Mahsa Farzad, Saiada Fuadi Fancy, A. Azizinamini, K. Lau
{"title":"Effect of Concrete Moisture on Macrocell Development in Repair of Reinforced Concrete Substructure with UHPC","authors":"Mahsa Farzad, Saiada Fuadi Fancy, A. Azizinamini, K. Lau","doi":"10.21838/uhpc.9682","DOIUrl":"https://doi.org/10.21838/uhpc.9682","url":null,"abstract":"","PeriodicalId":170570,"journal":{"name":"Second International Interactive Symposium on UHPC","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133778509","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Advanced behavior of Ultra High Performance Concrete (UHPC) is attracting a growing interest in the construction industry worldwide. Currently, UHPC is used widely in bridge deck joints and connections, while it has a great potential to be extended to larger structural applications. However, the structural behavior of UHPC for larger components is still not fully understood. The objective of this study is to better understand the overall behavior and failure mechanism of UHPC components (mainly bridge columns) using detailed finite element modeling. In particular, this paper investigates the validity of Total Strain Crack model, as a readily implemented model in DIANA FEA software, in capturing UHPC columns failure mechanism. The uniaxial behavior of UHPC in tension and compression are independently defined using the existing uniaxial stressstrain curves from the literature. The pushover response of a two-column bent of a prototype bridge with the typical geometry available in Caltrans Bridge Academy documents is studied. Besides, a reference two-column bent, of conventional concrete with the same geometry, is modeled. The reference bent is used to investigate the relative increases in strength and ductility capacities of UHPC column compared to the conventional one. Furthermore, the effect of different reinforcement ratios, steel grades and steel hardening effects on the overall behavior of UHPC columns are investigated.
{"title":"Pushover Analysis and Seismic Response of UHPC Two-Column Bridge Bent","authors":"Negar Naeimi, M. Moustafa","doi":"10.21838/uhpc.9664","DOIUrl":"https://doi.org/10.21838/uhpc.9664","url":null,"abstract":"Advanced behavior of Ultra High Performance Concrete (UHPC) is attracting a growing interest in the construction industry worldwide. Currently, UHPC is used widely in bridge deck joints and connections, while it has a great potential to be extended to larger structural applications. However, the structural behavior of UHPC for larger components is still not fully understood. The objective of this study is to better understand the overall behavior and failure mechanism of UHPC components (mainly bridge columns) using detailed finite element modeling. In particular, this paper investigates the validity of Total Strain Crack model, as a readily implemented model in DIANA FEA software, in capturing UHPC columns failure mechanism. The uniaxial behavior of UHPC in tension and compression are independently defined using the existing uniaxial stressstrain curves from the literature. The pushover response of a two-column bent of a prototype bridge with the typical geometry available in Caltrans Bridge Academy documents is studied. Besides, a reference two-column bent, of conventional concrete with the same geometry, is modeled. The reference bent is used to investigate the relative increases in strength and ductility capacities of UHPC column compared to the conventional one. Furthermore, the effect of different reinforcement ratios, steel grades and steel hardening effects on the overall behavior of UHPC columns are investigated.","PeriodicalId":170570,"journal":{"name":"Second International Interactive Symposium on UHPC","volume":"220 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124344135","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is a material characterized by very high compressive strength, excellent durability and damage tolerance. For a UHPFRC beam works under bending, steel fibers distributed in the beam compressive zone has insignificant effects on the improvement of its flexural capacity. To use the fibers more efficiently, this paper applies the concept of layered-structure to UHPFRC beam. A double-layered UHPFRC beam composed of a top plain UHPC layer and a bottom UHPFRC layer containing 2% steel fibers is designed. In the experimental section, basic mechanical properties of the individual UHPC and UHPFRC layers are investigated. Compression, split tension and bending tests are conducted, the results of which provide input parameters and model validation for the simulation section. The effects of layer thickness on the beam flexural properties and stress distributions are analyzed numerically with the validated model, and the results show that the peak flexural load and the energy increase with the increase of the UHPFRC layer thickness. Results from this study shed lights on the design of layered UHPFRC structures, and contribute to the application of layered UHPFRC in engineering constructions.
