Advances in Steel and Composite Steel—Concrete Bridges and Buildings

Construction steel has widely been used worldwide for developing infrastructure, e.g., bridges and buildings, because of its many advantages, including durability, light weight, high strength, and sustainability [1,2]. Moreover, combining such advantages with those of concrete, composite steel–concrete structures have increasingly been applied due to a growing demand for new research [3,4]. In recent years, a great variety of structural members have been developed, including post-tensioned thin-walled steel box-girders, steel–concrete composite decks with shear connectors, and concrete-filled steel tubular and concrete-encased steel members [5,6]. Particularly, research topics on steel and composite steel–concrete bridges and buildings cover corrosion, fatigue, fire scenarios, limit and ultimate state designs, linear and nonlinear analyses, maintenance, monitoring, post-tensioning applications, progressive collapse, resistance of components, retrofitting and strengthening, seismic, dynamic, and static loadings, stability, etc. [7,8].

This Special Issue aimed to gather new, genuine, and detailed contributions and future perspectives in the aforementioned arguments. Specifically, this Special Issue has presented 12 high-quality manuscripts (see the section “List of Contributions”) related to the following topics of steel and composite steel–concrete bridges and buildings, in which novel concepts, approaches, as well as predictive methodologies of their structural behavior have mainly been addressed: (a) advanced construction technologies and 3D Finite-Element (FE) modeling; (b) development of high-performance materials; (c) laboratory investigations; (d) linear and nonlinear analyses of geometric and material properties; (e) Destructive Testing (DT) and Non-Destructive Testing (NDT) methods; (f) serviceability issues under seismic, dynamic, and static loadings, fracture, fatigue and corrosion; and (g) strengthening and repair interventions. Particularly, the adopted concepts and approaches relied on (1) analytical formulas; (2) calibrations of experimental measurements from conducted tests; (3) earthquake mitigation strategies; (4) laboratory experiments on high-performance materials and structural member prototypes in the medium scale; and (5) numerical simulations.

Abbood at al. evaluated the effectiveness of a new concrete-encased column using small circular steel tubes filled with cementitious grouting material as the primary reinforcement instead of traditional steel bars. The authors’ study involved 3 different types of reinforcement: conventional steel bars, concrete-filled steel tubes with 30% of the reinforcement ratio of steel bars, and concrete-filled steel tubes with the same reinforcement ratio as steel bars. A total of 24 circular concrete columns were tested and categorized into six groups according to the type of reinforcement employed. Each group comprised four columns, with one subjected to concentric axial load, two subjected to eccentric axial load, and one tested under lateral flexural loads. The related experimental results were validated by FE analyses conducted by ABAQUS. Consequently, the findings for concentric load revealed that columns with the second type of reinforcement, concrete-filled steel tubes with 30% of the reinforcement ratio of steel bars, exhibited a failure load 19% lower than those with steel bars, while columns with the third type of reinforcement, concrete-filled steel tubes with the same reinforcement ratio as steel bars, achieved a failure load 17% greater than the conventional steel bars.

Askouni studied the seismic response of in-height 3D mixed models by assuming the effect of sustaining deformable ground compared to the conventional rigid soil hypothesis. Considering the seismic codes, buildings are commonly assumed to be made of the same material throughout the story distribution and based on an ideal, rigid soil. However, there are often cases of buildings formed by a bottom part constructed with Reinforced Concrete (RC) and a higher steel part, despite this construction type not being recognized by code assumptions. Additionally, soil deformability, commonly referred to as Soil–Structure Interaction (SSI), widely affects the earthquake response of residential structures, though it is not included in the design. Specifically, the authors considered two types of soft soil as well as the rigid soil assumption, while two limit interconnections between the steel part and the concrete part were included in the group analysis. The effect of the SSI on the nonlinear performance of 3D mixed models was identified, making it unique among the numerous studies available and pointing to findings that are useful for the enhancement of the seismic rules regarding the analysis of code-neglected mixed buildings.

