Use Of High-strength Materials Research Articles

Fire design of steel-reinforced CFST stub columns with high-strength materials

Innovative composite sections are gaining popularity as they reduce the environmental impact of construction and take advantage of the collaboration of concrete and steel properties at room temperature and in fire. By introducing high-performance materials, these synergies are boosted. One typology is the steel-reinforced concrete-filled steel tubular (SR-CFST) section, in which a steel profile is embedded inside a CFST section. Despite their impressive load-bearing capacity and fire resistance, the available investigations on their thermo-mechanical capabilities are scarce. The present paper develops a numerical model to analyse the thermo-mechanical behaviour of SR-CFST stub columns subjected to fire. The model is validated against previous experiments conducted by the authors by comparing the temperature distribution and the mechanical behaviour with the experimental measurements. Afterwards, an extensive parametric study (1440 cases) is conducted to analyse the influence of several geometrical parameters – cross-sectional shape, outer tube dimensions and thickness, inner steel profile dimensions, section factor – and the use of high-strength materials for the concrete and the inner steel profile. Afterwards, a simplified temperature distribution proposal formerly designed by the authors for SR-CFST sections was tentatively tested. Based on this previous simplified temperature field and in line with the current provisions of EN1994-1-2, a new proposal is developed to evaluate the cross-sectional plastic resistance of SR-CFST stub columns under a fire scenario. This method unifies the initially developed thermal method and provides practical guidance for designers to evaluate the thermo-mechanical behaviour of SR-CFST columns, filling an existing gap in the European design code.

Hydrogen trapping and embrittlement in metals – A review

Hydrogen embrittlement in metals (HE) is a serious challenge for the use of high strength materials in engineering practice and a major barrier to the use of hydrogen for global decarbonization. Here we describe the factors and variables that determine HE susceptibility and provide an overview of the latest understanding of HE mechanisms. We discuss hydrogen uptake and how it can be managed. We summarize hydrogen trapping and the techniques used for its characterization. We also review literature that argues that hydrogen trapping can be used to decrease HE susceptibility. We discuss the future research that is required to advance the understanding of HE and hydrogen trapping and to develop HE-resistant alloys.

Quasi-static tests and seismic fragility analysis of RC bridge piers with high-strength steel bars and high-strength/ultra-high performance concrete

The use of high-strength steel bars (HSSB), high-strength concrete (HSC) and ultra-high performance concrete (UHPC) in bridge piers can obviously improve bearing capacity and save material consumption. However, the use of high strength materials may detrimentally affect the seismic performance of reinforced concrete (RC) piers. This paper tries to study the seismic performance of RC piers with HSSB and HSC/UHPC by quasi-static tests and seismic fragility analysis. Three RC piers, solid pier with normal strength steel bars (NSB) and normal strength concrete (NSC), solid pier with HSSB and HSC, and hollow pier with HSSB and UHPC, were designed and tested under quasi-static loading. The failure mode, hysteretic performance, stiffness degradation and residual displacement of three specimens were compared and analyzed. A fiber-based beam-column finite element model (FEM) was developed to simulate the nonlinear response of RC piers with HSSB and HSC/UHPC. On this basis, the seismic fragility analysis was performed to study the effects of high-strength materials on the seismic performance of RC piers. Research results show that, compared with NSC piers, HSC piers reinforced with a small amount of HSSB still exhibited slightly larger lateral bearing capacity but lower deformability due to the higher brittleness of HSC. The UHPC hollow pier presented obviously larger deformation capacity, and more slow decline speed of lateral stiffness than NSC and HSC solid piers. Meanwhile, the matching use of UHPC and HSSB in hollow pier can improve the elastic deformation, and then reduce residual displacement of RC piers. The proposed fiber-based finite element model (FEM) can simulate the nonlinear response of RC piers with different high-strength materials with reasonable accuracy. Fragility results demonstrate that, HSC pier presents lower seismic fragility than NSC pier at different damage states except for collapse due to lower ductility of HSC pier. The UHPC hollow pier with HSSB has lower seismic fragility than NSC and HSC solid piers at the same seismic intensity. Overall, the hollow pier with HSSB and UHPC can maintain good seismic performance while greatly saving material consumption.

