• Geomechanics and Engineering
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• 제29권1호
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• pp.25-40
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• 2022

In this study, 3D coupled-consolidation numerical parametric study was conducted to predict the deformation mechanism of a 20 storey building sitting on (4×4) piled raft (with length of piles, L_p=30 m) to adjacent 6 m diameter (D) tunnelling in stiff clay. The influences of different tunnel locations relative to piles (i.e., z_t/L_p) were investigated in this parametric study. In first case, the tunnel was excavated near the pile shafts with depth of tunnel axis (z_t) of 9 m (i.e., z_t/L_p). In second and third cases, tunnels were driven at z_t of 30 m and 42 m (i.e., z_t/L_p = 1.0 and 1.4), respectively. An advanced hypoplastic clay model (which is capable of taking small-strain stiffness in account) was adopted to capture soil behaviour. The computed results revealed that tunnelling activity adjacent to a building resting on piled raft caused significant settlement, differential settlement, lateral deflection, angular distortion in the building. In addition, substantial bending moment, shear forces and changes in axial load distribution along pile length were induced. The findings from the parametric study revealed that the building and pile responses significantly influenced by tunnel location relative to pile.

• Steel and Composite Structures
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• 제46권4호
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• pp.471-483
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• 2023

This paper presents an analytical hyperbolic theory based on the refined shear deformation theory for mechanical stability analysis of the simply supported advanced composites plates (exponentially, sigmoidal and power-law graded) under triangular, trapezoidal and uniform uniaxial and biaxial loading. The developed model ensures the boundary condition of the zero transverse stresses at the top and bottom surfaces without using the correction factor as first order shear deformation theory. The mathematical formulation of displacement contains only four unknowns in which the transverse deflection is divided to shear and bending components. The current study includes the effect of the geometric imperfection of the material. The modeling of the micro-void presence in the structure is based on the both true and apparent density formulas in which the porosity will be dense in the mid-plane and zero in the upper and lower surfaces (free surface) according to a logarithmic function. The analytical solutions of the uniaxial and biaxial critical buckling load are determined by solving the differential equilibrium equations of the system with the help of the Navier's method. The correctness and the effectiveness of the proposed HyRPT is confirmed by comparing the results with those found in the open literature which shows the high performance of this model to predict the stability characteristics of the FG structures employed in various fields. Several parametric analyses are performed to extract the most influenced parameters on the mechanical stability of this type of advanced composites plates.

• Structural Engineering and Mechanics
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• 제85권5호
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• pp.679-691
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• 2023

Many codes allow designers to use the bending moment diagram computed by elastic analysis and modify it by a certain amount of moment redistribution (MR) to account for plastic behaviour of continuous beams. However, several researchers indicated that the MR at the ultimate limit state (𝛽_u) for some beams deviate significantly from the specified values of various codes. This paper examines the applicability of the provisions on 𝛽_u in ACI 318-19 and Eurocode 2 through numerical investigations and comprehensively explores the influencing factors. The results show that some parameters not considered in those codes influence 𝛽_u to a certain extent, where the ratio of tensile reinforcement ratio at intermediate support to tensile reinforcement ratio at midspan (𝜌_s1/𝜌_s2) and load type are crucial parameters to consider. The specific combination of these two parameters may make the codes overestimate or significantly underestimate the 𝛽_u. On the other hand, the yield state of both critical sections is found to have an important influence on the influence degree of each parameter on 𝛽_u. The yield conditions are investigated, and an empirical judgment equation is proposed. In addition, the influence laws of the critical parameters on 𝛽_u have been further proved by theoretical derivation. Finally, due to 𝜀_t is found to have a better linear correlation with 𝛽_u than x_u/d, equations as a function of 𝜀_t for predicting the 𝛽_u of continuous beams under the two loads are proposed, respectively.

• Structural Engineering and Mechanics
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• 제84권5호
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• pp.619-632
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• 2022

