flanges and wherein said means attaching said vertical plates to said horizontal beam comprise plate means welded to said vertical plates and wherein said plate means are further welded to said top and bottom flanges of said horizontal beam.

31. A steel moment resisting frame connection for joining a horizontal link beam with a vertical column, the combination which comprises:

a primary trunk assembly securing one end of said secondary branch assembly with said column; and