International Journal of Civil Engineering最新文献

The tunneling process in water-rich silty fine sand stratum often faces challenges such as arch collapse due to the instability of the initial support arch foot. The present study focuses on the Taoshuping 3# inclined shaft section, modifies the two-side heading method (THM), and introduces the double-heading at bottom method (DBM). Field monitoring and numerical simulations are employed to investigate the formation pressure, deformation evolution, and the advantages of the construction scheme using the loosened zone and stress distribution features. The obtained results show that DBM exhibits a maximu m settlement during arch excavation, constituting approximately 36% of the total settlement, with a total value of 222.21 mm. Furthermore, the plastic zone induced by DBM ranges from 1.23 to 2 times the tunnel diameter, with vertical and horizontal surrounding soil pressures of 140.72 kPa and 46.25 kPa, respectively. DBM is markedly superior to THM. This approach reduces the formation of wedge-shaped shear bodies caused by excessive stress at the sidewalls in THM excavation. Even with tunnel excavation support, the surrounding soil maintains an arch effect, validated through calculations using Protodyakonovco theory and Terzaghi theory, verifying the efficiency of the support structure design.

This study examines the Braess paradox in the context of the multiple-period restoration scheduling problem. A bilevel programming model is devised, where the upper-level problem is to determine the optimal sequence of recovery activities considering the limited resource constraint, while the low-level problem is the traffic assignment model that captures passengers’ responses to the changes in the transportation network capacity. Then, a novel genetic algorithm (GA) is developed to solve the proposed restoration scheduling problem. Our case study first shows that the optimal restoration schedule does not concur with the results obtained based on the link importance measurement, and the former can achieve a 4% total travel time reduction compared with the latter. Then, various numerical experiments are conducted to illustrate the occurrence and properties of the Braess paradox, which is that the network performance in some restoration periods can be better than that before the disruption or after a disrupted link is recovered. Moreover, it is revealed that with sufficient resources for multiple links to be repaired simultaneously, it is unnecessary to do so in the optimal rehabilitation schedule due to the existence of the Braess paradox. Finally, in terms of algorithmic performance, our proposed-GA outperforms the particle swarm optimisation algorithm and can reduce the computation time by up to 14%.

Investigations on the changes in pore water pressures and stress during the construction of stiffened deep cement mixing (SDCM) piles are scarce, resulting in an unsatisfactory understanding of the bearing capacity formation process. Thus, this paper presents a preliminary field study to investigate the variation characteristics of pore water pressures, total stress and effective stress during the construction of SDCM piles derived from field tests. In the meantime, cone penetration tests (CPTs) were conducted before and after the construction of SDCM piles. The results show that the variation ranges of pore water pressure, total stress and effective stress of soils around piles decreased with increasing distance between the measuring point and piles when the depths of the measuring points were the same. During the piling process, the effective stress increased by approximately 53–103%, and the pile side frictions increased accordingly, while the tip resistance and side resistance values of soils around piles increased by 27–106% and 2–145%, respectively. Additionally, SDCM piles successively formed different load-bearing components with decreasing bearing capacity along the pile diameter direction, which realized a better bearing efficiency than conventional piles made with homogeneous materials. In essence, they were also the source of significant economic advantages of SDCM piles. Through this study, we expect to provide a reference for further studies on the bearing mechanism of SDCM piles in soft soil regions.