Reinforced concrete (RC) structures may be subjected to sudden dynamic impact loads such as explosions occurring for different reasons, the collision of masses driven by rockfall, flood, landslide, and avalanche effect structural members, the crash of vehicles to the highway and seaway structures. Many analytical, numerical, and experimental studies focused on the behavior of RC structural elements such as columns, beams, and slabs under sudden dynamic impact loads. However, there is no comprehensive study on the behavior of the RC column-beam connections under the effect of sudden dynamic impact loads. For this purpose, an experimental study was performed to investigate the behavior of RC column-beam connections under the effect of low-velocity impact loads. Sixteen RC beam-column connections with a scale of 1/3 were manufactured and tested under impact load using the drop-weight test setup. The concrete compressive strength, shear reinforcement spacing in the beam, and input impact energy applied to test specimens were taken as experimental variables. The time histories of impact load acting on test specimens, accelerations, and displacements measured from the test specimens were recorded in experiments. Besides, shear and bending crack widths were measured. The effect of experimental variables on the impact behavior of RC beam-column connections has been determined and interpreted in detail. Besides, a finite element model has been established for verification and comparison of the experimental results by using ABAQUS software. It has been demonstrated that concrete strength, shear reinforcement ratio, and impact energy significantly affect the impact behavior of RC column-beam connections.

• Geomechanics and Engineering
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• 제31권5호
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• pp.505-518
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• 2022

This study introduces soil resistance multipliers at locations encompassed by the zone of influence of the helix plate to consider the added lateral resistance provided to the helical pile. The zone of influence of a helix plate is a function of its diameter and serves as a boundary condition for the modified soil resistance springs. The concept is based on implementing p-multipliers as a reduction factor for piles in group action. The application of modified p-y springs in the analysis of helical piles allows for better characterization and understanding of the lateral behavior of helical piles, which will help further the development of design methods. To execute the proposed method, a finite difference program, HPCap (Helical Pile Capacity), was developed by the authors using Matlab. The program computes the deflection, shear force, bending moment, and soil resistance of the helical pile and allows the user to freely input the value of the zone of influence and Ω (a coefficient that affects the value of the p-multiplier). Results from ten full-scale lateral load tests on helical piles embedded at depths of 3.0 m with varying shaft diameters, shaft thicknesses, and helix configurations were analyzed to determine the zone of influence and the magnitude of the p-multipliers. The analysis determined that the value of the p-multipliers is influenced by the ratio between the pile embedment length and the shaft diameter (D_p), the effective helix diameter (D_h-D_p), and the zone of influence. Furthermore, the zone of influence is recommended to be 1.75 times the helix diameter (D_h). Using the numerical analysis method presented in this study, the predicted deflections of the various helical pile cases showed good agreement with the observed field test results.

• Advances in concrete construction
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• 제14권5호
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• pp.299-307
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• 2022

Cement-based matrixes have low tensile strength and negligible ductility. Adding fibres to these matrixes will improve their mechanical properties and make these composites suitable for structural applications. Post-cracking tensile strength of steel fibers-reinforced cementitious composite materials is directly related to the number of transverse fibers passing through the crack width and the pulling-out behavior of each of the fibers. Therefore, the exact recognition of the pullout behavior of single fibers is necessary to understand the uniaxial tensile and bending behavior of steel fiber-reinforced concrete. In this paper, an experimental study has been carried out on the pullout behavior of 3D (steel fibers with totally two hooks at both ends), 4D (steel fibers with a total of four hooks at both ends), and 5D (steel fibers with totally six hooks at both ends) in which the fibers have been located either perpendicular to the crack width or in an inclined manner. The pullout behavior of the mentioned steel fibers at an inclination angle of 0, 15, 30, 45, and 60 degrees and with embedded lengths of 10, 15, 20, 25, and 30 millimetres is studied in order to explore the simultaneous effect of the inclination angle of the fibers relative to the alongside loading and the embedded length of fibers on the pullout response in each case, including the maximal pullout force, the slip of the maximum point of pullout force, pullout energy, fiber rupture, and concrete matrix spalling. The results showed that the maximum pullout energy in 3D, 4D, and 5D steel fibers with different embedded lengths occurs at 0 to 30° inclination angles. In 5D fibers, maximum pullout energy occurs at a 30° angle with a 25 mm embedded length.

• Advances in concrete construction
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• 제15권6호
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• pp.419-430
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• 2023

In this study, the effect of two types of aggregates (fly ash aggregate and shale aggregate) on the density, strength, and durability of preplaced lightweight aggregate concrete (PLWAC) was studied. The results showed that the 7 - 28 days strength of concrete prepared with fly ash aggregates (high water absorption rate) significantly increased, which could attribute to the long-term water release of fly ash aggregates by the refined pore structure. In contrast, the strength increase of concrete prepared with shale aggregates (low water absorption rate) is not apparent. Although PLWAC prepared with fly ash aggregates has a lower density and higher strength (56.8 MPa @ 1600 kg/m³), the chloride diffusion coefficient is relatively high, which could attribute to the diffusion paths established by connected porous aggregates and the negative over-curing effect. Compared to the control group, the partial replacement of fly ash aggregates (30%) with asphalt emulsion (20% solid content) coated aggregates can reduce the chloride diffusion coefficient of concrete by 53.6% while increasing the peak load obtained in a three-point bending test by 107.3%, fracture energy by 30.3% and characteristic length by 103.5%. The improvement in concrete performance could be attributed to the reduction in the water absorption rate of aggregates and increased energy absorption by polymer during crack propagation.

