Journal of Rehabilitation in Civil Engineering
Volume:7 Issue: 3, Summer 2019

The strength and ductility of concrete are improved under multi-axial compressive stress due to confinement effect. Some effective parameters for concrete confinement are longitudinal and transverse steel reinforcement. Some stress-strain relations for confined concrete with steel reinforcement have been proposed by different researchers. In this paper, various stress strain models with considering the steel confinement effect are reviewed briefly and used for simulating the lateral behavior of on an experimental reinforced concrete frame. Envelope curves, tension damage, yielding patterns, ductility ratio and energy absorption of the frames are discussed. Results from the finite element analysis compared with experimental findings show that in the case of lateral load and displacement, the analytical models which were presented by Fafitis et al. and Muguruma et al. had more compatibility with experimental results and the difference is less than 10%. Energy absorption of the model which was proposed by Khaje Samani & Attard had the most compatibility with experimental results and difference is about 1%.

Dams have been always considered as the important infrastructures and their critical values measured. Hence, evaluation and avoidance of dams’ destruction have a specific importance. In this study seepage of the embankmentof Boukan Shahid Kazemi’s dam in Iran has been analyzed via RBF (radial basis function network) and GFF (Feed-Forward neural networks) models of Artificial Neural Network (ANN). RBF and GFF of ANN models were trained and verified using each piezometer’s data and the water levels difference of the dam. To achieve this goal,based on the number of data and inputs,864piezometric data set were used, of which 80% (691 data) was used for the training and 20% (174 data) for the testing the network.The results showed good agreement between observed and predicted values and concluded the RBF model has high potential in estimating seepage with Levenberg Marquardt training and 4 hidden layers. Also the values of statistical parameters R2 and RMSE were 0.81 and the 33.12.

Nowadays, it is necessary to apply modern techniques for the design of road networks, especially roads passing through ecosystems such as forests, in order to reduce operating costs, prevent further degradation of the environment, increase road efficiency and achieve sustainable development goals. In this paper, a new way of designing the road is presented. New design method has the ability to analyze a large amount of information in a variety of digital layers using GIS while being able to store, recover, and analyze information through multi-criteria decision-making process (AHP) and routing algorithms at high speed and precision. The output of the proposed design method (combining information with AHP via Dijkstra algorithm in GIS software) is compared with the existing forest road in the 2nd series of Liresar in Mazandaran province of Iran, designed using common methods. According to experts, hydrological criteria (0.408) and environmental criteria (0.375) have the highest importance and weight in comparison with other criteria in forest road design. The results show the map of area's capability for road construction is prepared for road design with better functionality and less adverse effects on the environment using the divider method compared to conventional topographic maps. Finally, the design of the new road in comparison with the existing reduce the slope (5%), increase access (15%) and reduce the cost of construction (30%).

Assessment of pavement distresses is one of the important parts of pavement management systems to adopt the most effective road maintenance strategy. In the last decade, extensive studies have been done to develop automated systems for pavement distress processing based on machine vision techniques. One of the most important structural components of computer vision is the feature extraction method. In most of the application areas of image processing, textural features provide more efficient information of image regions properties than other characteristics. In this research, three different algorithms were used to extract the feature vector and statistically analyzing the texture of six various types of asphalt pavement surface distresses. The first algorithm is based on the extraction of images second-order textural statistics utilizing gray level co-occurrence matrix in spatial domain. In second and third algorithms, the second-order descriptors of images local binary patterns were extracted in spatial and wavelet transform domain, respectively. The classification of the distress images based on a combination of K-nearest neighbor method and Mahalanobis distance, indicates that two stages arranging of the gray levels of the distress images edges by applying wavelet transform and local binary pattern (third algorithm) had a superior result in comparison with other algorithms in texture recognition and separation of pavement distresses. Classification performance accuracy of the distress images based on first, second and third feature extraction algorithms is 61%, 75% and 97%, respectively.

