Load Resistance Factor Rating (LRFR) of Concrete Segmental ...
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Load Resistance Factor Rating (LRFR) of Concrete Segmental Bridges John Corven, P.E. Corven Engineering, Inc. American Segmental Bridge Institute Annual Convention, 2020
Transcript of Load Resistance Factor Rating (LRFR) of Concrete Segmental ...
Microsoft PowerPoint - john corven - ASBI Convention 2020 - Load
Rating - Corven 10-16-2020.pptxJohn Corven, P.E. Corven
Engineering, Inc.
American Segmental Bridge Institute Annual Convention, 2020
Presenter
John A. Corven, P.E. President and Chief Engineer Corven Engineering, Inc.
ASBI Member Since Inception Currently Serves on the Executive Board 1994 ASBI Leadership Award
Related Publications:
FDOT New Directions in Post-Tensioning PCI Bridge Manual – Segmental Chapter FHWA Tendon Installation and Grouting Manual FHWA Post-Tensioned Box Girder Design Manual FHWA/PCI Bridge Geometry Manual
Purpose and Learning Objectives
Purpose: The 2020 Virtual Convention provides an educational forum that will focus on a few of the latest innovations and technologies in the construction industry.
At the end of this presentation you will be able to: • Know the background of and basic principals of segmental bridge load
ratings in the MBE. • State the differences in reliability of inventory and operating ratings. • Identify documentation needed to perform a LRFR for a segmental bridge. • Develop the scope of work for a LRFR for a segmental bridge. • Understand difficulties that can be encountered when performing a LRFR
for a segmental bridge.
Segmental LRFR in the MBE
2002 - Florida DOT develops first approach to load rating segmental bridges (Dr. Dennis Mertz, Corven Engineering)
2003 - 1st Edition of Guide Manual for Condition Evaluation and Load Resistance Factor Rating (LRFR) of Highway Bridges (segmental bridges not addressed)
2005 - Interims Add FDOT Segmental Bridge Requirements
2008 - 1st Edition of the Manual for Bridge Evaluation (MBE). Currently on 3rd Edition.
2002 through 2020 – FDOT continues to supplement MBE for segmental bridges. (Load Rating Manual)
LRFR Timeline for Segmental Bridges
• AASHTO approved manual for rating all bridge types consistent with LRFD
• Chapter 6 – Load Rating Part A – Load and Resistance Factor Rating (LRFR) Part B – Allowable Stress Rating (ASR)
Load Factor Rating (LFR)
LRFR in MBE
3 Load Rating Procedures
“Each procedure geared to a specific live load model with specially calibrated load factors ... a uniform and acceptable … reliability …”
2 Load Rating Levels
Inventory Rating (design loads)
The design load level that can safely use a bridge for an indefinite period of time.
Operating Rating (design, legal, and permit loads)
Maximum load level to which a structure may be subjected.
With Numerous Vehicles to Evaluate
Segmental bridge load ratings must consider both strength and service limit states. Specifically,
• Flexural Strength • Flexural Service Compressive Stress • Flexural Service Tensile Stress • Shear Strength • Principal Tension Stress
5 Limit States (Segmental)
• 3 load rating procedures with multiple loads: Design Loads, Legal Loads, Permit Loads
• 2 Rating Levels: Inventory Level and Operating Level
• 5 Limit States: Strength – Flexure, Shear Service – Compression, Tension, Principal Tension
All of these are typically performed at each joint between precast segments!
A Lot of Numbers
I20/I59 Birmingham, AL
Number of Vehicles = 14 Number of Load Effects = 5 Number of Precast Segments 2,316
Total Longitudinal Rating Factors Computed > 162,120
Segmental Load Rating is Complex
Why? For the same reason they are complex to design.
• The state of permanent stress are dependent on the method and sequence of construction;
• The state of permanent stress is a function of time- dependent materials;
• Desired bridge performance is heavily dependent on service limit states;
• Incomplete calibration of service limit states leaves results open to interpretation.
Reliability Based Calibration
nQ
R Q
2 2 mean mean
( )R Q
3.5 f R Q
Calibration
• Selection of a set of ’s and ’s to approximate a target level of reliability (3.5 for design and 2.5 for load rating)
• The strength limit states are calibrated to achieve levels of reliability comparable to the Standard Specifications.
