Essay on Numerical Study of Stainless Steel Columns Under Transverse Impact Load

Introduction

Steel columns find applications in many areas compared to stainless-steel material. Very few projects use stainless steel as load-bearing. This underutilization is caused by the fact that they are least considered by structural engineers for such roles or recommended by architects as aesthetics for vicinities. However, Thairy and Wang (2011) note that underground columns and multi-story car parks are highly vulnerable to the impact of the load caused by moving vehicles. This cause-effect is dangerous, considering that most existing structures are subjected to dynamic loadings from extreme events such as vehicle impacts, earthquakes, and explosions, which cause progressive collapse (Yang et al., 2020). Columns are vulnerable to comparably less strenuous impacts and may exhibit structural failure resulting from accidental vehicle impact (Thairy & Wang, 2011). Despite their relatively enhanced performance potential, high strength stainless columns are not widely used due to a lack of guidance on designing this kind of structural elements. Specifically, there is little guidance on analysis design approaches that account for the high strength stainless steel column failure under impact loads. Yousef et al. (2013) observe that there are currently no engineering standards for designing structural elements that resist blast and impact loads.

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There is limited research on the impact behavior of hollow stainless-steel sections. Rasmussen (2000) summarized the design process of cold-formed stainless-steel sections. The insights drawn from this study were integral in developing the first Australian standard for the design of cold-formed stainless-steel structures. Adding to this, Burgan et al. (2000) highlighted the conservative nature of Eurocode 3, Part 1,4, particularly the limiting diameter-to-thickness ratio for circular hollow beams and lateral-torsional curve for I-section beams. Further developments to these studies remain critical for understanding the behavior and failure modes of axially compressed high strength stainless steel columns under transverse loading. Yousef et al. (2013) subjected transverse weight to the quarter and midpoints of stainless-steel columns and noted their enhanced strength over other mild steel columns under similar dynamics. High strength stainless steel columns thus demonstrate improved energy dissipating characteristics than those made of mild steel.

Further reinforcements improve the performance of stainless-steel columns. Han (2019) investigated the behavior of concrete-filled tubular high strength stainless steel columns under axial loading, subjected to lateral loading at different points. The study includes the bond behavior between the concrete and stainless steel in the columns due to external pressure. The results reflected the observations in the study by Yousuf (2013). Thus, the lateral or transverse impact may cause the bending and breaking off of the columns from their original position. This breaking occurs if the weight subjected is beyond the column's limits. If these columns exhibited much strength offered by the hefty high strength stainless steel, the impact of lateral loading would be minimal. Such strength is necessary for buildings and bridges where transverse loading on beams may significantly impact. This is because the beams lie horizontally and so the weight acting on them is directly above them.

There are other forms of reinforced high strength stainless steel, as presented in the study by Wang (2018). He presents concrete-filled double skin steel tubular with external stainless steel as the composite materials with improved advantages. These improved alternatives are highly malleable. Wang notes that the immensely high strength is derived from the external high strength stainless steel. Besides, duplex stainless steel is a combination of ferritic and austenitic stainless steel sheets with less composition of nickel that is mostly applied in underwater oil industries due to its high resistance to the corrosive threat of saltwater.

High strength stainless steel has a lot of advantages and can find applications in the making of concrete columns and beams. In their role of supporting and transmitting weight downwards, they are better than other mild steel as plant fibers. This advantage is due to its strength and resistance to corrosion. Nonetheless, structures such as beams and columns made with high strength stainless steel are not immune to external pressures such as axial compression and transverse impact on the axial loading. Failure modes such as global plastic failure, tensile tearing failure, transverse shear failure, and plastic buckling will be of concern. A larger number of research studies have investigated how these four failure modes may be quantified under different parameters, such as material type and impact location (Liu & Jones, 1987; Yu & Jones, 1989; Jilin & Norman, 1991; Al-Thairy, 2018), axial preloading (Yu & Jones, 1997), the impact speed (Mannan et al., 2008), a different type of cross-sections (Bambach et al., 2008). These failures occur for compressed columns under the transverse impact, mainly plastic global failure, tensile tearing failure, the transverse shear failure, and plastic buckling.

Numerical modelling is used by civil engineers to evaluate objects such as rocks and how they may affect constructed structures. In this case, it is the evaluation of how objects like rocks may affect high strength steel columns and beams. Axial and transverse compression is brought about by a force. Objects such as rocks may produce these forces that may axially or transversely compress stainless steel columns and beams. Axial compression on a column is the application of a certain amount of load or force to a column such that the load or force acts on the end of the column transmitting the weight downwards. Loads are applied to the ends of the member column to produce axial compressive stresses. The compression results in the transmission of the weight from the load downwards to the elements below. Axial compression in a column basically loading along the length of the column. Transverse impact or loading happens when the load or force is applied perpendicular to the axial loading. The transverse loading makes a 90% angle with the axial loading on a beam or a column. This has the effect of causing perpendicular stressing or bending. The impact of transverse loading on a beam or a column is illustrated in the pictures below.

Axially compressed columns under transverse impact have associated failure modes. In Zeinoddini et al. (2002 and 2008) determined plastic global buckling and local indentation and impact zone damage resulting from high axial compression and a combination of low axial load and thin tube, respectively. The kinetic energy of the transverse impact is used to control column buckling (Adachi et al., 2004; Sastranegara et al., 2006). According to an experiment conducted by Mounir (2019), and using finite element computer program seismo-structure, transverse impact on an axially compressed stainless steel beam will cause the beam to bend against the direction of the force. The degree of this bend will depend on the amount of force of the transverse impact. Further, Dario (2019), investigating the effect of different arrangements of transverse reinforcement on axially loaded stainless steel concrete columns, determined that unconfined concrete structures are very brittle. The experiment reveals that the transverse force on the concrete structure has little effect on causing ductility as long as its elastic limit is not met.

The objective of comparing experiments to see the variation or similarities found when high strength stainless steel columns are subjected to transverse or axially compressing impact loads. According to Azhari (2006), a transverse impact on an axially compressed high strength stainless steel beam will reduce its overall stiffness. The author conducted an experiment using finite element analysis. A small structure representing a more powerful stainless-steel beam is subjected to a transverse impact in this method. The results can be equated to the more powerful beam according to the ratio of the measurements. This paper aims to: (1) validate a method of numerical simulation for the behavior and failure modes of axially compressed stainless steel column subjected to transverse impact due to a rigid mass traveling low velocity. The simulation will be carried out using LS-DYNA software. (2) using the validated numerical model to investigate the effects of several parameters on the impacted column's response and failure modes.

Validation of The Numerical Model

In this section, the LS-DYNA model's capability to accurately track the behavior and predict the different failure modes of axially compressed high strength stainless steel columns under the transverse impact of a rigid mass at different speeds and locations is compared against published experimental tests. The reference experiments are carefully selected to ensure that different stainless steel column failure modes are covered.

Global Plastic Buckling Failure

Global plastic buckling tests on stainless steel were conducted by Arrayago et al. (2020). In these tests, all the single-story single-bay frames were 2m high, with a nominal span of 4m. The values, in addition to the pin-ended and fixed-ended boundary conditions, provided the column range λc and local slenderness, λp Values. The slenderness value was calculated using the equation, λp = 0.2cr.1 with 0.2=20% and cr.1 as the elastic local buckling stress for the entire cross-section.