Plain Rebars Research Articles

A comparative study on the microstructure, hardness and corrosion resistance of epoxy coated and plain rebars

Corrosion of steel rebars and susceptibility of reinforcement steel to chloride ion attacks are the two major problems for the construction industries and thereby a huge amount of money is spent to repair it. Epoxy coating on the steel rebars can be one cost-effective solution to alleviate the detrimental effects of corrosion in concrete structures. In the present research, plain and epoxy coated rebar (ECR) samples were chosen to study the correlation between microstructure, hardness and corrosion performance. The microstructures of the investigated thermomechanically treated (TMT) rebars primarily reveal tempered martensitic rings at the outer surface followed by a narrow bainitic transition zone in between along with a ferrite-pearlite microstructure at the inner core. The corrosion resistance of plain and epoxy-coated rebars in naturally aerated 3.5% NaCl and 1% HCl solutions were studied using gravimetric test, open circuit potential (OCP) test, and linear polarization monitoring techniques. It has been witnessed that the corrosion current (icorr) has been shifted towards lower values and polarization resistance (Rp) values are higher for ECR samples which is a clear indication of higher corrosion resistance of the ECRs than the plain rebars. Energy dispersive spectroscopy (EDS) analysis reveals the presence of iron hydroxides and iron oxides. However, x-Ray diffraction (XRD) analysis indicates the existence of various types of oxides, hydroxides, and oxy-hydroxides like iron chloride hydroxide [Fe2(OH)3Cl], goethite (α-FeO(OH)), lepidocrocite (γ-FeO(OH)), magnetite (Fe3O4) and bernalite [Fe(OH)3(H2O)0.25] in the epoxy coated rebar samples whereas, plain rebars indicate the presence of goethite (α-FeO(OH)), maghemite (γ-Fe2O3), magnetite (Fe3O4), hydrogoethite (Fe2O3.H2O), lepidocrocite (γ-FeO(OH)) and iron oxide (Fe21.34O32). All the experimental results confirm that ECR samples are more corrosion resistant under both acidic and saline environments.

Seismic Performance Assessment of RC Buildings Reinforced with Plain Rebars

Seismic Performance Assessment of RC Buildings Reinforced with Plain Rebars

Probabilistic structural performance of RC frames with corroded smooth bars subjected to near- and far-field ground motions

This paper investigates the seismic vulnerability of existing RC frames exposed to corrosion and subjected to near-field and far-field ground motions. A threefold approach for corrosion is adopted to illustrate the probabilistic framework and define time-dependent performance criteria for an accurate seismic fragility assessment. A bond-slip model is employed to simulate the fixed-end rotation and column-beam joints behaviour to account for the deficit in the bond strength of plain rebars. Such a model is calibrated using experimental studies from the literature and considering the effects of corrosion. An inelastic buckling model of steel bars is also incorporated in the finite element model through a hysteretic material to investigate its impact on the deformation capacity of RC members. The effects of near-field and far-field earthquakes are investigated through incremental dynamic analyses (IDA) and cloud analyses on a typical four-storey RC frame with plain bars. Results from the fragility analysis indicate that corrosion has significant effects on the seismic performance of such RC frames over time and near-field pulse-like motions are more destructive than both near-field no-pulse-like and far-field earthquakes.

