Search

Search Results

• 1. [Article] Model for Network Assignment Problem of Capacitated Freight with Disruptions

  A modeling framework is proposed for the freight network assignment problem with recourse, network travel time and cost disruptions, and link flow capacity constraints. "Recourse" is defined as the ability ...

  Citation × Citation Citation Abstract Copy Title: Model for Network Assignment Problem of Capacitated Freight with Disruptions Author: Figliozzi, Miguel, Unnikrishnan, Avinash, Shahabi, Mehrdad Year: 2012 A modeling framework is proposed for the freight network assignment problem with recourse, network travel time and cost disruptions, and link flow capacity constraints. "Recourse" is defined as the ability of a user to reconsider and adapt his or her routing decisions in response to newly acquired information about network disruption. When real-time tracking and monitoring of network shipments allow companies a routing recourse, network capacity must be simultaneously considered. If a disruption significantly alters network flows, the capacity of alternative or secondary routes may be quickly reached. A new freight mathematical model with a capacitated network and adaptive routing was developed and solved. Results showed that simultaneous consideration of recourse and capacity constraints was superior to benchmark results obtained with nonadaptive deterministic behavior. Title: Model for Network Assignment Problem of Capacitated Freight with Disruptions Author: Figliozzi, Miguel, Unnikrishnan, Avinash, Shahabi, Mehrdad Year: 2012 A modeling framework is proposed for the freight network assignment problem with recourse, network travel time and cost disruptions, and link flow capacity constraints. "Recourse" is defined as the ability of a user to reconsider and adapt his or her routing decisions in response to newly acquired information about network disruption. When real-time tracking and monitoring of network shipments allow companies a routing recourse, network capacity must be simultaneously considered. If a disruption significantly alters network flows, the capacity of alternative or secondary routes may be quickly reached. A new freight mathematical model with a capacitated network and adaptive routing was developed and solved. Results showed that simultaneous consideration of recourse and capacity constraints was superior to benchmark results obtained with nonadaptive deterministic behavior. Close

• 2. [Article] Congestion and Emissions Mitigation: A Comparison of Capacity, Demand, and Efficiency Based Strategies

  Capacity, demand, and vehicle based emissions reduction strategies are compared for several pollutants employing aggregate US congestion and vehicle fleet condition data. We find that congestion mitigation ...

  Citation × Citation Citation Abstract Copy Title: Congestion and Emissions Mitigation: A Comparison of Capacity, Demand, and Efficiency Based Strategies Author: Bigazzi, Alexander Y., Figliozzi, Miguel Year: 2012 Capacity, demand, and vehicle based emissions reduction strategies are compared for several pollutants employing aggregate US congestion and vehicle fleet condition data. We find that congestion mitigation does not inevitably lead to reduced emissions; the net effect of mitigation depends on the balance of induced travel demand and increased vehicle efficiency that in turn depend on the pollutant, congestion level, and fleet composition. In the long run, capacity-based congestion improvements within certain speed intervals can reasonably be expected to increase emissions of CO2e, CO, and NOx through increased vehicle travel volume. Better opportunities for emissions reductions exist for HC and PM2.5 emissions, and on more heavily congested arterials. Advanced-efficiency vehicles with emissions rates that are less sensitive to congestion than conventional vehicles generate less emissions co-benefits from congestion mitigation. Title: Congestion and Emissions Mitigation: A Comparison of Capacity, Demand, and Efficiency Based Strategies Author: Bigazzi, Alexander Y., Figliozzi, Miguel Year: 2012 Capacity, demand, and vehicle based emissions reduction strategies are compared for several pollutants employing aggregate US congestion and vehicle fleet condition data. We find that congestion mitigation does not inevitably lead to reduced emissions; the net effect of mitigation depends on the balance of induced travel demand and increased vehicle efficiency that in turn depend on the pollutant, congestion level, and fleet composition. In the long run, capacity-based congestion improvements within certain speed intervals can reasonably be expected to increase emissions of CO2e, CO, and NOx through increased vehicle travel volume. Better opportunities for emissions reductions exist for HC and PM2.5 emissions, and on more heavily congested arterials. Advanced-efficiency vehicles with emissions rates that are less sensitive to congestion than conventional vehicles generate less emissions co-benefits from congestion mitigation. Close

