Seismic Brace Design

Design andDetailing of

SeismicConnections for

Braced FrameStructures

Terry R. Lundeen

Author

Terry Lundeen is a principalwith the structural engineering

firm of Coughlin Porter Lundeen,Inc., in Seattle. His experienceover the past 20 years includesthe design of numerous buildingstructures as well as deep wateroffshore platforms and large air-craft assembly facilities. Hereceived his bachelor of sciencein civil engineering from BradleyUniversity in 1980 and his masterof science in civil engineeringfrom the University of Houston in1985.

Mr. Lundeen has a specialinterest in seismic design andretrofit of structures, he is activein the development of seismicdesign provisions for the UniformBuilding Code through theStructural Engineers Associationof Washington and for the federalNEHRP documents through theBuilding Seismic Safety Counciland the American Society of CivilEngineers. He contributes to thepreparation of the Western StatesStructural Engineers Exam andlectures on the seismic design ofsteel structures at the Universityof Washington. He is a registeredstructural engineer in California,Washington and British Columbia.

Summary

As a result of lessons learnedfrom recent earthquakes

(Loma Prieta, Northridge, Kobe)as well as on-going research, theseismic design and detailing ofbraced frame connections hasevolved significantly over the pastten years.

Using an example office build-ing, this paper presents thedesign of braced frame connec-tions according to the recentlyreleased 1997 Edition of theSeismic Provisions for StructuralSteel Buildings by AISC. Theexamples include various types ofbrace connections and columnsplices for SpeciallyConcentrically Braced Frames,Ordinary Concentrically Braced

25-1

Frames and Eccentrically BracedFrames. The seismic designapproach and details are basedon practical implementation of thecurrent provisions on numerouscommercial, industrial, education-al and residential buildings.

© 2003 by American Institute of Steel Construction, Inc. All rights reserved.This publication or any part thereof must not be reproduced in any form without permission of the publisher.

DESIGN AND DETAILING OF SEISMIC CONNECTIONSFOR BRACED FRAME STRUCTURES

TERRY R. LUNDEEN

INTRODUCTION

This paper presents the design and detailing ofbraced frame connections for seismic loading. Aprototype 4-story office building in Seismic Zone 3is used as the basis for the examples. A typicalfloor framing plan with braced frame locations isgiven in Figure 1.

The examples include the three basic braced frametypes: Special Concentrically Braced Frames(SCBF), Ordinary Concentrically Braced Frames(OCBF), and Eccentrically Braced Frames (EBF).A variety of brace types are provided includingpipes, structural tubes, and wide flanges.Additionally, both welded and bolted connectionsare provided for reference.

Table 1General Criteria

Code:

Structure:

MaterialSpecifications:

Loads:

• AISC Seismic Provisions forStructural Steel Buildings

• AISC Manual for Load &Resistance Factor Design

• Office building• Located in Seismic Zone 3• Soil profile type Sc• The frame configuration are

as follows:1. Special Concentrically

Braced Frame; R = 6.42. Ordinary Concentrically

Braced Frame; R = 5.63. Eccentrically Braced

Frame; R = 7

• Steel framing A572, Grade 50• High-strength A325/A490

bolts• Welding Electrodes: E70

• Roof Dead Load = 20psf• Roof Live Load = 25psf• Floor Dead Load = 80psf• Floor Live Load = 80psf

(reducible)

The overall forces on the structure are based on the1997 Edition of the Uniform Building Code. Thedesign of steel members and connections is basedon the AISC Seismic Provisions for SteelBuildings, dated April 17, 1997. A list of thegeneral design criteria is given in Table 1.

While most of the new code provisions are similarto those of older versions, there have been somechanges and updates. These changes includeexplicit consideration of material overstrength andmore direct integration of the AISC SeismicProvisions into the model building codes.Additional, more detailed, revisions are alsopresented in this paper.

While the subject of the paper is connection design,brace and column member issues that directlyeffect the connections are discussed. The detaileddesign of these members, however, is not provided.

Figure 1 - Typical Floor Plan

25-3© 2003 by American Institute of Steel Construction, Inc. All rights reserved.

This publication or any part thereof must not be reproduced in any form without permission of the publisher.

SPECIAL CONCENTRICALLY BRACEDFRAME (SCBF) CONNECTION DESIGN

For this system, a frame consisting of welded pipebraces and a frame consisting of bolted wide flangebraces are provided. Frame elevations for bothconfigurations are given in Figures 2 and 3. Thebraces are arranged in a Chevron pattern bothbecause it represents the most commonly usedarrangement and because of the additional designconsiderations given in the Provisions.

