Kinetics of Damage of Materials under Various Regimes of Re-Changeable Loads

Kinetics of accumulation of damages in engineering objects, which work at repeated-alternating soft and hard modes of loading of details and elements of constructions of vehicles (cars, cars, railway transport, etc.). When changing the direction of the load force to the opposite in the structural material there is a phenomenon of changing the kinetics of accumulation of damage, ie the damage factor at separation and shear changes, which affects the effective stresses and service life of equipment. This effect of the factor of the influence of repeated variables on the redistribution of the kinetics of damage accumulation is considered experimentally for materials with different plastic properties

Seismic Fragility Assessment of RC Plan-Asymmetric Wall-Frame Structures Based on the Enhanced Damage Model

The seismic response of reinforced concrete (RC) plan-asymmetric structures is significantly influenced by the input angle of seismic ground motions. Hence, it is challenging to assess the performance of plan-asymmetric structures. In this study, the classic probabilistic seismic fragility assessment method is used to assess RC plan-asymmetric wall-frame structures based on the enhanced damage model. First, the worst-case input angle of seismic ground motions for plan-asymmetric structures is identified using the wavelet transforms coefficient method, considering the coupling of bidirectional seismic ground motions. Accordingly, the maximum deformation and hysteretic energy dissipation can be determined. Then, an enhanced damage model, which is based on the combination of deformation and hysteretic energy dissipation, is used to identify floor damage factor. Note that the importance coefficients of structural components are considered in the identification. Meanwhile, the incremental dynamic analysis (IDA) is conducted to create the fragility curves by assuming floor damage factor as seismic performance index. In particular, the randomness of the threshold for floor damage factor is considered during the assessment. Afterwards, numerical simulations are employed to verify the fragility assessment method. Results show that the wavelet transforms coefficient method can evaluate the worst-case input angles with low time-consuming and high efficiency. Meanwhile, the story damage factors confirmed that the proposed damage model could accurately assess the structure during the failure process. Moreover, the typical failure modes of the RC wall-frame structure, which significantly depend on the story damage distribution, can be defined using the enhanced damage model. Note that the randomness of the threshold could significantly affect the probability of exceedance, which is important for fragility analysis.

Numerical Simulation of Steel-Reinforced Reactive Powder Concrete Beam Based on Bond-Slip

In this study, based on the concrete damaged plasticity (CDP) model in the ABAQUS software, various plastic damage factor calculation methods were introduced to obtain CDP parameters suitable for reactive powder concrete (RPC) materials. Combined with the existing tests for the bending performance of steel-reinforced RPC beams, the CDP parameters of the RPC material were input into ABAQUS to establish a finite element model considering the bond and slip between the steel and RPC for numerical simulation. The load-deflection curve obtained by the simulation was compared with the measured curve in the experiment. The results indicated that on the basis of the experimentally measured RPC material eigenvalue parameters, combined with the appropriate RPC constitutive relationship and the calculation method of the plastic damage factor, the numerical simulation results considering the bond-slip were in good agreement with the experimental results with a deviation of less than 10%. Thus, it is recommended to select a gentle compressive stress-strain curve in the descending section, an approximate strengthening model of the tensile stress-strain curve, and to use the energy loss method and Sidoroff’s energy equivalence principle to calculate the RPC plastic damage parameters.

MEASUREMENT OF SURFACE QUALITY AND OPTIMIZATION OF CUTTING PARAMETERS IN SLOT MILLING OF GFRP COMPOSITE MATERIALS WITH DIFFERENT FIBER RATIOS PRODUCED BY PULTRUSION METHOD

The final shape of fiber-reinforced polymer (FRP) materials is usually given by machining. However, machining FRP materials is complex and difficult. Appropriate cutting tools and cutting parameters should be determined to overcome these difficulties. In this work, glass fiber-reinforced polymer (GFRP) materials with 60% and 68% fiber ratio, produced by pultrusion method, were machined. End of the milling, surface roughness (Ra), delamination damage factor (Fdd), sound and vibration results were analyzed. Experiments were carried out with Taguchi L[Formula: see text] mixed design and the results were analyzed by Taguchi, ANOVA and Pareto charts. In Taguchi and Pareto analyses, the most effective parameter for surface roughness and delamination damage factor was the feed rate, and the cutting velocity for sound and vibration. Different regression models have been tried. Linear regression was found as most suitable. The significance values of the regression models are 92.04% for surface roughness, 87.12% for delamination damage factor, 98.64% for sound and 73.27% for vibration.

