Normal Strength Steel Research Articles

High strength steel unlipped channel sections subjected to ETF loading: Laboratory testing, numerical simulations and web crippling design

This paper presents web crippling and structural design of high strength steel unlipped channel sections under end-two-flange (ETF) loading based on experimental and finite element investigations. The experimental programme was composed of six grade S690 and four grade S960 test specimens, and the corresponding test set-up, procedures and results were reported in detail. The web crippling test results were used in the numerical modelling programme to validate the developed FE models, which were then adopted to perform parametric studies to enlarge parameter ranges of the bearing length, web slenderness and inside bend radius. Given that codified design rules for S690 and S960 high strength steel unlipped channel sections undergoing web crippling are absent, the corresponding normal strength steel design provisions, as stipulated in the European code EN 1993-1-3 and American specification AISI S100, were evaluated for their suitability to high strength steel unlipped channel sections. It is shown that the ultimate strength of high strength steel unlipped channel sections nonlinearly increases with increasing bearing length but with decreasing web slenderness and inside bend radius. The design methods of current EN 1993-1-3 and AISI S100 provide inaccurate and scattered resistance predictions for high strength steel unlipped channel sections. Finally, a modified AISI S100 design method and a slenderness-based design method were proposed, which can outperform the codified design methods.

Numerical model for time-dependent cracking and deflection of large-span concrete bridge structures

A new computational framework is proposed to analyse the simultaneous occurrence of multiple physical processes affecting the long-term behavior of large-scale concrete structures. Relying on the additivity of small strain, the framework comprehensively takes the nonlinearity of concrete creep, cyclic creep induced by traffic load, concrete shrinkage, concrete cracking, normal-strength steel rebars and prestressing strands relaxation into account, and other physical processes are further imagined. The algorithm is implemented with Abaqus/Standard with the aid of several user-supplied subroutines. The implicit time integration scheme is deemed appropriate for large-scale structures. The framework is systematically validated by several classical experimental results. Finally, a three-dimensional study of a three-span continuous rigid frame bridge with 270 m main span is performed. Comparison between the experimental and numerical results further reveals the contributions of various potential influencing factors. The proposed model shows promise for predicting the time-dependent performance of large-scale reinforcement concrete (RC) structures.

Tests, simulations and web crippling design of S690 and S960 high strength steel unlipped channel sections under end-one-flange loading

This paper presents experimental and numerical investigations into the web crippling behaviour and structural design of high strength steel unlipped channel sections under end-one-flange loading. An experimental programme including six grade S690 and four grade S960 steel test specimens was firstly carried out, and the corresponding test set-up, procedures and results were reported. The web crippling test results were subsequently used in a finite element programme to validate developed finite element models, which were then adopted to perform parametric studies to cover wider parameter ranges of the bearing length, web slenderness and inside bend radius. It is found that the ultimate web crippling strength of high strength steel unlipped channel sections increases with increasing bearing length but decreasing web slenderness and inside bend radius. Considering that relevant codified design provisions are absent, the design rules of normal strength steel unlipped channel sections, as prescribed in EN 1993-1-3, EN 1993-1-5 and AISI S100, were assessed for their suitability to high strength steel unlipped channel sections. The codified design methods provide inaccurate and scattered resistance predictions for high strength steel unlipped channel sections under end-one-flange loading. Thus, an improved AISI S100 design method and a novel slenderness-based design method were proposed, which can outperform the codified design methods.

Experimental and numerical investigations of high strength steel unlipped channel sections under interior-two-flange loading

This paper presents laboratory tests, numerical simulations and web crippling design of high strength steel unlipped channel sections under interior-two-flange loading. An experimental programme comprising 10 test specimens (with six for grade S690 high strength steel and four for grade S960 high strength steel) was firstly implemented, and test results including failure modes, full load-deformation curves and ultimate loads were reported. Subsequently, finite element models were constructed and validated against the obtained test results, and then used to conduct supplementary parametric studies to widen the examined parameter ranges of high strength steel unlipped channel sections. Considering that relevant codified design rules are absent, the applicability of the design rules of EN 1993–1-3, EN 1993–1-5 and AISI S100 for normal strength steel unlipped channel sections to their high strength steel counterparts was evaluated against the obtained test and numerical results. It is shown that the resistance predictions from the codified design provisions were generally inaccurate and scattered. Hence, a modified AISI S100 design method and a slenderness-based design method were proposed and demonstrated to be accurate, consistent and reliable for the web crippling design of high strength steel unlipped channel sections under interior-two-flange loading.