• The service, and fatigue-and-fracture limit states were established to achieve member proportions comparable to the Standard Specifications.
Calibration
• Construction Documents:
• Maintenance Inspection Reports
• Field surveys and measurements
Data Collection
• Dates of casting and erection of precast segments • Cylinder strengths (or cores) • Dates of making span closures, moving supports • Temporary fixity at piers and towers • Erection equipment loads and dates • Magnitude of temporary construction loads • Post-tensioning forces and dates stressed • Type of PT ducts, friction and wobble coefficients • Current condition of structure and components
Data Collection
Material Properties
Prestressing Steel:
Jacking:
• Time-Dependent Analysis
• Account for locked-in erection loads
• Redistribution of creep and shrinkage effects from casting to the current day in the life of the bridge.
• Account for PT effects – primary, secondary, losses (friction, wobble, elastic shortening, anchor set)
• Material properties concrete and prestressing steel
Analysis Requirements - Longitudinal
Analysis Requirements - Longitudinal
Analysis Requirements - Longitudinal
Traditional:
• Influence surfaces or simple finite element analyses (cantilevers or slabs with fixed supported edges)
• Use 2-D frame model to distribute fixed moments • Use superposition to sum moments. • Incorporate Fauchart’s Method for multiple girder cross
sections
In-Depth:
• Complete FEM modeling (caution to use most conservative demands found along the length of the model)
Analysis Requirements - Transverse
Analysis Requirements - Transverse
LRFR Rating Equation
( )( ) ( )( ) ( )( )= ( )( )
= c s nC R
Capacity (MBE Equation 6A.4.2.1-2)
System Factor considers: • Longitudinal continuity • Continuum of the box girder • Multiple tendon load paths • Number of webs • Post-Tensioning details=Nominal ResistancenR
Bridge Type Span Type # of Hinges to Failure
System Factors ( fs)
I/web 2/web 3/web 4/web Precast Balanced Cantilever Type A Joints
Interior Span 3 0.90 1.05 1.15 1.20 End or Hinge Span 2 0.85 1.00 1.10 1.15 Statically Determinate I n/a 0.90 1.00 1.10
Precast Span-by-Span Type A Joints
Interior Span 3 n/a 1.00 1.10 1.20 End or Hinge Span 2 n/a 0.95 1.05 1.15 Statically Determinate I n/a n/a 1.00 1.10
Precast Span-by-Span Type B Joints
Interior Span 3 n/a 1.00 1.10 1.20 End or Hinge Span 2 n/a 0.95 1.05 1.15 Statically Determinate I n/a n/a 1.00 1.10
Cast-in-Place Balanced Cantilever
Interior Span 3 0.90 1.05 1.15 1.20 End or Hinge Span 2 0.85 1.00 1.10 1.15 Statically Determinate I n/a 0.90 1.00 1.10
a For box girder bridges with three or more webs, table values may be increased by 0.10.
System Factors (MBE Table 6A.5.11.6-1)
Rating Equation 6A.4.2.1-1 (FDOT Expanded)
=
LL
LL IM
Inventory Ratings
Permanent Loads • DC and DW as per LRFD • CR, SH as per LRFD • EL as per LRFD (LF = 1.0 all limit states) • PS as per LRFD (LF = 1.0 all limit states)
Live Loads • HL-93 Notional Load • Number of Lanes (Strength) = Number of Design Lanes • Number of Lanes (Service) = Number of Design Lanes • Impact, multi-presence as per AASHTO (1.0 max for trvs) • Strength I: LF = 1.75 • Service I: LF = 1.0 (compression check) • Service III: LF = 0.8 (tension and principal tension check)
Other Transient Loads • TU and TG as per LRFD (TG for service limit states only)
Operating Ratings
Permanent Loads • DC and DW as per LRFD • CR, SH as per LRFD • EL as per LRFD (LF = 1.0 all limit states) • PS as per LRFD (LF = 1.0 all limit states)
Live Loads • HL-93 Notional Load, Legal Loads, Permit Vehicles • Number of Lanes (Strength) = Design Lanes • Number of Lanes (Service) = Striped Lanes • Impact & Multi-Presence as per AASHTO (1.0 max for trvs) • Strength I: LF = 1.35 • Service I: LF = 1.0 (compression check) • Service III: LF = 0.8 (tension and principal tension check)
Other Transient Loads • TU as per LRFD – No TG
• Three load rating procedures: Design Loads, Legal Loads, Permit Loads
• Two Rating Levels: Inventory Level and Operating Level
• Five Limit State Verifications: Flexural Strength Flexural Service Compression Flexural Stress Tension Shear Strength Principal Tension Stress
Segmental LRFR in MBE
Principal Tension - Example
• Balanced Cantilever • Span Length = 225’ • Roadway Width = 40’ • Depth = 10’ • Web Width = 2.5’ • Draped External
Continuity Tendons
Components with bonded or combined with unbonded prestressing with no reinforcement across the joint (Type A Joint1), extremely aggressive environment.
