Behavior and strength of headed stud shear connectors in ultra-high performance concrete of composite bridges

This study presents an experimental and numerical investigation on the static behavior of headed stud shear connectors in ultra-high performance concrete (UHPC) of composite bridges. Four push-out specimens were tested. It was found that no cracking, crushing or splitting was observed on the concrete slab, indicating that UHPC slab exhibited good performance and could resist the high force transferred from the headed studs. The numerical and experimental results indicated that the shear capacity is supposed to be composed of two parts stud shank shear contribution and concrete wedge block shear contribution. The stiffness increment of a stud in UHPC was at least 60% higher than that in normal strength concrete. Even if the stud height was reduced from 6d to 2d, there was no reduction in the shear strength of a stud. Short stud shear connectors with an aspect ratio as small as 2 could develop full strength in UHPC slabs. An empirical load-slip equation taking into account stud diameter was proposed to predict the load-slip response of a stud. The reliability and accuracy of the proposed load-slip equation was verified by the experimental and numerical load-slip curves.

Insight into the role of binding interaction in the transformation of tetracycline and toxicity distribution

The transformation of free state organic micro-pollutants(MPs)has been widely studied;however,few studies have focused on mixed and bound states MPs,even though numerous ionizable organic MPs process a strong tendency to combine with dissolved organic matters in aquatic environments.This study systemically investigated the distribution and toxicity assessment of tetracycline(TET)transformation products in free,mixed and bound states during UV,UV/H2O2,UV/PS and CNTs/PS processes.A total of 33 major transformation products were identified by UPLC-Q-TOF-MSMS analysis,combining the double bond equivalence and aromaticity index calculations.The binding interaction would weaken the attack on the dimethylamino(-N(CH3)2)group and induce the direct destruction of rings A and B of TET through the analysis of 2D Kernel Density changes and density functional theory(DFT)calculations.Toxicity assessment and statistics revealed that the intermediate products with medium molecular weight(230
m/z
380)exhibited higher toxicity,which was closely related to the number of the rings in molecular structures(followed as 2»3>1z4).A predicted toxicity accumulation model(PTAM)was established to evaluate the overall toxicity changes during various oxidation processes.This finding provides new insight into the fate of bound MPs during various oxidation processes in the natural water matrix.

Probing the roles of pH and ionic strength on electrostatic binding of tetracycline by dissolved organic matters: Reevaluation of modified fitting model

The binding performance of dissolved organic matters (DOM) plays a critical role in the migration,diffusion and removal of various residual pollutants in the natural water environment. In the currentstudy, four typical DOMs (including bovine serum proteins BSA (proteins), sodium alginate SAA (polysaccharides), humic acid HA and fulvic acid FA (humus)) are selected to investigate the binding roles inzwitterionic tetracycline (TET) antibiotic under various ionic strength (IS ¼ 0.001e0.1 M) and pH (5.0e9.0). The dialysis equilibration technique was employed to determine the binding concentrations ofTET, and the influence of IS and pH on binding performance was evaluated via UVevis spectroscopy, totalorganic carbon (TOC), and Excitation-Emission-Matrix spectra (EEM), zeta potentials and molecule sizedistribution analysis. Our results suggested that carboxyl and phenolic hydroxyl were identified as themain contributors to TET binding based on the fourier transform infrared spectroscopy (FTIR) analysis,and the binding capability of four DOMs followed as HA > FA » BSA > SAA. The biggest binding concentrations of TET by 10 mg C/L HA, FA, BSA and SAA were 0.863 mM, 0.487 mM, 0.084 mM and 0.086 mM,respectively. The higher binding capability of HA and FA is mainly attributed to their richer functionalgroups, lower zeta potential (HA/FA ¼ 15.92/-13.54 mV) and the bigger molecular size (HA/FA ¼ 24668/27750 nm). IS significantly inhibits the binding interaction by compressing the molecular structure andthe surface electric double layer, while pH had a weak effect. By combining the Donnan model and themultiple linear regression analysis, a modified Karickhoff model was established to effectively predict thebinding performance of DOM under different IS (0.001e0.1 M) and pH (5.0e9.0) conditions, and the R2 oflinear fitting between experiment-measured logKDOC and model-calculated logKOC were 0.94 for HA and0.91 for FA. This finding provides a theoretical basis for characterizing and predicting the binding performance of various DOMs to residual micropollutants in the natural water environment.

Synthesis and Photoluminescence Enhancement of Silver Nanoparticles Decorated Porous Anodic Alumina

Silver nanoparticles（Ag NPs） were successfully assembled in porous anodic alumina（AAO） templates via a green silver mirror reaction.The Ag NPs/AAO composite templates then were characterized by field emission scanning electron microscopy（FESEM）,energy-dispersive X-ray microanalysis（EDX）,and X-ray diffraction（XRD）.Furthermore,the photoluminescence（PL） properties were also investigated.Compared with the blank AAO,the PL intensity of Ag NPs/AAO templates are enhanced and the maximum enhancement is 2.58 times.Based on the local electric field enhancement effect,the theoretical values were also deduced,which are basically coincident with the experimental.

Seismic stability of earth slopes with tension crack

Cracks at the crest of slopes frequently occur during earthquakes. Such cracks result from limited tension strength of the soil. A tension cut-off in Mohr-Coulomb shear strength can represent this limited strength. Presented is an extension of variational analysis of slope stability with a tension crack considering seismicity. Both translational and rotational failure mechanisms are included in a pseudo-static analysis of slope stability. Developed is a closed-form to assess the seismic stability of slopes with zero tensile strength. The results indicate that the presence of the tension crack has significant effects on the seismic stability of slopes, i.e., leading to small value of the yield acceleration. Considering soil tension strength in seismic slope analysis may lead to overestimation on the stability, as much as 50% for vertical slopes. Imposing tension crack results in transit of the critical failure mode to a straight line from a log-spiral, except for flat slopes with small soil cohesion. Under seismic conditions, large cohesion may increase the depth of crack, moving it closer to the slope.