•A novel precast ultra-lightweight ECC-concrete composite slab is investigated.•The four-point bending tests were conducted on six full-scale composite slabs.•The proposed slabs exhibited excellent ...flexural behavior and cracking resistance.•The specific bearing capacity of slabs was increased significantly by using ULECC.
Precast concrete (PC) slab has extensive application in PC structure. The conventional PC slab is susceptible to cracking during transportation and hoisting, due to the low tensile performance of normal concrete. Besides, the large self-weight of normal concrete also impedes efficient PC slab construction. Unlike normal concrete, ultra-lightweight engineered cementitious composite (ULECC) with a combination of low density and high tensile performance is a promising material for PC slab construction. The objective of this research is to investigate the feasibility of using ULECC in novel PC composite slab to reduce its self-weight, while improve the flexural performance. The effects of precast ULECC thickness, lattice girders configuration, and overall slab thickness on the structural performance of ULECC composite slab were investigated. The introduction of ULECC for the precast plank improved load bearing capacity by 29% with the self-weight decreased by 24% than the control specimen. Multiple micro-cracks appeared in tensile zone due to high tensile performance with excellent crack width control capacity of ULECC. The structural performance of PC slab is further simulated by ABAQUS and demonstrates good consistent with the experimental results. This research lays the groundwork for the application of ULECC in PC slab for an efficient construction and high flexural performance.
Summary
Traditional consolidation theories cannot provide good predictions of consolidation settlement in land reclamation because of their assumptions that the influence of soil's self‐weight is ...often neglected, and the drainage boundary is considered as fully pervious/impervious. In view of these limitations, an analytical solution is derived for one‐dimensional self‐weight consolidation problems with a continuous drainage boundary using the finite Fourier sine transform method. Following the classical Terzaghi's small strain theory, the soil's self‐weight is considered to produce consolidation settlement in dredged materials with a constant coefficient of consolidation. The continuous drainage boundary can essentially describe the time‐dependent variation of drainage capacity at the interface between two adjacent soil layers. By reducing the interface parameters, the effectiveness of the calculation is demonstrated against the Terzaghi's solution. The influence of interface parameters and soil's self‐weight stress coefficient on self‐weight consolidation is discussed. As expected, the rate of consolidation considering the self‐weight stress is faster, although the dependency of consolidation rate on the material property of void ratio is neglected. Moreover, the plane of maximum excess pore‐water pressure is estimated as a function of time factor, based on which a design chart is developed to optimize the layout of horizontal drains in land reclamation.
To study the settling characteristics of Ili loess, a field immersion test was implemented on thick collapsible loess with seepage holes to speed up the collapse. The loess at the test site belongs ...to the Q3eol stratum and had a thickness of 30 m. The on-site settlement, the degree of saturation, and other observations, such as surface cracks and dolinas, were continuously monitored. The experimental results show that Ili loess is a typically collapsible eolian soil with a large thickness, strong water sensitivity, low anti-erosion capability, and strong self-weight collapsibility. The collapsibility of the Ili loess was basically eliminated by the field immersion test. One primary reason was the significant reduction in the numerous trellis pores. In comparison with other similar tests, a much higher settling rate and self-weight collapsible settlement were observed. The correction coefficient of collapsibility for Ili loess is 1.64, which is calculated as the measured self-weight collapsible settlement divided by the calculated value. It is a key parameter for evaluating the loess collapsibility in the area. A four-stage settling trend was characterized; it is distinguishable from other regular five-stage models. It was confirmed that the pre-immersion method with seepage holes is an effective method of foundation treatment for the Ili loess region.
This paper proposes an analytical solution for 2D (two‐dimensional) consolidation of unsaturated soil with impeded drainage boundaries by considering the combined effects of self‐weight stress of ...soil and time‐dependent loading. The governing equation of the 2D consolidation model was first formulated, followed by an analytical solution employing the methods of the Laplace transform technique and separation of variables. The solution is then degraded to validate the correctness against two classical lab tests and existing solutions. Subsequently, the proposed solution is further verified against finite element calculations. The results indicate that the self‐weight stress of soil acts as an additional load applied to the unsaturated soil, the larger the self‐weight stress, the greater the value of initial EPPs (excess pore pressures). Meanwhile, it can be easily found that the larger the value of self‐weight stress, the larger the consolidation settlement. Without accounting for the effect of self‐weight stress, the settlement of the soil will certainly be underestimated and the dissipation characteristics of EPPs will not be accurately captured. It can be also found that the ratio of ka/kw also significantly influenced the consolidation behavior.
