Mild Steel Reinforcement Research Articles

NONLINEAR FINITE ELEMENT ANALYSIS OF FULL-SCALE EXTERNAL POST-TENSIONED CONCRETE BOX GIRDER AT JACKING AND SERVICE

This paper presents the modelling of a 47-meter of simply supported full-scale external post-tensioned concrete box girder in a bridge using in-house software 3D-NLFEA. The Girder was designed with sections, adequate reinforcements, and the jacking force according to the codes to resist the live load. The objective of this work is to assess the global structural response i.e., the load and deflection capacity under service loading. The detailed response of anchorage and deviator segments concerning their micro-cracking behavior during jacking transfer and service load conditions was also discussed. The constitutive model of materials applied to the modelling covered the hardening and softening of concrete under tension and compression, the nonlinearity of mild steel reinforcement, and prestressing tendons. The first stage was to simulate the self-weight of the girder simultaneously with the application of jacking forces from the tendons. The second stage was to load the girder under three-point bending to replicate the typical wheel axle from vehicles. The load was in the form of displacement-controlled and it was applied at the top midspan. From the results obtained, it was shown that under service limit state conditions, the load-displacement curve of the girder was linear at elastic. Cracks in allowable limit manifested in several parts of anchorage and deviator segments by the end of prestressing sequences. This highlighted the importance of providing crack control reinforcement to alleviate the progression of cracks under jacking service load conditions.

Theoretical model of shear capacity of steel fiber reinforced concrete beams

One of the barriers to implementation of steel fiber reinforced concrete (SFRC) into structural applications is the lack of understanding of the shear behaviour of SFRC members. This paper proposes a theoretical model for the shear capacity of SFRC members with mild steel reinforcement based on the shear-carrying mechanisms and sectional analysis. The model is derived completely theoretically, based on concepts from the literature, and does not include new empirical aspects. The approach is then compared to 323 experiments from the literature of beams with slender, rectangular cross-sections failing in shear. It is found that the model is slightly conservative, and experimental research necessary to further develop the model is described. The presented theory aims to be a framework for a fully theoretical description of the shear capacity of SFRC members with longitudinal reinforcement and without shear reinforcement.

Investigating the standard sizes of steel reinforcement used in the Ghanaian industry

The study aimed to explore and determine whether the steel reinforcement bars manufactured and used in Ghana meet the standard sizes. The research adopted a positivist philosophy and a market survey approach. The various organizations manufacturing and supplying steel reinforcement were purposively selected and visited, and the different steel reinforcement bars were measured against the standard sizes. When the measured sizes were compared to the standard sizes, the results revealed that all the mild steel reinforcement bars measured did not meet the required standard sizes. The results showed that all the high tensile steel reinforcement bars met the necessary standard sizes in the Ghanaian construction market. The research empirically demonstrated that non-standard steel reinforcement bar sizes impact most project outcomes. The regulatory authority (National Standard Authority) must ensure that both manufactured and imported steel reinforcement bars meet the standard sizes on the construction market in Ghana to keep the project under control and enable the structure to achieve its maximum strength.

Comparative Analysis of Aluminum Alloy 6061-T6 and Mild Steel Tubes in Sacrificial Protection System under Blast Loading

A sacrificial cladding consist of hollow metal tubes and steel sheet, is proposed in this study to protect a square concrete panel subjected to blast loading. Herein, comparative analysis of aluminum alloy 6061-T6 (Al 6061-T6) and mild steel tubes in sacrificial cladding is done using 3-D non-linear Finite Element (FE) software ABAQUS/Explicit®. Blast load is applied through ConWep program developed by US Army. Simplified Concrete Damage Plasticity (SCDP) model is used to define the material behavior of concrete slabs of thickness 250 mm. Johnson-Cook (J-C) plasticity model is used to model the stress-strain response of Al 6061-T6 and mild steel tubes, reinforcement bars and steel sheet. Diameter (D) and thickness (t) of circular metal hollow tubes are taken from IS1161:1998. Comparative analysis of Al 6061-T6 and mild steel tubes is carried out for blast loading using TNT with scaled distance of 0.425 m/kg1/3. It was observed that mild steel tubes perform better than Al 6061-T6 tubes and save concrete panel from degradation under blast loading.

