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DESIGN OF COLUMN BASE 
PLATES AND STEEL 
ANCHORAGE TO 
CONCRETE 
Khaled Eid
Outline 
 Introduction 
 Base plates 
Material 
Design using AISC Steel Design Guide 
 Concentric axial load 
 Axial load plus moment 
 Axial load plus shear 
 Anchor Rods 
Types and Materials 
Design using ACI Appendix D 
 Tension 
 Shear
Introduction 
 Base plates and anchor rods are often the last 
structural steel items to be designed but the first 
items required on the jobsite 
 Therefore the design of column base plate and 
connections are part of the critical path
Introduction 
 Anchors to appear in concrete drawings with 
location of each anchor in x and y direction 
 Pedestal should be designed to suit the 
supporting column and anchors 
 Usually allow for enough edge distance of 6d 
bolt 
 Usually use to nuts to avoid slip
Introduction 
 Vast majority of column base plate connections 
are designed for axial compression with little or no 
uplift 
 Column base plate connections can also transmit 
uplift forces and shear forces through: 
 Anchor rods 
 Bearing end plate 
 Shear lugs under the base plate or embedding the 
column base to transfer the shear force. 
 Column base plate connections can also be used 
to resist wind and seismic loads 
 Development of force couple between bearing on 
concrete and tension in some or all of the anchor rods
Introduction 
 Anchor rods are needed for all base plates to 
prevent column from overturning during 
construction and in some cases to resist uplift or 
large moments 
 Anchor rods are designed for pullout and breakout 
strength using ACI 318 Appendix D 
 Critical to provide well-defined, adequate load 
path when tension and shear loading will be 
transferred through anchor rods 
 In seismic zones the pedestal should carry 2.5 the 
factored design load
Introduction 
 Grout is needed to adjust the level 
 Grout to transfer the load from steel plate to 
foundation 
 Grout should have design compressive strength at 
least twice the strength of foundation concrete 
 When base plates become larger than 600mm, it 
is recommended that one or two grout holes be 
provided to allow the grout to flow easier
Base plate Materials 
 Base plates should be ASTM A36 material unless 
other grade is available 
 Most base plates are designed as to match the 
pedestal shape 
 A thicker base plate is more economical than a 
thinner base plate with additional stiffeners or 
other reinforcements
Base Plate Design
Design of Axially Loaded Base 
Plates 
 Required plate area is based on uniform allowable 
bearing stress. For axially loaded base plates, the 
bearing stress under the base plate is uniform 
` 
A 
` 2 
f   f  
max 0.85 1.7 p c c c f 
A 
1 
A2 = dimensions of concrete supporting foundation 
A1 = dimensions of base plate 
 Most economical plate occurs when ratio of concrete 
to plate area is equal to or greater than 4 (Case 1) 
 When the plate dimensions are known it is not 
possible to calculate bearing pressure directly and 
therefore different procedure is used (Case 2)
Case 1: A2 > 4A1 
1. Determine factored load Pu 
2. Calculate required plate area A1 based on maximum 
concrete bearing stress fp=1.7f`c (when A2=4A1) 
P 
u 
req f 
A 
1( ) 0.6  
1.7 ` c 
 
3. Plate dimensions B & N 
should be determined so m 
& n are approximately 
equal 
  1(req) N A 
0.95 0.8 f d  b 
2 
  
N 
A 
B 1(req) 
Case 1: A2 > 4A1 
4. Calculate required base plate thickness 
N 0.95d 
2 
 
0.8 f B b 
P 
u 
2 
where l is maximum of m and n 
m 
 
5. Determine pedestal area, A2 
2 
n 
 
 
F BN 
t l 
y 
0.90 
min  
A 4BN 2 
Case 2: Pedestal dimensions 
known 
1.Determine factored load Pu 
2.The area of the plate should be equal to larger 
of: 
2 
A ` 
1 0.6 1.7 ` c 
1 
 
1 0.60 0.85 
2 
 
 
 
