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STRUCTURAL STEEL EDUCATIONAL COUNCIL
TECHNICAL NFORMATION PRODUCTSERVICE
JULY 999
P r a c t i c a l D e s i g n a n d D e t a i l i n g
o f S t e e l C o l u m n a s e P l a t e s
y
W i ll i am C H o n e c k
D e r e k W e s t p h a l
F o r e l l E l s e s s e r E n g i n e e r s
Inc
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cknowledgments
T h e a u t h o r s w i s h t o t h a n k t h e f o ll o w in g p e r s o n s f o r t h e i r i np u t , r e v i e w a n d c o m m e n t s o n t h e c o n t e n t o f th i s
teel Tips
pub l i ca t i on :
M e m b e r s o f t h e S t r u c t u r a l S t e e l E d u c a t i o n a l C o u n c i l
R o g e r F e r c h , H e r r i c k C o r p o r a t i o n
B e r n i e L o r i m o r , R o c k y M o u n t a i n S t e e l
S t e v e R i c h a r d s o n , W W S t e e l C o m p a n y
R i c k W i lk e n s e n , G a y l e M a n u f a c t u r in g
D a v e M c E u e n , C a l i fo r n ia E r e c t o r s
J i m M a l le y , D e g e n k o l b E n g i n e e r s
J im P u t k e y
M a s o n W a i t e r s , F o r e l l / E l s e s s e r E n g i n e e r s .
P r o f e s s o r S u b h a s h G o e l , U n i v e rs i ty o f M i c h i ga n
Disclaimer
T h e i n fo r m a t io n p r e s e n t e d i n t h i s p u b l i c a ti o n h a s b e e n p r e p a r e d i n a c c o r d a n c e w i t h r e c o g n i z e d e n g i n e e r i n g
p r inc ip le s a nd cons t ruc t i on p rac t ices and i s fo r gen e ra l i n fo rm a t ion on ly . W hi l e i t i s be l i eved to be ac cu ra t e ,
t h i s i n fo rma t ion shou ld no t be u sed o r re li ed upon fo r any spec if ic app l i ca ti on w i thou t com pe te n t p ro fess ion a l
exam ina t ion and ve r i fi ca ti on o f i ts accu ra cy , su i tab i li ty , an d app l i cab i li t y by a l icensed p ro fess iona l eng ine e r
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o n t h e p a r t o f t h e S t r u c t u r a l S t e e l E d u c a t i o n a l C o u n c i l, o r o f a n y o t h e r p e r s o n n a m e d h e r e i n , th a t t h is
i n f or m a t i o n i s s ui ta bl e f o r a n y g e n e r a l o r p a r t i c u l a r u s e o r o f f r e e d o m i n f r in g e m e n t o f a n y p a t e n t o r p a t e n t s .
A n y o n e u s i n g t h i s i n f o r m a t i o n a s s u m e s a l l li a bi li ty a r i si n g f r o m s u c h u s e .
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No
PRACTICALDESIGNAND DETAILINGOF STEEL COLUMNBASE PLATES
Table of Contents
Description Page No.
1 0
2 0
3 0
4 0
5 0
6 0
I N T R O D U C T I O N 2
1 1 Prefa ce 2
1 2 P u rp o se 2
1 3 O rg a n iz a t io n 2
D E S I G N G U I D E L I N E S F O R M A T E R I A L S A N D F A B R I C A T I O N
2 1 M a te r i a l s
2 1 1 A n c h o r B o l t s a n d N u t s
2 1 2 P l a t e s
2 2 B a se P l a t e D e s ig n fo r F a b r i c a t io n
2 2 1 Ma te r i a l v e r su s L a b o r
2 2 2 W e l d i n g
2 2 3 B a se P l a t e D im e n s io n s
D E S I G N G U I D E L IN E S R E L A T E D T O E R E C T IO N
3 1 A n c h o r B o l t s
3 1 1 A n c h o r B o l t P o s i t i o n M is lo c a t io n
3 1 2 R o t a t e d A n c h o r B o l t P a t t er n s
3 1 3 A n c h o r B o l t s S e t T o o L o w o r T o o H i g h
3 1 4 C o l u m n s N e x t to W a l l s
3 2 W a s h e r s
3 3 B a se P l a t e L e v e l in g
E N G I N E E R I N G G U I D E L I N E S F O R D E S IG N O F B A S E P L A T E S
4 1
4 2
4 3
4 4
4 5
4 6
4 7
D e s i g n f o r T e m p o r a r y C o n s t r u c ti o n L o a d s
D e s i g n f o r G r a v it y an d O t h e r D o w n w a r d L o a d s
D e s ig n fo r G ra v i ty L o a d s in C o m b in a t io n w i th U p l i f t L o a d s
D e s ig n fo r G ra v i ty L o a d s in C o m b in a t io n w i th S h e a r F o rc e s
D e s ig n fo r G ra v i ty L o a d s in C o m b in a t io n w i th S h e a r F o rc e s a n d Mo m e n t s
D e s ig n fo r Mo m e n t s d u e to S e i sm ic F o rc e s
A rc h i t e c tu ra l I s su e s
C O N C L U S I O N S
R E F E R E N C E S
3
3
3
3
4
4
4
5
8
8
9
10
10
12
13
14
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PRAC TICA L DESIGN AND DETAILING OF STEEL COL UMN BASE PLATES
1 0 INTRODUCTION
1 1 P r e f a c e
St e e l c o l umn ba s e p l a t e s a re on e o f t he mos t
~ nda me n t a l pa r t s o f a s t e e l s t r uc t u r e , ye t t he
de s i gn o f ba s e p l a t e s is c omm on l y no t g i ve n t he
a t ten tion tha t it should by engineers . This resu l t s
in base plate detai ls tha t are expensive , diff icul t to
f a b r i c a t e a nd ma y e ve n c on t r i bu t e t o t he ha z a r ds
o f t he s t ee l e r e c t ion p r oc e s s by no t p r ov i d i ng
s tab i li ty for e rec t ion load s appl ied to the co lumn.
Base p la tes se rve tw o bas ic fianct ions :
1 . They t ransfe r co lumn loads to the suppo r t ing
mem ber or found a t ion . These loads inc lude ax ia l
due to grav i ty , moments , shears and somet imes
axial due to upl if t ;
2 . The y a l low the co lum n to s tand as a
tem porary vert ical cant i lever af ter the l i f t ing l ine is
r e l ea s e d w i t hou t ha v i ng t o guy o f f t he c o l umn .
T he c o l umn a nd ba s e p l a t e mus t w i t h s t a nd
tem pora ry wind and e rec t ion loads sa fely .
S teel fabr ica tors and e rec tors w ho a re m embers of
t he S t r uc tu r a l S t e e l E duc a t i ona l Counc i l SSE C )
ha ve c omm e n t e d t ha t t he r e a r e a va r i e ty o f ba s e
pla te des igns and de ta i ls f rom engineers. Som e
fabr ica tors a re c r i t i ca l o f many of these des igns
beca use they a re d i f f icu l t to fabr icate , o r spec i fy
ma t e r i a l s t ha t a r e ha r d t o ob t a i n o r t ha t do no t
ex is t in the s izes spec i fied . The des igns of ten
resu l t in co lumns tha t a re hard to e rec t o r a re
uns ta b le w i t hou t guy i ng t he c o l umn . W he n a nc ho r
bol t s a re no t p roper ly se t , expens ive cor rec t ive
wo rk i s required before the co lumn can be e rec ted ,
resu l t ing in de lays in the s tee l e rec t ion process .
This publ ica t ion of teel Tips a t tempts to address
these issues.
I n o r de r t o u nde r s t a nd be t t e r a nd re s pond t o t he
fabricat ion and erect ion issues, a qu est ionna ire was
dis t r ibu ted to severa l SSEC member f i rms
r e que s t i ng t he i r c omme n t s a bou t p r ob l e ms
expe r ienced in the i r shops dur ing fabr ica t ion and
in the f ie ld durin g steel erect io n. Specif ic issues
inc luded over ly expens ive des igns and problems
with obtaining the materials specif ied. S ugg est ion s
on how t he s e de s i gns c ou l d ha ve be e n mor e
e c onom i c a l we r e s o li c it e d . T he que s t ionna i r e
asked about ~ tee l e rec t ion problems exper ienced
a nd r e que s t e d s ugge s t i ons t o m i t iga t e t hos e
p r ob l e ms . T he r e s pons e s r e c e ive d we r e ve r y
i n f o r ma t i ve a nd ma ny o f t he s ugge s t i ons i n t he
r e s pons e s ha ve be e n i nc o r po r a t e d i n t o t h i s
publ ica t ion .
1 2 P u r p o s e
T he p u r pos e o f t h is is s ue o f teel Tips i s to
provide prac t ica l gu ide l ines for engineers ,
f a b r i c a to r s and c on t r a c t o r s r e ga r d i ng t he de s ign
and de ta i l ing of s tee l co lumn base p la tes .
