Hollow Steel Research Articles

CAST HOLLOW BILLET STRUCTURE SIMULATION MODELING FOR OIL GRADE PIPES

Simulation modeling of hollow billet casting processes for the production of seamless oil grade pipes was performed. The aim of the work was to study the influence of geometric shape on the quality and properties of a continuously cast pipe billet. Modeling parameters, initial and boundary conditions were selected taking into account the conditions of the current production. The object of the study was a pipe billet with a diameter of 210 mm. When modeling the process of casting and solidification of billets, low-alloy structural chromium-molybdenum steel was used. For the simulation processes, three-dimensional models of billets were created, as well as models of shapes. Several factors were taken into account when modeling continuous casting and crystallization of a hollow billet: casting speed, chemical composition of the alloy being poured; casting temperature; geometric dimensions of the billet section. Modeling of hollow billet casting in the «LVM Flow» software package predicted the non-shrinking structure formation a decrease in microporosity (more than 0.85 according to the Niyama criterion) of the billet. As a result of simulation modeling, the improvement of the structure is theoretically confirmed when using a hollow steel billet as a starting point for the production of seamless hot-rolled pipes. There were no signs of shrinkage and microporosity on the hollow billet exceeding the permissible value according to the Niyama criterion. Keywords: hollow billet, steel, modeling, pipe, 25CrMoV.

Numerical study on dynamic responses and residual axial bearing capacity of square CFDST columns under lateral impact

This paper presented a numerical investigation into the dynamic responses and residual axial bearing capacity of square concrete-filled double-skin steel tube (CFDST) columns under lateral impact using ABAQUS. The finite element analysis (FEA) model for lateral impact and post-impact axial compression of square CFDST members was established, where the material nonlinearity and strain rate of steel tubes and concrete were considered and validated by existing experiments and studies. Based on the verified FEA model, the failure mechanism of the impact response process of the square CFDST member was revealed. To further explore the behavior of CFDST under axial compression after lateral impact, the typical axial load-axial displacement curves, axial strains of the steel tube, failure mode, and stress development of different components of the members were analyzed in depth. Parametric studies were conducted to clarify the influence of each parameter (including hollow ratio, slenderness ratio, concrete strength, and steel strength) on the residual capacity of post-impact axial compression in square CFDST members at different impact energies. Results demonstrated a linear correlation between residual axial bearing capacity coefficient and mid-span residual deflection after impact. Finally, a simplified formula for calculating the residual axial bearing capacity of square CFDST columns after lateral impact was proposed, which provided a reference for practical engineering applications.

Experimental Investigation on the Axial Loading Performance of Grooving-Damaged Square Hollow Concrete-Filled Steel Tube Columns

Under the influence of material defects, structural grooving, environmental corrosion, and other factors in engineering, concrete-filled steel tubes incur local defects on their external surfaces that affect their structural integrity and service life. This work conducts axial compression tests on 10 grooving-damaged square hollow concrete-filled steel tube (SHCFST) columns to investigate the effect of grooving damage on their axial compressive ultimate bearing capacity and the effect of steel tubes on concrete confinement. It explores the effects of three parameters, namely, the length of grooves, presence of slots in internal and external steel tubes, and orientation of grooves, on structural static performance. This study analyzes the loading, failure mechanisms, and axial compressive ultimate bearing capacity of grooving-damaged SHCFST columns. Results indicate that grooving weakens the steel tube’s confinement effect on the concrete core, reducing the axial compressive ultimate bearing capacity of specimens. On the basis of this experimental research, a method for calculating the axial compressive ultimate bearing capacity and axial compressive stiffness of grooving-damaged SHCFST columns is proposed. The calculation results closely align with experimental outcomes, providing valuable insights for related scientific research and engineering applications.

