Piezoelectric-based sensors are low cost, highly stable, responsive, and changeable in shapes, allowing them to be easily embedded within concrete structures to perform various monitoring tasks. In this research, an in-built piezoelectric-based three-direction stress sensor is proposed, which could monitor the internal normal stresses in three mutually orthogonal directions. The sensor has a cubic shape with edges of about 25 mm. It consists of three PZT (lead zirconate titanate) patches, each of which is sandwiched between a steel base and a square steel plate with epoxy. To test the sensors’ characteristics, a finite element analysis was carried out to investigate stress transfer inside the sensor. Besides, a servo-hydraulic machine was used to conduct a cyclic loading test, delivering compressive stress up to 30 MPa on the three sensors. Both the numerical simulation and experiment results have shown that the cross-interference effect between different directions is negligible. Also observed was a high level of consistency in the sensitivity of measurements, regardless of the monitoring direction and sensor. With the advantages of a simple structure, low cross interference, and consistent sensitivity, the proposed three-direction normal stress sensor has a great potential to be mass produced and used in monitoring the health state of structural concrete.

In analysis and design of structures subjected to blast loading, equivalent Single-Degree-of-Freedom (SDOF) method is commonly recommended in design guides. In this paper, improved analysis method based on SDOF models is proposed. Both flexural and direct shear behaviors of structures subjected to blast load are studied using equivalent SDOF systems. Methods of deriving flexural and direct shear resistance functions are introduced, of which strain hardening and softening effects are considered. To collocate with the improved SDOF models, the improved design charts accounting for strain hardening and softening are developed through systematical analysis of SDOF systems. To demonstrate the effectiveness of the proposed analysis method, a model validation is made through comparing the predictions with laboratory shock tube testing results on reinforced concrete (RC) columns. It is found that compared to the conventional approach with elastic and elastic-perfectly-plastic model, the elastic-plastic-hardening model provides more accurate predictions. Additional non-dimensional design charts considering various levels of elastic-plastic-hardening/softening resistance functions are developed to supplement those available in the design guides with elastic-perfectly-plastic resistance function only, which provide engineers with options to choose more appropriate resistance functions in design analysis.

No abstract

No abstract

No abstract