Confinement-based direct design of square normal and high strength steel tube confined concrete (STCC) short columns

In this paper, a confinement-based direct design model is developed to estimate the axial compression resistance of square steel tube confined concrete (STCC) short columns, which differ from standard concrete-filled steel tube (CFST) columns in load application. While the load in CFST columns is applied to the entire section, it is applied to concrete only in case of STCC columns. Accordingly, STCC columns show superior confinement effect to the concrete core, which will be used directly in the design model. First, the experimental test results of axially-loaded STCC short columns were collected from the literature. The test resistances of the columns were then compared with the predictions obtained by EC4 (2004), American specifications (ANSI/AISC (2010) and ACI 318 R (2014)), AIJ (2001), British standard BS5400 (2005) and CISC (2007), as well as the available design models in the literature. This comparative study showed that all design codes as well as other design models are highly conservative and all do not have the same accuracy over the full range of steel tube slenderness. Then, the resistances of test specimens were used to propose a formula that evaluates the lateral confinement pressure (frp) provided by the steel tube on the concrete core. Finally, the confinement-based direct design model was proposed to estimate the strengths of square STCC short columns. The results of the proposed design model far outperform the available design predictions regardless of the slenderness ratio of the steel tube for all grades of steel and concrete.

Experimental investigation into corrosion effect on buckling and low-cycle fatigue performance of high-strength steel bars

The reinforcement in marine RC structures will inevitably be corroded under long-time erosion of chloride ions, which will weaken steel mechanical properties and then structural seismic resistance. The new metallurgical technology is adopted for manufacturing high-strength steel bars (HSSB), but that may affect the corrosion resistance of steel bars at the same time. This paper experimentally investigates the effects of corrosion on monotonic and low-cycle fatigue properties of HSSB HTRB600 and normal strength steel bars (NSB) HRB400E. The HRB400E and HTRB600 steel bars were corroded to different corrosion rates by electrochemical accelerated corrosion technique. The monotonic tensile and compressive, as well as low-cycle fatigue tests of corroded steel bars were conducted to investigate the effects of corrosion on steel mechanical properties, of which corrosion levels (0–20% target corrosion mass loss), slenderness ratios (L/D=6, 8, 10, 12) and strain amplitudes (2%, 4%) are considered. Test results show that, the corrosion morphology of steel bars under electrochemical accelerated corrosion is basically consistent with that observed under natural corrosion. Compared with uncorroded HRB400E and HTRB600 steel bars, 20% corrosion mass loss leads to 38% and 35% decrease in tensile strength, as well as 33% and 28% reduction in buckling stress, respectively. The HTRB600 steel bars present slightly superior monotonic tensile and compressive corrosion resistance than HRB400E steel bars. Corrosion obviously decreases the low-cycle fatigue (LCF) life of steel bars, resulting in reductions of 44% and 36% in LCF life at 20% corrosion mass loss for HTRB600 and HRB400E steel with a L/D of 6, respectively. Moreover, the HTRB600 steel bars present more significant corrosion degradation in total hysteretic dissipated energy, compared with HRB400E steel bars. The combined effect of corrosion and inelastic buckling further exacerbates the deterioration of LCF performance of steel bars. The corresponding deterioration models are proposed to determine the LCF life and energy dissipation capacity of corroded steel bars.

Unified machine-learning-based design method for normal and high strength steel I-section beam–columns

