With the development of additive manufacturing, attention to 3D printing concrete construction technology has been paid. Dynamic performance is one of the important material properties of concrete. ...However, the rate dependent behaviour of 3D printed concrete under dynamic tension has not been explored. In this study, the dynamic splitting tensile test of the 3D printed ultra-high performance fibre reinforced concrete (3DP-UHPFRC) was performed. The dynamic splitting tensile behaviour of 3DP-UHPFRC was analysed by varying the preparation method, with or without fibre, fibre length, impact velocity and tensile direction, and the anisotropic characteristics of 3DP-UHPFRC were evaluated. The test results revealed that the failure mode of 3DP-UHPFRC exhibited ductility in the X-direction and experienced brittleness in the Y- and Z-directions. When the strain rates are the same (12 s−1), the peak stress of 3D printing specimen with 6-mm steel fibre in the X-direction is 49.038% higher than that of 3D printing specimen without steel fibre in the X-direction, while 3D printing specimen with 6-mm steel fibre in the Y-direction is only 2.350% higher than that of 3D printing specimen without steel fibre in the Y-direction. The dynamic increase factor (DIFst) of tensile strength of the 3D printed ultra-high performance concrete (3DP-UHPC) without steel fibre demonstrated insignificant anisotropy, while DIFst for 3DP-UHPFRC in the X-direction was remarkably lower than that in the Y- and Z-directions. Moreover, a dynamic tensile orthotropic constitutive model was preliminarily proposed for further 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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•Reinforced UHPC beams are tested against repeated impact loads.•UHPC constitutive model and bond-slip behaviour are considered in the numerical analysis.•Energy evolution diagram, ...dynamic shear force and bending moment distribution diagram are discussed.•Failure mechanism of UHPC beam under repeated impact load are evaluated in the parametric study.
This paper investigates the dynamic response of hybrid fibre reinforced ultra-high performance concrete (UHPC) beams against single and repeated low-velocity impact loads. A brief description of the drop weight impact tests on the UHPC beams was presented first followed by the development of the material and structural model in finite element analysis. A plasticity-based concrete material model with validated compressive and tensile strength surface and damage algorithm was adopted for hybrid fibre reinforced UHPC material. Based on the test results, the bond-slip behaviour between steel rebar and UHPC matrix was developed in an empirical form and incorporated in the model. Compared to the model with the bond-slip definition, the model with perfect bonding was found to underestimate the maximum mid-span deflection, which highlighted the necessity of considering the bond-slip behaviour in dynamic analysis where large deflection occurs. The repeated impact tests were performed numerically, and the results were validated with experimental data. A parametric study was then performed to investigate the effect of key parameters, including different impact energy and the same impact energy but different impact numbers. The results indicated when the total energy increased, the repeated impact loads became more hazardous than the single impact load. With the validated model, the dynamic shear force and bending moment distribution diagrams were compared to study the failure mechanism in single and repeated impact loads.
•Drop weight impact tests were performed on axial-loaded hollow-core and steel wire mesh reinforced UHPC columns.•Failure mechanism and crack development were studied based on dynamic shear force and ...bending moment distribution.•The residual loading capacity of hollow-core and steel wire mesh reinforced UHPC columns was studied.
