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• 1. [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

• 2. [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

• 3. [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

• 4. [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

• 5. [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

• 6. [Article] Feasibility Determination Guide for the Road Diet Plus - A 5/4 Lane to 2 Lane Road Diet

  Road diets are a popular tool for corridor improvement. Road diets are normally defined as the conversion of a four-lane undivided road to a three-lane undivided road made up of two through lanes separated ...

  Citation × Citation Citation Abstract Copy Title: Feasibility Determination Guide for the Road Diet Plus - A 5/4 Lane to 2 Lane Road Diet Author: Williams, Michael Year: 2017 Road diets are a popular tool for corridor improvement. Road diets are normally defined as the conversion of a four-lane undivided road to a three-lane undivided road made up of two through lanes separated by a center two-way-left-turn-lane (known as a TWLTL). This new configuration has similar vehicular capacity, greater safety and frees up right-of-way for other uses. This work examines the possibility of going one step, or one lane, further. What is the possibility of reducing five- or four-lane roads to two-lanes? If this is possible, what are the corridor characteristics within which this process would be feasible? The transformation of five- or four-lane roads to two-lane roads becomes possible through the replacement of signalized and stop-controlled intersections with roundabouts. Roundabouts allow all left-hand turns along a street segment to be replaced with a U-turn at the roundabout followed by a right turn. With roundabouts, the TWLTL can be removed thereby creating a 2-lane road. Two major questions arise when determining the feasibility of this conversion. First, under what traffic conditions is this conversion possible? Second, does sufficient right-of-way exist for the conversion of standard intersections to roundabouts? This paper will examine corridors which have undergone this transformation to estimate the envelope within which this conversion is possible. It will provide estimates of the size of roundabouts for desired capacities and a traffic volume ceiling for the corridor. This work is limited to road diets resulting in corridors with two traffic lanes and single lane roundabouts. The final result of this work is a pamphlet similar to the 2014 FHWA Road Diet Informational Guide. The intent is to create a guide that accomplishes two goals. The first is to popularize a powerful strategy for roadway renovation. The second is to provide a tool that allows agencies to evaluate whether a chosen corridor is a possible candidate for this conversion. Title: Feasibility Determination Guide for the Road Diet Plus - A 5/4 Lane to 2 Lane Road Diet Author: Williams, Michael Year: 2017 Road diets are a popular tool for corridor improvement. Road diets are normally defined as the conversion of a four-lane undivided road to a three-lane undivided road made up of two through lanes separated by a center two-way-left-turn-lane (known as a TWLTL). This new configuration has similar vehicular capacity, greater safety and frees up right-of-way for other uses. This work examines the possibility of going one step, or one lane, further. What is the possibility of reducing five- or four-lane roads to two-lanes? If this is possible, what are the corridor characteristics within which this process would be feasible? The transformation of five- or four-lane roads to two-lane roads becomes possible through the replacement of signalized and stop-controlled intersections with roundabouts. Roundabouts allow all left-hand turns along a street segment to be replaced with a U-turn at the roundabout followed by a right turn. With roundabouts, the TWLTL can be removed thereby creating a 2-lane road. Two major questions arise when determining the feasibility of this conversion. First, under what traffic conditions is this conversion possible? Second, does sufficient right-of-way exist for the conversion of standard intersections to roundabouts? This paper will examine corridors which have undergone this transformation to estimate the envelope within which this conversion is possible. It will provide estimates of the size of roundabouts for desired capacities and a traffic volume ceiling for the corridor. This work is limited to road diets resulting in corridors with two traffic lanes and single lane roundabouts. The final result of this work is a pamphlet similar to the 2014 FHWA Road Diet Informational Guide. The intent is to create a guide that accomplishes two goals. The first is to popularize a powerful strategy for roadway renovation. The second is to provide a tool that allows agencies to evaluate whether a chosen corridor is a possible candidate for this conversion. Close

• 7. [Article] Seismic Retrofitting of Existing Structures

  This research project will give a brief presentation about earthquake resistant design and the methodology about seismic evaluation and rehabilitation of existing structures. It also provides certain aspects ...