• 3. [Article] Environmental Durability of Reinforced Concrete Deck Girders Strengthened for Shear with Surface Bonded Carbon Fiber-Reinforced Polymer

  This research investigated the durability of carbon fiber-reinforced polymer composites (CFRP) used for shear strengthening reinforced concrete deck girders. Large beams were used to avoid accounting for ...

  Citation × Citation Citation Abstract Copy Title: Environmental Durability of Reinforced Concrete Deck Girders Strengthened for Shear with Surface Bonded Carbon Fiber-Reinforced Polymer Author: Higgins, Christopher, Dawson, Matthew R., Mitchell, Mikal M., Sopal, Gautam, Senturk, A. Ekin Year: 2009 This research investigated the durability of carbon fiber-reinforced polymer composites (CFRP) used for shear strengthening reinforced concrete deck girders. Large beams were used to avoid accounting for size effects in the data analysis. The effort included determining the role of freeze-thaw, moisture, and fatigue on structural performance and developing analytical design procedures that account for durability. The results showed that moisture infiltration behind the CFRP, combined with freeze-thaw, was critical in reducing shear panel stiffness and shear capacity. Long-term moisture exposure alone produced only a minor decrease in shear capacity. Freeze-thaw, combined with fatigue, had little effect on shear capacity if water infiltration was minimized. Fatigue caused some debonding, but the debonding was not significant enough to affect capacity. Use of ACI-318 with ACI 440 provided conservative predicted shear strengths after environmental exposure. However, the ACI approach did not provide uniform levels of safety because the observed conservatism was built into the prediction for the unstrengthened base specimens but not for the CFRP contribution. Consequently, a recommendation of the research is to apply the environmental exposure factor at the final design step to limit the effective CFRP stress/strain. For locations with very large numbers of wet freeze-thaw cycles and extended exposure to continuous moisture, the environmental reduction factors should be reduced even further. To better predict the CFRP bond strength demands that can occur due to shear-moment interaction, a further check of the design should be made beyond those required by ACI-440. Title: Environmental Durability of Reinforced Concrete Deck Girders Strengthened for Shear with Surface Bonded Carbon Fiber-Reinforced Polymer Author: Higgins, Christopher, Dawson, Matthew R., Mitchell, Mikal M., Sopal, Gautam, Senturk, A. Ekin Year: 2009 This research investigated the durability of carbon fiber-reinforced polymer composites (CFRP) used for shear strengthening reinforced concrete deck girders. Large beams were used to avoid accounting for size effects in the data analysis. The effort included determining the role of freeze-thaw, moisture, and fatigue on structural performance and developing analytical design procedures that account for durability. The results showed that moisture infiltration behind the CFRP, combined with freeze-thaw, was critical in reducing shear panel stiffness and shear capacity. Long-term moisture exposure alone produced only a minor decrease in shear capacity. Freeze-thaw, combined with fatigue, had little effect on shear capacity if water infiltration was minimized. Fatigue caused some debonding, but the debonding was not significant enough to affect capacity. Use of ACI-318 with ACI 440 provided conservative predicted shear strengths after environmental exposure. However, the ACI approach did not provide uniform levels of safety because the observed conservatism was built into the prediction for the unstrengthened base specimens but not for the CFRP contribution. Consequently, a recommendation of the research is to apply the environmental exposure factor at the final design step to limit the effective CFRP stress/strain. For locations with very large numbers of wet freeze-thaw cycles and extended exposure to continuous moisture, the environmental reduction factors should be reduced even further. To better predict the CFRP bond strength demands that can occur due to shear-moment interaction, a further check of the design should be made beyond those required by ACI-440. Close

• 4. [Article] Experimental Investigation of CFRP Wrapped Square Non-ductile Reinforced Concrete Columns

  The use of fiber-reinforced polymers (FRP) for retrofitting or strengthening deficient concrete columns noticeably increased in the past few decades. Plenty of research has been conducted on the behavior ...