{"title":"Experimental and Modeling Study of Double-layered UHPFRC under Bending","authors":"Y.Y.Y. Cao, Q. L. Yu, J. Brouwers","doi":"10.21838/uhpc.9651","DOIUrl":"https://doi.org/10.21838/uhpc.9651","url":null,"abstract":"Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is a material characterized by very high compressive strength, excellent durability and damage tolerance. For a UHPFRC beam works under bending, steel fibers distributed in the beam compressive zone has insignificant effects on the improvement of its flexural capacity. To use the fibers more efficiently, this paper applies the concept of layered-structure to UHPFRC beam. A double-layered UHPFRC beam composed of a top plain UHPC layer and a bottom UHPFRC layer containing 2% steel fibers is designed. In the experimental section, basic mechanical properties of the individual UHPC and UHPFRC layers are investigated. Compression, split tension and bending tests are conducted, the results of which provide input parameters and model validation for the simulation section. The effects of layer thickness on the beam flexural properties and stress distributions are analyzed numerically with the validated model, and the results show that the peak flexural load and the energy increase with the increase of the UHPFRC layer thickness. Results from this study shed lights on the design of layered UHPFRC structures, and contribute to the application of layered UHPFRC in engineering constructions.","PeriodicalId":170570,"journal":{"name":"Second International Interactive Symposium on UHPC","volume":"59 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126274697","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is a relatively new construction material with superior mechanical properties. The addition of fibers in UHPFRC has been recognized to significantly enhance its tensile strength, post-cracking ductility and energy absorption capacity. This study investigates the influence of fiber content on the mechanical properties of UHPFRC with coarse aggregates. By applying the Brouwers design method, UHPFRC with a maximum particle size of 8 mm is achieved. The incorporation of coarse basalt aggregates reduces the powder volume fraction in the matrix, and hence brings economic and environmental benefits. Experiments are conducted to investigate the effects of fiber content on the tensile and compressive strengths, as well as the flexural behavior of the UHPFRC. The results show that the compressive strength of the UHPFRC is almost independent on the fiber content. On the contrary, the tensile and the flexural strengths are significantly increased with the increase of the fiber content, and consequently the toughness of the UHPFRC composite has a prominent enhancement with the addition of the steel fibers as well.
{"title":"Effects of Fiber Content on Mechanical Properties of UHPFRC with Coarse Aggregates","authors":"Y.Y.Y. Cao, Q. L. Yu, P. Li, J. Brouwers","doi":"10.21838/uhpc.9652","DOIUrl":"https://doi.org/10.21838/uhpc.9652","url":null,"abstract":"Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is a relatively new construction material with superior mechanical properties. The addition of fibers in UHPFRC has been recognized to significantly enhance its tensile strength, post-cracking ductility and energy absorption capacity. This study investigates the influence of fiber content on the mechanical properties of UHPFRC with coarse aggregates. By applying the Brouwers design method, UHPFRC with a maximum particle size of 8 mm is achieved. The incorporation of coarse basalt aggregates reduces the powder volume fraction in the matrix, and hence brings economic and environmental benefits. Experiments are conducted to investigate the effects of fiber content on the tensile and compressive strengths, as well as the flexural behavior of the UHPFRC. The results show that the compressive strength of the UHPFRC is almost independent on the fiber content. On the contrary, the tensile and the flexural strengths are significantly increased with the increase of the fiber content, and consequently the toughness of the UHPFRC composite has a prominent enhancement with the addition of the steel fibers as well.","PeriodicalId":170570,"journal":{"name":"Second International Interactive Symposium on UHPC","volume":"48 23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132216612","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
First structural applications in ultra-high performances fiber reinforced concretes (UHPFRC) were mainly precast solutions, such as bridge components and architectural panels. In that context, most studies concerning the impact of temperature on UHPFRC properties concerned high curing temperatures feasible in precast industry where a high control of the production process can be obtained. More recent applications of UHPFRC concerned also cast-in-place solutions involving field-cast joints and thin repairs. Limited data is available on the impact of low to moderate mixing and curing temperatures found on construction sites. This paper describes a research project focused on the evaluation of fresh state and hardened properties of UHPFRC in realistic cast-inplace conditions. UHPFRC were produced between 10 to 30 °C and cured between 10 to 35 °C, measurements of slump flow, air content, density, compressive and bending strengths are presented and discussed.