For a building of this size, the welded pipeconfiguration is preferable both from a design andconstruction perspective. The bolted wide flangeconfiguration is given as a reference for largestructures with brace forces that cannot beaccommodated with pipes. Similarly, the strongaxis column orientation given in the first frame isdesirable; however, a weak axis columnarrangement is also provided for reference.

The SCBF is a newer version of the traditionalsteel braced frame. This system was developed toprovide documented ductility, both analytically andthrough testing. In general, yielding and columnbuckling of the braces provide this ductility. Inorder for this behavior to be achieved, localbuckling in the braces or connections cannot occur.

Another requirement to guarantee the desirablebehavior of this system is to preclude plastic hingeformation in Chevron beams under unbalancedbrace buckling and yielding forces. Also, the beamflanges at Chevron connections must be bracedout-of-plane.

The connections in SCBF's must be stronger thanthe yielding members. For this system, theconnections must also have either the strength todevelop a strong axis plastic hinge or be arrangedto allow a weak axis yield line to form under thecyclic yielding and buckling of the braces.

A final consideration for this system is with thecolumns. In addition to having the strength toresist axial forces from the amplified earthquakeload combinations, the columns and splices aredesigned for a nominal shear force in the column.This shear strength requirement is providedbecause plastic hinges formed in the columns atlarge story drifts in some of the initial analyticalanalyses of the system.

Figure 2 - SCBF Elevation

Figure 3 - Frame Elevation

25-4


WELDED PIPE BRACE-TO-WIDE FLANGECOLUMN CONNECTION (Fig. 4)

Required Strength

The required strength of bracing connections, perAISC Sec. 13.3.a, is determined from the least ofthe following equations:

1. Bracing member's nominal axial tensilestrength:

where equals 1.1 per AISCSec. 6.2.

Figure 4 - Welded Pipe Brace-to-Wide FlangeColumn Connection

2. Maximum force, transferred to braceby system as determined by analysis

Brace-to-Gusset WeldThe required weld thickness for the brace-to-gusset, assuming 12 in. of weld along (4) edges:

Use 12" of ½" weld on (4) edges

• The weld thicknesses are relatively large tolimit the extension of the gusset plates beyondthe yield line.

Gusset-to-Beam and Column Welds

Using the Uniform Force Method as recommendedper LRFD Vol. II Part 11, the axial force from thebrace is resolved into the corresponding moment,horizontal, and vertical forces on the gusset plate.This is shown on the free body diagram of thegusset plate Fig. 5.

• As can be seen, the connection force to thebeam is much larger than that to the column.As such, larger welds are used at the beamflange to control the size of the gusset plate.

Figure 5 — Gusset-to-Beam and Column WeldForces

25-5

• Case 1 is normally used in design since Case 2basically requires static push-over analysis ornon-linear time history analysis to establishthe maximum system force.

• This connection was designed with a "yieldline" a distance of 2t from the brace in lieu ofthe flexural strength requirements of Section13.3c.


Weld of gusset-to-beam flanges

Use ½" weld for gusset to beam flanges.

Weld of gusset to column

Use ¼" weld for gusset to column.

Gusset Plate Thickness

Per AISC Sec. 13.3.b: The design tensile strength,determined from the limit states of tension ruptureand block shear rupture strength per LRFD ChapterD, shall be greater than or equal to the requiredstrength, as determined from above.

Also, the design compression strength, determinedfrom the plate buckling limit state, shall be greaterthan the buckling strength of the brace which isgiven from the following:

Finally, the plate must have adequate shearyielding strength for the designed fillet weld sizes.

Table 2

Criteria

Block Shear

Tension Yielding

Plate Buckling

Shear Yielding atFillet Welds

Required Gusset PlateThickness (in)

.42

.41

.54

.71

Use ¾" gusset plate

• Once the overall dimensions of the gussetplate are established by the welds and yieldline, the thickness is determined from thevarious remaining criteria.



WELDED PIPE BRACE-TO-BEAMCONNECTION (Fig. 6)

• The beam flanges of this connection must bebraced out-of-plane per AISC Sec. 13.4a.4.Perpendicular floor beams or angle bracingsimilar to that shown in the EBF section canbe used to provide this bracing.

Required Strength

The required strength is the same as for the pipe-to-column connection.

Brace-to-Gusset Weld

The brace-to-gusset weld is the same as for thepipe-to-column Connection.