3f'c (psi) 3f'c (psi)
Components with bonded or combined with unbonded prestressing with no reinforcement across the joint (Type A Joint1), slightly or moderately aggressive environment.
6f'c (psi) 6f'c (psi)
Components with bonded or combined with unbonded prestressing with auxiliary bonded reinforcement across the joint (Type A Joint1), extremely aggressive environment.
3f'c (psi) 6f'c (psi)
Components with bonded or combined with unbonded prestressing with auxiliary bonded reinforcement across the joint (Type A Joint1), slightly/moderately aggressive environment.
6f'c (psi) 6f'c (psi)
Components with unbonded prestressing only (Type A Joint1) without auxiliary bonded reinforcement across the joint, extremely aggressive environment.
Zero tension Zero tension
Components with unbonded prestressing only (Type A Joint1) without auxiliary bonded reinforcement across the joint, slightly or moderately aggressive environment.
Zero tension 3f'c (psi)
Components with unbonded prestressing (Type B Joint2), all environments.
100 psi (comp.) Zero tension
Longitudinal Tensile Stress in other areas Inventory Operating4
Area without auxiliary bonded reinforcement3. Zero tension Zero tension
In areas with auxiliary bonded reinforcement3. 6f'c (psi) 6f'c (psi)
Principal Tensile Stress at Neutral Axis in Web Inventory Operating4
All types of segmental bridges 3.5f'c (psi) 3f'c (psi) Transverse Stresses Inventory Operating4
Components with bonded prestressing and auxiliary bonded reinforcement, all environments 3f'c (psi) 6f'c (psi)
Allowable Stresses (FDOT Load Rating Manual, 2020)
Segmental LRFR Difficulties
• Bridges designed using AASHTO Standard Specifications:
Live load changes - Most likely will not rate at LRFR Inventory Level.
No principal stress requirement - may need to accept higher stress limits if operating without web cracks.
Change in shear design provisions – may need to revert to Vci/Vcw or reduce crack angle in traditional segmental approach to account for level of prestressing.
• Limited as-built information - plans, shop drawings, erection manuals, etc. May have to envelop ratings with assumptions (e.g. segment ages at erection, rate of construction, etc.)
LRFR Difficulties
• Standard bridge inspections do not always accurately assess the condition of the post-tensioning system. May need a site visit to audit condition of bridge
• Numerators in the Rating Equation are typically small for checking direct tensile and principal stresses. The controlling ratings can fluctuate significantly with small changes in assumptions. May need to perform a sensitivity analysis before recommending an appropriate rating factor.
• Review the concurrency of longitudinal and transverse ratings to not artificially over-estimate or under-estimate ratings.
• Owner’s expectation – costs are higher and schedules longer than load ratings for standard bridges. Need effective explanations for nuanced results.
LRFR Difficulties
Strength Limit State:
Service Limit State:
Service Load Calibration 56’ Roadway (10’-12’-12’ -12’-10’)
Strength Limit State:
Service Limit State:
Strength Limit State:
Service Limit State:
NCHRP 12-123 [Anticipated]
Load Rating Examples and Changes to the AASHTO Manual for Bridge Evaluation for Concrete Segmental Post-Tensioned Box Girder Bridges
Service Load Calibration
Don’t forget recent federal requirements for emergency vehicles EV2 and EV3
Last Thoughts
Last Thoughts Don’t apply calibrated load factors for highway notional load to fixed transit loads. Keep the design live load factors and review the applicability of other parameters.
