International Journal of Civil Engineering
Volume:18 Issue: 3, Mar 2020

Spectroscopic ellipsometry is a powerful technique for determining optical properties of any thin surface. A method for characterizing optical properties of warm asphalt binder using spectroscopic ellipsometry along with associated results has been presented in this paper. Thin films of warm asphalt binders were produced using LEADCAP and Sasobit and characterized using a variable angle spectroscopic ellipsometry. Refractive index and extinction coefficient of each of the samples (original and aged) were extracted from model fitted spectra. Clear variation in refractive index and extinction coefficient was observed among the samples before and after aging. The samples were found to be highly reflective with refractive index ‘n’ in the range 1.55–1.62 and extinction coefficient ‘k’ in the range of 0.01–0.06, both before and after aging. Reflectivity of PG 64-22 with LEADCAP exhibited the highest refractive index and the lowest extinction coefficient in visible wavelength of light among the samples. The results indicated that the highest reflection of visible light can be observed from LEADCAP-modified binder. Cracking properties and absorption coefficient of the binders are observed to have a correlation. The method reported here can be applied to any type of asphalt binder to determine its light absorption and reflection characteristics for a wide range of wavelength.

This paper presents a theoretical framework for developing a risk–cost optimised maintenance strategy for structures during their whole service life. A time-dependent reliability method is employed to determine the probability of structural failure and a generic form of stochastic model is developed for structural responses. To facilitate practical application of the proposed framework, a general algorithm is developed and programmed in a user-friendly manner. The merit of the proposed framework is that, in predicting when, where and what maintenance is required for the structure, all structural components and multi-failure modes are considered. It is found in the paper that, to ensure the safe and serviceable operation of the structure as a whole, some components need maintenance multiple times for different failure modes, whilst other components need “do nothing”. It is also found that ignorance of correlation amongst structural components and failure modes would underestimate the risk of structural failures in longer term and that the components with higher cost of structural failures require more maintenance actions. The paper concludes that the proposed framework can equip structural engineers, operators and asset managers with a tool for developing a risk–cost optimal maintenance strategy for structures under their management.

This study investigates the applicability of the Large Eddy Simulation method with a simple near-wall model to simulate flow separation due to complex immersed geometries. A numerical model was, therefore, developed to solve the governing equations on a staggered Cartesian grid system, in which the flow obstacles are modeled using the immersed boundary method. The near-wall region is approximated using simplified boundary layer equations, aiming at achieving reliable results with a low computational cost. In this study, the accuracy of the numerical model was first evaluated by considering a three-dimensional turbulent flow past an infinite-length circular pile. The corresponding numerical results, particularly the main flow features in the wake region, were found to be in good agreement with experimental and numerical results obtained from reference studies. The numerical model was then applied to simulate the flow around a pile-supported pier, a vital structure in the river and coastal environment, presenting results beyond the former background knowledge available for this case. The available experimental results for the pier case show the good accuracy of the present numerical results. Moreover, the numerical model enabled to characterize the most relevant flow features due to the pier demonstrated the efficiency of the numerical methods employed to study the flow structure formed around complex geometries.

Finite element analysis (FEA) models for sophisticated hybrid bored pre-stressed concrete cased piles, where the unique grouted interface between the pile and strata is highlighted by cohesive elements, are established in this paper and their applicability is demonstrated by comparing the in situ experiments and FEA simulations. The underlying bearing mechanism is investigated from the aspects of energy dissipation due to the damage of the grouted interface, the axial force along the pile length, and the deformation evolution in the surrounding strata. Under the failure criteria controlled by both the stiffness of the pile/soil system and pile head allowable settlement, the ultimate bearing capacity increases with the interfacial shear strength until reaching an asymptotic value. By energy analysis, it is demonstrated that the buffering effect of the strata to redistribute the stresses in the system is another key factor for the bearing capacity and failure mode of the pile foundations. The decrease in modulus attenuation (from approximately 90% to 50% in the studied case) leads to a larger asymptotic bearing capacity (from approximately 2.17 × 104 to 2.88 × 104 kN in the studied case, respectively) if the ductile failure mode of the pile foundations is guaranteed. However, the minimum interfacial strength needed for the presence of the preferred ductile failure mode is also increased (from 0.6 to 2.0 MPa in the studied case), which indicates more rigorous conditions for the grouting of pile/soil gap. As improved grouting quality and less modulus attenuation are commonly contradictory to each other from the aspects of construction practice, it is suggested that, if the grouting quality cannot be guaranteed, optimizations should be carefully carried out to achieve the presence of the preferred ductile failure mode of the pile foundations.

Cellular beams are those that present sequential web openings along the span, and are produced by thermal cutting and welding. Studies addressing the lateral-torsional buckling resistance curve of cellular beams according to the American standard are scarce. The objective of the present study is to investigate the lateral-torsional resistance in cellular beams, considering the Load and Resistance Factor Design. To this end, geometrical and material nonlinear analyses are conducted. The cellular beams are simply supported, with fork supports at the ends, and subjected to three types of loading: uniform bending, mid-span concentrated load and uniformly distributed loads. The geometric parameters of cross section and unrestrained length are varied. Results are compared with the nominal and design flexural strength. Failure modes are associated with non-dimensional lateral-torsional stiffness. Considering the application of uniform bending moment, failure modes such as LTB and WDB + LTB occurred. In contrast, considering the presence of shear stress, failure modes such as the Vierendeel mechanism, WPB, and WPB + LTB occurred. It was concluded that when compared with the numerical model results, the design flexural strength was ineffective under inelastic buckling regime, a situation in which interaction of modes of failure can occur. When considering only the pure lateral-torsional bucking, the Load Resistance Factor Design variation was observed. This variation presented an average value equal to 0.83, differing from the procedure in question by approximately 7.8%.

