The concrete permeability at low deformation of the chlorine ion is closely related to the porosity of concrete. Under stress, the porosity of concrete will change; at the same time, the chloride ion diffusion coefficient will also change. In this study, at the microscale, concrete was simplified as solid phase (zero porosity) and pore (the sum of various scales pores) of two phase composite materials. Based on the theory of elasticity, an analytical model was developed, and the quantitative relationship between the current porosity of concrete and the diffusion coefficient of the chloride ion, as well as the external equivalent stress, were evaluated. The primary parameters in the analytical model were the solid phase elastic moduli and the solid phase Poisson’s ratio, the initial porosity of the concrete and the external equivalent stress. The good agreement between the proposed model and the available test data illustrated the proposed model’s reliability and accuracy. The proposed model showed...

Prestressing steel bars are damaged in the typical pattern of corrosion fatigue under the combined action of chloride corrosion and fatigue load, in which the two damage types are mutually promoting. This study experimentally investigates the promotion effect of fatigue on corrosion. Twelve prestressed concrete beam specimens with steel strands that bore the combined action of corrosion and fatigue for 20 days were prepared using four chloride concentrations and three fatigue stress ranges. Moreover, the specimens were subsequently broken to measure the size of the corrosion pits. Based on these measured sizes, the volume and stress intensification factor (SIF) of the pits were calculated and their volumes and SIFs were statistically analyzed. The results show that the steel strands corroded in the typical pitting corrosion pattern with approximately anticlastic or spheroid shapes. The parameters of the pit’s volume and SIF showed both normal and lognormal distributions. Thus, it was observed that the greater the action intensity of fatigue, the larger were the averages of the two parameters and the 95th fractile of the lognormal distribution of the SIF.

Acoustic Emission (AE) technology may be used to quantify the accumulative crack damage of reinforcements, where, the attenuation of AE signal are needed to be studied for predicting the original AE strength with the received AE signal. Four groups of AE attenuation experiments on a steel strand embedded in concrete are conducted in this study to examine the basic influence of propagation length and the effect of the concrete status, such as cover layer depth, water-cement ratio, and saturation degree of pore water. Results show that AE strength (reflected by the parameters energy, amplitude, duration, and ringing count) attenuates with propagation length through an exponential function relation. The attenuation rate of AE strength increases with the increase in cover layer depth and water-cement ratio in an approximate exponential function and linear relations, respectively, and decreases with the increase in the saturation degree of pore water in an approximate elliptic function relation. General attenuation models of the four AE parameters were built based on the experimental results.

To accurately assess the seismic damage of high-rise structures under long-period ground motions (LPGMs), a 36-story SRC frame-RC core tube high-rise structure was designed. Twelve groups of LPGMs and twelve groups of ordinary ground motions (OGMs) were selected and bidirectionally input into the structure. The spectral acceleration S_90c considering the effect of higher-order modes was adopted as the intensity measure (IM) of ground motions, and the maximum inter-story drift angle θ_max under bidirectional ground motions was taken as the engineering demand parameter (EDP). Structural Incremental Dynamic Analysis (IDA) was conducted, the structural vulnerability was investigated, and seismic vulnerability curves, damage state probability curves, vulnerability index curves, as well as the probabilities of exceeding performance levels and vulnerability index of the structure during 8-degree frequent, design, and rare earthquakes were obtained, respectively. The results indicate that structural damage is significantly aggravated under LPGMs, and the exceeding probabilities for all performance levels are greater than those under OGMs, failing to meet the seismic fortification target specified in the code. When encountering an 8-degree frequent earthquake, the structure is in a moderate or severe damage state under LPGMs and is basically intact or in a slight damage state under OGMs. When encountering an 8-degree design earthquake, the structure is in a severe damage or near-collapse state under LPGMs and is in a moderate damage state under OGMs. When encountering an 8-degree rare earthquake, the structure is in a near-collapse state under LPGMs and in a severe damage state under OGMs.