By Prof' Jinan Wang

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Civil Engineering Construction

• By Prof. Jin-an Wang
• USTB 2009. 09

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CHAPTER 7 Structural Steel Frame

• Outline
• Structural Steel Shapes
• Principles of Structural Steel Frames
• Structural Steel Connections
• Erection of Steel Frame
• Preengineered Structural Steel Frames
• Construction Procedures and Practices
• Review Questions

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Introduction

• The use of structural steel in the construction
  of building frames was the beginning of a new
  concept in building design, the high-rise or
  multistory building.
• Because of its versatility and strength as a
  building material, steel has become one of the
  dominant materials in the construction industry.

Steel Frame High-Rise Office Building
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• The properties of steel for use in building
  frames.
• High strength to weight ratio
• Ductile
• Equally strong in compression and in tension
• Can be formed and fabricated into any shape
• To enhance the performance of concrete and timber
  as structural materials.

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7.1 Structural Steel Shapes

• W (wide flange)
• HSS (hollow structural sections)
• WT (tees cut from wide flange sections)
• S (standard I sections)
• Angle (equal leg and unequal leg)
• C (channels)
• HP (I-shaped pile sections)
• Plate.

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7.1 Structural Steel Shapes
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7.2 Principles of Structural Steel Frames

• The structural steel frame must be considered
  from two points of view
• (1) the strength of the individual sections that
  make up the frame
• (2) the overall stability of the frame.
• The stability of any structure is contingent on
  the arrangement of the framing members and the
  type of connections used to fasten them together.

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7.2 Principles of Structural Steel Frames

• Structural steel frames can be categorized into
  two basic types
• Braced frames some type of lateral bracing is
  used to prevent horizontal movement of the frame.
  
• Unbraced frames the stiffness of the
  load-carrying sections in the assembled frame
  must resist the horizontal movement that is
  anticipated.

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7.2 Principles of Structural Steel Frames

• The connections between the framing members can
  be considered as
• Pin-type connections are flexible and allow
  rotation to occur between the connected members
  when deflections occur due to applied loads.
• Rigid or moment-resisting connections add
  stability to the frame by their ability to resist
  the rotation that occurs between the frame
  sections when the frame is under the influence of
  lateral loads.

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Unbraced Structural Steel Frame
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Tension Cross-Bracing in a Braced Frame

• This type of bracing allows for load reversals
  and ensures that stability is provided in both
  directions.
• The removal of one of these braces will produce
  instability in the frame because tension braces
  are not designed to resist compression loads

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Rigid Frame Structural Steel Building Frame

• Where moment-resisting connections are used,
  bracing can be eliminated.
• An unbraced frame develops its stability through
  its rigid connection at the haunch.
• The connections used to join the bents to one
  another are considered to be pin type, and
  bracing is required along the length of the
  building to ensure stability in that direction.

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• In a three-dimensional structure, to ensure
  stability in all directions, the bracing must be
  provided in both planes of the structure.
• In some cases, masonry walls or reinforced
  concrete stairwells are used to provide lateral
  stability.
• Many structural steel frame buildings, especially
  multistory buildings, use a reinforced concrete
  core to provide the necessary resistance to
  lateral forces. Lateral forces are transferred
  through the floor slabs by diaphragm action to
  the core, which in turn transfers these loads
  into the foundations.

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Particular attention must be given to the
stability of the frame during the construction
phase !
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7.3 Structural Steel Connections

• The two most common methods used for connecting
  steel members in structural steel frames are
  bolting and welding.
• Welded connections are usually less expensive
  when done in the shop under controlled
  conditions
• Bolted connections are usually better suited to
  field conditions.

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Bolts (???)

• Structural bolts may be classified according to
  type of thread, type of steel, steel strength,
  shape of head and nut, and type of shank.
• Two types of bolted connections are used in
  structural steel connections bearing type and
  friction type.

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(1) Bearing-type connection

• The bolted parts bear on the shank of the bolt,
  thus using the bolt as a direct means of
  transferring load from one part to the other.
• Bearing-type connections are used in locations
  where the applied load acts primarily in one
  direction without much variation in magnitude.