Seismic behaviour of post-tensioned concrete shear wall: a review

Shear walls are specifically meant to withstand lateral forces exerted by either wind or earthquake loads on a structure. Due to their superior strength and stiffness, shear walls have been an integral feature of mid-rise and high- rise structures over the past two decades. Various studies have been performed in this field. Usage of post-tensioned tendons in the traditional shear wall is one of the major advancements in recent times so as to increase the stiffness and reduce the damage incurred by destructive earthquakes. The key advantage of post-tensioned shear walls is the potential to re-centre after a devastating earthquake which is lacking in conventional reinforced concrete (RC) shear walls that rely on yielding creating large deformations. Moreover, compared with conventional shear wall construction, post-tensioned shear walls can reduce the use of vertical mild steel reinforcement. This results in materials being used more effectively and eliminates congestion. This paper seeks to review and analyze the research studies based on post- tensioned shear wall focusing on works published within the last decade. Firstly, the benefits of using post-tensioned shear walls in seismically active areas are illustrated. The behaviour and parameters controlling the performance of post-tensioned shear walls are then studied. A critical study of the factors responsible for the performance of post- tensioned shear wall is the primary objective of this review.
 Keywords- Shear Wall, Post-Tensioning, Energy-Dissipation, Self-Centering

Flexural behaviour of ferrocement septic tank wall panels reinforced with glass fibers

This paper presents the load –deflection behaviour and energy absorption capacity of ferrocement glass fiber reinforced septic tank wall panels. Cement mortar 1:2 proportion and two layers of welded wire mesh along with 6 mm mild steel reinforcement are used in the manufacturing of septic tank wall panels. In additional glass fibers are added in five different volume fractions such as 0.1%, 0.2%, 0.3% 0.4% and 0.5%. Flexural test were conducted on five series of glass fiber reinforced septic tank wall panels. Load deflection behaviour, Energy absorption capacity and flexural strength are measured and compared with plain matrix behaviour. The addition of glass fibers improved the flexural strength upto 31% as well as it enhances the energy absorption capacity to 5 to 8 folds greater than the control specimens.

Effect of non-uniform corrosion on the cracking propagation of the RC specimens

This paper investigates the influence of non-uniform corrosion of the mild steel reinforcement on the cracking propagation of the concrete cover. Partial surface of the reinforcement was coated by an epoxy resin in order to prevent the covered surface of the steel from corrosion. As a result, the reinforcement was corroded partially along the surface by an impressed current in this way. The corrosion propagation of the steel reinforcement and the corrosion-induced cracking process was investigated during different corrosion periods. The width and the cracking paths were observed carefully. The results showed that two cracking paths would happen to the concrete cover due to the non-uniform corrosion of the steel reinforcement, including the corrosion-induced crack along the radius direction of the concrete cover and two branches in the secant direction of the corrosion zone. The aggregate of the concrete could also influence the propagation of the cracking path significantly.

Optimum design for unbonded posttensioned precast concrete frames with damping

SummaryPrecast concrete facilitates the construction process using durable and rapidly erectable prefabricated members to create cost‐effective and high‐quality structures, which has been widely used in some areas including those with high seismicity. A member of this precast structure family, the unbonded posttensioned precast concrete frames with damping, was proposed in the Precast Seismic Structural Systems (PRESSS) program. The PRESSS had presented a design procedure for the new system, which requires a time‐consuming iteration using trial and error. The aim of this study is to develop an automatic optimum design procedure as an alternative to the design of this system. Specifically, the objective of the optimum process is to find the minimum area of PT tendons, the maximum area of mild steel reinforcement, and the minimum unbonded length for mild steel while obtaining the maximum energy dissipation, maintaining moment capacity similar to design moment, and achieving zero residual drift, simultaneously. To this end, computer program MATLAB was utilized to develop an optimization design procedure using a genetic algorithm (GA). Comparing the results with that from the existing method indicates the proposed optimum design program is accurate, efficient, and direct. In addition, the program can present the optimum result within 1 min. Therefore, the existing iterative, step‐by‐step design method could be replaced.