As a vibration- free concrete, self- compacting concrete (SCC) can be easily used in the absence of consolidation, therefore; it is a good option for repairing and retrofitting concrete structures. The quality of repair layer is highly effective on a successful repair. Accordingly, in this study, factors affecting the quality of fiber-reinforced self-compacting concrete repair layer, including paste volume, the ratio of water to cementitious materials and the amount of fiber, are discussed. For this purpose, the in-situ strength of repair layers and cube samples with and without core are determined using pull- off method. Also comparisons between in-situ strengths in different methods (with and without core, on cubes or on repair layer) with compressive and tensile strength of specimens have been done. Results show that, considering the great influence of shrinkage and tensile strength, with reduced paste volume, cementitious material and increased fiber, in-situ strength of repair layer increases. Moreover, we found that even in the best condition of concrete substrate layer (i.e. saturated surface dry) a repair layer has a lower strength than a cube specimen. Also, presence of fibers has the huge effect on results of pull-off test depends on the method of the test (with or without core).

Warm mix asphalts (WMA), because of their low production and compact temperatures, may have different behaviors in long term. In the present work, the energy-based criteria along with the 50% reduction in initial stiffness (Nf50%) using four-point bending test under controlled-strain conditions of 1000 microstrain were applied to compare the prepared two warm mix and HMA samples. All these criteria illustrate properly the effect of mix asphalt properties (additive type) on its fatigue performance. A noteworthy point in this regard is the difference between Nf50% values of the studied samples with the real failure point. For HMA and zycotherm WMA (ZWMA), loading cyclic number at the failure moment occurs almost 80% higher than the fatigue life estimated using Nf50% while for Sasobit WMA (SWMA) this value is declined to 28%. The RDEC method, compared to other methods, indicated the maximum fatigue life and consistency with the failure point. Comparing the energy-based methods with Nf50% method revealed that ERR, ERR&B, and ERP have the maximum consistency with fatigue life in terms of 50% reduction in initial stiffness. For SWMA, the fatigue life at Nf50% was larger than that of various energy-based methods but almost equal to that of the RDEC method. However, for two WMA mixes prepared using ZWMA and HMA, all energy methods revealed a fatigue life longer than that of Nf50%.

One of the most important conflicts that shaft spillways have to deal with is vortex formation. This phenomenon leads to some unfavorable effects such as vibration in the body of structures, air entrainment and reduced overflow capacity of the spillway. Among all solutions for disrupted vortex formation, an innovative one called circular piano-key spillway, based upon piano key weir principles has not been noticed as well as other solutions. Hence, in this study, experiments were conducted on circular piano-key spillway models. Results showed that in a constant head, the greater amounts of discharge have been measured for circular piano key inlet with an angle of 90 degrees. Comparison between discharge coefficients of three circular piano key inlet models showed that for a constant amount of H/D (Head/Diameter), circular piano key inlet with an angle of 90, 60 and 45 degrees have the greater amount of discharge coefficients, respectively. Experiment results indicated that circular piano-key spillway (with an angle of 90 degrees) increases overflow discharge capacity about 15.16% compared with shaft spillway. Among circular piano key inlets, the model with an angle of 90 degrees has the best hydraulic performance.

A main challenge for performance-based seismic engineering is to develop simple, practical and precise methods for assessing existing structures to satisfy considerable performance objectives. Pushover analysis is a simplified nonlinear analysis technique that can be implemented for estimating the dynamic demands imposed on a structure under earthquake excitations. In this method, structure is subjected to specified load pattern to reach a target displacement. The present study provides a target displacement for estimating the seismic demand of eccentrically braced frames (EBFs). A parametric study is conducted on a group of 30 EBFs under a set of 15 accelerograms. The results of nonlinear dynamic analyses of EBFs have been post-processed by nonlinear regression analysis and a relation is proposed for target displacement. In order to verify the capability of the proposed procedure, three EBFs are assessed by the present method in which the results show that the proposed method is capable of reproducing the peak dynamic responses with relatively good accuracy. Additionally, the comparison of obtained results with those of other conventional target displacement methods such as N2 method, and displacement coefficient method confirms the efficiency of the suggested one.