Gusset-to-Beam Weld

Figure 7 - Gusset-to-Beam Weld Forces


The minimum gusset plate thickness follows thesame procedures as for the pipe-to-columnconnection.

Check minimum thickness of gusset

From pipe to gusset:

From gusset to beam:

• The Chevron beam is quite deep toprovide the required strength for theunbalanced brace loads. This depthresults in a relatively long gusset platewith large bending stresses.

• The angle between the brace and thegusset plate has been limited to 30° torecognize shear lag effects at the plate-to-beam weld.

• A stiffener plate has been added at thecenter of the gusset plate to help developthe yield line.

Figure 6- Welded Pipe Brace-to-Beam Connection

25-7

Weld size required


BOLTED WIDE FLANGE BRACE-TO-WIDEFLANGE COLUMN CONNECTION (Fig. 8)

Required Strength

The required strength follows the same provisionsand procedures as for the pipe-to-columnconnection.

Figure 8 - Bolted Wide Flange Brace-to-WideFlange Column Connection

Distribute brace force in proportion to web andflange areas

Force in flange

Force in web

• While the strength requirements are thesame as for the welded pipe, the bolted wideflange produces much higher connectionforces due to lower buckling-to-yield ratios(brace design based on buckling andconnection design based on yielding).

Brace-to-Gusset Connection

Using the connection layout shown, the followingbasic LRFD requirements are checked:

Table 3

Item

Single shear of braceflange bolts

Flange plate grosssection yielding

Flange plate net sectionrupture

Flange plate block shear

Bearing of bolts in braceflange

Single shear of braceweb bolts

Web plate gross sectionyielding

Web plate net sectionrupture

Web plate block shear

Bearing of bolts in braceweb

308

308

308

308

308

176

176

176

176

176

354

405

356

397

524

265

276

203

367

239

Note that the flange and web are sized to have aslightly higher sections than the brace flanges andweb are therefore acceptable by inspection.

The flange plate-to-gusset weld follows the sameprocedures as for the pipe-to-column connection.

Assume 15" weld along all (4) edges of the plate.

Use 15" of ¼" weld for the flange plate-to-gusset connection on (4) edges.

• While potentially easier to erect, the boltedconnection requires a much more extensivedesign effort as well as increased fabricationcost.

• For a bolted connection such as this, the netsection of the brace will by definition be theweak link in the connection. This situationoccurs because the Provisions require theremaining portions of the connection to besized for 110% of the tensile yield of thebrace gross section.



Gusset-to-Beam Welds Gusset-to-Column Bolts

The gusset-to-beam welds follows the sameprocedures as for the pipe-to-column connection.

However, since the column is bending about itsweak axis, is taken as approximately zeroresulting in the moment and horizontal componentof the column being approximately zero. Theforces are shown on the free body diagram of thegusset plate in Fig. 9.


• This connection has been configured for shopwelding the gusset plate to the beam andfield bolting the beam/gusset to the column.

• For the weak axis column connection,stiffeners have been added at the top andbottom of the gusset to preclude localbuckling.

Weld of gusset to beam flange

Use ¾" weld for gusset to beam flange.

Weld of shear tab to column

Use ¼" weld for shear tab to column.

Figure 10 — Gusset-to-Column Bolt Forces

From LFRD Vol II, Table 8-19

From table

Use (5) 1" A490-x bolts in two verticalrows


The minimum thickness of the gusset plate isdetermined following the same provisions andprocedures discussed earlier for the pipe-to-columnconnection.

Table 4

Criteria

Tension Yielding

Plate Buckling

Shear Yielding @Fillet Welds


.60

.73

1.09

Use gusset plate



BOLTED WIDE FLANGE BRACE-TO-BEAMCONNECTION (Fig. 11)

Required Strength

The required strength is the same as for the boltedwide flange brace-to-weak axis wide flangecolumn.

Brace-to-Gusset Connection

The wide flange brace-to-gusset connectionfollows the same procedures as that for the boltedwide flange brace-to-weak axis wide flangecolumn.

Gusset-to-Beam Weld


The gusset-to-beam weld follows the sameprocedures for welded pipe brace-to-beamconnection.


The minimum thickness of the gusset plate followsthe same procedures as for the pipe-to-columnconnection.

Use 1" gusset plate

WIDE FLANGE COLUMN SPLICE (Fig. 13)

Figure 13 - Wide Flange Column Splice

Web Plate and Weld

Per AISC Sec. 13.5.b: Splices shall be capable ofdeveloping nominal shear strength of smallersection.

