In this study, a novel 3D-printing ultra-high performance fibre-reinforced concrete (3DP-UHPFRC) was developed. The effect of fibre content, fibre type and printing direction on the mechanical ...properties of 3DP-UHPFRC was evaluated through compressive, flexural, splitting tensile and uniaxial tensile tests, and the anisotropic properties of 3DP-UHPFRC were investigated. The experiment results indicated that 3DP-UHPFRC prepared with 1 vol% 6 mm steel fibre was more suitable for construction than 3DP-UHPFRC prepared with 1 vol% 10 mm steel fibre under the printing conditions in this test. The maximum flexural strength of 3DP-UHPFRC with 1 vol% 6 mm steel fibre reached 45.21 MPa in the Z-direction (printing direction), which was substantially higher than those obtained in previous studies. The flexural and splitting tensile failures of 3DP-UHPFRC could be either ductile or brittle in different directions; thus, the printing mode could be flexibly adjusted according to different engineering requirements. The latest test results indicated that the compressive elastic modulus was anisotropic, but there was little difference in the tensile elastic modulus in each direction.
Summary
The deformations of ultrahigh arch dams can comprehensively indicate the dynamic variations of their structural behavior to judge the normal or not for timely discovering anomalies. First, ...the panel data features on the deformation behavior are extracted to effectively indicate the overall structural evolution of the Jinping I arch dam combing with the time series and the cross‐section series. Afterwards, a regression panel model (RPM) on the multi‐dimensional variables is proposed to model the deformation panel data consisted of multi‐monitoring points synchronously. Subsequently, an innovative functional relationship between the measured values and the real‐time risk probabilistic function is established due to the RPM estimation accuracy. In order to estimate the risk probability of the whole arch dam, the Copula function is used to build a multivariate joint probability distribution function to indicate the correlation among the random variables. The proposed methods are validated by an application on the Jinping I arch dam to evaluate its risk probability, which explores a novel approach for the arch dam safety assessment.
•Exposed to 1000 °C, the UHPC retained 69% of its original compressive strength.•Steel slag played a key role in improving fire resistance of the UHPC.•Mass loss of the UHPC mixtures mostly occurred ...between 200 and 400 °C.
Fire or high temperature is a big challenge to ultra-high performance concrete (UHPC). Strength loss of UHPCs can reach up to 80% after exposure to 800 °C. In this study, a total of six UHPC mixtures were designed and tested after subjected to elevated temperatures up to 1000 °C. The effects of aggregate type, fibre type and heating rate were investigated. Residual compressive strengths and stress-strain relationships were studied. Besides, attention was paid to explosive spalling since UHPCs are usually of compact structure and thus more vulnerable to explosive spalling than other concretes. Scanning electron microscope (SEM) analysis was conducted to help understand the mechanism of variation of internal structure under different temperatures. It was found the mixture containing steel slag and hybrid fibre had excellent fire resistance. After being subjected to 1000 °C, this mixture retained a residual compressive strength of 112.8 MPa or a relative value of 69%.
•Sudden stress reduction or stress fluctuations can be observed for the UHPFRC.•Steel fiber addition significantly influence the compressive behavior of UHPFRC.•UHPFRC in DSTCs can be more ...effectively confined than in FRP confined concrete.•The suitability of existing model for the UHPFRC in DSTCs is investigated.
This study presents the results of an experimental program on the compressive behavior of hybrid fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs) with ultra-high performance fiber-reinforced concrete (UHPFRC). In total 40 specimens, including 32 hybrid DSTCs and eight FRP confined solid concrete (FCSC) specimens, were prepared and tested under axial compression. In addition to hybrid UHPFRC DSTCs, hybrid DSTCs with ultra-high performance concrete without steel fiber addition (UHPC), high-strength concrete (HSC), and normal-strength concrete (NSC) were also tested. The investigated parameters included the FRP tube thickness, steel tube thickness, void ratio, steel fiber addition, concrete type, UHPFRC-filling inside the steel tube, and the column type. The test results indicate that the hybrid UHPFRC DSTCs can exhibit highly ductile behavior when a thick FRP tube is used. However, due to the ultra-high strength and the dense microstructure of UHPFRC, the hybrid UHPFRC DSTCs are likely to exhibit more brittle behavior than the hybrid DSTCs with NSC and HSC. Even though a high confinement level is provided, sudden stress reduction or stress fluctuations can be observed for the UHPFRC in hybrid DSTCs. The influences of FRP tube thickness, void ratio, steel fiber addition, and UHPFRC-filling inside the steel tube on the compressive behavior of the hybrid UHPFRC DSTCs are significant, while the influence of steel tube thickness is insignificant. Moreover, when compared to the FCSC specimens, the presence of an inner void is beneficial for the compressive behavior of UHPFRC in the hybrid DSTCs, especially when a thick FRP tube is used. Furthermore, the performance of existing stress-strain model to predict the compressive behavior of UHPFRC in the hybrid DSTCs is investigated.
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•Numerical models of segmental column are established.•Column with mores segments shows better blast resistance.•Shear key design mitigates stress wave propagation and blast induced ...damage.•Energy dissipation bar is inefficient resisting blast loads.•Posttensioning prestress is beneficial to column blast resistance.
