• Wind and Structures
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• v.38 no.3
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• pp.215-229
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• 2024

Guyed mast structures exhibit characteristics such as high flexibility, low mass, small damping ratio, and large aspect ratio, leading to a complex wind-induced vibration response mechanism. This study analyzed the time- and frequency-domain characteristics of the wind-induced response of a guyed mast structure using measured acceleration response data obtained from the Shenzhen Meteorological Gradient Tower (SZMGT). Firstly, 734 sets of 1-hour acceleration samples measured from 0:00 October 1, 2021, to 0:00 November 1, 2021, were selected to study the vibration shapes of the mast and the characteristics of the generalized extreme value (GEV) distribution. Secondly, six sets of typical samples with different vibration intensities were further selected to explore the Gaussian property and modal parameter characteristics of the mast. Finally, the modal parameters of the SZMGT are identified and the identification results are verified by finite element analysis. The findings revealed that the guyed mast vibration shape exhibits remarkable diversity, which increases nonlinearly along the height in most cases and reaches a maximum at the top of the tower. Moreover, the GEV distribution characteristics of the 734 sets of samples are closer to the Weibull distribution. The probability distribution of the structural wind vibration response under strong wind is in good agreement with the Gaussian distribution. The structural response of the mast under wind loading exhibits multiple modes. As the structural response escalates, the first three orders of modal energy in the tower display a gradual increase in proportion.

• Geomechanics and Engineering
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• v.36 no.6
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• pp.575-587
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• 2024

The contact pressure between the surrounding rock and the support is an important indicator of the surrounding rock pressure. There has been a bottleneck in the prediction of contact loads between surrounding rock and primary support in deep-buried mountain tunnels. The main reason is that a reliable method wasn't existed to quantify the contact loads. This study had been taken into account the flexible support role of the primary support, and the fitting curve of surrounding rock deformation for dynamic tunnel construction was proposed. New formulas for the calculation of contact loads between surrounding rock and primary support were obtained by inversion. Comparative analysis of the calculation results with numerical simulation verified the reliability of the calculation method in this study. It can be seen from the analyses that the contact load between surrounding rock and primary support increases, remains unchanged and decreases during acceleration, uniform velocity and deceleration, respectively, and the deformation of the surrounding rock in the acceleration and deceleration stages cannot completely converted into contact loads. The contact loads between surrounding rock and primary support of medium-strength and weak surrounding rock tunnels are generally within 150 kPa and 1 MPa, respectively. For tunnels with weak surrounding rock, advanced support can be installed to reduce the unique release coefficient λ₀ and the value of the constant D, with the purpose of reducing the contact loads between surrounding rock and primary support. Changes in support parameters have a small effect on the contact loads between surrounding rock and primary support, but increase or decrease the safety factor, resulting in a waste of resources or a situation that threatens the safety of the support. The results of this research provide guidance for the prediction of contact loads between surrounding rock and primary support for dynamic tunnel construction.

• Geomechanics and Engineering
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• v.36 no.5
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• pp.417-426
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• 2024

Shield tunneling method is widely used to build tunnels in complex geological environment. Stability control of tunnel face is the key to the safety of projects. To improve the excavation efficiency or perform equipment maintenance, the excavation chamber sometimes is not fully filled with support medium, which can reduce the load and increase tunneling speed while easily lead to ground collapse. Due to the high risk of the face failure under non-fully support mode, the tunnel face stability should be carefully evaluated. Whether compressive air is required for compensation and how much air pressure should be provided need to be determined accurately. Based on the upper bound theorem of limit analysis, a non-fully support rotational failure model is developed in this study. The failure mechanism of the model is verified by numerical simulation. It shows that increasing the density of supporting medium could significantly improve the stability of tunnel face while the increase of tunnel diameter would be unfavorable for the face stability. The critical support ratio is used to evaluate the face failure under the nonfully support mode, which could be an important index to determine whether the specific unsupported height could be allowed during shield tunneling. To avoid of face failure under the non-fully support mode, several charts are provided for the assessment of compressed air pressure, which could help engineers to determine the required air pressure for face stability.

