Steel Research

8/2/2019 Steel Research

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Steel Connections


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Introduction This presentation was developed as a teaching aid with

the support of the American Institute of Steel Construction.Its objective is to provide technical background andinformation for connections and bracing configurations.The information provided is based on common design andconstruction practices for structures of twelve stories orless.

The AISC Digital Library case study presentationsdocument the construction of a steel frame for an officebuilding. The case study includes photographs that weretaken throughout the construction of the structural steelframe including detailing, fabrication, and erection. Project

data including plans, schedules, specifications and otherdetails are also included. The case study presentationsare available in the Learning Opportunities section at

This presentation goes a step further in detail in the areasof connections and bracing configurations. A more in-depth background is provided and details of common

connections and bracing configurations are presented


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W hat W ill You Gain From ThisPresentation?

General knowledge of structural steel

Knowledge of the types of steel frameconnections defined in the American Institute of

Steel Construction design specification An understanding of different types of

connections used in structural steel frames

Insight into the impacts of using certainconnection types

Familiarity with common bracing systems used instructural steel frames


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Benefits of Structural Steel Some benefits associated with use

of structural steel for owners are:

Steel allows for reduced frameconstruction time and the ability toconstruct in all seasons

Steel makes large spans and baysizes possible, providing moreflexibility for owners

Steel is easier to modify andreinforce if architectural changes

are made to a facility over its life Steel is lightweight and can reduce

foundation costs

Steel is durable, long-lasting andrecyclable


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Unique Aspects of Steel Construction Procurement and

management of structuralsteel is similar to othermaterials, but there are someunique aspects to steel

construction: Steel is fabricated off-site

(above left)

On-site erection is a rapidprocess (above right)

This gives use of structuralsteel some schedulingadvantages

Coordination of all parties isessential for achieving

potential advantages


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Forces On Structures Forces from gravity, wind, and

seismic events are imposed onall structures

Forces that act vertically are

gravity loads Forces that act horizontally,

such as stability, wind andseismic events (the focus of thisdiscussion) require lateral loadresisting systems to be built intostructures

As lateral loads are applied to astructure, horizontaldiaphragms (floors and roofs)transfer the load to the lateral

load resisting system

Structural SteelFrame Elevation


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Initial System Planning

The type of lateral load resisting system to be used ina structure should be considered early in the planning

stage Lateral stability as well as architectural needs must be

met

The three common lateral load resisting systems are:

Braced Frames

Rigid Frames


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Braced Fram es and Rigid Frames

This presentation focuses on braced frames (left)and rigid frames (right)


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Steel Fram e

Connection Types

The Specification for Structural Steel Buildings(AISC 2005) defines two types of connections: Simple Connections (above left) Moment Connections (above right)

Fully-Restrained and Partially-Restrained


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Steel Frame Connection Types All connections have a certain

amount of rigidity

Simple connections (A above)

have some rigidity, but areassumed to be free to rotate

Partially-Restrained momentconnections (B and C above)are designed to be semi-rigid

Fully-Restrained momentconnections (D and E above)are designed to be fully rigid


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Simple Connections

Designed as flexible connections

Connections are assumed to be free to rotate

Vertical shear forces are the primary forcestransferred by the connection

Require a separate bracing system for lateral stability

The following few slides show some common simpleframing connections


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Com m on Simple Connections

Single Plate Connection (ShearTab)

A plate is welded to thesupporting member and bolted to

the web of the supported beam

Double Angle Connection

The in-plane pair of legs areattached to the web of the

supported beam and the out-of-plane pair of legs to the flange orweb of the supporting member


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Com m on Sim ple Connections