Constructions with precast technology have seen a fast development over the past several decades. Despite advantages including short construction period, better quality control, less environmental and traffic impact, a lack of study on their behaviour under dynamic loads have prevented the widespread use of precast constructions in high seismic zones and where terrorist attack could be a concern. Among all precast structural components, precast segmental columns have been found one of the construction techniques with great potentials. Intensive research efforts have been spent on investigating the segmental columns under seismic loadings in recent years. During its service life, besides seismic action, structure may subject to other dynamic loads like impact and blast. It is therefore important to perform multi-hazard analyse to better understand structural performance. This study investigates the blast loading resistance capacities of segmental reinforced concrete (RC) columns. RC segmental columns with or without shear keys and energy dissipation bars are considered. Influence of the number of segments and different levels of post tensioning forces on column dynamic performance is also investigated. Commercial code LS-DYNA is used to perform numerical simulations of the segmental columns under different blast loadings. Accuracy of the numerical model is verified against available testing data on RC columns. Numerical results of the segmental columns under different blast loadings are calculated and compared with those of the monolithic RC columns. Discussions on the capabilities of segmental RC columns in resisting blasting loads are made with respect to those of the monolithic RC columns.
A mesoscale model was developed to investigate the effect of steel fiber on the thermal conductivity of steel fiber-reinforced concrete (SFRC). Delaunay triangulation was employed to generate the ...unstructured mesh for SFRC materials. The model was validated using the existing experimental data. Then, it was used to study how model thickness affected simulation outcomes of thermal conductivity of models with different fiber lengths, by which an appropriate thickness was determined for the later analyses. The validated and optimized model was applied to the study of relationships between thermal conductivity and factors such as fiber content, fiber aspect ratio and different parts of an SFRC block by conducting steady-state heat analyses with the finite element analysis software ANSYS. The simulation results reveal that adding steel fiber increases thermal conductivity considerably, while fiber aspect ratio only has an insignificant effect. Besides, the presence of steel fibers has an obvious impact on the distribution of temperature and heat flux vector of the SFRC blocks.
•Multiaxial mechanical behaviour and rate sensitivity of UHPC are discussed.•Effects of fibre, coarse aggregate, binder and structural reinforcement on UHPC against HVPI are discussed.•UHPC models, ...modelling techniques and algorithms are summarized and commented.•Existing empirical formulae and semi-empirical formulae to predict DOP are examined for UHPC.•Discussions and recommendations for further research in this field are provided.
Known for its high mechanical strength and ductility, ultra-high performance concrete (UHPC) emerges as a promising material in civil and military constructions to resist hazardous loads such as high velocity projectile impact (HVPI). Due to its unique material properties, structures built with UHPC perform differently to its counterparts made of conventional concrete under HVPI, and thus the empirical and semi-empirical resistant functions for conventional concrete against HVPI require careful evaluation before application to UHPC structures. This study presents a comprehensive review of the research advances in thick UHPC targets to resist HVPI for projectiles at normal incidence. First, the static and dynamic material properties of UHPC are briefly introduced in comparison to conventional concrete. Second, based on physical tests, key aspects in UHPC design to resist HVPI are reviewed, which include fibre reinforcement, high strength coarse aggregate, alternative binder system as well as structural reinforcement and designs. Third, in a view of the development in material constitutive models under complex dynamic loads and computational techniques, numerical simulations of UHPC under HVPI are reviewed and discussed. Further, empirical and semi-empirical formulae to predict the depth of penetration (DOP) on conventional concrete are collected and evaluated on their suitability for UHPC.
This study presents the results of an experimental program on the compressive behavior of fiber reinforced polymer (FRP) confined ultra-high performance fiber-reinforced concrete (UHPFRC). A total of ...38 specimens were prepared and tested under axial compression. In addition to FRP confined UHPFRC, FRP confined ultra-high performance concrete without fiber addition (UHPC), high strength concrete (HSC), and normal strength concrete (NSC) were also tested to investigate their comparative performances. The test results indicate that the FRP confined UHPFRC can exhibit ductile behavior if sufficient FRP confinement is provided. However, due to their ultra-high strength as well as the unique microstructure, FRP confined UHPFRC is likely to exhibit more brittle behavior than FRP confined NSC and HSC. Compared to FRP confined NSC and HSC, the confinement efficiency is less for FRP confined UHPFRC. Sudden stress reduction or stress fluctuations are observed shortly after the initial peak stress (axial stress at the first peak point) for FRP confined UHPFRC. Based on the confinement level, the stress-strain behavior of FRP confined UHPFRC may experience a second ascending branch or a continuous descending branch after the sudden stress reduction or stress fluctuations. The influences of FRP layers, FRP types, and fiber addition on the compressive behavior of FRP confined UHPFRC are observed to be significant. Moreover, existing stress-strain models available for FRP confined UHPFRC are evaluated by using a database collected in this study.
Fire is a big risk to buildings and structures, posing a great threat to human lives. In this study, a newly developed ultra-high performance concrete (UHPC) was investigated experimentally. ...Quasi-static compression tests were conducted after the UHPC was first exposed to a high temperature, i.e. 200, 400, 600, 800 or 1000 °C, and then cooled down to room temperature, while dynamic tests were carried out under combined effect of a high temperature, i.e. 200, 400, 600, or 800 °C, and impact loading. The dynamic tests were done both at high temperatures and after cooling down and comparisons were made between these two scenarios. Based on the tests on this UHPC, mechanical and physical characteristics under the combined effect were studied. Besides, explosive spalling was analysed. It was interesting to find polypropylene (PP) fibre could play a negative role in preventing explosive spalling between 320 and 380 °C.
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