Bachinilla et al. discussed the gap of insufficient studies on large-diameter monopiles for supporting railway bridges subjected to buckling phenomena and the lack of simplified tools to quickly assess structural reliability. In fact, during devastating earthquakes, soil liquefaction has disastrous consequences on bridge foundations. Thus, to avoid foundation failures, a bridge’s pile foundation design can be such that the pier directly rests on the top of a large-diameter monopile instead of the traditional multiple small-diameter piles. Specifically, the authors focused on pure buckling with shear deformation and reliability assessment to calculate a monopile’s failure probability in fully liquefied soils. Therefore, in reliability assessment, with the critical pile length “L_crit” and the unsupported pile length “L_uns”, the limit state function “g(x) = [L_crit − L_uns]” formed the basis for assessing the safety of a structure. The “L_crit” formulation was accomplished with a differential equation. Furthermore, the “L_uns” assumed various depths of liquefied soil, while the reliability index’s formulation was obtained through the “Hasofer–Lind” concept. A case study was considered using a high-speed railway bridge model. Specifically, to validate the minimum pile diameter for buckling phenomena, when a fully liquefied soil’s thickness reached the condition “L_crit = L_uns”, the authors applied the theory of “Bhattacharya and Tokimatsu”. The corresponding results showed good agreement for monopile diameters equal to 0.85–0.90 m. With a monopile diameter smaller than 0.85 m, the “L_crit = L_uns” limit was at lower depths, while with a monopile diameter larger than 0.90 m, the “L_crit = L_uns” limit was at deeper depths. A load increase affected the large-diameter monopiles because the “L_crit” movement required a longer range. In fully liquefied soil, buckling likely happens in piles with a diameter between 0.50 and 1.60 m because the calculated probability of failure “Pf” value is nearly one. Conversely, buckling does not likely happen in monopiles with a diameter of 1.80–2.20 m because the “Pf” value is zero. Therefore, the authors’ outcomes suggested that the minimum reliable monopile diameter is 1.80 m for supporting a high-speed railway bridge.

Badarloo and Lehner proved the practical aspects of the numerical correlation of the results of the compressive strength test. The DT in a hydraulic press and the NDT using a Schmidt hammer in several process variations were evaluated. The goal was to evaluate the differences between the tool supplier’s curve and testing. Specifically, 150 cube specimens were produced using a mixture of three types of concrete classes (C30, C35, and C40). The tests were performed at 7 and 28 days of concrete curing. The Schmidt hammer test was executed in horizontal and vertical directions and using a series of 10 measurements. Additionally, the tests were performed in two sets: first, the sample was placed on the ground, and second, under a hydraulic jack with a load of 50% of the maximum bearing capacity of the specific concrete. Then, regression analysis was performed on the data sets to establish linear mathematical relationships between the compressive strength and the number of bounces. The authors’ findings showed that the correlation between the DT and NDT tests has a high value for each group, but the correlation equations are different and must be taken into consideration.

Basit et al. undertook an experimental and numerical study on the structural integrity of buried RC sewerage pipes, focusing on the performance of two distinct jointing materials, i.e., cement mortar and non-shrinkage grout. Through joint shear tests on full-scale sewer pipes under single-point loading conditions, notable effects on the crown and invert of the joint were observed, highlighting the critical vulnerability of these structures to internal and external pressures. Two materials—cement–sand mortar and non-shrinkage grout—were used in RC pipe joints to experimentally evaluate the joint strength of the sewerage pipes. Among the materials tested, cement–sand mortar emerged as the superior choice, demonstrating the ability to sustain higher loads until 25.60 kN and proving its cost-effectiveness for use in various locations within RC pipe joints. Conversely, non-shrinkage grout exhibited the lowest ultimate failure load, i.e., 21.50 kN, emphasizing the importance of material selection in enhancing the durability of urban infrastructure. The authors’ results revealed a 10% divergence between the experimental and numerical data regarding the ultimate load capacity of pipe joints, with experimental tests indicating a 25.60 kN ultimate load and numerical simulations showing a 23.27 kN ultimate load. Despite this discrepancy, the close concordance between the two sets of data underscored the utility of numerical simulations in accurately predicting the behavior of pipe joints.

