Cold Formed Steel

CONTENTS

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DEFINITION PROPERTIES AND DESCRIPTION CHARACTERISTICS FABRICATION APPLICATIONS CONNECTIONS YIELD ANALYSIS INDUSTRIAL STRUCTURES DESIGN

STEEL • ALLOY OF IRON AND CARBON IN WHICH THE CARBON CONTENT RANGES UP TO 2 PERCENT . • BY FAR THE MOST WIDELY USED MATERIAL FOR BUILDING THE WORLD'S INFRASTRUCTURE AND INDUSTRIES, IT IS USED TO FABRICATE EVERYTHING FROM SEWING NEEDLES TO OIL TANKERS.

HOT ROLLED STEEL • THE ROLLING OF HOT STRIP BEGINS WITH A SLAB, WHICH IS INSPECTED AND, IF NECESSARY, SURFACE CLEANED EITHER MANUALLY OR BY SCARFING MACHINES WITH OXYACETYLENE TORCHES. THE SLABS ARE THEN PUSHED, OR WALKED ON THEIR BROADSIDE, THROUGH GASFIRED FURNACES THAT HAVE A HEARTH DIMENSION OF ABOUT 13 METRES BY 30 METRES. IN A PUSHER-TYPE FURNACE, THE SLABS SLIDE ON WATER-COOLED SKIDS, AND, EACH TIME A NEW SLAB IS CHARGED, A HEATED SLAB DROPS THROUGH A DISCHARGE DOOR ONTO A ROLLER TABLE. IN WALKING-BEAM FURNACES, SEVERAL WALKING BEAMS LIFT THE WORKPIECES FROM THE HEARTH, MOVE THEM FORWARD, AND SET THEM BACK DOWN IN A SERIES OF RECTANGULAR MOVEMENTS. PREHEATING TEMPERATURE, AS WITH SLABS AND PLATES, IS ABOUT 1,250° C.

COLD ROLLED STEEL • THE ROLLING OF COLD STRIP BEGINS WITH THE RETRIEVAL OF HOT-ROLLED STRIP FROM A COIL STORAGE YARD, WHICH OFTEN USES FULLY AUTOMATED CRANES FOR SETTING AND RETRIEVING COILS ACCORDING TO ROLLING SCHEDULES. THE COILS ARE FIRST DESCALED IN CONTINUOUS PICKLE LINES, WHICH ARE DISCUSSED BELOW (SEE TREATING OF STEEL: SURFACE TREATING: PICKLING). THE CLEANED AND OILED COILS ARE FED INTO A COLDREDUCTION MILL, WHICH IS USUALLY A TANDEM MILL OF FOUR TO SIX FOUR-HIGH STANDS WITH AN UNCOILING REEL AT THE ENTRY AND A RECOILING REEL AT THE EXIT.

• WHEN ROLLING FROM, FOR EXAMPLE, 2 MILLIMETRES TO 0.3 MILLIMETRE, THE COLD REDUCTION IS USUALLY 35 PERCENT ON THE FIRST STANDS AND 15 PERCENT ON THE FINAL STAND. THE EXIT SPEED IS NORMALLY HIGH, OFTEN 100 KILOMETRES (60 MILES) PER HOUR, IN ORDER TO ACHIEVE PROPER PRODUCTION RATES WITH SUCH SMALL CROSS SECTIONS. SINCE THE STRIP TEMPERATURE MAY GO AS HIGH AS 200° C (390° F), PROPER COOLING OF STRIP AND ROLLS IS ESSENTIAL. HEAVY-DUTY LUBRICANTS ARE ALSO USED TO MINIMIZE FRICTION IN THE ROLL GAP.

Cold roll forming machine.

METHODS OF FORMING • 1. Cold roll forming • 2. Press brake operation • 3. Bending brake operation

Size ranges of typical roll-formed structural shapes.

DESCRIPTION AND PROPERTIES OF HOT ROLLED STEEL AND COLD ROLLED STEEL ACCORDING TO IISI

VARIOUS SECTIONS OF COLD FORMED STEEL

• As compared with thicker hot-rolled shapes, cold-formed light members can be manufactured for relatively light loads and/or short spans. • Unusual sectional configurations can be produced economically by cold-forming operations and consequently favorable strengthto- weight ratios can be obtained. • Nestable sections can be produced, allowing for compact packaging and shipping. • Load-carrying panels and decks can provide useful surfaces for floor,roof, and wall construction, and in other cases they can also provide enclosed cells for electrical and other conduits.

• Load-carrying panels and decks not only withstand loads normal to their surfaces, but they can also act as shear diaphragms to resist force in their own planes if they are adequately interconnected to each other and to supporting members.

Compared with other materials such as timber and concrete, the following qualities can be realized for coldformed steel structural members .

• 1. Lightness • 2. High strength and stiffness • 3. Ease of prefabrication and mass production • 4. Fast and easy erection and installation • 5. Substantial elimination of delays due to weather • 6. More accurate detailing

• 7. Nonshrinking and noncreeping at ambient temperatures • 8. Formwork unneeded • 9. Termite-proof and rotproof • 10. Uniform quality • 11. Economy in transportation and handling • 12. Noncombustibility • 13. Recyclable material

Composite truss-panel system used in World Trade Center Building,

Placement of prefabricated composite floor panel section in World Trade Center Building.

Cold-formed steel joists used together with hot-rolled shapes

Cold-formed steel sections used in space frames

Cold-formed steel sections used in space frames

TYPES OF COLD-FORMED STEEL SECTIONS AND THEIR APPLICATIONS

• 1. Individual structural framing members • 2. Panels and decks

Cold-formed sections used in structural framing

Building composed entirely of coldformed steel sections.

Decks, panels and corrugated sheets.

Numerical and experimental investigation on bolted moment connections in coldformed steel sections

Investigation on efficient beamcolumn connections in cold-formed steel structures scaffolds

Experimental investigation on lapped moment

Self-piercing Rivet (SPR) Connections: • SPR connections consist of the joining of two or more sheets of cold-formed steel with a rivet that is installed with proprietary tools, without a drilled or punched hole in the steel. The connection is formed by driving the rivet into the steel sheets, piercing the top layer or layers of steel sheets, with the rivet flaring, under the influence of a die under the of sheets, into the bottom layer without penetrating through the bottom layer.

SEQUENTIAL FORMATION OF A TYPICAL SPR CONNECTION

CLINCHED CONNECTIONS

Cold-formed steel members used in space grid system.

Cold-formed steel members used in a 100 3 220 3 30-ft (30.5 3 67.1 3 9.2-m) triodetic arch.

Hangar-type arch structures using cold-formed steel sections.

Rack Structures.

Cold-formed steel panels used in folded-plate roof.

Superbay hangar for American Airlines Boeing 747s in Los Angeles.

Arched roof curved at job site.

METHODS OF FORMING