{"title":"Impact of Mixing and Curing Temperatures on UHPFRC Properties","authors":"J. Charron, C. Androuët, Olivier Deaux","doi":"10.21838/uhpc.9693","DOIUrl":"https://doi.org/10.21838/uhpc.9693","url":null,"abstract":"First structural applications in ultra-high performances fiber reinforced concretes (UHPFRC) were mainly precast solutions, such as bridge components and architectural panels. In that context, most studies concerning the impact of temperature on UHPFRC properties concerned high curing temperatures feasible in precast industry where a high control of the production process can be obtained. More recent applications of UHPFRC concerned also cast-in-place solutions involving field-cast joints and thin repairs. Limited data is available on the impact of low to moderate mixing and curing temperatures found on construction sites. This paper describes a research project focused on the evaluation of fresh state and hardened properties of UHPFRC in realistic cast-inplace conditions. UHPFRC were produced between 10 to 30 °C and cured between 10 to 35 °C, measurements of slump flow, air content, density, compressive and bending strengths are presented and discussed.","PeriodicalId":170570,"journal":{"name":"Second International Interactive Symposium on UHPC","volume":"332 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122746701","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The exceptional compression strength and ductility of ultra-high-performance fiberreinforced concrete (UHP-FRC) can revolutionize the design of reinforced concrete structural members. While the maximum useable compressive strain, εcu, for conventional plain concrete is assumed to be 0.003 in current design codes (ACI 318 Building Code and AASHTO LRFD Bridge Design Specifications), UHP-FRC’s εcu is 5 to 10 times higher. Underestimating the compressive ductility of UHP-FRC limits the allowable maximum amount of longitudinal reinforcement, which in turn leads to limited flexural capacity of the members. Conventional reinforced concrete members are designed with a smaller amount of reinforcement to meet tension-controlled behavior. This design approach in turn leads to 1) a small ultimate flexural capacity, 2) a large amount of cracking and wider crack widths under service loads, which lead to a reduced member stiffness, 3) cracks that are less likely to close after overloading, 4) a small compression zone depth that allows cracks to propagate deeply, which further reduces the stiffness, 5) large strains in rebars, which reduce aggregate interlock and shear strength, and 6) considerable yielding of rebars, which causes bond deterioration. Contrary to the conventional design concept, a new ductileconcrete strong-reinforcement (DCSR) design concept is investigated in this study. A maximum useable compressive strain of 0.015 is considered for UHP-FRC, which allows a concrete member to maintain tension-controlled behavior while using a high amount of steel rebars. Accordingly, the flexural capacity of the section increases. This approach allows the UHP-FRC’s high compressive strength to be effectively utilized in the compression zone. The synergistic interaction of strong steel and tensile strength of UHP-FRC considerably increases the cracking resistance of the member. In addition, the number and size of initial microcracks are limited due to the strong bridging effect of a high amount of steel. Therefore, the member maintains its stiffness and small deflection under service loads. This feature permits eliminating prestressing in bridge girders, where an uncracked section is desired under service loads. Besides experimental evidence, a prototype single-span 250-ft long non-prestressed UHP-FRC decked bulb-tee (DBT) girder was designed using the DCSR concept. Finite element analysis with AASHTO loading confirms that the new UHP-FRC girder satisfies code requirements. The experimental and analytical results show that conventional precast prestressed concrete girders can be replaced by the new nonprestressed decked UHP-FRC girders.