Gu i da nc e i s p r ov i de d t owa r d r e s o l v i ng c ommon
des ign , fabr ica t ion and e rec t ion problems. M any
of the top ics d i scussed a re s imple to implement ,
ye t a r e o f t e n ove r l ooke d .
Unf o r t una t e l y t he be ha v i o r o f ba s e p l a t e s i n
mome n t f r a me s a nd b r a c e d f l a me s s ub j e c t e d t o
ear thq uake forces i s no t f ia lly unde rs tood .
Re s e a r c h a nd c ode gu i da nc e a r e l im i t ed . T he
e ng i ne e r i s f o r c e d t o u s e j udge me n t i n o r de r t o
achieve a des i red leve l o f per formance and i t i s
hope d , tha t th i s pu bl ica t ion wi l l in i t i a te more
r e s e a r c h a nd de ve l opme n t in t he a r e a s o f ba s e
pla te behavior and des ign guide l ines for base p la te
assembl ies tha t a re subjec ted to h igh moments
wh e r e s ome s o r t o f y i e l d ing i s ne c e s s a r y t o
achieve the des i red per form ance .
1 3 O r g a n i z a t i o n
T he f oc us o f t h i s i s sue o f
teel Tips
is directed
t ow a r d t he p r a c ti c a l a spe c t s o f t he de s i gn a nd
de ta i l in g of base p la tes par t icu la r ly as they re la te
to economica l fabr ica t ion and s tee l e rec t ion .
Sec t ion 2 .0 d i scusses fabr ica t ion issues. Sec t ion
3 .0 d i scusses e rec t ion and anchor bo l t p lacement
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issues. Section 4.0 discusses the issues involved
in the design of base plates, rather than providing
how to design methods or guidelines, and lists
the names of other authoritative publications
where the reader can find design formulas and
definitive procedures for design of base plates.
Section 4.0 also discusses fixed and partially fixed
column bases, for instance, moment frames which
resist wind or earthquake forces.
2 .0 D E SI G N G U I D E L I N E S FO R
MATERIAL S AND FABRI CATION
Engineers have numerous types of steel to choose
from when designing anchor bolts and base plate
assemblies. However, materials are often specified
that are not readily available or are not suitable for
specific applications. Base pla te details often are
hard to fabricate, overly complicated, call for
expensive welds and/or specify impossible welds.
The following sections provide design guidelines
for specifying suitable materials and suggestions
for details to make fabrication easier and more
economical.
2 1 M a t e r i a l s
A c c o rd in g to t h e A IS C S p e c i f i c a t io n fo r
Structural Steel Buildings Allowable Stress Design
and P las t ic Des ign (ASD Spec i f ica t ions) , there a re
1 6 A S T M d e s ig n a t io n s sp e c i f i e d fo r s t ru c tu ra l
appl ica t ions . Fo r spec i f ic mater ia l p roper t ies ,
su i tab le appl ica t ions and comple te d imens iona l
in format ion , the reader should re fe r to the ASTM
Speci f ica t ions .
2 1 1 A n c h o r B o l ts a n d N u t s
T h e m o s t c o m m o n a n d r e a d i ly a v a i la b l e a n c h o r
bol t mater ials a re AS TM A36 and A307. Smal le r
bo l t s ge0era l ly a re suppl ied in A307 and la rger
diameter in A36. Th e material prop ert ies fo r thes e
re la t ive ly low s t reng th bo l t s a re very s imi la r.
T h e se tw o g ra d e s a r e w e ld a b le a n d sh o u ld b e
spec i f ied when poss ib le .
Wh e n h ig h - s t r e n g th b o l t s a r e r e q u i r e d , t h e
mater ia ls typ ica l ly ava i lab le a re A449, A354 and
A 1 9 3 ty p e B 7 (o f te n r e f e r re d to a s B 7 ) . B 7
b o l t s a r e th e s a m e m a te ri a l a s A IS I 4 1 4 0 a n d c a n
b e su b s t i t u te d fo r A 4 4 9 b e c a u se A 4 4 9 a n d B 7
bol ts bo th have mater ial p rop er t ies th a t a re a lmost
id e n ti c a l. A 3 2 5 b o l t s o n ly c o m e in h e a d e d
form, a re limi ted to 1 1 /2 inch d iame ter max imum
and are limi ted in the leng ths ava ilab le. The
propert ies and chemistry for A325 bo lts are s im ilar
to A449 and B7. Genera l ly , it i s be t te r to spec i fy
A 4 4 9 , A 3 5 4 o r B 7 b o l t s w h e n h ig h - s t r e n g th b o lt s
a r e n e c es sa ry . H ig h - s t r e n g th b o l ts c o m e a s p la in
bar s tock and th reads must be cu t in to bo th ends .
H e a d e d b o l t s f a b r i c a t e d f ro m A 3 2 5 , A 4 9 0 o r
A588 should no t be spec i f ied s ince these a re no t
read i ly ava i lab le . A l l o f these h igh s t rength
mater ia ls a re hea t t rea ted a l loy s tee ls and a re
therefore no t su i tab le fo r weld ing . Before
specifying a bolt material , c on tact local fabric ators
for in format ion reg ard ing mater ia l av a i lab i li ty and
re v ie w th e A S T M s t a n d a rd s fo r t h e g ra d e s b e in g
cons idered to de te rmine th e i r su i tab i l ity .
I t i s im p o r t a n t t o sp e c ify t h e c o r r e c t g r a d e o f n u t
th a t c o r r e sp o n d s to t h e sp e c i f i e d a n c h o r b o l t
m a te r i a l. A S T M A 5 6 3 sp e c if i e s t h e v a r io u s n u t
g ra d e s t h a t a r e t y p i c a l ly u se d in b u ild in g
c o n s t ru c t io n a n d n u t s su i t a b l e fo r u se w i th t h e
v a r io u s g ra d e s o f b o l t s ( s e e R e fe re n c e 4 ). T h e
H e a v y H e x n u t s ty le sh o u ld b e sp e ci fi e d
regard les s o f the nu t g rade tha t i s se lec ted .
F o o tn o te A b e lo w t a b l e X 1 . 1 m a k e s r e f e r e n ce to
A S T M A 1 9 4 g ra d e 2 H a s a su b s t i t u t e fo r A 5 6 3
w h e n c e r t a in s i z e s c o n fo rm in g to A 5 6 3 a r e n o t
ava i lab le . A19 4 is a spec i f ica t ion for p ressure
vesse l and non-bui ld ing uses , bu t the grades
re f e r e n c e d in fo o tn o te A a re su it a b le fo r u se fo r
anch or bo l t s in bu i ld ings .
2 1 2 P l a t e s
T h e m o s t c o m m o n b a se p l a t e m a te r i a l s a r e A 3 6 ,
A 5 7 2 a n d A 5 8 8 . F a b r i c a to r s r e sp o n d in g to t h e
q u e s t io n n a i re r e c o m m e n d e d th a t A 3 6 m a te r ia l b e
spec i fied i f poss ib le becau se i t is the mo st read i ly
available material. Th e table on the follow ing pa ge
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contains material availabilityguidelines based on
plate thickness
T a b l e 1 - A v a i l a b i l i t y o f P l a t e M a t e r i a l
T hi c kne s s ( t )
t _< 4
4 < t _< 6
Pla te Avai lab i l ity
A 3 6
A572 G r 42 o r 50
A588 G r 42 o r 50
A 3 6
A 5 7 2 G r 4 2
A588 G r 42
t > 6 A36
2 .2 B a s e P l a t e D e s i g n fo r F a b r i c a t i o n
Typica lly , except for very la rge c o lum ns w i th very
heavy base p la tes , such as for h igh r ise bu i ld ings ,
base p lates a re shop welded to the co lumn. Unless
the weld i s a co mp le te pene t ra t ion , weld , the
bo t t om e nd o f the c o l um n ne e ds to be c u t s qua r e
so tha t there wil l be fu ll bear ing w here the co lum n
is in contac t wi th the base p la te . Som e years ago ,
th i s was accompl i shed us ing mi l l ing machines in
t he s hop . T od a y t he c o l d s a wi ng e qu ipme n t u s e d
in mos t shops provides a co lu mn f in i shed end w i th
a ma x i mum AN SI r oughn e s s he i gh t va l ue o f 500
wh i c h i s s a t i s f a c t o r y f o r c on t a c t be a r i ng
c ompr e s s i on j o i n t s.
