جستجوی مقالات مرتبط با کلیدواژه "laboratory study" در نشریات گروه "عمران"

The present research aimed to evaluate the effect of industrial steel fibers on the mechanical properties of reactive powder concrete (RPC). A series of reinforced RPC specimens containing different percentages of steel fibers having different diameters were built. By performing resistance tests on the samples, the mechanical properties (compressive, bending and tensile strengths) of RPC were determined. The results of the compressive tests showed that by increase in the curing age from 7 to 42 days, the strength of RPC containing group 2 steel fibers (medium fibers: diameter 0.6 mm) increases compared to the control concrete. This is attributed to the continued reactions between the cement paste and the interlocking of most of the quartz-silica sand aggregates and micro-silica powder in the RPC specimens with steel fibers. The highest compressive strength of RPC compared to the control concrete was obtained for the sample containing 2% group 1 steel fibers (small fibers: diameter 0.4 mm) equal to 421 MPa (29.11% growth compared to the control concrete). By reduce in the diameter of fibers, the number of fibers in the sample and subsequently the interlocking between aggregates and fibers increases and the replacement distribution of aggregates improves. Based on the flexural strength tests, 2% of groups 1 and 2 steel fibers and 3% of group 3 (large fibers: diameter of 0.8 mm) were determined as the optimal value of fibers to achieve the maximum flexural strength of RPC. Based on the tensile tests, it was found that with the addition of 1%, 2% and 3% of groups 1, 2 and 3 steel fibers, the growth of RPC tensile strength is completely upward. The reason was attributed to the bridging effect of steel fibers in the concrete matrix. Empirical equations obtained from regression analysis have high accuracy for estimating resistance properties.

During the construction of steel structures, the executive groups often fabricate some stories and tighten the connection bolts, defined as the snug-tightened bolt in this research. The lower stories, in which the connection bolts are snug-tightened, will be pre-tensioned at least to the level of preloading based on design codes, called pre-tensioned bolts, in this paper. The connections will be complete, while some upper stories will have snug-tightened bolts. As a result, the stiffness of the bolted connections varies throughout construction, and the structural characteristics change with time. So it is necessary to investigate the seismic behavior of bolted extended end-plate moment connections in both snug-tightened and pre-tensioned bolts while constructing high-rise structures. Bolted unstiffened end plate moment connections are one of the most usable connections used as prequalified connections in special steel moment frames. According to the AISC design code, this connection can be considered one of the most important parts of moment-resisting frames with enough bolt pre-tension levels. In this paper, using three full-scale bolted unstiffened end plate moment connections designed according to AISC, the effects of bolt pre-tension levels have been examined experimentally under SAC cyclic loading protocol. Bolt pre-tension level has been defined as α coefficient to show the pre-tensioning level in three specimens. The bolts of the first specimen are not pre-tensioned, called snug-tightened bolts, and is reference connection. The bolt pre-tension levels of the second and third specimens were created in accordance with AISC and Iranian National design code and more to Fu of bolts, called pre-tensioned and fully pre-tensioned, respectively. The bolts' moment capacity, total energy absorption, initial rotational stiffness, ductility of connection, and stress and strain variation are investigated. According to the results, an increase in bolt pre-tension level would significantly improve the cyclic behavior of connections. Further, an increase in bolt pre-tension led to the initiation of the inelastic deformation from a minor rotation, and the ductility of the connection improved. The results show that the increase in moment capacity and energy dissipation in the pre-tensioned compared to snug-tightened is 27 and 23%, respectively. However, In comparison with the pre-tensioned, the fully pre-tensioned specimen has increased by 11 and 9%, respectively. As a result, the connection with bolt pre-tension level, under design regulations in comparison with the reference connection, can be considered a connection of a special moment resisting frames. So bolt pre-tension level higher than the value mentioned in the design code is better but not needed.

Many concrete structures have been damaged due to natural disasters such as earthquake, wind, or corrosive fatigue. Therefore, the use of new technologies to modernize and improve these structures is important. Fiber reinforced polymer (CFRP) composites are widely used in retrofit and strengthening of reinforced concrete (RC) structures. FRP composites are applicable for strengthening various structural elements including beams, columns and plane elements such as floor slabs and shear walls. In this paper, the effect of surface preparation on concrete beams with carbon fabrics has been investigated. 8 Reinforced concrete beams were made by composite fibers and a concrete sample beam in the laboratory and tested for four-point bending loading Took. The experimental and Theoretical results of the proposed method have been presented in which the preparation in sandblasting, in addition to increasing the flexural strength, delayed the early detachment in the beams tested. It was also observed that the bending capacity in the beam increased with a 45.9% CFRP reinforcement layer and CFRP reinforcement layer 64.8% higher than that of the sample beam