  Citation × Citation Citation Abstract Copy Title: Seismic Retrofitting of Existing Structures Author: Sahin, Cetin Year: 2014 This research project will give a brief presentation about earthquake resistant design and the methodology about seismic evaluation and rehabilitation of existing structures. It also provides certain aspects of computer software modeling against seismic loads and shows the necessity of seismic upgrading in a steel moment-frame building. The seismic evaluation process consists of investigating if the structure meets the defined target structural performance levels. The main goal during earthquakes is to assure that building collapse doesn’t occur and the risk of death or injury to people is minimized and beyond that to satisfy post-earthquake performance level for defined range of of seismic hazards. Also seismic evaluation will determine which are the most vulnerable and weak components and deficiencies of a building during an expected earthquake. The seismic rehabilitation process aims to improve seismic performance and correct the deficiencies by increasing strength, stiffness or deformation capacity and improving connections. Thus, a proposed retrofit implementation can be said to be successful if it results an increase in strength and ductility capacity of the structure which is greater than the demands imposed by earthquakes. Performance-based design aims to utilize performance objectives to determine acceptable levels of damage for a given earthquake hazard for new buildings or upgrade of existing buildings. These performance objectives can be such as limiting story drift, minimizing component damage etc. This study shows how to model a building in computer software and analyze its seismic resistance with linear methods and propose concentrically braced frame rehabilitation in order to increase the drift capacity. It also describes how the linear analysis may be followed by the pushover analysis in order to estimate the seismic resistance of retrofitted structure. One of the most significant advantages of nonlinear pushover analysis beyond the linear analyses is the opportunity to evaluate damage. The pushover analysis can give valuable information about performance of building in expected future seismic events. Generally, the structural retrofit of concentrically braced frames improved the seismic resistance of the building and it can be considered in the retrofit of moment frame structures to prevent the risk of structural collapse under the design load with much more confidence. Title: Seismic Retrofitting of Existing Structures Author: Sahin, Cetin Year: 2014 This research project will give a brief presentation about earthquake resistant design and the methodology about seismic evaluation and rehabilitation of existing structures. It also provides certain aspects of computer software modeling against seismic loads and shows the necessity of seismic upgrading in a steel moment-frame building. The seismic evaluation process consists of investigating if the structure meets the defined target structural performance levels. The main goal during earthquakes is to assure that building collapse doesn’t occur and the risk of death or injury to people is minimized and beyond that to satisfy post-earthquake performance level for defined range of of seismic hazards. Also seismic evaluation will determine which are the most vulnerable and weak components and deficiencies of a building during an expected earthquake. The seismic rehabilitation process aims to improve seismic performance and correct the deficiencies by increasing strength, stiffness or deformation capacity and improving connections. Thus, a proposed retrofit implementation can be said to be successful if it results an increase in strength and ductility capacity of the structure which is greater than the demands imposed by earthquakes. Performance-based design aims to utilize performance objectives to determine acceptable levels of damage for a given earthquake hazard for new buildings or upgrade of existing buildings. These performance objectives can be such as limiting story drift, minimizing component damage etc. This study shows how to model a building in computer software and analyze its seismic resistance with linear methods and propose concentrically braced frame rehabilitation in order to increase the drift capacity. It also describes how the linear analysis may be followed by the pushover analysis in order to estimate the seismic resistance of retrofitted structure. One of the most significant advantages of nonlinear pushover analysis beyond the linear analyses is the opportunity to evaluate damage. The pushover analysis can give valuable information about performance of building in expected future seismic events. Generally, the structural retrofit of concentrically braced frames improved the seismic resistance of the building and it can be considered in the retrofit of moment frame structures to prevent the risk of structural collapse under the design load with much more confidence. Close

• 8. [Article] A Coordinated Location-Inventory Problem in Closed-Loop Supply Chain

  This paper considers a coordinated location-inventory model under uncertain demands for a closed loop supply chain comprising of one plant, forward and reverse distribution centers, and retailers. The ...

