Sludge ejection from the foundation of a wind turbine tower fixed by the anchor-ring method and the resulting sludge buildup have been confirmed to cause the undesirable phenomenon of lifting of the tower. Using specimen that is a model part of the wind turbine foundation, this study investigates the influence of liquid water, differences in W/C, and differences in loading speed, to analyze developing factors on the concrete damage . The results shows that penetration of liquid water from rainfall and snowfall produces a wedge effect, breakdown of the concrete pore skeleton structure, grinding by sludge particle, cavitation and other effects, and leads to rapid deterioration of the anchorage performance of concrete foundation. Based on the knowledge on the deterioration process, rational countermeasures on design and maintenance are proposed.
The strut-tie model approaches of current design codes have proven to be effective in the ultimate strength analysis and design of disturbed regions in structural concrete. For the reliable analysis and safe design of disturbed regions using these approaches, the effective strength of concrete struts must be determined accurately. In this study, we proposed equations for the effective strengths of concrete struts that are useful for the three types of statically determinate and indeterminate strut-tie models of reinforced concrete deep beams with shear span-to-effective depth ratio of less than 3.0. The effects of the shear span-to-effective depth ratio, the compressive strength of concrete, and the flexural and shear reinforcement ratios were reflected in the proposed equations. To validate the proposed equations, the ultimate strengths of 395 reinforced concrete deep beams, tested to failure, were evaluated by using the three types of strut-tie models with existing and proposed equations.
The effectiveness of a commercially available sacrificial point anode for corrosion prevention of steel in cracked concrete is presented. Reinforced concrete prisms with dimensions of 150 mm x 150 mm x 500 mm were prepared with a water to cement ratio (W/C) of 0.4 showing crack widths ranging from 0.1 to 0.4 mm obtained by pre-cracking. These specimens were exposed to three conditions: (1) laboratory air (temperature of 20±2°C and relative humidity of 60%); (2) immersed in 3% NaCl solution; and (3) dry/wet cycles of above mentioned conditions. Measurements included the free corrosion potential, polarization behavior of the sacrificial point anode, anodic-cathodic polarization curve of the reinforcement steel and visual observation. The test results show that the sacrificial point anode was effective to prevent the embedded steel from corrosion in cracked concrete. Specimens exposed to dry/wet cycles or immersed in 3% NaCl solution demonstrated a better protection than those exposed to laboratory air due to the high moisture condition. Thus, a sacrificial point anode becomes active to protect the steel bars even in cracked concrete.
This paper is to apply the multi-scale thermo-hygro-mechanistic modeling to full-scale RC structural systems under combined long-term ambient and short seismic actions. The authors also aim to dissolve numerical difficulty for full-scale performance assessment of huge degree-of-freedom. First, the multi-scale modeling is experimentally checked by using corroded RC columns under high axial compression. Second, the steel corrosion is computationally reproduced to a multi-story RC building under long-term fictitious ambient conditions. The seismic ground motion is subsequently applied to the corrosion damaged mockup. Beforehand, the effect of drying shrinkage, which is inevitable for structural concrete in air, is discussed so as to clarify the pure corrosion impact to the whole structural system. The steel corrosion deteriorates the ductility of seismic resistant members, but as a global influence, steel corrosion is validated to reduce the base-shear input of floors owing to the decayed stiffness by corrosion. Through these case-studies, the authors raise the points of discussion to take into account the local and global effects of corrosion all at once for seismic performance assessment, and that the knowledge solely on the capacity of corroded RC members cannot lead to an engineering solution.
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