Current Issue : April - June Volume : 2020 Issue Number : 2 Articles : 5 Articles
Even though large-scale projects, such as sea-crossing bridges and tunnels, have complex structures and service conditions, the\nstructural health monitoring (SHM) system can comprehensively monitor the stress situation and damage evolution law in the\nentire construction and service process of such structures. Based on the background of the Hong Kong-Zhuhai-Macao Bridge,\nthis study systematically introduces the overall goal and framework of the SHM system, monitoring content, and sensor information.\nMoreover, the structural health condition evaluation methods and data analysis methods are presented in detail. Then,\non the basis of a multilayer data storage system, a fault-tolerant data center platform design, an open integrated supervision\nplatform design, and other measures, a set of reliable and advanced large-scale software systems are built to achieve the SHM\nsystem for the Hong Kong-Zhuhai-Macao Bridge. Finally, the wind characteristics around the Hong Kong-Zhuhai-Macao\nBridge and some of the monitored structural responses from the Super Typhoon Mangkhut in 2018 are shown, which verified that\nthe SHM system can accurately and reliably monitor and feedback the environmental load and structural response of the principal\nparts of the Hong Kong-Zhuhai-Macao Bridge under complicated service environment....
Superabsorbent polymer (SAP) is attracting attention as a water-entraining admixture\nthat reduces shrinkage or heals cracks in concrete. Cross-linked sodium polyacrylate SAPs, which\nare the most widely produced SAPs in the global market, are applicable as concrete admixtures.\nHowever, there have been contradictory results on the freezeâ??thaw resistance of concrete with SAPs.\nThis study aims to clarify these results considering the water absorption behavior of SAPs in hardened\nconcrete when effective water-to-cement ratios are different. Firstly, the absorbencies of one kind of\ncross-linked sodium polyacrylate SAP (SAP_SP) in pore solution and fresh mortar were measured\nby a tea bag test and flow test, respectively. Pore size distribution, capillary water absorption, and\ndeformation during freezeâ??thaw cycles were analyzed for mortar samples with varying SAP_SP\ndosages. In the main tests, concrete samples with three different SAP_SPs/cement ratios (0.1%, 0.2%,\nand 0.3%) and a reference sample were prepared, and internal damage and salt scaling were measured\nunder freezeâ??thaw cycles. Because SAP_SP absorbs water in fresh mixtures, additional water was\nadded to the mixture considering the water absorbency of the SAP_SP. It was found that the used\nSAP_SPs prematurely release their stored water so the effective water-to-cement ratio was increased\nwhen a larger amount of SAP_SP was used. The higher effective water-to-cement ratio caused more\ninternal damage and salt scaling due to the weaker cementitious matrix. In addition, mortar samples\nwith a high SAP_SP content show a larger absorption of capillary water than the reference sample.\nThe result can be interpreted by an observation that SAP_SP in air voids absorbs water and expands\nto relatively large capillary pores or neighbor air voids during the capillary water absorption process....
This work introduces a recent application of the online nondestructive damage assessment system into a cable-stayed bridge. A set\nof ambient modal parameters are automatically extracted every 20 minutes using real-time signal data collected from a total of 26\naccelerometers attached on the deck plate of the bridge. Then, a set of modal flexibilities are reconstructed by the combination of\nthe extracted modal parameters with the approximated modal mass of the girder. Next, the curvature of the modal flexibility is\napproximated by a central difference formula. Finally, the set of flexural damage index equations is constructed by comparing the\nmodal curvature of the damaged state to that of the undamaged state. Solving the overdetermined flexural damage index\nequations, the desired damage index is finally quantified. The resulting index clearly indicates the location and severity of the\npotential structural damage on the girder. Based on the overall performance of the implemented health monitoring system, the\nbridge operatorâ??s damage index control criteria are set to ................................
To investigate the optimal longitudinal seismic energy dissipation system of straddle-type monorail-cum-road long-span cablestayed\nbridges, the Niutianyang Bridge was selected as the engineering background, and the explicit time-domain dimensionreduced\niteration method was adopted to carry out nonlinear time-history analysis. To consider the dynamic characteristics of\nlongitudinal movable supports, the static and dynamic responses of four kinds of energy dissipation systems were studied,\nincluding longitudinal unconstrained, elastic cable, viscous damper, and speed lock-up devices.The damping effect of four types of\nschemes in which viscous dampers were installed at piers or towers was analysed, and the parameters of the viscous dampers were\noptimised. The influences of the straddle-type monorail train braking force and the running vibration of the straddle-type\nmonorail traffic on the parameters of the viscous dampers were analysed. This study shows that the viscous damper system had the\nlowest bending moment at the bottom of the tower and a smaller displacement response, and the energy dissipation was the best.\nEach viscous damper had the highest energy dissipation efficiency when they are installed only at the main tower����.....
This paper is focused on exploring the dynamic mechanical properties and damage process of siltstone. For this purpose, different\nstress wave wavelengths (0.5m approximately 2.0 m) and different strain rates (25 s^-1 approximately 120 s^-1) were applied to siltstone specimens in the SHPB\ndynamic impact test. The experimental results show that the dynamic compressive strength of siltstone is linearly positively correlated\nwith the strain rate, and the dynamic increase factor is linearly positively correlated with the natural logarithm of strain rate; the peak\nstrain is linearly positively correlated with the strain rate, and the increase in wavelength causes the peak strain to increase. Through\nmultiple impact tests, it is concluded that the cumulative damage to siltstone increases with the number of impacts. The cumulative\ndamage curve exhibits an initial rapid rise, followed by a stable development, followed by another rapid rise. With increasing\nwavelength of the stress wave, the stable development of the curve gradually decreases, the cumulative damage to the siltstone is\nintensified, and the number of repeated impacts is reduced. Meanwhile, a model for damage evolution is established based on the\ninverse of the Gompertz function, and the physical meanings of the model parameters are determined. The model can reflect the\ninfluence of both stress wave parameters and impact times. Verification of the model demonstrates the rationality of the model and the\ncorrectness of the physical meaning of the parameters. The model could be applied in future studies of damage to sedimentary rocks....
Loading....