Steel-reinforced Concrete Structures Research Articles

Predicting long-term tensile degradation of GFRP rebars embedded in concrete with a reconsidered environmental reduction factor [formula omitted]

Glass fiber reinforced polymer (GFRP) has been considered as an advanced material to replace conventional steel reinforcements in concrete structures to address the corrosion issue. The degradation of GFRP rebars, which may threaten both the durability and safety of infrastructures, is a major concern. To predict the 100-year strength retention of GFRP under various temperature and relative humidity conditions, the environmental reduction factor (CE) is applied in engineering. The conventional CE based on the assumption of logarithmic degradation model is commonly utilized during the degradation phase spanning from a few years to decades; however, it is not applicable to the initial and perpetual degradation phases. To address this issue, a novel environmental reduction factor (CE′) based on the exponential degradation model considering temperature and relative humidity is proposed in this study. Both CE and CE′ are mathematically deduced from empirical degradation data and then evaluated in a case study involving GFRP-concrete samples soaked in water at 23, 40 or 60 °C for up to 12 months within the authors’ dataset. Experimental results show that the GFRP tensile strength degradation is closer to the exponential model, reaching a plateau (47.4%) after 12-month exposure to 60 °C water. Moreover, the tensile strength retention of GFRP rebars in Vancouver (10 °C), Shanghai (16 °C) and Houston (22 °C) is predicted considering various scenarios of relative humidities (0–90%). Further research indicates that CE′ (0.65–0.78) exhibits a smaller value compared to CE (0.81) at a temperature of 22 °C and a relative humidity of 90% following a 100-year exposure period, thereby providing engineers with a more conservative design approach for GFRP in real-world scenarios. Nevertheless, this exponential degradation model requires a thorough consideration of severe degradation state during the extended aging period, which may not be applicable to GFRP structures exhibiting exceptional durability.

Durability of Steel-Reinforced Concrete Structures Under Effect of Climatic Temporality and Aggressive Agents (CO2, SO2) in Boca del Rio, Veracruz

The development of sustainable infrastructure is essential to address the challenges of climate change and reduce CO2 emissions. The use of alternative materials, such as agro-industrial ashes and silica fume, emerges as a promising option to enhance the durability of concrete and diminish its environmental impact. These materials can partially replace conventional cement, contributing to the construction of more sustainable infrastructure without compromising performance, even under adverse environmental conditions. In this study, we present an analysis of the use of sugarcane bagasse ash (SBA) and silica fume (SF) as a 15% cement replacement. The behavior of these materials was investigated under coastal conditions, analyzing climatic variables and degrading gases such as CO2, CH4, and N2O. Electrochemical techniques were employed to measure corrosion rate and potential, in addition to conducting carbonation and compressive strength tests. The mixtures with a 15% addition of SBA and SF showed improvements compared to conventional mixes. SBA reduced the corrosion rate by 25% and increased compressive strength by 12% after 150 days, while SF enhanced carbonation resistance by 20% and compressive strength by 25%. The incorporation of SBA and SF provides significant durability in coastal environments, contributing to the sustainability of infrastructure exposed to adverse weather conditions.

Investigation of kinetics of passive layer formation on various microstructures in thermo-mechanically treated steel in simulated concrete pore solution

Carbon steel bars are critical in steel-reinforced concrete structures, and their corrosion can lead to significant deterioration. This research explored the passive layer formation on different carbon steel microstructures using a high throughput approach. Thermomechanically treated steel bars with three distinct microstructures, i.e., martensite in the outer layer, bainite in the middle, and pearlite in the center, were vertically cut and immersed in the simulated concrete pore solution. Scanning electrochemical microscopy was employed to study the formation of the passive layer, the kinetics of the passivation, and the effective rate constant of the species inside the solution on each microstructure. Results showed that the formation of the passive layer is a time-dependent process, and passivation was influenced by the local microstructure. Martensite demonstrated superior passivation behavior compared to pearlite and bainite.