  Citation × Citation Citation Abstract Copy Title: A Coordinated Location-Inventory Problem in Closed-Loop Supply Chain Author: Zhang, Zhi-Hai, Unnikrishnan, Avinash Year: 2016 This paper considers a coordinated location-inventory model under uncertain demands for a closed loop supply chain comprising of one plant, forward and reverse distribution centers, and retailers. The inventory of new and returned products is managed at forward and reverse distribution centers respectively through a periodic review policy. The proposed model determines the location of forward and reverse distribution centers and the associated capacities, the review intervals of the inventory policy at distribution centers, and the assignments of retailers to the distribution centers. We model six different coordination strategies. All the models are formulated as nonlinear integer programs with chance constraints and transformed to conic quadratic mixed-integer programs that can be efficiently solved by CPLEX. An outer approximation based solution algorithm is developed to solve the conic quadratic mixed-integer program. The benefit of different types of coordination strategies is shown through extensive computational testing. Title: A Coordinated Location-Inventory Problem in Closed-Loop Supply Chain Author: Zhang, Zhi-Hai, Unnikrishnan, Avinash Year: 2016 This paper considers a coordinated location-inventory model under uncertain demands for a closed loop supply chain comprising of one plant, forward and reverse distribution centers, and retailers. The inventory of new and returned products is managed at forward and reverse distribution centers respectively through a periodic review policy. The proposed model determines the location of forward and reverse distribution centers and the associated capacities, the review intervals of the inventory policy at distribution centers, and the assignments of retailers to the distribution centers. We model six different coordination strategies. All the models are formulated as nonlinear integer programs with chance constraints and transformed to conic quadratic mixed-integer programs that can be efficiently solved by CPLEX. An outer approximation based solution algorithm is developed to solve the conic quadratic mixed-integer program. The benefit of different types of coordination strategies is shown through extensive computational testing. Close

• 9. [Article] Behavior of Reinforced Concrete Beams Retrofitted in Flexure Using CFRP-NSM Technique

  A variety of retrofitting methods are used to upgrade existing structures. For example, steel plates and Fiber Reinforced Polymer (FRP) jackets are externally bonded to members to increase their capacity ...

  Citation × Citation Citation Abstract Copy Title: Behavior of Reinforced Concrete Beams Retrofitted in Flexure Using CFRP-NSM Technique Author: Al-Obaidi, Salam Year: 2015 A variety of retrofitting methods are used to upgrade existing structures. For example, steel plates and Fiber Reinforced Polymer (FRP) jackets are externally bonded to members to increase their capacity in flexure and shear. However, due to the issue of corrosion these strengthening systems may lose their efficiency with time. FRP materials have been used to strengthen many structural components of different shapes and types. FRP jackets, FRP Strips, and FRP rods have commonly been used to rehabilitate existing structural components. The many advantages of using FRP as strengthening materials have made this material an attractive alternative: advantages such as lightweight, high strength, and ease of setting up. Among the many applications using FRP, Near Surface Mounted -- Fiber Reinforced polymer (NSM-FRP) is a promising technique used to strengthen concrete members. However, de-bonding issues have to be overcome to make this technique efficient and reliable. The NSM-FRP technique consists of making a groove along the surface of the concrete member to be retrofitted with depth less than the cover of the member. After cleaning the groove, epoxy paste is used to fill two-thirds of the groove's depth. The FRP element is then mounted in the groove. Finally, the groove is filled with epoxy and the excessive epoxy is leveled with surface of the concrete. This technique makes the FRP material completely covered by epoxy in the cover of the concrete. This method can be used for strengthening both the positive and negative moment regions of girders and slabs. Groove size, paste, concrete, and rods properties are the main variables that control the efficiency of the NSM-FRP rods. The main objective of this research project is to determine the behavior of reinforced concrete beams that are strengthened with NSM-CFRP reinforcement bars. In this research project, the bond characteristics of NSM-CFRP reinforcement bars are first determined from pullout tests. Then, NSM-CFRP rods are installed in reinforced concrete beams and the beams are tested. Loads, strains, and deflections are measured and theoretical and measured capacities are compared. Finally, the reliability and efficiency of using NSM-CFRP rods technique in retrofitting existing structures is observed. Title: Behavior of Reinforced Concrete Beams Retrofitted in Flexure Using CFRP-NSM Technique Author: Al-Obaidi, Salam Year: 2015 A variety of retrofitting methods are used to upgrade existing structures. For example, steel plates and Fiber Reinforced Polymer (FRP) jackets are externally bonded to members to increase their capacity in flexure and shear. However, due to the issue of corrosion these strengthening systems may lose their efficiency with time. FRP materials have been used to strengthen many structural components of different shapes and types. FRP jackets, FRP Strips, and FRP rods have commonly been used to rehabilitate existing structural components. The many advantages of using FRP as strengthening materials have made this material an attractive alternative: advantages such as lightweight, high strength, and ease of setting up. Among the many applications using FRP, Near Surface Mounted -- Fiber Reinforced polymer (NSM-FRP) is a promising technique used to strengthen concrete members. However, de-bonding issues have to be overcome to make this technique efficient and reliable. The NSM-FRP technique consists of making a groove along the surface of the concrete member to be retrofitted with depth less than the cover of the member. After cleaning the groove, epoxy paste is used to fill two-thirds of the groove's depth. The FRP element is then mounted in the groove. Finally, the groove is filled with epoxy and the excessive epoxy is leveled with surface of the concrete. This technique makes the FRP material completely covered by epoxy in the cover of the concrete. This method can be used for strengthening both the positive and negative moment regions of girders and slabs. Groove size, paste, concrete, and rods properties are the main variables that control the efficiency of the NSM-FRP rods. The main objective of this research project is to determine the behavior of reinforced concrete beams that are strengthened with NSM-CFRP reinforcement bars. In this research project, the bond characteristics of NSM-CFRP reinforcement bars are first determined from pullout tests. Then, NSM-CFRP rods are installed in reinforced concrete beams and the beams are tested. Loads, strains, and deflections are measured and theoretical and measured capacities are compared. Finally, the reliability and efficiency of using NSM-CFRP rods technique in retrofitting existing structures is observed. Close