Self-compacting concrete is one of the most High potential Concrete Currently available due to its wonderful fresh and hardened properties. fresh properties of concrete include the ability to pass, flow and stability, and with these properties will increase the efficiency of self-compacting concrete in all stages from making to utilization. One of the most important wastes in the steel industry is the electric arc furnace slag and one of its applications is the use as aggregate in concrete .The steel slag of Khuzestan Steel Company consists of fine and coarse aggregates, and in this research we first seek to design a suitable mix of self-compacting concrete And then we replace the amounts of coarse and fine slag by 10% incrementally as long as the concrete remains self-compacting. Replacement of coarse and fine slag has been possible up to 30%. fresh concrete tests include slump flow, V Funnel, J-ring and L-box which is evaluated according to the EFNARC guideline.. Hardened concrete tests include compressive and Split tensile strength performed on standard cubic and cylindrical specimens after curing saturation of concrete at 3,7,28 days. Replacement of coarse slag up to 30% improves hardened concrete properties, But slight decrease in fresh properties. By modifying the mix design and the use of super plasticizer to 3% by weight of cement The coarse slag has been 100% replaced by coarse aggregate and has achieved good fresh and hardened results. Replacement of fine slag by 10% of fine particle is the most optimal condition for fresh and hardened concrete properties, And replacing more than this percentage will greatly reduce the fresh and hardened properties.

One of the important applications of geosynthetics in the earth's slopes, such as landfills and waste disposal areas, is to use them as liner system. Proper assessment of the interaction of geosynthetics at slopes, such as landfill, is an important issue in preventing the slip and instability of the slopes. The inclined plane is a suitable method for assessing the interaction between the geosynthetics interacting in a sloping and tilted state under low normal stresses. The European Standard EN ISO 12957-2 provides a "standard displacement" for estimating the geocynthetic interface's friction angle. In this paper, inclined plane device, which for the first time in Iran was completely designed and constructed, describes the technical characteristics of the device and prepares the sample. This apparatus has the ability to perform experiments to investigate the interaction of soil-soil, soil-geosynthetics and geosynthetic-geosynthetic interfaces at low normal stress. Experiments are carried out on geomembrane and geotextile types to investigate the interaction of their surface. By changing the type of geosynthetics, it was observed that friction angle of geosynthetic interfaces is not constant and depends on the type of geomembrane and the woven or non-woven geotextile. The geomembrane-geotextile interface is the least amount of geomembrane with hard polyethylene, and the highest amount is used when polyvinyl chloride is used.

Soft clayey soil generally has high compressibility and low strength. Presence of this soil type in the site of ‎civil projects can always be a challenge for construction issues. Soil stabilization is one of the useful ways to ‎improve problematic soils. Cutter Soil Mixing (CSM) is almost a new method for deep stabilization. This ‎experimental study, investigate the effect of different depths on soft clay ‎properties which stabilized by CSM ‎method. To simulate various depths and related surcharge pressures, new devices were designed, modified ‎and used for laboratory tests. Moreover, mixture of blast furnace slag and hydrated lime slurry was used in this ‎method for the first time. The samples were cured for 28 and 56 days ‎under various surcharge pressures, which actually represent different depths. The results revealed that by increasing the depth, mositure content and saturated/dry densities of the samples were decreased and increased respectively. In addition, by ‎passing the critical depth, fewer changes were obsorved in the moisture contents and saturated/dry densities of the samples. Finally, the strength parameters of stabilized samples were icreased significantly.

In this paper, a laboratory study of the Bored Pile Retaining Wall with Anchorage Bracing in sandy soils has been conducted. To this end, the physical modeling in laboratory condition was used. The results of the experiments suggest that the ratio of maximum lateral displacement of wall to the depth of excavation () is in the range of 0.145% to 0.51%. Also, the ratio of maximum ground surface settlement to the depth of excavation () is estimated in the range of 0.11% to 0.76. Furthermore, this study investigated the location of maximum lateral displacement of the walls, the ground surface settlement pattern to be used in laboratory studies and determination of the depth of penetration pile.

Developing different method in construction of deep footing plays a major role in optimized and economized performing of civil projects especially in problematic soils. One of the common types of deep footing is helical piles which have several advantages such as fast procedure, useful in different soil types, performing without noise and vibration, effective in pressure and tension and etc. In this paper, the performance of 1-helix & 2-helixes and 3-helixes in an un-grouted and grouted with the field and laboratory studies are discussed. Field studies include of helical piles behavior in sand. Laboratory tests with physical FCV modeling is also carried out on the soil of the site. Grouting effect on helical piles resistance is evaluated. Comparison load test results with analytical method were compared. Results show that performance cylindrical in sandy soils in helical piles is not suitable and increasing helical number pile capacity is decreases. Also, after grouting helical pile with three helixes increases more resistant compare to one helix and double helixes.