 
 
c 
u 
f 
P 
A 
u 
f 
P 
A 
 
 
3. Same as Case 1 
4. Same as Case 1
Design of Base Plates with 
Moments 
 Equivalent eccentricity, e, is calculated equal to moment 
M divided by axial force P 
 Moment and axial force replaced by equivalent axial 
force at a distance e from center of column 
 Small eccentricities  equivalent axial force resisted by 
bearing only 
 Large eccentricities necessary to use an anchor bolt 
to resist equivalent axial force
Design of Base Plate with Small 
Eccentricities 
If e<N/6 compressive bearing stress exist everywhere 
Mc 
P 
f   1,2 
If e is between N/6 and N/2 bearing occurs only over a 
portion of the plate 
P 
AB 
f 
2 
1  
I 
BN
Design of Base Plate with Small 
Eccentricities 
1. Calculate factored load (Pu) and moment (Mu) 
2. Determine maximum bearing pressure, fp 
A 
` 2 0.85 1.7 p c c c f 
f   f  
A 
3. Pick a trial base plate size, B and N 
4. Determine equivalent eccentricity, e, and maximum 
bearing stress from load, f1. If f1 < fp go to next step, 
if not pick different base plate size 
5. Determine plate thickness, tp 
plu 
4 
1. Mplu is moment for 1 in wide strip 
p F 
y 
M 
t 
0.90 
 
` 
1
Design of Base Plate with 
Shear 
 Four principal ways of transferring shear from column 
base plate into concrete 
1. Friction between base plate and the grout or 
concrete surface 
n u c c V P f A `  m  0.2 
The friction coefficient (m) is 0.55 for steel on grout 
and 0.7 for steel on concrete 
2. Embedding column in foundation 
3. Use of shear lugs 
4. Shear in the anchor rods (revisited later in lecture)
Design of Shear Lugs 
1. Determine the portion of shear which will be resisted by 
shear lug, Vlgu 
2. Determine required bearing area of shear lug 
u 
f 
V 
A 
 
lg 0.85 c 
` 
lg 
 
3. Determine shear lug width, W, and height, H 
4. Determine factored cantilevered end moment, Mlgu 
 
 
 
 
H G 
  
  
 
 
 
 
 
M u 
  
 
2 
V 
lg 
lg 
W 
u 
5. Determine shear lug thickness 
4 lg 
u 
F 
y 
M 
t 
0.90 
lg 
Anchor Rods 
 Two categories 
 Cast-in place: set before the concrete is placed 
 Drilled-in anchors: set after the concrete is hardened
Anchor Rod Materials 
 Preferred specification is ASTM F1554 
 Grade 36, 55, 105 ksi 
 ASTM F1554 allows anchor rods to be supplied 
straight (threaded with nut for anchorage) , bent or 
headed 
 Wherever possible use ¾-in diameter ASTM F1554 
Grade 36 
 When more strength required, increase rod 
diameter to 2 in before switching to higher grade 
 Minimum embedment is 12 times diameter of bolt
Cast-in Place Anchor Rods 
 When rods with threads and nut are used, a more 
positive anchorage is formed 
 Failure mechanism is the pull out of a cone of 
concrete radiating outward from the head of the bolt 
or nut 
 Use of plate washer does not add any increased 
resistance to pull out 
 Hooked bars have a very limited 
pullout strength compared with that of 
headed rods or threaded rods with 
a nut of anchorage
Anchor Rod Placement 
 Most common field problem is placement of anchor 
rods 
 Important to provide as large as hole as possible to 
accommodate setting tolerances 
 Fewer problems if the structural steel detailer issued 
anchor bolt layout for placing the anchors form his 3d 
model
Anchor Rod Layout 
 Should use a symmetrical pattern in both 
directions wherever possible 
 Should provide ample clearance distance for 
the washer from the column 
 Edge distance plays important role for 
concrete breakout strength 
 Should be coordinated with reinforcing steel to 
ensure there are no interferences, more critical 
in concrete piers and walls
Design of Anchor Rods for 
Tension 
 When base plates are subject to uplift force Tu, 
embedment of anchor rods must be checked for 
tension 
 Steel strength of N anchor  A f 
in tension 
s se ut Ase =effective cross sectional area of anchor, AISC Steel Manual Table 7-18 
fut= tensile strength of anchor, not greater than 1.9fy or 125 ksi 
 Concrete breakout strength of single anchor in 
A 
tension 
N  N 
  
