Journal of Science and Technology in Civil Engineering (JSTCE) - HUCE

Lightweight expanded polystyrene concrete (EPS-C) offers several advantages, including low density, sound resistance, and good thermal insulation. These characteristics are contributed by the use of expanded polystyrene (EPS) with a closed cellular structure, which is non-absorbent, hydrophobic, and low-density (around 6.9 kg/m³). Since EPS is much lighter than cement paste, the viscosity of the paste plays an important role indirectly affecting segregation and the properties of EPS-C mixtures. This paper presents the experimental results of the viscosity and its influence of cement paste on both the segregation of the concrete mixture and thecompressive strength of EPS-C. The research revealed that a viscosity of cement paste below 50 mPa.s resultsin segregation of the concrete mixture. As the viscosity increases, the degree of segregation decreases. However, when the viscosity exceeds 180 mPa.s, using a viscosity-modifying admixture becomes a good solution to prevent segregation in EPS-C mixtures. Therefore, the optimal viscosity range for the binder paste to ensure the concrete mixture does not segregate is between 50 and 180 mPa.s.

The dependence of load-carrying capacity on span length of beams, which contained a combination of normal strength concrete (NC) - High-performance fiber-reinforced concrete (HPFRC), was investigated in this study. The used HPFRC contained 1.0 vol.% long hooked blended with 0.5% short smooth fibers. Two types of span length were designed as 300 mm and 450 mm while dimensions of beam sections were identical with depth × width of 150 × 150 mm2. Each span included five types of partial structural materials as follows: Short 1 and Long 1 had no reinforcement with full of section using HPFRC, Short 2 and Long 2 had reinforcements with a full of section using HPFRC, Short 3 and Long 3 had reinforcements with a half of section using HPFRC at beam bottom, Short 4 and Long 4 had reinforcements with a third of section using HPFRC at beam bottom, Short 5 and Long 5 had reinforcements with a half of section using HPFRC at beam top. All beams were tested under three-point bending test. The shorter beam generally exhibited the greater load-carrying capacity than the long beam using same section type. The shear failure mode was dominant in case of the span/depth ratio less than 3. The HPFRC located at bottom of beam created the more effectiveness for enhancement of load-carrying capacity and stiffness of the beam, in comparison with the HPFRC placed at top of beam. The most effective zone of beam for HPFRC strengthening was at extreme tension fiber. Keywords: high-performance; composite beam; shear failure; bending resistance; load-carrying capacity.

This research deals with the influences of macro, meso and micro steel-smooth fibers on tensile and compressive properties of strain-hardening fiber-reinforced concretes (SFCs). The different sizes, indicated by length/diameter ratio, of steel-smooth fiber added in plain matrix (Pl) were as follows: 30/0.3 for the macro (Ma), 19/0.2 for the meso (Me) and 13/0.2 for the micro fiber (Mi). All SFCs were used the same fiber volume fraction of 1.5%. The compressive specimen was cylinder-shaped with diameter × height of 150 × 200 mm, the tensile specimen was bell-shaped with effective dimensions of 25 × 50 × 100 mm (thickness × width × gauge length). Although the adding fibers in plain matrix of SFCs produced the tensile strain-hardening behaviors accompanied by multiple micro-cracks, the significances in enhancing different mechanical properties of the SFCs were different. Firstly, under both tension and compression, the macro fibers produced the best performance in terms of strength, strain capacity and toughness whereas the micro produced the worst of them. Secondly, the adding fibers in plain matrix produced more favorable influences on tensile properties than compressive properties. Thirdly, the most sensitive parameter was observed to be the tensile toughness. Finally, the correlation between tensile strength and compressive strength of the studied SFCs were also reported. Keywords: aspect ratio; strain-hardening; post-cracking; ductility; fiber size.

Bài báo giới thiệu một cách tiếp cận số cho bài toán tối ưu trọng lượng dầm FGM với ràng buộc về tần số dao động riêng. Phương pháp phần tử hữu hạn dựa trên lý thuyết biến dạng trượt bậc nhất được áp dụng để phân tích dao động riêng của dầm. Luật phân bố bốn tham số và năm tham số được sử dụng để mô tả phân bố thể tích của các vật liệu thành phần trong dầm theo phương chiều cao dầm. Mục tiêu là tối ưu chiều cao dầm và phân bố vật liệu trong dầm để dầm đạt trọng lượng tối thiểu trong khi đảm bảo tần số dao động riêng cơ bản lớn hơn một giá trị cho trước. Một thuật giải tiến hóa vi phân cải tiến được xây dựng nhằm giải hiệu quả bài toán tối ưu có ràng buộc trên. Hiệu quả của phương pháp đề xuất được minh họa thông qua hai ví dụ số.

Optimization of steel moment frames has been widely studied in the literature without considering shear deformation of panel-zones which is well-known to decrease the load-carrying capacity and increase the drift of structures. In this paper, a robust method for optimizing steel moment frames is developed in which the panel-zone design is considered by using doubler plates. The objective function is the total cost of beams, columns, and panel-zone reinforcement. The strength and serviceability constraints are evaluated by using a direct design method to capture the nonlinear inelastic behaviors of the structure. An adaptive differential evolution algorithm is developed for this optimization problem. The new algorithm is featured by a self-adaptive mutation strategy based on the p-best method to enhance the balance between global and local searches. A five-bay five-story steel moment frame subjected to several load combinations is studied to demonstrate the efficiency of the proposed method. The numerical results also show that panel-zone design should be included in the optimization process to yield more reasonable optimum designs. Keywords: direct design; differential evolution; optimization; panel-zone; steel frame.