Seismic Response of Post Tensioned Hybrid Shear Walls with External Energy Dissipating Reinforcement (EEDR)

ABSTRACT A major limitation with conventional post-tensioned (PT) shear wall in seismic areas is its low energy dissipation, which is tackled by placing additional mild steel reinforcement at the intersection of the wall and the foundation, called internal energy dissipating reinforcement (EDR). While the behavior of hybrid walls with internal EDR is satisfactory, the replacement of them post-yielding (i.e., after an earthquake) poses a major concern. Therefore, in this study, a new simple arrangement is proposed with external-energy-dissipating-reinforcement (EEDR) to facilitate its easy placement and replacement. This proposed system is expected to enable convenient rehabilitation of the wall after an earthquake and will keep it ready for next seismic shock. A detailed numerical study has been conducted to examine the feasibility of the proposed configuration. The proposed model depicts rocking behaviour with sufficient self-centering and energy dissipation. Having external EDR in the hybrid PT shear wall resulted in an increase in energy dissipation but keeping the strength and stiffness of the wall nearly unaffected. This study has highlighted the effectiveness of proposed external EDR system without significantly compromising the performance of a hybrid PT shear wall during an earthquake.

Flexural Strength Test For Concrete Beam With Mild Steel and Reinforcing Iron

Mild steel in buildings tends to only be used as a roof frame. The phenomenon in the field that lightweight steel roof truss can be combined with mortar mixture. In general this union is found on the walls of the construction of the red stone horses. This phenomenon is captured and applied dynamically, creatively, and innovatively with new idioms. Mild steel can be used as a beam reinforcement. This research is important in order to find alternative reinforcement of beams other than iron and strong beam reinforcement. This study aims to determine the ratio of flexural strength between concrete from mild steel reinforcement and concrete from steel reinforcement. This study uses a concrete flexural strength test and simple test beam method. The test beam is loaded and centered directly. Press testing machine is used as a flexural test device. The machine is equipped with two support beams and one load beam, load construction, and support blocks. Six beams are used as specimens. Test objects are made of different reinforcement. Concrete beams are made from a cross section of 600 mm x 150 mm x 150 mm, used reinforcing iron diameter of 6 mm, and amounting to three (first test object). Concrete beams are made from a cross section of 600 mm x 150 mm x 150 mm, mild steel is used with the profile shape C73.35.10 mm, and there are three pieces (second test object). This study concluded that the test beam was made from a cross section of 600 mm x 150 mm x 150 mm. and mild steel (profile C73.35.10 mm) has twice the maximum flexural strength compared to 600 mm x 150 mm x 150 mm cross section beam and reinforcing iron (6 mm diameter).

Experimental investigation of bond behavior of mild steel reinforcement in UHPC

Ultra-High Performance Concrete (UHPC) is a relatively new class of advanced cementitious composite material, which exhibits high compressive and tensile strengths. The discrete steel fiber reinforcement included in UHPC allows the material to maintain a tensile capacity beyond cracking of the cementitious matrix. The bond behavior of deformed reinforcing bar in UHPC is investigated in this study by conducting pull out tests and beam tests with lap splices. The rebar used for these tests are #4 (M13), #5 (M16) A615 grade 60 bars and # 6(M19), #7 (M22) A615 grade 80 bars. The embedment length and side cover for the pull out tests were varied from 6db to 8db (db = diameter of the rebar) and 1db to 3.5db, respectively. The beam tests were conducted under four-point loading and the clear cover for these tests was varied from 1db to 3db. The rebar for all beam specimens were spliced at mid-span for a length of 8db. The beam specimens were instrumented to capture the strains at different points along the splice length. 16 pull out and 12 beam tests were completed and the effect of embedment length, concrete cover, bar size and bar type on the bond strength were investigated. This paper presents the details of this experimental investigation and adds significant new data on the bond stress distribution along the development length. It was found that the development length of embedded reinforcement in UHPC can be significantly reduced when compared to normal concrete.

