Additional device for dynamic bond slip test of SHPB steel bar and concrete

Abstract

The invention relates to an additional device for dynamic bond slip test of an SHPB steel bar and concrete. The device comprises an SHPB, an additional device A is arranged at the inner end of an incident bar of the SHPB, an additional device B is arranged at the inner end of a transmission bar of the SHPB, a bond slip test piece is clamped between the additional device A and the additional device B, a slip stroke is provided for a reinforcing steel bar through the additional devices, the flatness and the straightness of the contact surface of the bond slip test piece and the SHPB are improved, the strain gauge attached to the interior of the steel bar can be smoothly guided out, and the test piece can break through the limitation of the size, so the test range of the SHPB is further widened.

Description

technical field [0001] The invention relates to the technical field of civil engineering, in particular to an additional device for the dynamic bond-slip test of SHPB steel bars and concrete. Background technique [0002] Based on the Split Hopkinson Pressure Bar (SHPB for short), the SHPB device has a simple structure, and the achievable strain rate loading range is relatively high, which can reach 102s-1~104s-1; the data acquisition and processing during the test are relatively Convenient, the loaded stress wave waveform is easy to adjust and measure. The transmitted wave can be directly measured on the transmission rod of SHPB, which is the impact load acting on the test piece; the impact load can be realized by adjusting the firing speed and length of the bullet. and shape changes. Generally, obtaining the stress-strain curve of a material requires measuring the stress and strain at the same position on the specimen at different times, but the SHPB technology measures t...

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Problems solved by technology

[0003] However, due to the characteristics of the SHPB device itself, it is impossible to directly conduct the bond-slip test of reinforced concrete, which limits its application range.

This is because, firstly, SHPB cannot provide enough sliding travel for the steel bar in the test piece, and the steel bar will inevitably slip in the bond-slip test, which requires sufficient displacement range for the steel bar. If the The specimen is loaded directly between the incident rod and the projection rod, and there is no deformation interval for the steel bar, which will only cause buckling of the steel bar under compression and cannot slip; The presence of steel bars in the bond-slip test piece and the processing of the steel bars are difficult to meet the accuracy of the test flatness and straightness, which means that the contact between the test piece and the rod end surface cannot be guaranteed

If there is non-planar contact, it is easy to cause the test piece to not be uniformly stressed, which increases the dispersion of the test results. If the introduced deformation error is large, it may even lead to invalid test results; third, when SHPB conducts bond-slip tests There is a strain gauge lead inside the steel bar that cannot be derived. At present, many bond-slip performance tests are based on the method of sticking strain gauges inside the steel bar to measure the distribution of the bond force. It is required that a certain number of strain gauges are attached to the inside of the steel bar. The lead wires of the gauges need to be exported to connect with the dynamic strain acquisition instrument. It is difficult and unrealistic to drill holes on the surface of the end of the steel bar in large quantities, so that the lead wires of the strain gauges cannot be exported; fourthly, the diameter of the SHPB incident rod and projection rod is too small to limit the specimen Dimensions. At present, the diameter of the SHPB incident rod and projection rod is generally between 50mm and 100mm. In the bond-slip test, the thickness of the outer protective layer of the steel bar is a very important parameter. Refer to the "Code for Design of Concrete Structures" (GB50010-2015 ) Table 8.2.1, according to different environments, the minimum protective layer thickness of beams and columns is between 20mm and 50mm, so when the steel bar diameter is 25mm and the protective layer thickness is 50mm, the cross-sectional diameter of the specimen is 125mm. SHPB cannot be loaded effectively

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