Cracking of the concrete cover due to corrosion is defined as the serviceability limit state of reinforced concrete structures. This study evaluated the influence of a mineral admixture i.e. nano wollastonite on corrosion performance and serviceability of reinforced concrete structures by performing an accelerated corrosion test on ten reinforced concrete beams under a sustained load. To do so, five concrete beams were treated with nano wollastonite (NCW), while the others were normal concrete beams (NC). The results were discussed in terms of corrosion crack patterns, crack width, half-cell potentials, rebar mass loss, and rebar diameter degradation at different corrosion levels. The results showed that the incorporation of nano wollastonite in reinforced concrete beams increased the service life by increasing the initial cracking time, decreasing the corrosion crack growth rate and rebar mass loss. Given the maximum 0.3 mm corrosion crack width as limit state criteria, the lifetime of the NCW reinforced beams was 3.6 times longer than that of Group NC. The experimental results were compared with existing models. However, these models were unreliable in predicting the steel cross-section loss based on crack width. To solve this problem, a GMDH-type neural network model was developed and evaluated using obtained experimental data for NC and NCW beams.

Due to architectural, mechanical and even structural considerations, in some cases there is need to create some openings in the composite steel shear walls. Presence of the openings can considerably affect the wall behavior. Therefore, in this study, the effects of the opening on the behavior of composite steel shear walls are investigated. For this purpose, first an experimental specimen without opening is developed and tested. The outcomes of the experimental study are verified by existing data Then three series of the CSPSW specimens (four specimens in each series) with opening are built and tested. Accuracy and precision of these experimental outcomes is verified by twelve numerical models which are developed using ABAQUS software. Therefore, general behavior of the CSPSWs with opening are investigated according to the attained outcomes from numerical and experimental tests. In addition, some methods are proposed to reduce the negative effects of the opening on the behavior of CSPSW. Then a parametric study is performed to evaluate effects of different parameters namely concrete cover thickness, steel plate thickness, thickness of the strengthening plate installed around the opening and bolt spacing on general behavior of the CSPSW. In addition to study the effects of opening in behavior of CSPSW, in this paper a thorough investigation about the influence of different parameters on drift of the system is performed .Finally, a formula is proposed based on the developed numerical models to compute lateral displacements of the composite shear walls with openings. This formula can be utilized for deriving an intensification factor which can be applied to calculate displacement of the composite shear wall with openings from the responses of a wall without openings.

Seismic pounding occurs as a result of lateral vibration and insufficient separation distance between two adjacent structures during earthquake excitation. This research aims to evaluate the stochastic behavior of adjacent structures with equal heights under earthquake-induced pounding. For this purpose, many stochastic analyses through comprehensive numerical simulations are carried out. About 4.65 million time-history analyses were carried out over the considered models within OpenSees software framework. Various separation distances effects are also studied. The response of considered structures is obtained by means of Hertzdamp contact element. The models have been excited using 25 earthquake records with different peak ground accelerations. The probability of collision between neighboring structures has been evaluated. An efficient combination of analytical and simulation techniques is used for the calculation of the separation distance under the assumptions of non-linear elasto-plastic behavior for the structures. The results obtained through Monte Carlo simulations show that use of the current provision’s rule may significantly overestimate or underestimate the required separation distance, depending on the natural vibration periods of adjacent buildings. Moreover, based on the results, a formula is developed for stochastic assessment of required separation distance.

This study investigates the reinforcement correction factor of concrete core in more detail to prepare appropriate outlines for interpretation of results. This investigation aims to minimize uncertainties involved to carry out the more realistic condition assessment of suspect buildings before taking up retrofitting/strengthening measures. For this purpose, an extensive experimental program including different concrete strength level, moisture condition, core size, length-to-diameter (L/D) ratio of core and steel bar size with various configurations was under taken. The effect of variation of foregoing parameters on the ratio of average compressive strength of cores containing steel bars to that of corresponding plain specimens was probed. The results show that the correction factors are highly dependent on the values of volume percentage and position of reinforcing bars in the core, which are extremely interrelated. Hence, the experimental results do not show a good agreement with the provisions by the British Standard 6089 and Concrete Society Report No.11. Therefore, a statistical analysis on the prediction of cube compressive strength using linear and nonlinear regression models is accomplished. The results showed that regression models have great ability as a feasible tool for prediction of compressive strength on the basis of core testing in the presence of steel bars. However, the most accurate results obtained by nonlinear equations in comparison with linear models.