STRSTR654654Inspection, Repair and Inspection, Repair and p , pp , p

Maintenance of Steel StructuresMaintenance of Steel StructuresMaintenance of Steel StructuresMaintenance of Steel StructuresLectureLecture 99aa NovemberNovember 2020 20122012Lecture Lecture 99a, a, November November 2020, , 20122012

Sh if A M dSh if A M dSherif A. MouradSherif A. Mourad

Professor of Steel Structures and BridgesProfessor of Steel Structures and BridgesProfessor of Steel Structures and BridgesProfessor of Steel Structures and BridgesFaculty of Engineering,Faculty of Engineering,

Cairo UniversityCairo University

St th i St l El tSt th i St l El tStrengthening Steel ElementsStrengthening Steel Elements

TopicsTopicspp Why strengthen.Why strengthen. Beams. Beams.

J iJ i Joints.Joints. Systems.Systems.Systems.Systems.

Why Strengthen?Why Strengthen? Inadequate design.Inadequate design.Heavier live loads.Heavier live loads. Local deterioration.Local deterioration.

Strengthen or Replace?Strengthen or Replace?

Age of the structure.Age of the structure.gg Quality of material.Quality of material. Fatigue effect on operation.Fatigue effect on operation. Estimated costEstimated cost Estimated cost.Estimated cost. Added length of life.Added length of life.gg Possible future increase in loadPossible future increase in load

Strengthen or Replace?Strengthen or Replace?

Typically, strengthening is undertaken Typically, strengthening is undertaken yp y, g gyp y, g gonly to improve certain weak parts, not only to improve certain weak parts, not the entire memberthe entire memberthe entire member.the entire member.If it is found that the entire member (the If it is found that the entire member (the ((entire span of a bridge, for example), it entire span of a bridge, for example), it may be more economical to replace themay be more economical to replace themay be more economical to replace the may be more economical to replace the member, rather than strengthen it.member, rather than strengthen it.

S T k B f I l iS T k B f I l iSteps Taken Before Implementation Steps Taken Before Implementation of Strengtheningof Strengtheningof Strengtheningof Strengthening

Physical condition.Physical condition.ff Evaluation of stresses.Evaluation of stresses.

Effect of eccentricityEffect of eccentricity Effect of eccentricity.Effect of eccentricity. Use of welding.Use of welding.gg

Physical ConditionPhysical Condition

Physical condition shall be determined by Physical condition shall be determined by y yy ya detailed inspection.a detailed inspection.E bli h h f l d i h i lE bli h h f l d i h i l Establish the type of steel and its physical Establish the type of steel and its physical and chemical properties by examining and chemical properties by examining p p y gp p y goriginal documents and/or taking original documents and/or taking specimens for testingspecimens for testingspecimens for testing.specimens for testing.

Carry out load test to check actual Carry out load test to check actual yystresses, deflections, and vibrations..stresses, deflections, and vibrations..

Evaluation of StressesEvaluation of Stresses

Allowable stresses of the added materials Allowable stresses of the added materials under the load for which they are under the load for which they are strengthened shall conform to thestrengthened shall conform to thestrengthened shall conform to the strengthened shall conform to the Egyptian Code.Egyptian Code.

New material shall be considered New material shall be considered effective in carrying additional (live) loadeffective in carrying additional (live) loadeffective in carrying additional (live) load effective in carrying additional (live) load only, unless dead load stresses are only, unless dead load stresses are

d il f h bd il f h bremoved temporarily from the members.removed temporarily from the members.

Evaluation of StressesEvaluation of Stresses The stresses of the original section shall be The stresses of the original section shall be

h k d d d d l d d ddi i lh k d d d d l d d ddi i lchecked under dead load and any additional checked under dead load and any additional live loads.live loads.

Members shall be investigated for any loss of Members shall be investigated for any loss of strength resulting from the temporary removalstrength resulting from the temporary removalstrength resulting from the temporary removal strength resulting from the temporary removal of rivets, cover plates or any other parts.of rivets, cover plates or any other parts.S h i h ll b fi d iS h i h ll b fi d i Strengthening shall not be confined to main Strengthening shall not be confined to main members only, but shall include bracing, lacing, members only, but shall include bracing, lacing, battens, …battens, …

EccentricityEccentricity

The added material shall preferably be The added material shall preferably be p yp yapplied so as to obtain a symmetric applied so as to obtain a symmetric sectionsectionsection.section.