PENURUNAN MASA PELAYANAN JALAN AKIBAT KENDARAAN DENGAN BEBAN BERLEBIH

Kerusakan jalan disebabkan oleh beberapa faktor yaitu: tanah dasar yang tidak stabil, iklim, sistem drainase yang buruk, material dan proses kerja yang tidak memenuhi persyaratan. Selain itu beban lalu lintas kendaraan memiliki pengaruh yang lebih besar. Beban lalu lintas normal dapat mempertahankan masa layan sesuai rencana. Masalah muncul ketika banyak kendaraan melintas dengan beban melebihi batas yang dipersyaratkan. Karenaberdampak pada pengurangan umur layanan. Karena itu, pengawasan yang ketat di jembatan timbang terhadap kendaraan dengan beban lebih, memerlukan perhatian khusus. Apalagi jika jalan tersebut merupakan jalan arteri yang didominasi oleh kendaraan angkutan barang. Pengaruh penurunan umur pelayanan perkerasan akibat beban lebih dapat dilakukan dengan membandingkan umur layan dengan beban normal dan beban lebih. Penelitian dilakukan pada ruas jalan nasional yaitu Jalan Raya Ahmad Yani yang terletak di Narmada, Kabupaten Lombok Barat. Analisis dilakukan terhadap data sekunder yaitu jumlah kendaraan yang memasuki jembatan timbang dan lalu lintas harian rata-rata tahun 2018 dan 2019. Hasil analisis berupa jumlah beban sumbu ekivalen dan efek kerusakan (Vehicle Damage Factor/ VDF) pada masing-masing jenis kendaraan dengan muatan normal atau lebih yang menggunakan Metode Bina Marga. Selanjutnya, analisis pengurangan umur layan dilakukan berdasarkan hasil kumulatif Equivalent Standard Axle Load (ESAL) pada kondisi beban normal dan beban berlebih. Hasil analisis menunjukkan bahwa angka ekivalen atau VDF kendaran muatan normal sebesar 385120.1870 dan VDF muatan berlebih sebesar 643207.3800 sehingga diperoleh persantase peningkatan nilai VDF sebesar 67.01% serta terjadi penurunan umur sebesar 3.1 tahun dari umur rencana 10 tahun.

Determination of Dynamic Modulus Master Curve of Damaged Asphalt Pavements for Mechanistic–Empirical Pavement Rehabilitation Design

For pavement rehabilitation design, the current mechanistic–empirical (ME) pavement design guide provides three levels of analysis methodology to determine dynamic modulus master curves for existing asphalt pavements. First, the ME pavement design guide recommends that Witczak’s predictive equation is employed to obtain the “undamaged” modulus master curve. Depending on the chosen level of analysis, either a falling weight deflectometer test (Level 1) or a condition survey (Levels 2 and 3) is conducted to determine the damage factor(s). The damage factor is used to shift the undamaged master curve downward to match the field conditions and obtain the “damaged” master curve. In this study, two pavement structures in North Carolina Highway 96 were selected to evaluate the accuracy of the ME pavement design guide using its three levels of analysis. Because this roadway is a multilayer full-depth pavement, the extracted field cores were divided into a top layer, bottom layer, and total core for investigative and comparative purposes. Accordingly, both laboratory measurements and pavement ME predictions of the dynamic modulus values were conducted separately. Results show that the predicted undamaged master curves are always higher than the measured master curves and Levels 1, 2, and 3 can each lead to significantly different damaged master curves. Considering both efficiency and accuracy for transportation agency practice, the Level 1 method is recommended, and if the existing pavement is a multilayered asphalt pavement, a total core extracted from all the layers is recommended to generate the input properties for Witczak’s predictive equation.

Quantifying damage in the steel shims of seismic isolation rubber bearings due to support rotation

<p>Seismic isolation is an effective technique for mitigating the earthquake movements on important infrastructures such as bridges and hospitals. Rubber bearings are one of the most common seismic isolation devices used for the protection of critical infrastructure assets. Isolators are critical elements of an isolated structure, and as such, they should experience limited, if any, damage during earthquake shaking. Damage associated with yielding of the reinforcing steel shims in seismic isolation rubber bearings has received limited attention in the literature. This study investigates the effect of the steel reinforcement characteristics on the behavior of rubber bearings under combined axial load, shear displacement, and rotation. The potential damage of the steel shims and the rubber bearings under design-level lateral loads is investigated using a damage index, <i>r</i>pl, and a damage factor, <i>Ω</i>, respectively, with emphasis placed on the thickness of steel shims.</p>