ABSTRACT This study aims to comprehend the effect of pile dimensional variations and to elucidate the superior pile dimension under frequency-dependent coupled vibration. The study performed field vibration tests on two different sets of piles to understand the effect of diameter and length alterations, by assuming a 90 mm diameter pile of 1.7 m length as the standard pile. The first set of piles, say Phase 1, deals with a 35 % dimension decrement as compared with the standard pile (60 mm diameter pile of 1.7 m length and 90 mm diameter pile of 1.1 m length), whereas Phase 2 deals with a dimension increment, as compared with the standard pile (114 mm diameter pile of 1.7 m length and 90 mm diameter pile of 2.3 m length). As a preliminary investigation, site characterization was done using both in situ and laboratory testing. Forced vibration tests were conducted in the field on all five piles for five different chosen eccentric moments (0.131, 0.186, 0.214, 0.241, and 0.304 Nm) under a static load of 5 kN. The responses were acquired in terms of frequency-amplitude responses, and the plots show two prominent peaks and nonlinear behavior. The responses showcased that the diameter alteration of piles exemplified a prominent role in the dynamic performance of the pile as compared to length increment. Finally, this research underscored that prioritizing pile diameter is more effective for optimizing pile performance in scenarios involving coupled dynamic loading.
ABSTRACT Foam concrete suffers from low intrinsic toughness originating from its porous microstructure, which restricts its engineering application. In this work, polypropylene fibers, fly ash, and hydroxypropyl methylcellulose were adopted to improve the toughness of A06-grade foam concrete. Response surface methodology was used to optimize additive dosages for flexural performance, and the optimal mixing proportions of the three additives were obtained. Drying-shrinkage tests, together with scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDS) microscopic characterizations, were performed to evaluate the compactness of the interfacial transition zone (ITZ) and reveal the underlying modification mechanism. The ternary composite system achieves superior performance compared with single-component modification. The synergistic effects, including fiber bridging, foam stabilization, and the pozzolanic-filling effect, jointly contribute to a denser ITZ, which effectively enhances the toughness of foam concrete. This study provides a reference for the performance optimization of lightweight functional foam concrete materials.
ABSTRACT Electropolishing (EP) is a commonly used surface finishing technique, particularly known for enhancing the corrosion resistance of treated workpieces. In this study, the effects of EP processing parameters on the surface gloss and corrosion resistance of AISI 304 stainless steel were systematically investigated by examining the influence of applied current densities ranging from 1.5 to 10 A/dm2 and electrolyte operating temperatures between 30°C and 50°C. A Taguchi L9 orthogonal array, along with signal-to-noise ratio analysis, analysis of variance, and second-order regression modeling, was utilized to evaluate and optimize the individual and combined effects of these two control factors. AISI 304 stainless steel was employed as both the anode and cathode in the EP process. The electrolyte consisted of phosphoric acid, sulfuric acid, and deionized water. This study involved treating AISI 304 stainless steel specimens with a standardized process. The treatments included degreasing for 10 min at 25°C, pickling for 15 min at the same temperature, and EP under varying current densities and electrolyte temperatures for 15 min. Afterward, chemical passivation was conducted for 30 min at 25°C. The effects of current density and temperature on surface gloss and corrosion resistance were evaluated. Finally, the specimens were tested for corrosion performance by exposing them to neutral salt spray for 1,000 h. The results indicate that the EP process significantly enhances the corrosion resistance and surface gloss of AISI 304 stainless steel. Unlike most previous studies, which primarily focus on short-term electrochemical characterization, this study provides a systematic experimental assessment of the effect of EP current density on the long-term corrosion performance of AISI 304 stainless steel under standardized ASTM B117, Standard Practice for Operating Salt Spray (Fog) Apparatus, neutral salt spray conditions.
ABSTRACT Active structural control systems offer potential improvements in the serviceability of dynamically sensitive bridges. This study experimentally evaluates a Direct-Drive Neutral Equilibrium Mechanism (DNEM) for precision displacement control of a 2.5 m laboratory-scale steel bridge under dynamic loading. The system integrates a rotary-arm-and-tendon actuation mechanism with a composite real-time control strategy (proportional-derivative feedback and harmonic compensation). The 1,000 Hz closed-loop control relies exclusively on LVDT measurements for real-time precision feedback, while a Digital Image Correlation (DIC) system (500 fps) is employed in parallel solely for offline independent spatial validation. Controller gains were optimized using NSGA-II (Kp=42.3 N/mm, Kd=3.7 N·s/mm) within a fixed structural configuration. Experimental results demonstrate a 99.2 % peak displacement reduction under impact loading (6.00–0.05 mm) and steady-state cyclic precision of 0.128±0.0076 mm under a sustained 5 kN moving load. Phase-portrait analysis confirmed stable closed-loop operation without limit-cycle behavior. The close agreement between LVDT and DIC measurements validates the experimental methodology. This study establishes quantitative performance benchmarks for controller tuning, actuator evaluation, and future full-scale implementation of active bridge control technologies.
ABSTRACT Weld seams in membrane structures exhibit a significantly higher failure probability than the base material and often act as initiation points for structural damage. Their mechanical properties are strongly influenced by welding process parameters, including temperature, time, and pressure. This work investigated the effects of welding parameters on the mechanical performance of Polyvinyl Chloride (PVC)- and Polytetrafluoroethylene (PTFE)-coated fabric weld seams through orthogonal experiments, analyzing the failure modes, mechanical characteristics, and microstructural variations of three weld configurations to reveal the failure mechanism and establish a high-accuracy strength prediction model. Joint efficiency is defined as the ratio of the ultimate bearing capacity of welded joints to that of the base material. For PVC-coated fabrics, the lap weld seams reached a joint efficiency of 108.23 %, with 78 % of specimens failing in the base material. The joint efficiency of single-covered and double-covered butt weld seams dropped to a minimum of 78.54 %, attributed to stress concentration and bending effects. For PTFE-coated fabrics, the maximum joint efficiency reached 101.57 %. The error of the established strength prediction model is less than or equal to 5 %. For the optimal parameter combination (380°C/80 s/0.5 MPa), the predicted strength is 6,954.98 N, with an error of only 0.89 % compared to the measured value.