A simple and safe brick masonry infill construction for high seismic-prone area

West Sumatera Province has been known as one of the high seismic-prone areas in Indonesia. In this area, peoples commonly use the brick masonry as infill in the Reinforced Concrete (RC) frame structures. Field investigation after the earthquake informed that there were many bricks masonry infill collapsed caused by the earthquake motion. In this study, a simple and safe brick masonry infill construction in the RC frame structure is proposed for applying in the high seismic-prone area such as West Sumatera. The proposed construction method was defined based on the experimental works of the three 1/4 reduced-scale singe-bay and single-story RC frame specimens. The specimens include one specimen of RC frame infilled with brick masonry, one specimen of RC frame infilled with strengthened brick masonry by using chicken wire mesh, and one specimen of RC frame infilled with brick masonry infill and anchored to the columns with plain steel rebars. The wire mesh was sewn on both sides of the diagonal area of the brick masonry infill. All the specimens have subjected to lateral static reversed loading. The structural test results have shown that the strengthening using the chicken wire mesh increase the lateral strength of the RC frame about 22.%, while the use of the plain rebars anchor decreases the lateral strength about 1.8% and both methods can delay the failure of the brick masonry infill.

Effect of Deformed and Plain Rebars on the Behavior of Lightly Reinforced Boundary Elements

In recent earthquakes common failure modes of lightly reinforced shear walls includes rebar fracture and out of plane buckling of boundary elements. In latest edition of ACI 318 and also latest amendment of NZS 3101-2006 to avoid rebar fracture in boundary elements, minimum longitudinal reinforcement ratio is increased. This experimental study investigates that rather than increasing the reinforcement ratio, is it possible to avoid rebar fracture by use of plain rebars in the critical sections of boundary elements in lightly reinforced shear walls. Experimental program includes specimens with plain and deformed rebars tested under monotonic and cyclic loading. Strain profile of the rebars are evaluated employing correlation between hardness and residual strain. Results indicate that failure of specimens with plain rebars occurs on single crack, however they have more uniform strain profile. On the other hand, in the specimens with plain and deformed rebars, out of plane buckling occurs at same crack width, but different elongations. It is shown that local strain demand (crack width) has better correlation with out of plane buckling in comparison with average axial strain.

Bond strength of rebars in cement stabilised rammed earth

Rammed earth construction involves compacting processed soil in progressive layers inside a rigid formwork. Rammed earth structural elements experience bending stresses under lateral loads such as wind and earthquake loads. The flexural strength of cement stabilised rammed earth (CSRE) walls is low. Reinforcing the rammed earth will improve the flexural strength of rammed earth to resist lateral loads. There is hardly any information on the bond strength of rebars embedded in CSRE matrix. There is a need to examine the bond developed between rebar and CSRE matrix. This paper focuses on determining the bond strength between rebar and CSRE; establish bond force – slip relationships for reinforced CSRE. The variables considered in the study included two dry densities (1800 and 1900 kg/m3), two cement contents (7% and 10%) and three types of rebars. The CSRE cubes embedded with different types of rebars were tested for pullout loading under two testing conditions (dry and wet). The bond strength of rebars in CSRE matrix was found to be greatly influenced by the dry density of the CSRE and the type of reinforcement. The bond strength of deformed rebars is higher than the plain rebars irrespective of the specimen density.

Rotation Capacities of RC Columns Reinforced with Plain Rebars

ABSTRACT Plain rebar-induced failure mechanisms in reinforced concrete columns shed new light on seismic assessment and risk mitigation strategies of historical reinforced concrete structures. However, the assessment provisions have not been evaluated and compared for RC columns reinforced with plain rebars on probability of failure scale. Thus, a database of 81 rectangular RC columns was constituted in which the yield and plastic rotations were revealed strongly dependent on shear span to depth ratio and axial load, respectively. All code provisions related to plastic rotation estimations were adjusted to 15%of failure probability while abiding by the code characteristics.

Damage and Loss Assessment of Pre-70 RC Frame Buildings with FEMA P-58

Past earthquakes have shown that seismic events may incur large economic losses in buildings. FEMA P-58 provides engineers a practical tool for the performance seismic assessment of buildings. In this article, FEMA P-58 is applied to a typical Italian pre-1970 reinforced concrete frame building, characterized by plain rebars as steel reinforcement and masonry infills and partitions. Given that suitable tools for these buildings are missing in FEMA P-58, in the first part of the article, specific fragility curves and loss functions for the main structural and non-structural components of the building type under consideration are proposed. In the second part, building performance is evaluated following a time-based assessment approach. Expected economic losses in form of repair costs are then derived. Finally, results are compared with those from past applications to old RC frame buildings.

