Fatigue strengthening of tubular X joint using un-bonded CFRP laminates

C

Structural Damage Detection in the Wooden Bridge Using the Fourier Decomposition, Time Series Modeling and Machine Learning Methods

In this article, a novel approach has been employed to identify structural damage in the wooden bridge structure by utilizing vibration data. This method encompasses the Fourier decomposition method that decompose the response of the bridge into a sequence of Fourier Intrinsic Band Functions (FIBF). These functions comprise the responses of the structure that contain inherent information of structure as well as noise from the vibrations. The time series modeling is utilized to extract damage-sensitive features. The residuals of the time series model of both undamaged and damaged structures are extracted for detecting any damage. To ascertain the presence of damage, supervised classification machine learning algorithms are employed. The algorithms are utilized consist of Artificial Neural Network (ANN), K-Nearest Neighbors (KNN), support vector machines (SVM), ensemble learning, and decision tree. The results indicate that the proposed method of feature extraction is highly effective and reliable in detecting damages. In addition, the capacity of decision tree and ANN algorithms to minimize type 2 error and enhance accuracy is demonstrated when evaluating different machine learning algorithms. The value of the type II error in the ANN model and the decision tree is equal to 13.85% and the accuracy of the model is 93.02%

Applying a new systematic fuzzy FMEA technique for risk management in light steel frame systems

Light Steel Frame (LSF) system is mainly used for construction of short and intermediate-height buildings in developed countries whereas considerable heed is not given to it in developing countries. Unfamiliarity to LSF risks is one of the main reasons for this averseness so risk management can remedy this challenge and develop application of the LSF. Hence, this paper investigates the risk management of LSF system considering design, construction and operation phase. Three main steps entailing risk identification, assessment and responding using fuzzy Failure Mode and Effect Analysis (FMEA) technique are suggested for risk management implementation and for validation of responses, a novel index with respect to weighted combination of project quality, time and cost are calculated. The methodology is demonstrated on a pilot study in a developing country. By using interview, 29 significant risks are extracted in design, construction and operation and then evaluated by proposed fuzzy method. Results showed that the share of the risks in these steps are 21%, 31% and 48% respectively. The results revealed that the risks in the construction and operation phases are higher than those in the design phase. The results also show that involving safety as a project object in the risk management process could eventuate acceptable results

An investigation of seismic response of connections in precast concrete double-tees /

An experimental study of typical connections commonly used in precast concrete buildings subjected to reversed cyclic loads is presented, along with an analytical study of nonlinear behaviour of these specimens subjected to monotonically increasing loads until failure.Five different connection specimens were constructed and tested under reversed cyclic loading to determine their seismic responses. The specimens represent a series of horizontal connections between double-tee flanges or between a double-tee flange and lateral load resisting element in a typical roof of a precast concrete structure.The analytical study consisted of two parts: linear finite element analysis of the connection to determine the test specimen geometry and to define its boundary conditions, and non-linear finite element analysis, using the NONLACS program, to predict the complete responses of the connections subjected to monotonically increasing loads.The experimental results were compared with the predictions made using theoretical calculations, the CPCI design method and non-linear finite element analysis.It is noted that the CPCI design method gives conservative predictions for the ultimate strength of the connection reinforced with a bent deformed bar anchor and a 90$sp circ$ hook, and the one with two deformed bars oriented at 45$sp circ$ and headed studs, both welded to a steel plate. The predicted ultimate strength of the connection with a bent deformed bar anchor welded to a steel plate and one with two straight deformed bar, oriented at 90$sp circ$ and welded to an embedded steel angle, are close to the experimental results. The ultimate strength of the connection wit the headed studs welded to a steel plate predicted by CPCI method is overestimated. Design guidelines to increase the strength of the connections and to improve the displacement ductility are presented

Seismic response of connections in precast concrete double-tees

Thirty full-scale specimens of five types of connection were constructed and tested under: (a) monotonically increasing shear forces, (b) reversed cyclic shearing forces, (c) reversed cyclic axial forces, and (d) various combination of reversed cyclic shearing and axial forces-all increased gradually in stages until failure using displacement control. These connections were reinforced with anchor bars welded to the steel angle at angles of 45$sp circ$ and 90$sp circ$, and/or with 90$sp circ$ standard hooks at the ends, headed studs welded to a steel plate and some combinations thereof, representing the connections between precast double-tee flanges, or between a double-tee flange and lateral load resisting elements, One full-scale specimen (Connection Type Ap) was designed and subjected to reversed cyclic shearing loads to investigate the efficiency of utilizing the steel angle versus the steel plate.The effect of the varying ratios of reversed cyclic axial and shear forces on the different behavioral aspects of the connection, especially the shear response, including the hysteretic responses, yielding and ultimate loads, mode of failure, energy dissipation, displacement ductility ratios, etc. are reported.Based on the experimental results, the shearing force - axial force interaction diagrams and the associated equations and their normalized versions are derived for the different connection types subjected to combined cyclic loads. The design interaction curves and the associated equation for each connection type are also developed along with the simplified version as a useful tool for design of the connections subjected to combined seismic in-plane shearing and axial forces induced in joints during an earthquake.On the basis of the resisting mechanism observed experimentally and the physical models describing the ultimate behaviour of the connections, equations are proposed for shear and axial strengths of the various connections under static loads.Non-linear finite element analyses, using the NONLACS program, are conducted to study the nonlinear response of the connections subjected to pure monotonically increasing pull-out and shear loads, and their combinations until failure. The analytical interaction curves and the associated equations under combined monotonic pull-out (axial force) and shear forces are derived. The reduction factors to account for the lower strength under cyclic loads are derived empirically for these analytical equations. The simple modified analytical curves (for response under reversed cyclic loads) and their associated equations are developed for combined cyclic loading.The experimental results were compared with the predictions made using proposed methods, the CPCI design method and non-linear finite element analysis.In the final stage of this experimental-analytical program, practice-oriented methods are developed to determine the connection strength under shear and axial forces, and combinations of these forces at ajoint between elements in a precast system. Design guidelines are provided for increasing the strength and the displacement ductility of the connections and to improve connection performance. It is concluded that properly designed and detailed connections of these types, except Connection Type E, can be designed to perform adequately in an earthquake-resistant structure

