Glass fiber reinforced polymer bars have potential application in the seawater sea sand concrete. In this study, an analytical method was proposed to examine the internal crack development in glass fiber reinforced polymer–sea sand concrete composites. The method was derived by analyzing the strain dissipation and shear-lag behavior. Thus, the internal cracks can be quantitatively identified by the proposed model with Fourier transform analysis. The proposed approach was experimentally verified through pullout tests for the specimens with artificial cracks. The results indicated that the prediction errors were less than 10%. In addition, the piezoelectric sensors were adopted to verify the proposed model. A damage index (DI) defined by the energy loss of received signals was used to characterize cracks inside the composite. Loading test results indicated that the DI-calculated cracks were consistent with the proposed analytical model. Finally, the cyclic loading tests of the glass fiber reinforced polymer composite were conducted using both strain gauges and PZT sensors. The results have shown that the differences between the proposed approach and PZT sensors were less than 15%. Thus, the proposed approach in this study could provide an alternative approach for quantitative evaluation of internal cracks in the glass fiber reinforced polymer–coral sand–cement composites.

A fibre Bragg grating (FBG)-based load and vibration transducer (FLVT) was developed using a 3D fused deposition modelling (FDM) approach. A newly FLVT was designed by the equal-strength cantilever beam in which the FBG sensors were embedded in the beam during the FDM process. The temperature effect was eliminated by the temperature sensor in the vibration sensing unit. The parameters of the proposed FLVT was examined by the finite element method. The simulated results were matched well with the theoretical analysis results and laboratory calibration results. The proposed transducer has the pressure measurement sensitivity of 0.01274 nm kPa ⁻¹ for the earth pressure below 150 kPa. In addition, the proposed transducer could accurately measure low-frequency vibration signals with maximum frequency of 4 Hz and the maximum displacement amplitude of 4 mm with sensitivity of 117.6 pm g ⁻¹ . The measurement accuracy and stability were carried out. Results shown that the maximum relative errors between the calculation results and the experimental results was 1.3%. The effect of vibration direction was also analysed for the proposed FLVT. The results indicated that the transversal vibration has less influence on the longitudinal vibration. The outcome of this study indicated that the proposed FLVT provide a newly approach for the measurement of earth pressure and soil vibration in one transducer which is quit suit for soil mass.