Shear End Plate Connection

A plate is welded perpendicular tothe end of the supported web and

attached to the supporting member

Single Angle Connection

One leg is attached to the web ofthe supported beam and the other

leg to the flange or web of the

supporting member


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Seated Connection

An angle is mounted with oneleg vertical against the

supporting column, and theother leg provides a seat upon

which the beam is mounted

A stabilizer connection is also

provided at the top of the web

Tee Connection

The stem of a WT section isconnected to the supportedmember and the flange attached

to the supporting member

Com m on Sim ple Connections


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Mom ent Connections

Designed as rigid connections which allow little or norotation

Used in rigid frames Moment and vertical shear forces are transferred

through the connection

Two types of moment connections are permitted: Fully-Restrained


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Partially-Restrained


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Comm on FR Connections

Bolted Flange Plate ConnectionWelded Flange Plate Connection

Top and bottom flange-plates connect the flanges of the supported member to

the supporting column

A single plate connection is used to transfer vertical shear forces


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Com mon FR Connections

Bolted Extended End-PlateConnection

A plate is welded to the flangesand web of the supported memberand bolted with high-strength bolts

to the supporting column

Welded Flange Connection

Complete-joint-penetration

groove welds directly connectthe top and bottom flanges ofthe supported member to the

supporting column

A shear connection on the web

is used to transfer vertical shearforces


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PR Moment Connection WindOnly

A double angle simpleconnection transfers vertical

shear forces while top andbottom flange plates resistmoment forces produced by wind

Note that the size of the flangeplate is relatively small in

comparison to the beam flange

Top and Bottom Angle withShear End Plate Connection

Angles are bolted or welded tothe top and bottom flanges of

the supported member and tothe supporting column

A shear end plate on the web isused to transfer vertical shear

forces


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Rigid Frames

Rigid frames, utilizing moment connections, are wellsuited for specific types of buildings where diagonal

bracing is not feasible or does not fit the architecturaldesign

Rigid frames generally cost more than braced frames


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Braced Fram es

Diagonal bracing creates stable triangular configurationswithin the steel building frame (AISC 2002)

Braced frames are often the most economical method ofresisting wind loads in multi-story buildings (AISC 1991).

Some structures, like the one pictured above, are designedwith a combination braced and rigid frame to takeadvantage of the benefits of both


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Tem porary Bracing Structural steel frames require temporary bracing during construction

Temporary bracing is placed before plumbing up the structural frame This gives the structure temporary lateral stability

Temporary bracing is removed by the erector

In a braced frame, temporary bracing is removed after final

bolt-up is complete and the permanent bracing system is in

placeIn a rigid frame, temporary bracing is removed after final

bolt-up is complete


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Concentric Braced Fram es

Bracing is concentric when the center lines of the bracing members intersect

Common concentric braced frames used in buildings today include:

X brace (above left)

Two story Xs

Chevron (above right)

Single diagonals

X bracing is possibly the most common type of bracing

Bracing can allow a building to have access through the brace line depending onconfiguration


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X Bracing The diagonal members of X bracing go into tension andcompression similar to a truss

The multi-floor building frame elevation shown above hasjust one braced bay, but it may be necessary to bracemany bays along a column line

With this in mind it is important to determine the locationsof the braced bays in a structure early in a project

X-braced building elevationTypical floor plan with X bracing


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Connections for X bracing are located at beam to column jointsBracing connections may require relatively large gusset plates at

the beam to column joint

The restriction of space in these areas may have an impact on themechanical and plumbing systems as well as some architectural

features


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Chevron Bracing

Typical floor plan with Chevron bracing Elevation with several bracingconfigurations

The members used in Chevron bracing are designed for both tensionand compression forcesChevron bracing allows for doorways or corridors through the bracing

lines in a structureA multi-floor frame elevation using Chevron bracing is shown above


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Chevron bracing members use two types of connectionsThe floor level connection may use a gusset plate much like the

connection on X braced frames

The bracing members are connected to the beam/girder at the topand converge to a common pointIf gusset plates are used, it is important to consider their size when

laying-out mechanical and plumbing systems that pass through braced

bays


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Eccentrically Braced Frames

Eccentric bracing is commonly used in seismic regions and allows fordoorways and corridors in the braced bays

