Abstract in English:Abstract The seismic behavior of full-scale exterior reinforced concrete (RC) beam-column joints retrofitted with externally bonded Carbon Fiber Polymers (CFRP) is examined in this paper. Casting and testing of two similar reinforced concrete beam column connections in the absence of transverse reinforcement at the joints took place under opposing cyclic loading with regulated displacement so as to examine their fundamental seismic performance. The first joint was examined as the control specimen and the other specimen was then retrofitted with CFRP sheets, with rounded border of the column and beam at and close to the joint region to change them from square to squircle segments. It is demonstrated in the experimental findings that the retrofitted beam column joint shows significantly greater strength, energy dissipation and ductility in comparison to the control specimen. There was a shift in the failure from the joint region to the beam ends in the retrofitted specimens, which would help in preventing the structure from disintegrating progressively. Because of the change in the beam and column from square to squircle segments, the debonding potential of the CFRP decreased and the restrictive impact of the CFRP increased. As a result, the experimental findings were verified using a 3D nonlinear finite element (FE) model. When the finite element and experimental findings are compared, it is determined that the suggested model is quite accurate.
Abstract in English:Abstract The present investigation is concerned with the dynamic seismic response of subway station built in loess site by a series of shaking table tests. Firstly, according to the Bockingham π theorem, the scale ratio is determined and then the model system is designed. Then, based on the geological environment and seismological background of Xi’an, the input ground motions and loading scheme are determined. On the basis of the test data, the acceleration responses of model system, strain response characteristics of the structure, distribution of dynamic soil pressure between loess and structure, the settlement of model ground and the seismic damage mode of model system are analyzed systematically. The results show that the peak accelerations in model soil increase gradually from the bottom to the top of the soil. The peak tensile strains measured at the top and bottom of the center columns are larger than those obtained at the side walls, while the peak tensile strains in the floor slab are the smallest. Moreover, the relationship between structure uplift and soil pressure difference can be fitted by exponential function.
Abstract in English:Abstract The existence of holes in rock is one of the key factors for the instability of underground rock mass engineering. Combined with acoustic emission equipment, uniaxial compression tests of rock specimens with different numbers of holes in the rock were carried out. The results show that with the number of holes increases, the value of peak strength and elastic modulus of the rock decrease. The acoustic emission (AE) counts gone through stable, slow increase, a sudden increase and towards zero four stages and there are corresponding to the initial compaction stage, elastic stages, strain hardening stage and post-peak strain softening stage of the stress-strain curves approximately. Based on the AE events, damage variables of rocks were obtained. The damage evolution process of rock can also be divided into three parts, including stable damage stage, slowly increasing damage stage and sharply increasing damage stage. According to Duncan model, the damage variable is introduced to obtain the rock damage constitutive model. No matter it is the pre-peak initial compaction stage, the linear elasticity stage, the strain hardening stage or the post-peak strain softening stage, the fitting curves are in good agreement with the test curves. It also illustrates the rationality of the damage constitutive model.
Abstract in English:Abstract The effectiveness of seismic dampers to improve the lateral performance of timber structures may be heavily diminished if restrictive lateral drift limits as set by building codes, governs the design of the structure. This paper presents an innovative approach to improve the performance of seismic dampers installed in stiff wood-frame shear walls. U-Shape Flexural Plate dampers with a novel internal restraint system, were installed in a 4880x2475 mm wood-frame shear wall with an Eccentric Lever-Arm System which aimed at amplifying the displacements by transferring them from the shear wall to the dampers. Cyclic tests were conducted to four specimens. Initial test results showed that the presented amplifying system suffered concentrated losses of stiffness at some connections joints reducing its real efficiency. The loss of displacement transmission to dampers was retrofitted, and the results showed a great benefit in terms of resilience for the damped shear wall in contrast with unprotected ones. It was found that this approach provides a feasible solution to enhance the lateral performance of wood-frame structures.
Abstract in English:Abstract In this research, the multilayered composite plates made of glass/epoxy material were experimentally and numerically investigated under compressive loading conditions. The intact and defected structures were analyzed with the use of finite element method. The influence of the thickness and geometrical imperfection level were carried out in the linear buckling analysis. The nonlinear analysis was performed to determine the influence of the delamination length on the buckling behavior of the plate. The numerical results were validated by experiments. Experimental tests were performed for structures having artificial delamination between laminate layers. The buckling behavior was monitored using the nondestructive and noncontact structural vision-based health monitoring system (the digital image correlation (DIC)). The influence of the different delamination behavior during the tests on the compressive load capacity was determined by a detailed analysis of DIC measurements. The 20% reduction of the compressive load was noticed in the cases with local buckling of delamination.
