Structural Steel Research

Expanded tradition – lookingahead

Engineering research: refinedmodels, analysis, tests, practice,economy

THEORY TO PRACTICE

MATERIALS• Traditional steels: mild (C-Mn),HSLA, weathering• Newer steels:– High performance steels (HPS)– Fire-resistant steels– Seismic steels– Off-shore structures steel– Low yield stress steels– Very high strength steels– Hot-rolled vs cold-formed shapes andplates– Structural stainless steels and shapes

Global Steel Production 1930through 2017 (forecast)

AN EXAMPLE FROM CHINA

Steel and Steel Production HaveChanged

Continuous Casting, Scrap and BeamBlanks Have Replaced Ore, Coke, BOFand Ingots

The Steel MaterialThe changes in steel productionmethods have resulted in:– Much higher quality material– More uniform crystalline structure– Much closer defined and improvedmechanical and other properties– Significantly lower carbon content– Excellent toughness and weldability– The old problem of lamellar tearing haseffectively gone away

Weldability of Steel

Where are we headed?• For most structures, the traditional steels willcontinue to be most practical, serving allperformance needs• For special applications and certain structuralforms, HPS and seismic steels will be common• For certain structural applications, very highstrength steels will be the choice• Cold-formed steels and structures will occupya significantly increasing market share• Structural stainless has potential, but costs arestill very high

STRUCTURAL BEAMS ANDCOLUMNS

SOME CURRENT ISSUES• Curved plate and box girders• Cold-straightened columns• Composite columns, especiallywith very high strength concrete• Buckling-restrained braces forbraced seismic frames• Deflection of cambered beams• Members in existing and olderstructures

Cambered Beam Deflections:Influence of Bauschinger Effect?

Cambering Can Be Problematic“It is easy to just bend the shape a little”But if there are holes in flanges, fracturemay take placeSpecify that holes should be madeAFTER cambering

CONNECTIONS• Major influence on constructioneconomy: 50 % and more of a projectframing cost is tied to connections• Connections influence member responseand frame response• Analysis with suitable connectionproperties can be very complex – but isneeded and now required by many codes• Consequently, there is a very largenumber of current studies of connectionbehavior and strength

CONNECTION STUDIES• Fasteners and fastening systems:mostly traditional, apart fromstudies of very high strengthbolts, undermatched welds, novelmechanical fasteners (especiallyfor cold-formed structures)• Compression joints (splices)• High strength tension joints

CONNECTION STUDIES – CONT’D• Beam-to-column connections:– Simple– Semi-rigid (PR)– Moment connections (FR)• Two-dimensional• Three-dimensional• Analysis and full-scale tests

Joints with Unequal Beam Depth

Conventional and Extended SinglePlate Shear Tabs

The Infamous k-Areak-region (area)has higherstrengthand hardness,as well as lowerductility andfracturetoughness

A ROBUST CONNECTIONFracturedk-areashowingarrestmarks onthefracturedsurfaces

SOME OTHER CONNECTIONS

Solutions for Connections toConcrete-Filled Tubes (CFT)

Beam-to-Column Connection with ShapeMemory Alloy and Post-Tension Rods

Where are we headed?With constantly evolving framingsystems, novel materials andfastening procedures, refinedanalytical and testing tools,improved knowledge of loads andother structural actions, etc. – thereis no limit to the types ofconnections – and research mustcontinue

FRAMING SYSTEMS• Gravity and lateral loads• Stability• Energy absorption• Resistance to extreme events• Redundancy• Robust details and systems• Structural integrity

MOMENT-RESISTINGFRAMING SYSTEMS

Some Robust and DuctileConnectionsRBS (dog bone)ConnectionSide-Plate Connection

Frames with RBS Connections

Frame with Side-Plate Connections

ECCENTRICALLY BRACEDFRAMES

Bolted Eccentrically Braced FrameConnections

CONCENTRICALLYBRACED FRAMES FORIMPROVED PERFORMANCE

Close-up of Bracing Connection

Bracingconnectionwith W-shape braceand beam

Bracing system fuseView from belowView from above

STRUCTURAL FUSESFuses are now used in various formsof structures. They are specificallyused to ensure that yielding will occurin designated members and locations,providing ductility and energyabsorption while preventing nonductilefailures in other elements andareas

Typical Buckling-Restrained Brace

Some Typical BRB End Details

SPECIAL PLATE SHEARWALLS (SPSW)(previously called steel plateshear walls)

Steel Plate Shear Wall Panel–in Japan

Federal Court House in Seattle

Steel-Plate Shear Wall in Low-YieldSteel (130 to 165 MPa)

SOME SPECIAL SYSTEMS

Steel Frame with ReplaceableEnergy Dissipating Fuses andSelf-Centering PT Bars

Staggered Truss

Slopingcolumnsin multistorystructure

Seattle Public Library

Composite Beam with Hollow-Core Slab

Where are we headed?• Three-dimensional inelastic frameanalysis will be the norm• Framing systems and their detailsmust be robust, in all respects• Seismic-type detailing will becomethe norm for most structures• Checks for structural integrity willbe the norm

ROBUST STRUCTURESEXTREME EVENTS

Blast test ofsteel elementsand connectionverified veryhigh andductile energyabsorption andclose agreementwith analysis

ROBUST CONNECTION UNDERFIRE CONDITIONS

FULL-SCALE FIRE TEST

SOME OTHER SUBJECTS

BRIDGE STRUCTURES ANDSYSTEMSViaduc de MillauSutong Bridge

NOVEL COMPOSITE JOININGTECHNIQUES

NEW STRUCTURES ANDINDUSTRIES

BIMBuilding Information Modeling

A BIM for Nationals Stadium inWashington, DC

Actual Structure from BIM

BIM for Entire Nationals Stadium

SOME CURRENT BUSINESSISSUES – AS SEEN IN THEUNITED STATES

Success in the Market

Steel Prices 2003 - 2008

Cost Percentages – January 2008

Cost Adjustment May 2008

A FINAL – AND VERYIMPORTANT SUBJECT

SUSTAINABILITY

CONCLUSIONS• Structural steel research is aliveand very strong, world-wide• Most projects are truly forwardlooking,offering significant newknowledge and practicalapplications• Leading efforts focus on thecomplete structure under realisticservice and ultimate conditions

CONCLUSIONS – CONT’D• Full-scale testing continues to bedone, but in limited fashion due tocost considerations• Analytical techniques are highlyadvanced and accurate• Many connection projects,including high strength steel• Many composite constructionprojects

CONCLUSIONS – CONT’D• Many projects addressing robuststructures, structural integrity anddisproportionate collapse• Many research efforts aim todevelop practical code criteria• Numerous studies focus on novelconnections and framing systems• Performance-based codes mayevolve over the next decade

MANY THANKS!• Gracias• Danke• Takk• Þakka þér fyrir• Qujanaq• Dank U• Dankie• Obrigado• Efkaristo• Děkuji• Dziękuję• Köszönöm• Mulţumesc• Eskerrik asko• Hvala lepo• Faleminderit• Tešekürler• Tashakor• Merci• Grazie• Tack• Kiitos• Tänan väga• Spasibo• Arigato• Mahalo• Xie xie• Dortse• Tou che chi• Kamsahamnide• Khopkun• Terima kasih• Salamat po• Shukran• Asante• Ndiyabulela