Compression Reinforcement Research Articles

Fiber-reinforced polymers bars for compression reinforcement: A promising alternative to steel bars

Abstract Fiber-reinforced polymers (FRP) have been introduced as alternative reinforcement for concrete members since decades. Nevertheless, current design codes prohibit the use of FRP bars as main reinforcement in compression members such as columns. Recently, several studies came into sight focusing on evaluating the compressive response of FRP-reinforced concrete (RC) columns. While many of these studies have praised the performance of FRP bars in RC columns, others conservatively neglected their contribution to the columns’ capacities. The objective of this study is to present a comprehensive literature review on FRP-reinforced columns in order to better understand their performance under various loading conditions. To do so, the authors collected and analyzed the results of more than 300 tests published in 43 different experimental and analytical studies in the scientific literature. The collected columns were classified according to their slenderness, loading regime, cross sections, concrete type, and reinforcement. The design equations proposed by several authors to predict the load-carrying capacities of the tested columns were collected and assessed. The work presents a critical review of the existing research on FRP-reinforced columns, identifies gaps in knowledge, and outlines directions for future research. The analysis of the collected data and the accuracy of several design approaches in predicting the behavior of FRP-reinforced columns suggests that it is time for code authorities to recognize the use of FRP in compression members.

Effects of the Reinforcement Positions and Number of Nickel-Titanium SMA Wires on the Structural Properties of HIHFR Beams

This study investigated the effects of the reinforcement positions and the number of shape memory alloys (SMAs) on the structural characteristics of highly intelligent hybrid fiber reinforced concrete (hereinafter, HIHFR) beams. First, tests were conducted under monotonic loading conditions. To examine such structural characteristics, the load-deflection curve relationship and crack patterns, temperature and energy absorption, temperature and displacement ductility, displacement ductility and energy absorption, and the relationship between the displacement ductility and resilience were compared and analyzed. The reinforced concrete beam (RCB) exhibited somewhat excellent values in terms of displacement ductility, but showed the lowest values in terms of strength, resilience, and energy absorption capacity. HIHFR1 exhibited the most excellent results among the test samples in terms of resilience and energy absorption capacity. Therefore, SMAs were partially substituted for the compressive, tension, and shear reinforcement of the existing RCBs. As a result, the substitution for the compressive and tension reinforcement exhibited the best results, confirming the possibility of using SMAs as a substitute for steel reinforcement.

Uniaxial compression mechanical properties and fracture characteristics of brucite fiber reinforced cement-based composites

In this work, the mechanical properties, stress-strain behaviors, and microstructure of brucite fiber reinforced cement-based composites are determined. The results reveal that the incorporation of brucite fiber limits the compressive strength reinforcement of cement-based composite but leads to a significant increase of tensile strength by 136% and flexural strength by 73%. The employment of brucite fiber increases the fracture toughness KIcS and KIcQ of the cement-based composite by 450% and 98%. The incorporation of brucite fiber increases the linear elastic fracture toughness energy GF by 455% and elastic-plastic fracture toughness energy JC by 279%. The constitutive model of brucite fiber reinforced cement paste is also established. The diameter of the brucite fiber bundle is 1.5–16.3 μm, and the diameter of the single dispersed fiber is around 45–110 nm. There are about 15–363 single fibers in a bundle. Due to the brucite fiber possesses an intrinsic fibrous anisotropy, and network topology, the brucite fiber reinforced cement composites exhibit advantages of greater bending strength and crack bridging, as well as better crack resistance properties.

Experimental and numerical evaluation of reinforced dry-stacked concrete masonry walls

In dry-stack concrete masonry systems, masonry units are laid without mortar joints, reducing the cost and the time required for construction. Despite these advantages, mortarless construction has not been widely implemented, which is attributed to the fact that the behavior of dry-stack masonry wall systems is not yet fully understood. To help fill this knowledge gap, experimentally-validated finite element models of dry-stacked concrete masonry walls have been developed to investigate the effect of various design parameters (e.g., unit and grout compressive strength, yield strength, and reinforcement and grouting ratios) on the out-of-plane load-carrying capacity of the walls. The present paper reports the findings obtained from this combined experimental and numerical study to support the development of future design guidelines for dry-stack concrete masonry systems.