Abstract

The objective of this study, concerning the soil–structure interaction of shallow reinforced concrete foundations of wind towers with circular cross-sections, was determination in a closed form of the monotonic moment–rotation curve of the soil–foundation complex. This study was based on elastic and plastic analyses of shallow rigid foundations assuming a Winkler soil type including the flexibility of the foundation in the elastic range and the nature of the soil (cohesive and non-cohesive types) through corrective factors of the constant of the Winkler model. The flexibility of the foundations influences the moment–rotation response through the initial rotational stiffness with a coefficient between 1 and 0.7 for a width-to-span ratio between 5 and 2. The nature of the soil is considered through corrective factors of 0.75 and 1.3 of the Winkler constant for cohesive and non-cohesive soil, respectively. Analyses carried out stressed that a possible design valued to be adopted in a steel wind tower with shallow foundations is a diameter of the steel tube 1/15 of the height of the tower, a diameter of foundation 0.75 of the length, and a depth of foundation 1/10 of the diameter and thickness of steel tower ratio diameter equal to 1/10. In this range it was observed that the effects of the soil-to-foundation interaction in the elastic range influences the critical length in the stability of the steel wind tower, with values between 2.5 and 2 (column fixed at the base) in a range of Winkler constant between 0.1 and 1 daN/cm³. Finally, an experimental validation of the proposed model was carried out with the data available from the literature.

Abstract

This paper presents verification of the numerical model of masonry infill walls against the experimental results. Three cases are investigated: an undamaged model, a damaged model, and a carbon fiber-reinforced polymer (CFRP) strip. ABAQUS commercial finite element model (FEM) software was used in the modeling. Nonlinear behavior as well as cracking and crushing of masonry bricks were simulated using the Concrete Damaged Plasticity (CDP) model. To solve this, a three-dimensional simplified micro-model was used. Experimental and simulation of the hysteresis curve, skeleton curve, damage patterns, maximum and minimum stresses, and plane strain distribution were compared. The changes in natural frequencies, and mode shapes before and after CFRP strengthening masonry wall are evaluated. A sensitivity analysis was done to study the effect of damage and strengthening on the nonlinear behavior of steel frames with masonry infill. This investigation demonstrated that the numerical model was able to effectively simulate and predict the strength of these models. Then a look at the effect on seismic performance is reported and commented on.

This study investigates the behavior of beam–column (B-C) joints made of ultra-high performance concrete (UHPC) under constant axial force and increasing bi-directional bending. Third-scale corner B-C specimens, comprising a UHPC joint, two column segments, and two beams at right angle, were fabricated and tested to failure. The studied parameters were joint type, evaluating two materials UHPC and normal strength concrete (NSC), and spacing of transverse reinforcement in beams and columns. Test results indicated that utilizing UHPC in the joint region instead of conventional NSC results in increasing the ultimate capacity of the joint by 47%, changing the failure mode from brittle shear within the joint to a ductile beam flexure, increasing the joint ductility by 35–70%, and increasing the initial and secant stiffnesses by 27–50% and 57–74%, respectively. Leveraging the results from the study such as utilizing only half the transverse reinforcements required in national codes and removing transverse reinforcement in the joint, UHPC seems a viable option to solving the construction problems associated with NSC joints such as reinforcement congestion and concrete segregation. An analytical investigation is also included and showed the ACI-ASCE 352 code to significantly overpredict the joint shear capacity.

The present study aims to assess the effect of using recycled aggregates (RA) derived from construction and demolition waste (CDW) on the development of the unconfined compressive strength (UCS) of a silty-cement soil from the Guabirotuba Formation, located in the southern region of Brazil. Was considered the influence of various parameters, including RA content, compaction effort, maximum dry specific mass, and porosity/volume cement content (η/Civ). RA contents of 10%, 20%, and 30%, combined with 5% cement by dry soil weight, are studied at curing times of 0, 7, 14, and 28 days, using standard, intermediate, and modified compaction efforts. The results reveal that the addition of RA leads to an increase in the maximum dry specific mass, directly correlating with an increase in the rate of compressive strength gain over time. In the case of the modified compaction effort, the UCS value for the mixture with 30% RA at 28 days of curing reaches 2318 kPa, which is 35% higher compared to the mixture without RA, which has an RCS value of 1711 kPa. Equations establishing a relationship between η/Civ and UCS show that smaller η/Civ values result in greater UCS. Furthermore, a correlation between η/Civ and RA content with UCS suggests that η/Civ has a stronger influence on UCS than RA content. Lastly, Scanning Electron Microscopy (SEM) indicates that incorporating 30% RA reduces the number of pores as well as their size, which enhances the soil structure and its increases stability, resulting in a more compact structure.