For very la rge co lumns , the base p la te i s e rec ted
f i r s t , us ing three leve l ing bol t s a round the
per im eter of the base p la te to leve l i t, then the
c o l umn i s e r e c t e d on t o t he ba s e p l a t e a nd
c onne c t e d u s i ng a ng l e s o r o t he r c onne c t i on
me t hods . T he ba s e p la t e i s g r ou t e d be f o r e t he
column i s e rec ted . Th e ma t ing sur faces should be
p r e pa r e d by mi l li ng o r o t he r me a ns s o t ha t t he
colum n i s in fu ll con tac t wi th the base p la te . Use
o f t h i c k ba s e p l a t e s c a n i n t r oduc e we l d i ng
p r ob l e m s . due t o d i ff i cu l ty o f me e t i ng p r e he a t
requi rements .
2 . 2 . 1 M a t e r i a l v e r s u s L a b o r
A c om mo n s ugge s t i on f r om s te e l fa b r i c a to r s fo r
engin eers to remem ber is tha t mater ia l i s cheap
re la t ive to labor . I f spec i fy ing th icke r base p la tes
wi l l resu l t in no t hav ing to add s t i ffener p la tes to
the base plate , this wil l resul t in less labor to
fabr ica te and wi l l resu l t in a more economic
des ign . Add ing s ti f feners and o the r p la tes to a
base p la te assembly i s l abor in tens ive com pared to
us ing a th icker base p la te tha t cou ld e l imina te the
need for these addi t iona l s t i f fener p lates .
2 . 2 . 2 W e l d i n g
T he e ng i ne e r s hou ld a t t e m p t t o a t l e a s t ma t c h t he
th ickness of the base p la te wi th the co lum n f lange
t h i c kne s s i n o r de r t o p r e ve n t wa r p i ng du r i ng
weld ing , par t icu la r ly i f heavy weld ing , such as
par t ia l o r com ple te pene t ra t ion welds , i s requi red
t o c onnec t t he c o l umn t o t he ba se p la t e. T h i c ke r
base p la tes wi thout s t i f feners a re of ten more
e c onom i c a l tha n u s i ng a t h i nne r ba s e p l a t e w i t h
st i ffeners . St i ffeners , i f used, w il l hav e an imp act
on co lum n f in i sh d imens ions . See Sec t ion 4 .7
Arc hi tec tura l I ssues for fur ther d i scuss ion .
Ano ther com mo n sugges t ion from fab r ica tors i s to
reduce we ld s izes as much as possible (but acc ou nt
f o r m i n i mum AW S we l d s iz e s ba s e d on m a t e ri a l
th icknesses ) and spec i fy f i l l e t welds in l i eu of
c om pl e t e pe ne t r a t i on we l ds w he r e pos si b le .
Compl e t e pe ne t r a t i on we l ds r e qu i r e mor e l a bo r
due to the need to beve l the end o f the co lum n and
fi t up, and require extens ive inspect ion . I t is m ore
eco nom ica l to d e ta i l l a rger f il l e t welds , ev en i f
more w eld meta l i s requi red for the f i ll e t welds , as
a subs t i tu te for par t ia l pene t ra t ion welds .
Fabr ica tors have a lso po in ted out th a t a l l a roun d
welds should be avoided . F i l l e t welds tha t wrap
a r ound t he f l a nge t oe s ( e nds o f c o l umn f l a nge s)
a nd t he c o l um n we b- t o - f l a nge f il le t s ( t he k
reg ion) can cause c racks due to h igh res idua l
s t resses in the welds . Such welds of ten requi re
weld ing repa i r . S top f i l l e t welds 1 /2 inch f rom
these loca t ions . See F igure 1 for c la r if ica t ion .
W elds should be de ta i led to a ccoun t for c learances
a nd a c c e s s o f we l d i ng e qu i pme n t . Obv i ous l y t he
e ng i ne e r s hou l d no t s how we l ds t ha t a r e
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impossible to access. For example, a common
mistake is to specify all around welds at plate
washers that are backed up against the column
flange or web.
High strength bolts fabricated from high strength,
heat treated steel (such as A354, A449 or B7)
cannot be welded - not even tack welded - without
adversely affecting the properties of these steels.
2 2 3 B a s e P l a te D i m e n s i o n s
Wh e re p o s s ib l e , t h e p l a t e d im e n s io n s a n d b o l t
pa t te rn of base p la tes should be symm etr ica l about
b o th a x e s. T h i s w i l l p r e c lu d e w e ld in g th e b a se
p la t e ro t a t e d 9 0 d e g re e s f ro m th e c o r r e c t
o r i e n ta t i o n . H a v in g a d o u b ly sy m m e t r i c al b o l t
pa t te rn wi l l a l so he lp avoid po ten t ia l f ie ld
problems (See Sec t ion 3 .1 .2) .
T h e e n g in e e r sh o u ld t ry t o sp e c i fy t h e s a m e b o l t
h o le d i a m e te r w h e n e v e r p o s s ib l e to e l im in a t e t h e
need fo r mul t ip le d r il l b i t s izes . This a lso appl ies
to a n y v e n t h o le s re q u i r e d to v e n t o u t a i r f ro m
u n d e r t h e l a rg e r b a se p l a t e s d u r in g th e g ro u t in g
opera t ion .
O b v io u s ly t h e b a se p l a t e d im e n s io n s sh o u ld b e
suff ic ien t to accommodate the co lumn d imens ions
p lus anchor bo l t ho les wi th suf f ic ien t d imens ions
to t h e c o lu m n f l a n g e s a n d to t h e e d g e o f t h e b a se
p la te . A lso acco unt fo r any square p la te wash ers ,
i f used . Severa l fabr ica tors have s ta ted tha t
e n g in e e r s so m e t im e s e r ro n e o u s ly a s su m e th e i r
typical base plate detai l wil l cov er al l cond it ions.
C o lu m n s th a t a r e i n d i ff e r e n t s iz e g ro u p s r e q u i re
d i f fe ren t base p la te s izes . I t is genera l ly more
economica l to des ign a typ ica l la rger base p la te
to c o v e r m o re th a n o n e c o lu m n s i z e i n a c o lu m n
g ro u p ( su c h a s Wl0 , W1 2 , W1 4 g ro u p in g s ) , t h a n
to design specific base plates for each colum n size.
T h e f e w e r v a r i a t io n s o f b a se p l a t e s r e q u i r e d w i l l
g e n e ra l ly r e su lt i n e c o n o m y in f a b r ic a t io n e v e n i f
more mater ia l i s requ i red . This is t rue because o f
the labor sav ings in shop draw ing prep ara t ion and
the d i f fe ren t shop se tups requi red for each
var ia t ion in base p la te conf igura t ion . I t i s a l so
t ru e th a t h a v in g f e w e r d i f f e r e n t a n c h o r b o l t
pa t te rns wi l l lead to less conf iasion dur ing anchor
b o l t p la c e m e n t . S e e F ig u re 1 o n th e fo l lo w in g
page for sugges ted de ta i l s .
3 .0 D E S I G N G U I D E L I N E S R E L A T E D T O
E R E C T I O N
A n c h o r b o l t s a n d b a se p l a t e s sh o u ld b e d e s ig n e d
and de ta i led to a ccom mo date s tee l e rec t ion loads .
Som e simple, yet effecctive, at ten tion to detai ls a nd
d im e n s io n s c a n g o a l o n g w a y in h e lp in g to
p re v e n t so m e c o m m o n p ro b le m s e n c o u n te re d
dur ing s tee l co lum n erec t ion . A prev ious ed i t ion
o f teel Tips (Reference 7) con ta ins usef ia l
s t ra teg ies fo r dea l ing wi th common f ie ld e rec t ion
errors .
3 1 A n c h o r B o l ts
Anch or bo l t p lacement i s obvio us ly a d i f f icu l t task
but too of ten e r rors resu l t due to poor qua l i ty
cont ro l and qua l i ty assurance or lack of
prepa redne ss in the des ign . The re a re severa l
ways to mis loca te anchor bo lt s and typ ica l ly one of
the fo l lowing wi l l occur .
3 1 1 A n c h o r B o l t P o s i t i o n M i s l o c a t io n
P o s i t i o n m is lo c a t io n i s u n fo r tu n a t e ly a c o m m o n
p ro b le m . T h e h o r i z o n ta l l o c a t io n o f t h e a n c h o r
bolts is often incorrect by as muc h as 1 to 2 inche s.
In some cases one o f the anch or bo l t s i s no t in the
correc t loca t ion wi th respec t to the rem ain ing bo l t s
and in o ther cases the en t i re layou t i s in the w ron g
loca t ion . There a re severa l wa ys to avoid th is
prob lem dur ing the des ign phase .