Experimental study on seismic performance of seismic-damaged precast steel reinforced (recycled) concrete frame structure after strengthened and repaired

In order to understand the seismic performance and failure mechanism of the seismic-damaged prefabricated steel (recycled) concrete frame after strengthening and repairing, this paper uses four different strengthened methods, including carbon fiber reinforced polymer (CFRP), high-strength steel wire cloth (HSSWC), oblique support and enveloped steel jacket. Four seismic-damaged prefabricated steel (recycled) concrete frames were strengthened by single or composite strengthening, and low-cycle reciprocating failure tests were carried out on all frame specimens. The final failure mode of the reinforced specimens under simulated seismic load was observed. The seismic performance indexes such as load-displacement (P-Δ) hysteresis curve, skeleton curve, and stiffness degradation of each specimen before and after strengthening were compared and analyzed. The test results show that the strengthening methods used in this test can effectively restore the seismic performance of the seismic-damaged prefabricated steel (recycled) concrete frame. The specimens show a typical ductile failure mode, and the P-Δ hysteresis curve of the specimens is relatively full. For a single strengthened form, CFRP strengthened can more significantly restore and improve the ductility of the specimen than HSSWC strengthened, but the cumulative energy dissipation capacity of the specimen after HSSWC strengthened is stronger. The bearing capacity of the specimens after composite-strengthened is significantly improved, and the damage degree of the structure is reduced. The addition of oblique support and an enveloped steel jacket can provide greater lateral stiffness for the specimens and improve the failure mode of the specimens. The results of this paper can provide a scientific basis for the selection and design of strengthened methods for prefabricated steel-reinforced concrete structures after earthquake damage.

Development and Validation of a Segment Fiber Model for Simulating Seismic Collapse in Steel-Reinforced Concrete Structures Using the Discrete Element Method

Development and Validation of a Segment Fiber Model for Simulating Seismic Collapse in Steel-Reinforced Concrete Structures Using the Discrete Element Method

Carbonation modelling of hardened cementitious materials considering pore structure characteristics: A review

Carbonation of cementitious materials is one of the most important reasons leading to the deterioration of steel-reinforced concrete structures. After years of research, different models have been developed to investigate and predict the carbonation process. This review paper provides a comprehensive overview of carbonation modelling approaches at different scales considering pore structure characteristics. As a typical porous material, the microscopic characteristics of hardened cementitious materials will greatly affect the carbonation rate, and the complex physicochemical carbonation process will alter the pore structure, which will, in turn, affect the carbonation process. Currently, the importance of considering the evolved pore structure and its influence on concrete durability modelling has also gained more and more attention. Therefore, this review paper first introduces the fundamental mechanism of carbonation process in cementitious materials and the existing models for carbonation modelling. By dividing these models into macro-, meso- and micro-scales, this review summarises the modelling approaches, assumptions, pore structure consideration approaches and current limitations of the empirical, kinetic, three-phase, neural network, voxel-based lattice, pore network, and thermodynamic models. The different features of carbonation modelling and ways to consider the effect of pore structure characteristics in those models are comprehensively compared. This review also discusses the future perspectives of different models, especially the pore structure-dependent analysis approaches, to better link the microscopic and macroscopic properties and improve the applicability of carbonation modelling at different scales.

A Reliability-Based Design Approach for the Flexural Resistance of Compression Yielded Fibre-Reinforced Polymer (FRP)-Reinforced Concrete Beams

Fibre-reinforced polymer (FRP) reinforcement has been employed as an alternative to conventional steel reinforcement in concrete structures, which is attributed to its excellent strength and corrosion resistance. However, one drawback is that FRP reinforcements are brittle and affect the ductility of concrete structures. One of the recent effective techniques proposed to overcome ductility issues is the compression yielding (CY) concept. The CY mechanism allows the structure to fail differently than the conventional FRP-reinforced concrete structure. Thus, the existing design recommendations as per the current codes for FRP-reinforced concrete structures are not appropriate. Hence, reliability studies are crucial for the development of a functional CY beam design in order to emphasise the structure’s lifetime performance and to guarantee safety requirements. In this study, a reliability-based design approach is developed for a compression-yielded FRP-reinforced concrete beam (CY beam) using load and resistance factor design (LRFD). Firstly, the flexural failure modes of CY beams are discussed. The uncertainties involved in the development of the probabilistic model for the CY beam are defined. A case study is consequently conducted for a CY beam with random variables that are associated with the statistical characteristics of material properties and load. The reliability analysis method employed in this research is the Hasofer–Lind method. The results suggest the importance of choosing appropriate design variables and stochastic parameters for CY blocks that contribute to a higher level of reliability. The reliability index and resistance factors of a CY beam are then evaluated using the Monte Carlo Simulation computational method. The reliability index value of 3.336 is obtained from the simulation, which indicates that the CY beam demonstrates ductile behaviour. The results not only demonstrate ductile behaviour but also contribute to a possible reduction in material costs and a substantial safety margin. When compared to conventional FRP-reinforced concrete beams, for different load ratios, CY beams showed higher resistance and better reliability levels.

