Description
As the core vertical prestressed force member of the bridge structure, the finish rolling rebar can not effectively control the stress loss in the whole process of anchoring and is affected by environmental corrosion and other factors during the actual construction, resulting in the vertical prestress can not meet the design requirements or even failure, which seriously threatens the durability and safety of the structure. In this paper, ultrasonic guided wave technology and acoustic elasticity theory are combined to detect the effective prestress of rebar, and the key problems such as guided wave propagation characteristics and acoustic elasticity effect under different stress states after bare rebar and rebar wrapped mortar are studied. Taking the center frequencies of 50 kHz, 75 kHz and 100 kHz as excitation signals and considering different excitation powers, the post-tensioning test and guided wave propagation test of rebar and outer mortar were carried out, and the variation law between the first wave velocity of guided wave and the tensile force was analyzed. The results show that the first wave velocity of the guided wave of the rebar decreases with the increase of the excitation frequency, which is consistent with the theoretical dispersion curve. With the gradual increase of the excitation power, the amplitude of the guided wave waveform received by the rebar only increases gradually in the time domain and frequency domain, while the shape and position of the waveform do not change, so the influence of the excitation power can be ignored in the experiment. The law between the first wave velocity and the tensile force of the rebar after outsourcing mortar is consistent with that of the bare rebar, but the first wave velocity and energy are significantly lower than those of the bare rebar. It is feasible to establish the identification method of rebar prestress based on acoustic elastic effect.
