Orthotropic steel–concrete composite bridge deck is a structure composed of an orthotropic steel bridge deck and a cement-based rigid overlay. In recent years, it has been increasingly used to strengthen existing steel decks and build new bridges. Although composite decks with various structural forms and materials have been widely used, studies on the structural behavior of composite bridge decks are still somewhat lacking, and the design approach has not been fully clear. In this study, the mechanical behaviors of a composite bridge deck composed of 80 mm steel-fiber-reinforced concrete (SFRC) and longitudinal bulb-flat ribs were investigated under negative bending. Loading tests of two full-scale composite decks were carried out to study the variations of stiffness, concrete cracks, and structural strain during the loading process. The elastoplastic cross-sectional analysis method and the rigid-plastic analysis method were used in theoretical calculation and the results were compared with the experimental results. It was found that when the composite bridge deck was subjected to negative bending, both the structural deformation and strain variation showed two stages, i.e., elastic stage and elastic–plastic stage, indicating good ductility. In the ultimate failure state, the longitudinal bulb-flat ribs buckled, and the adverse effect of the buckling on bending resistance was revealed. The contribution of the tensile strength of SFRC to the bending resistance was also studied. Furthermore, a new calculation method for the negative bending resistance of this type of composite decks was proposed.

Nowadays, using performance-based design procedures are widely applied by structural engineers. The direct displacement-based design (DDBD) approach is also one of the most efficient and popular procedures in these frameworks. This paper investigates the residual inter-story drift ratio (RIDR) demands in the mid-rise steel structures equipped with fluid viscous dampers (FVDs) designed by the modified DDBD approach. For this purpose, the capability of three approximate methods, i.e., the FEMA P-58, Erochko et al. and coefficients methods for estimating RIDR demands is studied. These methods have been proposed for moment-resisting frames (MRFs) without dampers. In order to evaluate the estimated RIDR demands in the approximate methods, three mid-rise steel MRFs with different velocity exponents for FVDs are designed according to the modified DDBD approach. Nonlinear time-history analyses are carried out by a set of spectrum-matched records at two seismic hazard levels including the designed earthquake (DE) and maximum considered earthquake (MCE). The results show that in most cases the Erochko et al. method overestimates the mean of maximum RIDRs at both the DE and MCE hazard levels. On the other hand, although the FEMA P-58 method overestimates the median of maximum RIDRs, when compared with the corresponding values obtained from analyses at the DE level, it underestimates the values at the MCE level. Also, the coefficients method is calibrated for the structures studied. Finally, a modified equation for a more precise estimation of RIDR demands is presented, by implementing the particle swarm optimization (PSO) algorithm.

The axial-shear-flexural interaction behavior of a double-span steel beam in a column-loss state is a complex phenomenon that demands more explanation. Nowadays, it is common practice to study the column loss scenario of a double-span steel beam using the pushdown method. Generally, two pushdown methods are commonly used: the Monotonic Pushdown Force (MPF) and the Distributed Pushdown Force (DPF) methods. Many current researchers adopted the MPF approach due to its practical and straightforward instrumentation for experimental testing compared to the DPF approach. However, the DPF approach would better approximate the actual collapse behavior of the structure in a column-loss event since it resembles the proper form of gravity loads. This paper aimed to demonstrate how these two approaches result in significantly different behavior in double-span steel beam collapse, particularly on the axial-shear-flexural interaction behavior. A finite element analysis using ABAQUS software was undertaken on a validated double-span steel beam model. In the MPF approach, the results have highlighted the importance of the tensile catenary action in the overall structural resistance of the double-span beam against collapse. The tensile catenary action dominated the load-resisting mechanism of the double-span beam at a large deformation state and interrupted the flexural resistance development. The stretching effect induced by the tensile catenary action has avoided the inelastic local buckling and allowed for greater rotation capacity on the beam assembly. However, under the DPF approach, the double-span beam has limited tensile catenary action build-up with high shear force development after the plastic hinge formation. The significant effects of the high shear force development on the double-span beam behavior were highlighted in this study.