Influence of Internal Pressure on Hollow Section Steel Members in Fire

Structural steel hollow section members are extensively utilized in civil engineering due to their excellent mechanical performance, favourable geometry for corrosion protection, and aesthetic appeal. Degradation in material properties of steel and thermal expansion at high temperatures must be regarded in designs for fire situations. The closed inner space of hollow sections presents challenges at elevated temperatures. The present study examines the effect of expanding air on the stress state in section walls of hermetically sealed circular and rectangular hollow sections. The effect of the gas pressure is calculated analytically and numerically. The pressure of the expanding air may substantially reduce the capacity of a tubular member. The influence on resistance depends on temperature, volume of the air in the tubular member, and geometry of the hollow section. The results of the study indicate that rectangular hollow sections with relatively large width-to-thickness ratios are more sensitive to internal pressure than circular hollow sections. The temperature range where the adverse effect of internal pressure occurs can include realistic critical temperatures in practical design and therefore deserve special attention to ensure the required safety.

Proposal and application of onshore lattice wind turbine support structure and integrated multi-scale fatigue assessment method

To accommodate the development of wind turbines in areas with weak wind speeds, an upright ultra-high lattice support structure is proposed for the large wind turbine, which is prefabricated and assembled mainly from thin-walled circular hollow steel (CHS) tube elements. As a practical example, a 180 m wind turbine support structure is presented. To evaluate the fatigue performance of the new structure type with modular assembly, a new integrated multi-scale fatigue assessment method is proposed to address the shortcomings of the equivalent fatigue load method commonly used in engineering design. For any fatigue load condition, the integrated multi-scale fatigue assessment method enables accurate and efficient calculation of the relationship curve between fatigue load and hot spot stress, and identification of the locations in the structure where fatigue accumulation damage is the greatest. Furthermore, fatigue damage accumulation and fatigue life can also be predicted accurately and efficiently by the proposed method. The results show that for the maximum fatigue cumulative damage of the proposed new structural systems, as the effect of average stress is not considered and the assumption of superposition of principal stresses, the traditional equivalent fatigue load method is too conservative compared to the proposed integrated multi-scale fatigue assessment method, detrimental to cost decreasing and benefit increasing of the wind turbine structures.

Mode I fracture behavior of glass fiber composite-steel bonded interface – Experiments and CZM

Debonding is characterized as the governing failure mode in the innovative wrapped composite joints made with glass fiber composite material wrapped around steel hollow sections without welding. The prerequisite for predicting debonding failure of wrapped composite joints is to obtain fracture behavior of the composite-steel bonded interface. The mode I fracture behavior of the bonded interface was experimentally investigated using glass fiber composite-steel double cantilever beam (DCB) specimens. The crack length a and the crack tip opening displacement (CTOD) during the test were accurately measured by analyzing the digital image correlation (DIC) data while the strain energy release rate (SERR) was calculated through the extended global method (EGM). The cohesive zone modeling (CZM) was utilized in the finite element model with the proposal of a four-linear traction-separation law to simulate the mode I fracture process. An approach is introduced to determine the critical stages of the proposed four-linear cohesive law by combining accurate measurements of crack length a and CTOD, along with SERR values. The validity of the four-linear cohesive law and the introduced approach to determine the critical stages were confirmed by good agreement in both global and local behavior between the testing and the FEA results.

Research on the Residual Bearing Capacity of Square Hollow Concrete-filled Steel Tube After Fire

In order to study the change of the residual bearing capacity of square hollow concrete-filled steel tube after fire, the finite element analysis software ABAQUS was used to establish the finite element model of square hollow concrete-filled steel tube under the ISO-834 standard fire heating condition, and the temperature distribution and deformation of the model were simulated and analyzed. Based on that, the influence of parameters such as the strength grade of concrete, the strength grade of steel, the calculated length of member and the hollow ratio of section on the residual bearing capacity of member after fire is simulated and analyzed. The results show that the temperature distribution of the component is mainly affected by the section size, concrete strength grade and steel yield strength, but is less affected by the calculated length. The temperature of the inner concrete and the inner steel tube decreases with the increase of the thickness of the member. The strength of steel and the size of section have more influence on the stress characteristics of the member after fire, but the strength grade of concrete and the length of the member have less influence. Among them, the increase of steel strength, concrete strength will enhance the fire-resistant limits of components. When the hollow ratio of the section increases, the fire resistance limit of the component increases first and then decreases. The increase of the calculated length will reduce the fire resistance limit of the member. The residual bearing capacity of the component decreases with the increase of fire time.