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(2) Friction-type Connections

• They transfer load from one member to the other
  by means of the friction developed between the
  connected surfaces.
• The bolt acts as a clamp only and is not used in
  the transfer of load from one member to the other
  as in the bearing-type connection.
• Because the friction between the connected parts
  determines the capacity of the connection, no
  movement in the connection is expected.
• This type of connection can be used where the
  load direction varies without producing any
  undesirable effects on the connection.

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The bolts in all bolted connections must be
properly tightened to produce good results.
Tightening High-Strength Bolts with Torque Wrench
Pneumatic Impact Wrench
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Welds(??)

• Two types of welds are most often used in welded
  connections the fillet weld and the groove or
  butt weld.

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Typical Welded Joints
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7.4 Erection of Steel Frame

• (1)Anchor Bolts
• The successful erection of a steel frame depends
  on the proper positioning of the anchor bolts
  that will tie the frame to the foundation.
• They are cast into the concrete foundation to
  hold the first members of a steel frame to be
  placedthe column bearing plates.
• The anchor bolts must be positioned carefully,
  according to the plans, so that the bearing
  plates can be lined up accurately.

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Anchor Bolts and Hairpins Anchor
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• (2)Bearing Plates
• The column bearing plates are steel plates of
  various thicknesses in which holes have been
  drilled to receive the anchor bolts.
• The holes are slightly larger than the bolts so
  that some lateral adjustment of the bearing plate
  is possible.
• The angle connections by which the columns will
  be attached to the bearing plates are bolted or
  welded on them.

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Column Bearing Plates
Fig. 7-13 Column Bearing Plates
Fig. 7-14 Leveling Base Plates
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(3)Columns

• First-tier columns are the next group of members
  to be erected. They are often two stories long or
  in any case, the same size for at least two
  stories.
• Column lengths are such that splices will come
  450 to 600 mm above the floor levels, which is
  done to prevent splice connections from
  interfering with girder or beam-to-column
  connections.
• Column ends are milled to exactly the right
  length and to make sure that column loads will be
  evenly distributed over the entire bearing area.

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Shape of Column

• HP shapes, as nearly square in cross section as
  possible,are often chosen for columns.
• Round or square HSS sections may also be used,
  though the round column may present some
  connecting problems.
• Columns may also be built up by welding or
  bolting a number of other rolled shapes into a
  single unit.

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(4)Column Splices

• Column sections are joined together by splice
  plates that are bolted or welded to the column
  flanges and, in special cases, to the webs.
• If the column flanges match reasonably well, it
  is common to butt the column ends directly and
  join the column sections with splice plates.
• When the columns are of different sizes, a plate
  is used between the two column ends to provide
  bearing for the smaller column.

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(5)Girders

• Girders, the primary horizontal members of a
  flame, span from column to column and support the
  intermediate floor beams.
• They carry wall and partition loads and the point
  loads transmitted to them by the beams.
• Rolled W shapes or three-plate welded I shapes
  are normally used as girders.
• Connections between girders and columns can be
  either pin-type connections or moment resisting
  connections.

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Pin-Type Connections

• Pin-type connections are designed to resist
  vertical loads only.
• These connections consist of angles or plates
  bolted or welded to the girder web and usually
  bolted to the supporting column flange or web.

(a) Double-Angle Bolted Connections (b)
End-Plate Connection (c) Seated Connection.
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Pin-Type Connections

• Pin-type connections cannot resist lateral loads.
  They provide no lateral stability to the
  structural frame.
• Cross-bracing, shear walls, or a concrete core
  must be used to absorb the effects of lateral
  forces and to provide the necessary stability.

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Moment Connections

• Building frames that are designed as rigid frames
  that depend on the stiffness of the column
  sections to provide lateral stability use
  moment-resisting connections.
• Moment connections between the girders and the
  columns provide lateral stability in the
  structural frame by preventing rotation between
  the girders and the columns.
• Moment connections may be welded, bolted, or a
  combination of bolts and welds.