Improving the structural performance and sustainability of slabs has been a major concern through the journey of research, due to the economic, self-weight, structural and environmental advantages that could be obtained, especially in high-rise buildings. Therefore, the challenge was to design lighter-weight and sustainable slabs either by modifying the cross sections or by using light-weight concrete. This paper discusses and compares the properties, experimental, analytical and numerical studies that were conducted on the structural behavior of two types of slabs: Hollow core slabs and Composite slabs. Hollow core slabs contain longitudinal voids of various shapes with the aim of reducing the self-weight by average of 40%. On the other hand, composite slabs consist of concrete and steel sheets of different profiles, that is known for its superior ultimate load that exceeds by almost 90%. However, Hollow core slabs integrated with profiled steel sheets amalgamate both longitudinal voids in the concrete and steel sheets, which in result combine the properties of both of them. This is the first paper that discusses voided composite slabs in the light of previous research by reason of the tremendous economic and structural enhancements that could be attained.

The article focuses on detecting structural deterioration in damaged steel beam structures by investigating changes in power spectral density (PSD) using deep learning. To simulate damage, cracks are introduced to alter the stiffness of the steel beams. The study aims to replicate a realistic traffic scenario over bridges by measuring vibration signals obtained from acceleration sensors distributed along the steel beams. The article proposes a new parameter that tracks the deterioration of structures by analyzing the PSD when a moving load is applied to the steel beams with defects. Features generated from modified forms of the PSD are used to identify structural deterioration via steel beam damage and deep learning in a training dataset. The study found that differences in PSD shape caused by damage are more effective in detecting damage in various beam structures than those in the value of the fundamental beam frequency. Although the PSD method has been utilized in earlier research to identify steel beam defects, the use of deep learning in this study offers numerous novel and advantageous benefits.

Concrete-steel composite columns have been utilized prevalently as load-bearing members in structures. The present study investigates the uniaxial behavior of concrete-filled steel tube (CFST) columns, which were proposed to provide high-strength steel bolts as external confinement to enhance the structural behavior of CFST columns. A total of 18 CFST columns were designed, out of which 12 columns were confined with steel bolts and 6 columns were unconfined; all columns were tested under axial compression. A mixture of self-compacting concrete (SCC) was utilized to fill all the test specimens. This study proposed an innovative approach to increase the restriction on lateral expansion of steel wall during elastic loading stage, which is expected to enhance structural behavior of CFST column. Test parameters included the effect of steel bolt spacing, three different (L/D) ratios, and two diffrent (D/t) ratios. The test findings demonstrated that the compression strength, axial stiffness, toughness, and ductility behavior of CFST columns increase as the spacing of steel bolts decreases and the improvement becomes more pronounced as the (L/D) and (D/t) ratios decrease. In addition, the compression capacity of the improved CFT short, medium, and long columns were enhanced by 25.3, 9, and 3.5%, respectively. A design model was developed to estimate the ultimate compression behavior of the improved CFST columns using steel bolts, and a close correlation was obtained between experimental findings and the proposed model.

In order to discuss the effect of corrosion results on fatigue properties of corroded steel, the morphology measurements and fatigue tests were performed to 10 corroded steel specimens obtained by artificial accelerated corrosion tests. And the corroded morphological characteristics and fatigue fracture of corroded specimen were studied. The results found the fracture mode and fatigue life were closely associated with the corroded morphological characteristics, especially for the fracturing source corrosion pit (FC-corrosion pit). So, based on the systematically analysis, the fatigue life prediction method of corroded steel was proposed.

This paper investigates the influence of commonly used screw connections on the integrity of built-up beams formed by connecting two lipped channel sections in a back-to-back configuration. An experimental investigation on the behaviour of 6 built-up CFS beams connected by self-drilling screws is presented in this paper. The screw spacing was varied along the length as well as the depth of the beams. The test results indicate that the screw spacing has some influence on the capacity of the built-up beams. An increase in screw spacing leads to an undesirable separation of channels and thus has a negative impact on the composite action between the members. Finite element models were developed and after successful validation, a parametric study involving 124 models was carried out, to investigate the impact of larger longitudinal screw spacings on the integral behaviour of the beams. It was observed that the flexural capacity decreased by 11%, 14%, 17% and 19% when the longitudinal distance between the screws increased from 50 to 1050 mm for beams with web depths 150 mm, 200 mm, 250 mm and 300 mm respectively. It can be concluded that flexural capacity is directly proportional to the decrease in the screw spacing and increase in the number of screw rows. The results also indicate that the percentage decrease in strength is greater for beams with larger web depths. An idealized cross section assuming complete composite action was simulated for each web depth using FE modelling and the capacities of all the screw-connected “semi-rigid” beams were compared against it. The capacity of screw connected built-up beams with web depths 150 mm, 200 mm, 250 mm and 300 mm was found to be 0.71, 0.64, 0.61 and 0.59 times that of the idealized cross-section on average, respectively. The moment capacities of screw-connected beams were also compared against the theoretical values obtained from AISI S-100. It was observed that the design guidelines provided in AISI S-100 were unable to account for the reduction in the moment capacity due to the screw connection in built-up members. AISI S-100 is conservative by as much as 34%, 42%, 46% and 48% for beams with web depths 150 mm, 200 mm, 250 mm and 300 mm respectively.