N 
cb 2 3 b N  k f ` h 
1.5 
b c ef No 
A 
hef=embedment 
k=24 for cast-in place anchors, 17 for post-installed anchors 
2, 3 = modification factors
Design of Anchor Rods for 
Tension 
 ANo=Projected area of the 
failure surface of a single 
anchor remote from edges 
 AN=Approximated as the base 
of the rectilinear geometrical 
figure that results from 
projecting the failure surface 
outward 1.5hef from the 
centerlines of the anchor 
Example of calculation of AN with edge 
distance (c1) less than 1.5hef 
2 No 9 ef A  h 
( 1.5 )(2 1.5 ) N 1 ef ef A  c  h  h
Design of Anchor Rods for 
Tension 
 Pullout strength of anchor 
` 
pn 4 brg8 c N  A f 
 Nominal strength in tension Nn = min(Ns, Ncb, 
Npn) 
 Compare uplift from column, Tu, to Nn 
 If Tu less than Nn ok 
 If Tu greater than Nn must provide tension 
reinforcing around anchor rods or increase 
embedment of anchor rods
Design of Anchor Rods for 
Shear 
 When base plates are subject to shear force, Vu, and 
friction between base plate and concrete is inadequate 
to resist shear, anchor rods may take shear 
 Steel Strength of single anchor in shear 
s se ut V  A f 
 Concrete breakout strength of single anchor in shear 
A 
0.2 
l 
 
 
V  v 
  V 
1.5 
cb 6 7 b 
A 
vo 
b   
  
V o c 
7 d f c 
1 
` 
d 
o 
 
 
 
6, 7 = modification factors 
do = rod diameter, in 
l = load bearing length of anchor for shear not to exceed 8do, in
Design of Anchor Rods for 
Shear 
 Avo=Projected area of the failure 
surface of a single anchor remote 
from edges in the direction 
perpendicular to the shear force 
 Av=Approximated as the base of a 
truncated half pyramid projected on 
the side face of the member 
Example of calculation of Av with edge 
distance 
(c2) less than 1.5c1 
 2 
A 4.5 c1 vo  
1.5 (1.5 ) 1 1 2 A c c c v  
Design of Anchor Rods for 
Shear 
 Pryout strength of anchor 
cp cp cb V  k N 
 Nominal strength in shear Vn = min(Vs, Vcb, 
Vcp) 
 Compare shear from column, Vu, to Vn 
 If Vu less than Vn ok 
 If Vu greater than Vn must provide shear 
reinforcing around anchor rods or use shear 
lugs
Combined Tension and Shear 
 According to ACI 318 Appendix D, anchor rods must 
be checked for interaction of tensile and shear forces 
T 
  
V 
u 
 1.2 
n 
n 
u 
V 
N
References 
 American Concrete Institute (ACI) 318-02 
 AISC Steel Design Guide, Column Base Plates, by John T. DeWolf, 
1990 
 AISC Steel Design Guide (2nd Edition) Base Plate and Anchor Rod 
Design 
 AISC Engineering Journal Anchorage of Steel Building Components 
to Concrete, by M. Lee Marsh and Edwin G. Burdette, First Quarter 
1985
Common mistakes
Careful when considering the location of 
anchors to concrete walls
Bolts miss alignment or clash with gusset 
plate

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Design of column base plates anchor bolt

