decking plate girders lecture 21 steel construction 2arch...

1

F2012abn

APPLIED ARCHITECTURAL STRUCTURES:

STRUCTURAL ANALYSIS AND SYSTEMS

ARCH 631

DR. ANNE NICHOLS

FALL 2017

twenty one

steel construction

and designSteel Construction 1

Lecture 21

Applied Architectural Structures

ARCH 631

lecture

http://nisee.berkeley.edu/godden

F2009abn

Steel

• cast iron – wrought iron - steel

• cables

• columns

• beams

• trusses

• frames

Steel Construction 2

Lecture 21

Architectural Structures III

ARCH 631



Lecture 20


ARCH 631

F2007abn

Steel Construction

• standard rolled shapes

• open web joists

• plate girders

• decking

F2012abn

Steel Construction

• welding

• bolts


Lecture 21


ARCH 631

AISC Education

2


Lecture 20


ARCH 631

F2007abn

Steel Construction

• fire proofing

– cementicious spray

– encasement in gypsum

– intumescent – expands

with heat

– sprinkler system


Lecture 20


ARCH 631

F2007abn

Steel Materials

• high strength to

weight ratio

• ductile

• beam size

often limited by

deflection

• column size

limited by

slenderness

F2007abnSteel Construction 7

Lecture 20


ARCH 631

Steel Beams

• types

– manufactured shapes

castellated



Lecture 20


ARCH 631

F2007abn

Steel Beams

• types

– wide flange

3


Lecture 20


ARCH 631

F2007abn

Steel Beams

• types

– open web joists

(manufactured

trusses)


Lecture 20


ARCH 631

F2007abn

Steel Beams

• types (more)

– plate girder

– decking

F2009abn

Steel Beams


Lecture 21


ARCH 631



Lecture 20


ARCH 631

F2007abn

Steel Beams

• lateral stability - bracing

• local buckling - stiffen

4


Lecture 20


ARCH 631

F2007abn

Local Buckling

• steel I beams

• flange

– buckle in

direction of

smaller radius

of gyration

• web

– force

– “crippling”


Lecture 20


ARCH 631

F2007abn

Local Buckling

• flange

• web


Lecture 20


ARCH 631

F2007abn

Shear in Web

• panels in plate girders or webs with large shear

• buckling in compression direction

• add stiffeners


Lecture 20


ARCH 631

F2007abn

Steel Beams

• end conditions

• a) away from

connection - full

section effective

• b) high shear –

only web

effective

5


Lecture 20


ARCH 631

F2007abn

Steel Beams

• end conditions

• c) bolt holes –

less material

• d) local web

buckling


Lecture 20


ARCH 631

F2007abn

Steel Beams

• bearing

– provide

adequate

area

– prevent

local yield

of flange

and web


Lecture 20


ARCH 631

F2007abn

Steel Beams

• connections

– welds

– bolts


Lecture 20


ARCH 631

F2007abn

Steel Design – Open Web Joists

• SJI: www.steeljoist.com

• Vulcraft: www.vulcraft.com

– K Series (Standard)

• 8-30” deep, spans 8-50 ft

– LH Series (Long span)

• 18-48” deep, spans 25-96 ft

– DLH (Deep Long Spans)

• 52-72” deep, spans 89-144 ft

– SLH (Long spans with high strength steel)

• pitched top chord

• 80-120” deep, spans 111-240 ft

6


Lecture 20


ARCH 631

F2007abn


load for live load

deflection limit in RED

total in BLACK

Su2011abn

load for live load deflection

limit (L/360) in RED

total in BLACK



Lecture 21


ARCH 631


Lecture 20


ARCH 631

F2007abn

Steel Beam Design

• American Institute of Steel Construction

– steel grades

• ASTM A36 – carbon

– plates, angles

– Fy = 36 ksi & Fu = 58 ksi

• ASTM A572 – high strength low-alloy

– some beams

– Fy = 60 ksi & Fu = 75 ksi

• ASTM A992 – for building framing

– most beams

– Fy = 50 ksi & Fu = 65 ksi

F2012abn

Steel Beam Design

• AISC: 14th ed.