1. T h e b e s t m e th o d fo r p r e v e n t in g a n c h o r b o l t
m i s lo c a t io n i s f o r t h e c o n t r a c to r t o p ro p e r ly s e t
a n d h o ld a n c h o r b o l t s i n t h e c o r r e c t p o s i t io n fo r
p lan loca t ion and e leva t ion . I t i s the cont rac tors
respons ib i l i ty to se t anc hor bo l t s cor re c t ly wi th in
th e to l e ra n c e g iv e n in t h e A IS C C o d e o f S t a n d a rd
P ra c t i c e (R e fe r t o R e fe re n c e 3 ). A c h e c k b y a n
in d e p e n d e n t su rv e y o r w i ll h e lp l o c a t e m i sp l ac e d
bolts before steel is erected so that corrections can
b e m a d e b y th e c o n t r a c to r b e fo re s t e e l e r e c tio n
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r ~ V ~
WHEN REQUIRED@
GROUT P i N
I
L ~ J ~
~Tqq ~ - , ~ ~ ~ ~ ~L~ :
~ ~ . . . . . . ~
~
f~C] ~
II ~ ~
~
L = V J
~
SQUARE PLATE ~
_1
O W E L D T Y P . ~
2
GROUTHOLE
IF REQUIRED ~
NOWELDTYP ~
T O P
W S H E R
P L A T E r Y P .
OVERSIZE HOLE ~
~ LEVELINGNUT
AND WASHER~
ANCHOR BOLT~
~ Use square p la te and ho le pa ttem d imens ions where poss ib le to avo id p rob lems assodated w i th m is-p laced anchor bo lts , ro ta ted anchor
bo l t pa t te rns o r p la tes tha t a re a cc identa l ly ro ta ted 90 degrees du r ing fabr ica t ion .
~ T ry to reduce numerous base p la te var ia tions by s iz ing typ ica l p la te based on the la rgest co lumn in a s ize g roup (e .g . W l0 ' s , W 12 's o r
W 14 's ) . Reduc ing the n umbe r o f var ia t ions wi l l reduce the chance fo r e r ro r dur ing e rec t ion and fabr ica tion , and a l low fo r s im p ler
ver i fi ca t ion in the f ie ld . P rov ide max imum edge d is tance to bo l t to a l low b ase p la te s lo tt ing i f bo l ts a re m is loca ted .
~ W he n add i t iona l bo l ts a re requ i red , add add i t iona l ho les to make doub le symm et r ic bo lt pa t te rns . Th is is use fu l even i f no t a l l ho les and
bo l ts a re n eeded. Four bo l ts is the suggested m in imum fo r any b ase p la te .
~ :~ Anchor bo l ts shou ld be a t leas t 1 d iameter . Th is is benef ic ia l fo r e rec t ion sa fe ty and the ancho r bo l ts a re harder to acc identa l ly bend
in the f ie ld . Spec i fy A307 or A36 m ater ia l when poss ib le . Bo th a re eas ie r to ob ta in and we ldab le .
~ Overs ize ho les in base p la tes shou ld be used when ever poss ib le to accom mod ate anchor bo l t p lacemen t to le rances.
(~ ) P la te washe rs wi th f ie ld we lds sh ou ld be used in con junct ion wi th overs ize ho les to res is t nu t pu l l- th rough and to t rans fe r shear f rom the
base p la te to the anc hor bo l ts . Spec ia l a t ten t ion shou ld be d i rec ted toward we ld a ccess. P la te wash er shou ld have ho le 1 /16 la rger than
bo l t d iameter . W elds ma y no t be needed i f the co lumn is fo r g rav i ty on ly and there a re no shear fo rces a t the ba se o f the co lumn.
~ Lev e l ing nu ts a re recommen ded in l ieu o f leve l ing p la tes o r sh ims fo r ease o f const ruc t ion , sa fe ty and e f f ic iency .
~ The th ickness o f g rou t spec if ied shou ld accommodate the leve l ing nu ts and be in p ropor t ion to the d imens ions o f the base p la te
( fo r exam ple do no t spec i fy 3 inches o f g rou t under a W6 co lumn) .
~ Spec i fy an add i t iona l bo l t ex tens ion above the top o f the base p la te to accomm odate bo l ts tha t a re se t too low. A lso spec i fy ex t ra
th readed leng th to accomm odate bo l ts se t too h igh .
~ Spec i fy f i lle t we lds whenever poss ib le . P ar t ia l penet ra t ion we lds and comple te penet ra t ion we lds shou ld on ly be spec i fied when requ i red .
~ Avo id spec i fy ing a l l-a round we lds . There shou ld be no we ld a t the ends o f the flanges and in the fi lle t ( k reg ion) o f the co lumn.
~ I f a g rou t ho le is needed, spec i fy the same d iameter as the anchor bo l t ho les to reduce the num ber o f d ri ll b i t s izes requ i red dur ing
fabr icat ion.
F I G U R E 1 S U G G E S T E D B A S E P L A T E D E T A I L S
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b e g in s . T h i s r e q u i r e m e n t sh o u ld b e in c lu d e d in
the job sp ec i f ica t ions . In addi t ion , the engine er
should spec i fy 1 /8 shee t meta l templa tes fo r every
b a se p l a te . T y p ic a l ly c o n t r a c to r s m a k e o n e m e ta l
t e m p l a t e a n d c o n s t r u c t p l y w o o d c o p ie s o f t h e
t e m p la te . T h i s m e th o d o f c o n s t ru c t in g t e m p la t e s
a n d p l a c in g a n c h o r b o l t s i n t ro d u c e s s e v e ra l
obvious oppor tun i t ies fo r e r ror .
A n c h o r b o l t s n e e d to b e r i g id ly h e ld i n p o s i t i o n
b o th to p a n d b o t to m to p re v e n t m o v e m e n t d u r in g
c o n c re t e p l a c e m e n t a n d to p r e v e n t t h e a n c h o r
b o l t s f ro m t i lt i n g. P l a t e s t h a t c o n n e c t t h e a n c h o r
b o l t s a t t h e b o t to m sh o u ld b e c o n s id e re d ,
par t icu la r ly for la rge anch or bo l t s .
2 . Spec i fy overs ize bo l t ho les in the base p la te
w i th w a sh e r p la t e s ( w e ld w a sh e r s ) t h a t a r e f i eld
welded to the base p la te (See F igure 1). The w eld
wash er should have a s tandard ho le (bo l t d iam eter
p lu s 1 /16 in c h) . T h e A IS C C o d e o f S t a n d a rd
P ra c t i c e a l l o w s th e fo l lo w in g o v e r s i z e d h o le
d iameters ,
B o l t D ia m e te r i O v e r s i z e H o le D ia .
3 /4 to 1 5 /16
1 to
2 1/2
over 2 1
F o r l a rg e r b o lt s t h i s m a y n o t b e e n o u g h o v e r s i z e
a l lo w a n c e ; a l a rg e r o v e r s i z e o f u p to 2 i n c h e s
w o u ld b e b e t t er . W e ld w a sh e r s a re n e c e s sa ry
w h e n u s in g o v e r s i z e h o le s t o p r e v e n t n u t p u l l -
t h ro u g h a n d fo r sh e a r t r a n s f e r t o t h e a n c h o r b o l t.
T h e e x t r a c o s t o f t h e w e ld w a sh e r s i s sm a l l
c o m p a re d to t h e c o s t o f m a k in g f i e ld c o r re c t io n s
and e rec t ion de lays due to misp laced anch or bo l t s .
3 1 2 R o t a t e d A n c h o r B o l t P a t te r n s
A n c h o r b o l t s w i th a n o n sy m m e t r ic a l p a t t e rn a r e
so m e t im e s tu rn e d 9 0 d e g re e s f ro m c o r r e c t
o r i e n ta t i o n . D e ta i l i n g a n c h o r b o l t p a t t e rn s w i th
d o u b ly sy m m e t r i c p a t t e rn s w i l l p r e v e n t t h i s
prob lem. See Sec t ion 2 .2 .3 .
3 1 3 A n c h o r B o lt s S e t T o o L o w o r T o o
H i g h
Spec i fy ing ancho r bo l t s wi th ex t ra bo l t p ro jec t ion
wi l l he lp for anchor bo l t s se t too low. The ex t ra
p ro j e c t io n w i l l a l so p re v e n t t h e p ro b le m o f n u t s
tha t d o n o t ha ve f ia ll th read engag eme nt . I f a f i~ ll
n u t c a n n o t b e o b ta in e d , t h e re a r e m e th o d s to
e x te n d th e b o l t l e n g th . S p e c i fy in g A 3 6 b o l t
mater ia l a l lows weld ing a s tub on to the low bol t .
Somet imes , the nu t cav i ty above a low anch or bo l t
can be f il led ou t wi th weld meta l i f weldab le nu t
and bo l t m ate r ia ls were spec i f ied .
Engineers should spec i fy more of the b o l t shank to
be th readed than i s ac tua l ly needed . I f the bo l t i s
se t h igh , the ex t ra th read s w i l l a l low the nu t to be
ru n d o w n th e b o l t w i th o u t r e q u i r in g a d d i t i o n a l
washers .