{"title":"Toward A Non-Prestressed Precast Long-Span Bridge Girder Using UHP-FRC","authors":"S. Chao, Venkatesh Kaka, Missagh Shamshiri","doi":"10.21838/uhpc.9661","DOIUrl":"https://doi.org/10.21838/uhpc.9661","url":null,"abstract":"The exceptional compression strength and ductility of ultra-high-performance fiberreinforced concrete (UHP-FRC) can revolutionize the design of reinforced concrete structural members. While the maximum useable compressive strain, εcu, for conventional plain concrete is assumed to be 0.003 in current design codes (ACI 318 Building Code and AASHTO LRFD Bridge Design Specifications), UHP-FRC’s εcu is 5 to 10 times higher. Underestimating the compressive ductility of UHP-FRC limits the allowable maximum amount of longitudinal reinforcement, which in turn leads to limited flexural capacity of the members. Conventional reinforced concrete members are designed with a smaller amount of reinforcement to meet tension-controlled behavior. This design approach in turn leads to 1) a small ultimate flexural capacity, 2) a large amount of cracking and wider crack widths under service loads, which lead to a reduced member stiffness, 3) cracks that are less likely to close after overloading, 4) a small compression zone depth that allows cracks to propagate deeply, which further reduces the stiffness, 5) large strains in rebars, which reduce aggregate interlock and shear strength, and 6) considerable yielding of rebars, which causes bond deterioration. Contrary to the conventional design concept, a new ductileconcrete strong-reinforcement (DCSR) design concept is investigated in this study. A maximum useable compressive strain of 0.015 is considered for UHP-FRC, which allows a concrete member to maintain tension-controlled behavior while using a high amount of steel rebars. Accordingly, the flexural capacity of the section increases. This approach allows the UHP-FRC’s high compressive strength to be effectively utilized in the compression zone. The synergistic interaction of strong steel and tensile strength of UHP-FRC considerably increases the cracking resistance of the member. In addition, the number and size of initial microcracks are limited due to the strong bridging effect of a high amount of steel. Therefore, the member maintains its stiffness and small deflection under service loads. This feature permits eliminating prestressing in bridge girders, where an uncracked section is desired under service loads. Besides experimental evidence, a prototype single-span 250-ft long non-prestressed UHP-FRC decked bulb-tee (DBT) girder was designed using the DCSR concept. Finite element analysis with AASHTO loading confirms that the new UHP-FRC girder satisfies code requirements. The experimental and analytical results show that conventional precast prestressed concrete girders can be replaced by the new nonprestressed decked UHP-FRC girders.","PeriodicalId":170570,"journal":{"name":"Second International Interactive Symposium on UHPC","volume":"219 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122851098","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ultra-high performance concrete (UHPC) is being considered as an alternative ductile material to be used in the expected plastic hinge regions of structural components in buildings and bridges. Although several experimental studies of reinforced UHPC structural elements have been conducted for proof-of-concept seismic application, quantification of the plastic hinge length and associated rotation at ultimate limit states remains the most significant aspect for the ductile design of UHPC components in new structures. To that end, this study utilizes two-dimensional finite element models incorporating recently developed bond-slip constitutive model, which aids in simulating multiple damage states, such as yielding of reinforcement and reinforcement fracture. Several finite element models with variations in geometrical properties and loading scheme were simulated to compute the equivalent plastic hinge length values for reinforced UHPC flexural members. The existing empirical equations available for reinforced concrete and reinforced highperformance fiber-reinforced cementitious composite (HPFRCC) were found to over-predict the equivalent plastic hinge length in reinforced UHPC members. In addition, a mechanics-based approach was used to estimate the ultimate rotation capacity utilizing the plastic hinge length values obtained from numerical simulation techniques. This study can be used as starting point to develop a more robust empirical expression of plastic hinge length for reinforced UHPC flexural members and formulate a simplified approach to compute non-linear modeling parameters for displacement-based seismic design of UHPC structural components.
