Strain Rate Sensitivity Of Steel Research Articles

Experimental investigation of welded steel T-stub components under high loading rates

The equivalent steel T-stub approach is widely used in practice to analyse and design bolted steel joints that are otherwise complex to study. The available analytical and empirical models for characterizing the response of T-stub components are based on numerous experimental and numerical research studies. This research is mostly concerned with the pseudo-static response of the T-stub. However, natural and man-made hazards (such as earthquakes and impacts) are dynamic. Considering the strain-rate sensitivity of steel, dynamic effects may have a notable effect on structural behaviour. A limited number of studies investigated the response of steel components/joints at high loading rates with inconclusive, and sometimes conflicting, observations. Accordingly, an experimental study is undertaken to address the data shortage. A total of 57 welded steel T-stubs were tested under monotonic tension. The main test parameters included the T-stub flange plate thickness, the loading rate, and the bolt preload condition. The test data underscored the influence of the loading rate and bolt preload. Notably, at a loading rate of 50 mm/s, an average of 35% reduction in the elastic stiffness, a 5% amplification of strength, and a 22% reduction in ductility is observed compared to the reference pseudo-static loading rate. The paper discusses the test observations in detail, evaluates the findings considering past research, and assesses potential implications on design.

Dynamic fractures of concrete made of recycled aggregate or reinforced with fibres

In recent decades, there has been a lot of interest in using construction waste as a source of aggregate for the production of new concrete. Another topic of intense study is the optimal characteristics of reinforcing fibres. However, in contrast to the constant value of the static strength, it is widely known that the dynamic strength of concrete is highly dependent on the strain rate. The wide variety of possible concrete additives further complicates the assessment of the dynamic strength of concrete. Therefore, it is necessary to search for new material parameters that will allow evaluating and comparing the dynamic strength of concrete with various modifications of additivities. In this work, the effects of recycled aggregate and fibres on the fracture critical stress of original, natural aggregate concrete were studied using the incubation time criterion. It was confirmed that by estimating only one additional parameter, the incubation time, which is responsible for the preparatory processes of fracture and is invariant with respect to the history of loading in dynamic and static tests, it is possible to construct the stress/strain rate dependences of the critical stress. The intersections of the theoretical rate dependences of the critical fracture stress under static and dynamic loading considering various percentages of recycled aggregate (from 0% to 100%) and carbon, steel, and synthetic fibres were analysed. The decrease in the dynamic strength of steel- and carbon-fibre-reinforced concretes was interpreted in terms of a change in the incubation time characteristic. The influence of the fibre shape on the strain rate sensitivity of steel- and synthetic-fibre-reinforced concretes was analysed. It is here shown that the incubation time parameter can be considered to be a convenient tool for assessing the influence of recycled aggregate or fibres on the dynamic strength of concrete.

Influence of Torsion Effect on the Mechanical Characteristics of Reinforced Concrete Column

The purpose of this paper is to study the effect of torsional effect and loading rate on the flexural capacity of RC members. Based on the fiber model of finite element software ABAQUS, a model has been established with the consideration of the strain rate sensitivity of steel and concrete. The model is used to reflect the influence of the rotational component of ground motion by applying the initial angular displacement. The mechanical properties of RC columns under monotonic loads are simulated. The simulation results show that there has been a decrease in the carrying capacity and initial stiffness of RC columns for high initial torsion angle. With the increase of initial torsion angle, the influence of loading rate on RC columns gradually increases.