High strength steel is regarded as a promising construction material due to its superior mechanical properties. However, the codified failure load predictions for high strength steel welded I-section beam–columns are not accurate in some cases owing to the lack of relevant design codes for high strength steel structures. In addition, current design codes ignore the interaction effect of the cross-section plate elements, leading to the inaccuracy of codified predictive ultimate resistances for both normal and high strength steel beam–columns. In this paper, a unified and accurate design method was proposed based on machine learning for both normal and high strength steel welded I-section beam–columns failing by different failure modes. Firstly, a total of 812 experimental and numerical data on welded I-section beam–columns with various steel grades, geometric dimensions, including cross-section dimensions and member lengths, and failure modes, including global buckling, local buckling and local–global interactive buckling were collected to establish a database. Seven machine learning algorithms, including Decision Tree, Random Forest, Support Vector Machine, K-Nearest Neighbour, Adaptive Boosting, Extreme Gradient Boosting and Categorical Boosting were applied to develop regression models to predict failure loads. Based on the established database, each machine learning model was then trained and key hyperparameters were optimised. The model performance was evaluated through a series of statistical indicators and the feature importance analysis, and the evaluated results indicated that the XG-trained regression model had the highest level of accuracy. Finally, the predictions given by the XG-trained regression model were compared with those of the existing codified design provisions, as given in Eurocode and American codes. The evaluation results indicated that the codified predictive bearing capacities of I-section beam–columns were scattered and inaccurate, while the XG-trained regression model provided substantially improved failure load predictions.

Hybrid machine learning model and predictive equations for compressive stress-strain constitutive modelling of confined ultra-high-performance concrete (UHPC) with normal-strength steel and high-strength steel spirals

Stress-strain constitutive model for confined ultra-high-performance concrete (UHPC) plays a pivotal role in the design and modelling of UHPC structures. However, while extensive research exists on the stress-strain responses of unconfined UHPC, a notable dearth of studies focuses on the stress-strain constitutive model for confined UHPC. Accordingly, this study introduces a novel hybrid machine learning (ML)-based stress-strain constitutive model for UHPC confined with normal-strength steel (NSS) or high-strength steel (HSS) spirals. Given the limited experimental data available, a numerical model was developed and validated against experimental results of confined UHPC. Subsequently, it was employed to generate a comprehensive dataset of confined UHPC stress-strain responses, which were then used to train the hybrid ML model. Hyperparameters of the model are subsequently optimized using Optuna along with a cross-validation technique. The optimized hybrid ML model exhibited exceptional accuracy in predicting the stress-strain response of confined UHPC with NSS or HSS spirals, as demonstrated by high coefficients of determination (R2) values ranging from 0.905 to 0.999 and low error metrics across varying stress levels and datasets. Moreover, the capability of the model to simultaneously predict both stress and strain responses was further validated through canonical correlation analysis (CCA). The results of the analysis demonstrated robust predictive performance of the model, with high CCA scores that ranged between 93.3% and 99.4%. To facilitate the practical implementation of the model, an end-to-end interactive software tool is developed. In addition, this study proposes predictive equations for the peak and ultimate stress-strain responses of confined UHPC. The evaluation of the developed predictive equations demonstrates their efficacy in accurately predicting the stress-strain responses of confined UHPC, as evidenced by the high R2 values, which ranged from 83–91%.

Impact behavior of high-strength steel beam with different web opening forms

This paper investigates the performance of high-strength steel beams with web openings (HSSBWOs) under impact by methods of tests and finite element. Based on the experimental data of 10 specimens, which were made of high-strength steel Q550D, and the effects of impact energy and web opening forms on the impact behavior of HSSBWOs are investigated emphatically. In particular, two specimens made of steel Q235D were used to study the differences in impact behavior from HSSBWOs. The test results reveal that the high-strength steel beams with circular web openings (HSSBCWOs) have better impact resistance than the high-strength steel beams with hexagonal web openings (HSSBHWOs), and the HSSBWOs have better impact resistance than the normal-strength steel beams with web openings (NSSBWOs). Moreover, HSSBWOs has excellent abilities to absorb energy, the average energy absorption rate of HSSBHWOs and HSSBCWOs is 95.78% and 93.55%, respectively. In addition, finite element models that can accurately predict the dynamic responses of HSSBWOs under impact load are established to analyze the shear force evolutions, as well as investigate the differences of impact behavior between steel beams with a variety of web openings forms. The results show that the shear force distribution ranges of HSSBCWOs are larger than that of HSSBHWOs at the time when impact force reached peak value. The HSSBWOs can sustain more impact load with the web opening shape that closer to the circle. The solid webbed steel beam (SWSB) has better impact resistance than the steel beams with web opening (SBWO).