Considering the nonlinear rheological properties of saturated clay, the modified unified hardening (UH) constitutive relation was introduced to describe the nonlinear rheological deformation. ...Meanwhile, Swartzendruber's flow law was used to simulate the non‐Darcian flow of pore water in the progress of rheological consolidation. Consequently, a nonlinear rheological consolidation model (NRCM), for one‐dimensional consolidation, that simultaneously incorporates nonlinear stress‐strain‐time relationship, Swartzendruber's flow, self‐weight stress, and variable permeability coefficient has been developed here. The finite volume method (FVM) was utilized to solve the NRCM system, and its effectiveness was verified by comparing with the existing consolidation data. The parametric analysis results indicate that the soil's nonlinear rheological effect induced the excess pore water pressure (EPWP)’s accumulation in the initial loading. This phenomenon became more significant when considering the self‐weight stress or as the initial overconsolidated parameter, soil thickness, and seepage parameter increased. In contrast, it weakened with the increase of external loading. Additionally, considering the self‐weight stress slowed down the whole dissipation of EPWP in the initial period of loading. Nevertheless, it accelerated the nonlinear consolidation process in the middle and late loading stages.
•Design and analysis of a novel origami-inspired vibration isolator.•A three-mass body with multiple-degree-of-freedom motion is modelled.•Quasi-zero stiffness feature is achieved with compliant ...mechanisms.•Influence of structural weights are considered during dynamic behaviours.•Investigation of strong nonlinearity on isolation performance.•Nonlinear damping due to complex geometrical linkages is investigated.
Origami-inspired structure has shown strong nonlinearity on its force response during morphing process between phases. When the origami-inspired structure is applied as vibration isolation system, the structural weight is rare to be considered and discussed in the modelling and analysis of vibration isolation system. The effects of the structural self-weight on the dynamic behaviour of the isolation system is not yet fully understood. Thus, this study aims to investigate the influence of the self-weight induced structural and damping nonlinearity on the dynamic performance of an origami-based vibration isolator. A three-mass body, which includes the payload mass, top facets’ mass and bottom facets’ mass, with multiple degree-of-freedom (DOF) motion is proposed to describe the vibration isolation system. First, a quasi-zero-stiffness feature is designed and its static performance is discussed for a set of specifically selected system parameters. Then, the equation of motion for such three-mass body with spring damping considered is derived by using the harmonic balance method (HBM) on its Lagrange's formulation, where the effects of strong nonlinearity on its dynamic performance can be investigated. The analytical expression is verified with the numerical solutions, which are obtained using the Newmark numerical integration method. The influences of each important system parameter on the dynamic nonlinearity are also discussed. It is expected that this study would provide valuable insights to the effects of structural self-weight in a quasi-zero-stiffness isolation system.
Studies have revealed that rheological characteristics and self‐weight stress are nonnegligible during a consolidation process, especially for land reclamation projects or dredged soils. However, ...they are rarely considered simultaneously in traditional consolidation theories. This paper presents a general solution to the consolidation system of rheological soils that incorporates a fractional derivative model and self‐weight stress. First, the theory of the fractional derivative is introduced to the Merchant model to describe the consolidation behaviours of rheological soils, and the self‐weight stress of soils is simultaneously considered. Based on this model, the governing equation of a rheological consolidation system that considers self‐weight stress is obtained. Second, the analytical solutions of the effective stress and settlement in the Laplace domain are obtained by applying the Laplace transform to the consolidation governing equation. Further, the actual solutions in the real domain are obtained by a numerical Laplace transform inversion method (Abate's fixed Talbot method). Finally, the reliability and correctness of the consolidation theories and the proposed solutions are verified by comparing the calculated results with the degenerate solutions and experimental results in the existing literature. Furthermore, parametric studies are conducted to investigate the influence of rheological parameters and self‐weight parameters on the consolidation settlement and consolidation rate.