Seismic Behavior of Hybrid Post-Tensioned Cast in Place Concrete Shear Walls

A hybrid concrete shear wall system is created by combining the conventional reinforced concrete construction with post-tensioning technology. Such hybrid shear wall with continuous mild steel combined with post-tensioned (PT) steel provides superior restoring, energy dissipation, and ductile behavior over larger lateral displacements. Hence, both mild steel and high-strength post-tensioning steel contribute to the flexural strength. This leads to a reduction in the total area of steel when compared to the conventional reinforced concrete shear wall. When using a hybrid system, the lateral load response varies based on the ratio of post-tensioning steel to the mild steel reinforcement. In this research, the seismic behavior of hybrid unbonded PT concrete shear walls is investigated. Finite element analysis using ABAQUS for multi-hybrid shear walls of different ratios of post-tensioning steel area to mild steel area is performed. Results show that the large nonlinear displacements in PT shear wall may be reduced by using more mild steel reinforcement in the hybrid unbonded PT system. The post-tensioning steel provides a restoring force that eliminates the permanent deformation after cyclic load and reduces the displacement peaks during a cycle. However, PT walls incorporating only post-tensioning bars do not provide a sufficient amount of energy dissipation to limit seismic displacement adequately. By increasing the mild steel reinforcement area concerning the post-tensioning steel area, seismic energy can be dissipated by the yielding of mild steel.

Pseudo-static cyclic loading comparison of reinforced masonry walls strengthened with FRCM or NSM FRP

Fiber reinforced polymer (FRP) composites have demonstrated poor performance in high temperature environments where the glass transition temperature of the resin is exceeded and this justifies the need to examine alternative strengthening techniques such as near surface mounted (NSM) reinforcement with cementitious adhesive or fabric-reinforced cementitious matrix (FRCM) systems. Evaluation of pseudo-static cyclic performance of these strengthening systems is of high interest. In this study, twelve reinforced masonry walls were strengthened in out-of-plane direction using FRCM composite or NSM with cementitious adhesive that were built as a part of this study. FRCM strengthening composite materials consisted of one or two plies of carbon or PBO (polyparaphenylene benzobisoxazole) fabric embedded in cementitious mortar. The NSM technique consisted of carbon or glass bar(s) installed in slots that had been grooved into the masonry tension surface. For all these specimens, a constant mild steel reinforcement ratio (ρ) was used in fully grouted walls. These simply supported walls were tested under out-of-plane constant-amplitude displacement cycles. The key parameters for this investigation were bond pattern (stack and running) and the type and amount of fabric/NSM product. The behavior of the specimens is discussed with emphasis on the load deflection response, flexural capacity, energy dissipation, stiffness degradation, and ductility index. The test results indicated that the behavior of the slender (i.e. non-arching) reinforced masonry walls was significantly dependent on the type of fiber used. The maximum flexural enhancement was found to be 97% and 75%, and the dissipated energy of the specimen with stack bond pattern was increased by 38% and 62% for masonry walls strengthened with FRCM and NSM system, respectively, compared to the control specimen. Different modes of failure occurred in the strengthened reinforced walls, including crushing of concrete block, as well as a debonding of NSM bar or fabric sheet from the masonry substrate and slippage of fabric within the cementitious matrix.

Bond of steel reinforcement with microwave cured concrete repair mortars

This paper investigates the effect of microwave curing on the bond strength of steel reinforcement in concrete repair. Pull-out tests on plain mild steel reinforcement bars embedded in four repair materials in 100 mm cube specimens were performed to determine the interfacial bond strength. The porosity and pore structure of the matrix at the steel interface, which influence the bond strength, were also determined. Test results show that microwave curing significantly reduces the bond strength of plain steel reinforcement. The reduction relative to normally cured (20 °C, 60% RH) specimens is between 21 and 40% with low density repair materials and about 10% for normal density cementitious mortars. The corresponding compressive strength of the matrix also recorded similar reduction and microwave curing resulted in increased porosity at the interface transition zone of the steel reinforcement. A unique relationship exists between bond strength and both compressive strength and porosity of all matrix materials. Microwave curing reduced shrinkage but despite the wide variation in the shrinkage of the repair mortars, its effect on the bond strength was small. The paper provides clear correlations between the three parameters (compressive strength, bond strength and porosity), which are common to both the microwave and conventionally cured mortars. Therefore, bond-compressive strength relationships used in the design of reinforced concrete structures will be also valid for microwave cured elements.