Effects of Tension Reinforcement Ratio on Ductility of Mid-Rise Reinforced Concrete Structures

Failure mode of reinforced concrete (RC) structures are classified according to tension reinforcement ratio of beam elements. To determine effect of tension reinforcement ratio on performance of RC structure, two planar RC structure were selected. One of them is 5 stories other of them is 7 stories. Two different concrete class, C20 and C25, were considered for analysis. Three tension reinforcement combinations were considered, three different tension reinforcement ratios were used. First case is the ratio of the tension reinforcement is lower than that of the compression reinforcement, second case is the ratio of the tension reinforcement is equal to the ratio of the compression reinforcement and third case is the ratio of the tensile reinforcement is higher than the compression reinforcement.

Reinforced Concrete Beam-Column Inverted Knee Joint Behaviour after Ground Corner Column Loss-Numerical Analysis

Abstract Beam-column joints are critical component in the load path of reinforced concrete (RC) frames, due to their role in transferring loads among different RC frame components. The loss of a ground corner column in a RC frame turns an exterior joint into an inverted knee joint and recent code provisions for exterior joints are not sufficient to knee joints because of reinforcement defects in terms of joint vertical stirrups and improper column bar anchorage. This paper investigates numerically the behaviour of these joints under a closing moment using nonlinear finite element (FE) analysis with LS-DYNA. Beam’s bar anchorage type and joint vertical stirrups are the main parameters considered next to concrete compressive strength, longitudinal reinforcement ratio and lateral beam effect. This study indicates that, anchorage beam’s bar with U shaped produces better behaviour than 90° standard hooks or headed ends. Contribution of joint vertical stirrups is more influential with headed bars anchorage. Increasing concrete compressive strength and beam reinforcement ratio improve joint ultimate capacity. The presence of lateral beams reduces the rate of concrete degradation in the joint after reaching ultimate capacity and increases joint carrying capacity.

Development mechanism of plastic hinge in reinforced engineered cementitious composite beams under monotonic loading

Engineered cementitious composites (ECCs) are materials featuring strain‐hardening behavior with the formation of multiple cracks. When ECC is incorporated in structural applications such as beam, it is expected to significantly improve their mechanical performance. In this study, finite element analysis is performed to investigate the characteristics of the plastic hinge in reinforced ECC (RECC) beams. The plastic hinge lengths of RECC beams, involving rebar yielding zone, concrete crushing zone and curvature localization zone, are found to be much larger than those for reinforced concrete (RC) beams. Based on the above results, parametric studies on the plastic hinge lengths in RECC beams are conducted to study the influences of the tensile\compressive properties of ECC, yielding strength\hardening modulus\ultimate strain of tensile reinforcement, tensile\compressive reinforcement ratio and beam size. This theoretical study has shown that the existing empirical models for RC beams' plastic hinge length are not applicable to RECC beams which exhibit much longer plastic hinge length. A new empirical equation for predicting the plastic hinge lengths of RECC beams is thus proposed.

Load and Deflection Recovery Capacities of PSC Girder with Unbonded PS H-Type Steel

Generally, a precast prestressed concrete (PSC) beam is used as girders for short-to-medium span (less than 30 m) bridges due to the advantages of simple design and construction, reduction of construction budget, maintenance convenience. In order to increase the span length beyond 50 m of precast PSC girder, PSC hollow box girder with unbonded prestressed H-type steel beam placed at the compressive region is proposed. The unbonded compressive prestressing in the H-type steel beams in the girder is made to recover plastic deflection of PSC girder when the pre-stressing is released. Also, the H-steel beams allow minimization of depth-to-length ratio of the girder by reducing the compressive region of the cross-section, thereby reducing the weight of the girder. A quasi-static 3-point bending test with 4 different loading steps is performed to verify safety and plastic deflection recovery of the girder. The experimental results showed that the maximum applied load exceeded the maximum design load and most of the plastic deflection was recovered when the compressive prestressing of H-type steel beams is released. Also using prestressed H-type steel as compression reinforcements in the upper part of cross section, repair and restoration difficulty and cost of PSC girders should be significantly reduced. The study result and analysis are discussed in detail in the paper.