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Moment Connections
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(6)Beams

• Beams, generally smaller than girders, may be
  connected to either a column or a girder.
• Beam connections at a column are similar to the
  girder-to-column connections.
• In beam-to-girder connections, the main
  consideration is the shear connection, because
  the beams are considered to be carrying the floor
  loads and transferring them to girders as
  vertical loads.

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Floor Beams Framed between Girder Flanges

• The simplest is to frame the beam between the top
  and bottom flanges of the girder.

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Coped and Blocked Beam Ends

• If the top or bottom flanges of girders and beams
  will be flush, it is necessary to cut away a
  portion of the upper or lower beam flange.
• If the girder is an S shape, the end of the beam
  is coped, whereas if it is a W shape, the end is
  blocked.
• In many cases, the shear connection angles are
  bolted or welded to the beam ends in the shop,
  and the member comes to the job ready for
  connection to the girder web.

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(7)Channels and Angles

• Channels and angles, because of their shape,
  light weight, and wide range of sizes, have many
  different uses in the structural frame.
• Channels are usually used as secondary framing
  members when loads and spans are not too great.

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(7)Channels and Angles

• They are used as wall girts and roof purlins,
  girts being the horizontal members attached to
  the columns to support siding and purlins being
  the roof framing members spanning between the
  roof beams and supporting the roof deck.
• Other uses for channels are as
• framing for doors and windows
• stair stringers
• web and chord members in trusses
• built-up sections (eave struts and spandrel beams)

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7.4 Construction Procedures and Practices

• There are two distinct stages in the construction
  of a steel frame.
• The first stage is performed in the shop where
  the individual pieces are cut to length, coped or
  blocked, and punched or drilled for bolts. Detail
  material such as gusset plates, clip angles, and
  end plates for beams are attached so that the
  connections in the field can be made quickly.

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7.4 Construction Procedures and Practices

• The second stage begins when the fabricated steel
  arrives on the site.
• The field crew, with the aid of a crane,
  assembles the individual pieces according to the
  erection drawings.
• The connections are aligned with drift pins, and
  temporary bolts are used to hold the sections
  together.

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7.4 Construction Procedures and Practices

• The building is plumbed using a building transit
  and held in alignment with temporary cable
  bracing equipped with turnbuckles (to allow for
  adjustments) until permanent bracing has been put
  in place and final bolting and welding have been
  completed.
• The final stages of completing a bolted
  connection--removal of a drift pit that was used
  to align the bolt holes--so that the final
  structural bolt can be put in place.

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Structural Steel Floor Frames Hang from Straps

• The conventional methods of steel erection,
  beginning at the bottom and working up, do not
  always apply. Unusual designs sometimes require
  unorthodox erection schemes to be used.

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Some general safety rules

• 1. Do not attempt steel erection on rainy days.
  It is dangerous to work on wet steel.
• 2. Wear shoes with sewn leather or rubber soles.
• 3. Do not allow anyone to stand beneath a load
  boom.
• 4. Do not allow anyone to ride a load.
• 5. Wear heavy gloves that do not have loose cuff
• 6. Do not wear loose clothing that could easily
  catch on projections or swinging objects.
• 7. Use shackles instead of hooks.
• 8. Use cable slings instead of chains for lifting
  steel.
• 9. Make sure that the brakes on hoisting drums
  are inspected daily.
• 10. Keep a constant lookout for frayed or broken
  strands in cables and repair or replace them if
  necessary.

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Some essential site requirements

• 1. Proper ladders are provided for access from
  one level to another.
• 2. Handrails are provided around elevator shafts
  and the building perimeter once floor decking is
  in place.
• 3. Safety nets are provided, not only for the
  safety of the workers above, but also to protect
  personnel working below from falling objects.
• 4. All equipment must be maintained and have the
  proper warning devices when in operation.
• 5. Conduct weekly safety meetings to ensure that
  all personnel are aware of all safety rules.

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Summary

• Structural Steel Shapes
• Principles of Structural Steel Frames
• Structural Steel Connections
• Erection of Steel Frame
• Construction Procedures and Practices
• Homework
• P.144 1, 2, 3, 6/8, 9

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Gerneral Report

• To illustrate the general process of a civil
  engineering construction