Flexural Behavior of High-Strength Steel and Ultra-High-Performance Fiber-Reinforced Concrete Composite Beams

The flexural performance of steel and concrete composite beams can be further enhanced by utilizing advanced construction materials such as ultra-high performance fiber-reinforced concrete (UHPFRC) and high-strength steel. In this paper, the concept of critical elastic moment resistance is proposed and the equation for its estimation is derived. It was found that the high yield strength of steel calls for a narrow UHPFRC top layer to reach the critical state, whereas this ideal condition is not realistic for composite beams with normal-strength steel and UHPFRC. Small-scale composite beams composed of both high-strength and low-strength steel materials were tested under four-point bending to verify the critical state and performance of different types of connectors. The headed studs and plate connectors were first tested through small-scale push-out tests and then implemented in the composite beam with different spacing. The connection utilizing headed studs with 150 mm spacing performed the best among the three tested specimens in helping reach the critical elastic moment resistance. Finite element analyses of the composite beam were performed based on the estimated material properties under axial and biaxial stress conditions and the results align with the experiment results.

Mechanical properties of corner material in cold-formed steel structure: From normal strength to high strength

Cold-forming effect varies from normal strength steel to high strength steel due to the different chemical compositions and mechanical properties of parent materials. To date, research studies on material characterisation of cold–formed steels have been mainly focusing on the normal strength structural steel, while systematic research on high strength structural steel remains scarce. In this paper, an experimental investigation into changes in mechanical properties of high strength steel undergoing various levels of plastic deformation is firstly presented. The test results have been combined with other available high strength steel data, and compared to the normal strength steel data. Of the analysis results indicated, unified predictive equations, modified from Karren’s model in 1967 can predict the strength enhancement behaviours of normal strength and high strength steel, utilising the ultimate-to-yield strength ratio of parent materials fu,f/fy,f and inner radius-to-thickness ratio after cold–forming ri/t. Moreover, the decreases in the Young’s modulus, ultimate strain and elongation at fracture of normal strength and high strength steel after cold-forming can be predicted with no further grouping required. Statistical evaluation results confirm the accuracy of the proposed predictive expressions. This paper extends the scope of the strength enhancement equation in current north American cold-formed steel design code AISI S100–16 to high strength steels with grade up to 960 MPa, and provides key predictive material equations that can be further used in the design or numerical modelling of cold-formed steel structures.

Slab Reinforcement Contributions to Negative Moment Strength of Reinforced Concrete T-Beam with High Strength Steel at Exterior Beam-Column Joints

Previous studies have revealed that the contribution of slab reinforcement to the T-beam flexural strength in negative moment regions are not negligible for the seismic capacity design. An effective slab width (i.e., effective width of flanged section) has been proposed, within which the slab reinforcement needs to be included in the calculation of the beam nominal flexural strength in negative moment regions. These studies mainly focused on the cases using normal-strength steel in moment resisting frames. However, recently high-strength steel has been widely used in reinforced concrete moment resisting frames in high seismic regions to avoid congestion near beam-column joints. The use of high-strength steel may affect the beam stiffness due to the fact that it will require less amount of reinforcement, and result in a different normal stress distribution compared to the case with normal-strength steel. Therefore, this paper investigates the slab reinforcement contribution to the flexural strength of the reinforced concrete T-beam designed with high-strength steel in negative moment regions at exterior beam-column joints, for which nonlinear pushover analyses were conducted. Beam reinforcement grade was considered as a primary parameter with several other design variables including slab thickness, height, and span length of the beam. Analytical results show that the use of high-strength steel can result in a wider effective slab width than the case of normal-strength steel for calculating the beam nominal flexural strength under the negative moment. Based on these results, new design equations were proposed.

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.

Hysteretic energy dissipation capacity of dual-steel welded-plate preloaded bolted T-stubs

With the high- and ultrahigh-strength steels applied in the construction industry, the seismic safety of their structural components is very concerned due to the inferior material ductility of those steels. The current studies on bolted high-strength steel T-stubs mainly focus on their monotonic loading behavior. There is limited research work conducted to study their cyclic loading behavior. In this study, cyclic tests of bolted dual-steel T-stubs were conducted. Their T-elements were produced by Q690 high-strength steel flanges and Q355 normal-strength steel webs, and class 10.9 high-strength bolts with pretension were used to connect the groove-welded T-elements. Failure modes, force-deformation hysteretic and backbone curves, cumulative plastic deformation and energy dissipation capacities were tested and analyzed. The test results indicated that an optimal β ratio between the plastic resistances of Mode 1 (neglecting the influence of bolt action on a finite contact area) and Mode 3 in Eurocode 3 Part 1–8, could be 0.3 for those bolted T-stubs to maximize hysteretic energy dissipation. Accordingly, predictive formulas with good precision were proposed for the low-cycle fatigue failure criterion and hysteretic energy dissipation capacity of those bolted T-stubs, respectively.

