This paper presents experimental and analytical studies on the punching shear behavior of concrete-filled steel-tube (CFT) bridge column to pile-foundation connections. Five CFT bridge column to reinforced-concrete (RC) four-pile cap connections were constructed and tested under monotonic downward vertical loads to the columns, and the effects of the connection details, including embedment depths of CFT columns, shear studs, face annular rings, and headed shear reinforcement, on punching shear behavior were evaluated. Test results indicate that the connection details significantly affected the cracking patterns of pile caps and the failure modes of connections. The use of shear studs, face annular rings, headed shear reinforcement, and reduced embedment depths of CFT columns can substantially enhance the punching shear strength of CFT column to RC-pile cap connections. The tested specimen with a face annular ring welded onto the CFT column base showed the most favorable punching shear behavior with the highest loading capacity and the most ductile failure mode. On the basis of the experimental observations, the effective depths of pile caps for CFT columns under punching were proposed, and then the punching shear strength of the tested connections was predicted using current design codes for the design of RC footings. A modified empirical strength model was also developed on the basis of experimental and finite-element analysis results.

In the process of service, reinforced concrete structures have to bear both load and multi-environmental factors. The deterioration of reinforced concrete beams is critical to the durability, safety, and sustainability of reinforced concrete structures. The main aim of the present research is to determine the degradation mechanism of reinforced concrete beams subjected to sustained loading and multi-environmental factors. Reinforced concrete beam specimens were prepared, loaded and then exerted multi-environmental factors. At the end of each degradation period, the degradation of concrete (chemical contents of concrete beam surfaces, carbonation depth, compressive strength and maximum cracks) and the corrosion of steel bars (corrosion ratio and tensile strength) were continuously measured. Moreover, degraded reinforced concrete beams were flexural loaded in four-point bending failure tests. The degradation mechanism of reinforced concrete beams subjected to sustained loading and multi-environmental factors was analyzed. Thus, this study can promote a comprehensive understanding of reinforced concrete beams subjected to sustained loading and multi-environmental factors.

Besides the inspection of material behaviors of the collapsed raw-coal surge bunker, comprehensive safety of the loading bunkers and the clean-coal bunkers were inspected. The parameters involve apparent characteristics, carbonized depth, compression strength of concrete, corrosion rate of steel bar, decline degree of bunkers and so on. In addition, analyses were made on the special natural, technologic, mechanical and geologic environment around the bunkers. On this basis, this paper studied the deterioration and collapse mechanism of reinforced concrete (RC) bunkers. The results suggest that the coupling action of poor concrete quality, severe natural environment, complex technologic and mechanical environment, and also special geologic environment speed up the deterioration rate of RC, which is a major reason for collapse of raw-coal surge bunker. And then further investigation was made on the curing techniques of degraded RC bunkers. It can provide theoretical basis for ensuring the long-term safety, workability and durability of degraded RC coal bunkers.

Purpose: The purpose of this paper is to investigate the mechanical behavior of textile-reinforced concrete (TRC)-strengthened concrete columns with small eccentricity under chloride-wet-dry cycles.Design/methodology/approach: A total of ten reinforced concrete (RC) columns were constructed and subjected to eccentric compression, and the effects of the slenderness ratio, a variable number of wet-dry cycles and the coupled effect of loading and a chloride environment were analyzed. One of the columns tested was unreinforced, whereas the remaining columns were strengthened laterally with TRC.Findings: The results showed that a reduction in the slenderness ratio was conducive to the improvement of the bearing capacity of the reinforced column; however, the reinforcement effect of TRC tended to decrease with an increasing number of wet-dry cycles, and the coupled effect of loading and a chloride environment significantly degraded the compression performance of TRC-strengthened columns, with the damage becoming more serious with increase in the sustained load ratio.Research limitations/implications: In the next test, the duration of chloride-wet-dry cycles will be extended. In the same time, to obtain a clearer trend, the authors will also increase the number of specimens to obtain more data for drawing general conclusions.Originality/value: The originality is to explore the feasibility of using cement-based materials (TRC) as a confinement technique in chloride environment. The investigations demonstrate that TRC has a good reinforcement effect on the concrete columns under chloride-wet-dry cycles. Finally, influence of each parameter is analyzed, which can be used as reference and foundation in actual application.

In the whole lifetime of structures, fatigue damage accumulation will exist in the shear connector of steel–concrete composite beams. It is essential to determine the residual mechanical properties of shear connectors under long-term fatigue loads, e.g., the vehicle load on bridges. In this regard, a shear-strength degradation model is proposed for shear connectors. The Bayes theorem is used to develop posterior estimates of the unknown parameters in the degradation model based on the collected pushout test data of pre-damaged stud connectors caused by high-cycle fatigue loads. In addition, according to the proposed shear-strength degradation model, the service reliability assessment is performed with a composite bridge beam. The results indicate that (1) There is a large diversion in the traditional strength degradation model under the action of fatigue cumulative damage. More importantly, this proposed physics-based degradation model can effectively reduce uncertainty. (2) The effects of steel type and test specimen size can be well considered in the proposed shear-strength degradation model, which is beneficial for improving the reliability of risk assessment for fatigued bridges.