• Steel and Composite Structures
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• 제45권3호
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• pp.437-454
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• 2022

Elliptic-braced simple resisting frame as a new lateral bracing system installed in the middle bay of frame in building facades has been recently introduced. This system not only creates a problem for opening space from the architectural viewpoint but also improves the structural behavior. Despite the researches on the seismic performance of lateral bracing systems, there are few studies performed on the effect of the stiffness parameters on the elastic story drift and calculation of period in simple braced steel frames. To overcome this shortcoming, in this paper, for the first time, an analytical solution is presented for calculating elastic lateral stiffness in a simple steel frame equipped with elliptic brace subjected to lateral load. In addition, for the first time, in this study, a precise formulation has been developed to evaluate the elastic stiffness variation in a steel frame equipped with a two-dimensional single-story single-span elliptic brace using strain energy and Castigliano's theorem. Thus, all the effective factors, including axial and shear loads as well as bending moments of elliptic brace could be considered. At the end of the analysis, the lateral stiffness can be calculated by an improved and innovative relation through the energy method based on the geometrical properties of the employed sections and specification of the used material. Also, an equivalent element of an elliptic brace was presented for the ease of modeling and use in linear designs. Application of the proposed relation have been verified through a variety of examples in OpenSees software. Based on the results, the error percentage between the elastic stiffness derived from the developed equations and the numerical analyses of finite element models was very low and negligible.

• Geomechanics and Engineering
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• 제32권3호
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• pp.245-254
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• 2023

Through qualitative analysis and quantitative analysis, the contradictory conclusions about the stability of the settled goaf with two-layer coal seams subject to building load were obtained. Therefore, it is necessary to combine the additional stress method and numerical simulation to further analyze the foundation stability. Through borehole analysis and empirical formula analogy, the height of water-conducting fracture zone in No.4 coal and No.9 coal were obtained, providing the calculation range of water-conducting fracture zone for numerical simulation. To ensure the accuracy of the elastic modulus of broken gangue, the stress-strain curve were obtained by broken gangue compression test in dried state of No.4 coal seam and in soaking state of No.9 coal seam. To ensure the rationality of the numerical simulation results, the actual measured subsidence data were retrieved by numerical simulation. FISH language was used to analyze the maximum building load on the surface and determine the influence depth of building load on the foundation. The critical building load was 0.16 MPa of No.4 settled goaf and was 1.6 MPa of No.9 settled goaf. The additional stress affected the water-conducting fracture zone obviously, resulted in the subsidence of water-conducting fracture zone was greater than that of bending subsidence zone. In this paper, the additional stress method was analyzed by numerical simulation method, which can provide a new analysis method for the treatment and utilization of the settled goaf.

• Steel and Composite Structures
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• 제47권1호
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• pp.51-69
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• 2023

In tied-arch bridges, a properly designed connection between the arch and the deck may become crucial, since the forces in the structure may be significantly reduced. This implies substantial material savings and, consequently, cheaper constructions. The introduction of the Nielsen cable arrangement (composed of V-shaped inclined hangers) in the last century was a milestone because it was able to reduce deflections and bending moments both in the arch and in the deck. So far, the Nielsen cable arrangement has proven to be successful in traditional vertical arch bridges. However, despite its advantages, it has not been widely applied to spatial arch bridges. Thus, this article analyses the difference between the structural behavior of spatial arch bridges with Nielsen-type cable arrangements with respect to those with classical vertical hanger configurations. The main goal is to verify whether the known effectiveness of the Nielsen cable arrangement for classical arch bridges is still preserved when applied to spatial arch bridges. In order to achieve this objective, and as the first part of our study, a set of different all-steel bridges composed of vertical and inclined arches with straight decks have been compared for both cable arrangements. As a major conclusion, for planar vertical arch bridges, the Nielsen-type cable arrangement is always the most effective. In addition, it also seems that, for spatial arch bridges composed of a straight deck and an inclined arch, it still keeps most of its effectiveness as long as the arch is moderately inclined.