  Citation × Citation Citation Abstract Copy Title: Experimental Investigation of CFRP Wrapped Square Non-ductile Reinforced Concrete Columns Author: Al-Khafaji, Hayder Lateef Year: 2016 The use of fiber-reinforced polymers (FRP) for retrofitting or strengthening deficient concrete columns noticeably increased in the past few decades. Plenty of research has been conducted on the behavior of FRP-strengthened circular concrete columns, but far less research has dealt with non-circular columns. In the current study, the focus was to investigate the behavior of square columns with low to medium grade concrete and low steel reinforcement that were strengthened using carbon fiber reinforced polymer (CFRP) wrap. In the experimental portion of this investigation, twelve short square reinforced concrete columns (5" x 5" in cross section and 12" high) were cast and tested under concentric axial loading. The specimens were divided evenly into two series, named C2 and C4. In the first series, C2, six column specimens were cast with 2000-psi concrete, representing low-grade concrete. One column was a "control specimen" designed based on older non-seismic codes. A second column, another "control specimen", was designed based on the current seismic design code, ACI 318-14. The four remaining columns were wrapped with CFRP sheets, but with a different number of CFRP wraps. The same scheme was followed for the specimens of the second series (C4), but they were cast with 4000-psi concrete, representing medium grade concrete. Thus, the main parameters considered in the current study were the concrete compressive strength and the thickness of the CFRP jacket (number of wraps). Those two parameters were utilized to investigate the effectiveness of the CFRP confinement in enhancing the axial load carrying capacity and ductility of the strengthened columns. Test results confirmed that the confinement produced by the CFRP jacket enhanced the axial load-carrying capacity, axial strain capacity, and energy absorption if compared to unwrapped columns. In addition, the results showed that there should be an effective thickness for the CFRP jacket in order to achieve a significant enhancement in the performance of the strengthened columns. Moreover, the test results demonstrated that the effectiveness of the CFRP confinement was more pronounced in the case of the low-grade concrete columns (Series C2). Title: Experimental Investigation of CFRP Wrapped Square Non-ductile Reinforced Concrete Columns Author: Al-Khafaji, Hayder Lateef Year: 2016 The use of fiber-reinforced polymers (FRP) for retrofitting or strengthening deficient concrete columns noticeably increased in the past few decades. Plenty of research has been conducted on the behavior of FRP-strengthened circular concrete columns, but far less research has dealt with non-circular columns. In the current study, the focus was to investigate the behavior of square columns with low to medium grade concrete and low steel reinforcement that were strengthened using carbon fiber reinforced polymer (CFRP) wrap. In the experimental portion of this investigation, twelve short square reinforced concrete columns (5" x 5" in cross section and 12" high) were cast and tested under concentric axial loading. The specimens were divided evenly into two series, named C2 and C4. In the first series, C2, six column specimens were cast with 2000-psi concrete, representing low-grade concrete. One column was a "control specimen" designed based on older non-seismic codes. A second column, another "control specimen", was designed based on the current seismic design code, ACI 318-14. The four remaining columns were wrapped with CFRP sheets, but with a different number of CFRP wraps. The same scheme was followed for the specimens of the second series (C4), but they were cast with 4000-psi concrete, representing medium grade concrete. Thus, the main parameters considered in the current study were the concrete compressive strength and the thickness of the CFRP jacket (number of wraps). Those two parameters were utilized to investigate the effectiveness of the CFRP confinement in enhancing the axial load carrying capacity and ductility of the strengthened columns. Test results confirmed that the confinement produced by the CFRP jacket enhanced the axial load-carrying capacity, axial strain capacity, and energy absorption if compared to unwrapped columns. In addition, the results showed that there should be an effective thickness for the CFRP jacket in order to achieve a significant enhancement in the performance of the strengthened columns. Moreover, the test results demonstrated that the effectiveness of the CFRP confinement was more pronounced in the case of the low-grade concrete columns (Series C2). Close

• 5. [Article] Torsional Strengthening of Reinforced Concrete Beams Using CFRP Composites

  Few decades ago, there were no guidelines for torsion design of reinforced concrete (RC) beams. Hence, many existing beams in older buildings have a lack of adequate torsional strength since they were ...

