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Volume 1, Issue 1, 2023

Abstract

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In regions characterized by extreme cold and elevated altitudes, notably in the northwest, the mechanical characteristics of construction materials such as Ultra-High Performance Concrete (UHPC) are critically impacted by ambient temperatures. This study investigates the mechanical properties of UHPC subjected to low-temperature curing environments, conducting uni-axial compressive and splitting tensile strength tests on UHPC specimens, which comprise water, dry mix, and steel fibers. These specimens were cured at varied temperatures (-10℃, -5℃, 5℃, 10℃). Utilizing damage theory principles, the loss rate in compressive strength of UHPC post-curing was quantified as a damage indicator, revealing internal degradation. A predictive model for damage under low-temperature maintenance was developed, grounded in the two-parameter Weibull probability distribution and empirical damage models. Parameter estimation for this model was achieved through the least squares method, informed by experimental data. The findings indicate a rapid increase in UHPC’s mechanical strength at all curing temperatures, with 7-day strength achieving approximately 90% of its 28-day counterpart. A positive correlation was observed between the mechanical strength of UHPC, curing temperature, and age. Despite a reduction in mechanical strength due to low-temperature curing, UHPC was found to attain anticipated strength levels suitable for construction in cold environments. The proposed model for predicting UHPC damage under low-temperature conditions demonstrated efficacy in estimating the strength loss rate, thereby offering substantial technical support for UHPC’s application in northwest regions.

Abstract

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In addressing the challenge of precise lateral attitude adjustment during high-altitude hoisting of non-standard steel structures, such as the rotating platforms in rocket launch towers, a novel approach involving an adjustable counterweight balance beam has been developed. This method entails the strategic placement of movable counterweight blocks on the balance beam, thereby enabling the manipulation of the gravity center's distribution for refined posture control of the load suspended beneath the beam. A theoretical model encompassing static balance and deformation coordination has been formulated for this adjustable balance beam system. Utilizing Matlab for computational analysis, the model elucidates the effects of various parameters, including the counterweight block position, block weight, lifted load, sling length, and balance beam length on the beam's attitude. The findings suggest that the beam's performance can be optimized in accordance with the weight of the load. Through the judicious design of the sling and beam lengths, as well as the counterweight block mass, continuous fine-tuning of the hoisting posture is achievable via progressive adjustments of the counterweight block's position on the balance beam. The theoretical calculations and analyses derived from this study offer valuable insights for the design of new balance beams and the enhancement of hoisting operations, catering to the specific demands of high-precision, high-altitude lifting tasks.
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