Study of Flexural and Crack Propagation Behavior of Layered Fiber-Reinforced Cementitious Mortar Using the Digital Image Correlation (DIC) Technique

By optimizing the distribution of steel fibers in fiber-reinforced cementitious mortar (FRCM) through the layered structure, the role of fibers can be fully utilized, thus improving the flexural behavior. In this study, the flexural behavior of layered FRCM at different thicknesses (25 mm, 50 mm, 75 mm, 100 mm) of the steel fiber layer was investigated. The evolution of the crack propagation behavior was analyzed using the digital image correlation (DIC) technique. The results showed that the steel fiber layer thickness of 75 mm has the best flexural behavior. Moreover, the crack propagation path is more tortuous. The maximum value of crack opening displacement (COM) increases with the increase in fiber thickness. In addition, increasing the bottom layer thickness can increase the height of the tensile zone, but the interface inhibits the increase of the tensile zone.

Experimental Work on Using Fully Wrapped Post-Tensioned Metal Straps Around Normal Steel Reinforced Beams to Increase Flexural Strength of R.C Beams

To increase the capacity load carrying of the beams, post tensioned metal straps are fully wrapped around the beams in their tensile zone in this study. In total four normal R.C beams with the depth of 160 mm, height of 240 mm and total length of 2100 mm are cast and tested under four-point load testing. The number of variables is kept to minimum of two which are the number and location of the straps. It is found that using post tensioned metal straps fully wrapped around the beams can increase the load-carrying capacity of the beams by 36% at least and 39% at a max. The main factor in influencing the rate is the location of the straps. A complete guide on using the material along with its application on the beams are explicitly described in the paper.

BEHAVIOR OF NON-BRITTLE ROCKS UNDER BENDING CONDITION

Experimental results of determining the bearing capacity of a marble beam are presented. A significant influence of plastic properties on the strength characteristics of the beam is noted. On the basis of a model of strength-different materials, an elastoplastic profile of stresses in a beam is constructed. It is proposed to use elastic stress distribution in the compression zone for rocks and similar heterogeneous materials with different compressive and tensile strengths, and elastic-plastic distribution in the tensile zone. Such a stress diagram makes it possible to explain the high values of bending strength in comparison with the tensile strength of the presented materials.

Strength Properties of Structural Glulam Elements from Pine (Pinus sylvestris L.) Timber Reinforced in the Tensile Zone with Steel and Basalt Rods

The study analyzed potential applicability for asymmetric reinforcement of glulam beams using materials with a higher modulus of elasticity. Reinforcement elements included smooth and ribbed steel rods as well as basalt rods. These rods were placed only in the tensile zone, assuming that they will not only impart increased rigidity but first of all will reduce the scatter of bending strength values. What is significant, tests were conducted on timber with defects, as it is most commonly used in industrial practice. Analyses showed that this provides an increase in rigidity close to the assumed level. A significant increase in strength was observed. The manufactured beams reinforced with steel and basalt rods were characterized by mean bending strength amounting to 54 and 47 N/mm2, respectively. However, no significant improvement was found in the scatter of the observed variable. Beams reinforced with steel exhibit a 20% higher strength than unreinforced beams. The lower strength of beams reinforced with basalt bars may be related to the lower modulus of elasticity of the basalt itself.

Shear resistance of prestressed concrete beams with the constant and variable height

One of the methods of increasing the efficiency of using prestressed reinforcement involves transferring a certain amount of longitudinal tensioned reinforcement from the tensile zone in the span to the upper compressed zone on the support, where it is not fully used to ensure the bending resistance. More effective may be a solution in which, due to the broken outline along the length of the element, the pre-stressed tendons are arranged at an angle to the longitudinal axis, creating vertical compression of the support zone and increasing the beam shear resistance. In this study presented information about stress-strain state of prestressed concrete straight and curved beams based on the experimental investigations.

Strengthening of tensile zone of the reinforced concrete beams with composite fabrics

A fabric, tapes, that are glued to the outer tensile surface, which are considered as the external composite reinforcement with tensile steel reinforcement, are currently used to strengthen reinforced concrete beams. The results of the experimental studies presented in this article have shown the possibilities of effective application of technical polyamide (nylon) fabric produced by «Khimvolokno Plant» JSC «Grodno Azot», and glass fabrics, produced by JSC «Polotsk-Steklovolokno» for strengthening the reinforced concrete beams. Experimental studies have shown that the external reinforcing of the tensile zone with technical polyamide (nylon) fabric and fiberglass changes the beam failure mode, increases the bearing capacity of reinforced concrete beams in comparison with beams without strengthening by 16% – 38%, depending on the material and the method of strengthening.

Torsional Strain Energy of Normal Concrete and SCC with Glass and Steel fibers

Concrete is a two phase material with initial internal micro cracks before loading. When the load is applied on the specimen these internal cracks propagate and material fails after reaching its maximum allowable stress. There are different force systems like tensile, compressive, shear, torsion and combination of above. The strain energy is the energy which develops internally in the material to resist deformation because of application of external load. So if the minimum energy level is reached the deformation exceeds its plastic limit and cracks start propagating from tensile zone to compressive zone. Usually the torsional strain energy is studied to define the material characteristics for taking twisting and rotational effects in the member. A study is made regarding the torsional strain energy of ordinary and SCC with glass and steel fibers. Also a comparison is made for strain energy by experimental and analytical models. To give additional strength to the concrete, steel, and glass fibers are also added to SCC and their torsional strain energy was estimated.

The Influence of the Height of Fiber Reinforcement Zone on the Crack Resistance of Rubcon Beams with Mixed Reinforcement

In order to research on the influence of the height of the fiber reinforcement zone on the normal sections crack resistance, we produced and tested rubcon beams of rectangular cross section with mixed reinforcement; our studies showed that the height of the fiber reinforcement zone has a similar effect on the normal sections crack resistance with the percentage of longitudinal reinforcement. It is important to note that the arrangement of fiber reinforcement at 3/4 of the section height greatly complicates the process of manufacturing the beam while not increasing the strength of the tensile zone compared to the beams with the location of the fiber over the entire height of the section.