Strengthening Of Structural Elements Research Articles

Enhancing load capacity of reinforced concrete columns using high strength concrete and fiber reinforcement

Strengthening of structural elements is sometimes necessary for architectural purposes to withstand additional loads without cross-section enlargement. This study evaluates the structural performance of reinforced concrete columns toughened using high-strength concrete, steel fiber concrete of 1% volume fraction, and near-surface mounted NSM steel or carbon fiber reinforced polymer CFRP bars. Five columns of 0.15×0.15×1 m were cast and axially loaded till failure. The investigational consequences revealed that a load-carrying capacity and stiffness augmented by 55.1 and 91.1% when the compressive strength is 1.5 times the normal with a ductility decrease of 28.2% whereas steel fiber concrete raised them by 34.3, 6.4, and 11.6%. In addition, NSM steel or CFRP bars exhibited ultimate loads and stiffness 13.6 to 29.7% and 17.2 to 21.7% higher than the non-strengthened column. However, the ductility decreased by 2.5 to 12.4%.

The reliability index estimation of truss rods with interval uncertainty of the initial data

The article presents an approach to evaluation the reliability index of steel truss bars with the uncertainty of random variables expressed in the presence of information only about the bounds of variability. Different methods of estimating the bounds of v
 ariability for random variables are presented. The new approach is also developed using the provisions of the theory of possibility and the Dvoretzky–Kiefer–Wolfowitz inequality (DKW). The reliability index allows to compare various design solutions by the safety criterion, identify structural elements with the highest failure probability for monitoring the technical state and to quantify the increase in the safety level with strengthening of structural elements. The Monte Carlo statistical simulation data reflect the analogy of the non-probabilistic reliability index in the considered approach with the non-failure probability of the truss bar.

Experimental Strengthening of the Two-way Reinforced Concrete Slabs with High Performance Fiber Reinforced Cement Composites (HPFRCC) Prefabricated Sheets

Reinforced concrete structures are required to be strengthened and retrofitted for various reasons, including errors during design and/or construction, so in most cases, strengthening of structural elements is much more economical than rebuilding the structure. Employing HPFRCC with tensile stiffening behavior has been developed in order to strengthen the concrete structures over the recent few years. In this paper, applying HPFRCC for strengthening two-way reinforced concrete slabs has been investigated. A total of five two-way slabs were constructed and examined to reach their own collapse stage, one of the specimen was as non-strengthened control slab, and the others were strengthened in various forms. The strengthening was carried out in two ways; by installing precast plate in the tensile area and the other by installing precast plate in both tensile and compression area at two different percentages of the fiber. The bending behavior, cracking, yielding and rupture of the experimental specimens were evaluated. The results revealed that the installation of HPFRCC pre-fabricated laminates significantly ameliorated the bending performance of reinforced slabs, so that the ductility, energy absorption value, cracking strength, and initial hardness of the slabs was increased and the crack width was decreased. Therefore, the proposed precast HPFRCC sheets can be employed in order to strengthen the deficient slabs.

Numerical Investigation of Behavior of RC Columns Strengtheneg with RC Jacket

Strengthening of structural elements which are insufficient in terms of earthquake performance is very important for the safety of existing structures. Nowadays, one of the most commonly used methods is strengthening such members with RC jacketing. Several experimental studies have been conducted in the literature to investigate behavior of structural elements reinforced with RC jacketing. Moreover, numerical studies are frequently preferred due to the high cost of experimental studies and the limited availability of laboratory facilities. In this study, a finite element model has been created with OpenSees program in order to investigate the behavior of strengthened RC columns with jacketing. Later, the accuracy of the model has been verified successful by the experimental results selected from the literature. By using that verified model, the effects of concrete strength and amount of spacing of transverse reinforcement used on the jacketing part on reinforced column behavior were investigated. As a result of the study, it is deduced that the change in the concrete strength and amount of transverse reinforcement results in a significant change in ductility, load capacity and rigidity of the reinforced concrete columns.

Experimental and Numerical Investigation of CFRP-Strengthened Steel Beams under Impact Load

AbstractUse of carbon fiber–reinforced polymer (CFRP) strengthening of structural elements has been gaining increased traction over the past few years. Although some research has been carried out o...

Flexural Behavior of Carbon Textile-Reinforced Geopolymer Composite Thin Plate

Textile-reinforced Portland cement-based concrete has been researched and developed over the last few decades. It was widely used in a different range of applications, such as repair and/or strengthening of structural elements, thin walls, lightweight structures, façade elements, and others. Due to its varied application, this study aims to develop the carbon textile-reinforced geopolymer composite. Specimens of rectangular form with the dimensions of 400 × 100 × 15 mm3, reinforced with carbon textile, were produced. Four-point bending test was used to evaluate the effect of carbon textile on the mechanical strength of reinforced geopolymer composite based on the three factors: the different mortar compositions corresponding to the addition of the chopped basalt fiber (BF), the number of carbon textile layers, and the different thicknesses of the mortar cover layer. Besides that, a small part of the pull-out test was also considered to assess the adhesion strength at the interface between carbon textile and geopolymer mortar. The experimental results from the four-point bending test showed that the mechanical strength of composite specimens increased when the content of the chopped basalt fiber increased. With the increasing number of the textile layers, the specimens improved the flexural strength significantly. However, the flexural toughness of the specimens reinforced with three textile layers did not improve, as compared to those reinforced with two textile layers. The experimental results for the specimens related to the mortar cover thicknesses indicated that specimens with the mortar cover thickness of 2 mm provide the best strength. The experimental results from the pull-out tests showed that all the specimens have the same failure mode by slipping of the fiber yarn from the matrix.