El-Zohairy et al. presented a set of findings from fatigue loading tests on composite beams with various arrangements. Indeed, fatigue in steel–concrete composite beams can result from cyclic loading, causing stress fluctuations that can lead to cumulative damage and eventual failure over an extended period. Specifically, fatigue tests were performed up to 1,000,000 cycles using four-point loading, encompassing various ranges of shear stress at a consistent amplitude. Additionally, the effects of external post-tensioning and the strength of the shear connection were investigated. Static tests were conducted until failure to assess the enduring strength of the specimens subjected to fatigue. The authors found that the damage region that the shear studs caused in the concrete slab, which resulted in a reduction in stiffness within the shear connection, grew as the loading cycles increased, leading to an increase in residual deflections and plastic slippages. Controlling the longitudinal fatigue cracks in the concrete slab was largely dependent on the strength of the shear connection between the steel beams and concrete slabs. Moreover, the applied fatigue loading range affected the propagation and distribution of fatigue cracks in the concrete slab. In addition, the strains in different parts of the composite specimens were significantly reduced by applying the external post-tensioning.

Gómez-Gamboa et al. determined the equivalent Stress Intensity Factor (SIF) model that best fits the behavior of low-carbon steel under mixed modes. Particularly, the authors’ study assessed the equivalent SIF models of “Tanaka, Richard, and Pook”. The theoretical values adopted for comparison corresponded to the experimental results in a modified geometry by machining a hole ahead of the crack tip subjected to fatigue loads with a load ratio equal to 0.1. The comparison involved the SIF for six experimental points and the values computed through the numerical simulation. The “Paris, Klesnil, and Modified Forman–Newman” crack growth models were utilized with each equivalent SIF to analyze the prediction of the number of cycles. The “Klesnil” model showed the closest identification since the error between the calculated and experimentally recorded number of cycles was the lowest. However, the material behavior reflected a reduced crack propagation rate attributed to plasticity in the crack tip. Additionally, the authors’ results suggested that the “Asaro” equivalent SIF conservatively estimates the element lifespan with increasing errors from 2.3% at the start of growth up to 27% at the end of calculation.

Hussein and Hussein presented an investigation into the axial compressive behavior of Cold-Formed Steel Channel (CFSC) sections. In fact, CFSC section columns have achieved widespread adoption in building construction due to their advantages, including energy efficiency, expedited construction timelines, sustainability, material efficiency, and ease of transportation. Specifically, an FE model for CFSC columns was implemented against experimental data from the literature. The FE model was employed for a parametric analysis encompassing a data set of 208 CFSC members. Furthermore, the efficacy of the design methodologies outlined in the AISI specification and AS/NZS standard were evaluated by comparing the axial load capacities obtained from the numerically generated data with the results of four conducted experiments. The authors’ outcomes revealed that the design equations, based on compressive resistances and determined using the direct strength method, exhibited a conservative bias. On average, these equations underestimated the actual load capacities of the CFSC columns by approximately 11.5%. Additionally, the authors explored the influence of eccentricity, cross-sectional dimensions, and the point-of-load application on the axial load capacity of the CFSC columns. Their results demonstrated that a decrease in section thickness, an increase in column length, and a higher degree of eccentricity reduce the axial capacity of CFSC columns.

Khan et al. investigated the use of a cement-less recycled aggregate concrete as a sustainable approach for building construction. Indeed, the production of Ordinary Portland Cement (OPC) emits harmful CO₂ gasses, which, in turn, contribute to sporadic heatwaves, flash flooding, and food shortages. Specifically, the authors used fly ash, an industrial waste of coal power plants, as a 100% substitute for the OPC. Moreover, the authors used Recycled Coarse Aggregates (RCA) as a partial to complete replacement for Natural Coarse Aggregates (NCA) to preserve natural resources. A total of 60 pull-out specimens were utilized to investigate the influence of steel bar diameter, bar embedment length, db (4 db and 6 db), and percentage replacements of NCA with RCA on the bond stress behavior of cement-less RA concrete. The authors’ results showed that the bond stress of cement-less RCA concrete decreased by 6% with increasing steel bar diameter. Moreover, the bond stress decreased by 5.5% with increasing bar embedment length. Additionally, the bond stress decreased by 7.6%, 7%, 8.8%, and 20.4%, respectively, with increasing percentage replacements of NCA with RCA. A model was also developed correlating the bond strength to the compressive strength of cement-less RCA concrete, which matched with the experimental results and predictions of the CEB-FIP model for the OPC.