– combined ASD & LRFD

in one volume in 2005


Lecture 21


ARCH 631

7

Su2011abn

• ASD

– bending (braced) = 1.67

– bending (unbraced*) = 1.67

– shear = 1.5 or 1.67

– shear (bolts & welds) = 2.00

– shear (welds) = 2.00

* flanges in compression can buckle

Ra ≤ Rn

Unified Steel Design


Lecture 21


ARCH 631

F2012abn

Unified Steel Design

• braced vs.

unbraced


Lecture 21


ARCH 631

Su2011abn

LRFD Steel Beam Design

• limit state is yielding all across section

• outside elastic range

• load factors & resistance factors


Lecture 21


ARCH 631

E

1

fy = 50ksi

001724.0y

f


Lecture 20


ARCH 631

F2007abn

Load Types

• D = dead load

• L = live load

• Lr = live roof load

• W = wind load

• S = snow load

• E = earthquake load

• R = rainwater load or ice water load

• T = effect of material & temperature

8

F2012abn

LRFD Load Combinations


Lecture 21


ARCH 631

ASCE-7

(2010)

• 1.4D

• 1.2D + 1.6L + 0.5(Lr or S or R)

• 1.2D + 1.6(Lr or S or R) + (L or 0.5W)

• 1.2D + 1.0W + L + 0.5(Lr or S or R)

• 1.2D + 1.0E + L + 0.2S

• 0.9D + 1.0W

• 0.9D + 1.0E• F has same factor as D in 1-5 and 7

• H adds with 1.6 and resists with 0.9 (permanent)


Lecture 20


ARCH 631

F2007abn

Pure Flexure

Mu - maximum moment

b - resistance factor for bending = 0.9

Mn - nominal moment (ultimate capacity)

Fy - yield strength of the steel

Z - plastic section modulus*

ZFMMR ynbuii 9.0


Lecture 20


ARCH 631

F2007abn

Internal Moments - at yield

yyy fbh

fc

IM

6

2

• material hasn’t failed

y

2

y

2

f3

bc2f

6

c2b


Lecture 20


ARCH 631

F2007abn

Internal Moments - ALL at yield

• all parts reach yield

• plastic hinge forms

• ultimate moment

• Atension = Acompression

yyp MfbcM2

32

E

1

y = 50ksi

y = 0.001724

9


Lecture 20


ARCH 631

n.a. of Section at Plastic Hinge

• cannot guarantee at

centroid

• fy·A1= fy·A2

• moment found from

yield stress times

moment area

1.

p y y i in a

M f A d f A d


Lecture 20


ARCH 631

F2007abn

Plastic Hinge Development


Lecture 20


ARCH 631

F2007abn

Plastic Hinge Examples

• stability can be effected


Lecture 20


ARCH 631

F2007abn

Plastic Section Modulus

• shape factor, k

= 3/2 for a rectangle

1.1 for an I

• plastic modulus, Z

y

p

M

Mk

y

p

f

MZ

SZk

10


Lecture 20


ARCH 631

Shear

Vu - maximum shear

v - resistance factor for shear = 1.0

Vn - nominal shear

Fyw - yield strength of the steel in the web

Aw - area of the web = twd

iRi = Vu ≤ vVn = 1.0(0.6FywAw)

Su2011abn

Flexure Design

• limit states for beam failure

1. yielding

2. lateral-torsional buckling*

3. flange local buckling

4. web local buckling

• minimum Mn governs


Lecture 21


ARCH 631

1.76y

p y

FL r

E

i i u b nR M M

Su2011abn

Compact Sections

• plastic moment can form before any

buckling

• criteria

–

– and


Lecture 21


ARCH 631

0.382

f

f y

b E

t F

3.76c

w y

h E

t F

Su2011abn

Cb = modification factor

Mmax - |max moment|, unbraced segment

MA - |moment|, 1/4 point

MB = |moment|, center point

MC = |moment|, 3/4 point

Lateral Torsional Buckling


Lecture 21


ARCH 631

pbn MCM moment based on

lateral buckling

CBAmax

maxb

MMMM.