Feasibility of suppressing debonding failure for CFRP-hollow section steel tube composite member with a thick-walled section under tensile loading

Carbon fiber reinforced polymer (CFRP) is extensively utilized to strengthen steel structures. However, the premature debonding failure of CFRP inhibits its validity in strengthening tensile steel structures. Accordingly, the introduction of a thick-walled hollow section steel tube located at both ends of the CFRP-hollow section steel tube (CFRP-HSST) composite member was developed for the strengthening of tensile members. The steel tube in the novel composite member is constituted of a middle thin-walled section and a pair of thick-walled sections at each end providing anti-debonding resistance. The strengthening efficiency of the novel composite member under axial tensile loading was experimentally investigated by 8 specimens, comprising 4 circular cross section and 4 square cross section composite members. It was found that the presence of thickened section could achieve the stress gradient of CFRP and distribute the adhesive's interfacial shear stress. In addition, the finite element model (FEM) of the proposed CFRP-HSST composite member was developed and examined the adhesive damage distribution and evolution, and subsequently, a parametric analysis was carried out. The results indicate that the novel CFRP-HSST composite member can be regarded as an efficient strengthening solution for suppressing the premature debonding failure as well as increasing the strengthening efficiency.

Shear stability and resistance design of novel vertically-flexible stiffened steel plate shear walls

Steel plate shear walls (SPSWs) have been widely employed in practical engineering projects. The steel plates inevitably endure axial loads due to the gravitational forces and structural settling. However, vertical pre-compressive loads have detrimental effects on the buckling behavior and shear resistance of the steel plates. Instead of strengthening the SPSWs to resist the vertical loads, a new type of vertically-flexible stiffened steel plate shear wall (VFS-SPSW) is proposed to minimize these adverse effects. The incorporation of hollow steel tube reduces the vertical compressive stiffness of the VFS-SPSW, leading to a decrease in the proportion of axial compressive loads transmitted to the steel plate wall from the boundary frame. Consequently, this feature facilitates the installation of VFS-SPSW without the necessity of awaiting the completion of the upper structure. In this paper, finite element (FE) analysis is conducted to obtain a threshold out-of-plane bending stiffness ratio for the stability of the VFS-SPSW. Subsequently, a formula for threshold out-of-plane bending stiffness ratio is proposed, including parameters of the ratio of torsional to bending stiffness and aspect ratio of the subpanel. Then, the anchoring mechanism of hollow steel tube to the tensile field of the steel plate is investigated. The threshold in-plane anchor stiffness ratio is defined to ensure the full development of the tension field in the steel plate. A formula for predicting this ratio is proposed by theoretical and numerical analysis. Finally, the reduction factor of vertical compressive stiffness for the VFS-SPSW at the threshold in-plane anchor stiffness ratio is calculated. The results indicate that the vertical compressive stiffness of the VFS-SPSW, which meets the threshold stiffness design requirements, can be decreased to below 50% of the traditional stiffened SPSW, while ensuring that the reduction in ultimate shear stress remains within the limit of 5%.

Bending resistance of austenitic stainless steel hollow sections at elevated temperatures

The present research aims to increase the knowledge of the structural behaviour of stainless steel members under fire. Eight experimental bending tests at elevated temperatures (500, 700 ºC) built with RHS 150×100×3 austenitic stainless-steel beams, using two different grades (1.4301, 1.4571) also known as 304 and 316Ti, are presented. Both grades 1.4301 (X5CrNi18–10) and 1.4571 (X6CrNiMo17–12–2) have almost the same core chemical composition but there are some differences, especially the grade 1.4571 has 2–2.5% molybdenum and a small amount of titanium (less than 0.7%). Grade 1.4301 presents good rust resistance, sufficient acid resistance and good weldability, while grade 1.4571 presents very good rust resistance, very good acid resistance and also good weldability. Both have almost the same strength, but grade 1.4571 has superior strength at elevated temperatures. Both material grades were experimentally characterised with coupon tensile tests at room temperature. The load-displacement behaviour is validated with 3D shell finite element models, assuming a true stress-strain material model, based on the two-stage Ramberg Osgood constitutive law. With the developed numerical model, a parametric analysis is presented to study the fire resistance of beams from both materials, using three different cross-sections and eleven different temperatures. The bending resistance obtained with the finite element model is in good agreement with the cross-sectional design moment resistance, when considering the effective area, confirming that the design rules from EN1993–1–2 are safe for less slender cross-sections and unsafe for the most slender cross-sections.

