Journal of Structural Engineering

Population growth, economic development, and rapid urbanization in many areas have led to increased exposure and vulnerability of structural and infrastructure systems to hazards. Thus, developing risk-based assessment and management tools is crucial for stakeholders and the general public to make informed decisions on prehazard planning and posthazard recovery. To this end, structural risk and resilience assessment has been an ongoing research topic in the past 20 years. Recently, machine learning (ML) techniques have been shown as promising tools for advancing the risk and resilience assessment of structure and infrastructure systems. To date, however, there is a lack of a holistic review on ML progress across various branches of structural engineering; an in-depth analysis of literature that can provide a timely evaluation of risk and resilience assessment methods of the built environment, where different types of structural and infrastructure facilities are interconnected. For this reason, this study conducted a comprehensive review on ML for risk and resilience assessment in four main branches of structural engineering (buildings, bridges, pipelines, and electric power systems). To cover the crucial modules in the prevailing risk and resilience assessment frameworks, existing literature is thoroughly examined and characterized in terms of six attributes of ML, including method, task type, data source, analysis scale, event type, and topic area. Moreover, limitations and challenges are identified, and future research needs are highlighted to move forward the frontiers of ML for structural risk and resilience assessment.

Predicting the axial capacity and behavior of concentrically, eccentrically, and slender loaded fiber-reinforced polymer (FRP)-RC columns is not completely established, and the current design codes lack design provisions for FRP-RC columns. Rather, it requires ignoring the contribution of FRP bars in compression conservatively. To bridge this knowledge gap, this study proposes an artificial neural network (ANN)-based model capable of predicting the axial capacity and slenderness limit and constructing an interaction diagram for FRP-reinforced columns. The aforementioned model was trained with Bayesian regularization utilizing a comprehensive database of 241 tested FRP-RC columns. Parameters included in the model are column cross-sectional area, compressive strength, FRP elastic modulus, reinforcement ratio, eccentricity ratio, and slenderness ratio. The predictions of the ANN-based model match well with the experimental results of the compiled database; the model predictions have a COV of 15% and root-mean square error of 130 kN. In addition, a parametric study was conducted to investigate the effect of parameters and ensure the generalizability of the proposed model.

Masonry-infilled wood frame walls are widely used in vernacular buildings all over the world. Based on traditional European wood frame walls, this paper proposes wood bracing as reinforcement for traditional Chinese masonry-infilled wood frame walls to compensate for premature cracking of masonry infill and the resulting performance degradation of the walls. Five wall frames were prepared and loaded cyclically in lateral direction. Wood bracings of different forms and their contribution to the wall performance were studied. The hysteretic curves, stiffness and strength degradation, energy dissipation, and equivalent viscous damping coefficient were determined and discussed for their relationship with the bracing provisions. It was found that the bare frame was flexible and resilient and the masonry-infilled frame was stiff and prone to brittle failures, while the frames reinforced by wood bracing exhibited good load-carrying capacity, deformability, and energy dissipation capacity. The peak load and the ultimate displacement of the frame reinforced by X-bracing were 49% and 85% higher than those of the masonry-infilled frame, and the equivalent viscous damping coefficient was increased by 81% at most. The asymmetric Z-bracing and double crossing bracing led to a slight decrease in the initial stiffness compared to the masonry-infilled frame due to the pull-out of the intermediate mortise-tenon connections.

Considered nonstructural elements, infill walls and their participation in earthquake resistance are often neglected in structural design, which leads to deviations in the predictions of seismic responses. Generally, infill masonry walls are the most extensively used type, but they often exhibit out-of-plane vulnerability and insufficient reliability during earthquakes. To overcome the drawbacks and further improve the beneficial contributions of infill walls, a reinforced concrete (RC) infill wall isolated by polyvinyl chloride (PVC) tubes, abbreviated as PVCIW, was proposed to incorporate with coupled shear walls. Featuring flexible connections, the PVC tubes were adopted to eliminate the unfavorable constraints between infill walls and the main structure. RC panel was adopted for the infill because of its excellent compressive properties and out-of-plane resistance. Compression of the PVCIW was allowed during extreme quakes to contribute to anticollapsing of the coupled shear walls. Cyclic loading tests were applied to compare the hysteretic properties between coupled shear wall specimens equipped with RC infill walls, PVCIWs, and without infill walls, and the advantages of PVCIWs were validated. Finite-element analysis (FEA) was performed to simulate the test results, and parametric cases were investigated to optimize the design of PVCIWs. Finally, based on a modified coupling ratio $C{R}_{\mathrm{M}}$ considering the influence of PVCIWs, a new seismic design approach was developed to obtain the optimized properties of this novel system.