• Advances in nano research
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• v.16 no.3
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• pp.289-301
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• 2024

In this work, an analytical model employing a new higher-order shear deformation beam theory is utilized to investigate the bending behavior of axially randomly oriented functionally graded carbon nanotubes reinforced composite nanobeams. A modified continuum nonlocal strain gradient theory is employed to incorporate both microstructural effects and geometric nano-scale length scales. The extended rule of mixture, along with molecular dynamics simulations, is used to assess the equivalent mechanical properties of functionally graded carbon nanotubes reinforced composite (FG-CNTRC) beams. Carbon nanotube reinforcements are randomly distributed axially along the length of the beam. The equilibrium equations, accompanied by nonclassical boundary conditions, are formulated, and Navier's procedure is used to solve the resulting differential equation, yielding the response of the nanobeam under various mechanical loadings, including uniform, linear, and sinusoidal loads. Numerical analysis is conducted to examine the influence of inhomogeneity parameters, geometric parameters, types of loading, as well as nonlocal and length scale parameters on the deflections and stresses of axially functionally graded carbon nanotubes reinforced composite (AFG CNTRC) nanobeams. The results indicate that, in contrast to the nonlocal parameter, the beam stiffness is increased by both the CNTs volume fraction and the length-scale parameter. The presented model is applicable for designing and analyzing microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) constructed from carbon nanotubes reinforced composite nanobeams.

• Geomechanics and Engineering
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• v.36 no.6
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• pp.545-561
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• 2024

Piled raft foundation has become widely used in the recent years because it can increase bearing capacity of foundation with control settlement. The design for a piled raft in terms vertical load and lateral load need to understands contribution load behavior to raft and pile in piled raft foundation system. The load-bearing behavior of the piled raft, especially concerning lateral loads, is highly complex and challenge to analyze. The complex mechanism of piled rafts can be clarified by using three dimensional (3-D) Finite Element Method (FEM). Therefore, this paper focuses on free-standing head pile group, on-ground piled raft, and embedded raft for the piled raft foundation systems. The lateral resistant of piled raft foundation was investigated in terms of relationship between vertical load, lateral load and displacement, as well as the lateral load sharing of the raft. The results show that both vertical load and raft position significantly impact the lateral load capacity of the piled raft, especially when the vertical load increases and the raft embeds into the soil. On the same condition of vertical settlement and lateral displacement, piled raft experiences a substantial demonstrates a higher capacity for lateral load sharing compared to the on-ground raft. Ultimately, regarding design considerations, the piled raft can reliably support lateral loads while exhibiting behavior within the elastic range, in which it is safe to use.

• Structural Engineering and Mechanics
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• v.89 no.6
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• pp.589-599
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• 2024

This study presents the usability of the high-rate single-frequency Precise Point Positioning (SF-PPP) technique based on 20 Hz Global Positioning Systems (GPS)-only observations in detecting dynamic motions. SF-PPP solutions were obtained from post-mission and real-time GNSS corrections. These include the International GNSS Service (IGS)-Final, IGS real-time (RT), real-time MADOCA (Multi-GNSS Advanced Demonstration tool for Orbit and Clock Analysis), and real-time products from the Australian/New Zealand satellite-based augmentation systems (SBAS, known as SouthPAN). SF-PPP results were compared with LVDT (Linear Variable Differential Transformer) sensor and single-frequency relative positioning (SF-RP) solutions. The findings show that the SF-PPP technique successfully detects the harmonic motions, and the real-time products-based PPP solutions were as accurate as the final post-mission products. In the frequency domain, all GNSS-based methods evaluated in this contribution correctly detect the dominant frequency of short-term harmonic oscillations, while the differences in the amplitude values corresponding to the peak frequency do not exceed 1.1 mm. However, evaluations in the time domain show that SF-PPP needs high-pass filtering to detect accurate displacement since SF-PPP solutions include trends and low-frequency fluctuations, mainly due to atmospheric effects. Findings obtained in the time domain indicate that final, real-time, and MADOCA-based PPP results capture short-term dynamic behaviors with an accuracy ranging from 3.4 mm to 8.5 mm, and SBAS-based PPP solutions have several times higher RMSE values compared to other methods. However, after high-pass filtering, the accuracies obtained from PPP methods decreased to a few mm. The outcomes demonstrate the potential of the high-rate SF-PPP method to reliably monitor structural and earthquake-induced ground motions and vibration frequencies of structures.

• Steel and Composite Structures
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• v.50 no.6
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• pp.675-688
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• 2024

Cold-formed steel (CFS) is prone to buckling failure under loading. Lightweight concrete (LC) made of lightweight aggregate has light weight and excellent thermal insulation performance. However, concrete is brittle in nature which is why different materials have been used to improve this inherent behavior of concrete. The distortional buckling (DB) performance of cold-formed steel-lightweight concrete (CFS-LC) composite columns was investigated in this paper. Firstly, the compressive strength test of foam concrete (FC) and ceramsite concrete (CC) was carried out. The performance of the CFS-LC members was investigated. The test results indicated that the concrete-filled can effectively control the DB of the members. Secondly, finite element (FE) models of each test specimen were developed and validated with the experimental tests followed by extensive parametric studies using numerical analysis based on the validated FE models. The results show that the thickness of the steel and the strength of the concrete-filled were the main factors on the DB and bearing capacity of the members. Finally, the bearing capacity of the test specimens was calculated by using current codes. The results showed that the design results of the AIJ-1997 specification were closer to the experimental and FE values, while other results of specifications were conservative.