An approximate block factorization preconditioner for mixed-dimensional beam-solid interaction

This paper presents a scalable approximate block factorization preconditioner for mixed-dimensional models in beam-solid interaction and their application in engineering. In particular, it studies the linear systems arising from a regularized mortar-type approach for embedding geometrically exact beams into solid continua. Due to the lack of block diagonal dominance of the arising 2 × 2 block system, an approximate Block-LU preconditioner is used. It exploits the sparsity structure of the beam sub-block to construct a sparse approximate inverse, which is then not only used to explicitly form an approximation of the Schur complement, but also acts as a smoother within the prediction and correction step of the arising Block-LU preconditioner. The Schur complement equation is tackled with an algebraic multigrid method. Although, for now, the beam sub-block is tackled by a one-level method only, the multi-level nature of the computationally demanding Schur equation delivers a scalable preconditioner in practice. In numerical test cases, the influence of different algorithmic parameters on the quality of the sparse approximate inverse is studied and the weak scaling behavior of the proposed preconditioner on up to 1000 MPI ranks is demonstrated. In addition, the robustness of the proposed method regarding material parameters and geometric properties is shown, before the preconditioner is finally applied for the analysis of steel-reinforced concrete structures in civil engineering.

Seismic Performance of Corroded ECC-GFRP Spiral-Confined Reinforced-Concrete Column.

Preventing corrosion in the steel reinforcement of concrete structures is crucial for maintaining structural integrity and load-bearing capacity as it directly impacts the safety and lifespan of concrete structures. By preventing rebar corrosion, the durability and seismic performance of the structures can be significantly enhanced. This study investigates the hysteresis behavior of both corroded and non-corroded engineered cementitious composite (ECC)-glass-fiber-reinforced polymer (GFRP) spiral-confined reinforced-concrete (RC) columns. Employing experimental methods and finite element analysis, this research explores key seismic parameters such as crack patterns, failure modes, hysteretic responses, load-bearing capacities, ductility, stiffness degradation, and energy dissipation. The results demonstrate that ECC-GFRP spiral-confined RC columns, compared to traditional RC columns, show reduced corrosion rates, smaller crack widths, and fewer corrosion products, indicating superior crack control and corrosion resistance. Hysteresis tests revealed that ECC-GFRP columns, at a 20% target corrosion rate, exhibit an enhanced load-bearing capacity, ductility, and energy dissipation, suggesting improved durability and seismic resilience. Parametric and sensitivity analyses confirm the finite element model's accuracy and highlight the significant influence of concrete compressive strength on load-bearing capacity. The findings suggest that ECC-GFRP spiral-confined RC columns offer promising applications in coastal and seismic-prone regions, enhancing corrosion resistance and mechanical properties, thus potentially reducing formwork costs and improving construction quality and efficiency.

A new model for chloride ion diffusion in cracked concrete with consideration of damage and strain fields

In this paper, a new model for chloride diffusion in cracked concrete is presented. The model was developed within a standard continuum damage mechanics framework but newly considers both an irreversible damage variable and a strain field, gaps identified through a literature review, offering a more comprehensive description of the diffusion-like processes in concrete with small and moderate cracks than current models. The model utilizes a realistic dependence for the diffusion coefficient on the damage state and employs a bi-logistic mapping function or an S-curve mapping function to effectively describe the non-linear effects of cracks on diffusion in concrete. The dependence on the strain field introduced by this model not only allows examination of diffusion in opening cracks, it also enables the process of crack closing to be simulated, whatever the irreversible damage variable may be. This paper also proposes a novel calibration procedure for experimental testing involving the use of the Brazilian splitting test on samples enclosed in a steel ring. This innovative approach simplifies the process of creating a portfolio of cracks with varying widths. In the calibration tests described here, samples were subjected to natural diffusion while chloride content was monitored in inlet and outlet chambers attached to the samples, eliminating the need for laborious chloride profiling. Our in-depth examination of chloride diffusion in cracked concrete is applicable to analyses of corrosion in steel-reinforced concrete structures worldwide, with the new calibration procedure offering a straightforward method for populating the model with realistic material parameters, thus providing a valuable tool for accurately predicting chloride penetration in real-world scenarios.