  Citation × Citation Citation Abstract Copy Title: Torsional Strengthening of Reinforced Concrete Beams Using CFRP Composites Author: Rafeeq, Ranj Year: 2016 Few decades ago, there were no guidelines for torsion design of reinforced concrete (RC) beams. Hence, many existing beams in older buildings have a lack of adequate torsional strength since they were not properly designed for torsion. One way to regain/rehabilitate adequate torsional strength is through application of externally bonded carbon fiber reinforced polymers (CFRP). To date, American Concrete Institute (ACI) code, as well as other building codes, do not have recommendations or provisions for strengthening RC beams for torsion using fiber-reinforced polymer (FRP) composites due to the inexistence of conclusive experimental and analytical data. Of the very limited works on this behavior, the majority of the focus has been devoted to experimental works. Realistic spandrel beams in a building that lack torsional strength were modelled in this research, and strengthened to examine various behaviors such as load capacity, deflection, torque, twist, crack propagation, ductility, and failure modes. For this purpose, six RC beams were tested: four reference beams and two strengthened beams were used to observe additional capacity through the use of carbon fiber-reinforced polymer (CFRP) sheets. To strengthen the beams, one layer of sheets was completely wrapped around them. Results show an additional torsional capacity of 63% and 178% relative to their respective reference beams. Through strengthening, modes of failure of the beams changed from brittle torsion-dominated failure to shear-flexure failure in both beams. The study also included crack pattern and ductility of test beams. Cracks became smaller in width and more evenly distributed across the torsion-loaded area, and torsional ductility was enhanced by 266% and 165% respectively. Flexural ductility was also greatly enhanced by more than five folds. Finally, using ACI 318-14, ACI 440.2R-02, and available formulae in the literature, the beams were analyzed and the respective values were compared. Title: Torsional Strengthening of Reinforced Concrete Beams Using CFRP Composites Author: Rafeeq, Ranj Year: 2016 Few decades ago, there were no guidelines for torsion design of reinforced concrete (RC) beams. Hence, many existing beams in older buildings have a lack of adequate torsional strength since they were not properly designed for torsion. One way to regain/rehabilitate adequate torsional strength is through application of externally bonded carbon fiber reinforced polymers (CFRP). To date, American Concrete Institute (ACI) code, as well as other building codes, do not have recommendations or provisions for strengthening RC beams for torsion using fiber-reinforced polymer (FRP) composites due to the inexistence of conclusive experimental and analytical data. Of the very limited works on this behavior, the majority of the focus has been devoted to experimental works. Realistic spandrel beams in a building that lack torsional strength were modelled in this research, and strengthened to examine various behaviors such as load capacity, deflection, torque, twist, crack propagation, ductility, and failure modes. For this purpose, six RC beams were tested: four reference beams and two strengthened beams were used to observe additional capacity through the use of carbon fiber-reinforced polymer (CFRP) sheets. To strengthen the beams, one layer of sheets was completely wrapped around them. Results show an additional torsional capacity of 63% and 178% relative to their respective reference beams. Through strengthening, modes of failure of the beams changed from brittle torsion-dominated failure to shear-flexure failure in both beams. The study also included crack pattern and ductility of test beams. Cracks became smaller in width and more evenly distributed across the torsion-loaded area, and torsional ductility was enhanced by 266% and 165% respectively. Flexural ductility was also greatly enhanced by more than five folds. Finally, using ACI 318-14, ACI 440.2R-02, and available formulae in the literature, the beams were analyzed and the respective values were compared. Close

• 6. [Article] Behavior of Concrete Beams with Corroded Reinforcement Retrofitted with Carbon Fiber Reinforced Polymer

  Severe premature deterioration has been reported in a large number of reinforced concrete (RC) structures in corrosive environments. This research project focused on the behavior of beams that contained ...

