مجله تحقیقات بتن ایران
سال پانزدهم شماره 4 (زمستان 1401)

The great depth of the deep beams allows the opening in the web. Openings in deep beams are intended for the passage of pipes and installation ducts. The presence of openings in the web cuts the members of the tie and strut in the equivalent truss and reduces the load-bearing capacity and ductility of the beam, which can even cause rupture. One solution to this problem is to use FRP reinforcing strips. In this research, the effect of FRP reinforcement sheets on the bearing capacity of deep concrete beams with rectangular opening has been investigated. For this purpose, reference laboratory samples were modeled and validated by finite element method with Abaqus software, then a number of parameters that may affect the response of the deep beam, such as the number, dimensions and distances of openings, were selected and kept constant. Other parameters, the response of the beam to its changes were examined. The results showed that the samples with BOX shaped reinforcement sheet had less bearing capacity than U-shaped reinforcing sheet. Also, samples with U-shaped FRP sheet have 38% more load capacity than sample without sheet and 13% more than BOX sheet. By comparing the reinforced specimens in terms of ductility and coefficient of behavior, it was found that the U-shaped reinforcing sheet has better performance.

The use of post tensioned flat slabs is common in structures that require the construction of long span. The main advantages of using this type of slabs are increasing the span to thickness ratio, deflection control and reducing the thickness of the floor. Post tension slabs are usually designed to withstand gravitational loads in the building. However, slab column connections in these systems must be able to withstand the deformations created by lateral loads and have sufficient ductility. In this research, an exterior unbonded post tensioned slab column connection is validated in ABAQUS finite element software. After ensuring the accuracy of the numerical model results, the effect of concrete compressive strength, the amount of effective prestressing levels and the tendon bonding influence in the seismic behavior of post tension slab joints are investigated. The results showed that the compressive strength of concrete and the prestressing level of concrete have a significant effect on the load-bearing capacity and ductility of the joints, while the bonding condition does not have much effect on the behavior of the joints.

Strengthening of RC columns using FRP composites is done with the aim of increasing bearing capacity and ductility. One common method in this case is to enclose the entire outer surface of the column with FRP. In this paper, it has been done to strengthen this columns under eccentricity axial load, with the FRP layers. The specimens used have a circular cross-section with a diameter of 125 mm and a height of 800 mm, which are loaded in two cases by eccentricity. First case, the eccentricity is twice the radius of the column (2R) and the second case the eccentricity is four times the radius of the column (4R). Due to the eccentricity of the load, parts of the column are subjected to bending tension. Ten numerical models in two groups (2R and 4R) were analyzed using Abaqus software. In order to verify the accuracy of the modeling, first two existing experimental specimens were simulated with software and then the results were evaluated. The results showed that by increasing the eccentricity of the load, the longitudinal composites are more effected than transverse composites on force bearing and displacements. Also, the fiber has been effected on ductility increasing more than force tolerance in the column. In the 2R group, specimens with transverse composite have been increased about 14% in forcing and 15% in displacement capacities than longitudinal. Conversely, in the 4R group, the above mentioned numbers in samples with longitudinal composite increased by about 7% and 332% relative to transverse.

Fiber Reinforced Polymers (FRP) are often used for structural repairs to improve the strength and ductility of the structures. Previous studies have shown that utilizing active confinement in concrete structures can improve the seismic behavior of concrete columns under pressure. In this study, the behavior of concrete columns actively confined by AFRP fibers was investigated under the combined effects of axial compressive and cyclic lateral loads. Two concrete columns were actively confined by AFRP strips. In addition, a non-confined column (SCR) was utilized as a control specimen. Then all specimens were tested under axial and lateral cyclic loading. Experimental results showed that the ultimate compressive strength and axial strain of specimens with active confinement are improved compared to the SCR specimen. Also, due to the increased number of small cracks in the specimen, a higher extent of energy was absorbed under the applied loading. The loading protocol caused no rupture in the AFRP strips, and no shear crack and brittle failure in the specimens were observed.

Reinforced concrete structures on the shores of the Persian Gulf experience a severe corrosion environment, and in the case of the structures that are in tidal conditions or some of their members are submerged in the sea, such as piers and ports, this problem is more acute due to the penetration of chloride ions. To increase the efficient life of concrete structures in the Persian Gulf, the use of self-compacting concrete along with cement substitutes has been suggested by researchers. In this paper, two powdered materials, slag and micro-silica, have been selected to replace part of the cement content in concrete. The durability test in submerged and tidal conditions has been performed on the specimens. Based on the results of experiments on 216 concrete specimens, the use of the proposed concrete on average increases the compressive strength by 22%, electrical resistance by 50% and decreases the permeability of volumetric water absorption by 12% and capillary water absorption by 30% in tidal conditions.

One of the main challenges of conventional concrete canvas is the separation of the geo-membrane layer from the fabric concrete substrate, which has caused major problems in the discussion of the application of this product. In this work, the method of casting polymer paste based on acrylic resins was used to create a single-layer coating of sealing resin with the high overall mechanical strength of the product, and the properties of the product were investigated. In this method, polymer paste is formed in one step without the use of adhesive and geo-membrane layer on the three-dimensional substrate bed, and the overall productivity of concrete canvas is formed. The results showed that concrete canvas produced based on polymer paste casting method with suitable mechanical strength (30 (kN / mm2)), better sealing (up to 30 days without changing weight against water), non-layering, Suitable chemical resistance against hexane, toluene, benzene and octane and better temperature resistance (from -20 to 100 C) than conventional concrete canvas product.

Sewage sludge is one of the subsidiary products of sewage treatment that should be managed in an appropriate way due to its pollutant components and massive production. One of these methods is incineration. In recent decades, many studies have been done on sewage sludge ash (SSA) as a supplementary cementitious material (SCMs) in concrete. On the other hand, one phenomena leading to deterioration of concrete, is alkali-silica reaction (ASR). One way to control this reaction is through using SCMs that prevent the formation of alkali-silica gel and expansion by consuming alkalis available in cement paste. According to results obtained from SSA utilized as SCM in former studies, it is possible that it could prevent ASR in concrete by decreasing the alkali content. However, very few studies have been done on this issue. In this study, SSA was used as a replacement for cement at 10, 30 and 50% levels in order to assess its ability to control ASR. In addition, the effect of trass and pumice as natural pozzolans in improving its ability to control ASR was investigated. The results revealed that only at 50% replacement level, SSA was able to control the ASR expansion in mortars. However adding 5% trass or 10% pumice improved this ability to a considerable extent.

Today, staying in economic markets depends on maintaining the quality and cost of production due to the intense competition of producers. It has also led governments to take tougher approaches to improve the environmental situation of industries. Therefore, the use of new technologies that leads to maintaining or increasing product quality and reducing costs without harming the environment will be desirable. Today, the use of high-power ultrasonic waves, due to the lack of noise pollution, has been highly regarded by various industries to improve engineering processes. The effectiveness of these waves in the manufacturing and production industries, such as reducing machinery, increasing surface smoothness, grinding metals during freezing, etc., can also be the motivation for its use in the construction industry. Therefore, the widespread use of high-power ultrasonic waves in various fields of engineering and the identification of the positive effects of these waves on the properties of materials and materials is the reason for the present study. For this purpose, for the first time in this study, the use of high ultrasonic power waves with different powers, different times, and a frequency of 20 kHz in concrete compaction and its effect on concrete compressive strength has been investigated. The results of this study show that the use of ultrasonic high-power waves as a complementary process in the compaction of fresh concrete will increase the compressive strength of concrete by up to 10%.