نشریه مصالح و سازه های بتنی
سال ششم شماره 1 (پیاپی 11، بهار و تابستان 1400)

This paper presents a model to simulate shear mode (mode II) of fracture mechanics in concrete cold-joint. The simulation is performed using nonlinear static analysis of materials and geometry. The specimens used for modeling are S-shaped specimens used in the push-off test. The specimens modeled in three situations with 2, 4, and 6 steel connectors and validated with the results of corresponding the experimental specimens. The results of the analysis show that the proposed method has a good ability to simulate the behavior of the shear mode of fracture mechanics in concrete cold-joint. The proposed simulation method can be useful to investigate the behavior of reinforced concrete frames with cold-joint and repair, retrofitting, and strengthening reinforced concrete structures.

Soil-structure interaction is one of the important and influential factors on the seismic behavior of structures, especially reinforced concrete structures. In this study, the effect of soil-structure interaction on a 9-story reinforced concrete structure with a flexural frame system designed based on low-risk seismic requirements and for nonlinear analysis with OpenSees finite element software in two different modes with rigid base without considering the interaction And with a flexible base, the effect of soil-structure interaction has been modeled and evaluated. The results show that due to the interaction, the base shear, the shear within the floors and the amount of relative displacement are reduced, while the actual periodicity of the building and the absolute displacement of the floors is increased.

One of the conventional retrofitting methods for reinforced concrete beams is flexural strengthening of beams with CFRP materials. In this study, a full scale reinforced concrete beam is constructed and evaluated under four-point flexural test. Afterward, a same beam is retrofitted in flexural region by monolayer of CFRP. These experimental tests are carried out to be the basis of verification for numerical specimens. The first, an unreinforced beam is subjected to four-point loading in the laboratory. Then, to strengthen the beam in the flexural zone, three similar beams is reinforced and reinforced in the flexural zone using a layer of CFRP sheet, a layer of steel sheet and GFRP rebar. The reinforcement of the beams is done in the middle range, and after loading, bending failure occurred in all the beams. The results show that the reinforced concrete beam has much impact on carrying capacity, but would crash out of the range of the bending beam will be soon. The results also show that by performing local reinforcement in the flexural zone, in some beams, the first cracks occur outside the flexural range, while the final flexural failure occurs in the middle range of the beam.

In light of the importance of reinforced concrete reservoirs, as well as the increasing number of terrorist attacks, this study attempts to evaluate the performance of reinforced concrete reservoirs containing a fluid with response to TNT explosion at different distances while considering the Fluid-structure interaction (FSI) in relation to the loading impact from the blast wave. The LBE method in the LS-DYNA software was used for this research. The amounts of TNT used are 20, 40, 60, and 80 Kg at distances of 3, 4.5, 6 and 7.5 meters from the top of a concrete reservoir in simulated buried and non-buried situations. One of the most important results of this research is an increase of 14%, 33%, 35% and 41% of pressure in the blast impact on the reservoir with respectively 1.2, 1.4, 1.6 and 1.8 times of the TNT amount in the buried situation at a distance of 3 meters. Furthermore, the maximum pressure on the reservoir in the buried state at a distance of 3 meters was associated with an increase of 13%, 23%, 30% and 36%, respectively. The simulation results also illustrate the effect of soil as a protective cover in reducing the blast impact on the reservoir.

Earthquakes are one of the major phenomena affecting structures and engineers use design criteria to deal with their effects. In terms of the specific degree of safety for dams ‌, it is necessary that the design of large dams include the largest believable earthquake in hazard analysis and probability consideration regardless of the amount of time it returns in the design. Pebble dams have mainly concrete or asphalt coating, which in addition to impermeability to water, increases the stability of the dam. Since a number of gravel dams have been constructed in Iran and several other gravel dams are under construction, the study and analysis of this type of dam is very important for current and future studies of dam engineering. In this research, pebble dam modeling will be done in Abacus software as well as model validation. First, the model presented in the reference article is modeled and validated. The model used in validation and this research is Musouchura Dam. After ensuring the accuracy of modeling and analysis, the effect of concrete strength of dam cover under the effect of selected accelerometers and by changing the strength of concrete and also the effect of considering the damping of concrete were measured and finally the results were compared. The accelerometers used in this study are Northridge, Bam, San Fernando and Tabas. Changes in concrete strength in three types C20, C25 and C30 with nominal strength of cylindrical compression specimens of 20, 25 and 30 MPa were made and this increase in strength is about 8 to 10% in reducing lateral displacement under selected accelerometers in the dam crown has it. Considering the damping effect in concrete with a value of 0.0325, under selected accelerometers, there is a change of about 3% in the lateral displacement of the dam crown, while it has little effect on the tensile degradation of the concrete surface.