“ASBI has met the standards and requirements of the Registered
Continuing Education Program. Credit earned on completion of this
program will be reported to RCEP at RCEP.net. A certificate of
completion will be issued to each participant. As such, it does not
include content that may be deemed or construed to be an
approval or endorsement by the RCEP.”
Thank you for your time!
This concludes the educational content of this activity
Code Word = Rating
www.corveneng.com [email protected]
American Segmental Bridge Institute Annual Convention, 2020
Presenter
John A. Corven, P.E. President and Chief Engineer Corven Engineering, Inc.
ASBI Member Since Inception Currently Serves on the Executive Board 1994 ASBI Leadership Award
Related Publications:
FDOT New Directions in Post-Tensioning PCI Bridge Manual – Segmental Chapter FHWA Tendon Installation and Grouting Manual FHWA Post-Tensioned Box Girder Design Manual FHWA/PCI Bridge Geometry Manual
Purpose and Learning Objectives
Purpose: The 2020 Virtual Convention provides an educational forum that will focus on a few of the latest innovations and technologies in the construction industry.
At the end of this presentation you will be able to: • Know the background of and basic principals of segmental bridge load
ratings in the MBE. • State the differences in reliability of inventory and operating ratings. • Identify documentation needed to perform a LRFR for a segmental bridge. • Develop the scope of work for a LRFR for a segmental bridge. • Understand difficulties that can be encountered when performing a LRFR
for a segmental bridge.
Segmental LRFR in the MBE
2002 - Florida DOT develops first approach to load rating segmental bridges (Dr. Dennis Mertz, Corven Engineering)
2003 - 1st Edition of Guide Manual for Condition Evaluation and Load Resistance Factor Rating (LRFR) of Highway Bridges (segmental bridges not addressed)
2005 - Interims Add FDOT Segmental Bridge Requirements
2008 - 1st Edition of the Manual for Bridge Evaluation (MBE). Currently on 3rd Edition.
2002 through 2020 – FDOT continues to supplement MBE for segmental bridges. (Load Rating Manual)
LRFR Timeline for Segmental Bridges
• AASHTO approved manual for rating all bridge types consistent with LRFD
• Chapter 6 – Load Rating Part A – Load and Resistance Factor Rating (LRFR) Part B – Allowable Stress Rating (ASR)
Load Factor Rating (LFR)
LRFR in MBE
3 Load Rating Procedures
“Each procedure geared to a specific live load model with specially calibrated load factors ... a uniform and acceptable … reliability …”
2 Load Rating Levels
Inventory Rating (design loads)
The design load level that can safely use a bridge for an indefinite period of time.
Operating Rating (design, legal, and permit loads)
Maximum load level to which a structure may be subjected.
With Numerous Vehicles to Evaluate
Segmental bridge load ratings must consider both strength and service limit states. Specifically,
• Flexural Strength • Flexural Service Compressive Stress • Flexural Service Tensile Stress • Shear Strength • Principal Tension Stress
5 Limit States (Segmental)
• 3 load rating procedures with multiple loads: Design Loads, Legal Loads, Permit Loads
• 2 Rating Levels: Inventory Level and Operating Level
• 5 Limit States: Strength – Flexure, Shear Service – Compression, Tension, Principal Tension
All of these are typically performed at each joint between precast segments!
A Lot of Numbers
I20/I59 Birmingham, AL
Number of Vehicles = 14 Number of Load Effects = 5 Number of Precast Segments 2,316
Total Longitudinal Rating Factors Computed > 162,120
Segmental Load Rating is Complex
Why? For the same reason they are complex to design.
• The state of permanent stress are dependent on the method and sequence of construction;
• The state of permanent stress is a function of time- dependent materials;
• Desired bridge performance is heavily dependent on service limit states;
• Incomplete calibration of service limit states leaves results open to interpretation.
Reliability Based Calibration
nQ
R Q
2 2 mean mean
( )R Q
3.5 f R Q
Calibration
• Selection of a set of ’s and ’s to approximate a target level of reliability (3.5 for design and 2.5 for load rating)
• The strength limit states are calibrated to achieve levels of reliability comparable to the Standard Specifications.
• The service, and fatigue-and-fracture limit states were established to achieve member proportions comparable to the Standard Specifications.