3 1 4 C o l u m n s N e x t t o W a l l s
A n o th e r p ro b le m th a t f r e q u e n t ly o c c u r s i s
inaccess ib le anch or bo l t s due to a co lumn loca ted
next to a wall . Th is occu rs wh en the anc hor bo l t s
a r e l o c a t e d b e tw e e n th e c o lu m n f l a n g e s o r a t a
c o m e r w h e re tw o w a l l s i n t e r s ec t (S e e F ig u re 2 ) .
Fo r these condi t ions, spec ia l base p la te /anch or bo l t
pa t te rns a re necessary so tha t a l l anchor bo l t s a re
accessible. Refer to the AS D M anual , C onn ec t ion
S e c t io n , f o r a s se m b ly c l e a ra n c e r e q u i r e m e n t s a t
nuts .
WALL
FIGURE 2 INACCESSIBLE ANCHOR BOLT LOCATIONS
7
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3 2 Washers
If high strength anchor bolts are tensioned ,
hardened cut washers should be used in addition
to any weld washer plates used. This will prevent
the nuts from galling the weld washer or base
plate. Normally, anchor bolts are not tensioned;
nuts are usually tightened with a wrench using a
cheater .
3 3 Base Plate Leveling
Some erectors favor the use of leveling nuts
instead of shim packs or leveling plates (See
Figure 1), other erectors favor shim packs.
Leveling nuts are easier to level and provide a
more stable base for resisting erection loads than
shim packs. Generally, levelingplates are reserved
for special cases and should not be specified for
typical use.
4 .0 ENGINE ERING GUIDELINES FOR
DESIGN OF BASE PLATES
This section covers the engineeringdesign of base
plates. The focus of this section is not so much
how to calculate base plates, but what the
engineer needs to consider when engineeringand
detailing base plates. The reader is referred to
other publicationswith formulas, design aids and
procedures. See References 1, 2, 3, 5, and 6.
The base plate assembly must be designed to
transfer all forces from the column to the
supporting member whether it is a girder or a
foundation. These forces include axial forces,
shears and moments from the column. The
magnitude and combinations of these loads will
determine he design and details of the base plate.
The simplest and most common condition
encountered in practice is a column supporting
gravity loads only. When there are high shear
forces and moments, such as in a moment frame,
the design becomes more complicatedand the base
plate and anchor bolts become heavier. Thd
followingsubsectionsdiscuss the issues related to
the various loads and combinationsof loads.
4.1 Design for Temporary Construction
Loads
The first fianctionof a base plate is to temporarily
support the column from overturning due to
temporary wind, earthquake, and erection loads,
and from the column getting bumped during
erectionuntil the,beamsare attached to tie in the
column. Therefore he base plates and anchor bolts
need to be at least sufficient to resist the
overturningmoment and shear from these forces.
Although erectors often check the column by
assuming a one kip load applied horizontally t the
top, this does not relieve the engineer from
providingan adequate design.
If the anchorbolts and base plate are too small, fo r
example, with only two anchor bolts or anchor
bolts that are too close together, the base plate
assembly may not be capable of resisting erection
loading (See Figure 3).
1~ h
4
FIGURE 3 UNSAFE ANCHOR BOLT CONFIGURATIONS
This can resu l t in a dangerous condi t ion dur ing
e r ec t i on i f t he f ab r i ca t o r and e r ec t o r h ave no t
checked the base p la te assembly for e rec t ion loads
and have not recognized that this con dit io n exists .
E i ther the base p la te assembly mus t b e en la rged by
the fabr icator dur ing the shop draw ing s tage or the
co l um n wi l l need t o be gu yed o f f o r he l d w i th
ano ther li f t ing l ine and t ied in before re leas ing
the column. This process is expen sive and i t s low s
the e rec t ion progress . Engine ers should recogn ize
t h i s and no t unde r s i ze ancho r bo l t s , make ba s e
p l a t e s t oo t h i n , o r have ancho r bo l t s t oo c l o s e
t oge t he r i n the anch o r bo l t pa t t er n . A t l e a s t f ou r
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a n c h o r b o l ts s h o u l d b e d e t a i l ed a n d s p r e a d a p a r t a s
m u c h a s p o s s i b le . S e e F i g u r e 1 f o r s u g g e s t e d
d e t a i l s .
4 2 D e s ig n f o r G r a v i ty a n d O t h e r D o w n w a r d
L o a d s
T h e m o s t c o m m o n b a s e p l a t e c o n d i t i o n i s a b as e
p l a t e t h a t tr a n s f er s g r a v i t y l o a d s t o t h e s u p p o r t i n g
e m b e r o r f o u n d a t i o n w i t h r el a ti v e ly l o w s h e a r
f o r c e s a n d m o m e n t s a t th e b a s e o f t h e c o l u m n .
T h e s e a r e g r a v i t y o n l y c o l u m n s t h a t a re n o t p a r t
o f m o m e n t f r a m e s o r b r a c e d f ra m e s . T h e b a s e
p l a t e m u s t b e l a r g e e n o u g h s o t h a t t h e a r e a o f t h e
c o n c r e t e b e n e a t h i t i s s u f f ic i e n t t o s u p p o r t t h e
l o a d s . U s u a l l y t h e s e c o l u m n s w i l l t r a n s f e r n o m i n a l
s h e a r a n d m o m e n t s t o t h e s u p p o r t i n g m e m b e r o r
f o u n d a t i o n . S u c h f o r c e s a r e n o r m a l l y c a u s e d b y
s t o r y d ri f t d u e t o w i n d o r e a r t h q u a k e l o a d s .
T h e A I S C M a n u a l o f S te e l C o n s t r u c ti o n
( R e f e r e n c e 3 ) p r o v i d e s a tw o s t ep p r o c e d u r e f o r
t h e d e s ig n o f a x i a l l y l o a d e d b a s e p l a t e s . F i r s t , t h e
a r e a o f t h e p l a t e i s c a l c u l a t e d b a s e d o n t h e
a l l o w a b l e b e a t i n g s t r e s s d e f i n e d b y t h e f o l l o w i n g
e q u a t i o n s .
ASD : Fp ; 0.35 f/c A'-~ ~ 0.70 f/c
2
L RFD: %
P p
0 8 5 t p c f' c A) ~'~ -< qL 1.7f'c A~
w h e r e ,
F p
A l l o w a b l e b e a r i n g s t r e s s ( k s i )
f o = C o n c r e t e c o m p r e s s i v e s t r e n g t h ( k s i )
A ~ = B a s e p l a t e a r e a ( i nz)
A 2 = A r e a s u p p o r t i n g b a s e p la t e t h a t i s
g e o m e t r i c a l l y s i m i l a r (i nz)
q~o = 0 . 8 5 f o r c o m p r e s s i o n
Pp = U l t i m a t e c a p a c i t y o f t h e c o n c r e t e i n
b e a r i n g
B a s e d o n t h i s e q u a t i o n , t h e m o s t e f f i c ie n t b a s e
p l a t e a r e a ( A ~) is a t m o s t o n e - f o u r t h o f th e
c o n c r e t e s u p p o r t a r e a ( A 2) ; o r t h e c o n c r e t e
s u p p o r t i n g a r e a ( A 2 ) i s i d e a l l y f o u r t i m e s t h e b a s e
p l a t e a r e a ( A 0 .
II ]
E l
0 80bf
d
0 80D
~ 0 95b ~
F I G U R E 4 C R I T I C A L B E N D I N G
D I M E N S I O N S
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I m I r
REBAR
~
DOW E L S~
STUDS
OR LU S
a ANCHORBOLTS
WITH PLATE
WASHERS
b SHEARKEY c
EMBEDDED SHEAR
PLATE WITH
WELDED SlOE PLATES
d EMBEDDEDSHEAR
STRUT
F IG U R E 5 - M E T H O D S T O T R A N S F E R S H E A R F O R C E F R O M C O L U M N T O F O U N D A T I O N
The f ina l s tep in de te rmining the requi red base
pla te th ickness i s def ined by ca lcu la t ing the
f lexura l dem and fo r a c r i t ica l sec t ion o f p la te
ac t ing as a can t i lever . Fo r Al low able S t ress
De s i g n ( ASD ) t he e l a st i c s e c t ion modu l us ( S ) i s
u s e d ; whe r e a s f o r L oa d a nd Re s i s t a nc e Fa c t o r
Des ign (LR FD ) the p las t ic sec t ion modulus (Z) i s
used . Th e d imen s ions o f the c r i t i ca l sec t ion are
based on 0 .95d and 0 .8bf for wide f lange sec t ions ,
0 . 80 t i me s t he ou t e r d i a m e t e r o f p i pe s a nd 0 .95
t i me s t he o u t - t o - ou t d i me ns i on o f t ube s ( Se e
F i gu r e 4 ) . Ac c o r d i ng t o ASD, t he a l l owa b l e
bending c apaci ty is equal
t o 0 7 5F y
w h e r e
Fy
is the
a l l owa b l e y i e ld s t r e ng th o f t he s t e el . I f L RF D i s
prefe r red , the des ign s t rength i s equa l t o 0 9 0 F y
See Refe rence s 1 , 2 , 3 , 5 and 6 for usefu l des ign
equa t ion s and des ign a ids .