One of the seismic retrofit methods is applying heat to transfer the failure location from the near column into the beam. In this method, by heating a section of the beam, changes the mechanical characteristics of the beam, such as enhancing the ductility and decreasing the yield as well as the ultimate strength in that section, thus causing an altered place of failure as well as changes in the failure mode. In this study, via experimental and numerical methods an investigation was conducted on the ultra-low cycle fatigue capacity in retrofitted St-37 steel connection with three models of thermal improvement with the titles HBS1, HBS1&RIB, and HBS2 which differ in the cooling rate after the heating operation. The connection without retrofit failed in the cycle of 5% drift angle of SAC protocol loading. Retrofitted connections with HBS1 and HBS1&RIB thermal models failed in the cycle of 6% drift angle of SAC protocol loading. The results of modeling these connections in software and using the ultra-low cycle fatigue failure index also revealed a failure in a cycle with a 6% drift angle. The seismic capacity of the retrofitted connection with the HBS2 thermal model, with one percent increase in seismic capacity, failed in the cycle of 7% of the drift angle. The result of numerical modeling of this connection in the software was the same and indicated the ultra-cycle fatigue failure occurring in the cycle of 7% of the drift angle.

Rapid and effective ‘TIG-MAG hybrid welding (TMHW)’ technique overcomes the disadvantages associated with traditional welding setups. This research aims to study how different welding parameters affect the appearance of TMHW weld bead geometry (WBG). The study compares the penetration, reinforcement, and weld bead width of TMHW with metal active gas welding (MAGW). The results show that TMHW yields higher penetration and weld bead width with less reinforcement height than MAGW. Microhardness analysis revealed a subtle variation in the microhardness with regard to the heat input conditions and direction from the weld zone. TMHW produces slightly more microhardness in the weld zone. However, no discernible increase in microhardness was observed. The morphological analysis shows that TMHW causes a coarsening of the grains and a weakening of the Widmanstatten structure (WS) compared to MAGW. Grey-based Taguchi optimisation analysis was conducted to determine the best welding parameters for improved welding performance. The polynomial regression analysis determines the relationship between three welding parameters and WBG. The weld toe geometry has also been examined to provide a reference for future studies regarding fatigue. The findings suggest that TMHW with vertical torches can enhance penetration and reduce reinforcement, making it a viable alternative to conventional welding setups for improving welding performance on mild steel (MS) A-2062.

With the span of steel truss girder cable-stayed bridge (STGCB) increases, it is easy to have local stability problems caused by the increase of axial forces, and the whole steel truss girder uses a large amount of steel. To solve these problems, a new laminated girder single tower cable-stayed bridge (NLGCB) is proposed in this paper. The structure of NLGCB is similar to STGCB, the difference is that the lower chords of the main girder near the cable tower are changed into the concrete structure, while the web members and upper chords are made of steel. Thus, a new type of concrete-steel laminated girder is formed, so as to improve the stress characteristics of the main girder. In order to verify the superiority of mechanical properties of NLGCB, a test bridge with an unequal span (5 m + 6 m) was constructed. The natural frequency of the first in-plane vibration of the bridge was measured by the pulsation test, and the stresses and deflections of the structure were tested by the static load test. The static and dynamic characteristics of a 300 m + 300 m span bridge were analyzed by finite element software and compared with STGCB. The results show that the natural frequency of the first in-plane vibration of the structure is close to the calculated value, and the vibration modes are consistent with the finite element simulation ones. When the steel consumption is reduced by 13.7% and the concrete consumption is not much, the strength, stiffness, natural vibration frequency, and stability of the structure are greatly improved.

