Failure Loads Of Specimens Research Articles

Effectiveness and response of replacing web reinforcements with steel fibers reinforced in shear for non-stirrup UHPC beams

This paper reports the shear behavior of non-stirrup ultra-high performance concrete (UHPC) beams to fully use the high strengths of UHPC. A total of nine simply-supported beams were entailed based on steel fiber contents (0%, 1%, 2%, and 3%), equivalent stirrup ratios (0.6%, 0.8%, and 1.1%), and shear span-to-depth ratios (1.0, 2.0 and 3.0). Test results indicate that the failure loads of specimens using steel fibers achieved about 1.5, 2.5, and 3.75 times the specimens with equivalent stirrups. Also, the shear cracking loads increased by 100%, 200%, and 250%; meanwhile 20% higher global stiffness was found relative to the specimens using stirrups. Note that the longitudinal crack along the tensile reinforcements at the shear span-to-depth ratio of 1.0 led to the anchorage failure whereby the used straight steel fibers and reduced interlock and/or friction along the shear crack enabled greater fiber-composite strain hardening. Additionally, replacing stirrups with steel fibers could decrease the maximum crack width from 0.04 to 0.01 mm despite carrying twice the cracking load. These findings demonstrated that substituting steel fibers for stirrups could improve the structural both service and ultimate performance. In closing, too-conservative predictions from the current codes warranted a rational theoretical method.

Experimental and Numerical Investigation of the Buckling Performance of Tubular Glass Columns under Compression

This study investigates the buckling performance of tubular glass columns under axial compression. A total of two cases are considered (i) single glass tubular column and (ii) bundled column constructed using structural silicone sealants. A series of compression test were carried out on different geometrical dimensions of these two cases to determine their failure mechanism, load carrying capacity and to evaluate the buckling performance. Prior to the load carrying capacity (LCC) that was measured at the ultimate, a distinctive remaining structural capacity (RSC) was characterized especially for bundled glass based on the first crack. The shear connection in the bundled system was justified in comparison to the monolithic glass. This study showed that the failure mechanisms depended strongly on the slenderness ratio of the columns and that the failure occurred either by crushing or by buckling depending on the lengths of the column. The scatter in the failure load for specimens that had a higher slenderness ratio was much lower than for those that had a lower slenderness ratio. In order to justify the variability of the glass strength, a Weibull statistical distribution was used. Finite element modelling (FE) based on the simplified Riks method was performed using ABAQUS v6.10 to compliment the test results and to provide methods of analysis which could be used as a guideline for structural engineers to predict structural behaviour of tubular glass columns in general. An overestimation was predicted in the FE models which suggested modification of the imperfection factor.

Study of the deformation characteristics and fracture criterion of the mixed mode fracture toughness of gypsum interlayers from Yunying salt cavern under a confining pressure

Based on the project background of salt caverns used for oil and gas storage in laminated salt rock, this study examined the combined mode fracture toughness, the fracture pattern, the morphological evolution of fracture surfaces, and the fracture criterion of gypsum interlayers under confining pressure. Series of laboratory tests, including fracture strength tests and scanning electron microscopy tests, were performed at four confining pressures. The results indicate that the failure load of gypsum increased with the increase of confining pressure. By contrast, the failure load of specimens first decreased and then increased with the increase of pre-existing flaw inclination angle. As the confining pressure increased, the residual energy gradually decreased and the brittleness index gradually increased. Although increasing the confining pressure (i.e., 1–7 MPa) shifted the behaviour of a specimen from brittle to ductile, the major failure mechanism still fell within the brittle failure regime. For the case where the confining pressures are 1 MPa and 3 MPa, cleavage fractures characterized by cleavage steps, river lines, and tearing ridges were observed on the surface, indicating that typical brittle failure occurred in the specimens. However, typical ductile failure occurred in the specimens subjected to confining pressures of 5 MPa and 7 MPa. Subsequently, the size of the fracture process zone at varying confining pressures was obtained using a modified maximum tangential stress criterion to optimally fit the experimental results. The results of this study can be used to evaluate the safety of salt caverns in bedded salt formations.

Tool geometry effect on the characteristics of dissimilar friction stir spot welded bulk metallic glass to lightweight alloys

Abstract A small-scale joining technique for dissimilar friction stir spot welding (FSSW) of a BMG alloy to lightweight crystalline alloys has been developed. An experimental apparatus which could possible give a precise control of the friction time, the plunge speed and the plunge depth of the tool was used. In this study, the influences of tool geometry with different pin shape on the joining characteristics and on the failure load of specimens after dissimilar FSSW were investigated. As a result, it was found that the tool geometry influenced on the welding performance of the BMG alloy to lightweight crystalline alloys at small tool plunge depth and the extent of BMG particles penetrated onto the lightweight alloy side, especially for the Mg alloy/BMG material combination.

Behaviour of concrete under shear and normal stresses

Thirty-eight concrete specimens were tested in a servo-controlled shear box test machine. The aim of the tests was to determine the combination of stresses that would cause failure in the concrete and to compare the failure stresses with Mohr–Coulomb theory. It was found that the failure load of specimens tested under a constant normal force could be predicted using Mohr–Coulomb theory with an assumed friction angle of 35°, provided that the normal stress was greater than 0·15fc. For normal stresses less than 0·15fc Mohr–Coulomb theory overestimated the shear capacity of the concrete unless a modified cohesion value and friction angle were used.