This paper examines the life-cycle wind resistant performance of a constructed long-span suspension bridge in the coastal region of China, aiming to quantify the multisource time-variant effects and uncertainties and offering a reference for designs of long-span bridges in the future. Randomness from modal frequencies, damping ratios, and identification uncertainty of flutter derivatives (FDs) was considered; then, their effects on probability of flutter failure and probability of exceeding the predefined buffeting response root-mean square (RMS) are discussed. Firstly, results of full-track tropical cyclone (TC) simulation under various climate warming scenarios are reviewed; then, the time-variant probability density function (PDF) of annual extreme wind speed is discussed. Secondly, 6-year modal frequencies and damping ratios of a long-span suspension bridge with a center-slotted section were extracted by fast Bayesian FFT method with structural health monitoring (SHM) data, which were utilized to explore the deterioration rules of structural properties. Thirdly, FDs were modeled from a probabilistic perspective based on complex Wishart distribution, which were identified in the turbulent flow and the frequency domain by Bayesian inference. The posterior distributions of FDs, namely identification uncertainty, were quantified by Markov chain Monte Carlo (MCMC) sampling. This paper finds that for flutter resistant performance, the time-variant effects (i.e., modal frequencies and PDFs of extreme wind speed) will make the flutter failure probability seven times larger than the initial value; for the probability of exceeding the predefined buffeting response RMS, however, the time-variant effects will make a negligible difference.

This paper proposes damage index–based limit-state criteria for seismic design of midrise cold-formed steel (CFS) buildings instead of the drift-based ones, and the Park-Ang damage model was used to calculate the damage indexes. Two 5-story CFS buildings with different wall configurations were tested, and a test-validated numerical model was developed. An incremental dynamic analysis was conducted on a typical midrise CFS building to obtain the degradation parameter $\beta$ of different CFS walls. The damage indexes computed from numerical analyses were compared with the damage indexes estimated from test observations and the proposed damage index–based limit-state criteria. The results showed that the calculated degradation parameter as well as the proposed damage index–based limit-state criteria are effective for seismic damage assessment and damage level classification of midrise CFS buildings according to the validations by shaking-table tests on two CFS buildings. The Park-Ang damage index used in this paper and the proposed limit-state criteria could be used for performance-based seismic design of midrise CFS buildings.

This paper reports an experimental and numerical investigation into the minor-axis flexural buckling behavior and capacity of press-braked S690 high-strength steel channel–section columns. The experimental investigation comprised initial geometric imperfection measurements and 10 pin-ended column tests. This was accompanied by a numerical modeling program, in which finite-element models were developed and validated against the test results and then adopted to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and member lengths. The obtained test and numerical data were adopted to assess the accuracy of the buckling curves, as given in the Eurocode, North American specification, and Australian/New Zealand standard, for press-braked S690 high-strength steel channel–section columns prone to minor-axis flexural buckling. Overall, it was found that the Eurocode buckling curve yields many conservative capacity predictions, whereas the buckling curves in the North American specification and the Australian/New Zealand standard lead to an overall good degree of design accuracy. A revised Eurocode buckling curve is proposed, and was shown to offer accurate capacity predictions for press-braked S690 high-strength steel channel–section columns prone to minor-axis flexural buckling.

Casting nodes are used to connect branch members at joints of freeform grid shell structures. In this study, the structural performance of a rectangular hollow section (RHS) branch-to-casting node connection was investigated. A RHS branch member with an access hole (i.e., opening) for temporary bolting was weld-connected to the T-shaped node fabricated by a conventional casting method. Six RHS branch-to-node connection specimens were tested under tensile and compressive loading. The eccentricity of axial loads was considered as the main test variable. Tests showed that, despite the opening near the weld joint, the RHS branch-to-casting node connections exhibited good performances. For tensile specimens, the ultimate strengths were greater than the yield strengths of the casting nodes, and weld rupture eventually occurred at the stiffener-to-casting node wall joints. On the other hand, for compressive specimens, the ultimate strengths were limited by flexural and torsional buckling modes accompanying local buckling and crippling of the casting node walls. The ultimate strengths degraded by the eccentric loading and openings were evaluated in accordance with current design codes. The failure modes and consequent strengths of compressive specimens were further investigated through finite-element analysis. Based on the investigations, design recommendations of RHS branch-to-casting node connections with openings were given.