Mechanical behavior of the sustainable square spiral stirrup-confined recycled aggregate concrete filled steel tubular columns under compression

Owing to the inherited structural defects of recycled aggregate concrete (RAC), such as deficiencies in durability and mechanical properties, its further applications in modernized civil engineering practices are significantly limited. To this end, this study aims to achieve the sustainable application of RAC and improve its mechanical properties by infilling it into the steel tube to form the recycled aggregate concrete filled steel tubular columns (RA-CFST columns). Numerous studies have indicated that embedding steel spiral stirrups inside the steel tube is helpful in improving the ultimate strength (Nu) and ductility of square CFST columns. Thus, this paper designed several square RA-CFST columns confined by high-strength steel (HSS) spiral stirrups (HSS-RA-CFST columns) and their concentric and eccentric compression behavior were experimentally studied. The test specimens were divided into two different parts, including (i) axial compression and (ii) eccentric compression test specimens. For the former, 16 columns were designed, including 4 traditional non-confined RA-CFST columns, 4 normal-strength steel (NSS) spiral-confined RA-CFST columns (NSS-RA-CFST columns), and 8 HSS-RA-CFST columns. For the latter, 8 specimens were prepared, including 2 non-confined and 6 HSS-RA-CFST columns. Effects of the critical test parameters, such as the steel tube thickness, steel spiral pitch, replacement ratio of recycled aggregate (RA) to natural aggregate (NA), and eccentricity ratio on the compression behavior of the specimens were examined. Subsequently, the failure modes, load-deflection responses, strain distributions, ductility, and the composite confinement mechanism of the columns were comprehensively studied. Finally, this paper also suggested the improved design models in predicting the Nu of the spiral-confined CFST columns (i.e., NSS-RA-CFST and HSS-RA-CFST columns), and the effectiveness and accuracy of the recommended design models were validated by using the experimental results acquired from this study and those studies collected from the literature. This study could serve as the experimental and theoretical references for the mechanical properties and determination of the Nu for the spiral confined-RA-CFST columns under both the concentric and eccentric compression.

Performance of high strength steel bar splice with novel grouted deformed sleeve under tensile load

High-strength steel (HSS) bars can solve bar congestion problem in beam-column joints of monolithic precast concrete frame structure. Unfortunately, its application in precast concrete structures is greatly hindered by few researches on HSS bar grout splice. In this paper, utilizing large-diameter HRB600 reinforcements with specified yield strength of 600 MPa, 34 splice specimens were prepared considering the parameters of embedded length, grout strength and inner cavity structure of sleeve. Through uniaxial tension test, it is shown that the embedment length has the greatest effect on the structural performance of grouted splice. For the d28 bar grout splice, 8db is the minimum embedded length to ensure bar fracture failure, which is longer than the normal-strength steel bar grout splice. For the splices with embedded length not smaller than 5db and concentric ribs not less than five, excessive ribs set on the sleeve cannot significantly increase the tensile strength of the grouted splice, but further adding one rib still can effectively reduce the elastic residual deformation. Similar test results have been observed for the effect of grout strength. As the compressive strength increases from 95.3 MPa to 118.2 MPa, the tensile strength improves only by about 2.52%, but the residual deformation decreases significantly by 11.68% on average. For a high-strength large-diameter bar grout splice, it is recommended to set six concentric ribs at each side of the sleeve, and select 8db as the minimum embedded length to achieve reliable performance.