Behavior of Foam Particles Lightweight Concrete with Time

Lightweight Concrete with polystyrene foam particles (LWC) was obtained through the use of polystyrene foam as a partial aggregate’s replacement to reduce the concrete dry unit weight from 23 KN/m3 to 18.50 KN/m3. This research presents an experimental and theoretical investigation in the long-term behavior of LWC in compression and flexure. Two experimental programs were conducted; namely, creep and shrinkage of LWC under compressive loading test, and the time-dependent flexural behavior of reinforced LWC beams. The main variable in the first experimental program was the percentage of sustained load, while the main variables in the second experimental program were the percentage of sustained load and the percentage of compression reinforcement. Experimental results showed that LWC exhibits a significantly higher time-dependent strain (shrinkage plus creep) than normal weight concrete (NWC) under sustained compressive load and at the same compressive strength, with an increasing percentage about 9%. The creep strains of LWC seemed to be proportional to the stress to strength ratio. The timedependent deflections of the LWC beams were higher than those of NWC beams with increasing percentage about 25%. Addition of compression steel reinforcement (As`) to LWC beams reduced time-dependent deflections. Sustained load level and LWC time-dependent deflection were directly proportional. Finally, models and equations proposed by different codes were used to evaluate the obtained experimental results. From the theoretical study, it was found that Bazant-Baweja B3 Model gave superior shrinkage strains prediction for LWC. The ACI 209R-92 presented preferable predictions of creep strain and time-dependent deflection of LWC.

Review of near-surface mounted FRP plates in the strengthening of continuous flexural members and bond behaviour

ABSTRACTBonding carbon fibre-reinforced polymers (FRP) to reinforced concrete (RC) flexural members has become a popular means to enhance load carrying capacity and prolong service life. Considering the type of FRP strengthening system, the near-surface mounting (NSM) technique of embedding FRP strips in saw-cut grooves within the concrete cover of RC members to flexurally strengthen beams and slabs is known to have desirable bond behaviour benefits over external bonded FRP plates. Further the NSM technique has attracted growing attention in strengthening of statically indeterminate RC members. However, little is known about the durability of the critical bond between the embedded FRP and the concrete when installed using this technique. In this paper, experimental results of continuous flexural members strengthened with NSM FRP is collated and reviewed to investigate failure modes, ductility and moment redistribution capability. Ductility and moment redistribution characteristics of strengthened RC members relies on the bond performance of reinforcement to concrete and hence this paper also reviews durability testing of NSM joints. Regression analysis shows that concrete compressive strength and steel reinforcement ratios are paramount to maintaining ductility under all strengthening schemes.

Experimental and Numerical Study on the Compression Behavior of Square Concrete-Filled Steel Tube Stub Columns with Steel Fiber-Reinforced High-Strength Concrete

This study was conducted to evaluate the applicability of concrete-filled steel tube (CFT) columns made from high-performance construction materials. KBC2016, South Korea’s current building code, limits the maximum compressive strength of concrete at 70 MPa and the maximum yield strength of steel at 650 MPa. Similar restrictions to material properties are imposed on major composite structural design parameters in other countries worldwide. With the recent acceleration of the pace of development in the field of material technology, the compressive strength of commercial concrete has been greatly improved and the problem of low tensile strength, known to be the major limitation of concrete, is being successfully addressed by adding fiber reinforcement to concrete. Therefore, the focus of this study was to experimentally determine the strength and ductility enhancement effects, which depend on material composition. To this end, we performed concentric axial loading tests on CFT stub columns made from steel with a yield strength of 800 MPa and steel fiber-reinforced high-strength concrete. By measuring the strain at the yield point of CFT steel during the test, we could determine whether steel yields earlier than ultimate failure load of the member, which is a key design concept of composite structures. The analysis results revealed that the yield point of steel preceded that of concrete on the stress-strain curve by the concurrent action of the strain increase at the maximum strength, attributable to the high compressive strength and steel fiber reinforcement, and the strain increase induced by the confining stress of the steel tube. Additionally, we performed parametric study using ABAQUS to establish the broad applications of CFT using high-performance materials, with the width-to-thickness ratio as the main parameter. Parametric study was undertaken as experimental investigation was not feasible, and we reviewed the criteria for limiting the width-to-thickness ratio as specified in the current building code.

Performance of lightweight concrete one-way slabs using medium-K basaltic andesite pumice and scoria

An investigation was conducted on bending tests of 24 reinforced lightweight concrete one-way slabs using medium-K basaltic andesite pumice and scoria and 1 reinforced normal concrete slab as a control. The compressive strengths and reinforcement ratios were varied to evaluate their flexural behaviors. The ultimate bending moment at failure, midspan deflections and maximum crack widths at assumed service, cracking patterns and failure modes were evaluated to indicate their performance. The results showed that medium-K basaltic andesite pumice and scoria as coarse aggregates can be used to produce pumice and scoria concrete one-way slabs with a relative satisfactory performance. Both behaved typically as reinforced concrete beams with first cracking load, ultimate load and stiffness were lower than the control. The reinforcement ratio was an important factor that influenced significantly the observed parameters compared to compressive strength and type of coarse aggregates. Theoretically, the ultimate bending moment can be estimated accurately by provision compared to midspan deflection and maximum crack width. Cracking patterns were a typical flexural crack, while failure modes were a reinforcement yielding without spalling on compressive concrete zone.