M.C

34352

512

11

Su2011abn

Beam Design Charts


Lecture 21


ARCH 631


Lecture 20


ARCH 631

Deflection Limits

• based on service condition

• no “impairment” to serviceability

• avoid ponding

• L/360 due to live load for beams &

girders supporting plaster (service)

F2009abn

Steel Arches and Frames

• solid sections

or open web


Lecture 21


ARCH 631



Lecture 20


ARCH 631

F2007abn

Steel Shell and Cable Structures

12


Lecture 20


ARCH 631

F2007abn

Approximate Depths

Su2011abn

Unified Column Design

• limit states for failure

1. yielding

2. buckling

Fe – elastic buckling stress (Euler)


Lecture 21


ARCH 631

ncu PP gcrnc AFP. 900

ye

y

F.ForF

E.

r

KL440714

ye

y

F.ForF

E.

r

KL440714

n

a

PP

Su2011abn

Unified Column Design

• Pn = FcrAg

– for

– for

– where


Lecture 21


ARCH 631

yF

E.

r

KL714 y

F

F

cr F.F e

y

6580

ecr F.F 8770

22

rKL

EFe

yF

E.

r

KL714

Su2011abn

Procedure for Analysis

1. calculate KL/r• biggest of KL/r with respect to x axes and y axis

2. find Fcr from appropriate equation• tables are available

3. compute Pn = FcrAg

• or find fc = Pa/A or Pu/A

4. is Pa Pn/ or Pu Pn?• yes: ok

• no: insufficient capacity and no good


Lecture 21


ARCH 631

13

Su2011abn

1. guess a size (pick a section)

2. calculate KL/r• biggest of KL/r with respect to x axes and y axis

3. find Fcr from appropriate equations• or find a table

4. compute Pn = FcrAg

• or find fc = Pa/A or Pu/A

Procedure for Design


Lecture 21


ARCH 631

Su2011abn

Procedure for Design (cont’d)

5. is Pa Pn/ or Pu Pn?• yes: ok

• no: pick a bigger section and go back to step 2.

6. check design efficiency

• percentage of stress =

• if between 90-100%: good

• if < 90%: pick a smaller section and

go back to step 2.


Lecture 21


ARCH 631

%P

P

c

r 100

Su2011abn

Column Tables


Lecture 21


ARCH 631

Su2011abn

Beam-Column Design

• moment magnification (P-)

Cm – modification factor for end conditions

= 0.6 – 0.4(M1/M2) or

0.85 restrained, 1.00 unrestrained

Pe1 – Euler buckling strength


Lecture 21


ARCH 631

factoredmaxu MBM 1 )PP(

CB

eu

m

1

11

22

1

rKl

EAPe

14

Su2011abn

Beam-Column Design

• LRFD (Unified) Steel

– for

– for

Pr is required, Pc is capacity

c - resistance factor for compression = 0.9

b - resistance factor for bending = 0.9


Lecture 21


ARCH 631

019

8.

M

M

M

M

P

P

nyb

uy

nxb

ux

nc

u

:.P

P

c

r 20

012

.M

M

M

M

P

P

nyb

uy

nxb

ux

nc

u

:.P

P

c

r 20


Lecture 20


ARCH 631

F2007abn

Construction Supervision

• proper grade material

– high strength bolts

• quality welds

• proper bolted

conditions (ex. sc)

• fabrication and erection

of steel frame

connection details

decking plate girders lecture 21 steel construction 2arch...

Documents