  • 1. DESIGN OF COLUMN BASE PLATES AND STEEL ANCHORAGE TO CONCRETE Khaled Eid
  • 2. Outline  Introduction  Base plates Material Design using AISC Steel Design Guide  Concentric axial load  Axial load plus moment  Axial load plus shear  Anchor Rods Types and Materials Design using ACI Appendix D  Tension  Shear
  • 3. Introduction  Base plates and anchor rods are often the last structural steel items to be designed but the first items required on the jobsite  Therefore the design of column base plate and connections are part of the critical path
  • 4. Introduction  Anchors to appear in concrete drawings with location of each anchor in x and y direction  Pedestal should be designed to suit the supporting column and anchors  Usually allow for enough edge distance of 6d bolt  Usually use to nuts to avoid slip
  • 5. Introduction  Vast majority of column base plate connections are designed for axial compression with little or no uplift  Column base plate connections can also transmit uplift forces and shear forces through:  Anchor rods  Bearing end plate  Shear lugs under the base plate or embedding the column base to transfer the shear force.  Column base plate connections can also be used to resist wind and seismic loads  Development of force couple between bearing on concrete and tension in some or all of the anchor rods
  • 6. Introduction  Anchor rods are needed for all base plates to prevent column from overturning during construction and in some cases to resist uplift or large moments  Anchor rods are designed for pullout and breakout strength using ACI 318 Appendix D  Critical to provide well-defined, adequate load path when tension and shear loading will be transferred through anchor rods  In seismic zones the pedestal should carry 2.5 the factored design load
  • 7. Introduction  Grout is needed to adjust the level  Grout to transfer the load from steel plate to foundation  Grout should have design compressive strength at least twice the strength of foundation concrete  When base plates become larger than 600mm, it is recommended that one or two grout holes be provided to allow the grout to flow easier
  • 8. Base plate Materials  Base plates should be ASTM A36 material unless other grade is available  Most base plates are designed as to match the pedestal shape  A thicker base plate is more economical than a thinner base plate with additional stiffeners or other reinforcements
  • 10. Design of Axially Loaded Base Plates  Required plate area is based on uniform allowable bearing stress. For axially loaded base plates, the bearing stress under the base plate is uniform ` A ` 2 f   f  max 0.85 1.7 p c c c f A 1 A2 = dimensions of concrete supporting foundation A1 = dimensions of base plate  Most economical plate occurs when ratio of concrete to plate area is equal to or greater than 4 (Case 1)  When the plate dimensions are known it is not possible to calculate bearing pressure directly and therefore different procedure is used (Case 2)
  • 11. Case 1: A2 > 4A1 1. Determine factored load Pu 2. Calculate required plate area A1 based on maximum concrete bearing stress fp=1.7f`c (when A2=4A1) P u req f A 1( ) 0.6  1.7 ` c  3. Plate dimensions B & N should be determined so m & n are approximately equal   1(req) N A 0.95 0.8 f d  b 2   N A B 1(req) 
  • 12. Case 1: A2 > 4A1 4. Calculate required base plate thickness N 0.95d 2  0.8 f B b P u 2 where l is maximum of m and n m  5. Determine pedestal area, A2 2 n   F BN t l y 0.90 min  A 4BN 2 
  • 13. Case 2: Pedestal dimensions known 1.Determine factored load Pu 2.The area of the plate should be equal to larger of: 2 A ` 1 0.6 1.7 ` c 1  1 0.60 0.85 2      c u f P A u f P A   3. Same as Case 1 4. Same as Case 1
  • 14. Design of Base Plates with Moments  Equivalent eccentricity, e, is calculated equal to moment M divided by axial force P  Moment and axial force replaced by equivalent axial force at a distance e from center of column  Small eccentricities  equivalent axial force resisted by bearing only  Large eccentricities necessary to use an anchor bolt to resist equivalent axial force
  • 15. Design of Base Plate with Small Eccentricities If e<N/6 compressive bearing stress exist everywhere Mc P f   1,2 If e is between N/6 and N/2 bearing occurs only over a portion of the plate P AB f 2 1  I BN
  • 16. Design of Base Plate with Small Eccentricities 1. Calculate factored load (Pu) and moment (Mu) 2. Determine maximum bearing pressure, fp A ` 2 0.85 1.7 p c c c f f   f  A 3. Pick a trial base plate size, B and N 4. Determine equivalent eccentricity, e, and maximum bearing stress from load, f1. If f1 < fp go to next step, if not pick different base plate size 5. Determine plate thickness, tp plu 4 1. Mplu is moment for 1 in wide strip p F y M t 0.90  ` 1
  • 17. Design of Base Plate with Shear  Four principal ways of transferring shear from column base plate into concrete 1. Friction between base plate and the grout or concrete surface n u c c V P f A `  m  0.2 The friction coefficient (m) is 0.55 for steel on grout and 0.7 for steel on concrete 2. Embedding column in foundation 3. Use of shear lugs 4. Shear in the anchor rods (revisited later in lecture)