Currently, many studies seek to find materials that are friendlier towards the environment. Warm mix asphalt (WMA) technology helps to decrease manufacturing temperature in traditional hot mix asphalts (HMA), which reduces emissions that are detrimental to the environment. For the case of asphalt pavements, WMA technology, which uses recycled materials such as blast furnace slag (BFS), this could be an interesting alternative technique. Reutilizing these types of industrial waste materials for roadway project constructions could help to minimize negative impacts on the environment. In this study, the coarse fraction of natural aggregate in a control HMA was replaced with BFS. Additionally, a chemical additive was used to lower mixing temperature by 30 °C, and thus manufacture WMA. Marshall, indirect tensile strength, resilient modulus and permanent deformation tests were carried out. This additive helps to reduce air void content, reduces mixing and compacting temperatures and increases asphalt stiffness. Studied WMA that has a 12.5% substitution of coarse natural aggregate fraction with BFS, results in a significant increase in stiffness (under monotonic and cyclic loads), as well as an increase in resistance to moisture damage and to permanent deformations, when compared to control HMA.

This paper proposes a simplified envelop curve model for evaluation of capacity curve of reinforced recycled aggregate concrete (RAC) columns subjected to seismic loads. A seismic research database containing 53 reinforced RAC columns was established and applied to calibrate the envelop curve model. The effective initial stiffness, feature drift ratio, and various loads of collected RAC columns were discussed and modelled by a database analysis and a simplified sectional analysis. According to comparative results, effective initial stiffness, yield stiffness, and various drift ratios of RAC columns could be modelled simply considering the effects of axial load ratio and replacement ratio of recycled aggregate in RACs. Considering the weak self-properties of recycled aggregates, the study suggested the yield load of reinforced RAC columns under seismic loads could be taken simply as 80% of calculated peak load of the columns. The ultimate drift ratios of RAC columns were evaluated by a simplified linear function of peak drift ratios. The paper found that the lateral confinement index of columns has a significant influence on the flexural envelop curves of reinforced RAC columns. The comparative results verified that the proposed envelop curve model can evaluate the experimental behaviour with a good agreement.

Base isolation provisions in ASCE 7 Standard have been historically shown to be conservative in estimating seismic demands. New torsional bearing base isolation displacement expressions have been proposed recently by the latest ASCE 7–16 Standard. This study compares the accuracy of the new ASCE 7–16 static-based isolation expressions for additional bearing displacement due to plane torsion to the response obtained using simplified structural dynamics’ plane torsion theory expressions. In addition, it conducts a parametric study to assess the effect of accidental eccentricity, damping ratio, and plan aspect ratio on the accuracy of ASCE 7–16 bearing displacement expression. The results showed that the ASCE 7–16 undamped displacement estimations improved compared to the significant conservatism of ASCE 7–10 by 7–33% depending on the eccentricity condition and ratio, which may further promote the use of base isolation in the US as a seismic hazard mitigation solution. However, the study also revealed that a considerable conservatism of the new base isolation bearing displacement provisions of ASCE 7–16 still exists in some cases, which ranged from 52 to 105% in the case of three equal fundamental frequencies and 5–20% in the case of equal lateral frequency and distinct torsional frequency. The study also showed that the ASCE 7–16 conservatism is proportional to the eccentricity and is more pronounced with biaxial eccentricity compared to single eccentricity. Furthermore, the results show that ASCE 7–16 expression accuracy significantly declines with damped systems with a possibility of un-conservative estimation of bearing displacements that can reach 25–40% with larger eccentricities. In addition, the ASCE 7–16 torsional displacement was shown to be inversely proportional to the plan aspect ratio with a discrepancy that can reach ± 20%. The study also exhibited that the ASCE 7–16 torsional displacement conservatism is slightly affected by increasing damping ratio above 4%.

In order to understand the effect of porous media on hydraulic jumps, a smoothed particle hydrodynamics (SPH) model is applied to investigate the characteristics of hydraulic jumps interacting with porous media. Various porosities including cases without an obstacle or with a solid obstacle or porous media are considered. The opening of a gate was altered to adjust the hydraulic jump. The conjugate depth ratio, bottom shear stress distribution, and energy dissipation are reported. In the present study, validations are in a good agreement with previous studies. Overall, the result showed that the average error between numerical and experimental data was less than 7.2%. Energy dissipation is compared among cases with three porosities, with and without a solid obstacle. The porosity of 0.68 is found to dissipate more energy than do other porosities. Thus, porous media can be used to enhance energy dissipation of hydraulic jumps in an open channel. In conclusion, the proposed SPH model can simulate the effect of porous media on hydraulic jump characteristics.

A numerical study is carried out to investigate the importance of three-dimensionality and turbulence in supercritical bend flow. The CFD-based model, FLUENT, is applied for solving the three-dimensional equations of continuity and Navier–Stokes. The volume of fluid method has been employed to simulate the free-surface flow. The turbulence closure of the mean flow system is acquired using the standard k − ε turbulence model. The model is applied to three different bend geometries. The three-dimensional modeling is done with and without considering turbulence effects. Results, in the form of non-dimensional water-surface profiles, are compared with the available two-dimensional model results as well as available experimental data. The results indicate that three-dimensional approach makes highly improved predictions in comparison with the results of two-dimensional model. Furthermore, the height and the location of maximum flow depth, which are important in designing the supercritical bend channels, are predicted better in three-dimensional model than the two-dimensional model results. However, turbulence modeling does not show a significant contribution in supercritical bend flow.