• 10. [Article] Experimental Investigation of Fiber Reinforced Concrete Beams

  Shear strength of fiber reinforced concrete beams was studied in this research project. Three types of fibers were examined: hooked-end steel fiber, crimped-steel fiber, and crimped-monofilament polypropylene ...

  Citation × Citation Citation Abstract Copy Title: Experimental Investigation of Fiber Reinforced Concrete Beams Author: Al-lami, Karrar Ali Year: 2015 Shear strength of fiber reinforced concrete beams was studied in this research project. Three types of fibers were examined: hooked-end steel fiber, crimped-steel fiber, and crimped-monofilament polypropylene fibers. The experimental program included five beam specimens. Two of the beams were control specimens in which one was reinforced with minimum shear reinforcement according to ACI 318, while the other one did not have any shear reinforcement. Each one of the other three specimens was reinforced with one of the above mentioned fibers by 1% volumetric ratio. In addition to the beam specimens, three prisms were also made for each type fiber to determine their toughness. The aim of this research was to investigate the following questions for medium-high concrete strength 1) to evaluate the effectiveness of each type of fibers on the shear strength, 2) to investigate the shear strength, toughness, crack patterns and near ultimate load crack width of each beam, and 3) to determine if using 1% volumetric ratio of fibers as shear reinforcement in beams would provide adequate strength and stiffness properties comparable to reinforcing steel used as minimum shear reinforcement. The results showed that all three types of fibers increased the shear capacity of the beam specimens more than the beam reinforced with minimum shear reinforcement. Moreover, some of the fibers used could shift the type of failure from a pure shear failure to a combined flexural-shear or pure flexural failure. Title: Experimental Investigation of Fiber Reinforced Concrete Beams Author: Al-lami, Karrar Ali Year: 2015 Shear strength of fiber reinforced concrete beams was studied in this research project. Three types of fibers were examined: hooked-end steel fiber, crimped-steel fiber, and crimped-monofilament polypropylene fibers. The experimental program included five beam specimens. Two of the beams were control specimens in which one was reinforced with minimum shear reinforcement according to ACI 318, while the other one did not have any shear reinforcement. Each one of the other three specimens was reinforced with one of the above mentioned fibers by 1% volumetric ratio. In addition to the beam specimens, three prisms were also made for each type fiber to determine their toughness. The aim of this research was to investigate the following questions for medium-high concrete strength 1) to evaluate the effectiveness of each type of fibers on the shear strength, 2) to investigate the shear strength, toughness, crack patterns and near ultimate load crack width of each beam, and 3) to determine if using 1% volumetric ratio of fibers as shear reinforcement in beams would provide adequate strength and stiffness properties comparable to reinforcing steel used as minimum shear reinforcement. The results showed that all three types of fibers increased the shear capacity of the beam specimens more than the beam reinforced with minimum shear reinforcement. Moreover, some of the fibers used could shift the type of failure from a pure shear failure to a combined flexural-shear or pure flexural failure. Close