To further investigate the nonlinear creep properties of soft soils and the effect of variable loading, a one‐dimensional (1D) nonlinear creep consolidation system of soft soils under construction ...load is established, including time‐dependent drainage (TDD) boundary, elastic‐viscous‐plastic deformation, non‐Darcy flow (NDF), and self‐weight stress. The consolidation problem is presented by virtue of the finite volume method, and the associated calculation program is compiled. The efficiency of the numerical solutions is validated by comparing the degenerated solution against analytical, semi‐analytical, and numerical solutions. Then the influences of construction load and nonlinear creep model parameters on consolidation are studied. The results show that TDD boundary and construction load significantly affect consolidation, and the larger the loading rate and interface parameter, the faster soil's overall dissipation process of excess pore‐water pressure (EPP). Meanwhile, at the earlier consolidation stage, considering the secondary consolidation effect will cause an increase in excess pore‐water pressure (EPP). Prolonging the construction period, decreasing the interface parameter, considering the self‐weight stress, or increasing the non‐Newtonian index will all aggravate this phenomenon. Additionally, the TDD boundary, construction load, and non‐Newtonian index flow (NNIF) are not a determinant for final soil settlement.
In this study, a shell-based finite element model based on Technical University of Denmark 10MW reference wind turbine (DTU 10 MW RWT) is used to study its dynamic responses under seismic loads. The ...natural vibration frequencies of blades and wind turbines from this study and the results from the literature Bak et al. (2013) are compared. The difference in natural vibration frequencies of the blades arises from simple assigned orientation in composites blades in Bak et al. (2013). The differences in natural vibration frequencies of the wind turbines are suggested to be due to shell elements used in this study whereas beam elements are used in Bak et al. (2013). The built shell-based finite element model of DTU 10MW reference Wind Turbine is then subject to artificially generated earthquake converted from codes of European union earthquake response spectrum. The simulation results show that the foundation has a significant impact on the responses of DTU 10 MW RWT. That is, the DTU 10 MW RWT suffers less stress in the flexible foundation than in the more rigid foundation . The results also show that neglecting the self-weight effect could significantly underestimate the dynamic responses of wind turbines under seismic loadings. This study suggests that shell-element based model should be used in company in the process for certification.
Thermoset polymer composites show promise for additive manufacturing (AM) applications to address some of the limitations of the more widely used thermoplastic feedstock materials. Thermosets offer ...attractive mechanical properties while providing excellent interlayer bonding, high thermal and chemical stability, and reduced energy consumption as a result of deposition at room temperature. However, since thermoset resins rely on a crosslinking reaction to solidify, rather than quickly cooling like thermoplastics, viscoelastic properties must be relied upon to maintain deposited shape after deposition until crosslinking can occur. This fact has not impeded development and characterization of new thermoset feedstocks on the small scale, but recent efforts to increase scale of thermoset printing have highlighted issues with structural stability under self-weight. This study addresses issues of self-weight by investigating the mechanisms that cause collapse of tall, thin printed walls. Using nanoclay- and fumed silica-filled epoxy feedstocks, this work compares the collapse height for printed walls to stability models based on yielding and buckling mechanics. Inputs for these models – shear yield stress and storage modulus – were taken directly from parallel plate rheometry measurements. Model predictions were found to be in good agreement with experimental results, where both yielding and buckling behavior were observed, provided the rheological properties after a shear excursion were used as inputs. This work establishes a direct link between basic rheological properties of the feedstock, geometry of the printed object, and achievable height. The results presented highlight the importance of understanding recovery behavior in thermoset feedstocks and provide valuable guidance on the development of more effective direct-ink writing feedstock materials.
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•Yielding and buckling due to self-weight limit the stable height of printed viscoelastic materials.•Self-weight instability is linked to the yield stress and storage modulus of the ink, as measured by oscillatory rheometry.•Rheological properties measured after a shear excursion better predict stability than values taken before a shear excursion.•Post-shear recovery behavior of viscoelastic feedstocks is critical to understanding structural stability during 3D-printing.
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