PRECAST CONCRETE CONNECTIONS -

US PRACTICE

SPEAKERS

Larbi Sennour, PhD, SE

President – Consulting Engineers Group, Inc.

Precast Connections

3 General Types

•Wet Connections

•Semi Dry

•Dry

Wet System - Definition

P/CP/C

PIP

SPLICED REINFORCING

Wet System - Connection

Wet System - Connection

Semi Dry System - Definition

P/CP/C

PIP

SPLICED REINFORCING

CAVITY IN PRECAST

Semi Dry - Definition

•Emulation of CIP

•Forming using precast

•Self supported

•Cast in-situ

Semi Dry– Beam/Column Joint

AREA THAT CAN BE USED FOR MOMENT FRAME ANALYSIS

BEAMTROUGH

COLUMNSHEAR KEY

Semi Dry– Beam/Column Joint

SLIM SLEEVE SLIM SLEEVE

Semi Dry– Beam/Column Joint

SLIM SLEEVE

Semi Dry– Beam/Column Joint

MOMENTS SHEAR TENSION/COMP.

Semi Dry– Beam/Column Joint

SLIM SLEEVE

Dry System - Definition

P/CP/C

MECHANICAL CONNECTION

Dry System - Definition

•Spliced

•Sleeved

•Welded

•Bolted

Dry – Spliced

Procedure

• Cast splice sleeve with precast

• Cast bar in foundation at proper location

• Erect precast element with projected bar in the sleeve

• Pump grout from bottom port to upper port

Spliced - Example

Spliced - Design

Design considerations• Fully emulates CIP

• Develops 150% fy

• Tested for cyclic loading

• Same design and requirements as CIP

• Used in all seismic zones

Spliced - Design

Tu MuCu

2)2.09.0( DL

DSu

u

PS

d

MT

PDL

d

Moment Resistance

Spliced - Design

Design Spectrum Used in the US

Period T

To 1.0Ts TL

SD1

SDS

T

SS D

a1

2

1

T

TSS LD

a

Spliced - Design

Vu

Vu £ mj(As fy + PDL )

PDL

Moment Resistance

m – Shear Friction Coefficientf – Shear Strength Reduction Factor

Spliced - Architectural Wall

Spliced - Architectural Wall

Spliced - Architectural Wall

Spliced - Architectural Wall

Spliced - Architectural Wall

Spliced - Architectural Wall

Spliced - Framing

Dry – Sleeved

Principal

Dry – Sleeved

Procedure

• Cast rebar spliced or extend bar in precast element

• Cast bar sleeve in connecting member or core drill

• Fill sleeve with grout

• Erect Panel

Dry – Sleeved

Dry – Bolted

Procedure

• Base plate is cast into precast element

• Base plate is anchored to develop tension force

• Bolts are cast into the lower element

• Connection is achieved by bolting

Dry – Bolted

Limited Fixity

• Can be modeled by calculating the rotation stiffness

• Depends on soil capacity

• Usually assumed pinned except for erection as semi fixed.

Dry – Welded

Dry – Welded

Transfer shear to increase capacity

Transfer diaphragm loads to walls

Transfer loads to each other and foundations

Dry – Welded - Analysis

Diaphragm Shear Out of plane lateral loads

Dry – Welded - Analysis

Diaphragmshear

Out of plane lateral loads

Uplift tension or compression from overturning moment

Dry – Welded - Analysis

Horizontal shear also known as VQ/I

Connections - Resources

Resources for Welded Connections

• PCI Design handbook 7th Edition – Has the theoretical background on the macro level

• PCI Connections Manual – Has the design example of almost every type. Deals with the practical aspect of design

• fib Connections – Has the theory for connection behavior down to the micro level

CONNECTION DESIGN METHODOLOGY

Shear friction

•Shear Friction

•Dowel Effect

•Combination

s

w

c

s s

Strut & tie models

DESIGN & MODELING

Design assumptions

• Design for worst case scenario

• Satisfy load resistance in all its aspects

• Limit displacements and allow movements

Modeling

• Determine and use actual Behavior

• Testing results if available should be incorporated

Remember:You assumptions should always reflect a conservative behavior to give you a reasonable factor of safety.