Effect of corrosion on bond slipping between steel and concrete in SRC structures

Corrosion critically impacts bond performance in steel-reinforced concrete (SRC) structures. In this study, we investigate the impact of corrosion on bond-slipping between steel components and concrete within SRC structures. Initially, SRC specimens were subjected to electrochemical corrosion tests to induce varying corrosion rates. Then, pull-out tests were conducted to study the specimens' failure modes, bond stress–slip curves, and displacement distribution. The experimental results indicate that lower corrosion rates can increase bond strength due to enhanced steel surface roughness. As the corrosion rate increased from 0% to 5%, the initial bond stress, peak bond stress, and residual bond stress increased by 133%, 101%, and 102%, respectively. However, when the corrosion rate increased from 5% to 15%, these stresses decreased by 57.1%, 49.6%, and 49.6%, respectively. Furthermore, with an increase in corrosion rate from 15% to 20%, the initial, peak, and residual bond stresses decreased by 100%, 67.6%, and 69.0%, respectively. Corrosion considerably affected the initial and peak slipping observed between the steel components and the concrete, yet its impact on residual slip was relatively minor. In addition, a nonlinear finite element model for characterising the corrosion and pull-out tests was developed and validated according to the experimental results. The numerical results showed that the four shear transfer mechanisms, including chemical bonding, micromechanical interlocking, macromechanical interlocking, and rust interface bonding, exhibited distinct behaviours at different loading stages. Finally, a parametric study was conducted using a finite element model. With variations in corrosion rates, four modes of cracking patterns on the concrete surface were observed.

Effect of ICCP on tensile performance of carbon fiber bundles in seawater sea-sand cementitious matrix

Impressed current cathodic protection (ICCP), carbon fabric reinforced cementitious matrix (CFRCM) composites, and piezoresistive effect have been widely studied in delaying steel bar corrosion, strengthening steel-reinforced concrete structures, and structural health monitoring, respectively. In this study, the effect mechanism of the ICCP procedure on the tensile performance degradation of CFRCM bundles with the two types of matrix (normal matrix (i.e., sand conforming to ISO standard) and seawater sea-sand matrix), as well as the tensile performance differences between them, were investigated through carbon fiber bundle tensile tests and CFRCM bundle tensile tests. The piezoresistive effects of CFRCM with the two types of matrix after the ICCP procedure and the effect of ICCP on the piezoresistive effect were analyzed. Prediction formulas for the tensile performance were established based on the different charge densities. Based on the dual functionality of carbon fiber strengthening and self-sensing, this study lays a foundation for the development of a triple-functional system of impressed current cathodic protection, structural strengthening, and structural health monitoring (ICCP-SS-SHM). The study indicates that seawater sea-sand positively influences the delay of CFRCM degradation through ICCP. This is advantageous in tackling the issue of scarce freshwater river sand resources.

Calculation method for a steel-reinforced concrete bridge span structure with material separation along the neutral axis

Introduction. In steel-reinforced concrete spans, the strength of reinforced concrete is not fully used due to the twostage inclusion of the cross section in the work and the irrational distribution of materials in the section. To increase the efficiency of the materials used, it is proposed to combine the steel and reinforced concrete parts along the neutral axis of the cross section. With such a cross-section design, the steel will always be in the tension zone, and the concrete in the compression zone. It is possible to implement such a design by constructing a span in one stage from prefabricated steel-reinforced concrete blocks.Materials and methods. It is possible to implement the calculation method with the separation of the material along the neutral axis when organizing the installation of the span structure in one stage, assuming that the section of the span structure operates in the elastic stage and following the laws of structural mechanics. To cover the features of the calculation of split and continuous span structures, a cantilever-beam static scheme was adopted.Results. The presented results of analytical calculations make it possible to estimate the consumption of materials in the manufacture of the span. The steel consumption of the span under study is 6.12 t/lm, the reinforced concrete consumption is 6.54 m3/lm.Installation of the span. The installation of the span is described, considering the design features.Conclusions. The optimal static layout of the span structure has been determined. A method for calculating a steel-reinforced concrete span with material separation along the neutral axis has been developed. An analytical calculation was performed to select the geometric parameters of the cross sections of the span.

