4 v 7 Gusset Plate Inadequacy (1)

8/2/2019 4 v 7 Gusset Plate Inadequacy (1)

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Office of Research and Engineering

Gusset Plate Inadequacy

Carl R. Schultheisz


2/21

Board Meeting HWY07MH024

Presentations

1. Bridge description and collapse2. Construction activities on bridge at

time of collapse3. Gusset plate inadequacy

4. Finite element analysis5. Design and review process6. Bridge load rating and bridge load

analysis7. Bridge inspections8. Gusset plate inspections


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Introduction

January 15, 2008, interim safetyrecommendation to the Federal HighwayAdministration Require bridge owners to evaluate gusset

plates when modifications were beingconsidered

Based on Initial on-scene findings

Federal Highway Administration analysis


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Overview

Bridge design basics Allowable Stress Design methodology

Design forces

I-35W design Review of design documents

Evaluation of gusset plates

Clearly inadequate capacity of gussetplates at U10 and other nodes


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Bridge Design Basics

Design began in 1962 Governed by AASHO specifications

1961 AASHO Standard Specifications forHighway Bridges

1961/1962 AASHO Interim Specifications

1964 Minnesota Highway DepartmentStandard Specifications for Highway

Construction


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Bridge Design Basics

Allowable Stress Designmethodology

Stress= Force/Area

Truss member forces counteract theweight of structure and traffic


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Bridge Design Allowable Stress

AASHO allowable stress no morethan 55 percent of the yield stress

Yield stress defines limit of usable

load-carrying capacity of a material The allowable stress level ensures

a substantial margin of safety


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Bridge Design - Forces

Design force: calculated in accordancewith AASHO specifications

Design force calculated from dead loadplus live load plus impact

Live load = AASHO-specified lane loads

AASHO-specified lane load

Represents unusual, heavy traffic load Provides additional margin of safety

B id D i G l


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Bridge Design

GeneralReview Design documents obtained from Mn/DOT

and Jacobs Engineering

Included drawings and computation sheets

Complete and detailed documentation,

except for main truss gusset plates Design was also evaluated using finite

element models

Appropriate design methodology No significant deficiencies, other than in

main truss gusset plates


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Bridge Design Gusset Plates

AASHO specifications stated that gussetplates shall be of ample thickness toresist shear, direct stress, and flexure

No documents showing main truss

gusset plate design Documents did show design

methodology for welded floor trussgusset plates

Analysis guided by gusset plate designfor welded floor trusses


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Compression

diagonal2,288,000 lbsTension

diagonal1,975,000 lbs

Vertical540,000 lbs

tension

Upper chord2,147,000 lbs

tension

Upper chord924,000 lbscompression

U10 - Member Forces Transferred by the Gusset Plate


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Compressiondiagonal

Horizontalcomponent

1,361,000 lbs

Tension

diagonalHorizontalcomponent

1,363,000 lbs

U10 - Design for Shear


tension


A A


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tension


Compressiondiagonal

Horizontalcomponent

1,361,000 lbs

Tension


1,363,000 lbs

SHEAR


tension


Compressiondiagonal

Horizontalcomponent

1,361,000 lbs

Tension


1,363,000 lbs


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SHEAR


tension


Compressiondiagonal

horizontalcomponent

1,361,000 lbs

Tension

diagonalhorizontal

component1,363,000 lbs

Total = 3,071,000 lbs

Total = 2,724,000 lbs


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Bridge Design U10 Calculations

Shear stress = Shear forceArea

3,071,000 pounds100 square inches

=

= 30,710 pounds persquare inch


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Bridge Design U10 Calculations

Demand= Shear stress from member design

forces

= 30,071 pounds per square inch Capacity

= AASHO specified allowable stress

= 15,000 pounds per square inch

Demand-to-Capacity ratio = 2.05


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R lt G t Pl t Sh


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Results - Gusset Plate ShearAnalysis

L1 U2 L3 U4 L5 U6 L7 U8 L9 U10 L11 U12 L13 U14

Gusse

tPlateD/C

ratio

0.0

0.5

1.0

1.5

2.0

2.5

U2 U4 U6 U8 U10 U12 U14

L3L5

L7 L9L11 L13

L1

U4 U10 L11


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Gusset Plate Analysis Summary

Analysis showed that the U10gusset plates had clearly

inadequate capacity

Other gusset plates had similarinadequate capacity

No records were found for design of

main truss gusset plates No other design deficiencies found


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Result

January 15, 2008

Interim safetyrecommendation to the Federal

Highway Administration


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