aashto abc guide specifications, seismic design ... · aashto abc guide specifications, seismic...

Module 2 –

AASHTO ABC Guide Specifications, Seismic Design Requirements for Connections

Lee Marsh, Ph.D., P.E

Deputy Director – America’s Technical Excellence Center

Greg Banks, P.E., S.E

Project Manager and Senior Bridge Engineer

AASHTO LRFD Guide Specifications for ABC

AASHTO Guide Specifications for ABC

NCHRP 12-102 Final Report provides

additional commentary and background

2

Outline

I. Overview of AASHTO LRFD Guide Specifications for ABC- Seismic

II. Seismic Design for ABC (3.4)

III. Seismic Connection Design and Detailing (3.6.4-7 & 3.4.12)

Overview Seismic Design Connections 3

I. Overview of Guide Specifications for ABC- Seismic

• Aims to ensure minimal damage of the structure under moderate earthquake and collapse prevention under rare earthquakes.

• Adopts a Type I design strategy exclusively (inelastic behavior under ductile limit state should occur only in the substructure).

• Written to supplement (not to replace) the current specifications.

• Future editions of Guide Specifications for ABC are expected to incorporate ongoing ABC seismic research.



• Force-Based Design

(AASHTO LRFD, 2017)

OR

• Displacement-Based Design

(AASHTO SGS, 2011)

Regardless of the seismic analysis/design method the Earthquake Resisting Systems (ERS) and Elements (ERE) shall be identified.


II. Seismic Design for ABC

Ductile LinkBrittle Links Brittle Links

Force, F F

FdFib

Ductile Behavior, Fd < All Fib

Brittle Behavior, Any Fib < Fd

Displacement, ∆

F


The Designer should evaluate the implications of

using prefabricated elements and/or connections

in or near the plastic hinge zones.

CP – Capacity Protected

(Non-ductile)

ED – Energy Dissipating

(Ductile)




All members of the ERS

must have sufficient

strength and ductility to

form the intended

structural plastic

mechanism.



• Ensure continuity of load path under load reversals.

• Ensure development of cyclic inelastic deformations.

• Realize that maximum demands typically occur at connections of

prefabricated elements.

• Limit the occurrence of conditions leading to rapid loss of

resistance (local buckling, stress concentrations, etc.)

DETAILING IS IMPORTANT!


II. Seismic Design for ABC

All connections and Earthquake Resisting Elements

(EREs) in the GS for ABC only permitted with the

Owner’s approval.


III. Seismic Connection Design and Detailing (3.6)

Other details are permitted provided that:

1. They are approved by the Owner,

AND

2. The designer demonstrates adequate load transfer with consideration for compatibility of deformations and constitutive relations of materials.

11Overview Seismic Design Connections

III. Seismic Connection Design and Detailing (3.6)

• Mechanical bar connectors (3.6.4)

• Grouted duct connections (3.6.5)

• Pocket connections (3.6.6)

• Socket connections (3.6.7)

• Two-stage integral pier cap (3.6.12)

Mechanical connectors Grouted duct Pocket Socket Two-stage integral12

Source: Haber et al.,(2013)

Headed Bar

Coupler (HC)

PC Column

Footing

3.6.4 Mechanical Bar Connectors

Grouted Sleeve

Coupler

PC Column

Note: No more than one connector per bar in

plastic hinge zone is allowed (3.6.4.4) so this

detail does not meet the GS for ABC.

(GC)

Mechanical connectors Grouted duct Pocket Socket Two-stage integral 13

• Connector Types as defined in ACI 318-14

• Type 1: Capacity ≥(1.25 fy )Ab

• Type 2: Capacity ≥(fu )Ab


fy

fu

Connector

Stress

Strain

Bar Bar

(Limited to bars with fy≤60 ksi)

Ab



Column

Dc

2Dc

Type 1 connector: not allowed



Plastic

hinge

zone

(PHZ)

Type 2: Allowed

• For SDC A/Seismic Zone 1.

• Seismic SDC B/Zone 2 with

Owner’s approval.

• Seismic SDCs C&D/Zones 3&4

w/ add’l requirements

(3.6.4.4).Column


Type 2 Connectors in Plastic Hinge Zone for SDCs C&D Seismic Zones 3&4 (3.6.4.4)

Only grouted sleeve coupler

(GC) or headed reinforcement

coupler (HC) allowed.

PHZ<15db

db

Column


• 0.8 for Lsp ≤ 4 db

• 0.5 for Lsp > 4 db

Type 2 Connectors in Plastic Hinge Zone for Seismic Zones 3&4 (Force-based Design)

• Reduced modification factor ��PHZ

Lsp


[AASHTO ABC EQ. 3.6.4.4.1-1]

Type 2 Connectors in Plastic Hinge Zone for Seismic Zones 3&4 (Displacement-based Design)

• Use plastic moment capacity based on moment-curvature

analysis of the column section with no mechanical

connector.