Modelling and experimental studies of the stress-strain state of compressed concrete filled steel tube elements of a continuous section

Modern building structures must meet the requirements of efficiency and resource-saving. The main direction for implementing these requirements is to reduce the consumption of steel (14–16%) and save cement (10–12%). These tasks can be solved through the rational combination of concrete and steel when they work together and the use of high-strength materials. One embodiment of this task is the use of Concrete Filled Steel Tube (CFST) structures. The purpose of this study is to identify the possibility of using the Drucker-Prager model by comparing the results of test studies on short compressed Concrete Filled Steel Tube (CFST) elements with different strength and deformation characteristics of the concrete core to the results from finite element analysis (FEA) modelling of corresponding CFST elements. Additionally, the behaviour of a steel pipe without a concrete core was investigated. The results show that the FEA method used in this work is sufficiently accurate for studying the behaviours of short CFST elements. The modelling technique adopted in the study made it possible to consider the redistribution of stresses in the concrete and pipe dynamically. The stress distribution patterns inside the concrete during both linear and non-linear deformations of CFST elements, as well as the characteristics of the interaction between the concrete and pipe in the contact zone, have been revealed.

High-strength rectangular concrete-filled steel tube long columns: Parametric studies and design

High-strength steel and concrete materials (i.e., steel with yield stress Fy > 525 MPa and concrete with compressive strength f'c > 70 MPa) have been applied in various types of structures because they can increase the resistance and space efficiency of the structure. However, the AISC Specification (AISC 360-16) does not permit the use of high-strength materials in concrete-filled steel tube (CFT) members due to a lack of adequate research. This paper aims at investigating the behavior of high-strength CFT long columns and evaluating the applicability of current design equations for high-strength rectangular CFT long columns. Firstly, an experimental database including 74 tests of high-strength rectangular CFT long columns was compiled and gaps in the database were identified. Then, finite element (FE) models were developed and benchmarked for parametric studies. The effects of width-to-thickness ratio of the steel tube, yield stress of steel, compressive strength of concrete, and length-to-depth ratio of the member were investigated. Finally, new design equations for high-strength rectangular CFT long columns were proposed based on the modified slenderness reduction factor in AISC 360-16.

Design of High-strength Material Non-dismantling Docking Assembly

The construction technology of tower erection by segments with the cranes on the basis of the docking assembly has been applied in multiple cities and provinces in China. The docking assembly reduces the number of hoisting times, and lowers the safety hazards. However, the docking assembly which is an independent structure and made of common materials currently needs to be installed on and dismantled from the tower for each use, and each component is heavy. To address the above problems, the high-strength material non-dismantling docking assembly is studied to develop a design scheme which reduces the weight and eliminates the installation and dismantling work of docking assembly. Its successful engineering application shows that the use of high-strength materials effectively reduces the weight of the docking assembly and the docking assembly developed is safe and reliable, which greatly improves the efficiency of tower erection and reduces labor intensity. The project study results provide a reference for the design of high-strength material non-dismantling docking assembly for other types of transmission towers in the construction of power grids.

Test and design of eccentrically-loaded slender circular tubed columns filled with high-strength concrete and reinforcement

The tubed-reinforced concrete (TRC) column is an original reinforced concrete column in which the stirrups are mostly replaced with the steel tube to enhance the confinement to the concrete core. In this study, the eccentrically-loaded behavior of slender circular TRC (CTRC) columns with high-strength materials was experimentally and numerically investigated. Six slender columns with high-strength concrete of 81 MPa and high-strength rebar of 583 MPa were tested to failure under eccentric loading, considering the main parameters of length-to-diameter ratio and load eccentricity. A three-dimensional finite element (FE) model was established and verified for conducting parametric studies and investigating the moment magnification and eccentricity magnification which reflect the second-order effect on the strength of slender columns. The results indicate that all columns fail in a bending mode and show good deformability, even with the use of high-strength materials, and the strength of high-strength rebars can be fully utilized due to the enhanced concrete compressive strain and ductility. Based on the test results and parametric study, a design method is proposed to assist designers to evaluate the load capacity of slender CTRC columns.

EVOLUTION OF USA COMPOSITE CODES: CHANGES IN CHAPTER I (COMPOSITE CONSTRUCTION) OF THE AISC 360‐22

AbstractThis paper briefly reviews the evolution of composite codes in the USA in the context of important changes for the 2022 edition of the American steel design specification for buildings Major changes include the incorporation of composite walls as a new type of composite member, the addition of new provisions for shear capacity of filled members, and the introduction of a performance‐based procedure for qualifying new types of anchors. An appendix also allows for the use of high strength materials for concrete filled rectangular members. The paper then describes the write's opinion on (1) important issues that need to be addressed on the direction of future codes, (2) areas where more research work is needed to provide more consistent and simpler design rules and (3) the desirability of including additional topics into the main specification.