Experimental Study of Longitudinal and Transverse Bending of Pipe Concrete Rods

The results of experimental studies of pipe-concrete rods during longitudinal and transverse bending tests, since these stress-strain states are of interest from the point of view of the operation of building structures, are presented. To carry out the experiments, several series of laboratory samples 700 mm long were made, which were steel pipes with a monolithic core made of fine-grained concrete. Diagrams of test installations are presented and methods for conducting experiments on axial compression with subsequent loss of stability and three-point bending with concentrated lateral load are described. Based on experimental data, deformation diagrams are constructed and compared with the deformation of a hollow steel pipe. It is noted that the presence of a concrete rod prevents premature loss of stability of the pipe wall during longitudinal bending, limits local deformations due to the curvature of sections during transverse bending, increases the elastic region of deformations, and also prevents the brittle nature of destruction, which is an important advantage in the design of buildings.

Flexural performance of T-shape light-weight concrete filled steel tubular girder

This paper proposes an optimization study for both structure and materials to obtain an affordable, long-span, light-weight, and fast-constructing T-shape lightweight concrete-filled steel tubular (LWCFST) girder in order to be used in bridge construction. This research was performed on a hollow steel tube of Steel-52 (yield limit 360 MPa), which was filled with LWC. A set of parameters had been investigated to illustrate its effect on T-shape LWCFST girder stiffness, toughness, resilience, and ultimate carrying load capacity in order to obtain an equivalent stiffness to that of the typically used precast concrete girder. Based on design codes (EN 1994-1-1/Euro code 4 and ANSI/AISC 360-10) that permit the use of LWC as a filler material, the parameters considered were: the thickness of the steel tube, compressive strength of the filler concrete, and the bond condition between the steel tube and filler lightweight concrete. The yielding and ultimate bending capacity were determined based on the interpreted failure criteria of T-shape LWCFST girder, considering non-linear analysis for both material and loads using ANSYSWORKBENCH software. The results showed that T-shape LWCFST girder can be employed as a significant relative economic alternative to a typical precast girder in the bridge construction field, thanks to its high stiffness/weight ratio. The lightweight concrete inside was effectively employed to delay the local web buckling of the steel tube to increase its bending capacity. In addition, it reduced the total self-weight of the bridge’s superstructure by 20% compared with a typical precast concrete girder. The dominant failure of T-shape LWCFST girders was found in the upper concrete slab due to the compression stress, even though the tensile cracks in the filler concrete occurred after reaching tensile yield stress in the steel tube. Additionally, increasing the value of friction coefficient between steel tube and lightweight concrete up to 0.8 was found to significantly affect the girder stiffness and has a slight effect after, no matter how high it is.

Effectiveness of lag Bolts, CFRP, and HSS in retrofitting salvaged timber girders

This paper presents the effectiveness of various retrofit techniques in improving the flexural behavior of structural timber. For realistic representation with regard to site application, timber girders are salvaged from a decommissioned highway bridge that has been in service over several decades and are strengthened using lag bolts, carbon fiber reinforced polymer (CFRP) sheets, and hollow steel sections (HSS): the retrofitted girders are referred to as Bolt, CFRP, and HSS, respectively. Each category is repeated three times, and the responses of the 12 unstrengthened and strengthened girders are comparatively evaluated. From a load-carrying capacity point of view, lag bolting is not effective. However, CFRP and HSS result in a capacity increase of up to 156.2% relative to the control girder (Cont). Regarding the load–displacement relationship of these girders, the retrofit systems alter the post-peak behavior of the timber. For instance, the lag bolts that are periodically embedded along the specimens bring about pseudo-yield plateaus. The abrupt failure of the Bolt girder is thus precluded. In addition, the amount of dissipated energy increases in all upgraded girders owing to the presence of the retrofit systems. The failure modes of the individual girders are unique, depending upon the type of retrofit. Except for the HSS girder, the effective elastic moduli of the Cont, CFRP, and HSS girders agree with those measured by a stress wave timer. Parameter estimation theoretically infers the possible range of the experimental findings and ensures the adequacy of the test program.