The capabilities of data-driven models based on machine learning (ML) algorithms in offering accurate predictions of structural responses efficiently have been demonstrated in numerous recent studies. However, efforts to date have relied on essentially deterministic approaches, and prediction confidence measures were either derived from verification data sets or completely ignored. This study examined the potential of a new algorithm—natural gradient boosting (NGBoost)—that directly produces probabilistic predictions. This type of output fits the reliability and performance analysis frameworks naturally, and also opens the pathways to utilization of self-learning algorithms and optimal design of experiments and field measurement campaigns in engineering applications. After introducing NGBoost’s fundamentals, two representative problems in structural engineering were investigated to examine NGBoost’s feasibility: (1) prediction of the strengths of squat shear walls, and (2) classification of the seismic damage levels in ordinary bridges. The results indicate that NGBoost attains mean prediction accuracy levels comparable to those of conventional ML algorithms while providing robust estimates of prediction uncertainties.

A bolted–welded hybrid demountable shear connector for use in deconstructable steel–concrete composite buildings and bridges was proposed. The hybrid connector consisted of a partially threaded stud, which was welded on the flange of a steel section, and a machined steel tube with compatible geometry, which was bolted on the stud. Four standard pushout tests according to Eurocode 4 were carried out to assess the shear performance of the hybrid connector. The experimental results show that the initial stiffness, shear resistance, and slip capacity of the proposed connector were higher than those of traditional welded studs. The hybrid connector was a ductile connector, according to Eurocode 4, with slip capacity higher than 6 mm. A nonlinear finite-element model was calibrated against the pushout tests and found capable of reproducing the experimental behavior with good agreement. The verified finite-element model was then used to conduct a series of parametric studies in order to assess the effect of infilled grout, concrete slab strength, stud diameter, stud tensile strength, tube thickness, and tube tensile strength on the shear resistance and stiffness of the hybrid connector. Based on the experimental and numerical results, a design equation is proposed for the prediction of the shear resistance of the novel connector.

Although time-domain response analyses have been commonly used in the design of tall buildings, the code-based wind design continues to rely on prescriptive static methods. Moreover, buildings subjected to both earthquakes and wind, where both are critical, could be prone to ineffective seismic response (increasing bottom-floor member sections due to wind demand reduces the system’s ductility) and noneconomic lateral force–resisting system (design for elastic response under wind loads). The incompatibility in the current building code when addressing the seismic and wind design such as: the consideration of different return periods for wind and earthquake; design for ductility under earthquake versus the elastic response under wind; and the governing lateral load for tall steel buildings of rectangular floor plans located in moderate-to-high seismic zones, are discussed herein. First, a design methodology for developing along-wind history series, generated from wind-tunnel pressure records available from the Tokyo Polytechnic University aerodynamic database, is provided. Then, incremental dynamic analyses under winds and earthquake loads are carried out independently in a case study, and insights into the collapse mechanisms are presented. The findings show that the annual failure probability under wind is greater than that under earthquakes.

This study numerically investigated the elevated temperature resistance of earthquake-damaged square hollow section (SHS) T-joints subjected to brace axial compressive load. The residual stresses and deformations due to the earthquake were obtained from a pushover analysis. The extensive numerical simulations were analyzed using nonlinear finite-element software to examine the effects of the $\beta$ ratio, $\gamma$ ratio, damage level ($\check{D}$), and initial applied load ($n_f$) on the fire resistance of SHS T-joints after verification of the numerical simulations based on the available test results in the literature. The results indicated that the fire resistance of SHS T-joints with axial compressive load in the brace member decreased significantly due to the residual stresses and deformations from the earthquake. This situation worsened in all numerical models as the damage level increased. The reduction rate of the critical temperature at various damage rates was independent of the initially applied load ratio, but the loading rate directly affected the fire resistance of the joint regardless of the earthquake. As the $\beta$ ratio decreased, the yielded area at the brace-to-chord intersection region increased. Thus, the critical temperature of the joints at a constant damage level was inversely proportional to the $\beta$ ratio. Joints with a large $\gamma$ ratio had larger residual stresses and deformations than those of corresponding joints with a small $\gamma$ ratio. Therefore, the fire resistance of the joints after the earthquake decreased as the chord-wall thickness decreased. The critical temperature of the joints with either a large $\beta$ or $\gamma$ ratio was limited by the deformation limit at high damage levels. The fire resistance of the SHS T-joints after the earthquake decreased due to residual stresses and deformations. That effect increased even more in joints with high $\beta$ and $\gamma$ ratios.

