Improved resistance calculation for steel truss gusset platessp.bridges.transportation.org/Documents/2014 SCOBS... · 2014. 7. 29. · IMPROVED RESISTANCE CALCULATION FOR STEEL TRUSS

IMPROVED RESISTANCE CALCULATION

FOR STEEL TRUSS GUSSET PLATES –

THE TRUNCATED WHITMORE SECTION

METHOD

“Method 2” in Appendix I of NCHRP 12-84 Report by Ocel (2013)

Don White

Georgia Tech

Method 2 Concepts, Non-Truncated Sections

WWhitmore = 24.4

Lmid = 13.2Fcr

30o30o

30o

Wconn = 10 Lconn = 12.5

345 kips

716 kips

141 kips

507 kips

520 kips

E1-U-307SS(3/8)-WV

• “Standard” application of the traditional Whitmore section

• No Partial Shear Plane check

• Professional factor (Test strength / predicted strength) of 1.12, versus 1.30

using “Method 1”, the AASHTO Whitmore Section/Partial Shear Plane Method

Method 2 Concepts, Truncated Sections

Method 2 Concepts, Truncated Sections

Method 2 Truncated Section Parameters

Method 1 Professional Factors

No-Chamfer cases governed by DB or PSPY

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Pro

fess

ion

al F

acto

r R

test

/R

n

0.35(Fy/E)0.5 (Lmid/tg)

Diagonal Buckling, No Chamfer Cases

P14-U(0.3125)-W-INFP14-U(0.25)-W-INF

Rtest/Rn > 2.0 for 3 tests


No-Chamfer cases governed by DB

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Pro

fess

ion

al F

acto

r R

test

/Rn

0.35(Fy/E)0.5 (Lmid/tg)

Diagonal Buckling, No Chamfer Cases


No-Chamfer cases governed by DB-TWS

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Pro

fess

ion

al F

acto

r R

test

/Rn

0.35(Fy/E)0.5 (LM/t)

Diagonal Buckling - Truncated Whitmore Section, No Chamfer Cases


Chamfered cases governed by DB or PSPY

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Pro

fess

ion

al F

acto

r R

test

/Rn

0.35 (Fy/E)0.5 (Lmid/tg)

DB, Chamfer Cases

P14-C(0.25)-W-INF


Chamfered cases governed by DB-TWS

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Pro

fess

ion

al F

acto

r R

test

/Rn

0.35(Fy/E)0.5 (LM/tg)

DB-TWS, Chamfer Cases

P5-C-HS(0.2)-WV-NP

T-14 Gusset Plates:

Comparison of Gusset Plate Analysis

Methods using TDOT’s SR56 over

Caney Fork River

Todd J. Stephens, PE

John M. Kulicki, PhD, PE, SE

New Gusset Plate Provisions

• Gusset plates OK for all but partial plane shear yielding

(PPSY)

• Gusset Plate

U8 Capacities:

Methodology Factored

Capacity (k)

MBE (PPSY) 630

FHWA FEA+ 1,175*

WJE Corner

Check+ 1,064*

Method 2 1,135

*Includes a 10% refined analysis reduction +Courtesy FHWA

Big Picture – Critical Diagonals

• Case summarized: 2 striped lanes of HL-93 w/o FWS

– Showing only joints with failing inventory ratings for MBE

– 23 total joints with compression diagonals after symmetry

Methodology Inventory RF

Range

Operating RF

Range

# of Failing

Joints (Inv.)*

MBE 0.23 – 0.90 0.30 – 1.16 14

Method 2 1.02 – 1.83 1.32 – 2.38 0

*Times 4 for total bridge

Big Picture – Critical Diagonals

• Case summarized: 3 lanes of HL-93 w/o FWS

• Case summarized: 3 lanes of HL-93 w/ FWS


Range

Operating RF

Range

# of Failing

Joints (Opr.)*

MBE 0.23 – 0.90 0.30 – 1.17 13

Method 2 0.87 – 1.68 1.13 – 2.18 0

*Times 4 for total bridge


Range

Operating RF

Range

# of Failing

Joints (Opr.)*

MBE 0.10 – 0.92 0.13 – 1.20 14

Method 2 0.73 – 1.58 0.95 – 2.05 1

Ratio of Strengths, Method 2 vs Method 1

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.5 1.0 1.5 2.0

Rn

(Me

tho

d 2

) /

Rn

(Me

tho

d 1

)

0.35(Fy/E)0.5 (Lmid/t)

P14-U(0.25)-W-INF

P8-C(0.25)-WV-INF-HS

P14-C(0.25)-W-INF

P5-U(0.25)-WV-NP

Summary

• The Truncated Whitmore Section Method (Method 2)

provides somewhat better accuracy than the Partial Shear

Plane Check Method (Method 1) at the cost of relatively

minor additional calculation effort in some cases

• The calculation effort is actually less when the Whitmore

section is not truncated by the adjacent geometry lines