{"title":"Predicting UHPC Structural Response at Ultimate Limit State through Numerical Simulation Technique","authors":"M. Pokhrel, M. Bandelt","doi":"10.21838/uhpc.9691","DOIUrl":"https://doi.org/10.21838/uhpc.9691","url":null,"abstract":"Ultra-high performance concrete (UHPC) is being considered as an alternative ductile material to be used in the expected plastic hinge regions of structural components in buildings and bridges. Although several experimental studies of reinforced UHPC structural elements have been conducted for proof-of-concept seismic application, quantification of the plastic hinge length and associated rotation at ultimate limit states remains the most significant aspect for the ductile design of UHPC components in new structures. To that end, this study utilizes two-dimensional finite element models incorporating recently developed bond-slip constitutive model, which aids in simulating multiple damage states, such as yielding of reinforcement and reinforcement fracture. Several finite element models with variations in geometrical properties and loading scheme were simulated to compute the equivalent plastic hinge length values for reinforced UHPC flexural members. The existing empirical equations available for reinforced concrete and reinforced highperformance fiber-reinforced cementitious composite (HPFRCC) were found to over-predict the equivalent plastic hinge length in reinforced UHPC members. In addition, a mechanics-based approach was used to estimate the ultimate rotation capacity utilizing the plastic hinge length values obtained from numerical simulation techniques. This study can be used as starting point to develop a more robust empirical expression of plastic hinge length for reinforced UHPC flexural members and formulate a simplified approach to compute non-linear modeling parameters for displacement-based seismic design of UHPC structural components.","PeriodicalId":170570,"journal":{"name":"Second International Interactive Symposium on UHPC","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122782188","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yiming Yao, Farrokh Kianmofrad, A. Arora, N. Neithalath, B. Mobasher
Several procedures for design of UHPC use formulations based on a strain compatibility analysis, which can be extended to a serviceability-based design by incorporation of full material stress-strain relationship. The material models can be implemented in finite element and elastic-plastic solution methodologies in order to close the gap among properties, analysis, modeling, and design. The tensile characteristics of UHPC can be defined in the context of fiber content and response after the matrix has fully cracked. The general terms of strain softening and/or strain hardening are defined, and additional subclasses of deflection-softening and -hardening may be outlined based on the behavior in bending.
{"title":"Development of Structural Design Procedures for UHPC","authors":"Yiming Yao, Farrokh Kianmofrad, A. Arora, N. Neithalath, B. Mobasher","doi":"10.21838/uhpc.9697","DOIUrl":"https://doi.org/10.21838/uhpc.9697","url":null,"abstract":"Several procedures for design of UHPC use formulations based on a strain compatibility analysis, which can be extended to a serviceability-based design by incorporation of full material stress-strain relationship. The material models can be implemented in finite element and elastic-plastic solution methodologies in order to close the gap among properties, analysis, modeling, and design. The tensile characteristics of UHPC can be defined in the context of fiber content and response after the matrix has fully cracked. The general terms of strain softening and/or strain hardening are defined, and additional subclasses of deflection-softening and -hardening may be outlined based on the behavior in bending.","PeriodicalId":170570,"journal":{"name":"Second International Interactive Symposium on UHPC","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125875851","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. K. S. Pachalla, Christopher Levandowski, S. Sritharan
The use of UHPC continues to grow rapidly and a great deal of present-day research focuses on understanding and fine tuning of this material composition. This work is aimed at understanding the effects of size on the tensile behavior of UHPC in relation to the fiber percentage. The paper also discusses the variation in the stress-strain responses based on the chosen gauge length for the tension characterization. Several UHPC dog bone shaped specimens have been tested in the laboratory under the displacement controlled mode. The size effect is assessed by comparing the results of the specimens with cross sections of 2 in. x 2 in., 2 in. x 4 in., and 4 in. x 4 in. The response of the specimens was measured with LVDT and a 3D optical tracking system. The LEDs for the optical tracking measurements were placed at 1 in. interval over a length of 14 in. in the critical zone of the specimen where failure was anticipated. The results show that the effect of size on the stress-strain curves is not consistent between different fiber ratios and there is noticeable variation in the formation of micro cracking along the member length. The chosen gauge length for the measurement of the stress-strain curves can have significant effect on the peak and ultimate strain values. Larger gauge lengths can include micro-cracks over a longer length, averaging the micro-crack behavior more accurately. However, they can have significantly lower peak strain and post-peak behavior when compared with a smaller gauge length.