• Steel and Composite Structures
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• v.50 no.6
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• pp.627-641
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• 2024

This paper presents an experimental and numerical study to investigate the behavior of the precast segmental concrete beams (PSCBs) utilizing high-strength concrete (HSC) connected in the zone of the maximum bending moment using steel extended endplate connections (EECs). The experimental study consisted of five beams as follows: The first beam was the control beam for comparison, which was an unconnected one-piece beam made of HSC. The other four other beams consisted of two identical pieces of precast concrete. An important point to be noted is that at the end of each piece, a steel plate was used with a thickness of 10 mm. Moreover, this steel plate was welded to the lower and upper reinforcing bars of the beam. Furthermore, the steel plate was made to connect the two pieces using the technique of EECs. Several variables were taken in these four beams, whether from the shape of the connection or enhancing the behavior of the connection using the post-tensioning technique. EECs without stiffeners were used for some of the tested beams. The behavior of these connections was improved using stiffeners and shear bolts. To get accurate results, a comparison was made between the behaviors of the five beams. Another important point to be noted is that Abaqus and SAP2000 programs were used to investigate the behavior of PSCBs and to ensure the accuracy of the modeling process which showed a good agreement with the experimental results. Additionally, the simplified modeling using SAP2000 was able to model the nonlinear behavior of PSCBs connected using steel EECs. It was found that the steel pre-tensioned bolted EECs, reinforced with steel stiffeners and shear anchors, could be used to connect the precast HSC segmental beams via the internal pre-stressing technique.

• Structural Engineering and Mechanics
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• v.90 no.3
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• pp.219-232
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• 2024

In current study, for the first time, Nonlinear Bending of a skew microplate made of a laminated composite strengthened with graphene nanosheets is investigated. A mixture of mechanical and thermal stresses is applied to the plate, and the reaction is analyzed using the First Shear Deformation Theory (FSDT). Since different percentages of graphene sheets are included in the multilayer structure of the composite, the characteristics of the composite are functionally graded throughout its thickness. Halpin-Tsai models are used to characterize mechanical qualities, whereas Schapery models are used to characterize thermal properties. The microplate's non-linear strain is first calculated by calculating the plate shear deformation and using the Green-Lagrange tensor and von Karman assumptions. Then the elements of the Couple and Cauchy stress tensors using the Modified Coupled Stress Theory (MCST) are derived. Next, using the Hamilton Principle, the microplate's governing equations and associated boundary conditions are calculated. The nonlinear differential equations are linearized by utilizing auxiliary variables in the nonlinear solution by applying the Frechet approach. The linearized equations are rectified via an iterative loop to precisely solve the problem. For this, the Differential Quadrature Method (DQM) is utilized, and the outcomes are shown for the basic support boundary condition. To ascertain the maximum values of microplate deflection for a range of circumstances-such as skew angles, volume fractions, configurations, temperatures, and length scales-a parametric analysis is carried out. To shed light on how the microplate behaves in these various circumstances, the resulting results are analyzed.

• Advances in materials Research
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• v.13 no.3
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• pp.161-171
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• 2024

This study aimed to investigate the effect of physicochemical properties and mix ratios of iron ore (oxide feed): coke (reductant) on the carbothermic reductions of iron ore. Coke size was fixed at ≤63 ㎛ while iron ore size varied between 150-63 ㎛ and ≤63 ㎛ respectively. Mix ratios were changed from 100:0 (reference) to 80:20 and 60:40 while the temperature, heating rate and soaking duration in muffle furnace were fixed at 1100 ℃, 10 ℃/min and 1 hour. Particle size analyzer, XRF, CHNS and XRD analyses were used for determination of raw feed characteristics. The occurrence of phase transformations from various forms of iron oxides to iron during the carbothermal reductions were identified through XRD profiles and supported with weight loss (%). XRF analysis proved that iron ore is of high grade with 93.4% of Fe₂O₃ content. Other oxides present in minor amounts are 2% Al₂O₃ and 1.8% SiO₂ with negligible amounts of other compounds such as MnO, K₂O and CuO. Composite pellet with finer size iron particles (≤63 ㎛) and higher carbon content of 60:40 exhibited 45.13% weight lost compared to 32.30% and 3.88% respectively for 80:20 and 100:0 ratios. It is evident that reduction reactions can only occur with the presence of coke, the carbon supply. The small weight loss of 3.88% at 100:0 ratio occurs due to the removal of moisture and volatiles and oxidations of iron ore. Higher carbon supply at 60:40 leads into better heat and mass transfer and diffusivity during carbothermic reductions. Overall, finer particle size and higher carbon supply improves reactivity and gas-solid interactions resulting in increased reductions and phase transformations.