Influence of nano-SiO2 and nano-Al2O3 additions on steel-to-concrete bonding

The research on nanoparticles is quite recent and potentially relevant in different contexts, including the concrete field. Fiber reinforced concrete presents several advantages, one of which its capacity to best control cracking. In this scope, the bond between steel rebars and/or fibers and the binding paste plays a most relevant role. The study herein described was developed aiming at analyzing the influence on the latter, and as a consequence on cracking, of nano-Al2O3 and nano-SiO2 additions.In the experimental analysis, the following materials were adopted: both plain and ribbed rebars, eight different concrete mixtures, two types of nanoparticles additions, namely nano-Al2O3 and nano-SiO2, and, in some mixtures, steel fibers. Overall, thirty-two pull-out tests, plus sixteen tensile tests on reinforced concrete ties, were performed. It was concluded that adding nanoparticles to the concrete paste leads to an increase of the steel-to-concrete bond, for mixtures with higher percentage of cement. It was also concluded that Al2O3 nanoparticles induce a beneficial effect in terms of cracking, decreasing the width of these when plain rebars are used.

Stiffness modeling of RC columns reinforced with plain rebars

Inaccurate predictions of effective stiffness for reinforced concrete (RC) columns having plain (undeformed) longitudinal rebars may lead to unsafe performance assessment and strengthening of existing deficient frames. Currently utilized effective stiffness models cover RC columns reinforced with deformed longitudinal rebars. A database of 47 RC columns (33 columns had continuous rebars and the remaining had spliced reinforcement) that were longitudinally reinforced with plain rebars was compiled from literature. The existing effective stiffness equations were found to overestimate the effective stiffness of columns with plain rebars for all levels of axial loads. A new approach that considers the contributions of flexure, shear and bond slip to column deflections prior to yielding was proposed. The new effective stiffness formulations were simplified without loss of generality for columns with and without lap-spliced plain rebars. In addition, the existing stiffness models for the columns with deformed rebars were improved while taking poor bond characteristics of plain rebars into account.

Cyclic Behavior of Nonconforming Full-Scale RC Columns

Capacity models to assess structural safety are primarily based on experimental outcomes typical of new constructions. In order to analyze deformation and strength mechanisms of members that do not comply to current seismic codes and practices, an experimental investigation was undertaken on full-scale columns reinforced with deformed or plain rebars. The experiments involved eight tests under monotonic or cyclic actions on square or rectangular reinforced concrete columns designed according to provisions, construction practice, and material properties enforced between the 1940s and 1970s. Experimental outcomes allowed pointing out global and local behavior of RC columns typically found in existing constructions, in which both plain and deformed bars can be found. Theoretical plastic rotation capacities provided by the proposed supplement to the current ASCE standard are discussed in this paper and compared to those experimentally obtained. The results indicate that predicted plastic rotations corresponding to significant loss of lateral-force capacity are very conservative if compared with experimental outcomes. This seems especially clear in the case of columns reinforced with plain rebars. For these columns, the contribution of the base rotation on the global deformation mechanism is considerable.

PEMBANDINGAN KEKUATAN TARIK TULANGAN DENGAN MENGGUNAKAN ALAT BRINEL DAN MENGGUNAKAN UTM (UNIVERSAL TEST MACHINE)

Brinnel portable equipment is the most practical tool used in the field to determine the tensile strength of reinforcement. Basically brinnel validity of the tool is still very doubtful, as well as tools that existed at the Laboratory brinnel State Polytechnic of Jakarta. Based on these problems, research needs to determine the validity of the tool. The research was conducted by comparing the tensile strength test results between testing with tools brinnel and with UTM (Universal Test Machine). This test uses a test specimen plain rebars of 8 mm and 10 mm and 10 mm threaded bars, 13 mm and 16 mm. The length of the test object for testing using the UTM is 300 mm while for testing using a tool which is 700 mm brinel. From the test results comparing the data obtained between the tensile strength testing using the UTM and testing using tools brinnel. From testing the difference of tensile strength test results are quite significant. Testing with tools brinnel have lower results than testing with UTM with a difference of about 30%.
 