Experimental study on bamboo-shaped buckling-retrained energy dissipater with different grades of steel

Buckling-restrained energy dissipaters are miniature energy dissipaters that constrain an inner core through an outer tube and have been widely utilized to improve the seismic performance of fabricated structures. Low yield point steel is often used to produce energy dissipaters, but the mechanical behavior of low yield point steel energy dissipater is rarely investigated. In this paper, a quasi-static test of bamboo-shaped energy dissipaters with different grades of steel was carried out. The influence of the material and configuration of the core on the fatigue performance and failure mode was evaluated. Test results showed that all specimens demonstrated stable hysteretic performance. The equivalent viscous damping ratio of low yield point steel energy dissipaters was relatively large at small strain amplitudes. At large strain amplitudes, both had a similar energy dissipation capacity. The compressive strength adjustment factors and strain hardening factors of low yield point steel energy dissipaters were higher because of their lower post-yield stiffness and significant isotropic hardening. The fracture mode on the low yield point steel energy dissipaters was similar to flat rupture, and significant necking was observed here. However, the normal strength steel energy dissipaters exhibited slant fracture, and no evident necking occurred. Two deformation modes were proposed. A calculation method for the buckling wavelength of the energy dissipater was proposed. When the effective length of the yielding region was smaller than the buckling wavelength, the fatigue performance of low yield point steel energy dissipater was better than that of normal strength steel energy dissipater, and the low yield point steel energy dissipater had a better reserve performance.

Hysteretic performance of structural steels after exposure to elevated temperatures

This paper presents both experimental and analytical investigations on the hysteretic behaviour of normal strength and high strength structural steels after being exposed to elevated temperatures. The test parameters include the highest temperature experienced, the cooling method and the loading protocol. The metallographic analysis is conducted to study the change of micro structure after elevated temperature exposure. The test results show that the yield strength of Q355 and Q620 steels cooled in the air decreases up to 21% and 45%, respectively; while the energy consumption capacity decreases up to 25% and 42%, respectively. For specimens cooled in water, the energy consumption capacity of Q355 increased by 39% when the strain level was 0.6%, while that of Q620 decreased by 21% at the same strain level. A hysteretic model for steels after being exposed to elevated temperatures is proposed by regression analysis, where the key coefficients are calibrated from the experimental data. The proposed model captures well the hysteretic behaviour of both normal and high strength steels after exposure to elevated temperatures, which provides the basis for the post-fire seismic performance assessment of steel structures.

Imperfections for Local and Global Interaction Buckling of Welded Square High-strength Steel Box-section Columns

The interaction behavior between local and global buckling modes in high-strength steel box-section columns has received limited research attention. Currently, there is a lack of a validated equivalent geometric imperfection that can be effectively employed in nonlinear plastic analysis to estimate the interaction buckling resistance. This research aims to find equivalent geometric imperfections that can be used in geometrical and materially nonlinear analysis using imperfections (GMNIA) to estimate the interaction buckling resistance of square welded box-section columns made of high-strength steel. It extends prior investigations by the authors on equivalent imperfections for normal-strength steel welded box-sections. A developed and validated numerical model is used to perform parametric studies to estimate the accurate buckling capacity using previously developed and verified combinations of imperfections and residual stresses. The accurate buckling capacities are used to calibrate equivalent local and global imperfection combinations that can be used in FEM-based design. A reliability assessment study is also performed to check the safety level of the proposed imperfection combinations.

Comparative Evaluation of Flexural Toughness of Steel Fiber-Reinforced Concrete Beams.

Specifications are available to quantify flexural performance of steel-fiber reinforced concrete beams with several parameters. Each specification provides different results. This study comparatively evaluates existing flexural beam test standards that are used to evaluate the flexural toughness of SFRC beam specimens. Two standards, EN-14651 and ASTM C1609, were followed to test SFRC beams under the three-point bending test (3PBT) and the four-point bending test (4PBT), respectively. Both normal tensile strength steel fiber (1200 MPa) and high tensile strength steel fiber (1500 MPa) in high-strength concrete were considered in this study. The reference parameters recommended in the two standards, which include equivalent flexural strength, residual strength, energy absorption capacity, and flexural toughness, were compared based on the tensile strength (normal or high) of the steel fiber in high-strength concrete. The 3PBT and 4PBT results indicate that both standard test methods yield similar results to quantify the flexural performance of SFRC specimens. However, unintended failure modes were observed for both standard test methods. The adopted correlation model shows that the flexural performance of SFRC is similar for 3PBTs and 4PBTs, but the residual strength obtained from the 3PBTs tends to be greater than that obtained from 4PBTs with an increase in the tensile strength of steel fiber.