Research on the Influence of Design Parameters on the Seismic Capacity of High Rise Prefabricated Structure Buildings

Building industrialization and resilience are the goals and trends of structural engineering development. Prestressed assembly design and construction is an effective way to achieve this goal. The birth of prefabricated buildings has met people's demand for diversified buildings from many angles. At the same time, prefabricated buildings have also broken the limitations of long construction time and low efficiency of traditional buildings, and gained broader development prospects in construction work. Compared with cast-in-place concrete structure, prestressed prefabricated concrete structure has the advantages of good performance, small residual deformation after earthquake, full use of high-strength materials to reduce self-weight, industrial production and fast construction speed. Each part of the prefabricated building can be disassembled and assembled. When designing the structure, it is necessary to consider the characteristics of the structural system, and set up the connection mode reasonably during assembly to ensure the stability of the structure. This paper expounds the influence of design parameters on the seismic capacity of high-rise assembled structure buildings, and puts forward the seismic design strategy of high-rise assembled structure buildings.

IN MECHANICS OF DEFORMABLE SOLIDS PRIMARY PLASTIC ON PANEL DURING POWER UP DEVELOPMENT OF DEFORMATIONS

One of the most important issues in solid mechanics is the development and application of optimal methods for estimating the resistance of dispersion materials. Currently, the theory of propagation of cracks in solid bodies is widespread due to the wide use of high-strength materials and large-sized structures and devices in various fields of technology. The article discusses the methods of studying the problems of the interaction of two factors - strengthening the panel with stiffening ribs made of unidirectional composite material and weakening it with a number of circular holes and cracks protruding from its contour. An infinite isotropic elastic riveted panel weakened by a periodic system of circular holes and two cracks along the abscissa axis segments near each hole is considered. The contours of the holes and the edges of the cracks are free from external forces. Transverse stiffness ribs made of metal composite material are riveted to the plate. In the calculation scheme, the effect of riveted reinforcing ribs is replaced by the concentrated forces applied at the points of location of the rivets. The values of the concentrated forces are found depending on the geometrical and physical parameters of the problem. Stress intensity factors and ultimate loadings were calculated depending on the geometrical and physical parameters of the problem. It has been shown that there is a stable phase of crack development under certain specified conditions. The development of initial plastic deformations (embryonic cracks) emerging from the contour of circular holes in a plate reinforced with stiffness ribs is studied. The material of the plate is elastic-perfect-plastic satisfying the Tresca-Saint-Venant condition. It is assumed that the plastic deformations are concentrated along some slip lines emanating from the contour of the hole. By satisfying the boundary conditions, the solution of the problem leads to a singular integral equation. Then the singular equation of the problem is brought to a system of algebraic equations without the intermediate step of bringing it to the Fredholm equation. The resulting system was solved by the Gaussian method with the selection of principal elements for different values of n (n is the number of Chebyshev nodes in the division of the interval). The values of concentrated forces are found depending on the geometrical and physical parameters of the problem. The dependences of the length of the plasticity bands on the applied load, the geometrical parameters of the problem and the yield point of the material were found. Using the local dissipation condition (KPT-criteria), a ratio was obtained to determine the destructive edge loading.

Prediction and control of temperature rise of massive reinforced concrete transfer slab with embedded cooling pipe

Reinforced concrete (RC) transfer slabs (or beams) are common support structures for high-rise or multi-use buildings. The structure serves as a new base for the upper zones and transfers considerable loads to the foundation; hence, the RC transfer slab necessitates a massive thickness design, as well as the use of high-strength material, and should be constructed without cracks. In this paper, the temperature rise of the massive RC transfer slab controlled by embedded cooling pipes was predicted by the Ansys program, and the numerical prediction was verified by recorded data of the temperature rise of the massive RC transfer slab. Regarding to the temperature rise, both prediction data and recorded data showed that, initially, the temperature at the bottom surface and the core of the RC transfer slab rose fast, resulting in a substantial temperature differential (20.4 °C) with the top surface, and, during the cooling stage, the top surface then retained heat and cooled more slowly than the bottom surface; moreover, the model fitted quite well with the measurement at the peak temperature. Regarding cooling pipe operation, within the first four days, it was recommended that the flow rate of 30 °C cooling water was set as high as 26.5 L/m (liters/minute), and this number was subsequently increased to 30 L/m when the temperature differential within the concrete peaked at 20 h.