The formation of steel–concrete composites using individual steel and concrete elements is commonly ensured by two different connection techniques at connected interface level: mechanical connectors and structural adhesives. Among these two connection techniques, the use of structural adhesive for bonding steel and concrete elements is rapidly increasing; primarily owing to uniform transfer of stresses over the entire bonded area. The behaviour of bonded connection with change in adhesive bond layer thickness at the level of composite interface are analysed using finite element analysis under static loading to examine the ultimate strength and shear stresses. The failure governing parameters of bonded connections, such as engendered stresses in terms of von-mises and hydrostatic stresses at bearing ends of the composite interface along with changes in failure patterns (from adhesive to cohesive) are discussed. Also, the maximum engendered stresses along the failure plane for different bond layer thicknesses are examined. In case of one mm bond layer thickness the variation in shear stresses is very high along (39.28 MPa to 23.15 MPa) and perpendicular (34.62 MPa to 16.97 MPa) to the loading direction. While, the specimen with three mm thickness exhibits maximum load bearing capacity, it also has relatively smaller variation in shear stresses along (34.91 MPa to 21.72 MPa) and perpendicular (32.72 MPa to 17.20 MPa), which shows uniformity of stresses with increase in thickness. However, a further increase in the thickness of the bond layer results in reduction in the shear capacity of the specimen.

In this study, mechanical properties of lead core rubber bearing (LCRB) under variable pulse-like ground motions have been optimized to minimize the response quantities of interest at the level of the base isolation system, e.g., bearing acceleration and bearing displacement. Since the isolator period, effective damping ratio, superstructure mass, design displacement, and yielding displacement are major parameters that characterize the general behavior of the base isolation system, they have been selected as random variables. A single degree of seismically-isolated building as a shear beam-stick model has been implemented. Then, the dynamic response of the seismic isolation system is investigated considering the variability of mechanical properties of LCRB and superstructure mass over the base isolation system. In this investigation, the isolation device is developed using the Bouc–Wen model of hysteresis. To this end, Monte Carlo simulation has been conducted to provide comprehensive insight into the variability of seismic responses. Thus, 37,800 time-history analyzes have been performed and the effect of levels of uncertainty of the input parameters on the seismically isolated building's dynamic response is studied for 126 natural pulse-like ground motions whose pulse periods are between 0.6 and 13 s. Moreover, to find the best compound properties of LCRB parameters, the “desirability function optimization” method has been employed. Finally, the behavior of the LCRB has been optimized and increased its effectiveness to reduce the response criteria considering uncertainties in natural excitation parameters.

Truss string structures (TSSs) are often prone to the risk of progressive collapse owing to critical member failures in accidental events. Moreover, the randomness of material properties, cross-sectional dimensions, and construction errors can inevitably lead to fluctuations in the collapse resistance of structures. Thus, to avoid catastrophic collapse of TSSs, it is essential to investigate the resistance to progressive collapse of TSSs considering structural uncertainties. In this study, three limit states of TSSs under key member failures are defined. In addition, a probabilistic evaluation methodology for the progressive collapse resistance of single TSSs considering structural uncertainties is proposed and extended to spatial TSSs. The analysis reveals that the external load of single or spatial TSSs reaching different limit states due to cable failure is less than that of the failure of the bottom chord of the support. Furthermore, the fragility analysis shows that the progressive collapse resistance of TSSs exposed to the failure of the bottom chord of the support is greater than that of cable failure, the cable failure should be given more attention than the failure of the bottom chord of the support in the structural design and post-maintenance of TSSs. The sensitivity analysis indicates that the performance of single TSSs against progressive collapse is more sensitive to the variability of random parameters. In addition, the spatial effect can considerably enhance the performance of TSSs against progressive collapse when the bottom chord of the support fails, whereas the improvement is marginal when the cable fails.

This paper reported a new interlocked angle connector (IAC) for steel-concrete-steel sandwich structures. Shear performances of IACs embedded in normal concrete were studied via a push-out testing program, and the failure mode, shear resistance, and load–slip responses of IACs in normal concrete were obtained. The influences of height, width, thickness, orientation of steel angles, and interlocking bolts on shear behaviours of IACs were experimentally studied. The experimental results indicated that the ultimate shear resistances and slip capacities of IACs were improved via increasing the height, width and thickness of steel angles, while the orientation of steel angles exhibited limited influence on the ultimate shear resistances and failure modes of IACs. In addition, the analytical models were proposed for predicting ultimate shear resistances and load–slip behaviours of IACs. The experimental results were employed to validate the analytical models, and the proposed analytical models were found to provide more accurate predictions on ultimate shear resistances and load–slip behaviours of IACs as compared to the existing design codes.