  Citation × Citation Citation Abstract Copy Title: Behavior of Concrete Beams with Corroded Reinforcement Retrofitted with Carbon Fiber Reinforced Polymer Author: Lingga, Needa M. Year: 2016 Severe premature deterioration has been reported in a large number of reinforced concrete (RC) structures in corrosive environments. This research project focused on the behavior of beams that contained corroded steel and were retrofitted with CFRP. The steel in RC beams were assumed to be fully corroded, representing the most severe loss in steel cross-section. Unidirectional CFRP sheets were used to strengthen the deteriorated beams. The experimental program included testing five simply supported rectangular cross section concrete beams. All beams were approximately 1/3rd scale models, 4in. x 6in. cross sections, and 6ft. long. In three beams, the oiled steel rebars for flexure and shear were safely pulled out of the formwork after the concrete had cured a few hours, leaving voids. This technique was used to represent the total loss in steel cross-section in an extremely corrosive environment. The first specimen was a control beam with voids representing deteriorated steel. The second specimen was a plain concrete beam without voids. The third beam was another control specimen with flexural and shear reinforcement intact, representing the “original” beam before steel corrosion. The two remaining deteriorated beams were strengthened by externally bonding one and two layers of CFRP in the longitudinal and transverse directions. Beams were tested under third-point loading. Load carrying capacity, deflection, and ductility of the beams were measured. Test results showed that one layer of CFRP increased the load capacity to slightly higher than the “original” control beam, and two layers of CFRP increased it by a factor of two. The retrofitted specimens had a higher stiffness under service load conditions. The predict contribution of CFRP to flexure and shear capacities based on ACI 440.2R guidelines were in good agreement with test results. Title: Behavior of Concrete Beams with Corroded Reinforcement Retrofitted with Carbon Fiber Reinforced Polymer Author: Lingga, Needa M. Year: 2016 Severe premature deterioration has been reported in a large number of reinforced concrete (RC) structures in corrosive environments. This research project focused on the behavior of beams that contained corroded steel and were retrofitted with CFRP. The steel in RC beams were assumed to be fully corroded, representing the most severe loss in steel cross-section. Unidirectional CFRP sheets were used to strengthen the deteriorated beams. The experimental program included testing five simply supported rectangular cross section concrete beams. All beams were approximately 1/3rd scale models, 4in. x 6in. cross sections, and 6ft. long. In three beams, the oiled steel rebars for flexure and shear were safely pulled out of the formwork after the concrete had cured a few hours, leaving voids. This technique was used to represent the total loss in steel cross-section in an extremely corrosive environment. The first specimen was a control beam with voids representing deteriorated steel. The second specimen was a plain concrete beam without voids. The third beam was another control specimen with flexural and shear reinforcement intact, representing the “original” beam before steel corrosion. The two remaining deteriorated beams were strengthened by externally bonding one and two layers of CFRP in the longitudinal and transverse directions. Beams were tested under third-point loading. Load carrying capacity, deflection, and ductility of the beams were measured. Test results showed that one layer of CFRP increased the load capacity to slightly higher than the “original” control beam, and two layers of CFRP increased it by a factor of two. The retrofitted specimens had a higher stiffness under service load conditions. The predict contribution of CFRP to flexure and shear capacities based on ACI 440.2R guidelines were in good agreement with test results. Close

• 7. [Article] Key Aspects for LRFD Implementation of Driven Pile Capacity by Dynamic Methods

  Inputs and interpretation procedures for pile wave equation analysis, which correlates measured field dynamic driving response to axial pile static capacity, are highly dependent on site-specific soil ...