This study proposes a new relationship between the return period values of the annual maximum ground snow depth and the ground snow load for northeastern China. The proposed relationship is based on a statistical evaluation of the ground snow depth data and concurrent snow water equivalent data from many meteorological stations in the considered region. Such a relationship is the first of its kind for the considered region and could be used for different return periods. Reliability analysis for structures designed based on the newly developed relation is evaluated in the context of structural design code calibration. The estimated reliability is compared with that obtained based on the currently applicable structural design code for the region. The results indicate that the use of the proposed relation could lead to enhanced reliability consistency, while the use of the current code approach could be inadequate for some sites within the regions because of the spatially varying uncertainty in climate conditions.

This study validates the use of available tools for nonlinear finite element dynamic analysis (NLFEDA) modeling of unbonded post-tensioned reinforced concrete (PT-RC) members under drop weight impact and is the first attempt at low-velocity impact to the authors’ knowledge. The study was performed in two parts. The first portion of the study determined the appropriate mesh and material properties of the testing setup and specimens that were generated by the authors. The second portion of the study then established the level of convergence of the model based on a wide range of design and loading parameters. The NLEFDA was validated using experimental data obtained from laboratory investigations on the behavior of shear-critical and flexural PT-RC members. The interaction between the prestress, as applied from the PT tendon, and the surrounding concrete was well modeled in the presence of large shear failures of the concrete. The modeling techniques, coupled with experimental studies, can be helpful in expanding the range of understanding of the behavior of unbonded PT-RC members.

The use of prequalified welded unreinforced flange-welded web (WUF-W) beam-to-column connections in capacity-designed steel moment-resisting frames necessitates the removal of the weld backing bar at the bottom beam flange-to-column flange groove welded portion. Weld root back gouging and fillet weld reinforcement is also necessary to minimize the fracture potential at this location. This paper revisits the current detailing of WUF-W connections in order to propose simplifications in their fabrication process by intentionally keeping a customized beveled backing bar in place without impairing the connection’s ductility under seismic loading. The analysis relies on traditional fracture mechanics applied in three-dimensional continuum finite element models. The modeling approach is validated with welded unreinforced flange-bolted web (WUF-B) pre-Northridge connection tests. The results suggest that field-welded connections with the proposed beveled backing bar reach lateral drift demands of at least 4%–6% rads even when flange groove welds feature a low-toughness E70T-4 weld electrode, which was typical in pre-Northridge WUF-B connections. Fillet weld reinforced backing bars provide inferior connection ductility compared to the proposed beveled backing bar. The simulation results from a series of prequalified WUF-W connections that respect the current seismic design and fabrication requirements, indicate that when the beveled backing bar configuration is intentionally left in place after completing the complete joint penetration groove welds, WUF-W connections can sustain lateral drift demands of at least 6% rads prior to fracture regardless of the panel zone strength, the steel beam depth, and the flange thickness of the respective beam and column. Limitations as well as suggestions for future work are also discussed.

By installing unsymmetrical chamfers on the soffits of beams, it has been proved in the earlier studies to be effective for strengthening nonseismically designed beam-column joints (BCJs). To generalize this, this study aims to extend the strengthening strategy to BCJs having upper and lower columns of different sizes. Such column eccentricity is not uncommon in gravity-load designed structures. In this study, experimental studies were conducted on six $2/3$ scale specimens designed for joint shear failure, including three interior and three exterior specimens. The performance of specimens with nonseismic detailing was compared with that of having joint shear reinforcements or strengthened with chamfers. All specimens were under constant axial load and were subjected to cyclic displacements until failure. Response of chamfer under cyclic horizontal displacement was studied by analyzing the strains in chamfer. First and foremost, column eccentricity has both positive and negative influences on BCJs when subjected to cyclic displacements. Chamfer contributes to joint shear capacity when it is in compression. This leads to formation of an additional strut within the chamfer. For exterior joints, this phenomenon becomes obvious, and performance is improved when displacement is applied in one loading direction only. Lastly, width of additional strut formed in chamfer is associated with chamfer size.

