Design of the case studies Eccentrically Braced Steel Frames

1
Design of the case studiesEccentrically Braced
Steel Frames
OPUS - OPtimizing the seismic performance of
steel and steel-concrete strUctures by
Standardizing material quality control

• Walter Salvatore, Massimo Badalassi University of
  Pisa, Department of Structural Engineering
• Aurelio Braconi Riva Group - Corporate
  Research Policies

Pisa, October 15th, 2007
2
Introduction

• The initial design of the Eccentrically Braced
  steel frame is presented two frames have been
  designed
• Frame 1 in which long/intermediate links are
  considered (bending)
• Frame 2 in which short links are considered
  (shear).

• The design has been executed using a p.g.a. equal
  to 0.25g
• Other two frames will be then designed using a
  p.g.a. equal to 0.10g

• The seismic analysis of the frames has been
  realized using the lateral force method
• When the design of all the frames will be
  completed (designing also the structural
  connections rigid and full strength), respective
  non-linear structural models will be realized

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Geometry of the case study

• Lateral view

• Materials
• Steel profiles S355
• Concrete slabC25/30

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Geometry of the case study

• Plan view

• Slab type

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Loads

• Dead Load concrete slab self weight 3,00 kN/m2
• superimposed load 2,00 kN/m2
• partition walls 0,80 kN/m2
• Live load office category B 3,00 kN/m2
• Wind load Wind Zone 2 (qref) 0,40 kN/m2
• according to the value proposed by RWTH
• Snow load Snow Zone 2 1,00 kN/m2
• according to the value proposed by RWTH

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Loads

• Damage limit state
• Drift limits imposed by EC8 ductile
  non-structural elements (0,005 h)

• Earthquake

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Position of the secondary beam and braces

• Bracing systems

• Presence of secondary beam in correspondence of
  the link could interfere with the flexural/shear
  behavior of the link

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Position of the secondary beam

• The secondary beam could be doubled to move the
  vertical load away from the link

• There are only some general prescriptions in the
  EC8 concerning with doubler paltes or holes

• The slab will not change.

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Frame (1) bending link selected profiles

• Main beam for exterior frame IPE500

• Main beam for interior frame IPE500

• Beam containing the link sized according to
  EC8 requirements

• Main beam simply supported. Secondary beams
  designed as continuous

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Frame (1) selected profiles

• Interior and exterior column are realized using
  HE300B

• Braces are realized with HE200B

• Braces are sized using maximum force (capacity
  design) the same for the columns

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Frame (1) selected profiles

• Top floor

• The design of main beams and secondary beams have
  been controlled by the vertical drift limitations

• During the design the following drift limits have
  been assumed according to EN1991 and National
  Italian Regulations

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Frame (1) capacity design and over-strength

• For a homogenous spreading of plasticity in the
  seismic link along the height of the frame the
  over strength factor Wi for each link must be
  defined.
• The difference between the minimum W and each Wi
  must be less than 25

• The sizing of link become critic, conditioning
  the design of all other elements through the
  capacity design of braces and columns

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Frame (2) shear link selected profiles

• Main beam for exterior frame IPE500

• Main beam for interior frame IPE500

• Beam containing the link sized according to
  EC8 requirements

• Main beam simply supported. Secondary beams
  designed as continuous

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Frame (2) selected profiles

• Interior column are realized using HE300B while
  exterior using HE320B

• Braces are realized with HE200B and HEB220B

• Braces are sized using maximum force (capacity
  design) the same for the columns

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Frame (2) selected profiles
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Frame (2) selected profiles
HE260 B
HE260 B
HE320 B
HE300 B
HE320 B
HE300 B
HE300 B
HE260 B
HE260 B
HE260 B
HE260 B
HE300 B
HE320 B
HE320 B
HE300 B
HE300 B
HE280 B
HE280 B
HE320 B
HE320 B
HE300 B
HE300 B
HE300 B
HE280 B
HE280 B
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Frame (2) selected profiles

• Top floor

• The design of main beams and secondary beams have
  been controlled by the vertical drift limitations

• During the design the following drift limits have
  been assumed according to EN1991 and National
  Italian Regulations

18
Frame (2) capacity design and over-strength

• For a homogenous spreading of plasticity in the
  seismic link along the height of the frame the
  over strength factor Wi for each link must be
  defined.
• The difference between the minimum W and each Wi
  must be less than 25

• The sizing of link become critic, conditioning
  the design of all other elements through the
  capacity design of braces and columns

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Design of the concrete slab

• The types of slab section designed for the EBF is
  characterized by a prefabricated lab with steel
  trussed girder (as reinforcement for the casting
  phase propped or unpropped).
• For an optimized design of the trussed girder an
  interaction domain between shear and bending
  moment has been defined

Shear limit for avoiding instability of diagonals
Stability upper bar
Resistance of lower bar
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Tests on concrete slabs

• Simply supported r.c. slab (Sagging moment
  condition)

2 tests

• Cantilever scheme (Hogging moment condition)

2 tests
Designed section
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Conclusions

• homogeneous distribution of the plastic
  deformation through the structure W impose a
  strict control during the sizing of the link
  profile (25 of variation between Wi)
• interaction between static load combination and
  seismic load combination could produce high
  values of Wi
• An optimization of the structural behaviour could
  be obtained using short and long link in the
  structure (to be evaluated)
• using simply supported beams cannot optimize the
  structural size under vertical load conditions
• the presence of secondary beam, also if not
  specified in the EC8, in correspondence of the
  link should be avoided.

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Work to be completed

• Completing of the design of the case studies with
  the design of the structural connections

Base joint
Brace to column connection
Brace to beam connection
Beam to column connection

• design of the EBF in low seismicity areas
• design of the car park
• definition of the non-linear models

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Software and Computers

• The department of structural engineering has the
  following software for the execution of numerical
  analyses
• Ansys (finite elements concentrated and
  distributed plasticity some fiber element
  simple hysteretic laws)
• Ruaumoko (structural models - various hysteretic
  laws)
• OpenSees (finite elements - concentrated and
  distributed plasticity, fiber elements, various
  hysteretic laws)
• ADINA (finite elements concentrated and
  distributed plasticity some fiber element
  simple hysteretic laws)

• Hardaware
• Personal computers of the internal calculation
  centre
• A work station with four CPUs Intel XEON for the
  execution of the parallel calculation