Push-off Test Research Articles

Behavior of Headed Stud Shear Connectors in Composite Beam

In composite beam design, headed stud shear connectors are commonly used to transfer longitudinal shear forces across the steel–concrete interface. Present knowledge of the load–slip behavior and the shear capacity of the shear stud in composite beam are limited to data obtained from the experimental push-off tests. For this purpose, an effective numerical model using the finite element method to simulate the push-off test was proposed. The model has been validated against test results and compared with data given in the current Code of Practices, i.e., BS5950, EC4, and AISC. Parametric studies using this model were preformed to investigate variations in concrete strength and shear stud diameter. The finite element model provided a better understanding to the different modes of failure observed during experimental testing and hence shear capacity of headed shear studs in solid concrete slabs.

The effect of temperature, matrix alloying and substrate coatings on wettability and shear strength of Al/Al2O3 couples

A fresh approach has been advanced to examine in the Al/Al2O3 system the effects of temperature, alloying of Al with Ti or Sn, and Ti and Sn coatings on the substrate, on contact angles measured using a sessile-drop test, and on interface strength measured using a modified push-off test that allows shearing of solidified droplets with less than 90 deg contact angle. In the modified test, the solidified sessile-drop samples are bisected perpendicular to the drop/Al2O3 interface at the midplane of the contact circle to obtain samples that permit bond strength measurement by stress application to the flat surface of the bisected couple. The test results show that interface strength is strongly influenced by the wetting properties; low contact angles correspond to high interface strength, which also exhibits a strong temperature dependence. An increase in the wettability test temperature led to an increase in the interface strength in the low-temperature range where contact angles were large and wettability was poor. The room-temperature shear tests conducted on thermally cycled sessile-drop test specimens revealed the effect of chemically formed interfacial oxides; a weakening of the thermally cycled Al/Al2O3 interface was caused under the following conditions: (1) slow contact heating and short contact times in the wettability test, and (2) fast contact heating and longer contact times. The addition of 6 wt pct Ti or 7 wt pct Sn to Al only marginally influenced the contact angle and interfacial shear strength. However, Al2O3 substrates having thin (<1 µm) Ti coatings yielded relatively low contact angles and high bond strength, which appears to be related to the dissolution of the coating in Al and formation of a favorable interface structure.

Composite steel beams with precast hollow core slabs: behaviour and design

AbstractThis article reviews the design and behaviour of composite beams with precast hollow core slabs in multi‐storey buildings for gravity loading. A brief history of composite construction and introduction to precast–composite construction is given, followed by an overview of recent research work on various factors affecting the design. This includes the push‐off test procedure, the load–slip characteristic of the headed shear studs and the design procedures for this type of construction. Finite element modelling of the headed stud shear connectors and the composite beams with precast hollow core slabs are presented. Finally, recommendations and future research work is also suggested.

Damage process detection of a ceramic tile system by acoustic emission

The debonding and falloff of ceramic tile systems are common failure modes for ceramic finishes of buildings and infrastructures due to the damage accumulation caused by application of mechanical load or changes in environmental conditions. To better understand the mechanism of the damage, a newly developed push-off test was conducted and a quantitative acoustic emission (AE) technique was developed to detect the damage processes during the loading history. The source locations of internal damage were determined by a new three-dimensional algorithm. Test results show that the growth of damage and the onset of failure can be monitored by AE technique. Also, the experimental results indicate that a probability density function of AE activity can be used to quantitatively describe the degree of damage of a material. It was found that the ceramic tile system with a lower strength adhesive displayed a higher AE rate than that with a higher strength adhesive at the same loading level prior to failure.