This study intends to find out the correlation between the cover depth and the bond characteristics of UHPC through pull-out tests of UHPC specimens with different cover depths and bond tests of rebar using flexural m...This study intends to find out the correlation between the cover depth and the bond characteristics of UHPC through pull-out tests of UHPC specimens with different cover depths and bond tests of rebar using flexural members. In this experimental study, specimens are fabricated with the lap-splice length as test variable in relation with the calculation of the lap-splice length for 180- MPa UHPC. Moreover, specimens are also fabricated with the cover depth as test variable to evaluate the effect of the cover depth on the UHPC flexural members. The load-displacement curves are analyzed for each of these test variables to compute the lap-splice length proposed in the K-UHPC structural design guideline and to evaluate the influence of the cover depth on the flexural members. As a result, the stability of the structural behavior can be significantly enhanced by increasing slightly the cover depth specification of the current UHPC Structure Design Guideline from the maximum value between 1.5 times of rebar diameter and 20 mm to the maximum value between 1.5 times of rebar diameter and 25 mm.展开更多
Prefabricated internal structures of road tunnels,consisting of precast elements and the connections between them,provide advantages in terms of quality control and manufacturing costs.However,the limited construction...Prefabricated internal structures of road tunnels,consisting of precast elements and the connections between them,provide advantages in terms of quality control and manufacturing costs.However,the limited construction space in tunnels creates challenges for on-site assembly.To identify feasible connecting joints,flexural tests of precast straight beams connected by welding-spliced or lap-spliced reinforcements embedded in normal concrete or ultra-high-performance fiber-reinforced concrete(UHPFRC)are first performed and analyzed.With an improvement in the strength grade of the closure concrete for the lap-spliced joint,the failure of the beam transforms from a brittle splitting mode to a ductile flexural mode.The beam connected by UHPFRC100 with short lap-spliced reinforcements can achieve almost equivalent mechanical performance in terms of the bearing capacity,ductility,and stiffness as the beam connected by normal concrete with welding-spliced reinforcements.This favorable solution is then applied to the connection of neighboring updeck slabs resting on columns in a double-deck tunnel.The applicability is validated by flexural tests of T-shaped joints,which,fail in a ductile fashion dominated by the ultimate bearing capacity of the precast elements,similar to the corresponding straight beam.The utilization of UHPFRC significantly reduces the required lap-splice length of reinforcements owing to its strong bonding strength.展开更多
The effects of structural modeling （bar slip in lap splice）, ground motion selection process （epsilon effect） and size of a structure （number of bays and stories） on the fragility of reinforced concrete ordinary...The effects of structural modeling （bar slip in lap splice）, ground motion selection process （epsilon effect） and size of a structure （number of bays and stories） on the fragility of reinforced concrete ordinary moment resisting frames are investigated. An analytical model is developed to account for bar slip in lap splice, which exhibits good correlation with existing experimental data. Then, incremental dynamic analysis is used to derive the fragility curves for four model structures. The model structures simulate frames with a different number of bays and stories. Finally, the fragility curves are corrected for the epsilon effect. The results show that slip in the lap splice can significantly increase the failure probability, especially for the collapse prevention limit state. At the same time, it is found that spectral shape has a significant impact on the fragility curves. It is also found that accounting for or ignoring bar slip or epsilon effects increases the probability of failure for larger structures. This indicates an unconservative bias in the safety of larger structures.展开更多
As a solution against the serviceability problem caused by the cracks occurring at the UHPC precast deck-joint interface, this study proposes a method exposing the steel fiber at the interface and evaluates the corres...As a solution against the serviceability problem caused by the cracks occurring at the UHPC precast deck-joint interface, this study proposes a method exposing the steel fiber at the interface and evaluates the corresponding flexural performance of the lap spliced construction joint. After having slowed down the strength development of the concrete placed in the joint of the precast deck by means of a curing retardant, the concrete at the interface is crushed so as to expose the steel fibers and the change in the flexural performance is observed experimentally according to the exposure of the steel fibers. The results show that, even if the ultimate strength and stiffness of the UHPC precast deck including the joint are mostly determined by the arrangement details of the rebar lap splice, the exposure of the steel fibers can secure stable ductile behavior and reduce the width of the cracks generated at the precast deck-joint interface under service load.展开更多
文摘This study intends to find out the correlation between the cover depth and the bond characteristics of UHPC through pull-out tests of UHPC specimens with different cover depths and bond tests of rebar using flexural members. In this experimental study, specimens are fabricated with the lap-splice length as test variable in relation with the calculation of the lap-splice length for 180- MPa UHPC. Moreover, specimens are also fabricated with the cover depth as test variable to evaluate the effect of the cover depth on the UHPC flexural members. The load-displacement curves are analyzed for each of these test variables to compute the lap-splice length proposed in the K-UHPC structural design guideline and to evaluate the influence of the cover depth on the flexural members. As a result, the stability of the structural behavior can be significantly enhanced by increasing slightly the cover depth specification of the current UHPC Structure Design Guideline from the maximum value between 1.5 times of rebar diameter and 20 mm to the maximum value between 1.5 times of rebar diameter and 25 mm.