Adopting UHPC in practical construction is very expensive due to the high steel fibre content (>2.5 vol%) and passive flexure reinforcement. Aiming at balancing the performance and cost, two UHPC column designs (2000 × 168 × 168 mm) are proposed in the present study. Hollow-core components and steel wire mesh reinforced components were cast with UHPC that contained 1.5 vol% steel fibre, and the impact resistance of both structural types was studied. The test specimens included two hollow-core UHPC columns with square and circular hollow shapes, and two steel wire mesh reinforced UHPC columns with 6 and 10 layers wire mesh reinforcement. The impact scenario was modelled with a 411 kg drop hammer falling freely from 1.25 m height to the mid-span of the test specimen. The results demonstrated that all UHPC specimens remained a flexural response with minimal damage. The developed numerical model captured the impact force, structural deformation and damage with reasonable accuracy. With the validated model, the energy evolution, dynamic shear and moment distribution, residual axial capacity and damage level of post-impact columns were evaluated. The effects of hollow section shape and ratio, axial load level, and longitudinal reinforcement ratio for hollow-core UHPC columns and the effects of layers of steel wire mesh for steel wire mesh reinforced UHPC columns were investigated. Compared with other hollow-core UHPC columns under the impact velocities between 4.95 m/s – 6.64 m/s, UHPC columns with a circular hollow section and 15% hollow ratio was the most effective in balancing the cost and impact resistance. For steel wire mesh reinforced UHPC columns, the column with steel wire mesh strengthening in the whole section had better impact resistance than its counterpart that only had wire mesh reinforcement in the tensile zone.
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Concrete structures are widely used in modern constructions including energy storage system such as all concrete liquefied natural gas (ACLNG) storage tanks. In ACLNG tanks, concrete structure is ...exposed to cryogenic temperatures and freeze-thaw (FT) cycles. Cryogenic temperatures and FT cycles are recognized to influence the mechanical characteristics of concrete. To ensure safety of the critical energy infrastructure, it is crucial to explore the concrete structural response under the combined cryogenic FT cycles and accidental impact loading. This study aims to numerically examine the damage caused by impact loading on reinforced concrete panels after exposure to cryogenic FT cycles. A plasticity based continuous surface cap model was adopted to simulate concrete. The material modulus, uniaxial and triaxial strength surface as well as damage parameters were updated to incorporate the effect of cryogenic FT cycles. A numerical model was established to forecast the impact resistance of the reinforced concrete panels after various cryogenic FT cycles. Through the numerical simulation, it was evident that FT cycles exerted detrimental effects on the impact resistance of reinforced concrete panels. With an escalation in the number of FT cycles, there was a pronounced increase in the size of the crater formed on the top surface, accompanied by a corresponding rise in the penetration depth of the panel. The results of this research offer insights into the impact resistance of reinforced concrete structures following cryogenic FT cycles. Such insights are vital for the design and maintenance of critical structures like liquefied natural gas (LNG) storage tanks and other cryogenic facilities.
•Concrete constitutive models after cryogenic freeze-thaw cycles are established.•Cryogenic freeze-thaw cycles bring detrimental effect on structural impact resistance.•With increased freeze-thaw cycles, evident increase in impact induced crater size and penetration depth is observed.
The homogenization technique has been used to derive equivalent material properties of masonry units for many years. However, most previous research work has concentrated on the derivation of ...equivalent material properties of a solid brick masonry structure. Very few studies have been conducted to investigate the complex mechanical properties of a hollow concrete block masonry unit. In this paper, numerical simulations of laboratory tests are conducted to derive the equivalent material properties of a three-dimensional basic cell of hollow concrete block masonry. A double scalar damage model based on the concept of continuum damage mechanics is applied to modeling the failure of mortar joint and concrete. In the numerical model of the basic cell, the hollow concrete block and mortar with their nonlinear material properties are modeled in detail. By applying various displacement boundaries to the basic cell surfaces to simulate the displacement-controlled laboratory tests, the averaged stress and strain of the basic cell under different stress states are derived numerically. The homogenized or equivalent material properties of the hollow concrete masonry are determined from the averaged stress and strain relations of the basic cell. To check the validity of the derived equivalent material properties, the dynamic response and damage of a hollow concrete masonry panel subjected to airblast loading is modeled with the equivalent material properties or with the distinctive mortar and brick properties. The efficiency and accuracy of using the derived equivalent material properties in numerical modeling of hollow concrete brick masonry are demonstrated.
•Hybrid steel and polypropylene (PP) fibre reinforced UHPC showed reduced thermal spalling.•Ratio of cylinder strength to cube strength is independent of temperature.•UHPC strength increases after ...exposure to up to 400 °C.•Stress–strain relationship of UHPC under triaxial compression after thermal effects are established.