Lightweight HPC beam OMEGA

In the design and construction of precast bridge structures, a general goal is to achieve the maximum possible span length. Often, the weight of individual beams makes them difficult to handle, which may be a limiting factor in achieving the desired span. The design of the OMEGA beam aims to solve a part of these problems. It is a thin-walled shell made of prestressed high-performance concrete (HPC) in the shape of inverted Ω character. The concrete shell with prestressed strands is fitted with a non-stressed tendon already in the casting yard and is more easily transported and installed on the site. The shells are subsequently completed with mild steel reinforcement and cores are cast in situ together with the deck. The OMEGA beams can also be used as an alternative to steel - concrete composite bridges. Due to the higher production complexity, OMEGA beam can hardly substitute conventional prestressed beams like T or PETRA completely, but it can be a useful alternative for specific construction needs.

Determination of the seismic performance factors for post‐tensioned rocking timber wall systems

SummaryPost‐tensioned technologies for concrete seismic resistant buildings were first developed in the 1990s during the PREcast Seismic Structural Systems program. Among different solutions, the hybrid system proved to be the most resilient solution providing a combination of re‐centering and energy dissipative contributions respectively by using post‐tensioned tendons and mild steel reinforcement. The system, while providing significant strength and energy dissipation, reduces structural element damage and limits post‐earthquake residual displacements. More recently, the technology was extended to laminated veneer lumber (LVL) structural members, and extensive experimental and numerical work was carried out and allowed the development of reliable analytical and numerical models as well as design guidelines. On the basis of the experimental and numerical outcomes, this paper presents the evaluation of the seismic performance factors for post‐tensioned rocking LVL walls using the FEMA P‐695 procedure. Several archetype buildings were designed considering different parameters such as the building and story height, the type of seismic resistant system, the magnitude of gravity loads and the seismic design category. Lumped plasticity models were developed for each index archetype to simulate the behavioral aspects and collapse mechanisms. Non‐linear quasi‐static analyses were carried out to evaluate the system over‐strength factor; moreover, non‐linear time history analyses were performed using the incremental dynamic analysis concept to assess the collapse of each building. From the results of quasi‐static and dynamic analyses the response modification factor, R, system over‐strength factor, Ω0, and deflection amplification factor, Cd, values of, respectively, 7, 3.5 and 7.5 are recommended. Copyright © 2016 John Wiley & Sons, Ltd.

Behavior Comparison of Prestressed Channel Girders from High-Performance and Ultrahigh-Performance Concrete

In response to the demand for sustainable and improved bridge design practices, the development of emerging materials like ultrahigh-performance concrete (UHPC) is at the forefront of structural innovation. UHPC offers significant advantages to bridge superstructure design as it provides advanced mechanical and durability properties, including high compressive strength and increased tensile capacity. With the introduction of high-strength steel fibers into mixture proportions, postcracking tensile and flexural tensile capacities are increased. These increased tensile capacities provide greater ductility and reduce or possibly eliminate the need for mild steel reinforcement. The present research investigated the behavioral response of full-scale prestressed bridge girders subjected to four-point flexural loading. Two channel-shaped girders were designed to provide equal design moment capacities to facilitate comparative analyses of performance. The first of these girders was designed with high-performance concrete [HPC; 9.5 kips per square inch (ksi; 66 MPa)] and mild steel reinforcement typical of that used in New Mexico bridge designs. The second girder used nonproprietary UHPC [20 ksi (138 MPa)] mixture proportions consisting primarily of local materials, local mixing procedures, and a local curing regimen, all of which were developed at New Mexico State University, Las Cruces. Digital image correlation was used to capture deformations throughout the testing. This information creates a full field of displacements that captures tensile and compressive strain behaviors in the pure moment region. This investigation demonstrated the advantages and improved performance of UHPC and the contribution of steel fiber reinforcement to postcracking strength and flexural capacity.