 Keywords: tensile strength, brinnel tools, Universal Test Machine

Seismic Analytical Model for Retrofitted Old Reinforced Concrete Structures

Abstract In seismic areas, a majority of such old buildings have only been designed for gravity loads or according to outdated seismic codes. Before1970's, smooth rebars were also extensively used in RC structures. As some of these buildings are still functioning, they need to be reassessed against seismic demands. Load bearing behaviour of concrete structures reinforced with smooth rebars is considerably affected by the slip deformation of the plain rebars. In this study a specific finite element model has been proposed for evaluating the seismic performance of these structures. The slipping characteristics of the smooth rebar have been incorporated in this model. To this aim, a tailored stress-strain property has been assigned to the steel fibers in tension. The model has then been calibrated/verified against several sets of experimental results, from other. In general satisfactory correlations have been noticed between the experimental results and the predictions from the proposed fiber element model. The model has also been used for a full seismic assessment of an existing RC building, having smooth rebars. In addition, the structure has been retrofitted with steel bracing, viscose dampers and base isolators schemes and their nonlinear seismic performance have been evaluated using the proposed model.

Seismic retrofitting of R/C columns having plain rebars using CFRP sheets for improved strength and ductility

This experimental work focuses on the retrofitting of reinforced concrete columns using carbon fiber reinforced polymer (CFRP) sheets to improve their strength and ductility capacities. Plain rebars, inadequate splicing lengths and insufficient stirrup spacing were the main parameters to reflect the old construction practice. The effectiveness of CFRP strengthening technique was studied. The test results showed that retrofitting with CFRP sheets was effective for columns with continuous rebars. However, only a slight improvement in performance was obtained for the retrofitted lap-spliced column. When the column was retrofitted by welding of dowel rebars with longitudinal rebars near splicing region and then wrapped with CFRP sheets, its strength, ductility and energy dissipation capacity improved significantly.

Pullout Tests on Deformed and Plain Rebars in Cement-Stabilized Rammed Earth

Stabilized rammed earth offers a low energy durable alternative to conventional building materials, such as masonry and processed timber, for low-rise residential projects. To date, rammed earth construction has mainly been used in the developing world, particularly Africa and Asia. Despite recent applications in Australia and the United States, further development of rammed earth in these countries has been hindered by a lack of data on important aspects of material performance. In this paper, work undertaken to assess bond of rebars embedded in rammed earth is described. A variety of cement-stabilized rammed earth pullout test samples were fabricated with deformed, galvanized deformed, plain, and stainless steel rebar. Pullout bond resistance is shown to be a function of rammed earth compressive strength, rebar type, embedment length, and the method of specimen preparation.

Bond and Slip of Plain Rebars in Concrete

Plain rebars are often used in precast concrete elements. The provision of plain rebars along either side of the precast joint will strengthen its resistance and provide greater ductility. However, to fully utilize plain rebars as reinforcement for concrete, some aspects of their behavior have to be determined, including bond and anchorage in concrete. In this paper, the bond strength of plain rebars in concrete is studied. Results of pullout tests on short lengths of plain and deformed rebars in concrete are presented. The effects of rebar type, rebar diameter, embedment length, concrete strength, and loading rate on the bond behavior are examined. It was found that (1) the bond strength of plain rebars was only 28.6 that of deformed rebars; (2) the slip at failure was greater for the plain rebars than for the deformed rebars; and (3) increasing the concrete compressive strength was able to improve the bond properties.