A numerical analysis on bending capacity of steel pipe columns using a mechanical joint with concrete-filled steel tube

Structural steel pipes have been applied commonly in the bridge construction for foundations or piers with many advantages such as large bending capacity, high shear resistance, and rapid construction. However, site welded joints may face critical technical matters which need to be considered for steel pipe piers during construction stage. Current solutions for pipe joints require the use of high-strength materials with machining technology to ensure accuracy, quality, and increase construction costs with substantial number of joints. Therefore, these solutions, when applied in Vietnam, will also face limitations due to the contractor’s qualification and erection technology at construction site. This study proposes a type of joint for steel pipe piers of viaducts in a mountainous region to eliminate the welding work of the steel pipe at the construction site and to provide high bearing capacity, simple construction, and cost effectiveness. Finite element analyses are conducted to investigate and verify the bending capacity of steel pipes with the proposed joint. Nonlinear material and nonlinear geometry are considered to simulate behaviors of composite action, yielding, and buckling in the structures. Finally, comparative studies of bending capacity of the steel pipe with and without joint are performed. Stress distributions and deformations of the structural components in the joint region are also observed and discussed.

MODERN MATERIALS AND INNOVATIVE WELDING TECHNOLOGY USED IN THE CONSTRUCTION OF ANTENNA MOUNTS

Telecommunication, transport and civil engineering play an important role in new research areas. New antennas based on innovative materials are being developed. At the same time, the methods of antenna mounting with the use of high-strength materials to ensure high structural rigidity with the lowest possible weight are being planned. These materials include AHSS steels with ultimate tensile strength (UTS) up to 1700 MPa and elevated yield point (YS); however, welded joints made of these steels have much worse mechanical properties, compared to the native materials. In this paper, it was planned to test the MAG welding of DOCOL 1400M steel (AHSS group). Directly after welding, a micro-jet joint cooling was applied. It was determined to create thin-walled joints that could be used in the formation of antenna mounts.

Bond behaviour of high-strength steel bars in concrete with steel fibres

Reductions in materials consumption through the use of high-strength materials is important in building construction. However, high-strength steel applications have possible challenges such as their effects on bond behaviour and structural ductility. The bond behaviour, total energy capacity and failure modes of headed and straight high-strength and normal-strength steel bars were investigated using pull-out tests. In the experimental programme, 48 concrete specimens with a compressive strength of 40 MPa, different ratios of steel fibres and embedded steel bars with different yield strengths were subject to pull-out tests. The results showed that the headed bars had far greater bond stress and total energy capacity than the straight bars. It was also found that the higher the yield strength of the bars, the higher the energy capacity and bond stress. Although increases in fibre ratios led to increases in energy capacity, they did not absolutely increase the bond stress. The specimens with both headed and straight bars failed by splitting.

Towards in-process evaluation of the precise electrochemical machining (PECM)

Increasing environmental and economic concerns have increased the use of high-strength materials and superalloys, such as the well-known nickel-based alloys. Due to their very high strength, such materials push established machining methods to their economic limits. As a result, non-traditional machining methods such as precise electrochemical machining (PECM) are gaining importance. PECM has shown significant advantages such as high material removal rates and lower surface roughness. Despite these advantages, some challenges still need to be overcome, such as the implementation of an in-process monitoring system and the determination of optimal process parameters to achieve maximum material removal rates and good surface roughness. While the analytical determination of the optimal parameters is difficult due to the high complexity of the process, the empirical determination shows better results. However, a hitherto very unused approach in this respect is the data-driven model. Based on process data, such models have shown great results in other fields, especially for highly complex systems. The first step in developing such a model is to figure out what process data are needed. In this paper, the potential of a data driven model for PECM is presented. Furthermore, current waveforms for different PECM setups are analyzed and various parameters for the in-process monitoring of the process are formulated. The ability of these parameters to differentiate between different processes was investigated. It was found that the formulated parameters could be used to monitor the efficiency of flushing in the working gap.

Review on the Impact of Elements Used During Bridge Construction

The requirement of long span bridge is increase with development of infrastructure facility in every nation. Long span bridge could be achieved with use of high strength materials and innovative techniques for analysis of bridge. Generally, cable-supported bridges comprise both suspension and cable-stayed bridges. Cable-supported bridges are very flexible in behavior. These flexible systems are susceptible to the dynamic effects of wind and earthquake loads. The cable-stayed bridge could provide more rigidity due to the presence of tensed cable stays as a force resistance element.

Editorial: Composite Use of High Strength Steel and Concrete Materials for Sustainable Civil Engineering

The need for sustainable construction has been hastened world-widely aiming to reduce the use of construction materials and labor costs. To do so, high strength materials will be one option.The higher the strength, the smaller the member size is required. This will free up more usable floor area and require fewer materials and construction work. The composite use of them makes the aim easier to be achieved. To bridge the gap between theoretical development and practical application, a special issue with the research topic of "Composite Use of High Strength Steel and Concrete Materials for Sustainable Civil Engineering" has been organized by the Guest Surely the high temperature and cooling deteriorated the bond strength, and this would have an adverse influence on the ultimate load-carrying capacity of the composite members.The diverse nature of contributions in this collection is a testament to the cross-disciplinary research activities about the composite use of high strength materials. Nevertheless, there is a common thread running through all contributions where high strength, when properly achieved, can be the source of great creativity in achieving more sustainable construction.