The use of recycled concrete aggregate instead of natural coarse aggregate is of great interest from a sustainability perspective. The present study investigates the flexural design of unbonded, post-tensioned, precast recycled concrete beams. It also evaluates the application of unbonded prestressed tendons in recycled concrete beams. Flexural behavior tests were performed on 13 beams with different prestressed reinforcement indices, section heights, and comprehensive reinforcement indices. We thoroughly investigated stress changes in prestressed steel strands, beam failure forms, and crack development during loading. The results demonstrate that under the same load level, the average crack width of recycled concrete beams is 36% higher than that of conventional concrete beams. A theoretical analysis indicates that the factors affecting the stress increment of unbonded prestressed tendons are the comprehensive and prestressed reinforcement indexes. A theoretical model of stress increment during loading of prestressed reinforcement was obtained, allowing derivation of an ultimate bearing capacity formula for unbonded, post-tensioned, precast, recycled concrete beams. An influence coefficient for recycled coarse aggregate is introduced and set to 1.14, the experimental data is fitted to derive the calculation formula for the average crack spacing and width. The theoretical model of the stress increment in prestressed steel strands and the proposed crack width model provide a valuable design reference and theoretical support for engineering applications.

The present research assists in resolving the issues allied with the disposal of industrial solid wastes/industrial by-products (IBPs) by developing sustainable IBPs based cement mortars. The applicability of IBPs as a feasible alternative to river sand in cement mortar has been evaluated by investigating the synergy among the ingredients, resulting engineering properties and microstructural developments at early and late curing ages. The study could effectively substitute 30% volume of river sand with bottom ash and 50% in the case of slag sand mortars. The experimental outcomes disclose that the practice of IBPs as fine aggregate enhances the engineering properties of mortar and the optimum replacement level lies at 10% and 40% usage of bottom ash and slag sand, respectively. The advanced characterization studies and particle packing density illustrate the refinement of pores by void filing action and accumulation of additional hydration products through secondary hydration reactions. The consumption of portlandite followed by increased hydration products formation observed through thermogravimetric analysis, X-ray diffraction analysis and energy dispersive X-ray spectroscopy that confirmed the contribution of finer fractions of IBPs to secondary hydration reactions. This constructive development was also observed from the lowering of wavenumber corresponding to Si–O–Si/Al vibration bands in Fourier transform infrared spectroscopy spectra. The improved microstructure resulted in enhancing the compressive strength by 9.01% and 18.18% in optimized bottom ash and slag sand mortars, respectively at the curing age of 120 days. Similarly, the water absorption reduced by 1.03% and 1.24% in bottom ash and slag sand mortars, respectively.

The microbial induced partial saturation (MIPS) technique is the new environmentally friendly, cost-effective technique applicable under existing structures for mitigating sand liquefaction. The current study investigated the effectiveness of MIPS for mitigating sand liquefaction under undrained static loading. A series of undrained static triaxial tests were conducted to examine the influence of biogenic gas production through microbial denitrification on poorly graded sand at various relative densities. Initial batch experiments revealed that increased nitrate concentrations resulted in a decreased degree of saturation. Loosely and medium-dense saturated samples exhibited positive pore pressure during loading, which was reduced through biological desaturation, resulting in increased undrained shear strength ratios. Dense saturated and desaturated samples produced negative excess pore pressure, decreasing the undrained strength of treated samples due to dilative behavior. The undrained stress–strain behavior of loose and medium-dense sand transitioned from strain softening to strain hardening as the degree of saturation decreased from 100 to 90%. However, dense sand exhibited strain-hardening behavior with decreased saturation from 100 to 95%. Decreasing saturation levels reduced instability susceptibility, resulting in more stable soil behavior and decreasing the potential for large strains and instability. The study demonstrated a reduction in the Liquefaction Potential Index (LPI) for both loose and medium-dense sand as the degree of saturation decreased from 100 to 90%. These findings highlight the potential of MIPS as an effective technique for mitigating sand liquefaction and offer insights into its underlying mechanisms.

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