  Citation × Citation Citation Abstract Copy Title: Key Aspects for LRFD Implementation of Driven Pile Capacity by Dynamic Methods Author: Ehrlich, Natalie R Year: 2015 Inputs and interpretation procedures for pile wave equation analysis, which correlates measured field dynamic driving response to axial pile static capacity, are highly dependent on site-specific soil conditions and field practices. The 6th Edition of the AASHTO LRFD Bridge Design Specifications provide generalized guidelines for pile design, but do not account for variability in region-specific soils and field practices. A comprehensive literature review of region-specific resistance factor recalibration efforts across the U.S. has given insight into the range of implementation issues encountered, especially the key decisions around choosing a restrike (BOR), along with measures of efficiency and treatment of time-dependent capacity gain through pile set-up for BOR. A reevaluation and statistical exploration of cases within the extensive Portland State University (PSU) Pile Load Test Database offers special insight into the implementation issues for the PSU recalibration effort specific to Oregon Department of Transportation (ODOT) and Pacific Northwest Practice. The information gathered from this research provides a general commentary on increased foundation reliability and guidance for approaches to implementation of LRFD bridge pile foundation design into practice. Title: Key Aspects for LRFD Implementation of Driven Pile Capacity by Dynamic Methods Author: Ehrlich, Natalie R Year: 2015 Inputs and interpretation procedures for pile wave equation analysis, which correlates measured field dynamic driving response to axial pile static capacity, are highly dependent on site-specific soil conditions and field practices. The 6th Edition of the AASHTO LRFD Bridge Design Specifications provide generalized guidelines for pile design, but do not account for variability in region-specific soils and field practices. A comprehensive literature review of region-specific resistance factor recalibration efforts across the U.S. has given insight into the range of implementation issues encountered, especially the key decisions around choosing a restrike (BOR), along with measures of efficiency and treatment of time-dependent capacity gain through pile set-up for BOR. A reevaluation and statistical exploration of cases within the extensive Portland State University (PSU) Pile Load Test Database offers special insight into the implementation issues for the PSU recalibration effort specific to Oregon Department of Transportation (ODOT) and Pacific Northwest Practice. The information gathered from this research provides a general commentary on increased foundation reliability and guidance for approaches to implementation of LRFD bridge pile foundation design into practice. Close

• 8. [Article] Value of Travel Time Reliability Part II: A Study of Tradeoffs Between Travel Reliability, Congestion Mitigation Strategies and Emissions

  Capacity, demand, and vehicle based emissions reduction strategies are compared for several pollutants employing aggregate US congestion and vehicle fleet condition data. We find that congestion mitigation ...

  Citation × Citation Citation Abstract Copy Title: Value of Travel Time Reliability Part II: A Study of Tradeoffs Between Travel Reliability, Congestion Mitigation Strategies and Emissions Author: Figliozzi, Miguel A., Bigazzi, Alexander Y. Year: 2012 Capacity, demand, and vehicle based emissions reduction strategies are compared for several pollutants employing aggregate US congestion and vehicle fleet condition data. We find that congestion mitigation does not inevitably lead to reduced emissions; the net effect of mitigation depends on the balance of induced travel demand and increased vehicle efficiency that in turn depend on the pollutant, congestion level, and fleet composition. In the long run, capacity-based congestion improvements within certain speed intervals can reasonably be expected to increase emissions of CO2e, CO, and NOx through increased vehicle travel volume. Better opportunities for emissions reductions exist for HC and PM2.5 emissions, and on more heavily congested arterials. Advanced-efficiency vehicles with emissions rates that are less sensitive to congestion than conventional vehicles generate less emissions co-benefits from congestion mitigation. Title: Value of Travel Time Reliability Part II: A Study of Tradeoffs Between Travel Reliability, Congestion Mitigation Strategies and Emissions Author: Figliozzi, Miguel A., Bigazzi, Alexander Y. Year: 2012 Capacity, demand, and vehicle based emissions reduction strategies are compared for several pollutants employing aggregate US congestion and vehicle fleet condition data. We find that congestion mitigation does not inevitably lead to reduced emissions; the net effect of mitigation depends on the balance of induced travel demand and increased vehicle efficiency that in turn depend on the pollutant, congestion level, and fleet composition. In the long run, capacity-based congestion improvements within certain speed intervals can reasonably be expected to increase emissions of CO2e, CO, and NOx through increased vehicle travel volume. Better opportunities for emissions reductions exist for HC and PM2.5 emissions, and on more heavily congested arterials. Advanced-efficiency vehicles with emissions rates that are less sensitive to congestion than conventional vehicles generate less emissions co-benefits from congestion mitigation. Close