Calibration
• Construction Documents:
• Maintenance Inspection Reports
• Field surveys and measurements
Data Collection
• Dates of casting and erection of precast segments • Cylinder strengths (or cores) • Dates of making span closures, moving supports • Temporary fixity at piers and towers • Erection equipment loads and dates • Magnitude of temporary construction loads • Post-tensioning forces and dates stressed • Type of PT ducts, friction and wobble coefficients • Current condition of structure and components
Data Collection
Material Properties
Prestressing Steel:
Jacking:
• Time-Dependent Analysis
• Account for locked-in erection loads
• Redistribution of creep and shrinkage effects from casting to the current day in the life of the bridge.
• Account for PT effects – primary, secondary, losses (friction, wobble, elastic shortening, anchor set)
• Material properties concrete and prestressing steel
Analysis Requirements - Longitudinal
Analysis Requirements - Longitudinal
Analysis Requirements - Longitudinal
Traditional:
• Influence surfaces or simple finite element analyses (cantilevers or slabs with fixed supported edges)
• Use 2-D frame model to distribute fixed moments • Use superposition to sum moments. • Incorporate Fauchart’s Method for multiple girder cross
sections
In-Depth:
• Complete FEM modeling (caution to use most conservative demands found along the length of the model)
Analysis Requirements - Transverse
Analysis Requirements - Transverse
LRFR Rating Equation
( )( ) ( )( ) ( )( )= ( )( )
= c s nC R
Capacity (MBE Equation 6A.4.2.1-2)
System Factor considers: • Longitudinal continuity • Continuum of the box girder • Multiple tendon load paths • Number of webs • Post-Tensioning details=Nominal ResistancenR
Bridge Type Span Type # of Hinges to Failure
System Factors ( fs)
I/web 2/web 3/web 4/web Precast Balanced Cantilever Type A Joints
Interior Span 3 0.90 1.05 1.15 1.20 End or Hinge Span 2 0.85 1.00 1.10 1.15 Statically Determinate I n/a 0.90 1.00 1.10
Precast Span-by-Span Type A Joints
Interior Span 3 n/a 1.00 1.10 1.20 End or Hinge Span 2 n/a 0.95 1.05 1.15 Statically Determinate I n/a n/a 1.00 1.10
Precast Span-by-Span Type B Joints
Interior Span 3 n/a 1.00 1.10 1.20 End or Hinge Span 2 n/a 0.95 1.05 1.15 Statically Determinate I n/a n/a 1.00 1.10
Cast-in-Place Balanced Cantilever
Interior Span 3 0.90 1.05 1.15 1.20 End or Hinge Span 2 0.85 1.00 1.10 1.15 Statically Determinate I n/a 0.90 1.00 1.10
a For box girder bridges with three or more webs, table values may be increased by 0.10.
System Factors (MBE Table 6A.5.11.6-1)
Rating Equation 6A.4.2.1-1 (FDOT Expanded)
=
LL
LL IM
Inventory Ratings
Permanent Loads • DC and DW as per LRFD • CR, SH as per LRFD • EL as per LRFD (LF = 1.0 all limit states) • PS as per LRFD (LF = 1.0 all limit states)
Live Loads • HL-93 Notional Load • Number of Lanes (Strength) = Number of Design Lanes • Number of Lanes (Service) = Number of Design Lanes • Impact, multi-presence as per AASHTO (1.0 max for trvs) • Strength I: LF = 1.75 • Service I: LF = 1.0 (compression check) • Service III: LF = 0.8 (tension and principal tension check)
Other Transient Loads • TU and TG as per LRFD (TG for service limit states only)
Operating Ratings
Permanent Loads • DC and DW as per LRFD • CR, SH as per LRFD • EL as per LRFD (LF = 1.0 all limit states) • PS as per LRFD (LF = 1.0 all limit states)
Live Loads • HL-93 Notional Load, Legal Loads, Permit Vehicles • Number of Lanes (Strength) = Design Lanes • Number of Lanes (Service) = Striped Lanes • Impact & Multi-Presence as per AASHTO (1.0 max for trvs) • Strength I: LF = 1.35 • Service I: LF = 1.0 (compression check) • Service III: LF = 0.8 (tension and principal tension check)
Other Transient Loads • TU as per LRFD – No TG
• Three load rating procedures: Design Loads, Legal Loads, Permit Loads
• Two Rating Levels: Inventory Level and Operating Level
• Five Limit State Verifications: Flexural Strength Flexural Service Compression Flexural Stress Tension Shear Strength Principal Tension Stress
Segmental LRFR in MBE
Principal Tension - Example
• Balanced Cantilever • Span Length = 225’ • Roadway Width = 40’ • Depth = 10’ • Web Width = 2.5’ • Draped External
Continuity Tendons
Components with bonded or combined with unbonded prestressing with no reinforcement across the joint (Type A Joint1), extremely aggressive environment.