This paper presents a study on the bolted connections of cold-formed steel (CFS) sheets and hot-rolled steel (HRS) plates. The test strengths and failure modes were compared with the results predicted by the North American Specification (AISI S 100–16) and European Standard (EN1993-1–3) for CFS structures. Additionally, the influence of the fastener diameter and the thickness of the CFS sheets and HRS plates on the specimens were discussed. In addition, numerical modeling of the specimens was established to simulate the failure modes and load-deformation relationships. Finally, a modified equation for bearing strength is proposed, discussed, and verified by reliability analysis. The results showed that bearing failure, shear failure and net section failure were observed. The nominal strengths predicted by AISI S 100 and EN 1993–1-3 are generally conservative. The numerical models can predict the failure modes and load-deformation relationships of the specimens with good agreement. In addition, the proposed method for the bearing strength of the connections has better accuracy than the current specifications.

The Monte Carlo simulation method can easily provide an accurate estimate of the probability of failure. However, for complex engineering problems with a low probability of failure, it may be inappropriate to provide an inefficient estimate of the probability of failure. In this study, tests investigations were performed on pressure vessel separator plates made of marine steel A36 ASTM, which exhibited corrosion on all plates, and occurred during multiple operations. The results of the tensile tests show that the areas of fracture of the specimens were observed as follows: near the gage, in the allowable area, on the line of the gage, and outside. The data obtained here provide a quantitative understanding and benchmark of the tensile behavior of corroded plates. Strain energy and maximum force varied in corrosion rate (\(\eta\)) between 10 and 24 fluctuated, while for \(\eta > 24\) decreased significantly. A series of simulations based on the Monte Carlo method was performed to determine the effects of corrosion rate and thickness variance on the overall behavior. The results of the two methods show that the values of the mechanical properties of the corroded specimens are scattered and follow a statistically normal distribution.

This paper implements a meshless technique based on the multiquadric radial basis function to investigate the flexural response of thin to moderately thick laminated plates resting on elastic foundations and subjected to various types of transverse loads with simply supported boundary conditions. The laminated plates are modelled via the equivalent single-layered Higher-Order Shear Deformation Theory plate theory with five unknown variables. This study applied the energy principle to determine the governing differential equations of the elastically supported laminated plate and discretized with stable the multiquadric radial basis function. The program is compiled on the MATLAB platform, and numerous comparative studies are carried out to show the reliability and correctness of the suggested meshless numerical model. The flexural behaviour of the laminated plate is investigated using parametric studies to determine the impacts of the span-to-thickness ratio, two variable elastic foundations, aspect ratio, orthotropy ratio, and number of layers on flexural behaviours of the considered plates are presented.

Austenitic S30408 stainless steel exhibits good low-temperature resistance and good welding performance. This steel is often used in liquefied natural gas stainless steel storage tanks. During the construction process, the tank wall is primarily connected by butt weld joints. Because welded joints are easily affected by temperature, low-temperature weld cracking can reduce the safety of structures. To study the cryogenic mechanical properties of austenitic S30408 stainless steel welded joints at low temperatures, the low-temperature mechanical properties of austenitic S30408 stainless steel base metal and welded joint components were studied by tensile tests from − 60 to 20 °C and scanning electron microscopy analysis of fractures at various temperatures. The results show that when the temperature decreases, the stress–strain curve of base metal components changes from a power function type to an inverted "s" type; in addition, secondary hardening occurs. The yield strength and tensile strength of the welded joint and base metal increased with decreasing temperature, and the elongation and reduction of area decreased. The plastic deformation capacity of the welded joint was significantly lower than that of the base metal, and there were obvious inclusions in the microstructure.

In this study, the nonlinear dynamic analysis of steel structures against progressive collapse was examined, and the adequacy and validity of the analysis duration defined in the regulation were investigated. In addition, the effects of the seismic resistance and design against progressive collapse constraints on the structure were investigated. An optimization algorithm was used in order to conduct the iterative process with appropriate sections. The frames were analyzed to perform one cycle as recommended in the UFC, and then the analysis duration was extended until at least five cycles had been completed. When the UFC was considered only, it was observed that while some of the designs were classified as safe within the duration specified in the UFC, the structural integrity was seen to get into danger in the subsequent cycles. When constraints related to seismic effect are also included in the process, it was seen that the threat disappeared for the frames examined. In addition, it was observed that the steel frame resisted progressive collapse scenarios by creating formations like Vierendeel beams.