For open car park structures, adopting a performance-based structural fire design is often justified and allowed because the fire does not reach flashover. However, this design approach requires an accurate assessment of temperatures in structural members exposed to car fires. This paper describes a numerical study on the thermal exposure on steel framing members in open car park fires. Steel temperatures are computed by the coupling of computational fluid dynamics and finite element modeling, and by analytical models from the Eurocodes. In addition, the influence of galvanization on the steel temperature evolution is assessed. Results show that temperatures in unprotected beams and columns are influenced by the section geometry, car fire scenario, modeling approach, and use of galvanization. Galvanization slightly delays and reduces peak temperature. Regarding the different models, CFD-FEM (CFD: computational fluid dynamics, FEM: finite-element method) coupled models predict lower temperatures than the Hasemi model, because the latter conservatively assumes that the fire flame continuously touches the ceiling. Further, the Hasemi model cannot account for the effect of reduced emissivity from galvanization on the absorbed heat flux. Detailed temperature distributions obtained in the steel members can be used to complete efficient structural fire designs based on the member sections, structure layout, and use of galvanization.

Over the past several decades, a variety of technical ways have been developed in seismic retrofitting of existing reinforced concrete frames (RFs). Among them, pin-supported rocking walls (PWs) have received much attentions to researchers recently. However, it is still a challenge that how to determine the stiffness demand of PWs and assign the value of the drift concentration factor (DCF) for entire systems rationally and efficiently. In this paper, a design method has been exploited for seismic retrofitting of existing RFs using PWs (RF-PWs) via a multi-objective evolutionary algorithm. Then, the method has been investigated and verified through a practical project. Finally, a parametric analysis was executed to exhibit the strengths and working mechanism of the multi-objective design method. To sum up, the findings of this investigation show that the method furnished in this paper is feasible, functional and can provide adequate information for determining the stiffness demand and the value of the DCFfor PWs. Furthermore, it can be applied for the preliminary design of these kinds of structures.

Recent developments on high-performance double-hooked-end steel fibers have enhanced the wide applications of steel fiber reinforced concrete (SFRC). This study presents the compressive properties and the cyclic flexural performance of the SFRC that were experimentally examined. Three different double-hooked-end steel fibers at 0.25%, 0.5%, 0.75%, and 1% volume fractions were considered. All fiber types had similar length to diameter ratios, while the first two fiber types had similar anchorage mechanisms (4D) and tensile strength and the third type had different anchorage mechanism (5D) and a higher tensile strength. The increased volumetric ratio of the fibers increased the post-peak compressive strain (ductility), the tensile strength, and the cyclic flexural strength and cumulative energy dissipation characteristics of the SFRC. Among the 4D fibers, the mixtures with the larger steel fibers showed higher flexural strength and more energy dissipation compared to the SFRCs with smaller size fibers. For 1% steel fiber dosage, 4D and 5D specimens showed similar cyclic flexural responses. Finally, a 3D finite element model that can predict the monotonic and cyclic flexural responses of the double-hooked-end SFRC was developed. The calibration process considered the results obtained from the inverse analysis to determine the tensile behavior of the SFRC.

The presence of cracks in a concrete structure reduces its performance and increases in the size of cracks result in the failure of the structure. Therefore, the accurate determination of crack characteristics, such as location and depth, is one of the key engineering issues for assessment of the reliability of structures. This paper deals with the inverse analysis of the crack detection problems using triple hybrid algorithms based on Particle Swarm Optimization (PSO); these hybrids are Particle Swarm Optimization-Genetic Algorithm-Firefly Algorithm (PSO-GA-FA), Particle Swarm Optimization-Grey Wolf Optimization-Firefly Algorithm (PSO-GWO-FA), and Particle Swarm Optimization-Genetic Algorithm-Grey Wolf Optimization (PSO-GA-GWO). A strong correlation exists between the changes in the natural frequency of a concrete beam and the crack parameters. Thus, the location and depth of a crack in a beam can be predicted by measuring its natural frequency. Hence, the measured natural frequency can be used as the input parameter of the algorithm. In this paper, this is applied to identify crack location and depth in a cantilever beam using the new hybrid algorithms. The results show that among the proposed triple hybrid algorithms, the PSO-GA-FA and PSO-GWO-FA algorithms are much more effective than PSO-GA-GWO algorithm for the crack detection.

The out-of-plane stability of the two-hinged space truss circular arch with a rectangular section is theoretically and numerically investigated in this paper. Firstly, the flexural stiffness and torsional stiffness of space truss arches are deduced. The calculation formula of out-of-plane elastic buckling loads of the space truss arch is derived based on the classical solution of out-of-plane flexural-torsional buckling loads of the solid web arch. However, since the classical solution cannot be used for the calculation of the arch with a small rise-span ratio, the formula for out-of-plane elastic buckling loads of space truss arches subjected to end bending moments is modified. Numerical research of the out-of-plane stability of space truss arches under different load cases shows that the theoretical formula proposed in this paper has good accuracy. Secondly, the design formulas to predict the out-of-plane elastoplastic stability strength of space truss arches subjected to the end bending moment and radial uniform load are presented through introducing a normalized slenderness ratio. By assuming that all components of space truss circular arches bear only axial force, the design formulas to prevent the local buckling of chord and transverse tubes are deduced. Finally, the bearing capacity design equations of space truss arches are proposed under vertical uniform load.