Lateral impact response of circular hollow steel tubes with mid-span localized penetrating notches

Lateral impact response of circular hollow steel tubes with mid-span localized penetrating notches

Shear performance of centrifugal forming hollow circular SFRC piles: Feasibility study of replacing stirrups with steel fibers

This paper aims to investigate shear performance and develop an equation for shear strength assessment of centrifugal forming hollow circular steel fiber reinforced concrete (HSFRC) piles in a practical manufacturing condition. The centrifugal forming was optimized using concrete mixes with different steel fibers. The shear performance and size effect of HSFRC and conventional hollow circular reinforced concrete (HRC) piles with/without stirrups were investigated. Results of X-ray visualization show that, after centrifugal forming, steel fibers were evenly distributed and reoriented in the circumferential direction of the piles, effectively enhancing shear performance. Even with a low steel fiber content of 0.5%, HSFRC piles achieve equivalent shear performance and less brittle behavior compared to HRC piles with shear reinforcement ratios of 0.27%. This implies that higher steel fiber contents can potentially be used to replace stirrups for a flexural failure. SFRC remarkably inhibited the size effect of HSFRC piles. Moreover, a proposed equation considering fiber orientation can better predict the shear strength of centrifugal forming HSFRC piles compared to existing equations.

Flexural Behavior of Rectangular Double Hollow Flange Cold-Formed Steel I-beam

This research experimentally investigates the flexural behavior of rectangular hollow flange cold-formed steel I-beam (RHFCFSIB) under two concentrated loads at the same distance from the support. All specimens were at a constant clear span of (L=1500mm), a constant beam specifications (t=4mm) web, flange thickness (h=300mm) for beam′s depth, and flange width of (bf=150mm). The connecting distance between the bolts, i.e., connects the web to the flanges, was (L/6), and eight stiffeners for each beam were placed under the load bearing points and at the support points on each side. The experimental program included assembling the parts to make beams and testing four specimens under two-point loads. The major parameters adopted in the current research included the flange depth, i.e., hf=30,60,90, and 120mm. The results showed that the beam with a flange depth of 30 mm had a higher ultimate load than other beams; however, it was the highest beam deflection. The beam with a flange depth of 120mm was the best section as a flexural member. The ultimate capacity of this beam increased by 15.34% and 6.4% compared to beams with flange depths of 60mm and 90mm and decreased by 12.9% compared to a beam with a flange depth of 30 mm. The maximum deflection at beam mid-span with a flange depth of 120 mm decreased by 53.8%, 44%, and 19.94% compared to beams with flange depths of 30 mm, 60mm, and 90mm, respectively. Therefore, the flange depth significantly influenced the flexural behavior by increasing the flange depth. Also, the ultimate capacity increased, and the deflection was reduced. The main conclusions drawn from the study were discussed and summarized. The research showed that the Hollow flanged sections gave the best results for flexural behavior.

Axial compression behavior of square CFST short column with triangular-corner gap

In order to investigate the impact of the triangular-corner gap between the outer steel tube and the core concrete on the axial compression behavior of square concrete-filled steel tubular (SCFST) columns, this study conducted axial compression tests on 117 SCFST columns and three reference hollow steel tubes. The main test parameters included steel tube thickness, concrete strength, side length of the triangular gap, and axial gap depth. The test results revealed four typical damage modes in the SCFST columns with triangular-corner gaps. The presence of the gap defect had a significant effect on the ultimate bearing capacity of the SCFST columns, causing a decrease in the range of 1.66 %–17.72 % when the gap ratio ranged from 0.45 % to 12.50 %. Moreover, the influence of the gap ratio on the ductility and initial stiffness of the SCFST with triangular-corner gaps was dependent on the concrete strength and the steel tube thickness. Finally, a simplified formula for calculating the ultimate bearing capacity of SCFST columns with triangular-corner gaps was proposed based on the test data and force analysis. The maximum error between the theoretically calculated value and the test value is within 15 %.