Technical note: Risk detection in light steel frame buildings in design, construction and implementation phases

Light Steel Frame System that is briefly called "LSF" is a building system which is used for implying of short-rise and mid-rise buildings (up to five floors). It is a desirable building system for civil engineers (in terms of gravity and lateral load) in developing countries. This system gets significant benefits, although in Iran it is not much used due to the reasons such as: opposite with people’s culture, higher price in, lack of specialists, executive problems and etc. So in this article, we are tried to study LSF structures from the design and implementation stage to the operation and identify its risks exactly and finally offer a solution for each risk. Risk detections process is executed with interview technique in the Mashhad city and countryside. Totally, 56 projects are examined in this research. The study projects have been classified here. This classification includes residential buildings, villas, added-storey, schools, administrative, commercial, fastfood, industrial structures and LSF non-load-bearing walls. All the mentioned projects have been implemented in holy city of Mashhad or will be implemented in the future. Designers, administrators and employers are interviewed in person in all the above projects. Because of novelty of this system and its unknown risks, this research can be useful for managers decision making and for executing engineers in the field of choosing the best system for project and adoption of appropriate method for preventing these risks

Modeling of Buckling Restrained Braces Subjected to Dynamic loads

In this paper an effective, applicable method and a simple model are presented for accurate modeling of buckling restrained braces. In the beginning, all components of buckling restrained brace are defined. A test specimen of this brace type is completely modeled in ANSYS finite element program (complete model). The modeling is validated by comparing the nonlinear dynamic results with experimental results.A simple model consisted of core steel and spring is recommended, modeled, analyzed and evaluated. Based on the results a method is presented for calculating the spring stiffness. It elucidates that the spring prevents the buckling of steel core and fining the mesh elements size resulted in smaller spring constant. Comparison of the hysteresis curves indicates a good agreement between the experiment and models (simple and complete models). In general, the difference between the experimental and analytical results is less than five percent

Optimum Parameters for Tuned Mass Damper Using Shuffled Complex Evolution (SCE) Algorithm

This study is investigated the optimum parameters for a tuned mass damper (TMD) under the seismic excitation. Shuffled complex evolution (SCE) is a meta-heuristic optimization method which is used to find the optimum damping and tuning frequency ratio for a TMD. The efficiency of the TMD is evaluated by decreasing the structural displacement dynamic magnification factor (DDMF) and acceleration dynamic magnification factor (ADMF) for a specific vibration mode of the structure. The optimum TMD parameters and the corresponding optimized DDMF and ADMF are achieved for two control levels (displacement control and acceleration control), different structural damping ratio and mass ratio of the TMD system. The optimum TMD parameters are checked for a 10-storey building under earthquake excitations. The maximum storey displacement and acceleration obtained by SCE method are compared with the results of other existing approaches. The results show that the peak building response decreased with decreases of about 20% for displacement and 30% for acceleration of the top floor. To show the efficiency of the adopted algorithm (SCE), a comparison is also made between SCE and other meta-heuristic optimization methods such as genetic algorithm (GA), particle swarm optimization (PSO) method and harmony search (HS) algorithm in terms of success rate and computational processing time. The results show that the proposed algorithm outperforms other meta-heuristic optimization methods

Subset Simulation Method in Active Structural Control

When designing new civil, mechanical or aerospace systems that will experience dynamic excitation in their operating environment, it is desirable to quantify the predicted performance of a proposed design in terms of the reliability that it will achieve the specified design objectives. In view of the uncertainties about the modeling of systems and about the future dynamic excitation the system will experience, the design team can specify a set of possible dynamic inputs and a set of possible models of the system and then choose probability distributions over these sets to model the uncertainties. One can then evaluate the ‘failure probability’ of the design that measures how likely the system will achieve the desired performance over its operational lifetime, based on available information and the probability models chosen to represent the missing information. Because of the uncertainty inherent in engineering structures, consistent probabilistic stability/performance measures are essential to accurately assessing and comparing the robustness of structural control systems. Several reliability estimation methods, procedures and algorithms with various capabilities, accuracy and efficiency have been suggested in the past. A quantitative comparison of these approaches is considered to be most instrumental and useful for the engineering community. An approach is presented herein for calculating such probabilistic measures for a controlled structure. Subset Simulation method is shown to be appropriate for the required calculations. The original version of Subset Simulation, SubSim/MCMC, employs a Markov chain Monte Carlo (MCMC) method to simulate samples conditional on intermediate failure events it is a general method that is applicable to all the benchmark problems. The concepts are illustrated through several examples of seismically excited structures with active protective systems. The results show that the original version of Subset Simulation based on the Metropolis–Hasting algorithm is robust and efficient in estimating the probability of failure of structural systems with complex failure regions, large numbers of random variables, and small probabilities of failure.and applicable to all problems