Figure 11 — Bolted Wide Flange Brace-to-Beam Connection



Size weld of plate-to-column web using LRFDTable 8-42.

Use fillet weld

• Design the weld plate to resist the columnshear and the flange welds to resist the axialtension force.

• Load condition 4-2 becomes significant fortaller, more slender frames.

• It is difficult for partial-penetration welds tocomply with the column splice requirements.

• Although base plates have not been includedin this paper, there is strong analogybetween the strength and weld requirementsof column splices and base plates.

Flange Welds

Per AISC Sec. 8.3a.1: If partial penetration weldused, the design strength of the joints must be atleast 200 percent of the required strength perequation 4-2.

Equation 4-2 does not include the redundancyfactor.

Try partial joint weld

Since Equation 4-2 negligible, notapplicable.

Per AISC Sec. 8.3a.2: The minimum requiredstrength for each flange shall be 0.5 times

Partial penetration weld

Try complete penetration weld

Flexural Strength Check

Per AISC Sec. 13.5.b: Splices shall develop 50percent of the nominal flexural strength of thesmaller section.

Figure 14 — Splice Flexural Forces



ORDINARY CONCENTRICALLYBRACED FRAME (OCBF) CONNECTIONDESIGN

This system is the basic steel braced frame that hasbeen a part of seismic codes for many years. Theframe is configured with welded pipe braces (seeFigure 15) for a direct comparison with the SCBFin the previous section.

As opposed to the ductility approach for the SCBF,the design basis for the OCBF is primarily basedon strength. The provisions require braces withgreater stiffness (lower kl/r ratios) and greaterstrength (lower system R factor and 80% reductionof design strength). In addition to theserequirements, new provisions have been added topreclude local buckling of the braces.

The OCBF system also has special requirementsfor Chevron configurations. Instead of requiringincreased beam strength for unbalanced braceforces, the OCBF provisions amplify the designforces on the braces, resulting in even stronger,stiffer braces.

The connections have slightly lower demands thanthose of SCBF's. The design force can be based onthe amplified seismic load combination if it islower than the yielding of the brace. Also, untilrecently, there were no requirements for plastichinge formation or out-of-plane yielding of theconnection. These requirements were added to thecurrent version of the Provisions. Even though therequirements are slightly less, the actualconnections will be larger in the OCBF because ofthe larger forces in the stronger, stiffer braces.

Column splices must be designed for the amplifiedearthquake load combinations, but have no specialshear strength requirements. As for SCBF, theProvisions include special requirements for splicesmade with fillet welds or partial-penetration groovewelds.

Figure 15 - OCBF Elevation

WELDED TUBE BRACE-TO-WIDE FLANGECOLUMN CONNECTION (Fig. 16)

Figure 16 — Welded Tube Brace-to-Wide FlangeColumn Connection

Required Strength

The required strength of bracing connections, perAISC Sec. 14.3.a, is determined from the least ofthe following equations:

Bracing member's nominal axial tensile strength:

where equals 1.1 per AISC Sec. 6.2

Force in the brace resulting from the followingLoad Combinations per AISC Sec. 4.1

Eqn. (4-1)

Eqn. (4-2)



where for OCBF per UBC Table 16-Nand does not include the redundancy factor

• The connection design for this OCBF is basedon the amplified seismic forces instead of thebrace yield force.

Maximum force, transferred to brace by systemas determined by analysis


The required weld length for the brace to the gussetfollows the same procedures as for the SCBF pipe-to-column connection.

• This connection is arranged with the braceterminating close to the beam flange, resultingin a smaller gusset plate.

Assume 15in of weld along (4) edges.

Use 15in of weld on (4) edges


The gusset-to-beam and column connectionsfollow the same procedures used for the SCBFpipe-to-column connection. However, per AISCSec. 14.3c, an additional plastic moment equal to

will be included when the analysisindicates the brace will buckle.

Figure 17 — Gusset-to-Beam and Column WeldForces


Use weld for gusset-to-beam flange

• Because the connection cannot rotate freelyout-of-plane, the new version of the Provisionsrequires the welds to be designed for anadditional force based on the plastic momentStrength of the brace. This additionalrequirement results in very large welds and athick gusset plate.

Weld of gusset-to-column

Use 1¼" weld for gusset-to-beam column


Determining the thickness of the gusset platefollows the same procedures as for the SCBF pipe-to-column connection.

