Recent research promotes and aids steel construction

Instituto Mexicano de la Construcción en Acero (IMCA) X SIMPOSIO INTERNACIONAL Querétaro, Qro. - Marzo 2009

RECENT RESEARCH PROMOTES AND AIDS STEEL CONSTRUCTION

STRUCTURAL ENGINEERING RESEARCH AND DEVELOPMENT • • • • • • • •

Materials Members Connections Systems Demand vs supply Reliability Performance Codes

Tradition – and very practical

Expanded tradition – looking ahead

Engineering research: refined models, 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 and plates – Structural stainless steels and shapes

STEELMAKING CHANGES • Use of EAF, scrap and continuous casting is much more efficient and economical, gives a much higher quality steel, and is environmentally friendly • Problems such as laminations and lamellar tearing have essentially gone away • Continuous casting is now also used for very thin sheet steel (less than 1 mm) • The change from BOF, iron ore, coke and ingots has taken place in some, but not all countries

The Steel Material The changes in steel production methods have resulted in: – Much higher quality material – More uniform crystalline structure – Much closer defined and improved mechanical and other properties – Significantly lower carbon content – Excellent toughness and weldability – The old problem of lamellar tearing has effectively gone away

Where Are We Headed?

• For most structures, the traditional steels will continue to be most practical, serving all performance needs • For special applications and certain structural forms, HPS and seismic steels will be common • For certain structural applications, very high strength steels will be the choice • Cold-formed steels and structures will occupy a significantly increasing market share • Structural stainless has potential, but costs are still very high

RESEARCH ON STRUCTURAL MEMBERS: BEAMS AND COLUMNS

SOME CURRENT ISSUES • Curved plate and box girders • Cold-straightened columns • Composite columns, especially with very high strength concrete • Buckling-restrained braces for braced seismic frames • Deflection of cambered beams • Members in existing and older structures

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, fracture may take place Specify that holes should be made AFTER cambering

CONNECTIONS • Major influence on construction economy: 50 % and more of a project framing cost is tied to connections • Connections influence member response and frame response • Analysis with suitable connection properties can be very complex – but is needed and (now) required by codes • Consequently, there is a very large number of current studies of connection behavior and strength

CONNECTION STUDIES • Fasteners and fastening systems: mostly traditional, apart from studies of very high strength bolts, undermatched welds, novel mechanical fasteners (especially for 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 Single Plate Shear Tabs

The Infamous k-Area

k-region (area) has higher strength and hardness, as well as lower ductility and fracture toughness

A ROBUST CONNECTION

Fractured k-area showing arrest marks on the fractured surfaces

ADDITIONAL k-AREA COMMENTS • k-area extends about 1 inch (25 mm) into the web, beyond the k-distance • Do not place any welds into the k-area • Chamfer stiffeners (continuity plates), to avoid welds and especially weld ends in the k-area • Do not place doubler plates with longitudinal welds into the k-area (and as a general rule, if at all possible, avoid doublers all together)

SOME OTHER CONNECTIONS

Solutions for Connections to Concrete-Filled Tubes (CFT)

Beam-to-Column Connection with Shape Memory Alloy and Post-Tension Rods

AISI Seismic Moment Connection with Cold-Formed Channel Beams

Where Are We Headed?

With constantly evolving framing systems, novel materials and fastening procedures, refined analytical and testing tools, improved knowledge of loads and other structural actions, etc. – there is no limit to the types of connections – and research must continue

FRAMING SYSTEMS • • • • • • •

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

MOMENT-RESISTING FRAMING SYSTEMS

An Old Favorite: The T-Stub Connection

Original Pre-Northridge Connection

Improved Pre-Northridge Connection

Other Post-Northridge Connections

RBS (dog bone) Connection

Side-Plate Connection

Frames with RBS Connections

Frame with Side-Plate Connections

VARIOUS FORMS OF BRACED FRAMES FOR SEISMIC PERFORMANCE

ECCENTRICALLY BRACED FRAMES

Bolted Eccentrically Braced Frame Connections

CONCENTRICALLY BRACED FRAMES

Typical Concentrically Braced Bay

Close-up of Bracing Connection

Bracing system fuse

View from below

View from above

STRUCTURAL FUSES Fuses are now used in various forms of structures. They are specifically used to ensure that yielding will occur in designated members and locations, providing ductility and energy absorption while preventing nonductile failures in other elements and areas

Typical Buckling-Restrained Brace

Some Typical BRB End Details

Large-Scale Braced Frame Tests

NOVEL DEVELOPMENTS FOR BRACING CONNECTIONS AND GUSSET PLATES

Thornton Brace Connection to Minimize Distortion Forces

Thornton Brace Connection to Control Distortion Forces

Thornton High Seismic Brace Connection

SPECIAL PLATE SHEAR WALLS (SPSW) (previously called steel plate shear walls)

Federal Court House in Seattle

Steel-Plate Shear Wall in Low-Yield Steel Fy = 130 to 165 MPa (1,326 to 1,683 kg/cm2)

Where Are We Headed?

• Three-dimensional inelastic frame analysis will be the norm • Framing systems and their details must be robust, in all respects • Seismic-type detailing will become the norm for most structures • Checks for structural integrity will be the norm

ROBUST STRUCTURES EXTREME EVENTS

TEST FOR ROBUSTNESS

Blast test of steel elements and connection verified very high and ductile energy absorption and close agreement with analysis

ROBUST CONNECTION UNDER FIRE CONDITIONS

FULL-SCALE FIRE TEST

SOME OTHER SUBJECTS

BRIDGE STRUCTURES AND SYSTEMS

Viaduc de Millau

Sutong Bridge

NOVEL COMPOSITE JOINING TECHNIQUES

NEW STRUCTURES AND INDUSTRIES

BIM Building Information Modeling

Another BIM for Nationals Stadium

Actual Structure from BIM

BIM for Entire Nationals Stadium

CONCLUSIONS • Structural steel is alive and very strong, world-wide • Most projects are truly forwardlooking, offering significant new knowledge and practical applications • Leading efforts focus on the complete structure under realistic service and ultimate conditions

CONCLUSIONS – CONT’D • Full-scale testing continues to be done, but in limited fashion due to cost considerations • Analytical techniques are highly advanced and accurate • Many connection projects, including high strength steel • Many composite construction projects

CONCLUSIONS – CONT’D • Many projects addressing robust structures, structural integrity and disproportionate collapse • Many research efforts aim to develop practical code criteria • Numerous studies focus on novel connections and framing systems • Performance-based codes may evolve 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 Shukran

• • • • • • • • • • • • • • • • • • •

Merci Grazie Tack Kiitos Tänan väga Spasibo Arigato Mahalo Xie xie Dortse Tou che chi Kamsahamnide Khopkun Terima kasih Salamat po Asante Ndiyabulela Ameseginalehu Yekenyeley