Abstract in English:Abstract Unlike the classical truss model, the constitutive equation of the gradient truss model (GTM) earlier presented by the author introduces higher order strain gradient terms and a characteristic internal length parameter: Thus, considering the interaction between macroscopic and microscopic length scales in the constitutive response. Extra non-classical boundary conditions are required to solve the governing equation. In this paper, the microstructure of a material is defined in a simple manner by representing three typical underlying phenomena based on the spatial variation of strain and three combinations of extra non-classical boundary conditions of the derivative of displacement (strain) and higher order derivative of displacement (strain gradient) imposed at the bar support. To quantify the imposed strain gradient at the bar support, a simple relation is derived. Consequently, the influence of strain, strain gradient and the characteristic internal length parameter at the microstructure during deformation is readily captured and the three underlying phenomena qualitatively modelled by the three GTM bar elements. In addition, strengthening and weakening mechanisms in deformation are revealed. Numerical examples are presented as illustration.
Abstract in English:Abstract Short-time Fourier transformation (STFT) has been widely recognized as an intuitive time-frequency analysis method. However, its application in building structures is constrained by its low accuracy of low-frequency recognition in short data. Accordingly, an all-phase chirp-z transformation (AP-CZT) proposed for frequency recognition in building structures. Specifically, the autoregressive (AR) model, which has a proposed order determination algorithm, is used to solve the problem of data length limitation in the all-phase data process. Subsequently, an algorithm based on absolute inverse proportional function (AIP) is developed for post-refinement frequency correction. To verify its actual application, the ap-CZT method is used to analyze simulating finite element model and white noise feedback data from the actual shake table. The ap-CZT method is proven to be capable of correctly finding high-order frequencies. Moreover, it can accurately identify signal frequencies in short data. Therefore, the ap-CZT method can be applied as a frequency identification method in STFT in the field of building structures.
Abstract in English:Abstract Composite alveolar beams consist in the union of two structural systems largely employed in civil construction sector: the steel-concrete composite beams and the alveolar steel beams. Thus, its use allows their advantages to be enhanced, enabling to design even larger spans and to achieve more economical and sustainable solutions. Considering that Brazilian and international standards do not directly specify criteria for the analysis and design of these beams, in this paper it is presented the development and validation of an updated finite element model, using ANSYS software, capable of simulating different failure modes that may occur, such as web-post buckling, Vierendeel mechanism and flexural mechanism. The obtained results presented a good correlation with experimental results from previous works. After the model validation, the effect of the openings on the composite beam was investigated and discussed, and it was concluded that the web-post buckling may limit the structural gains on load capacity, so it is important to adopt opening patterns that enhance the resistance of the beam to this mode of failure.
Abstract in English:Abstract The effectiveness of magnesium (Mg) alloys to improve the capability of bone tissue generation may be severely diminished if the required mechanical properties are not provided. Here, the effort is directed to model the mechanical performance of severely plastically deformed biodegradable ZK60 Mg alloy in bone regeneration protocols. For this purpose, the effects of parallel tubular channel angular pressing (PTCAP) on yield strength (σ YS ), ultimate tensile strength (σ UTS ), and elongation to failure (δ) were addressed. Given the multifaceted variables of the PTCAP with nonlinear interactions, a precise determination of the mechanical properties requires a large number of experiments. Therefore, gene expression programming (GEP) and genetic programming (GP) models were proposed to achieve appropriate combinations of mechanical properties for bone implant purposes based on a rational hypothesis that for correlation coefficient (|R|) higher than 0.8, a strong correlation is established between the predicted and measured values. The results verified that the highest mechanical performance was achieved at the second pass of PTCAP, thus has a great potential to be the most promising candidate for biodegradable implant material. Besides, the proposed models were capable of precisely predicting the mechanical performance of the SPD-processed biodegradable ZK60 Mg.
Abstract in English:Abstract With the rapid development of China's economy, many long-span bridges have been built and put into service. Vehicle load has been changing year by year in terms of the gross vehicle weight (GVW), the wheelbase and the traffic volume, especially the overload of heavy vehicles, which is a major challenge to the safety and durability of bridges. It is necessary to establish the vehicle load model through the measured traffic data for actual traffic conditions of the given bridge. In this study, the weigh-in-motion (WIM) data collected from an operational long-span urban highway bridge located in Wuhan, China, were used to analyze the statistical characteristics of vehicle loads. On the basis of the types of vehicles, (1) Considering the double or multimodal Gauss distribution characteristics of the GVW, the expectation maximization (EM) algorithm was used to estimate the statistical parameters of the Gauss distribution; (2) The generalized extreme value distribution (GEV) was used to develop the statistical model of the vehicle load extreme value; (3) The vehicle load extreme values in the design reference period of the urban highway bridge were estimated by the extreme value type I distribution; (4) According to the axle weight and the axle spacing, a statistical fatigue vehicle load model for the small and medium span urban highway bridges located in Wuhan, China was presented based on the Miner linear accumulated damage hypothesis and the effective fatigue damage principle.