If a symmetric section cannot be If a symmetric section cannot be yyachieved, the eccentricity of the member achieved, the eccentricity of the member shall be taken into consideration in theshall be taken into consideration in theshall be taken into consideration in the shall be taken into consideration in the stress analysis.stress analysis.

WeldingWelding

Electric arc welding may be used subject Electric arc welding may be used subject g y jg y jto approval.to approval.W ld d i h ll b dW ld d i h ll b d Welds and rivets shall not be assumed to Welds and rivets shall not be assumed to work together.work together.gg

Welding shall be in accordance with the Welding shall be in accordance with the E ti C dE ti C dEgyptian Code.Egyptian Code.

WeldingWelding

When welds are added to existing rivets:When welds are added to existing rivets: Welds shall be designed to transmit the entire Welds shall be designed to transmit the entire

stresses except where the original memberstresses except where the original memberstresses, except where the original member stresses, except where the original member shall sustain the entire DL, then the welds shall shall sustain the entire DL, then the welds shall be designed to carry only the LLbe designed to carry only the LLbe designed to carry only the LL.be designed to carry only the LL.

When a few of the rivets are loose or defective, When a few of the rivets are loose or defective, HSB may be used to carry DL provided they HSB may be used to carry DL provided they are installed prior to welding.are installed prior to welding.p gp g

M i BM i BMain BeamsMain Beams

Flanges and web.Flanges and web. Stiffeners.Stiffeners. Initial tensionInitial tension Initial tension.Initial tension. Effective span.Effective span. Wind bracing.Wind bracing. Increasing the number of girdersIncreasing the number of girders Increasing the number of girders.Increasing the number of girders. Substitution.Substitution.

FlFlFlangesFlanges

Flange section may be increased by adding cover Flange section may be increased by adding cover l b l i h i i l bl b l i h i i l bplates or by replacing the existing cover plate by a plates or by replacing the existing cover plate by a

new one.new one. If the exposed surface of old cover plates is rough If the exposed surface of old cover plates is rough

or uneven from the effect of corrosion, they shall or uneven from the effect of corrosion, they shall be discarded and new plates provided.be discarded and new plates provided.

If more than one plate shall be replaced, it is better If more than one plate shall be replaced, it is better p p ,p p ,to replace them with a single plate with adequate to replace them with a single plate with adequate size.size.s e.s e.

FlFlFlangesFlanges

Cover plates added to plate girders without Cover plates added to plate girders without existing cove plates shall be full length and shallexisting cove plates shall be full length and shallexisting cove plates shall be full length, and shall existing cove plates shall be full length, and shall be connected with rivets, HSB, or continuous fillet be connected with rivets, HSB, or continuous fillet weld (if material is weldable).weld (if material is weldable).weld (if material is weldable).weld (if material is weldable).

Cover plates added to rolled sections without Cover plates added to rolled sections without existing cove plates shall be full length and shallexisting cove plates shall be full length and shallexisting cove plates shall be full length, and shall existing cove plates shall be full length, and shall be connected with rivets, HSB, or continuous fillet be connected with rivets, HSB, or continuous fillet weld (if material is weldable).weld (if material is weldable).( )( )

When secondary beams rest directly on main When secondary beams rest directly on main beams, flange angles may be strengthened by beams, flange angles may be strengthened by , g g y g y, g g y g ybolting new flange angles.bolting new flange angles.

FlFlFlangesFlanges

If it is difficult or expensive to remove the If it is difficult or expensive to remove the R.C. floor on top of beams, the flange R.C. floor on top of beams, the flange section may be increased by adding fullsection may be increased by adding full--y y gy y glength angles or plates just below the flange length angles or plates just below the flange anglesanglesangles.angles.

In this case, the vertical stiffeners must be In this case, the vertical stiffeners must be cut and replaced.cut and replaced.

Bottom flanges may be similarly reinforcedBottom flanges may be similarly reinforced Bottom flanges may be similarly reinforced Bottom flanges may be similarly reinforced to keep symmetry.to keep symmetry.

W bW bWebWeb

If the web cannot carry the loads, a bolted If the web cannot carry the loads, a bolted reinforcing web should be introduced.reinforcing web should be introduced.W ldi i d d d hW ldi i d d d h Welding is not recommended due to the Welding is not recommended due to the low fatigue strength of weld terminals.low fatigue strength of weld terminals.g gg g

New Splice PlateNew Splice Plate

StiffStiffStiffenersStiffeners

Bearing stiffeners may be strengthened by Bearing stiffeners may be strengthened by adding angles or plates, grinding the new adding angles or plates, grinding the new plates so that they fit tightly or by weldingplates so that they fit tightly or by weldingplates so that they fit tightly, or by welding plates so that they fit tightly, or by welding them to the flanges.them to the flanges.