3f'c (psi) 3f'c (psi)
Components with bonded or combined with unbonded prestressing with no reinforcement across the joint (Type A Joint1), slightly or moderately aggressive environment.
6f'c (psi) 6f'c (psi)
Components with bonded or combined with unbonded prestressing with auxiliary bonded reinforcement across the joint (Type A Joint1), extremely aggressive environment.
3f'c (psi) 6f'c (psi)
Components with bonded or combined with unbonded prestressing with auxiliary bonded reinforcement across the joint (Type A Joint1), slightly/moderately aggressive environment.
6f'c (psi) 6f'c (psi)
Components with unbonded prestressing only (Type A Joint1) without auxiliary bonded reinforcement across the joint, extremely aggressive environment.
Zero tension Zero tension
Components with unbonded prestressing only (Type A Joint1) without auxiliary bonded reinforcement across the joint, slightly or moderately aggressive environment.
Zero tension 3f'c (psi)
Components with unbonded prestressing (Type B Joint2), all environments.
100 psi (comp.) Zero tension
Longitudinal Tensile Stress in other areas Inventory Operating4
Area without auxiliary bonded reinforcement3. Zero tension Zero tension
In areas with auxiliary bonded reinforcement3. 6f'c (psi) 6f'c (psi)
Principal Tensile Stress at Neutral Axis in Web Inventory Operating4
All types of segmental bridges 3.5f'c (psi) 3f'c (psi) Transverse Stresses Inventory Operating4
Components with bonded prestressing and auxiliary bonded reinforcement, all environments 3f'c (psi) 6f'c (psi)
Allowable Stresses (FDOT Load Rating Manual, 2020)
Segmental LRFR Difficulties
• Bridges designed using AASHTO Standard Specifications:
Live load changes - Most likely will not rate at LRFR Inventory Level.
No principal stress requirement - may need to accept higher stress limits if operating without web cracks.
Change in shear design provisions – may need to revert to Vci/Vcw or reduce crack angle in traditional segmental approach to account for level of prestressing.
• Limited as-built information - plans, shop drawings, erection manuals, etc. May have to envelop ratings with assumptions (e.g. segment ages at erection, rate of construction, etc.)
LRFR Difficulties
• Standard bridge inspections do not always accurately assess the condition of the post-tensioning system. May need a site visit to audit condition of bridge
• Numerators in the Rating Equation are typically small for checking direct tensile and principal stresses. The controlling ratings can fluctuate significantly with small changes in assumptions. May need to perform a sensitivity analysis before recommending an appropriate rating factor.
• Review the concurrency of longitudinal and transverse ratings to not artificially over-estimate or under-estimate ratings.
• Owner’s expectation – costs are higher and schedules longer than load ratings for standard bridges. Need effective explanations for nuanced results.
LRFR Difficulties
Strength Limit State:
Service Limit State:
Service Load Calibration 56’ Roadway (10’-12’-12’ -12’-10’)
Strength Limit State:
Service Limit State:
Strength Limit State:
Service Limit State:
NCHRP 12-123 [Anticipated]
Load Rating Examples and Changes to the AASHTO Manual for Bridge Evaluation for Concrete Segmental Post-Tensioned Box Girder Bridges
Service Load Calibration
Don’t forget recent federal requirements for emergency vehicles EV2 and EV3
Last Thoughts
Last Thoughts Don’t apply calibrated load factors for highway notional load to fixed transit loads. Keep the design live load factors and review the applicability of other parameters.
“ASBI has met the standards and requirements of the Registered
Continuing Education Program. Credit earned on completion of this
program will be reported to RCEP at RCEP.net. A certificate of
completion will be issued to each participant. As such, it does not
include content that may be deemed or construed to be an
approval or endorsement by the RCEP.”
Thank you for your time!
This concludes the educational content of this activity
Code Word = Rating
www.corveneng.com [email protected]