INFLUENCE OF NEAR-SURFACE MOUNTED FRP WITH CEMENTITIOUS MATERIAL ON OUT-OF-PLANE BEHAVIOR OF REINFORCED MASONRY WALLS

Eight medium scale reinforced masonry walls were built as a part of this study. These reinforced walls were strengthened using carbon fiber reinforced polymer [FRP] (bars and tapes) and glass FRP (bars) using a near surface mounted technique (NSM) with cementitious material; constant mild steel reinforcement ratio (ρ) was used. These strengthened walls were supported as a simply supported wall under an out-of-plane cyclic load applied along two line loads. This study presented the effect of different parameters, these parameters related to FRP (type and amount), bond pattern (stack and running), and existing of FRP in compression face of the walls. This paper reveals the relation between these factors and the out-of-plane capacity of the reinforced wall strengthened with FRP. Different modes of failure occurred in the strengthened reinforced walls, including a punching shear failure through the concrete block, crushing of concrete block and debonding of FRP reinforcement from the masonry substrate.

Seismic Performance of Full-Scale Post-Tensioned Timber Beam-Column Connections

Structural frames made of prefabricated laminated timber beams and columns connected by unbonded post-tensioning and additional mild steel reinforcement have recently been proposed for multi-story timber buildings. The benefits of post-tensioning to assemble prefabricated timber elements are rapid erection, simple connections, and high seismic resistance. It has been shown that prefabricated post-tensioned timber members can be designed to have excellent seismic resistance, with the post-tensioning providing re-centering capacity after major earthquakes, while energy is dissipated through yielding of replaceable mild steel devices.This article summarizes the results of an investigation into the seismic response of full-scale timber beam-column joints, subjected to extensive experimental study and numerical modelling, performed as part of a larger research program on timber structures at the University of Canterbury, New Zealand. The beams and columns were fabricated from laminated veneer lumber (LVL). The tested joint was designed as part of a moment-resisting frame for a six-story building located in a high-seismic region. The timber members and the re-centering/dissipating elements were optimized to produce the intended dissipating-recentering behavior and commercially available prestressing arrangements were used to verify their applicability in a timber structure.The results of the experiments on both interior and exterior beam-column joints are presented, for both post-tensioned-only and hybrid models. The post-tensioned-only solutions exhibited nonlinear elastic behavior with full re-centering while the hybrid systems provided significantly greater levels of energy dissipation compared with the post-tensioned-only solution. The joints were also tested with a number of additional features such as steel armoring plates at the interface, reinforcement in the form of long screws embedded into the column and combination of the two. The armored the column faces with steel plates exhibited higher stiffness and smaller deformation in compression perpendicular to the grain. The joint region within reinforced column reduce the subsequent drop in prestressing forces in the system. Combination of armoring and reinforcements protect the joint region through minimizing joint shear panel deformation. In general, the tested arrangements exhibited high levels of ductility and negligible residual deformations with no significant damage of the structural elements. The numerical models accurately predict the behavior of different types of beam-column joints tested and can be used to design similar connections. These full-scale tests also demonstrate the practical feasibility of post-tensioned timber frames for multi-story timber buildings.

Nonlinear quasi-static analysis of hybrid sliding–rocking bridge columns subjected to lateral loading

In this paper, a nonlinear three-dimensional finite element (FE) model for a hybrid sliding–rocking (HSR) column is developed. The HSR columns are segmental members incorporating internal unbonded post-tensioning, rocking joints at the member ends, and intermediate sliding joints along the member height. The HSR columns introduce new design parameters (e.g., frictional properties at the sliding joints, amplitude of joint sliding, number/distribution of sliding joints along the column height) and additional modeling challenges (e.g., contact interactions between adjacent segments and between segments and the internal unbonded post-tensioning tendons) as compared with conventional monolithic or rocking-only members. In the proposed modeling approach, contact interaction amongst adjacent segments and between segments and unbonded tendons are captured. Concrete segments are modeled using solid elements, mild steel reinforcement is modeled by beam elements embedded into the concrete segments, and the unbonded tendons are modeled using truss elements. The FE model was validated against available experimental data and was then used to conduct a parametric pushover study. Variations of the external vertical load were found to have minor effects on the lateral column response. Increase of the initial post-tensioning force resulted in early onset of inelastic response of the tendons, while the peak lateral column strength remained unchanged. Joint sliding increased the lateral deformation capacity of the column. Propagation of sliding from bottom to top and vice versa had small effects on the lateral response of the column. Propagation of sliding was controlled by the friction properties at the sliding joints.