Numerical analysis of railway substructure with geocell-reinforced ballast

ABSTRACT With the commencement of high-speed trains in railway infrastructure, stresses throughout the railway substructure have increased. To have high bearing stress capacity, for construction of railway substructure, either use of high strength material or implementation of strength improvement techniques for substructure design is proposed. This study describes the process of development of the numerical model of railway substructure, focusing on its subgrade stress behaviour. In this study, a comparative numerical study for subgrade stresses of railway substructure with unreinforced and reinforced ballast was also conducted. The objective of this study is to understand the stress distribution in railway substructure with and without reinforcement due to train movement. The comparison study illustrates the inclusion of geocell in ballast as reinforcement and increment in its width, magnitude of stresses reaching subgrade is reduced and became uniformly distributed. Thus, it helps in constructing a better performing railway substructure with low strength ballast and soil subgrade. However, widening of geocell confinement is restricted, as higher confinement width results in stress accumulation on side-slope of ballast which may cause blowing of the constituent material.

Tool wear in dry gear hobbing of 20MnCr5 case-hardening steel, 42CrMo4 tempered steel and EN-GJS-700-2 cast iron

The demand for higher power densities in gear applications leads to the use of high-strength materials. This poses a challenge for manufacturing technologies with regard to the machinability of these materials. Even though gear hobbing is one of the most common technologies for gear machining, only limited investigations on the machinability of high-strength materials have been carried out. In this paper, the machinability of different workpiece materials by gear hobbing under dry cutting conditions is investigated. The tool life and wear behavior of powder metallurgical high-speed steel PM-HSS S390 and sintered tungsten carbide – cobalt WC-Co K30 tools with an AlCrN coating were analyzed. 20MnCr5 case-hardening steel, 42CrMo4 tempered steel and EN-GJS-700-2 cast iron were machined using the fly-cutting trial as an analogy process for gear hobbing. To identify a respective target tool life of LT,10 = 10 m, the cutting speed was varied while the feed rate was defined based on the respective tool concept and cutting substrate. The experiments showed a good machinability of the soft state material 20MnCr5 with PM-HSS S390 tools up to a cutting speed of vc = 350 m/min. A machining of the high-strength materials 42CrMo4 and EN-GJS-700-2 resulted in high tool wear or catastrophic tool failure. Even at low cutting speeds of vc = 50 m/min, the target tool life LT,10 could not be reached. When using WC-Co K30 tools, tool lives of LT > 6 m and cutting speeds up to vc = 400 m/min were feasible when machining 42CrMo4 tempered steel. For the machining of EN-GJS-700-2 cast iron, high abrasive tool wear was observed, which led to short tool lives of LT < 4 m at cutting speeds above vc ≥ 200 m/min. By reducing the cutting speed to vc = 100 m/min, a tool life of LT > 15 m could be achieved.

Low Cost Gas Diffusion Layer Materials and Treatments for Durable High-Performance PEM Fuel Cells

The gas diffusion layer (GDL) is a critical component of proton exchange membrane fuel cells (PEMFC). It serves as the primary mediator in electrical and thermal conductivity as well as gas and water transport within the cell. Currently, the production of GDLs is dependent on the use of high-cost materials and manufacturing methods. The most common base material for GDLs is polyacrylonitrile (PAN). PAN, in addition to its high base cost ($15 - 20/kg), requires high graphitization temperatures (> 1700°C) in order attain sufficient conductivity and post-carbonization treatment with Teflon to increase the hydrophobicity for improved water transport. The high strength of PAN based GDLs has been required to prevent fiber intrusion into the channel of the flow field. Some state-of-the-art flow fields no longer utilize the land/channel design, and as such may not require the use of high strength materials like PAN in order to be functional. This presents the opportunity to create novel GDLs with equivalent or superior performance at lower cost. We are investigating methods to significantly reduce the cost of GDL production while maintaining durability and performance characteristics necessary to PEM fuel cells. First, we are developing the use of inexpensive, natural fiber materials, such as cotton, jute, and bamboo. Second, we are developing methods to reduce the carbonization temperatures and eliminate manufacturing steps, such as the need for a microporous layer. Figure. SEM images of commercial (A) (without microporous layer), cotton (B), and jute (C) based GDLs. The cotton and jute GDLs had been carbonized at 1100°C in N2 atmosphere. Figure 1