4 .3 Des ign
f o r G r a vi ty L o a d s i n C o m b i n a t i o n
w i t h U p l if t L o a d s
W hen there a re ne t up l i ft loads , such as can oc cur
i n t he e nd c o l umns o f c onc e n t r i c o r e c c e n t r i c
b r a c e d f r ame s ( CBF o r E BF) , t he a nc ho r bo l t s
and base p la tes need to be checked and increased
in s ize i f necessary . W hen upl if t loads a re very
high , i t may be necessary to add s t i f fener p la tes
we l de d t o t he c o l umn f l a nge s a nd de s i gn l onge r
a nc ho r bo l ts a bove t he ba se p l a t e t o a c c om mo da t e
the s t i f feners . Ho we ver , i t s t il l ma y be more
e c onomi ca l t o u s e a t h i c ke r ba s e p l a t e t ha n t o a dd
t he s t if f e ner s be c a us e o f t he h i gh l a bo r c os t
involved wi th the s t i ffeners. An cho r bo l t s need to
be we l l e mbe dde d i n t he s uppo r t i ng f ounda t i on
c onc r e t e t o de ve l op t he t e n s il e c a pa c i ty o f t he
a nc ho r bo l t s, a nd t o p r e c l ude a nc h o r bo l t pu l lou t
due to shear cone fa i lu re in the concre te . This
de t a i l be c ome s e ve n mor e c r i t i c a l f o r b r a c e d
f r a me s o r mome n t f r a me s s ub j e c t e d t o w i nd o r
e a r t hq ua ke f o r c e s whe r e f a i l u r e o f t he ba s e p l a t e
a s s e mb l y wou l d c a us e ove r t u r n i ng due t o up l i f t
resu l t ing in loss o f l a te ra l res i s tance in the braced
f r a me o r mo me n t f ra me . Fo r e a r t hqua k e l oa ds ,
s i nc e a c t ua l l oa ds a r e muc h h i ghe r t ha n c ode
des ign forces (which have been reduced to acco unt
for duct i l i ty in the braced frame), yielding shou ld
oc c u r i n t he b r a c e f o r a CBF o r i n t he l i nk be a m
f o r a n E BF . T he ba s e p l a t e a s s e mb l y ne e ds to be
s t rong enough to ensure tha t y ie ld ing wi ll occu r in
these o ther e lements .
4 4 D e s i gn fo r G r a v i ty L o a d s i n C o m b i n a t i o n
w i t h S h e a r F o r c e s
Taking sec tion 4 .3 a s tep fur ther , i f a brace occurs
a t the base of a co lum n, a h igh shear force i s
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from the horizontal force component in
This force must be resisted by the base
assembly. There are various proposed
transfer this shear force:
1. Anchor Bolts See Figure 5a);
.
Shear Key - A steel shear key is welded to
the bottom of the base plate to inte rlock with
the concrete
See Figure 5b);
.
Embedded Shear Plate - Shear plates are
field welded to the sides of the base plate
and to an embed plate that has welded shear
studs or shear lugs to transfer shear forces to
the concrete foundation
See Figure 5c);
.
Embedded Shear Strut - A strut member
with welded shear studs or shear lugs is
connected to the base plate or a column
gusset plate. The shear studs or shear lugs
transfer the shear force into the slab concrete
and then to the founda tion through rebar
dowel s See Figure 5d).The following is a
discussion of the design issues pertaining o
these methods of transferring shear at the
base of a column.
1. Anchor bolts: When column shear forces are
resisted by the anchor bolts, they must be checked
for a combination of column shear, bending and
tension. If oversize holes are used in the base
plates for anchor bolt placement tolerance, welded
washer plates must be added so that the base plate
ill not slip before engaging he anchor bolts. The
washer plates are added to the top of the base
plate and the additional bending in the anchor bolts
must be accounted for due to the increased
distance from the concrete to the washe r plate.
There is a practical limit to the amount of shear the
anchor bolt/concrete nterface can resist before the
anchor bolts become very large. When shear
fcrces are high, methods 2, 3 or 4 should be
considered.
2. Shear Keys: Steel shear keys can be welded
to the underside of the base plate to provide a
shear interlock with the concrete foundation
below. The bending and shear forces that the steel
key imparts to the base plate must be accounted
for. The use of such keys requires block-out voids
to be formed in the top of the foundation to allow
space for the keys and surrounding grout. Any
rebars in the foundation under the base plate must
be positioned vertically and/or horizontally to
allow for the depression n the foundation concrete
to accommodate the steel key. Shear keys are
effective in transferring shear forces from a brace
into the foundation, so that the anchor bolts only
have to resist tension forces.
3. Side Plates; Another strategy would be to
cast an embed plate into the top of the foundation.
The embed plate would have shear studs or lugs
welded to the bottom to transfer shear forces into
the foundation. The embed plate would be larger
than the base plate to accommodate setting
tolerance and to accommodate side plates to
transfe r shear forces from the base plate to the
embed plate and foundation. The column would
be erected and leveled in the same manner as any
conventional column. Loose plates would be
added and field welded to the sides of the base
plate and to the embed plate. Grouting between
the base plate and embed plate would be the final
step in the process. This detail is practical because
it provides a template for the anchor bolts and
allows for confinement of the grout.
4. Struts; When shear forces are high and shear
keys or embedded plates are not practical for
detailing reasons, steel struts can be added that are
embedded into the slab concrete. The strut is
welded or bolted to the base plate or to a stiffener
or gusset plate welded to the base plate. The strut
should have shear studs or lugs welded to it to
transfer axial forces from the strut to the concrete
slab. The slab adjacent to the strut should be
doweled to the foundation to transfer forces from
the slab to the foundation. Attention to
construction details and sequencing is important
so that the rebars around the strut do not interfere
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with being able to positionand connect the strut to
the base plate.
4 5 Design for Gravity Loads in Combination
with Shear Forces and Moments
When a base plate assembly must transfer column
base moments to the foundation, the mechanism
for resisting the moments is typically aken by the
combinationof the tensile capacity of the anchor
bolts and the bearing capacity of the concrete or
masonry. This forms a couple consistingof the
tension force in the anchorbolts and the equivalent
force at the centroid of the bearing area under the
base plate. This is analogous o the internal forces
to resist bending in a concrete cracked section.
The other gravity, shear, and uplift forces acting in
combinationwith the bending moment must also
be added and accounted for.
Two methods are presented for consideration
when designing base plates subject to bending
moment. See References 1, 2, 3, 5 and 6 for
additional information on how to calculate and
design for this combinationof loads.
The first method is based on the assumption hat
stresses caused by the moment are linear across
the base plate length. The tensile force in the
anchor bolt is dependent on the bearing area. An
equation is provided in Reference 1 to calculate
the effective length of bearing. (See Figure 6,
Method 1). This may not be consistentwith actual
behavior since the assumption relies on linear
deformationof the base plate.
The second method is based on the assumption
that the resultant of the bearing length is directly
beneath the column flange. The basis of this
assumption s that the flange experiencesa greater
axial load compared to the web because of the
higher combinationof axial and flexural stresses,
and the relative width of the column flange to the
web (See Figure 6, Method 2). This method may
produce inaccurate results as well since the
bearing length may extend over to the anchor bolt
in tension. More testing and research is required
to confirm he validityof either method with actual
~ M
P T
M E T H O D 1
TENSIONB
FORCE
IN BOLT
AXIAl. FLEXURAL
STRESS N
COLUMN
FORCE
P I TRANSMITTED
~ ~ M TOBASE LATE
ANCHORBOLT
\
PT
M E T H O D 2
F I G U R E 6 - C O L U M N W I T H A X I A L
F L E X U R A L D E M A N D
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behavior. See References 1 and 5 for further
explanationand useful equations.
When the column moments are known the design
is more straightforward han if the moments are
more unpredictable such as at the base of
moment frame columns which resist earthquake
forces where ductilitybecomes an important issue.
See Section 4.6 for additional discussion of base
plate assemblies hat resist seismic forces.
4 6 D e s i g n f o r M o m e n t s d u e t o S e i s m i c
F o r c e s
Unfo r tuna te ly , the behav ior of base p la tes in
mome n t f r a me s a nd b r a c e d f l a me s s ub j e c t e d t o
ear thquake forces i s no t fu l ly unders tood .
