Energy Absorption Capacity of uPVC-Confined Concrete

This research documents the results of tests on stub columns tested under repeated monotonic compression load. Two unplasticized polyvinyl chloride (uPVC) tubes were filled with normal and high strength concrete. From each type of concrete three control specimens were also cast for comparison purposes. The experimental test results show that the unconfined specimens were crushed in the first cycle of loading in contrast to the confined specimens which continued to resist the applied load after several cycles of repeated loading. Furthermore, by using the polymeric tube, the failure of concrete core switches from sudden explosive failure to non-brittle failure with the composite specimen undergoing large progressive deformation in each cycle of loading. For each cycle of loading, the material damage in the composite system was evaluated in terms of the deformations in both the lateral and axial directions.

Stratigraphic reconstruction of the Víti breccia at Krafla volcano (Iceland): insights into pre-eruptive conditions priming explosive eruptions in geothermal areas

Krafla central volcano in Iceland has experienced numerous basaltic fissure eruptions through its history, the most recent examples being the Mývatn (1724‒1729) and Krafla Fires (1975–1984). The Mývatn Fires opened with a steam-driven eruption that produced the Víti crater. A magmatic intrusion has been inferred as the trigger perturbing the geothermal field hosting Víti, but the cause(s) of the explosive response remain uncertain. Here, we present a detailed stratigraphic reconstruction of the breccia erupted from Víti crater, characterize the lithologies involved in the explosions, reconstruct the pre-eruptive setting, fingerprint the eruption trigger and source depth, and reveal the eruption mechanisms. Our results suggest that the Víti eruption can be classified as a magmatic-hydrothermal type and that it was a complex event with three eruption phases. The injection of rhyolite below a pre-existing convecting hydrothermal system likely triggered the Víti eruption. Heating and pressurization of shallow geothermal fluid initiated disruption of a scoria cone “cap” via an initial series of small explosions involving a pre-existing altered weak zone, with ejection of fragments from at least 60-m depth. This event was superseded by larger, broader, and dominantly shallow explosions (~ 200 m depth) driven by decompression of hydrothermal fluids within highly porous, poorly compacted tuffaceous hyaloclastite. This second phase was triggered when pressurized fluids broke through the scoria cone complex “cap”. At the same time, deep-rooted explosions (~ 1-km depth) began to feed the eruption with large inputs of fragmented rhyolitic juvenile and host rock from a deeper zone. Shallow explosions enlarging the crater dominated the final phase. Our results indicate that at Krafla, as in similar geological contexts, shallow and thin hyaloclastite sequences hosting hot geothermal fluids and capped by low-permeability lithologies (e.g. altered scoria cone complex and/or massive, thick lava flow sequence) are susceptible to explosive failure in the case of shallow magmatic intrusion(s).

The Experimental Studies on Behavior of Ultrahigh-Performance Concrete Confined by Hybrid Fiber-Reinforced Polymer Tubes

This paper conducts axial compression test of ultrahigh performance concrete- (UHPC-) filled hybrid FRP (HFRP) tubes, using the alternating hybrid technology to improve the deformation capacity of FRP tube and measure the axial compressive responses of ultimate strength, strains, and stress-strain curve of confined specimens. The test results show that the local rupture of HFRP tubes did not lead to explosive failure of UHPC cylinder, and its ductility is better than that of UHPC confined by only one type of FRP tube; HFRP tube can effectively improve the compressive strength and ultimate strain of UHPC specimens; the stress-strain curves divide into three distinct regions: linear phase, transition phase, and linear strengthening phase. None of the models provided a reasonable prediction for strength and strain of HFRP-confined UHPC specimen; therefore, a new ultimate strength and strain perdition model considering the confinement effectiveness of different hybrid FRP series was proposed. The new proposed model presented the best fitting results. The stress-strain responses predicted by the existing models are all below the experimental curves; therefore, a new three-stage constitutive model was proposed, which relatively fits the test curves better than the existing models.

Utilization of the relative rigidity concept to predict the failure of pipe systems under explosive loads

The interaction between loading plates and supporting structures is very much dependent upon the relative rigidity of the system. This paper first illustrates how an indiscriminate application of the relative rigidity concept can lead to erroneous conclusions in such systems. The paper then applies the concept to explain reported observed failure modes in pipe systems under explosive loads. Numerical studies are presented which simulate the behaviour of square pipe systems under static and explosive loads using the concept of relative rigidity in conjunction with the finite element method. The results of the analysis confirm the hypothesis of the relative rigidity concept. Experimental verification of the theoretical predictions and numerical modelling results are obtained by simulating the explosive failure patterns in simple freezing experiments. The analysis presented in this paper demonstrates the importance of the concept of relative rigidity for explaining certain kinds of observed failure and fracture phenomena. Key words: cracks, explosives, geometric distortion, load transmitting plate, pipes, relative rigidity, soil – foundation interaction, stress waves.

Superhigh Direct Current Switching Failure

A technician was injured by steam and boiling water when the cooling jacket exploded on a shorting switch. The shorting switch was being used to make 130,000 amps d.c. bypass an electrochemical cell so the cell could be removed from the production line for repairs. Prior problems had resulted in a cold soldered joint in the connecting arm for the switch. Then when the current overheated the electrically weakened joint mechanical strain on the arm caused part of the cable to loosen rapidly increasing the heat and causing explosive failure of the water jacket.

The Influence of Biaxial Mean Stresses on the Failure of Tubes by Fatigue

SummaryThin-walled tubes, in. in diameter, of three hard aluminium alloys and of mild steel have been tested in fatigue under three systems of alternating stresses while subjected to biaxial mean tensions imposed by means of internal pressure. In fatigue under direct or bending stresses the hoop tension in the walls of the aluminium alloy tubes did not seriously reduce the fatigue endurance, but it did markedly affect the mode and rate of crack propagation; cracks initially transverse to the tube axis tended to develop very rapidly in the axial direction. This tendency was present under both fluid and gas pressure, and under gas pressure the cracks propagated so fast that the test piece was often blown to pieces before the gas pressure fell by leakage through the cracks. The gradual taper in wall thickness along the fillets joining the test section to the enlarged ends offered no barrier to propagation of the axial cracks and the whole test piece, including its enlarged ends, was often shattered. Propagation of the axial cracks was preventible by sufficiently reducing the fillet radius, or by a ring glued on. Under alternating torsion, both endurance and mode of failure were affected by internal gas pressure. The initial fatigue crack, either circumferential or axial, often extended over a length comparable with the diameter of the tube, except under low ranges of shear stress when the crack length was sometimes very short. At each end the cracks forked in a characteristic manner and under moderate gas pressure the portions of tHe wall between the prongs of the fork were blown outwards. Under high pressure explosive failure and fragmentation often occurred. Mild steel under alternating torsion with internal gas pressure exhibited the same modes of failure, and two or more fatigue cracks were often formed simultaneously. Under high hoop tension, cracks propagated rapidly and one test piece, after two million cycles endurance, failed by exploding. However, no mild steel test piece was fragmented. A tentative explanation is offered of the reason why, in tubes of small diameter, rather short fatigue cracks may be expected to lead to fast fracture under the static loading. Attention is drawn to the inference that the initial fatigue crack itself must develop very quickly to considerable length.