Non-Destructive Inspection Method Using Elastic Waves for Quality Management in the Bending Process Region of BFRTP

In order to establish a sustainable infrastructure, structures must maintain their minimum required performance for an extended period. Typically, existing concrete structures are reinforced with steel, but the susceptibility of steel reinforcements to corrosion, attributed to factors such as carbonation and chlorides, can lead to performance degradation, rendering the specified requirements unmet. As a remedy, there has been a growing interest in using lightweight and corrosion-resistant fiber-reinforced polymer (FRP) bars as an alternative to traditional steel reinforcement in concrete structures. Particularly noteworthy is the use of FRP bars manufactured with thermoplastic resins (FRTP) due to their ease of processing and convenient applicability on construction sites. This study delves into the mechanical behavior evaluation by examining the propagation characteristics of elastic waves in the curved section of basalt FRTP (BFRTP). Multiple BFRTP bars underwent a 180-degree bending process, subject to various conditions, including heat and twist variations. Subsequent measurements focused on the propagation characteristics of elastic waves in the curved sections, emphasizing wave attenuation, frequency features, and propagation velocity. Additionally, bending tensile tests were conducted on the curved bars, and a comparative analysis was performed between the tensile strength and the aforementioned elastic wave propagation characteristics. The results affirm a consistent correlation between the propagation characteristics of elastic waves (amplitude ratio, centroid frequency, velocity) during the traversal of the curved BFRTP section and its tensile strength. Notably, both centroid frequency and velocity exhibited correlation coefficients exceeding 0.7, suggesting their potential efficacy as reliable indicators for estimating tensile strength.

Experimental Investigation of GFRP-Reinforced Hollow Square Concrete Column

Due to their great structural efficiency and efficient utilization of materials, steel-reinforced hollow-core concrete columns are often employed in utility poles, ground piles, and piers for bridges. Based on research, these columns' performance is impacted by many design parameters. However, corrosion can be a problem in steel-reinforced concrete structures. This paper examines the differences between using steel and GFRP longitudinal bars in hollow-section square concrete columns and explores the potential benefits of using GFRP bars as an option that is economically viable and non-corrosive. According to the study results, the computational results clearly show how an increased longitudinal GFRP reinforcement ratio improves the columns' bearing capability, but when compared to steel reinforcement, it provides less bearing capability. For the same reinforcement ratio (1.46 %, 3.29 %, and 4.9 %), The findings demonstrated that GFRP columns had a decrease in the axial bearing load by 13.1%, 9.2 %, and 9.4%, respectively.

Crack detection and damage evaluation of asymmetrical steel-reinforced concrete frame nodes using acoustic emission technology

ABSTRACT Detecting cracks in steel-reinforced concrete (SRC) frame nodes is crucial for ensuring structural safety. This study employs acoustic emission (AE) technology to monitor the growth of concrete structural defects in real time. The aim is to establish a sensitive assessment method based on AE parameters to accurately assess the damage stages of SRC frame nodes by considering the complex crack extension mechanism in SRC structures. An experimental study of the AE characteristics of SRC frame nodes under low-cycle loading was performed. The crack evolution process of SRC frame nodes was monitored and analysed using the AE parameters. The results showed that ringing count is the AE parameter more sensitive to the damage of the SRC frame node. The damage evaluation method was established based on the variation coefficient analysis of the AE parameters. Considering the sudden change in the growth rate of the damage index, the damage evolution process of the SRC frame nodes can be accurately divided into three stages: initial crack compaction, rapid crack expansion, and crack penetration. These stages are consistent with the mechanical properties of SRC frame nodes.

Chloride binding by layered double hydroxides (LDH/AFm phases) and alkali-activated slag pastes: an experimental study by RILEM TC 283-CAM

Chloride binding by the hydrate phases of cementitious materials influences the rate of chloride ingress into these materials and, thus, the time at which chloride reaches the steel reinforcement in concrete structures. Chloride binding isotherms of individual hydrate phases would be required to model chloride ingress but are only scarcely available and partly conflicting. The present study by RILEM TC 283-CAM ‘Chloride transport in alkali-activated materials’ significantly extends the available database and resolves some of the apparent contradictions by determining the chloride binding isotherms of layered double hydroxides (LDH), including AFm phases (monosulfate, strätlingite, hydrotalcite, and meixnerite), and of alkali-activated slags (AAS) produced with four different activators (Na2SiO3, Na2O·1.87SiO2, Na2CO3, and Na2SO4), in NaOH/NaCl solutions at various liquid/solid ratios. Selected solids after chloride binding were analysed by X-ray diffraction, and thermodynamic modelling was applied to simulate the phase changes occurring during chloride binding by the AFm phases. The results of the present study show that the chloride binding isotherms of LDH/AFm phases depend strongly on the liquid/solid ratio during the experiments. This is attributed to kinetic restrictions, which are, however, currently poorly understood. Chloride binding by AAS pastes is only moderately influenced by the employed activator. A steep increase of the chloride binding by AAS occurs at free chloride concentrations above approx. 1.0 M, which is possibly related to chloride binding by the C–(N–)A–S–H gel in the AAS.

