Ferdowsi Civil Engineering
Year:2012 | Volume:23 | Issue:1|Papers Count:9

In this paper, using numerical methods and test results, the behavior of reinforced concrete beams strengthened with Fiber-Reinforced Polymers (FRP) is investigated. In the numerical analysis, the concrete damaged plasticity model is used for considering the nonlinear behavior and strain softening of concrete.The ABAQUS finite element program is utilized for the analysis of 12 flexural beams strengthened with FRP sheets. Comparison between the test results and values obtained from the analysis shows that the numerical method can accurately predict the load-deflection, failure load, strain distribution and failure mode of the strengthened beams. In order to evaluate the effect of different parameters on the numerical results, a sensitivity analysis was carried out. Based on the sensitivity analysis, it was found the concrete fracture energy is an important parameter in the prediction of the behavior of the strengthened beams.

Modified bituminous materials can bring real benefits to highway maintenance/construction, in terms of better and longer lasting roads, and savings in total road life castings. This paper present the effect of there novel modifier as Precipitated Calcium Carbonate (PCC) and two type of nanoclay on rheological properties of bitumen binder. Various blends of modifier and bitumen were selected and empirical rheological test were conducted on short term and long term aging condition. Nanocomposite morphology of bitumen and nanoclay was also investigated by using XRD technique to achieve the best structure. The result show that depends of type, properties and content of modifier, aging resistance improve.

Large panel precast structures are analyzed based on the connection rigidity. However, the connections undergo nonlinear and inelastic response, when subjected to seismic loads. Thus, to study the actual behavior of structure, the connection nonlinearity should be implemented in the joints. In this paper, three conventional connection types are modeled based on the envelope of their cyclic responses using ANSYS program. The results reveal that the behaviors of modeled connections are very close to experimental results. The nonlinearity of connection is modeled in the coupled-precast shear walls, as a lateral load resisting elements, and several analyses are preformed. The results show, when the nonlinear behavior of connection are considered the forces in the connections are smaller up to 6.7 times and the displacements are greater up to 4 times in comparison with those for rigid connection state, respectively.

Nowadays, distinctive methods are used in evaluation of the criteria in order to making decision.Among them the analytic hierarchy process (AHP) is one of the most efficient. Due to the seismicity of the vast majority part of the country and also the existence of the large number of the unreinforced masonry buildings, the application of the AHP method in order to reach to the best alternative of the strengthening of these buildings are developed. The effective parameters in the evaluation alternatives are classified and suitable alternatives for the rehabilitation are evaluated. The results illustrate the preference of the strengthening the masonry walls with the shotcrete, compared to the other alternatives.

Ant Colony Optimisation (ACO) algorithm and adaptive refinement mechanism are used in this paper for solution of optimization problems. Many of the real engineering problems are, however, of continuous nature and finding their solution by discrete ant based algorithms requires discretisation of the decision variables in which affected the convergence and performance of the algorithm. In this paper an adaptive refinement mechanism is suggested to improve the performance of ant algorithms in solving continuous optimization problems. The proposed mechanism is an iterative method in which the search space of the problem at each iteration is limited to a small range around the optimal solution obtained in previous iteration. The application of the proposed mechanism to solve some benchmark function optimization problems and reservoir operation problem is considered and the results are presented. Compression of the results indicate the efficiency and effectiveness of the proposed method to improve the performance of the ant algorithms for continuous optimization problems.

Scoure is the removal of particle sediment which results variation of flow pattern. Local scour is considered as one of the reasons of instability and ultimately failure of bridges. Therefore, proposing some controlling methods to reduce this phenomenon is essential. In the study, effects of two types of squar and circular collar on a single cylindrical model have been investigated. In the next step by providing a slot through the pier and combination of collar and slot was used to investigate the scouring reduction. The results showed that use of both collar, specically below bed level decreased the scour depth. Square collar was more effective than circular in decreasing the scour depth. Combination of slot and collar on the pier could further reduce the scouring depth in which a square collar with W/D=2.5 in the bed with a slot near the bed reduce scouring depth up to 80 percent consequence.

Invention of the self-compacting concrete has caused dramatic changes in the concrete industry within the past twenty years. Compared with the ordinary concrete, self-compacting concrete does not need any compaction and by itself can produce concrete with sufficient compaction and smooth surfaces with no voids or honeycombing. Since the compaction has great influence on the adhesion of the concrete repair layers and due to the fact that the compaction of any repair layer is a very difficult task, it seems that SCC can be used with wide spread application as concrete repair materials. In this paper results of studies on the adhesion of self-compacting concrete applied to different concrete surfaces are presented. These studies are undertaken by the use of "twist-off" and "friction-transfer" methods and the prediction of the results by fuzzy logic, is also presented. The results tend to show that surface conditions of the substrate, aggregate to cement ratio of the repair layer, compressive strength of the repair layer, nature of the repair layer (concrete or mortar) and the degree of the moisture of the substrate concrete affect the adhesion along the repair/concrete interface. It is also realized that compared with statistical methods, fuzzy logic can be used for the prediction of the adhesion, with higher accuracy.

Many studies have been conducted focusing on the effects of friction coefficient or texture depth on the highway accident risk. However, combined effects of these parameters have not been still addressed. In this research the interaction between friction coefficient, texture depth and accident rate in 30 freeway sections were examined. The accident data were gathered and an apparatus was designed to measure friction coefficient. A nonlinear regression analysis was performed and a combined exponential model was obtained.The results indicated that despite cross correlation between friction coefficient and texture depth, thess parameters have some independent effects on accident rates which can be used to decrease freeway accidents significantly.

Rutting of hot mix asphalt pavements due to increased number of heavy vehicles, especially in tropical regions, causes several performance problems. Large Stone Asphalt mixtures have more stiffness and shear resistance and so more rutting resistance compared to conventional mixtures. Hence, using these mixtures in thick layers of hot mix asphalt pavements at tropical regions could be an appropriate option for asphalt mix design. Large Stone Asphalt Mix (LSAM) is a mixture with the nominal maximum aggregate size between 25 and 63 mm. Modified Marshall mix design method according to ASTM-D5581 is used to design these mixtures. In this laboratory research, the rutting resistance of LSAM mixtures is evaluated and compared to conventional HMA mixtures. Large Stone Asphalt mixtures were designed with four different aggregate gradations as well as a conventional dense graded mixture. Rutting test specimens prepared at four different asphalt contents for Large Stone Asphalt mixtures and at optimum asphalt content for the conventional mixture. The rut depth of specimens at 60°C determined using Hamburg wheel tracking device after 12000 loading cycles. The data obtained from mix design and rutting tests analyzed using SPSS statistic software and the effects of various parameters such as asphalt content, air voids of compacted asphalt mixture and gradation on the rutting resistance of Large Stone Asphalt mixtures were evaluated. At the end, a mathematical model presented for predicting the rut depth of Large Stone Asphalt mixtures.