DESIGN ASSUMPTIONS

DesignAssumption

ACTUAL BEHAVIOR

Actual Behavior

Determine the spring constant – K factor

TYPICAL HARDWARE USED IN THE US PRACTICE

Hardware

• Steel

• Shapes – A36

• Plate – A283

• Tubes – A500

• Stainless – A666 Type 304

• Governed by AISC

• Anchors

• Provide anchorage into concrete

• Headed studs – HCA

• Deformed bar anchors – DBA

• Rebar

• Governed by ACI 318 Appendix D

• Also PCI Design Handbook

Hardware

Headed Concrete Anchors

• Specify AWS D1.1 Type A or B

• Automatic welding process• Can be stick welded

• Shallow anchorage• 100mm, 150mm common• 200mm maximum length

• Diameters 6mm to 20mm• 12mm most common

• Failure modes

• Steel yield

• Concrete breakout

• Supplemental reinforcement

• Enhances performance

Headed Concrete Anchors

Deformed Bar Anchors

• Similar to short lengths of rebar

• AWS D1.1 Type C

• Weldable

• Automatic weld process or stick weld

• Deeper anchorage into concrete

• Rebar – A706 is weldable

• A615 can be welded – have to know chemistry

Hardware

• Bearing Pads

• Chloroprene

• AASHTO grade

• Random Oriented Fiber

• No ASTM

• Reinforced Cotton Duck

• AASHTO

Hardware

• Shims

• Generally High Density Plastic

• No ASTM

• Thicknesses 1.5 to 12mm

• Slide bearings

• Steel

• Add if stack > 40 to 50mm

• Tack weld

Hardware

• Bolts

• Generally A307

• Not well defined mechanical properties

• A36 Threaded rod

• Better mechanical properties

• Used in sliding connections

• Snug tight

• Upset threads

• Be careful with tack welds

Bolts

• Sliding connections

• Volume change

• Drift

• Field tolerances

• Slotted holes

• Oversize holes

Bolts

• A325 Bolts – high strength bolts

• Generally used in structural steel construction

• Generally pretensioned in steel construction

• Rarely used in precast connections

Hardware

• Welding

• AWS D1.1 Structural Welding Code

• AWS D1.4 Structural Welding Code – Reinforcement

• Weld types

• Matching metals

Welding

• Low hydrogen weld rod

• Sensitive to moisture

• Ovens on site

• E7018 – common weld rod

Welding

• AWS D1.1 Environmental conditions

• No welding if

• Rain or surface moisture

• High wind velocities

• Inclement conditions

• Preheat below 32°F

• Lehigh Welding Study

• Surface moisture driven off by weld heat

• Acceptable profiles to 35 mph wind

• No preheat to 0°F

Proprietary Inserts

Post-installed Anchors

• Expansion bolts

• Depend on mechanical action

• Design by ACI 318 Appendix D

• Requires qualification by ACI 355.2

Post-installed Anchors

• Adhesive anchors

• Depend on chemical bond

• Currently depend on Manufacturers

• ACI 318-11 added adhesive anchors

• Will be Qualification standard

• Will be certified installer program

• Will be inspection requirements

Adhesive Anchors

• Fire resistance

• Overhead installations

• Resin creep with sustained loads

• Age of concrete

Connections - Summary

Summary

• Wet connections are mostly based on emulation –very useful for moment connections and splicing

• Semi dry connections are also based on emulation but eliminate the need for forming

• Dry connections are the most widely used connections. They have limited capacity on multidirectional force systems

THANKS to the SPONSORS and the AUDIENCE

QUESTIONS?