Re s e a r c h a nd c ode gu i da nc e a r e l im i t ed . T he
engineer i s forced to use judgment and the
in te rpre ta t ion of the resu l t s f rom tes t s o n
a s s e mb l i es w i t h s imi l ar c ompone n t s i n o r de r t o
achiev e a des ign tha t hopefu l ly wi l l have the
des i red leve l o f per formance .
Try ing to f ix , o r par t ia l ly f ix , the base of mo me nt
f r a me o r b r a c e d f r a me c o l umns a ga i n s t r o t a t i on
m ay be necessary to reduce the dr if t: in the s tory
above the base p la te loca t ion . Cons ider the
fo l lowing scenar ios :
1. Con t i nue t he c o l umn i n t o t he f ounda t i on o r
in to a basem ent leve l be low;
2 . De s ign a heavy base p la te assembly s t rong
enough to force a p las t ic h inge in the co lumn.
This i s d i f f icu l t to accom pl i sh even fo r re la t ive ly
smal l co lumns . The base p la te and anch or bo l t s
be c ome ve r y l a r ge a nd a nc ho r bo l t a nc ho r a ge
becom es difficul t. The found at ion must be capable
o f r e s i s t i ng t he h i gh mome n t s f r om t he c o l umn
base assembly (See F igure 7a). Curren t ly ,
research i s ong oing a t the U nivers i ty of Michigan
by P r o f e s s o r Subha s h Goe l on ba s e p l a t e
assembl ies o f th i s type ;
3 . I f the s tee l f rame i s suppo r ted on spread
f oo t i ngs w i t h mome n t r e s i s t i ng g r a de be a ms
be t we e n t he f oo t i ngs o r s uppo r t e d on a g r a de
beam gr id sys tem, par t ia l ly f ix the base of the
c o l umn by de s i gn i ng t he f oo t i ng / g r a de be a m
sys tem to form p las t ic h inges in the grade b eams
tha t b ehav e in a duc t ile manner . S ize the base
p l a t e a s se mb l y to de ve l op t he s t r e ng t h o f t he
f oo t i ng / g r a de be a m c ons i de ri ng t he ove r s t r e ng t h
o f t he c onc r e t e s e c t i ons . ' Any p l a s t ic h inge s
should occu r in the grade beam s;
4. Design a part ia l ly f ixed base plate assembly.
This wil l help l imit dr if t , and the base plate and
a nc ho r bo l t d i me ns i ons w i ll be m or e ma na ge a b l e
than wi th a f ixed base so lu t ion . Dr i f t can be
redu ced dramat ica l ly because the co lu mn wi l l be
forced to bend in double curva ture . The cha l lenge
is to des ign the base p la te assembly to b ehave in a
duc t i le manner . I f par tia l fix i ty i s los t dur ing an
e a r t hqua ke due t o t he f a i lu r e o f t he ba s e p l a t e o r
stretching or breakage o f the an chor bol ts , the drif t
o f the f i rs t s to ry wi l l increase dram at ica lly
resu l t ing in more damage and poss ib le fa i lu re of
the co lumn. A fa i lu re of the second f loo r beams
could al so occur i f they w ere no t des igned for the
ext ra bending or a re no t duc t i l e enough to
accomm odate the ex t ra ro ta t ion . (See F igures 7b ,
7c, and 7d);
5 . P in the base of the co lumn by des igning a
base plate assem bly that wil l have relat ively l i t t le
mo me nt res i s tance , bu t wi l l be du c t i le enough to
acc om m od ate the f i rs t s tory seismic drift :.
So m e d es ign i ssues re la tive to scenar ios 4 and 5 .
will be discussed further. Sc ena rios 1, 2 and 3 are
beyon d the scop e o f th i s paper .
For a l l co lumn to base p la te welded connec t ions ,
the same i ssues re la t ive to beam to co lumn
c onne c t i ons i n duc t il e mom e n t f r a me s s hou l d be
cons idered to prec lude a fa i lu re in or near the
weld , par t icu la r ly i f a fu l l p las t ic h inge in the
column above th e base p la te i s the des i red des ign
goa l . T he r e a de r shou l d r e f e r t o t he doc ume n t s
and research cur ren t ly be ing done by the SAC
J o i n t Ve n t u r e on m ome n t f r a me s ( Se e Re f e r e nc e
8).
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..c o M . j / \ .BAs E
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F IG U R E 7 - Y I E L D IN G M E C H A N I S M S
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B AS E P ~ T E
F o r . a p a r t i a l l y f i x e d c o l u m n b a s e a s d e s c r i b e d i n
s c e n a r i o 4 , t h e r e a r e t w o m e c h a n i s m s t o a c h i e v e
the duc t i l i t y in the base p la t e as sembly :
a . D e s i g n t h e b a s e p l a t e t o y i el d i n b e n d i n g b y
d e s ig n i ng t h e a n c h o r b o l t s t o b e s t r o n g e n o u g h t o
f o r c e p l a s t i c h i n g e s i n t h e b a s e p l a t e ( S e e F i g u r e
7 b ). T h e p l a t e m u s t b e la r g e e n o u g h , b u t n o t to o
t h i c k s o t h a t a p l a s t i c h i n g e r e g i o n c a n f o r m
b e t w e e n t h e c o l u m n f l a n g e s a n d t h e a n c h o r b o l t s
wi thou t induc ing a shear f a i lu r e in the base p la t e .
A l eve ling p la t e shou ld be p rov ided und er the b ase
p l a t e t o p r o t e c t t h e g r o u t w h i l e t h e b a s e p l a t e
u n d e r g o e s d e f o r m a t i o n s d u r i n g t h e c y c l i c a l
b e n d i n g e x c u r s i o n s .
b . D e s i g n t h e b a s e p l a te s tr o n g e n o u g h t o f o r c e
y i e l d i n g i n t h e a n c h o r b o l t s ( S e e F i g u r e s 7 c a n d
7 d ) . N u t s a n d w a s h e r s m u s t b e u s e d a b o v e a n d
b e l o w t h e b a s e p l a t e ( F i g u r e 7 c ) o r t h e t o p
h o r i z o n t a l p l a t e ( F i g u r e 7 d ) t o f o r c e t h e a n c h o r
bo l t s to r es i s t ax ia l fo rces in bo th t ens ion and
c o m p r e s s i o n s o t h a t t h e r e w i l l b e c y c l i c c a p a c i t y
a n d d u c t i l it y in t h e a s se m b l y . T h e r e m u s t b e
suff icient unbonded length in the bol ts to al low for
t h e r e q u i r e d e l o n g a t i o n w i t h o u t o v e r s t r a i n i n g t h e
b o l t s . T h e u l t i m a t e s t r e n g t h o f t h e b o l t m u s t b e
h i g h e n o u g h t o p r e c l u d e f a i l u r e a t t h e r e d u c e d
s e c t i o n in t h e t h r e a d e d p o r t i o n o f t h e b o l t b e f o r e
t h e b o l t y i el d s. T h i s c a n b e c o m e a p r o b l e m w h e n
the u l t imate s tr eng th o f the bo l t (F , ) i s too c lose to
t h e y i e ld s t r e n g t h ( Fy ). S o m e a c c o m m o d a t i o n
m u s t b e m a d e s o t h a t t h e b o l t s w i l l n o t b u c k l e
w h e n t h e y a r e in c o m p r e s s i o n . D e - b o n d i n g a n d
b u c k l in g r e s i s t a n c e c a n b e p r o v i d e d b y u s i n g p i p e
s l e e v e s w i t h i n t h e f o o t i n g ( F i g u r e 7 c ). I f t h e
y i e l d i n g p o r t i o n o f t h e a n c h o r b o l t s i s a b o v e t h e
b a s e p la te , s l e e v e s o r g u i d e s c a n b e p r o v i d e d t o
res i s t bo l t buck l ing (F igure 7d) .
V e r y f e w t e s t r e s u l t s a r e a v a i l ab l e to v a l i d a t e t h e
b e h a v i o r o f e i t h e r m e c h a n i s m d e s c r ib e d i n a o r b .
M o r e r e s e a r c h a n d d e v e l o p m e n t i n t o b a s e p l a t e
b e h a v i o r a n d d e s i g n g u i d e l i n e s a r e n e e d e d f o r
a n c h o r b o l t / b a s e p l a t e a s s e m b l i e s t h a t a r e
s u b je c te d to v e r y h ig h m o m e n t s w h e r e y i e ld i n g is
n e c e s s a r y t o a c h i e v e t h e d e s i r e d p e r f o r m a n c e .
4 7 Arch itectural Issues
A r c h i t e c t u r a l i s s u e s s h o u l d b e c o n s i d e r e d w h e n
des ign ing and de ta i l ing base p la t e as sembl ies .