Pneumatic formwork used in strengthening of structural elements during reconstruction of buildings and structures

The paper discusses the importance of building reconstruction and the need for improving the available formwork systems used for strengthening of structural elements during reconstruction. Citing the results of the analysis of the Russian and foreign scientific publications, the authors emphasize the necessity of replacing costly wooden formworks with high-technology reusable all-purpose and mobile formwork systems. Considering that such requirements are met by rubber-fabric formworks, the authors have developed a pneumatic formwork and showed by way of experiment that the labor intensity of installation and dismantling of such formworks is much lower as compared with conventional wooden formworks, which makes this research original. The paper further describes the design of the suggested formwork and the installation and dismantling techniques. The versatility of the formwork is confirmed by its ability to easily adapt to any structural elements (pier foundations, columns, beams etc.) ensured by the flexibility of rubber-fabric materials. This system can be used for structural elements having various geometric shapes (round, rectangle, trapezoidal) and dimensions. Their transportability is warranted not only by the dimensions and flexibility, but also by a small weight. The use of pneumatic formworks contributes to resolving the problem of conservation such valuable natural material as wood.

A nonlinear analytical model to predict the full-range debonding process of FRP-to-parent material interfaces free of any mechanical anchorage devices

Ever since Fibre Reinforced Polymers (FRP) began to be used in the repair or strengthening of structural elements, the premature debonding of the FRP composite from the substrate has been an important drawback that have been motive of several studies. The importance of knowing and describing the full-range behaviour of FRP-to-parent material interfaces rigorously is therefore urgent. However, at present, there are no analytical solutions that describe the full-range behaviour of such interfaces that help us to understand the full debonding phenomena of FRP-to-parent material interfaces free of any mechanical anchorage devices. Therefore, the aim of this study is to contribute the advances of that knowledge through an analytical solution by means of an exponential bond-slip model that is known to represent the nonlinearities involved in the debonding process of the FRP composite from the substrate. Analytical solutions for the slips, strains in the FRP composite, bond stress distributions along the bonded interface and stresses in the substrate are presented. A full-range load-slip analysis is also discussed.

Carbon fiber epoxy composites for both strengthening and health monitoring of structures.

This paper presents a study of the electrical and mechanical behavior of several continuous carbon fibers epoxy composites for both strengthening and monitoring of structures. In these composites, the arrangement of fibers was deliberately diversified to test and understand the ability of the composites for self-sensing low strains. Composites with different arrangements of fibers and textile weaves, mainly unidirectional continuous carbon reinforced composites, were tested at the dynamometer. A two-probe method was considered to measure the relative electrical resistance of these composites during loading. The measured relative electrical resistance includes volume and contact electrical resistances. For all tested specimens, it increases with an increase in tensile strain, at low strain values. This is explained by the improved alignment of fibers and resulting reduction of the number of possible contacts between fibers during loading, increasing as a consequence the contact electrical resistance of the composite. Laboratory tests on strengthening of structural elements were also performed, making hand-made composites by the “wet process”, which is commonly used in civil engineering for the strengthening of all types of structures in-situ. Results show that the woven epoxy composite, used for strengthening of concrete elements is also able to sense low deformations, below 1%. Moreover, results clearly show that this textile sensor also improves the mechanical work of the strengthened structural elements, increasing their bearing capacity. Finally, the set of obtained results supports the concept of a textile fabric capable of both structural upgrade and self-monitoring of structures, especially large structures of difficult access and needing constant, sometimes very expensive, health monitoring.

Water Tower Materials Experimental Investigations and Technical Condition Assessment after 55 years of Exploitation

The purpose of this work was to define the technical condition of the water tower building and an indication of the ways of repairing and strengthening the structure. The function of the building is to provide water under high pressure to water supply installation for a water railway distribution station. The structure was built in 1959. The building consists of four floors above the ground and the basement. The main masonry structure is made of brick casted on lime and cement mortar. Each story is separated by reinforced concrete ceilings constructed as two-way slabs supported by beams. A circumferential reinforced concrete water tank is situated on the top floor. The tank consists of two chambers with the total volume of 250 m3. Reinforced concrete stairs are located around the circumferential wall of the building and provide service and technological communication in the building. The roof is constructed with reinforced concrete panels. The scope of the study includes a technical condition assessment of masonry walls, reinforced concrete floors (slabs and beams), stairs, the tank and the dome. For this reason, experimental researches on structural elements were performed. Researches of structural concrete include destructive tests made on drilling trial elements and non-destructive tests, to qualify mechanical properties of the material. Supplementary tests concern the humidity measurements and concrete alkalinity examination. For detection of rebar in structural elements, scanning of the specimen surface was performed and the concrete cover was removed in several places. For brick walls the main attention was focused on moisture content measurements. Experimental investigations and on-site inspections made it possible to assess the level of consumption of individual elements and durability of the structure. On this basis, main guidelines for necessary repairs and strengthening of structural elements which endanger the safety of exploitation were proposed.