Strut-and-Tie Design: What They Didn't Teach You in School · OSEA 2017 Fall Seminar...

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design: What They

Didn't Teach You in School

Thomas Mendez, S.E.

WSP USA

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design

• First introduced in

Appendix A of ACI

318-02.

• Moved to Chapter

23 in ACI 318-14,

but remains largely

unchanged.

American Concrete Institute

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design

ACI 318-14

• When must strut-and-tie be used?

o Anywhere plane sections do not remain

plane (D-Regions).

o Any structural component not explicitly

mentioned in the code.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design

• When must

strut-and-

tie be used?

ACI 318-14

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design

• When must

strut-and-

tie be used?

ACI 318-14

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design

ACI 318-14

• When may strut-and-tie be used?

o Anywhere.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Procedure

1. Understand how the structural component

is behaving.

2. Develop a truss model.

• Struts (compression)

• Ties (tension)

• Nodes (intersections)

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Procedure

3. Verify truss geometry is appropriate.

• Is equilibrium satisfied?

• Are angles greater than 25 degrees?

• Do struts intersect only at nodes?

4. Analyze the truss and determine truss

member forces.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Procedure

5. Check design capacities of struts, ties and

nodes.

• Verify adequate As is provided in ties.

6. Verify reinforcement can be developed at

critical locations.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #1

ACI SP-208

• Use simple,

statically

determinate strut-

and-tie models.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #1

• Use simple,

statically

determinate strut-

and-tie models.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #1

• Use simple,

statically

determinate strut-

and-tie models.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #1

• Use simple,

statically

determinate strut-

and-tie models.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #1

• Use simple,

statically

determinate strut-

and-tie models.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #2

• Node geometry

does not need

to conform to

the triangular

shapes indicated

in most design

examples.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #2

• Node geometry

does not need

to conform to

the triangular

shapes indicated

in most design

examples.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #3

• Prevent bottle

shaped struts

by confining

concrete with

ties.

ACI 318-14

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #3

• Prevent bottle

shaped struts

by confining

concrete with

ties.

ACI 318-14

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #3

• Prevent bottle

shaped struts

by confining

concrete with

ties.

ACI 318-11

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #4

• Use local strut-

and-tie models to

design bottle

shaped struts

when

f’c > 6,000psi.ACI 318-14

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #4

• Use local strut-

and-tie models to

design bottle

shaped struts

when

f’c > 6,000psi.

ACI 318-14

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #4

• Use local strut-

and-tie models to

design bottle

shaped struts

when

f’c > 6,000psi.

ACI Structural Journal/November-December 2006

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #4

• Use local strut-

and-tie models to

design bottle

shaped struts

when

f’c > 6,000psi.

ACI Structural Journal/November-December 2006

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #5

• Be careful with

"incomplete" or

"partial" strut and

tie models.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #5

• Be careful with

"incomplete" or

"partial" strut and

tie models.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #6

ACI 318-14

• Don't consider steel plates with welded reinforcement as act as a compression face of a CCC node.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #6

• Don't consider steel plates with welded reinforcement as act as a compression face of a CCC node.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #7

• Discretize load

transfers at

intersections.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #7

• Discretize load

transfers at

intersections.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #7

• Discretize load

transfers at

intersections.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #7

• Discretize load

transfers at

intersections.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #7

• Discretize load

transfers at

intersections.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #7

• Discretize load

transfers at

intersections.

ACI 318-14

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #7

• Discretize load

transfers at

intersections.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #8

• Understand

how struts

may form in

tension zones.

ACI 318-14

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #8

• Understand how struts may form in tension

zones.

Reinforced Concrete,

James Wight

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #8

• Understand how struts may form in tension

zones.

Reinforced Concrete,

James Wight

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #9

• Be mindful of

potential

construction

joints crossing

struts.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #9

• Be mindful of

potential

construction

joints crossing

struts.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #9

• Be mindful of

potential

construction

joints crossing

struts.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #10

• Don’t forget

about self

weight.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #11

• Use

mechanical

terminators

to reduce

congestion.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #11

• Use

mechanical

terminators

to reduce

congestion.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #11

• Use

mechanical

terminators

to reduce

congestion.

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #12

• Don’t allow shear stress to exceed 10 ���.

ACI 318-11

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #12

• Don’t allow shear stress to exceed 10 ���.

ACI 318-14

www.oksea.org OSEA 2017 Fall Seminar

Strut-and-Tie Design Tip #13

• Don’t forget about serviceability and/or

stability.

www.oksea.org OSEA 2017 Fall Seminar

Questions?

ACI Structural Journal/November-December 2006