ENGM054 Unit 6 Presentation 9

7/30/2019 ENGM054 Unit 6 Presentation 9

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Earthquake Engineering

ENGM054

Ar is Theop h i louAssociate Lecturer

University of SurreyBEng (Hons) MEng (Structural) MEng (Geotechnical)MICE [email protected]

Dr Mar c us Mat t hew s Module CoordinatorSenior LecturerUniversity of [email protected]


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Unit 6 - Syllabus

Seismic behaviour of buildings

Steel structures design to EC3 and EC8 Beam design

Column design

Joint checks

Beam-column connections Moment resisting frames

Concentrically braced frames

Eccentrically braced frames

Modern trends in seismic design / protection


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Lateral Force Resisting Systems

Moment-resisting frames

Concentrically braced frames

Eccentrically braced frames

Hybrid (dual) systems


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Energy Dissipation Mechanism

Seismic design central aspects

Avoidance of hinge formationon columns

Increased shear forces due tohinge formation

Sufficient ductility of system member rotational ductility


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Beam Design

Maximum developed plastic bending moment resistance Mpl,Rd affected by

Slenderness Lateral torsional buckling

Axial force

EC3 and EC8 provisions

For MRF with q 4 Class 1 sections must be used, EC8, clause 6.5.3(2)

EC8 states that beams should be verified for lateral torsional buckling to EC3

Design for bending moment resistance

EC3, clause 6.2.5(1)

provided that EC3, clause 6.2.4(1)

0.1,

Rdpl

Ed

M

M

15.0,

Rdpl

Ed

N

N


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Beam Design


Design for shear resistance

Design for VEd which is the design shear force that results from theseismic design situation through an elastic analysis

Design for VEd,E


where VEd,G is the design shear force due to the gravity actions

and VEd,M is the design shear force when Mpl,Rd is reached

Design shear resistance


where M0 = 1.0 is the material partial factor, EC8, clause 6.1(1)

5.0

,

,,

,

,

+=

Rdpl

MEdGEd

Rdpl

EEd

V

VV

V

V

L

MMV

BRdplARdpl

MEd

,,,,

,

+=

0

,

3 M

yv

Rdpl

fAV

=


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Column Design


Design forces

Design axial force

Design bending moment

Design shear force

where ov = 1.25 is the overstrength factor, EC8, clause 6.2(3)

is the minimum value ofMpl,Rd/ MEd for all connected beams where MEd isthe bending moment of the seismic design situation, EC8, clause 6.2(3)

NEd,G, MEd,G, VEd,G are the forces due to the non-seismic actions of theseismic design situations, EC8, clause 6.2(3)

NEd,E, MEd,E, VEd,E are the forces due to the design seismic actions, EC8,clause 6.2(3)

EEdovGEdEd NNN ,, 1.1 +=

EEdovGEdEd MMM ,, 1.1 +=

EEdovGEdEd VVV ,, 1.1 +=






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Column Design


Design shear force check


Design for bending moment and axial force Class 1, I sections

Effect of axial force can be ignored when the following criteria are satisfied

EC3, clause 6.2.9.1(4)

Design plastic moment resistance due to axial force NEdEC3, clause 6.2.9.1(5)

where

Design axial force resistance


5.0,

Rdpl

Ed

V

V

0

,

5.0

25.0

M

yww

Ed

RdplEd

fthN

NN

( )a

NNMM

RdplEd

RdplRdN

=

5.01

/1,

,,

5.02

=tbA

af

0

,

M

y

Rdpl

fAN

=


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Rotational Ductility

Rotational ductility is the rotational capacity of plastic hinges beforefailing

Rotational ductility

where y is the curvature at yield point and u is the curvature at

ultimate point Rotational ductility relationship to behaviour factor for reinforced

concrete structures

EC8, clause 5.2.3.4(3) Not explicit requirement for steel structures in EC8

y

u

=

( ) CC

C

TT

T

Tq

TTq

=

1

1

0

10

if121

if12


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Beam-Column Joint

Need to avoid the formation of plastic hinges on columns as they causea very unstable mechanism

Only locations plastic hinges are permitted are the bases of groundstorey columns and where they are discontinued in the above storey

EC8 checks

EC8, clause 4.4.2.3(4)

Needs to be conducted for both axes and both directions

Mpl,

R

Mpl,

R

Mcolum

n,2

Mcolumn,1

RbRc MM 3.1


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Beam-Column Connections

Connections are the elements that connect the beams and the columns.

Bolted connections, welded connections

Plastic hinges are not permitted to develop within connections

Need to be stronger than connecting elements by about 20%

Typical modes of failure

Column web yielding, point A and diagonal

Column web buckling, point A and diagonal Column flange flexural failure

Column shear yielding

Weld fracture

Nc1, Vc1,Mc1

Nc2, Vc2,Mc2

Vb1, Mb1Vb2, Mb2 A


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Concentrically Braced Frames

Generally smaller drifts than moment-resisting frames

Main problem is ductility

Yielding of diagonal braces is intended to take place before theconnection failure or yielding/buckling of beams and columns

Ductile behaviour is attributed primarily to the tensile yielding ofdiagonal braces. Need to ensure that the yielding levels are similarunder load reversals. Check condition

A: horizontal projection area of tension braces, EC8, clause 6.7.1(3)

Design checks

Slenderness ratios 2 (V braces, non-X braces), 1.3 (X braces)

Design axial forces for beams and columns

05.0+

+

+ AA

0.1

,

Rdpl

Ed

N

N


1 2


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Eccentrically Braced Frames

Braces frame into beams

Link is the portion of beam in which plastic hinge develops

Link subjected to bending and shear forces

Short links associated with shear plastic deformation

Long links associated with flexural plasticity and plastic hinges

Diagonal braces and columns should be designed for unfavourable

combinations of axial forces, bending moments and shear forces:EC8, clause 6.2(3)

Link

EEdovGEdEd VVV ,, 1.1 +=




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Modern Trends

Transmissibility chart covered in Unit 2


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Modern Trends

Base isolation


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Modern Trends

Energy dissipation devices

Viscoelastic and frictional dampers


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Modern Trends

Tuned mass damping


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Coursework B - Guidance

Use response spectrum Type 1 (easier - not mandatory).

Conduct the seismic design situation analysis using two primaryloadcases (1) gravity actions (e.g. VEd,G) and (2) seismic actions (e.g.VEd,E). Combine the results.

Check the column bending moment resistance. Consider the combinedeffect of bending moment and axial force on columns.

Use any computer program you like. Include only printout of thestructural analysis results preferably in shematic form.

State all assumptions with reference to Eurocode.

ALWAYS make full reference to Eurocode provisions.

ALWAYS write the units.


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Recommended Studying

Eurocode 3, BS EN 1993-1-1:2005

Reading: 6.1, 6.2.1, 6.2.3, 6.2.4, 6.2.5, 6.2.6, 6.2.9 Accessible through MyAthens>British Standards Institution>

(bsol.bsigroup.com)

Eurocode 8, BS EN 1998-1:2004

Reading: 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8


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Thank you!

Documents

ENGM054 Unit 6 Presentation 9