The degradation of concrete structure in the marine environment is often related to chloride-induced corrosion of reinforcement steel. Therefore, the chloride concentration in concrete is a vital parameter for estimating the corrosion level of reinforcement steel. This research aims at predicting the chloride content in concrete using three hybrid models of gradient boosting (GB), artificial neural network (ANN), and random forest (RF) in combination with particle swarm optimization (PSO). The input variables for modeling include exposure condition, water/binder ratio (W/B), cement content, silica fume, time exposure, and depth of measurement. The results indicate that three models performed well with high accuracy of prediction (R²≥ 0.90). Among three hybrid models, the model using GB_PSO achieved the highest prediction accuracy (R² = 0.9551, RMSE = 0.0327, and MAE = 0.0181). Based on the results of sensitivity analysis using SHapley Additive exPlanation (SHAP) and partial dependence plots 1D (PDP-1D), it was found that the exposure condition and depth of measurement were the two most vital variables affecting the prediction of chloride content. When the number of different exposure conditions is larger than two, the exposure significantly impacted the chloride content of concrete because the chloride ion ingress is affected by both chemical and physical processes. This study provides an insight into the evaluation and prediction of the chloride content of concrete in the marine environment.

The accuracy of subgrade quality evaluation is important for road safety assessment. Since there is little research work devoted to testing lightweight cellular concrete (LCC) by an ultrasound-based method, the quantitative relation between ultrasonic testing results and the quality of LCC subgrade is not well understood. In this paper, the quality of LCC subgrade was evaluated with respect to compressive strength and crack discrimination. The relation between ultrasonic testing results and LCC quality was explored through indoor tests. Based on the quantitative relation between ultrasonic pulse velocity and compressive strength of LCC, a fitting formula was established. Moreover, after the LCC became cracked, the ultrasonic pulse velocity and ultrasonic pulse amplitude decreased. After determining the lower limiting values of the ultrasonic pulse velocity and ultrasonic pulse amplitude through the statistical data, it could be calculated whether there were cracks in LCC subgrade. The ultrasonic testing results showed that the compressive strength of the LCC subgrade was suitable for purpose and there was no crack in the subgrade. Then core samples were taken from the subgrade. Comparisons between ultrasonic testing results of subgrade and test results of core samples demonstrated a good agreement.

Liquefaction of sandy soils is a big threat to the stability and the safety of an earth embankment laid on saturated soils. A large number of liquefaction-induced damages on embankment due to different types of earthquakes have been reported worldwide. In this research, the dynamic behaviors of earth embankment and the reinforcement effects of grouting as remediation method, subjected to moderate earthquake EQ₁ and strong earthquake EQ₂, were numerically investigated. The seismic behaviors of ground composed of cohesionless sandy soil and cohesive clayey soil were uniformly described by the cyclic mobility (CM) model, which is capable of describing accurately the mechanical property of the soil due to monotonic and cyclic loadings by accounting for stress-induced anisotropy, over-consolidation, and soil structure. It is known from the numerical investigation that the embankment would experience destructive deformation, and that the collapse mode was closely related to the properties of input seismic motion because high intensities and long durations of an earthquake motion could lead to significant plastic deformation and prolonged soil liquefaction. Under the strong seismic loading of EQ₂, a circular collapse surface, combined with huge settlement and lateral spread, occurred inside the liquefication zone and extended towards the embankment crest. In contrast, in moderate earthquake EQ₁, upheaval was observed at each toe of the embankment, and instability occurred only in the liquefied ground. An anti-liquefaction remediation via grouting was determined to significantly reduce liquefaction-induced deformation (settlement, lateral spreading, and local uplift) and restrain the deep-seated circular sliding failure, even though the top sandy soil liquefied in both earthquakes. When the structure was subjected to EQ₂ motion, local failure occurred on the embankment slope reinforced with grouting, and thus, an additional appropriate countermeasure should be implemented to further strengthen the slope. For both input motions, the surface deformation of the considered embankment decreased gradually as the thickness of reinforcement was increased, although the reinforcement effect was no longer significant once the thickness exceeded 6 m.

Sandy gravel foundations exhibit non-linear dynamic behavior when subjected to strong ground motions, which can have amplification effects on superstructures and can reveal insufficient lateral resistance of foundations. Grouting methods can be used to improve the seismic performance of natural sandy gravel foundations. The strength and stiffness of grouted sandy gravel foundations are different from those of natural foundations, which have unknown earthquake resistance. Few studies have investigated the seismic behavior of sandy gravel foundations before and after grouting. In this study, two shaking table tests were performed to evaluate the effect of grouting reinforcement on seismic performance. The natural frequency, acceleration amplification effect, lateral displacement, and vertical settlement of the non-grouted and grouted sandy gravel foundations were measured and compared. Additionally, the dynamic stress-strain relationships of the two foundations were obtained by a linear inversion method to evaluate the seismic energy dissipation. The test results indicated that the acceleration amplification, lateral displacement amplitude, and vertical settlement of the grouted sandy gravel foundation were lower than that of the non-grouted foundation under low-intensity earthquakes. However, a contrasting result was observed under high-intensity earthquakes. This demonstrated that different grouting reinforcement strategies are required for different sandy gravel foundations. In addition, the dynamic stress-strain relationship of the two foundations exhibited two different energy dissipation mechanisms. The results provide insights relating to the development of foundations for relevant engineering sites and to the dynamic behavior of grouted foundations prior to investigating soil-structure interaction problems.