Evaluation of the Corrosion Activity of Reinforcement in Drainage Gallery of Concrete Dam using Half-cell Potential (HCP)

Dams are essential structures for water management, providing various benefits crucial for human survival and economic growth. However, steel corrosion in concrete dams poses a significant threat, leading to structural deterioration and potential collapse. Detecting corrosion in the early stage is critical to prevent catastrophic failures. This study investigates corrosion risk in a concrete dam's drainage gallery using half-cell potential (HCP) measurements, a common method for assessing corrosion activity in reinforced concrete. The electrochemical process of steel corrosion in concrete, influenced by factors like chloride or carbonation exposure and temperature, is discussed. The HCP method is a nondestructive technique for determining the corrosion rate of steel reinforcement in concrete structures. It involves measuring the potential difference between reinforcing steel and reference electrodes; typically, a copper/copper sulphate electrode is used. The potential difference between the two electrodes is then used to calculate the corrosion rate of the reinforcing steel. The HCP method is a reliable and cost-effective way to identify potential corrosion problems before they become severe. The present study used CorMap II® to measure HCP on the upstream face of the dam's drainage galleries. Results indicate predominantly low corrosion risk across tested locations, with minimal uncertainty. However, interpretations must consider environmental factors' influence on measurements. The study's findings offer valuable insights for future corrosion assessments and underline the importance of preventive measures for concrete dam integrity.

Damage Detection in FRP-Reinforced Concrete Elements.

Fiber-Reinforced Polymer (FRP) composites have emerged as a promising alternative to conventional steel reinforcements in concrete structures owing to their benefits of corrosion resistance, higher strength-to-weight ratio, reduced maintenance cost, extended service life, and superior durability. However, there has been limited research on non-destructive testing (NDT) methods applicable for identifying damage in FRP-reinforced concrete (FRP-RC) elements. This knowledge gap has often limited its application in the construction industry. Engineers and owners often lack confidence in utilizing this relatively new construction material due to the challenge of assessing its condition. Thus, the main objective of this study is to determine the applicability of two of the most common NDT methods: the Ground-Penetrating Radar (GPR) and Phased Array Ultrasonic (PAU) methods for the detection of damage in FRP-RC elements. Three slab specimens with variations in FRP type (glass-, carbon- and basalt-FRP, i.e., GFRP, CFRP, and BFRP, respectively), bar diameter, bar depths, and defect types were investigated to determine the limitations and detection capabilities of these two NDT methods. The results show that GPR could detect damage in GFRP bars and CFRP strands, but PAU was limited to damage detection in CFRP strands. The findings of this study show the applicability of conventional NDT methods to FRP-RC and at the same time identify the areas with a need for further research.

ОПТИМИЗАЦИЯ ПОЛУПЛОСКООВАЛЬНЫХ ГНУТОСВАРНЫХ ПРОФИЛЕЙ ДЛЯ БАЛОЧНЫХ КОНСТРУКЦИЙ.

A new technical solution for semi-flat bent-welded profiles is presented, optimized for bending strength characteristics, the originality of which has been confirmed by patent examination. Rectangular profiles with a ratio of width and height 1/3 along the middle section line served as the basis for their shaping, which ensures maximum strength. As a prototype, semi-flat profiles are assembled on the basis of flat-oval profiles with maximum strength due to the ratio of width and height 1/3.064 along the middle section line. The calculation of the optimal parameters of thin-walled sections using an approximate technique using their average lines, repeatedly tested in solving optimization problems for bent-welded profiles of various shapes and outlines, is presented. A comparative analysis of the design parameters revealed a positive effect of optimized profiles in truss and girder structures, including a reduction in the consumption of structural material, a decrease in stress concentration, and a reduction in building height. The prospects of expanding the scope of their rational use with the addition of pipe-concrete and steel-reinforced concrete structures are indicated.