Recent research promotes and aids steel construction by IMCA

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 â&#x20AC;&#x201C; and very practical

Expanded tradition â&#x20AC;&#x201C; 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. â&#x20AC;&#x201C; there is no limit to the types of connections â&#x20AC;&#x201C; 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