Owing to their convenient transportation, quick assembly, and high cost performance, gabion walls are widely used in the protection of critical infrastructure and personnel from explosions. To study the damage and response characteristics of the gabion wall under the action of large TNT-equivalent explosives, the blast resistant performance of the gabion wall under the ground explosions of one-ton and 10-ton TNT explosives was tested, and the shock wave and ground-motion time history of the explosions were obtained. Based on the data, the impact of shock waves and ground motion on the wall response is discussed, combined with numerical analysis. The critical overturning distance of the gabion wall and the factors affecting the stability of the wall are also discussed. The analysis results show that the shock wave played a decisive role in the response of the wall, whereas the effect of ground motion on the uplift of the wall was not significant. Under the action of the shock wave, the wall exhibited two main failure characteristics: flat overturning and bent overturning. In addition, scaled distance, structural form, and wall density primarily affected wall stability. A formula for the critical overturning distance of the wall subjected to ground explosion is proposed by combining experimental and numerical simulation data.

This paper presents the results of an experimental investigation on the performance of half-scale, unbonded, post-tensioning, precast concrete walls subjected to fully reversed cyclic loads. Moreover, this paper discusses the damage progression and failure mechanism of each specimen, associated with their construction details (damper types and confinement details of the boundary elements). Five isolated walls were tested, each consisting of precast concrete panels joined only by unbonded post-tensioning strands. The bottom joint of the walls featured two kinds of dampers: Three specimens had mild steel reinforcement, crossing the bottom joint, and the other two specimens had external replaceable hysteretic dampers, attached to the wall sides. Different types of confinement details at the boundary elements were used among the specimens. Steel fibers were mixed into the concrete of one specimen. The prestressing load ratio was 0.05 in most of the specimens. An additional axial load of 468.5 kN was applied to each specimen (additional axial load ratio of about 0.04), before any lateral loading. Quasi-static, displacement-controlled loads were applied to the specimens until a significant strength reduction was observed. Although only moderate axial loads were applied, most of the specimens sustained drifts above 3% while maintaining their lateral strength, gravity load stability, and self-centering. A better performance was observed in the specimens with external dampers, with drifts above 4%, less residual drifts and less cover concrete spalling, particularly in the specimen with steel fibers. The external dampers were very effective in dissipating energy before fracture, until 3% drifts. On the other hand, the specimens with internal dampers sustained unexpected damage at their bottom joint, after reaching their peak strength. For instance, the gravity load-carrying capacity of one specimen with internal dampers was compromised after 4% drifts. Then, the use of external replaceable dampers provided higher performance and post-earthquake recovery for unbonded post-tensioned precast walls. Additional design recommendations are provided based on the test results.

This paper presents an analytical procedure to assess the monotonic (envelope) force-deformation response (capacity curve) of unbonded post-tensioning precast concrete (UPT) walls with internal and external replaceable dampers. This procedure, which can also be used to design UPT walls, was compared and validated against experimental evidence. A close agreement (strength discrepancies of 2% on average) was found between the response predictions and experimental results. This agreement was maintained until peak strength was achieved. Moreover, fiber-based models were implemented to further study the cyclic behavior of UPT walls designed according to the proposed analytical procedure. The numerical models were accurate in representing the global cyclic behavior of UPT walls in terms of strength, displacement capacity, and energy dissipation; nonetheless, these models showed some discrepancies in capturing the residual drifts of some UPT walls with internal dampers. A parametric analysis was also conducted to explore the influence of some design parameters on the deformation capacity and energy dissipation of UPT walls. It was found that the ratio of damper reinforcement is critical for the energy dissipation and self-centering capacity of UPT walls, so ratios of 0.10 to 0.25 should be provided to follow the limit states indicated in this paper. Based on the results, the analytical procedure and limit states presented in this paper are considered suitable for UPT walls with external replaceable dampers under total axial load ratios equal or lower than 0.125.