• Calculate displacement capacity based on a reduced plastic

hinge length, . ��



L

Rigid FoundationHsp

LspMechanical

Couplers

ACTUAL CURVATURE

DIAGRAM

��

“EQUIVALENT”

CURVATURE DIAGRAM

Point of

Contraflexure

�� = �� − 1 − �� ≤ ��

= 0.65 for GC

= 0.75 for HC


[AASHTO ABC EQ. 3.6.4.4.2-1]


L

If <0.5Dc

If >4db

Point of

Contraflexure

z= Hsp+ Lsp

� = ��(� − �)

�

��

Mechanical connectors Grouted duct Pocket Socket Two-stage integral

Hsp

Lsp

AND

21

Debonding of Longitudinal Reinforcement for Mechanical Connectors in PHZ (3.6.4.5)

ld

��

�� ≥ max 0.4 $% 5000 Ɛye dbl

To be used

for joint

shear design≥


[AASHTO ABC EQ. 3.6.4.5-1]

3.6.5 GROUTED DUCT CONNECTIONS

Source: Brenes (2006)

ASTM A 760

(only)

≥ 0.67/�012�1′45

(grade 60 bars)

1′4 to be taken≤ 8.0 ksi

3 78 6/�0


[EQ. 3.6.5.1-1]

3.6.5 GROUTED DUCT CONNECTIONS

UHPC Grouted Duct

Column

PC Pier Cap

UHPC

Grouted Duct

Debonding

≥4db

db

(#8-#11)

fy≤75 ksi

≥4db

≥8db


3.6.6 POCKET CONNECTIONS

ASTM A 760

(only)

A A

SECTION A-A

(grade 60 bars)

≥ /�012�1′%�5

≥1.5 max agg.

≤ 4 in.

Source: Restrepo et al. (2011)


[EQ.3.6.6.3-1]

3.6.6 POCKET CONNECTIONSSteel Pipe Thickness 9=9� cos(=)

7�>�� = m?@( ABC�D EFGHEF�IJ�KL , 0.060 in)

Set:

Solve:

•M.NN EC�D5

EFGfor SDCs B and Zone 2

• Max ( M.NN EC�D5 EFG , 0.40 PQR (0SC)T ) For Zones 3 & 4

• Calculated min. joint shear reinf. for SDCs C & D

U� =

Fp

α

D’cp

FH

D’cp

(b) Corrugated

Steel Pipe(a) Spiral

s


[AASHTO ABC EQ. 3.6.6.4-2]

3.6.7 SOCKET CONNECTIONS

Wet (cast-in-place) Formed (precast)

Embedded

PC Column

Grout or

Concrete Pour

PC CapEmbedded

PC ColumnCIP Footing


3.6.7 SOCKET CONNECTIONS

PC Column in Socket

V

Le≥ Dc

Dc

if Le ≤ 1.5Dc

Roughening (0.25” )required

c, K1, K2, µ(concrete placed against a clean concrete surface)

µ limited to 0.5 when Le < 1.1 Dc


PC Column in Socket3.6.7 SOCKET CONNECTIONS

Mechanical connectors Grouted duct Pocket Socket Two-stage integral

Add’l confinement

bars at 45o

29

Socket in Shaft3.6.7 SOCKET CONNECTIONS

Spiral/Hoops Requirement

X�YZ[\] ≥ ^1_0X02a12b��

(^ = 0.5)

(^ = 1.0)

(^ = 2.0)

A

B

C

Location

le

≥ ls

+ e + cover

A

B

1’-0”

(^ = 1.0)

C

Le

Le /2

Le /2

covere

Mechanical Heads, if

used

cover

ls

Dc

Inte

ntio

na

l ro

ug

he

nin

g r

eq

uir

ed

fo

r L

e ≤

1.5

Dc


[AASHTO ABC EQ. 3.6.7.3.2-1]

[AASHTO ABC EQ. 3.6.7.3.1-1]

3.6.12 TWO-STAGE INTEGRAL PIER CAP

1) LOWER PIER CAP 2) GIRDERS ERECTED 3) UPPER-STAGE CAP CAST


3.6.12 TWO-STAGE INTEGRAL PIER CAP

Bcap

Ds1

Ds2

Dc

Joint Proportioning for SDC C&D or Seismic Zones 3 & 4


Thank you!

wsp.com

aashto abc guide specifications, seismic design ... · aashto abc guide specifications, seismic...

Documents