  • 18. Design of Shear Lugs 1. Determine the portion of shear which will be resisted by shear lug, Vlgu 2. Determine required bearing area of shear lug u f V A  lg 0.85 c ` lg  3. Determine shear lug width, W, and height, H 4. Determine factored cantilevered end moment, Mlgu     H G          M u    2 V lg lg W u 5. Determine shear lug thickness 4 lg u F y M t 0.90 lg 
  • 19. Anchor Rods  Two categories  Cast-in place: set before the concrete is placed  Drilled-in anchors: set after the concrete is hardened
  • 20. Anchor Rod Materials  Preferred specification is ASTM F1554  Grade 36, 55, 105 ksi  ASTM F1554 allows anchor rods to be supplied straight (threaded with nut for anchorage) , bent or headed  Wherever possible use ¾-in diameter ASTM F1554 Grade 36  When more strength required, increase rod diameter to 2 in before switching to higher grade  Minimum embedment is 12 times diameter of bolt
  • 21. Cast-in Place Anchor Rods  When rods with threads and nut are used, a more positive anchorage is formed  Failure mechanism is the pull out of a cone of concrete radiating outward from the head of the bolt or nut  Use of plate washer does not add any increased resistance to pull out  Hooked bars have a very limited pullout strength compared with that of headed rods or threaded rods with a nut of anchorage
  • 22. Anchor Rod Placement  Most common field problem is placement of anchor rods  Important to provide as large as hole as possible to accommodate setting tolerances  Fewer problems if the structural steel detailer issued anchor bolt layout for placing the anchors form his 3d model
  • 23. Anchor Rod Layout  Should use a symmetrical pattern in both directions wherever possible  Should provide ample clearance distance for the washer from the column  Edge distance plays important role for concrete breakout strength  Should be coordinated with reinforcing steel to ensure there are no interferences, more critical in concrete piers and walls
  • 24. Design of Anchor Rods for Tension  When base plates are subject to uplift force Tu, embedment of anchor rods must be checked for tension  Steel strength of N anchor  A f in tension s se ut Ase =effective cross sectional area of anchor, AISC Steel Manual Table 7-18 fut= tensile strength of anchor, not greater than 1.9fy or 125 ksi  Concrete breakout strength of single anchor in A tension N  N   N cb 2 3 b N  k f ` h 1.5 b c ef No A hef=embedment k=24 for cast-in place anchors, 17 for post-installed anchors 2, 3 = modification factors
  • 25. Design of Anchor Rods for Tension  ANo=Projected area of the failure surface of a single anchor remote from edges  AN=Approximated as the base of the rectilinear geometrical figure that results from projecting the failure surface outward 1.5hef from the centerlines of the anchor Example of calculation of AN with edge distance (c1) less than 1.5hef 2 No 9 ef A  h ( 1.5 )(2 1.5 ) N 1 ef ef A  c  h  h
  • 26. Design of Anchor Rods for Tension  Pullout strength of anchor ` pn 4 brg8 c N  A f  Nominal strength in tension Nn = min(Ns, Ncb, Npn)  Compare uplift from column, Tu, to Nn  If Tu less than Nn ok  If Tu greater than Nn must provide tension reinforcing around anchor rods or increase embedment of anchor rods
  • 27. Design of Anchor Rods for Shear  When base plates are subject to shear force, Vu, and friction between base plate and concrete is inadequate to resist shear, anchor rods may take shear  Steel Strength of single anchor in shear s se ut V  A f  Concrete breakout strength of single anchor in shear A 0.2 l   V  v   V 1.5 cb 6 7 b A vo b     V o c 7 d f c 1 ` d o    6, 7 = modification factors do = rod diameter, in l = load bearing length of anchor for shear not to exceed 8do, in
  • 28. Design of Anchor Rods for Shear  Avo=Projected area of the failure surface of a single anchor remote from edges in the direction perpendicular to the shear force  Av=Approximated as the base of a truncated half pyramid projected on the side face of the member Example of calculation of Av with edge distance (c2) less than 1.5c1  2 A 4.5 c1 vo  1.5 (1.5 ) 1 1 2 A c c c v  
  • 29. Design of Anchor Rods for Shear  Pryout strength of anchor cp cp cb V  k N  Nominal strength in shear Vn = min(Vs, Vcb, Vcp)  Compare shear from column, Vu, to Vn  If Vu less than Vn ok  If Vu greater than Vn must provide shear reinforcing around anchor rods or use shear lugs
  • 30. Combined Tension and Shear  According to ACI 318 Appendix D, anchor rods must be checked for interaction of tensile and shear forces T   V u  1.2 n n u V N
  • 31. References  American Concrete Institute (ACI) 318-02  AISC Steel Design Guide, Column Base Plates, by John T. DeWolf, 1990  AISC Steel Design Guide (2nd Edition) Base Plate and Anchor Rod Design  AISC Engineering Journal Anchorage of Steel Building Components to Concrete, by M. Lee Marsh and Edwin G. Burdette, First Quarter 1985
  • 33. Careful when considering the location of anchors to concrete walls
  • 34. Bolts miss alignment or clash with gusset plate