• 9. [Article] Modeling the Response of Dissolved Oxygen to Phosphorus Loading in Lake Spokane

  Mathematical models of hydrodynamics and water quality are often used to determine the assimilative capacity of a waterbody when waterbodies violate state water quality standards. A model of the Spokane ...

  Citation × Citation Citation Abstract Copy Title: Modeling the Response of Dissolved Oxygen to Phosphorus Loading in Lake Spokane Author: Wells, Scott A., Berger, Chris J. Year: 2016 Mathematical models of hydrodynamics and water quality are often used to determine the assimilative capacity of a waterbody when waterbodies violate state water quality standards. A model of the Spokane River and Lake Spokane in eastern Washington was developed to evaluate the assimilative capacity of the waterbody by setting a total maximum daily load (TMDL). A CE-QUAL-W2 model of this system was developed to establish the TMDL limits for the critical low-flow year of 2001. A recent paper evaluated this model and raised several issues about the validity of this model application as a regulatory tool related to its ability to predict total phosphorus, dissolved oxygen, and chlorophyll a relationships. This paper analyzes the validity of their critiques. For example, the critique used an incorrect formula to calculate total phosphorus inflows into Lake Spokane and used a volume-weighted minimum hypolimnetic dissolved oxygen (DOmin) that was not representative of hypolimnetic conditions. They also assumed incorrectly that the hydrologic, meteorological, operational, and sediment conditions of the 2001 TMDL model would be representative of conditions in other years. Although the water quality model of Lake Spokane can be improved, the critique does not invalidate the model as a tool to evaluate how the lake responds to nutrient environmental controls. Title: Modeling the Response of Dissolved Oxygen to Phosphorus Loading in Lake Spokane Author: Wells, Scott A., Berger, Chris J. Year: 2016 Mathematical models of hydrodynamics and water quality are often used to determine the assimilative capacity of a waterbody when waterbodies violate state water quality standards. A model of the Spokane River and Lake Spokane in eastern Washington was developed to evaluate the assimilative capacity of the waterbody by setting a total maximum daily load (TMDL). A CE-QUAL-W2 model of this system was developed to establish the TMDL limits for the critical low-flow year of 2001. A recent paper evaluated this model and raised several issues about the validity of this model application as a regulatory tool related to its ability to predict total phosphorus, dissolved oxygen, and chlorophyll a relationships. This paper analyzes the validity of their critiques. For example, the critique used an incorrect formula to calculate total phosphorus inflows into Lake Spokane and used a volume-weighted minimum hypolimnetic dissolved oxygen (DOmin) that was not representative of hypolimnetic conditions. They also assumed incorrectly that the hydrologic, meteorological, operational, and sediment conditions of the 2001 TMDL model would be representative of conditions in other years. Although the water quality model of Lake Spokane can be improved, the critique does not invalidate the model as a tool to evaluate how the lake responds to nutrient environmental controls. Close

• 10. [Article] Application of LRFD Geotechnical Principles for Pile Supported Bridges in Oregon: Phase 1

  Bridge foundations must be designed based on acceptable risks of failure. To secure rapid implementation of Load Resistance Factor Design (LRFD) principles for foundation design, the American Association ...