Equipped with excellent strength and energy absorption capacity, ultra-high performance concrete (UHPC) is a promising material to improve structural resistance against extreme loads. Material and structural tests at ambient temperature have been conducted extensively on UHPC specimens in recent years, and its mechanical properties have been well-documented. In this study, a hybrid steel and polypropylene (PP) fibre reinforced UHPC is investigated under uniaxial and triaxial compression states after exposure to elevated temperatures. Cubic (50 mm) and cylindrical specimens (50 mm diameter × 100 mm height) were first heated in electric furnace to target temperatures, i.e. 200 °C, 400 °C, 600 °C, 800 °C and 1000 °C. After naturally cooled down to ambient temperature, the specimens were tested under uniaxial compression and triaxial compression with confining pressure ranging from 5 to 40 MPa. The triaxial stress–strain relationships and failure modes after exposure to elevated temperatures were then compared and discussed. Several common failure criteria for concrete material were adopted to describe the high temperature effect on UHPC’s strength. An empirical model for reproducing the triaxial compression stress–strain curves of UHPC after elevated temperature was proposed.
•Blast resistance of UHPC column pre- and post-fire hazard was studied.•Exposure to elevated temperature changed blast induced column failure mode.•Bond-slip behaviour had varying impact on the blast ...resistance.•Pressure-impulse diagrams were developed for fire damaged UHPC columns.
Concrete structures may experience fire and blast during their service life as a result of accidental explosions or vehicular collisions. Both fire and blast can cause severe damage that threatens the structural safety. In the present study, reinforced concrete columns fabricated by ultra-high performance concrete (UHPC) are investigated under coupled fire and blast loads. Strength degradation and damage of UHPC and steel reinforcement after exposure to elevated temperature (up to 800 °C) were established based on the experimental data. In addition to the detrimental effect on individual material, bond-slip behaviour between the UHPC and reinforcement affected by the elevated temperature was considered. The findings revealed that material strength degradation and damage owing to elevated temperature significantly influenced the structural blast resistance, and the degraded bond-slip behaviour had varying impact on the structural response depending on the structural damage mode. Up to 10% mid-span displacement differences were noted in columns with/without the consideration of bond-slip behaviour. Different failure mechanisms pre- and post-fire damage were observed in the numerical simulations. To quickly assess blast induced damage on UHPC columns, Pressure-Impulse (P-I) diagrams of the UHPC columns before and after elevated temperature were established and empirical formulae were proposed to generate the P-I diagrams.
•Mat_72R3 is used to characterize UHPC under static and impact loadings.•The DOP is investigated under various compressive strengths of UHPC, striking velocities and CRHs of projectile.•The crater ...damage is investigated under various compressive strengths of UHPC, striking velocities and CRHs of projectile.•An empirical formula is proposed to determine the DOP for UHPC.
This paper presents a numerical study in evaluating impact response of ultra-high performance concrete (UHPC) cylinder targets under ogive-nosed projectile penetration with broad striking velocities from 300m/s to 1000m/s. Steel ogive-nosed projectiles with an average mass of 360g are launched to penetrate UHPC cylinder targets with 750mm diameter and 1000mm length. The Karagozian & Case (K&C) cementitious material model, namely, MAT_Concrete_Damage_Rel3 (Mat_72R3), is implemented into finite element package LS-DYNA for UHPC. In order to accurately predict depth of penetration (DOP) and cratering damage of UHPC cylinder targets, uniaxial compressive and four-point bending testing results are used to validate 3D finite element material model. With the validated numerical model incorporating dynamic increase factors (DIF) of UHPC, parametric studies are conducted to investigate effects of UHPC compressive strength, projectile striking velocity and projectile caliber-radius-head (CRH) ratio on both DOP and cratering damage of UHPC targets. Moreover, an empirical formula to predict DOP is derived according to the simulated data.
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