基金The work of the first author was sponsored by the Shanghai Pujiang Program(No.20PJ1406100)the National Natural Science Foundation of China(Grant No.52208398)+1 种基金In addition,the financial support from the Sino-German Center for Research Promotion,provided within project GZ 1574,is gratefully acknowledged.The last author acknowledges financial support from the Science and Technology Commission of Shanghai Municipality(No.21DZ1203504)the National Natural Science Foundation of China(Grant No.51808336).Moreover,the interesting discussions with Mr.Enjie HU are gratefully acknowledged.
文摘Prefabricated internal structures of road tunnels,consisting of precast elements and the connections between them,provide advantages in terms of quality control and manufacturing costs.However,the limited construction space in tunnels creates challenges for on-site assembly.To identify feasible connecting joints,flexural tests of precast straight beams connected by welding-spliced or lap-spliced reinforcements embedded in normal concrete or ultra-high-performance fiber-reinforced concrete(UHPFRC)are first performed and analyzed.With an improvement in the strength grade of the closure concrete for the lap-spliced joint,the failure of the beam transforms from a brittle splitting mode to a ductile flexural mode.The beam connected by UHPFRC100 with short lap-spliced reinforcements can achieve almost equivalent mechanical performance in terms of the bearing capacity,ductility,and stiffness as the beam connected by normal concrete with welding-spliced reinforcements.This favorable solution is then applied to the connection of neighboring updeck slabs resting on columns in a double-deck tunnel.The applicability is validated by flexural tests of T-shaped joints,which,fail in a ductile fashion dominated by the ultimate bearing capacity of the precast elements,similar to the corresponding straight beam.The utilization of UHPFRC significantly reduces the required lap-splice length of reinforcements owing to its strong bonding strength.
文摘The effects of structural modeling （bar slip in lap splice）, ground motion selection process （epsilon effect） and size of a structure （number of bays and stories） on the fragility of reinforced concrete ordinary moment resisting frames are investigated. An analytical model is developed to account for bar slip in lap splice, which exhibits good correlation with existing experimental data. Then, incremental dynamic analysis is used to derive the fragility curves for four model structures. The model structures simulate frames with a different number of bays and stories. Finally, the fragility curves are corrected for the epsilon effect. The results show that slip in the lap splice can significantly increase the failure probability, especially for the collapse prevention limit state. At the same time, it is found that spectral shape has a significant impact on the fragility curves. It is also found that accounting for or ignoring bar slip or epsilon effects increases the probability of failure for larger structures. This indicates an unconservative bias in the safety of larger structures.
文摘As a solution against the serviceability problem caused by the cracks occurring at the UHPC precast deck-joint interface, this study proposes a method exposing the steel fiber at the interface and evaluates the corresponding flexural performance of the lap spliced construction joint. After having slowed down the strength development of the concrete placed in the joint of the precast deck by means of a curing retardant, the concrete at the interface is crushed so as to expose the steel fibers and the change in the flexural performance is observed experimentally according to the exposure of the steel fibers. The results show that, even if the ultimate strength and stiffness of the UHPC precast deck including the joint are mostly determined by the arrangement details of the rebar lap splice, the exposure of the steel fibers can secure stable ductile behavior and reduce the width of the cracks generated at the precast deck-joint interface under service load.