Performance of Prefabricated Hollow Concrete-Filled Steel Tube Bracings on Transverse Bending: Experimental and Numerical Analyses

Due to the complex hydrogeological conditions in coastal regions, the use of internal bracing systems is necessary for supporting coastal foundation pits. This paper introduces a novel prefabricated foundation pit bracing system based on Hollow Concrete-Filled Steel Tube (H-CFST) structures that can be reused, offering significant economic and societal benefits. However, there is a severe lack of research on the application of H-CFST bracing systems. Through model tests and finite element simulations, the load-displacement characteristics and failure modes of prefabricated H-CFST bracing under transverse bending were investigated. The study revealed that when a wall thickness of 1.5 d was chosen, the self-designed hoop effectively mitigated strength and stiffness reduction at the bracing connection point. When the load reached 150 kN, the outer steel tube of the H-CFST components experienced localized yielding, and when the load was increased to 300 kN, the end supports exhibited cracking. Finite element analysis provided a more accurate prediction of bracing failure at 147.18 kN, and it offered valuable insights for optimizing the bracing design. Based on the above research, theoretical methods for calculating the bearing capacity of each bracing component under transverse bending conditions have been proposed and validated against experimental results.

Monitoring corrosion-induced concrete cracking adjacent to the steel-concrete interface

Substantial research effort has been devoted on linking corrosion-induced cracking of concrete with the internal corrosion damage level. Still, numerical models of the corrosion and cracking process require internal parameters, that cannot be directly evaluated from experimental data. Therefore, this study provides a novel experimental method for monitoring the effects of steel corrosion adjacent to the steel-concrete interface. This non-destructive method is suited for small-scale laboratory-made specimen, and was designed to provide missing information required for subsequent calibration of numerical models. Hollow steel bars were cast into concrete and subjected to accelerated corrosion using the impressed current technique. The deformations of the hollow steel bars were measured using distributed strain sensing in an optical fibre, attached to the inner surface of the hollow steel bars. After the corrosion period, X-ray Computed Tomography scans were performed to evaluate concrete cracking and corrosion level. The results reveal a non-uniform distribution of strain around the perimeter of the steel, indicating a non-uniform radial stress distribution. The non-uniformity correlated very well with the position of the corrosion-induced cracks; with extension hoop strains in the steel at the location of these cracks and contraction hoop strains in between. Further, the corrosion level varied around the perimeter, with higher values near cracks. The combination of non-destructive monitoring techniques used in this study on small-scale laboratory-made specimens show great potential to reveal new insights on how the corrosion pattern, corrosion-induced cracking of the concrete cover and stress (indirectly measured through the strain in the steel) interact throughout the corrosion process.

Stability and design of stainless steel hollow section columns at elevated temperatures

This paper investigates the stability and design of stainless steel circular, elliptical, square and rectangular hollow section (CHS, EHS, SHS and RHS) columns at elevated temperatures. Nonlinear shell finite element models are employed to conduct comprehensive parametric studies whereby extensive benchmark structural performance data on the behaviour and resistance of stainless steel hollow section columns at elevated temperatures is generated. In total, 26,760 cold-formed and hot-rolled austenitic, duplex and ferritic stainless steel CHS, EHS, SHS and RHS columns at elevated temperatures are taken into account, considering various member slendernesses, cross-section geometries, cross-section slendernesses and elevated temperature levels. New flexural buckling design rules are put forward for stainless steel hollow section columns in fire, which consistently considers the elevated temperature strength at 2% total strain f2,θ as the reference material strength for all cross-sections classes. The accuracy, safety and reliability of the proposed new design rules are assessed for a wide range of cases. Comparisons are also made against the results obtained through the column fire design rules of the European structural steel fire design standard EN 1993-1-2 [1]. It is demonstrated that the proposed new design rules furnish more accurate, safe-sided and reliable flexural buckling resistance predictions for stainless steel hollow section columns at elevated temperatures relative to the column fire design provisions of EN 1993-1-2 [1].