The difference between Chevron bracing and eccentric bracing is thespace between the bracing members at the top gusset connection In an eccentrically braced frame bracing members connect to separate points on

the beam/girder

The beam/girder segment or link between the bracing membersabsorbs energy from seismic activity through plastic deformation

Eccentrically braced frames look similar to frames with Chevron bracing

A similar V shaped bracing configuration is used


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Com bination Frames

1_ Combination Frame

2_Moment resisting

3_ Chevron braced As shown above (left) a braced frame deflects like a cantilever beam while a moment resisting frame deflects

more or less consistently from top to bottom

By combining the two systems, reduced deflections can be realized

The combination frame is shown above right

The plot shows the moment resisting frame alone, the braced frame alone, and the combined frame

The same wind load was used for each frame model


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The plot shows themoment resisting framealone, the braced framealone, and the combinedframe

The same wind load wasused for each frame

model

Combination Frames


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Facts about Steel Fram ing

Steel is well suited to Northern regions for many reasons. Homefab's steel products arecyclone rated by CMG Consulting Engineers. Steel lends itself to raised floors, largeopen living areas and large doors and windows, which encourages cool breezes to flowthrough and under the house, and is suited to sloping land.

The strength and durability of steel is unbeatable. Steel allows for wide spans betweenload bearing walls for wide-open living spaces and provides safety from cyclones. Thereis no design limitations.

Steel frames keep their shape as they are pre-braced,steel will not twist, shrink or

warp. Roofs and walls will stay straight and true virtually eliminating doors that jam,windows that stick and cornices that crack due to frame movement


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Non-combustibleSteel will not ignite and will not contribute to a fire. Please view the below video which is the testingresults of a bush fire scenario that was carried out in Mogo, New South Wales in April 2010.

No chemicalsSteel framing is free from the toxic chemical treatments used to protect other types of frames fromtermites.

EconomicalSteel framing is competitively priced

VersatileSteel framing suits both concrete slab and sub-floor construction, and is compatible with all interiorfloor, wall and ceiling lining materials. It is ideal for steeply sloping sites.

Electrically safeSteel frames are earthed so that any electrical leakage including lightning is conducted safely tothe ground.

Ideal for investorsSteel house framing wont burn, rot, shrink, warp or twist and it is safe from termites just what you

want for a long-term investment. Safe from Termites

If you live in a termite-prone areaand thats more likely than you might think there is no risk oftermite damage to your house frame if is made from steel.

Speed of ConstructionSteel is quicker to erect because the steel components used are pre-fabricated, which saves timeon-site. Quicker construction means you spend less time waiting and paying rent

Facts about Steel Framing


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References

AISC. (n.d.). Steel Connections: Behavior and Practice [35mm Slide Showwith Script]. American Institute of Steel Construction, Inc. Chicago, IL.

AISC. (1989). Specification for Structural Steel Buildings, Allowable StressDesign and Plastic Design, 9thed. American Institute of Steel Construction,Inc. Chicago, IL.

AISC. (1991). Design Guide for Low- and Medium-Rise Steel Buildings.American Institute of Steel Construction, Inc. Chicago, IL.

AISC. (1999). Load and Resistance Factor Design Specification For StructuralSteel Buildings. American Institute of Steel Construction, Inc. Chicago, IL.

AISC. (2002). Designing With Structural Steel A guide For Architects.American Institute of Steel Construction, Inc. Chicago, IL .

Earthquake Engineering Research Center, (EERC). (1997). W. G. Godden

Structural Engineering Slide Library. Godden J119. August, 2004.

Green, P. S., Sputo, T., and Veltri, P. (n.d.). Connections Teaching Toolkit ATeaching Guide for Structural Steel Connections. American Institute of SteelConstruction, Inc. Chicago, IL.

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