Climate change, population dynamics, the aging of built infrastructure, and their growing complexity have gradually increased the vulnerability of coastal communities around the world. Among the many critical coastal infrastructures, the residential coastal building stock has exhibited significant vulnerabilities in past storm and hurricane events. Beyond the initial impact of these hurricane events on the built environment, coastal communities struggle to recover even years after landfall. Moreover, the initial shock as well as the recovery phase do not evenly affect all sectors of the population and frequently uncover social vulnerabilities and inequalities in the preparedness, response, and recovery from disasters. This study explores and expands a performance-based coastal engineering (PBCE) framework that allows for consideration of time-varying aspects of the hazard, depreciation, and aging or deterioration of coastal structures and infrastructure systems by applying it to evaluate the future performance and recovery of a portfolio of residential structures subjected to surge and wave loads. Using the residential building stock of Galveston, Texas as a case study, a Bayesian network framework is leveraged to evaluate the uncertain damage and subsequent recovery of the portfolio for the years 2030 and 2050, and correlations with representative social vulnerability factors are drawn. The correlation analysis between immediate damage and social vulnerability factors, as well as between the recovery index and social vulnerability factors up to six years following the storm landfall, is pursued to expose potential disparities in the impact of the storm to different sectors of the community in the short- and long-term. Results show that changing climate conditions exacerbate the probability of failure of the building stock and associated housing recovery. Also, the correlations in the short- and long-terms show that the elderly and women might be most at risk in future hurricane events. The incorporation of multi-structure systems and time-varying factors in the performance assessment framework is of great importance to inform resilience and adaptation engineering models, in particular, when the effects of chronic hazards, a growing population, and increases in asset values are expected to grow in the future. The methodology and case study also provide useful tools to inform planning and decision-making, resilience assessment, and facilitate recovery efforts in coastal settings while accounting for the impact of the hazard on vulnerable populations.

Design provisions for axially compressed rectangular hollow section (RHS) members with slender elements were evaluated using an approximate first-order reliability method analysis. A total of 342 nonlinear finite-element models, covering a range of width-to-thickness, height-to-thickness, and nondimensional slenderness ratios, were developed and analyzed. Calculated ranges of reliability indexes (${\beta }^{+}$) were computed and compared with ${\beta }^{+}$ values obtained from the expanded separation factor approach and with target values in codes. The results showed that the Canadian Standards Association (CSA S16:19) design provisions for locally slender RHS compression members are imprecise, resulting in underpredictions of column strength by as much as 22%. AISC 360-16 design provisions, and a recently proposed modified CSA approach were shown to be better predictors. Considering all 342 columns together, the current resistance factor of $\varphi =0.9$ was shown to be acceptable in both codes.

Reinforced masonry (RM) shear walls are the main seismic force–resisting elements in masonry buildings. Current guidelines and nonlinear modeling methods for evaluating the seismic performance of existing RM shear walls were developed many years ago based on limited experimental data. They tend to underestimate the displacement capacity of RM walls by a significant amount. This paper presents a modeling method along with suitable material models, based on a fiber-section beam-column element idealization, to capture the nonlinear in-plane cyclic behavior of flexure-dominated RM walls. The modeling method accounts for the buckling and low-cycle fatigue of vertical reinforcing bars, which often occur in the toe regions of RM walls under severe seismic actions, in an approximate manner. The model has been validated by experimental data on fully grouted planar walls and T-walls constructed of concrete masonry units. Moreover, a simple and rational method to construct lateral force-versus-lateral displacement backbone curves for flexure-dominated RM walls is presented. The proposed method produces backbone curves that show a significantly better agreement with experimental data compared with that recommended in current guidelines.

This paper reports a comprehensive experimental and numerical investigation of the cross-section behavior and capacity of hot-rolled stainless steel channel sections subjected to combined compression and major-axis bending. An experimental program was first carried out and comprised measurement of initial geometric imperfections and 10 eccentric compression tests. This was accompanied by a numerical modeling program, in which nonlinear finite-element models were first built to replicate the test observations and subsequently utilized to carry out parametric studies for producing more numerical data over a broader spectrum of loading combinations and cross-section dimensions. The data obtained from experiments and parametric studies were utilized to assess the accuracy of the relevant codified interaction curves as used in Europe and the US. The assessments showed that the codified interaction curves resulted in conservative capacity predictions due to the lack of proper consideration of the beneficial stress redistribution and material strain hardening. To overcome these shortcomings, new interaction curves were developed and resulted in greatly improved design accuracy in comparison with the codified interaction curves.