Table 5

Criteria

Block Shear

Tension Yielding

Plate Buckling


Required GussetPlate Thickness (in)

.32in

.33in

.42in

1.92in

Use 2" gusset plate



WELDED TUBE BRACE-TO-BEAMCONNECTION (Fig. 18)

Required Strength

The required strength is the same as for the tube-to-column connection.


The brace-to-gusset weld is the same as for thetube-to-column connection.

Gusset-to-Beam Connection

The gusset-to-beam connection follows the sameprocedures for the SCBF pipe-to-columnconnection. Also included is the additional plasticmoment as discussed in the previous section.


The gusset plate thickness follows the sameprocedures as for the SCBF pipe-to-columnconnection.

use 1¼" gusset plate

Figure 19 — Gusset-to-Beam Connection

Figure 18 — Welded Tube Brace-to-Beam Connection



ECCENTRICALLY BRACED FRAME(EBF) CONNECTION DESIGN

The EBF system was introduced into the buildingcodes in the late 1980's and has received moderateuse in steel braced frame buildings since. Theframe in this example uses welded tubeconnections similar to the OCBF (see Figure 20 fora frame elevation).

As for the SCBF and OCBF examples, a Chevronconfiguration with the links in the center wasselected. The building codes currently also allowlinks to be placed adjacent to columns. For thatconfiguration, the connection design criteriacurrently being developed for welded steel momentframe connections needs to be considered inaddition to the topics presented in this paper.

The ductility in the EBF system comes from therotation and yielding of the link. The link in thisexample was configured for shear yielding (shortlink) rather than for flexural yielding (long link).

The EBF provisions are based on a capacity designapproach and therefore all members andconnections must be stronger than the link. Thebrace design is based on buckling strength underthe strain hardened link force. The requiredstrength of the connection then needs to exceed theexpected strength of the brace in compression.

Additional connection issues with the EBF areassociated with the design and detailing of the link.To assure stable yielding, web stiffeners arerequired at each end of the link and also atintermediate locations. In general, closer stiffenerspacing is required for shear links than for flexurallinks. The Provisions do not allow web doublerplates or brace gusset plates extending into the linkregion. Finally, the Provisions require the flangesof the link to be braced out-of-plane.

Column splices must be designed for the amplifiedearthquake load combinations, but have no specialshear strength requirements. As for SCBF, theProvisions include special requirements for splicesmade with fillet welds or partial-penetration groovewelds.

Figure 20 – EBF Elevation

WELDED TUBE BRACE-TO-WIDE FLANGECOLUMN CONNECTION (Fig. 21)

Figure 21 – Welded Tube Brace-to-Wide FlangeColumn Connection

Required Strength

The required strength of brace, per AISC Sec 15.6ais determined from the resulting forces generatedby the expected nominal shear strength of the link

increased by 125% to account for strainhardening.

Next, per AISC Sec. 15.6d, the required strength ofthe connection shall be at least the expectednominal strength of the brace. For the TS 8 x 8 x



• The required connection strength of the EBFis the lowest of the various frames shown inthis paper. The reason for this lower demandis that the EBF has the largest system R factorand that the connection force is based onbrace compression strength rather than braceyielding.


The required weld thickness for the brace to thegusset follows the same procedures as for theSCBF pipe-to-column connection.

Assuming 14" of weld along (4) edges

Use 14" of weld along (4) edges


Figure 22 - Free Body Diagram of Brace toBeam/Column Connection

Uniform Force Method as recommended per LRFDVol. II Part 11, the axial force from the brace isresolved into the corresponding moment,horizontal, and vertical forces on the gusset plate.This is shown on the free body diagram of thegusset plate Fig. 22.


Resultant

Use fillet weld for gusset-to-beam flange

Weld of gusset to column

Use weld (similar to weld along beam) forgusset to column

• As for the OCBF, the brace extends to thebeam flange to minimize the size of thegusset plate.


Table 6

Criteria

Block Shear

Tension Yielding

Plate Buckling



.33in

.21in

.31 in

.55in

Use gusset plate

25-16


WELDED TUBE BRACE-TO-BEAMCONNECTION (Fig. 23)

Required Strength

The required strength is the same as the EBFwelded tube brace-to-wide flange columnconnection.


The required weld length for the brace to the gussetis the same as the EBF welded tube brace-to-wideflange column connection.

Figure 24 – Free Body Diagram ofBrace-to-Beam/Column Connection

Elastic Vector Method

Choose weld

• Since the gusset plate cannot extend into thelink region, a stiffener is added at the end ofthe link to balance the loading on the welds.