  Citation × Citation Citation Abstract Copy Title: Application of LRFD Geotechnical Principles for Pile Supported Bridges in Oregon: Phase 1 Author: Smith, Trevor D., Dusicka, Peter Year: 2009 Bridge foundations must be designed based on acceptable risks of failure. To secure rapid implementation of Load Resistance Factor Design (LRFD) principles for foundation design, the American Association of State Highway and Transportation Officials (AASHTO) and the Federal Highway Administration (FHWA) are requiring their use through AASHTO code. The Bridge Section of the Oregon Department of Transportation (ODOT) has responsibility for satisfactory design of all the bridge structures across the state’s highway system. The widespread geotechnical adoption of the LRFD code throughout state DOTs has been difficult in the case of deep foundations due to regional differences and in some cases a lack of any close match to DOT foundation practices. This lack of matching stems from the source research conducted on which the code is based, documented as NCHRP 507. For ODOT, the evaluation of nominal axial static capacity for each driven pile in the field is conducted by dynamic methods and AASHTO offers resistance factors for these techniques. ODOT typically uses the wave equation software (WEAP) applied at the end of initial driving, EOID, and occasionally at the beginning of pile restrike (BOR) to capture increases in capacity from set-up. This study reports that, based on past and new surveys, ODOT practice is reasonably typical for DOT practice in sands, silts, and clays. The AASHTO resistance factor, φ, for WEAP is at EOID and is too low for the efficient design of piles to match the likely probabilities of pile failure. The survey of Northwest state DOTs revealed that 80% of the DOTs believe that a φ of 0.4 is conservative and 37.5 % do not use the AASHTO-sanctioned φ of 0.4. Matching LRFD to allowable stress design (ASD) by direct calibration for a single pile, without any reported capacity bias, sets φ as 0.55 to match the ASD factor of safety of 2.5. An ODOT case history of a recently completed pilesupported bridge designed and constructed to FHWA and AASHTO ASD standards in use at that time, shows the number of piles at the bent studied would be doubled under new AASHTO requirements. This suggests the standard will add considerable pile foundation costs to all new bridges. This cost increase is a strong incentive to complete statistical recalibration of GRLWEAP dynamic capacity resistance value in a Phase 2 of this study. Title: Application of LRFD Geotechnical Principles for Pile Supported Bridges in Oregon: Phase 1 Author: Smith, Trevor D., Dusicka, Peter Year: 2009 Bridge foundations must be designed based on acceptable risks of failure. To secure rapid implementation of Load Resistance Factor Design (LRFD) principles for foundation design, the American Association of State Highway and Transportation Officials (AASHTO) and the Federal Highway Administration (FHWA) are requiring their use through AASHTO code. The Bridge Section of the Oregon Department of Transportation (ODOT) has responsibility for satisfactory design of all the bridge structures across the state’s highway system. The widespread geotechnical adoption of the LRFD code throughout state DOTs has been difficult in the case of deep foundations due to regional differences and in some cases a lack of any close match to DOT foundation practices. This lack of matching stems from the source research conducted on which the code is based, documented as NCHRP 507. For ODOT, the evaluation of nominal axial static capacity for each driven pile in the field is conducted by dynamic methods and AASHTO offers resistance factors for these techniques. ODOT typically uses the wave equation software (WEAP) applied at the end of initial driving, EOID, and occasionally at the beginning of pile restrike (BOR) to capture increases in capacity from set-up. This study reports that, based on past and new surveys, ODOT practice is reasonably typical for DOT practice in sands, silts, and clays. The AASHTO resistance factor, φ, for WEAP is at EOID and is too low for the efficient design of piles to match the likely probabilities of pile failure. The survey of Northwest state DOTs revealed that 80% of the DOTs believe that a φ of 0.4 is conservative and 37.5 % do not use the AASHTO-sanctioned φ of 0.4. Matching LRFD to allowable stress design (ASD) by direct calibration for a single pile, without any reported capacity bias, sets φ as 0.55 to match the ASD factor of safety of 2.5. An ODOT case history of a recently completed pilesupported bridge designed and constructed to FHWA and AASHTO ASD standards in use at that time, shows the number of piles at the bent studied would be doubled under new AASHTO requirements. This suggests the standard will add considerable pile foundation costs to all new bridges. This cost increase is a strong incentive to complete statistical recalibration of GRLWEAP dynamic capacity resistance value in a Phase 2 of this study. Close