1. Researchers have suggested different equations for river bank profile, such as trigonometric, parabolic, exponential equations, etc [1]. In this research, a laboratory study has been conducted in a straight reach of sand-bed river in order to validate ten types of river bank profile equations. For this purpose, several stable channel geometry and especially experimental observations for channel bank shapes were compared with theoretical bank profiles and then the mean standard error of each equation was calculated and according to the results the closer ones were identified. 2. Experimental study:This research concerns a carefully controlled set of experiments, to study in detail on river bank profiles in sand-bed channels. All the experiments were carried out in the Water Research Institute (WRI) in Tehran, Iran. The flume in which the experiments were carried out is 12 x 0.75 x 0.6 meters as shown in Fig. 1. The side walls of the flume are made of glass, which allows the convenience of visual observations. Water is circulated by a pump, and the discharge is measured with a triangular weir equipped at the upper tank. An adjustable tailgate controls the flow depth at the downstream end, so as not to yield the drawdown backwater. Two samples of well-graded sands with median diameter, D50, of 1.2 and 1.6 mm, and the gradation coefficient, less than 1.3 were used, because for these sizes ripples or dunes were not produced [2]. The initial cross sections for both types of sand were semi-trapezoidal and modeled by steel templates. Only one side bank was made mobile to exclude the tendency toward meanders [2, 3]. The dimensions of the semi-trapezoid were computed using the Lacey, Julien and Wargadalam, Arbelaez et al. and Meija regime equations [4]. Finally, for D50=1.2 mm, the initial semi-trapezoidal section was made with a lateral slope of 30°, and 17-cm bottom width, 32-cm top width, and 8-cm depth. For this type of sand, the amounts of constant discharge were 11.09, 12.07 and 12.88 l/s throughout the runs. In the same way, for D50=1.6 mm, the initial semi-trapezoidal section was made with a lateral slope of 30°, and 22-cm bottom width, 41-cm top width, and 11-cm depth. For this type of sand, the constant discharge rates were set 14.17, 16 and 17.96 l/s throughout the runs. For each experiment, the flume was filled by the uniform sand. Then, a channel was carved along the left side of the flume with the help of mentioned steel former fixed on a carriage. The modeled channel (carved channel) filled slowly with still water before the start of experiments. Then the tailgate was opened and the water was re-circulated. The desired discharge was kept constant until a stable channel section was reached. In other words, the experiment was continued until a dynamically stable state had been achieved. The duration of the experiments was such that the channel would establish a regime was often lasted about 5 hours. In this research equilibrium was considered to exist when changes in channel shape (width and depth) were less than 4% and the longitudinal profile of the water surface was regular and nearly constant [2, 3].Finally, the elevations of free surface and channel geometry were measured by a point gage at four sections in the 4.5-m, 5.5-m, 6.5-m and 7.5-m section from the entrance which were named section A, B, C and D. 3. In order to validate ten types of river bank profile in comparison with experimental observations for sand-bed channel tests, the mean cross sections’ shape for channel banks according to the experimental results in section A, B, C and D were determined and with the other theoretical bank profiles were drown as Figs. 2 and 3. At the next step, mean standard error of each profile equation was calculated and the results are presented in Table 1.Table 1. MSE of river bank profiles in comparison with experimental dataSand size Type of river bank profile D50=1.6 mm D50=1.2 mm 6.3100 8.3914 (1951) Cosines of Glover & Florey2.5137 3.0459 (1978)Cosines of Parker 5.8349 9.7468 (1963) Sinus of Stebbings0.7343 0.9897 (1998) Parabolic of Cao & Knight0.0421 0.0507 (1981)Exponential of Ikeda 0.0499 0.0512 (1990) Exponential of Diplas0.0532 0.0177 (1998a)Hyperbolic of Babaeyan-Koopaei and Valentine 0.1043 0.1800 (1998b)Hyperbolic of Babaeyan-Koopaei and Valentine 0.5989 0.4378 (1992)Fifth-Degree Polynomial of Diplas and Vigilar 0.1205 0.762 (1998)Third-Degree Polynomial of Diplas and Vigilar 4. The results of this research indicate that stable river bank profile can not be introduced agreeably via trigonometric equations corresponding to stable condition and non-cohesive materials. In this manner, the hyperbolic and exponential equations have less diversion in comparison with others while trigonometric equations present the most diversion in comparison with observed data. In other words, it seems that the models which consider the Reynolds-stresses resulting from turbulent momentum transfer have more accuracy in comparison with the other ones.