Intermediate stiffeners may be added by Intermediate stiffeners may be added by riveting HSB or welding Ensure that theyriveting HSB or welding Ensure that theyriveting, HSB, or welding. Ensure that they riveting, HSB, or welding. Ensure that they are not welded to the tension flange.are not welded to the tension flange.

I iti l T iI iti l T iInitial TensionInitial Tension

Initial tension may be introduced to a new Initial tension may be introduced to a new cover plate by:cover plate by: Welding one end of the flange anglesWelding one end of the flange angles Welding one end of the flange angles.Welding one end of the flange angles. Heating the plate till it expands to a Heating the plate till it expands to a

predetermined length.predetermined length. Weld the other end of the plate and allow it toWeld the other end of the plate and allow it to Weld the other end of the plate and allow it to Weld the other end of the plate and allow it to

cool.cool. Complete welding of the plate in the Complete welding of the plate in the

longitudinal direction.longitudinal direction.gg

Initial TensionInitial Tension

Eff ti SEff ti SEffective SpanEffective Span

The effective span of the main beams may The effective span of the main beams may be reduced by:be reduced by: Mo ing the bearings nearer to the edge of theMo ing the bearings nearer to the edge of the Moving the bearings nearer to the edge of the Moving the bearings nearer to the edge of the

support (provided the seat is wide enough, and support (provided the seat is wide enough, and k d fk d fthat it is checked for the new eccentricity).that it is checked for the new eccentricity).

Introducing new knee bracing (provided the Introducing new knee bracing (provided the g g (pg g (pcolumns / abutment can sustain the lateral columns / abutment can sustain the lateral componentcomponentcomponent.component.

N b f M i Gi dN b f M i Gi dNumber of Main GirdersNumber of Main Girders

Strengthening may be done by doubling the Strengthening may be done by doubling the main girders (reducing the spacing by onemain girders (reducing the spacing by one--half) and providing the necessary lateralhalf) and providing the necessary lateralhalf) and providing the necessary lateral half) and providing the necessary lateral bracing for the new beams.bracing for the new beams.

Spacing should consider allowing for Spacing should consider allowing for inspection maintenance and painting of theinspection maintenance and painting of theinspection, maintenance, and painting of the inspection, maintenance, and painting of the interior surface of the beams.interior surface of the beams.

C tiC tiConnectionsConnections

BeamBeam--to beam connections.to beam connections. Lateral bracing connections.Lateral bracing connections. Riveted jointsRiveted joints..

Stringer BracketStringer Bracket

Modified BracingModified Bracing

T S tT S tTruss SystemsTruss Systems

Addition of new trusses:Addition of new trusses: New truss should be of stiffness New truss should be of stiffness

bl t th ld tbl t th ld tcomparable to the old trusses.comparable to the old trusses. New truss should be joined with the New truss should be joined with the

bracing system to ensure uniform bracing system to ensure uniform deflection.deflection.de ect o .de ect o .

T S tT S tTruss SystemsTruss Systems

Auxiliary Support System:Auxiliary Support System:y pp yy pp y New intermediate supports may be New intermediate supports may be

introduced to shorten the span.introduced to shorten the span.introduced to shorten the span.introduced to shorten the span. A complete reanalysis is necessary as A complete reanalysis is necessary as

straining actions may reverse directionstraining actions may reverse directionstraining actions may reverse direction.straining actions may reverse direction. Members having insufficient capacity Members having insufficient capacity

h ll b h d i i ll ih ll b h d i i ll ishall be strengthened prior to installation shall be strengthened prior to installation of the new supports.of the new supports.

T S tT S tTruss SystemsTruss Systems

Additional Chords:Additional Chords: Convert the existing truss by adding new Convert the existing truss by adding new

b t i th d thb t i th d thmembers to increase the depth.members to increase the depth. For the new system to be fully effective For the new system to be fully effective

for DL and LL, initial stresses must be for DL and LL, initial stresses must be provided into the new chord.provided into the new chord.p ov ded to t e ew c o d.p ov ded to t e ew c o d.

Additional ChordsAdditional Chords