Search

Detection of nitroaromatic compounds (NACs) has been investigated previously using fluorescent metal–organic frameworks (MOFs). However, the vagueness of the sensing mechanism has hindered the development of efficient sensors. Here we have explored a two-dimensional (2D) MOF, Zr-BTB nanosheets, as a rapid (as short as 10 s), sensitive, and selective sensor for detecting low-concentrations of 2,4-dinitrophenol (2,4-DNP); its limit of detection for 2,4-DNP was quantified to be as low as 0.013 μM (2.40 ppb). The molecular sensing mechanism and the specific interaction sites were investigated using FTIR, UV-vis absorption, XPS, and 2D ssNMR spectroscopy along with density functional theory (DFT) calculations. This work presents insight into florescence-quenching mechanisms for the sensitive sensing of NACs at the molecular level, which may provide valuable ideas for designing novel MOF sensors for NAC detection. [ABSTRACT FROM AUTHOR]

The objective of the current paper is to study and extend the exponential-polynomial-closure (EPC) method in analyzing the non-stationary response probabilistic solutions of nonlinear stochastic oscillators excited by combined deterministic harmonic and Gaussian white noise excitations. The probabilistic solution of the non-stationary responses of nonlinear stochastic oscillator is expressed as an exponential function of polynomial with time-variant coefficients and then the Fokker–Planck–Kolmogorov equation is solved approximately. Two validation examples are presented. The results obtained by Monte Carlo simulation (MCS) and EPC method are presented to show their good agreement, which confirms the effectiveness of the EPC method for the probabilistic solutions to nonlinear stochastic oscillators. The advantage of the EPC method for analyzing the oscillators with strong nonlinearities is investigated by comparison with Equivalent Linearization method. Furthermore, compared with MCS, the computational efficiency by using the EPC method is increased by about 56 times in the first example and 44 times in the second example. [ABSTRACT FROM AUTHOR]

A novel precast concrete (PC) frame with an innovative assembly pattern and optimised connection locations was proposed and evaluated. The PC column components were connected by extrusion sleeves and/or U-type reinforcement ferrules to realise cost-effective, efficient, and reliable assembly. Quasi-static cyclic loading tests and finite element analyses were conducted on a cast-in-place (CIP) frame and three PC frames with different connection types. The PC frames exhibited higher lateral stiffness and load bearing capacities than the CIP frame, as well as similar energy dissipation capacities. The PC frames employing the extrusion sleeve connections in the beam exhibited the best seismic performance. [ABSTRACT FROM AUTHOR]

This paper investigates a novel variable‐grade prefabricated concrete (PC) slab with surrounding composited which has high prefabrication rate, sufficient installation rigidity, high on‐site construction efficiency, and good overall working performance. To improve the crack‐resistance performance of the transverse superposed surface and the overall working performance of the proposed novel PC slab, we optimize the position of variable‐grade and arrange it at the location where the bending moment is close to zero. We perform comparatively bending tests on three two‐span full‐scale slab strips that include boundary and intermediate beam‐slab joints to systematically investigate the flexural behavior of the proposed novel slab. The load versus deflection relationship, failure mode, distribution of cracks, development law of crack width and development of steel strain are comparatively studied. The test results confirm that the flexural behavior of the proposed novel PC slabs are similar and slightly better than that of the cast‐in‐place slab in general. No crack or slippage appears at the interface between the precast panel and the post‐pouring concrete. The connection method of L‐shaped anchorage rebars lap splicing in this study is cost‐effective, efficient, and reliable. Furthermore, we establish a finite element model and perform a parametric investigation on the proposed novel PC slab. Parametric simulations conclude that the increase of the strength of post‐pouring concrete and post‐pouring layer thickness can improve the bearing capacity of the proposed novel PC slabs. [ABSTRACT FROM AUTHOR]

A new theoretical calculation method for the load-slip curve and the shear stiffness of the stud based on Winkler's elastic foundation beam theory and deflection differential equation of the stud is proposed. Different stress characteristics of the elastic and plastic zones of the concrete are considered in the proposed method. The accuracy of the theoretical calculation method is validated by the test results. Moreover, the effect of concrete strength, stud diameter, and yield strength on the stud load-slip curve is analyzed. The results show that the proposed model can effectively reflect the change process of the load-slip curve of the test specimen stud connector. The stud diameter, stud yield strength, and concrete strength affect the peak slip, shear stiffness, and shear capacity of stud shear connectors. With an increase in stud diameter, the peak slip, shear stiffness, and shear bearing capacity of the stud are all increased. An increase in the yield strength of the stud increases its elastic slip, peak slip, and shear capacity. Lastly, with an increase in concrete strength, the elastic slip and peak slip of the stud both decrease, whereas the shear stiffness and shear bearing capacity are increased. [ABSTRACT FROM AUTHOR]