Lerma Villa et al. demonstrated that pervious concrete’s corrosion current increases with increasing aggregate size. Indeed, pervious concrete has a great potential for use in many applications as a part of urban facilities that can add value through water harvesting and mitigating severe damage from floods. Also, corrosion is a factor to consider only when steel pieces are immersed and aggravated by the presence of chlorine, but it drains water and does not retain moisture. Particularly, steel-reinforced pervious concrete was investigated, and the grain size of the inert material and the corrosion process parameters were analyzed. The electrochemical frequency modulation technique was proposed as a suitable test, a reproducible assessment that, without damaging RC structures, particularly pervious concrete, indicated a trend in increasing corrosion current density as the size of the aggregate increases or density diminishes.

Pour et al. intended to measure the efficiency of different strengthening techniques to improve the flexural properties of RC beams using Glass Fiber-Reinforced Polymer (GFRP) laminates, including Externally Bonded Reinforcement (EBR), Externally Bonded Reinforcement on Grooves (EBROG), Externally Bonded Reinforcement in Grooves (EBRIG), and the Near-Surface Mounted (NSM) system. An NSM technique was also established using an anchorage rebar. Then, the effect of the NSM method with and without externally strengthening GFRP laminates was studied. Twelve RC beams were studied under a bending system. To perform the NSM method, both steel and GFRP rebars were utilized. The ductility of the RC specimens was evaluated, and a comparison was made between the experimental consequences and the existing design codes. Subsequently, a new regression was generated to predict the final resistance of the RC beams bound with various retrofitting techniques. The authors’ findings demonstrated that the NSM technique can enhance the load-bearing capacity and ductility of RC beams to 42.3% more than the EBR, EBROG, and EBRIG performances.

Tabiatnejad et al. studied the fatigue performance of the top flange in continuous steel I-girder bridges over skewed supports. In fact, skewed supports complicate load paths in such I-girder bridges, causing secondary stresses and deformations. For instance, in a continuous bridge, where tensile stresses are developed in the top flange of the girders over the intermediate supports, these effects can exacerbate fatigue issues for the top flanges. The authors’ results were gained based on an investigation consisting of 3D FE modeling to evaluate 26 skewed bridges in Florida. The analyses focused on the stress ranges in the top flanges and axial demands on end cross-frame members under fatigue truck loading. The maximum factored stress range of 3.63 ksi, obtained for the selected group of bridges, remained below the 10 ksi fatigue threshold for an AASHTO Category C connection, alleviating the concerns about the fatigue performance of the continuous girder top flange over the intermediate pier. Hence, fatigue is unlikely to be a concern in the flanges. A comparative FE analysis of two different types of end cross-frame to girder connections also provided useful insight into the fatigue sensitivities of the skew connections. Half-Round Bearing Stiffener (HRBS) connections performed better than the customary bent plate connections. Particularly, the HRBS connection reduced the girder flange stress concentration range by at least 18% compared to the bent plate connection.

All the manuscripts gathered in this Special Issue contributed to the crucial challenge of developing more durable steel and composite steel–concrete structures of bridges and buildings over time and with high lightweight, stability, strength, and sustainability (see the following section, “List of Contributions”). For this purpose, the continuous implementation of new members, due to the possibility of combining the advantages of steel with those of high-performance concrete materials, allowed the improvements of the service conditions of bridges and buildings [9,10]. This Special Issue also confirmed that calibrations of laboratory measurements from conducted tests, through 3D FE modeling and analytical formulas, is still a useful way to develop further advanced construction technologies for steel and composite steel–concrete bridges and buildings [11]. These approaches allowed the authors of the collected contributions to provide robust solutions to several necessities, such as the implementation of the numerical models with a low computational cost, fast training, validation, testing, visualization of the results, and fast notification to end users [12,13]. Yet, the presented approaches provided valuable operational tools that can be readily exploited by end users, whether modelers or decision makers, to study the structural performance of steel and composite steel–concrete bridges and buildings and to increase their safety capacity against severe long-age conditions and seismic events [14]. Therefore, the editor believes that this Special Issue can significantly contribute to enhancing the insight into construction technologies and analytical and numerical solutions aimed at “Advances in Steel and Composite Steel—Concrete Bridges and Buildings”.