Experimental characterization of the punch through shear strength of an ultra-high performance concrete

• Quasi-static and dynamic PTS tests are conducted on ultra-high performance concrete.
• Lead annular pulse-shaping system in SHPB testing is used to increase the rising time.
• Practicing eight notches allows removing self-confinement of the fibered sample.
• Dynamic tests show higher shear strength and radial stress compared to static results.
• Higher confinement is related to alteration of crack path prior to mode II cracking.

The paper describes the quasi-static and dynamic experimental methods used to examine the confined shear strength of an Ultra-High Performance Concrete, with and without the presence of steel fibers in the concrete composition. The experimental setup that employs a hydraulic press allows investigating the concrete shear strength under quasi-static loading regime while dynamic shear strength is characterized by subjecting concrete samples to dynamic loading through a modified Split Hopkinson Pressure Bar set-up. Both methods are based on a so called Punch Through Shear (PTS) test with a well-instrumented aluminum-alloy passive confinement ring that allows measuring the change of radial stress in the shear ligament throughout the test. First, four equally distributed radial notches have been performed on the concrete samples in order to deduce the radial stress in the shear ligament by suppressing self-confinement of the sample peripheral part. However, by analyzing the strain gauge data obtained from the confinement ring, it has been noticed that these were insufficient, especially for fiber-reinforced samples, resulting in subsequently practicing eight radial notches through the peripheral part of the samples. The results obtained from both procedures in addition to post-mortem observations are reported and discussed. It is concluded that the apparent increase of shear strength under dynamic loading compared to the quasi-static response is the consequence of higher radial confinement stresses at high strain-rates that results from an alteration of fracturing in mode I prior to mode II cracking in the ligament.