نشریه پژوهش های تجربی در مهندسی عمران
پیاپی 2 (پاییز و زمستان 1393)

Nanomaterials have been used for enhancing rheological properties of bitumen and mechanical properties of asphalt mixes. In this study، the effects of nano-clay، nano-hydrated lime and hydrated lime has been investigated on fatigue behavior of bitumen. Nano hydrated lime was produced using a planetary ball mill with average particle size of 281nm. Linear Amplitude Sweep (LAS) test has been performed to evaluate fatigue properties of samples. Nano-clay was used by 2%، 4% and 6% weight of bitumen. Hydrated lime and nano-hydrated lime were used at 5%، 10% and 20% of weight of bitumen. Results showed that nanoclay at 6% (by weight of bitumen)، increased fatigue life of the binder at 40% level. Specimen contained 10% nano-hydrated lime had a fatigue life 49% higher than that contained 10% hydrated lime.

Since there are plenty soils in the nature that sodium chloride is a part of their constituent materials، or they are affected by sodium chloride due to the proximity to saline water sources، and on the other hand because cementation is one the most common methods for soil stabilization due to its availability and abundance، in this study we have tried to evaluate the effects of sodium chloride in solution form on CBR resistance and compaction parameters of the initial selected soil as well as soil stabilizing by cement mixes (according to the proportion of different cement percentages). The obtained results indicate that، adding the sodium chloride in solution form to the initial soil as well as soil stabilized with cement (considering different percentages) will increase the maximum dry density and also decreases optimum moisture، compared to its initial state. Also، adding this solution to the soil will increase the CBR resistance of both types of soil samples (initial and stabilized) considering the amount of different effectiveness on the initial soil and soil stabilized.

Construction of spillway brings lots of expenditures for projects. In this study، the physical model of Germi-chai ogee spillway with curved plan and downward angle of convergence while the effective length of the spillway is reduced from the crest to the toe for several times، built in soil conservation and Watershed Management Research Institue. In this stage، a physical model of the prototype was prepared in the scale of 1:50 and was put to test. The physical model was constructed using polyethylene that is waterproof and Plexiglas was used to build walls and channels. In this article، experiments were performed for 8 different discharges making up to 25% to 150% of the design discharge of the prototype. The spillway demonstrated satisfactory performance up to the design discharge. Gradually an increase in the discharge led to a decrease in the performance of the spillway so that it was fully submerged and the downstream channel took control of the discharge. Gradually an increase in the discharge just slightly higher than design discharge، led to a decrease in the pressure at the crest while the pressure at the chute and toe increased. With higher discharges and submersion of the spillway due to regime changes، the pressure of the flow over the spillway reached from supercritical to sub-critical.

Nowadays، intelligent methods inspired from nature are implemented to resolve complex problems، there are very popular too. The most common one is artificial neural network; they are capable to collect huge amount of complex information through experiments and tests. On the other hand، combination of fiber concrete with self-consolidating concrete produces a new product with high fluidity and good adhesion. Due to the presence of fibers، this type of concrete presents high-quality advantages such as high resistance to impact، high fatigue performance، low rate of erosion، enhances the tensile and flexural strengths and reduces the segregation. In this study by considering the components of the concrete mix design as networks input and two kinds of neural network modelling، a Radial Basis function and a recurrent neural network (NARX) for predicting the properties of hardened concrete، were used. To improve networks training، 40 concrete mix fibers reinforced self-consolidating concrete and three fiber types including steel fibers، glass and polypropylene، were prepared. Comparison of experimental results and network outputs indicate that both networks have the sufficient accuracy in estimating the hardened properties of self-consolidating concrete and recurrent neural network (NARX) error is less than Radial Basis Function Neural Network.

In recent years with the progress of construction methods، the idea of using lightweight materials for reducing structure weight and earthquake load has been raised up. Crack in lightweight concrete passes through aggregates causing a smooth surface compared with fractured surface of normal concrete. This difference in cracking mechanism changes the overall behavior of members made of lightweight concrete compared to normal concrete. In this study the behavior of lightweight concrete deep beams has been investigated، experimentally. For this purpose four deep beams with shear span to height-ratio of 0. 5 have been prepared and loaded in static form in the structural laboratory of Tarbiat Modares University. Beams depth were 30، 45، 60 and 90 centimeters. Finally، the results were compared to truss method available in ACI، CSA and EC2 codes. Results show that by increasing the height of beam، the normalized ultimate load decreases and failure mode doesn’t vary and also relations in ACI and EC2 codes are conservative for all tested beams but results of CSA code are non-conservative for beams with 90 centimeters height، indicating more investigation is needed.

Block shear failure is one of the most common failure types of connections in steel structures which have been investigated by many researchers. In this study، block shear failure of welded connections subjected to a uniform tension field were experimentally investigated. For this purpose 6 specimens of welded connection of gusset plates to flat bar were developed. The mechanical behavior of the connection and pertaining failure types were identified. The tests parameters included the gusset plate thickness، the overlapped area، shear and tension plane of the gusset plates. Nonlinear load-displacement curve response for all specimens was presented. The failure load of block shear was assumed to be the maximum load reached during the loading history. For all Specimens the mode of failure was the block shear. Observation during the experiments showed that crack nucleation occurred at the maximum load (failure load) so that a single crack or two symmetrical cracks nucleated after the toe of the weld at the end of tension plane for all specimens and the load suddenly dropped after crack formed. Although، no shear fracture was observed at the time of the tension plane fracture in all of the tests، a significant deformation was observed at the shear plane because of yielding of this plane.

Abstract: Usually in the chute spillways designers are facing problems such as aeration، transverse waves، cavitations and erosion. Although many studies have been performed to determine the flow characteristics over these structures، however، little information are available on supercritical flow downstream of chutes piers and their effects on flow domain. Due to the flow interaction with the chutes piers، a supercritical and wavy flow known as rooster tail is formed. The result of this wavy flow is three kinds of transverse waves، the first one is formed downstream of the piers، the second is formed on the middle of the chute and the third is formed on the wall of the spillway. The importance of investigate this phenomenon is because of influencing on flow field and creating unbalanced hydraulics conditions. In this Study، experimental Investigation the formation of the transverse waves and its profiles are presented. Experiments were conducted on a scaled physical model of Kheirabad dam spillway، at Water Research Institute of Iran. The results showed that three types of waves are created by the placing gate''s pier on the chutes. The height of these waves can be more than twice the water depth and thus impact on the design of the side walls of chute. It was realized Froude number of flow and gate opening have the main effect on wave formation. Finally، the equations used to express the maximum height of waves and location of its formation was presented for the three types of waves.