Research on the Judgement Method for Catenary Action of Restrained Steel Beams in Fire

Meijing Liu,Shenggang Fan,Yang Guo,Heyang Gui,Runmin Ding,Hang Zhou 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.2

Based on fire tests, a parametric numerical simulation on the catenary action of restrained steel beams in fire was performed by the finite element software ABAQUS. It can be known that axial constraint stiffness, rotational constraint stiffness and load ratio are key factors that affect the catenary action in fire. The formation mechanism of catenary action under ISO-834 standard fire was studied; and the judgement method for catenary action in fire was presented. The results show that: (1) when axial constraint stiffness reaches a certain value, the catenary action of restrained steel beams will occur almost at the same time; (2) with the increase of rotational constraint stiffness or load ratio, the catenary action of steel beams will occur earlier; (3) for restrained steel beams under a small load ratio, the catenary action usually occurs in fire when the mid-span deformation reaches 1/15 of the span; but for restrained steel beams under a large load ratio, the catenary action usually occurs when the mid-span deformation reaches 1/18 of the span; (4) for restrained steel beams with a large rotational constraint stiffness, the judgement method for catenary action in fire can still adopt the same method as above, which will be a little conservative.

Psoralen synergies with zinc implants to promote bone repair by regulating ZIP4 in rats with bone defect

Meijing Liu,Junlong Tan,Shuang Li,Chaoyang Sun,Xiangning Liu,Hongtao Yang,Xiaogang Wang 한국생체재료학회 2023 생체재료학회지 Vol.27 No.00

Background The regulation of dose-dependent biological effects induced by biodegradation is a challenge for the production of biodegradable bone-substitute materials, especially biodegradable zinc (Zn) -based materials. Cytotoxicity caused by excess local Zn ions (Zn2+) from degradation is one of the factors limiting the wide application of Zn implants. Given that previous studies have revealed that delayed degradation of Zn materials by surface modification does not reduce cytotoxicity; in the present study, we explore whether preventing the entry of excess Zn2+ into cells may can reduce local Zn toxicity by applying Psoralen (PRL) to Zn implants and assessing its ability to regulate intracellular Zn2+ concentrations. Methods The effects of different concentrations of Zn2+ on cellular activity and cytotoxicity were investigated; briefly, we identified natural compounds that regulate Zn transporters, thereby regulating the concentrations of intracellular Zn2+, and applied them to Zn materials. Of these materials, PRL, a natural, tricyclic, coumarin-like aromatic compound that promotes the proliferation and differentiation of osteoblasts and enhances osteogenic activity, was loaded onto the surface of a Zn material using peptides and chitosan (CS), and the surface characteristics, electrochemical properties, and activity of the modified Zn material were evaluated. In addition, the ability of Zn + CS/pPRL implants to promote bone formation and accelerate large-scale bone defect repairs was assessed both in vitro and in vivo. Results We determined that 180 μM Zn2+ significantly induced pre-osteoblast cytotoxicity, and a 23-fold increase in Zrt- and Irt-like protein 4 (ZIP4) expression. We also found that PRL dynamically regulates the expression of ZIP4 in response to Zn2+ concentration. To address the problem of cytotoxicity caused by excessive Zn2+ in local Zn implants, PRL was loaded onto the surface of Zn implants in vivo using peptides and CS, which dynamically regulated ZIP4 levels, maintained the balance of intracellular Zn2+ concentrations, and enhanced the osteogenic activity of Zn implants. Conclusions This study reveals the importance of Zn2+ concentration when using Zn materials to promote bone formation and introduces a natural active ingredient, PRL, that can regulate intracellular Zn2+ levels, and thus may be clinically applicable to Zn implants for the treatment of critical bone defects.

Fabrication and Characterization of Moisture Slow-releasing Embroidered Electrode and ECG Monitoring Belt

Liyan Liu,Meijing Ma,Dongyu Tang,Yao Hu,Hao Liu 한국섬유공학회 2020 Fibers and polymers Vol.21 No.12

The microenvironmental humidity at the interface between the bioelectrical electrode and the human skin canaffect the quality of the bioelectrical signal collected by the electrode. This paper utilized superabsorbent polyacrylic fiber asthe base material to fabricate a novel moisture slow-releasing embroidered electrode. The moisture-locking capacity ofpolyester non-woven fabric (PENWF) substrate, polyacrylic non-woven fabric (PANWF) substrate, polyester-basedelectrode (PE-E) and polyacrylic-based electrode (PA-E) were compared in this paper. The non-woven fabric withpolyacrylic fiber owned excellent moisture-locking capacity, so it could realize the slow-releasing of moisture and provide asuitable wet environment for the dry bioelectric electrode to collect ECG signals. With the extension of time, the amplitude ofthe ECG signal collected by PA-E did not change much, and only decreased by 17.1 % after evaporating for 10 h; but afterevaporating for 10 h, the amplitude of the ECG signal collected by the PE-E decreased by 48.9 %. In addition, 5 mm, 10 mm,and 15 mm thick polyurethane sponge (PUS) filling materials were used to make the ECG monitoring belts, and their signalto-noise ratios were analyzed under different states of static, swinging arms and walking. The 5 mm thick elastic fillermaterial has the highest signal-to-noise ratio among the three thicknesses. It could collect ECG signals stably under swingarm and walking at a constant speed, and the signal-to-noise ratio (SNR) were 25.393 dB and 30.086 dB respectively. Thepolyurethane sponge filling materials with a thickness of 5 mm provided an appropriate pre-stress for the ECG signaldynamic measurement, which could provide a reference parameter for the production of smart ECG garment in the future.

Nonlinear Finite Element Modeling of Two-stage Energy Dissipation Device with Low-yield-point Steel

Shenggang Fan,Zhixia Ding,Li Du,Chunfang Shang,Meijing Liu 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.4

Equipped with many advantages, such as low yield strength, low yield ratio, high elongation, severe plastic deformation and good energy dissipation ability, low-yield-point steel is very suitable for use in metal energy dissipation devices. Based on different materials (Q235 steel and low-yield-point steel) and different parabola openings, two types of energy dissipation steel plates underwent different yield displacements and then were assembled into a new open-hole energy dissipation device, which could achieve the goal of two-stage energy dissipation under small and large earthquakes. To obtain the failure modes and energy dissipation mechanism under the low reversed cyclic horizontal loads and observe relevant hysteretic curves and skeleton curves, the new energy dissipation device was studied and analyzed by means of theoretical analysis, experimental research, and numerical simulation analysis. Based on parametric analyses, the effects of the height, thickness and opening coefficient of the steel plate on the energy dissipation ability of the new energy dissipation device were emphasized. Thus, the key parameters affecting the energy dissipation behavior were obtained. Finally, a force-restoring model of the new energy dissipation device was put forward, and the calculation formulas were given for many parameters, including stiffness, yield displacement, yield load, ultimate displacement and ultimate load. The results show that the new open-hole energy dissipation device has the advantages of superior energy dissipation performance, obvious energy dissipation in two stages, and wide application prospects in structural seismic design.