Ferdowsi Civil Engineering
Year:2018 | Volume:31 | Issue:3 |Papers Count:8

In this research, the effect of steel fibers on flexural cracking of fiber reinforced concrete beams with lap-spliced bars under static and loading/unloading cycles was investigated. Ten specimens of laboratory beam with the section width of 150mm, height of 200mm and length of 2300mm and with different splice lengths of tension rebars and different percentages of steel fibers were manufactured and tested. Four specimens were subjected to static loads and six specimens were subjected to loading/unloading cycles. Among the specimens, one was selected as the control specimen without having lap-spliced bars and steel fibers. Other 9 specimens were made using steel fibers with different volumetric percentages of 0, 1 and 2. The specimens were conducted under four-point bending tests. It was shown that the flexural crack width in beams decreases with increasing the volume percentage of steel fiber, significantly. Steel fibers in specimens subjected to static loading and loading/unloading cycles increased the energy dissipation.

Local scour at the culvert outlet is common event. In this study the effect of different angles of wing walls flare on scour in hydraulic conditions for type 1 and 4 flows at downstream of circular and box culvert investigated. Wing walls flare 15, 30, 45, 60 and 75-degrees to the outlet centerline were considered in this study. Result showed 15-degree flare wing walls reduced scour depth, scour length and mound height. So, 15-degree flare wing wall in box culvert and type1 flow reduced scour equal 35. 3% to the control test. Also, 30-degree flare wing walls in box culvert and type1 flow has shown a good performance in reducing scour depth equal 46%. Wing walls flare angle 60 and 75-degree, did not have good performance in reducing scour depth at downstream of culverts. In type 1 flow, scour can be reduced by using of wing walls with any angles. In type4 flow, only 15-degree wing walls flare reduced maximum scour depth equal 30% in circular culvert and 10% in box culvert. Also, the dimensions of the scour hole on downstream of the circular culvert is more than box culvert. So, in the circular culvert and type 1, scour depth increased equal 35% compared to box culvert and it was observed equal 95% in type-4 flow. The dimensions of the scour hole in type 1 flow is higher than type 4 at all angles, while the mound height in type 4 is higher than type 1 flow.

One of the important ways of identifying road accident potentialities is road safety audits. After identifying these points, appropriate strategies to reduce the number and severity of accidents can be considered for them. In this study, using road safety audits, access, pavements, signs, roadside, and geometric problems and accidents leading to the deaths of outlying urban road sections were identified and using these data, the model of crashes in them Was presented. In this paper, the Hamadan-Kermanshah axis was chosen as a case study. In this axis, Poisson's regression model was more reliable and the problems of drainage ditches and vertical alignment were the most important reasons for the accident and resulted in death.

Soil slope stability analysis, is one of the most important issues in the design of earth dams, roads, canals and levee. One of these methods is the limit equilibrium analysis with horizontal and vertical slices method. To evaluate the results of horizontal and vertical slice method in the calculation of stability safety factor, at first Two formulations of each method selected, then stability Safety factor has been achieved with the use of these methods for several slopes. The exact amount of stability safety factor by using of the analytical method has been obtained then the accuracy of the each method and comparison of their results with each other is studied. Considering studies at this research, concludes that at generally vertical slices method results exact and with a few confidence rand. Whereas horizontal slices method results have a relationship with selected formulation. In cases where the soil is layered horizontal or issues with horizontal forces, horizontal slices method provide greater ease of use. Finally, explained recommendations for using slice method.

Challenging and complex nature of the numerical analysis of crack problems have attracted the interest of many researchers in past decades and several techniques have been proposed for these problems. One of these techniques is the extended finite element method in which the crack tip field modeling is improved by enrichment of shape functions and the crack can intersect the elements. On the other hand, we have adaptive finite element method which aims to improve the accuracy of displacement and stress fields near the crack tip by remeshing process. Researchers have reported the drawbacks of each of these two techniques. In this paper the drawbacks of the previous techniques are covered with proper combination of these two techniques. By this combination the crack can pass through the elements and there is no need for crack tracking by mesh. In addition the estimated error is limited to desirable bands and stress intensity factor can be computed numerically with acceptable accuracy.

To determine the effects of meta-halloysite and micro-silica pozzolans on mechanical strength and durability of concrete, 8 mix designs with two water/cementitious (W/C) ratios of 0. 40 and 0. 45 were performed. The ordinary Portland cement (OPC) was replaced by incorporations of 10 and 20% of meta-halloysite, and 7% of micro-silica. Samples were cured until the ages of 14, 28 and 90 days. Results imply that the combination of meta-halloysite and micro-silica for both W/C ratios particularly in the case of the lower ratio (0. 40) when the sample contains 10% meta-halloysite, leads to a significant increase (89%) in the compressive strength of mixes (from 25. 3 to 47. 7 MPa). Also, the highest flextural strength (6. 18 MPa) resulted in the lower W/C ratio (0. 40). It is noteworthy that increases in W/C ratios for all mixes don’ t lead to remarkable decreases in flextural strengths. Notably, the ultrasonic velocity (UV) for all mixes in the lower W/C ratio (0. 40) shows a considerable increase particularly in 10% meta-halloysite compared with control samples. The findings above are all indications of better improvement of concrete strengths by natural pozzolan (meta-halloysite).

By adding perlite and leca to porous concrete, its physical characteristics were studied. Compression strength, hydraulic conductivity and porosity of two porous concretes (without fine grains and with 20% fine grains) were measured. Results showed that adding 20% fine grains to porous concrete highly decreases hydraulic conductivity and porosity and increases compression strength. The highest compression strength (20. 5 MPa) was seen in without-fine-grains samples (L10-0 treatment) and in with-fine-grains samples (34. 85 MPa) in L15-20 treatment. The L5-0 treatment in both cases of with/without additives, had the highest hydraulic conductivity and porosity. Leca had better performance than perlite.

In this paper, moment-curvature behavior of reinforced concrete column with constant axial load is determined by finite element method and then it is introduced to a single degree of freedom (SDOF) model based on Euler-Bernoulli theory. Using this SDOF model, dynamic response of the RC column under the blast loading is estimated. The introduced SDOF includes secondary moments (P-δ ) effects, nonlinear behavior of the material and effects of strain rate on concrete and steel materials through the calculation steps of the model. In order to validation, results obtained from SDOF model for transverse displacement of RC column under blast loading is compared to finite element analysis results (OPENSEES) and real-scale explosion test results on RC columns. Then, introduced SDOF method is used to draw Pressure-Impulse (P-I) diagram of the column with considering the presence of axial compressive load. According to the results, introduced SDOF approach, under the far field explosion conditions (Z>1 kg/m1/3), has acceptable accuracy. As well, the effect of axial load on P-I diagram of the RC column is very important.