Mechanical sieve analysis is a common method for determining concrete aggregates and soil classification. For facilitation and acceleration of this method, this paper reviews image processing and deep learning methods used in geotechnical and civil engineering applications. Combination of deep learning with image processing can result in a robust, human-independent approach (in terms of experience and recognition power), resulting in faster and accurate results. To better understand the performance of such methods, two convolutional neural network (CNN) architectures (e.g. AlexNet or GoogleNet) were evaluated for their capability in automatic feature extraction and image classification. It was observed that the accuracy of these networks in prediction of aggregate class is dependent on ratio of the number of training samples to the whole dataset size, epoch number and mini batch size. The number of training images between 80-90% of the total dataset was found to be suitable and a minimum of 10 epoch is required to obtain the maximum validation accuracy. Using this model, a validation accuracy of up to 100% was reachable. Furthermore, the model was capable to predict about 85% of new images correctly. The future improvement of this method can be associated to increasing its efficiency in training process by using optimization approaches.

The high weight is one of the most important deficient of any building that has a direct role at damages caused during an earthquake, so the application of new lightweight material is one of the attractive research issues. The effectiveness of replacing Polystyrene instead of regular aggregates on its density and also adding silica fume and zeolite and its effectiveness on concrete strength were investigated in this paper. Three mix designs consisting of zeolite, silica fume, and polystyrene on cubic, cylinder compressive specimen, and flexural beam specimens were cast and tested. The test results indicated that the mix design with 20% zeolite and 5% silica fume gave concrete with a special density equal 1756 kilogram per cubic meter and cylinder compressive strength equal 27 MPa, indicating one special structural high-strenght lightweight concrete. In addition, the complete structural design results showed that the total costs of building cast with structural lightweight concrete (concrete, steel bars, and casting cost) was almost 40% less than of regular reinforced concrete building.

This study experimentally examines types of rotational-friction dampers with two slip load and numerically analyze the behavior of a reinforced concrete frame with these dampers under cyclic loading. To this goal, the study will explain the mechanism of proposed damper’s action after the introduction. In the next step, two specimens of rotational-friction dampers with two different slip load are investigated in the laboratory. Using OpenSees software, the proposed behavioral model is validated by experimental results. In the final step, a frame of one-story reinforced concrete that had one bay was analyzed under cyclic loading in four states including (1) without damper, (2) with a rotational-friction damper that had one slip load (RFD), (3) with a rotational-friction damper that had two slip load type S01, and (4) with a rotational-friction damper that had two slip load type S02. The obtained results were discussed and examined after these analyses. The results of the numerical analysis also show that the concrete frame with S01 damper has better seismic performance. This is because its ultimate strength and dissipated energy are respectively 15% and 164% more than the ultimate strength and dissipated energy of the frame without damper, at the last cycle.

A paucity of parametric study does exist that has investigated the influential parameters affecting the effective flange width of non-rectangular reinforced concrete (RC) shear walls. Therefore, this paper attempts to present a novel approach to parametrically study the effective flange width of non-rectangular RC shear walls. In this regard, an analytical formulation has been established in the elastic region to estimate the effective flange width of a non-rectangular RC shear wall with a general geometry. Based on the proposed analytical formulation and by considering the shear-lag phenomenon, the influential parameters have then been determined which affect the stress distribution, and in turn, the effective width of the section. Moreover, a dimensional analysis has been carried out employing the Buckingham's Pi Theorem to derive the effective flange width of the section as a function of dimensionless parameters. The findings indicate that the influential parameters are respectively the flange width, axial as well as lateral force, and height of the wall which appear in the predictive formulations. Nevertheless, the exciting codes neglect the effect of the applied loading to the wall structure which fail to accurately predict the effective flange width of the wall section.

One of the most important issues in the design of concrete structures that are exposed to water is the reduction of permeability and water proofing. The innovation of this research is using iron concentrate as an inexpensive material for reduction of permeability. To determine permeability coefficient and compressive strength of concrete, 140 cubic samples with 7 mixing plan and different concentrate percentage have been studied in the laboratory. The results showed that the addition of concentrate has a significant effect on permeability reduction where for 5% to 10% concentrate, the permeability coefficient decreases from 78.76% to 96.44%, respectively. On the other hand, the compressive strength of concrete decreases with increasing concentrate. A comparison between the compressive strength and permeability diagrams showed that the optimal value of concentrate is between 5 to 15% by weight of cement. The failure results of the samples show that the percentage of concentrate has no effect on the failure of concrete.

The aggregates as a prominent part of concrete mixture have significant impact on durability and strength of concrete. One of the most important problems attributed to some part of aggregates in Iran are reported to possibly deleterious alkali silica reaction between the hydroxyl ions (OH−) in the pore solution and reactive silica in the aggregate over the time. So, investigation of alkali-silica reaction potential for aggregate in this area is so invaluable because of high consumption of these suspicious materials in the construction of varied hydraulic structures.In present study, alkali silica reactivity of aggregate in a number of mines in West of Iran including Zanjan, Kermanshah and Kordestan province has been investigated comprehensively. In this regard, in order to evaluate alkali silica reactivity of aggregates, petrography examination of aggregate according to ASTM C295, alkali silica reactivity mortar bar testing according to ASTM C1260 and determination of length change of concrete due to alkali silica reaction according to ASTM C1293 was used. Based on results obtained in present study, it was concluded that alkali silica reactivity was observed at a number of aggregates placed in every three studied province and in order to using of these aggregate at concrete structures exposed to water, preventive action including using low alkali cement or pozzolan could be useful.