A n c h o r b o l t a s s e m b l i e s n e e d t o f i t w i t h i n s l a b
th icknesses . Th ere nee ds to be su f f ic i en t d i s t ance
b e t w e e n t h e t o p o f f o u n d a t i o n a n d t h e t o p o f sl ab
t o a c c o m m o d a t e g r o u t , l e v e l i n g n u t a n d w a s h e r
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e , nu t and bol t p ro jec t ion p lus co ncre te
c ove r a bove t he t op o f bo l t. Us ua l ly , t h is
d imens ion i s a t l eas t 12 inches . Fo r pro jec t s wi th
la rge c o lum ns and th ick base p la tes , 12 inches is
not enough . This i s an imp or tan t d imens ion to
es tab l i sh ear ly because i t a f fec t s the founda t ion
depth.
Any s t i f fener p la tes added above the base p la te
mu st f i t wi th in the a rch i tec tura l f in ish a round th e
colum n. I f s t i ffeners a re needed , the d imens ions
should be c o-ord in a ted wi th the a rch i tec t ea r ly in
the design since i t ma y be necessary to increa se the
f in ish d imens ions , s ince th i s d im ens ion wi l l a f fec t
useable f loor space . Also , the d imens ions of any
vert ical s ti ffener plates should be check ed to insure
that the s t iffener plates will not p rotru de abo ve th e
s lab ou ts ide o f the co lum n f in i sh d imens ions .
5 . 0 C O N C L U S I O N S
Base plates serve a cr i t ical role in t ransferr ing
c o l um n l oa ds t o the founda t i on . T h i s
Stee l Tips
discusses des ign , fabr ica t ion and e rec t ion i ssues
re la ted to base p la tes and anchor bo l t s . Sugges ted
de tai ls a re presented and de ta i l s to be avoided a re
s hown . T he e ng i ne e r ne e ds t o be a wa r e o f
mater ia l s ava i lab le and should recognize tha t
spec ia l a t ten t ion to base p la te and anchor bo l t
de ta i l s can resu l t in reduced cos t s dur ing
fabr ica t ion and e rec t ion . Base p la te assembl ies
mus t be de s i gne d t o a c c ommoda t e t e mpor a r y
erect ion loads unt i l the colum n is t ied in with oth er
s t ruc tura l mem bers . Spec ia l a t ten t ion by
c on t ra c t o rs whe n p l a c ing a nc h o r bo l t s c a n r e duc e
field problems and delays due to mislocated an cho r
bolts .
6 0 R E F E R E N C E S
1. De s i gn o f We l de d S t r uc t u r e s by Ome r W.
Blodge t t , James F . L incoln Arc Weld ing
Fo und ation , 15 ~h Print ing , 1996
2 . AI SC M a nua l o f S t e el Cons t r uc t ion , L FRD
Design , Volumes I and I I , Second Edi t ion ,
1994
3 . AI SC M a nua l o f S t e el Cons t r uc t i on , ASD
Design , Nin th Edi t ion , 1989
4 . AST M S t a nda r ds i n Bu i l d i ng Code s , Vo l ume
1, 35 h Ed it ion, 1998
5. Column Base P la tes , S tee l Des ign Guide
Se r i e s 1 by J ohn T . D e W ol f a nd Da v i d T .
Ricker , AISC 1990
6 . AI SC E ng i ne e r i ng J ou r na l Be a m - Co l um n
Ba s e P l a te De s i gn - L RF D Me t hod by
Richard M. Drake and Sharon J . E lk in , F i r s t
Qua r t e r 1999 , Vo l ume 36 , Numb e r 1 .
7. Stee l Tips
Com mo n S t e el E r e c t i on P r ob le ms
and Suggested Solu t ion s by Jam es J . Putk ey,
SSEC publ ica t ion , Dec em ber 1993.
8 . SAC In te r im Guide l ines : Eva lua t ion , Repa i r ,
Mod i f i c a t i on a nd De s i gn o f We l de d S t e e l
Mome n t F r a me S t r uc t u r e s , FE MA 267 ,
Augus t 1995
More research and des ign guide l ines a re needed
for base plate assemblies subjected to high ben ding
mom ents , such as in mom ent f rames subjec ted to
earthquak e forces. Fo r part ia l ly f ixed colum n base
assembl ies , mechanisms tha t mus t behave in a
duc t i le ma nner a re needed . Som e a l te rna t ive
s t ra teg ies and con cepts a re presented .
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bout the uthors
Bi ll H one ck a P r inc ipa l o f Fore l l /E l s es se r
E n g i n e e r s I n c . h a s 3 4 y e a r s o f e x p e r i e n c e in
s t r u c t u r a l e n g i n e e r i n g 9 o f w h i c h w e r e i n
s t ruc tu ra l s t ee l des ign f abr i ca t ion and e rec t ion .
Th i s a l so inc luded 2 year s des ign ing e lec t r i c
t r a n s m i s s i o n t o w e r s a n d s u b s t a ti o n fr a m i n g . I n
a d d i t io n s e v e r a l o f h is la r g e - s c a l e p r o j e c t s h a v e
b e e n p r o d u c e d o n f a s t - t r a c k .
F r o m 1 9 6 5 t o 1 9 7 4 B i l l H o n e c k w a s p r o j e c t
m a n a g e r / e n g i n e e r f o r B e t h l e h e m S t e el in t h e
c o n s t ru c t io n o f n u m e r o u s h i g h r is e a n d l a r g e s c a le
s t ru c t u r e s . D u r i n g t h e s e 9 y e a r s B ill H o n e c k h a d
prac t i ca l exper i ence in s t ruc tu ra l s t ee l h ighr i s e
bu i ld ings an d l a rge b r idges . Hi s respons ib i li t ies
inc luded s t ruc tu ra l s tee l e r ec t ion cos t es t imat ing
a n d e r e c t io n e n g i n e e r in g c o o r d i n a t i n g j o b s
s c h e d u l in g r e v i e w i n g c o s t s a n d i m p l e m e n t i n g
s a v i n g s w h e r e p o s s ib l e .
H e w o r k e d i n t h e f i e l d a n d o f f i c e i n c o n n e c t i o n
wi th s t ee l e r ec t ion as a f i e ld eng ineer and wa s in
c h a r g e o f e r e c t i o n e n g i n e e r i n g f o r th e W e s t e r n
D i s t r ic t f r o m 1 9 6 7 t o 1 9 7 4 . H e w a s a l s o
r e s p o n s i b l e f o r d e s i g n i n g f a l s e w o r k a n d r e l a t e d
s t r u c t u r e s e r e c t i o n s c h e m i n g a n d c h e c k i n g
s t ruc tu ra l in t egr ity o f s t ee l f r am ew ork fo r e r ec t ion
re la t ed loads .
D e r e k W e s t p h a l a p r o j e c t e n g in e e r a n d a n a l y s t
wi th Fore l l/E l ses ser began h i s ca ree r wi th the f i rm
i n e a r l y 1 9 9 6 . I n h i s e x p e r i e n c e t o d a t e h e h a s
d e v e l o p e d a st r o n g b a c k g r o u n d in t h e s e is m i c
re t ro f i t o f h i s to r i c bu i ld ings as wel l as the new
c o n s t r u c t i o n o f o f f ic e b u i ld i n g s l a b o r a t o r y a n d
univers i ty faci l i t ies .
16
7/27/2019 Design & Detail Col Base Plate
19/19
S T R U C T U R L S T E E L E D U C T I O N L C O U N C I L
470 Fernwood Dr i ve
Moraga , CA 94556
925) 631 :9570
S P O N S O R S
A d a m s S m i t h
A l l i e d S t e e l C o . , I n c .
B a n n i s t e r S t e e l , In c .
B a r e se l C o r p .
B e t h l e h e m S t e e l C o r p o r a t i o n
C . A . B u c h e n C o r p o r a t i o n
B u t l e r M a n u f a c t u r i n g C o .
G . M . I r o n W o r k s C o .
T h e H e r r i c k C o r p o r a t i o n
H o e r t i g I r o n W o r k s
H o g a n M f g . , In c .
Ju n io r S t e e l C o .
L e e D a n i e l
M c L e a n S t e el , In c .
M a r t i n I r o n W o r k s , I n c .
M i d W e s t S t ee l E r e c ti o n
N e l s o n S t u d W e l d i n g C o .
O r e g o n S t e e l M i l l s
P D M S t r o ca l , In c .
R e n o I r o n W o r k s
H . H . R o b e r t s o n C o .
S M E I n d u s t r i e s
S o u t h l a n d I r o n W o r k s
S to c k to n S t e e l
V e r c o M a n u f a c t u r i n g , I n c .
V u l c r a f t S a l e s C o r p .
The local structural steel industry (above sponsors) stands ready to assist you in determining the mo st
econom ical solution for your products. Our assistance can range from budg et pr ices and estimated tonnage
to cos t com parison s, fabrication details and delive ry schedules.
Funding for this publication provided by the C alifornia Iron Workers A dministrative Trust.