Timely monitoring the large-scale civil structure is a tedious task demanding expert experience and significant economic resources. Towards a smart monitoring system, this study proposes a hybrid deep learning algorithm aiming for structural damage detection tasks, which not only reduces required resources, including computational complexity, data storage but also has the capability to deal with different damage levels. The technique combines the ability to capture local connectivity of Convolution Neural Network and the well-known performance in accounting for long-term dependencies of Long-Short Term Memory network, into a single end-to-end architecture using directly raw acceleration time-series without requiring any signal preprocessing step. The proposed approach is applied to a series of experimentally measured vibration data from a three-story frame and successful in providing accurate damage identification results. Furthermore, parametric studies are carried out to demonstrate the robustness of this hybrid deep learning method when facing data corrupted by random noises, which is unavoidable in reality. Keywords: structural damage detection; deep learning algorithm; vibration; sensor; signal processing.

In this paper, free vibration of a functionally graded material (FGM) beam is investigated based on the Timoshenko beam theory and dynamic stiffness method. Material properties vary continuously throughout the thickness direction according to the volume fraction constituent defined by power law function. First, a consistent theory of vibration is established for FGM Timoshenko beam taking into account the actual position of neutral axis that is a useful tool for analysis of coupled vibration in the beam. Then, frequency equation obtained provides an efficient method for free vibration analysis of FGM Timoshenko beam. The theoretical development has been illustrated and validated by numerical examples. Keywords: FGM; timoshenko beam; natural frequency; dynamic stiffness method; Received: July 21th, 2016, revised: August 4th, 2016, accepted: October 13th, 2016

This work aims at investigating the effect of aleatoric uncertainty of creep rock properties on the stability of an underground structure. This uncertainty relates to the spatial variability of the mechanical parameters representing the time-dependent behavior of geological rock formation due to the change in its mineralogy. The chosen methodology consists of representing the aleatoric uncertainty of rock properties by random fields, written as correlation functions with respect to the spatial correlation length. The adaptation of the well-known Expansion Optimal Linear Estimationmethod (EOLE) is performed to account for the cross-correlation of the random fields of the viscoplastic parameters of the host rock. Then, the Kriging-based reliability analysis is undertaken with respect to the discretized random fields, which allows elucidating the effect of spatial variability. As an application, the proposed approach is chosen to study the stability in the long-term of a deep double-lined drift within the geological disposal facilities (Cigeo project) conducted by the French National Radioactive Waste Management Agency (Andra). The drift will be excavated in Callovo-Oxfordian (COx) claystone (if the Cigeo project is licensed), considered as a potential host rock for the deep geological nuclear waste disposal in France. The results show that the chosen Kriging metamodel for the reliability analysis can be appropriate for the case of high correlation length represented by a moderate number of random variables (up to about 50) after the discretization of random fields. Further, the consideration of aleatoric uncertainty exhibits a lower probability of exceedance in comparison with the case where spatial variability is ignored. Still, more investigations need to be conducted in the future to conclude this observation.

This study investigated the mechanical properties of high-performance concrete using notched specimens. Allflexural specimens had an identical geometry of 40×40×160 mm3 with a span length of 120 mm. Four notchto-depth ratios were as follows: 0 (N0 series), 0.125 (N1 series), 0.250 (N2 series), and 0.375 (N3 series), whichwere designed at the specimen bottom of midspan section. The investigation focused on the four parametersof high-performance concrete, including load carrying, deflection capacity, flexural strength, and the criticalstress intensity factor. The results showed that the load-carrying and deflection capacities decrease with anincrease in the notch-to-depth ratios. Furthermore, the flexural strength was ranked as follows: N0 series > N3series > N2 series > N1 series, whereas ranking of the regarding critical stress intensity factor was opposite:N1 series > N2 series > N3 series.

This study deals with the effect of fiber content on fracture parameters of high-performance steel-fiber-reinforced concretes through a bending test program. All the high-performance steel-fiber-reinforced concretes flexural specimens were tested under configuration of three-point loading. The fracture parameters were hardening energy, softening energy and length of cohesive crack. Two steel fiber types were employed in the studied high-performance steel-fiber-reinforced concretes, including 35 mm long hooked fiber and 13 mm short smooth fiber. The high-performance steel-fiber-reinforced concretes were produced from the same matrix but added different fiber contents as follows: 0.0 vol.%, 0.5 vol.%, 1.0 vol.%, and 1.5 vol.%. The experimental resultsdemonstrated that two parameters, including the hardening energy and softening energy, were observed to increase with increasing of fiber content, regardless of fiber type. The hardening energy was lower than thesoftening energy at any fiber content. The short smooth fibers generally produced the higher fracture energyparameters than the long hooked fibers. The highest total fracture energies of the high-performance steel-fiber-reinforced concretes were observed at 1.0 vol.% as follows: 58.25 kJ/m2 for using short smooth and 59.16 kJ/m2 for using long hooked fibers. Besides, the addition of reinforcing fibers considerably improved the length of the cohesive crack of the high-performance steel-fiber-reinforced concretes: from 0.58 mm using no fiber to 519.85 mm using short smooth fibers 0.5 vol.%.