{"title":"Effects of Size and Gauge length on the Stress-Strain Response of UHPC in Tension","authors":"S. K. S. Pachalla, Christopher Levandowski, S. Sritharan","doi":"10.21838/uhpc.9678","DOIUrl":"https://doi.org/10.21838/uhpc.9678","url":null,"abstract":"The use of UHPC continues to grow rapidly and a great deal of present-day research focuses on understanding and fine tuning of this material composition. This work is aimed at understanding the effects of size on the tensile behavior of UHPC in relation to the fiber percentage. The paper also discusses the variation in the stress-strain responses based on the chosen gauge length for the tension characterization. Several UHPC dog bone shaped specimens have been tested in the laboratory under the displacement controlled mode. The size effect is assessed by comparing the results of the specimens with cross sections of 2 in. x 2 in., 2 in. x 4 in., and 4 in. x 4 in. The response of the specimens was measured with LVDT and a 3D optical tracking system. The LEDs for the optical tracking measurements were placed at 1 in. interval over a length of 14 in. in the critical zone of the specimen where failure was anticipated. The results show that the effect of size on the stress-strain curves is not consistent between different fiber ratios and there is noticeable variation in the formation of micro cracking along the member length. The chosen gauge length for the measurement of the stress-strain curves can have significant effect on the peak and ultimate strain values. Larger gauge lengths can include micro-cracks over a longer length, averaging the micro-crack behavior more accurately. However, they can have significantly lower peak strain and post-peak behavior when compared with a smaller gauge length.","PeriodicalId":170570,"journal":{"name":"Second International Interactive Symposium on UHPC","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116205112","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Steel reinforced ultra-high performance concrete (R/UHPC) flexural members commonly fail by fracture of the steel reinforcement after crack localization rather than crushing of the cement-based matrix as expected in traditional reinforced concrete. When failing after crack localization, R/UHPC specimens show low drift capacity and the high composite compressive strength is not utilized. In an effort to develop design approaches that might fully utilize the high compressive strength of UHPC and guarantee a minimum drift capacity, this study investigates an R/UHPC flexural element failing by crushing. Four-point bending tests are performed on two R/UHPC beams that are designed to fail in one case after crack localization and in the other after UHPC crushing. Experimental measurements include load, mid-span deflection, UHPC surface strain, and reinforcement strain. Surface strains are used to characterize compressive zone behavior for an ultimate strength prediction. Test results demonstrate that the R/UHPC specimen that failed after crushing had a larger drift capacity than the R/UHPC specimen that failed by fracture of the reinforcement after crack localization. The maximum compressive strain in the UHPC at crushing was measured to be 0.0065, at which point the reinforcement had significantly strain hardened. The observed compressive zone behavior and reinforcement behavior are incorporated into a new proposed strength prediction method.
{"title":"Utilizing Full UHPC Compressive Strength in Steel Reinforced UHPC Beams","authors":"Y. Shao, S. Billington","doi":"10.21838/uhpc.9699","DOIUrl":"https://doi.org/10.21838/uhpc.9699","url":null,"abstract":"Steel reinforced ultra-high performance concrete (R/UHPC) flexural members commonly fail by fracture of the steel reinforcement after crack localization rather than crushing of the cement-based matrix as expected in traditional reinforced concrete. When failing after crack localization, R/UHPC specimens show low drift capacity and the high composite compressive strength is not utilized. In an effort to develop design approaches that might fully utilize the high compressive strength of UHPC and guarantee a minimum drift capacity, this study investigates an R/UHPC flexural element failing by crushing. Four-point bending tests are performed on two R/UHPC beams that are designed to fail in one case after crack localization and in the other after UHPC crushing. Experimental measurements include load, mid-span deflection, UHPC surface strain, and reinforcement strain. Surface strains are used to characterize compressive zone behavior for an ultimate strength prediction. Test results demonstrate that the R/UHPC specimen that failed after crushing had a larger drift capacity than the R/UHPC specimen that failed by fracture of the reinforcement after crack localization. The maximum compressive strain in the UHPC at crushing was measured to be 0.0065, at which point the reinforcement had significantly strain hardened. The observed compressive zone behavior and reinforcement behavior are incorporated into a new proposed strength prediction method.","PeriodicalId":170570,"journal":{"name":"Second International Interactive Symposium on UHPC","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125456800","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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