Table 7

Criteria

Block Shear

Tension Yielding

Plate Buckling



.33in

.29in

.31in

.63in

Use gusset plate

Figure 23 – Welded Tube Brace-to-Beam Connection



BEAM LINK (Fig. 23) Link Stiffener Welds

Per AISC Sec 15.3c, fillet welds connecting linkstiffeners shall have a design strength:

is area of stiffener) for connectionof web to stiffener.

for connection of flange to stiffener.

Weld For Web

Choose a weld

Weld for Flange

Choose a weld

Lateral support of link

Per AISC Sec 15.5, lateral support is to beprovided at both the top and bottom of the linkflanges at each end.

End Link Stiffeners

Per AISC Sec. 15.3a, provide full depth webstiffeners on both sides of link at end of braces:

• Width

• Thickness or 3/8" whichever is greater

(2) sided, full beam width & depth

Use plate thick

Link stiffener requirements are prescriptive.

Intermediate Link Stiffeners

Per AISC Sec. 15.3b:

1.) Provide intermediate web stiffenersspaced at; since link length

and link rotation

2.) - Intermediate link web stiffeners shall befull depth.

-If link depth <25" deep, stiffener isrequired on one side only.

- Thickness of 1 sided stiffeners > orwhichever is greater.

-Width

Space intermediate web stiffeners atmaximum

Web stiffeners full depth/width

Only required on one side

• Because of the short link and high linkrotation, the intermediate stiffeners mustbe closely spaced. Figure 25 – Lateral Support of Link



Design support for 6% of flange strength

Lateral support of beam links @ ends of W18x40

Choose 3 x 3 x ¼

• The composite metal deck and concreteslab provide lateral support of the topflange.

BEAM-TO-COLUMN CONNECTIONS

Figure 26 - Beam-to-Column Connections

Required Strength

Per AISC Sec. 15.7, these connections shall havethe strength to resist (2) equal and opposite forcesequal to 2% of flange capacity - actinglaterally on the beam flanges.

• The Provisions require nominal torsionalrestraint of the beam away from the link.This requirement is met by adding stiffenerplates to a typical bolted shear connection.

Plates and Welds

Weld at Column:

Choose a weld

Weld at Beam

Choose a weld with a plate ¼" x 4" x 4"

WIDE FLANGE COLUMN SPLICE @ EBF

Figure 27 — EBF Column Splice

• The column splice for the EBF is essentiallythe same as for the OCBF.

Required Strength

Per AISC Sec 8.3 the design strength of columnsplices shall meet or exceed the required strengthof Sec. 8.2:

Eqn. 4-1

Eqn. 4-2

But need not exceed:

a. the maximum load transferred to thecolumn considering times thenominal strength of the member

b. limit as determined form the resistance ofthe foundation to overturning uplift

For this splice, Eqn 4-2 governs

However, for EBF also check axial tensionwhen nominal shear strength of links reached,



Flange Welds

Per AISC Sec. 8.3a and 8.3b:

Column splices made with fillet and partial jointpenetration groove welds shall not be locatedwithin 4' nor half the column clear height of beamto column connections, whichever is less.

If subjected to a tensile stress per load combination4-2 filler metal shall meet requirements of CVNtoughness as required by Sec. 7.3b, and

1.) The design strength of partial jointpenetration welds shall be at least equal to200% of required strength.

2.) The minimum required strength for eachflange shall be

Beveled transitions are not required when changesin thickness and width of flanges and web occur.

Initially try a partial penetration groove weld thatwill be at least equal to 200% of the requiredstrength.

Use a complete penetration weld at each flange,this will satisfy strength requirements of Sec 8.2and Sec. 8.3a.

Locate splice @ 4' from floor or 14/2 - 7/2 = 3'-6";4' from floor governs

*provide shear plate to web for erection

CONCLUSION

Properly designed and detailed connections arecritical to achieve the expected performance ofbraced frames in earthquakes. As can be seen inthe design examples, there are numerous buildingcode provisions that address connection design.These provisions have evolved over the years asnew braced frame systems have been introducedand as more experience has been gained from thebehavior of buildings in actual earthquakes.

ACKNOWLEDGEMENTS

The author wishes to acknowledge the considerableefforts of Garo Pehlivanian, Kristie Fromhold,Steve Curran and Michael Townsend in assisting inthe development of this paper.



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Seismic Brace Design