Shear transfer capacity of reinforced concrete exposed to fire

Shear transfer capacity of reinforced concrete elements is a function of concrete compressive strength and reinforcement yield strength. Exposure of concrete and steel to elevated temperature reduces their mechanical properties resulting in reduced shear transfer capacity of RC elements. The objective of present study is to find the effect of elevated temperature on shear transfer capacity of reinforced concrete. For this purpose pushoff specimens were casted using normal strength concrete. After curing, specimens were heated to 250°C and 500°C in an electric furnace. Cooled specimens were tested for shear transfer capacity in a universal testing machine. It was found that shear transfer capacity and stiffness (slope of load-slip curve) were reduced when the specimens were heated to 250°C and 500°C. Load level for the initiation of crack slip was found to be decreased as the temperature was increased. A simple analytical approach is also proposed to predict the shear transfer capacity of reinforced concrete after elevated temperature.

Automated optimization of steel reinforcement in RC building frames using building information modeling and hybrid genetic algorithm

Abstract Design of steel reinforcement is an important and necessary task for designing reinforced concrete (RC) building structures. Currently, steel reinforcement design is performed manually or semi-automatically using computer software such as ETABS, with reference to building codes. These approaches are time consuming and sometimes error-prone. Recent advances in building information modeling (BIM) technology allow digital 3D BIM models to be leveraged for supporting different types of engineering analyses such as structural engineering design. With the aid of BIM technology, steel reinforcement design could be automated for fast, economical and error-free procedures. This paper presents a BIM-based framework using the developed three-stage hybrid genetic algorithm (GA) for automated optimization of steel reinforcement in RC frames. The methodology framework determines the selection and alignment of steel reinforcement bars in an RC building frame for the minimum steel reinforcement area, considering longitudinal tensile, longitudinal compressive and shear steel reinforcement. The first two stages optimize the longitudinal tensile and longitudinal compressive steel reinforcement while the third stage optimizes the shear steel reinforcement. International design code (BS8110) and buildability constraints are considered in the developed optimization framework. A BIM model in Industry Foundation Classes (IFC) is then automatically created to visualize the optimized steel reinforcement design results in 3D thereby facilitating design communication and generation of construction detailing drawings. A three-storey RC building frame is analyzed to check the applicability of the developed framework and its improvement over current design approaches. The results show that the developed methodology framework can minimize the steel reinforcement area quickly and accurately.

Required tie spacing to prevent inelastic local buckling of longitudinal reinforcements in RC and FRC elements

Compressed reinforcement buckling in concrete columns can reduce ductility in structural elements. In order to avoid this, design codes propose maximum required tie spacing. Nonetheless, they do not incorporate the positive effect of concrete fibers in their formulation, whose capability of delaying buckling has been proved. For this reason, recommendations for maximum required tie spacing for elements made with concrete, with or without steel fibers, and with normal or high strength, are proposed in this article. In order to achieve this, the mixed model proposed by Pereiro-Barceló and Bonet was extended to consider elements made of HSC with and without steel fibers thanks to the results of an experimental campaign of HSC columns with and without fibers, under monotonic loading. In these tests, the buckling critical load in compressed reinforcement was experimentally determined in all the columns. In addition, a comparison of the proposed transverse concrete separation with respect to the recommendations proposed by the main existing codes was made.

Shear strength of interior beam–column joints with lightweight aggregate concrete

Lightweight aggregate concrete (LWAC) elements can effectively reduce dead load and improve the seismic resistance capacity of building structures. However, the shear performance of LWAC remains questionable due to its specific brittle failure mechanism. In this work, four one-third-scale LWAC interior beam–column joints were prepared and tested under reversed quasi-static cyclic loading. Two levels of axial compressive forces and joint transverse reinforcement ratios were considered for each specimen to quantify and analyse the shear performance of LWAC joints. The test results indicate that all LWAC specimens experienced shear failure at the joint core and presented satisfactory shear resistance capacity in terms of shear strength, displacement ductility, stiffness degradation and energy dissipation compared to normal-weight concrete (NWC) specimens. The test results were used to examine the applicability and accuracy of six shear design models based on the behaviour of NWC elements for LWAC beam–column joints. A comparison of the results indicated that there is no apparent difference between the ultimate shear strengths of LWAC and NWC specimens, and all six previously proposed shear equations examined can accurately predict the ultimate shear strength of LWAC interior beam–column joints.

Partial Prestress Concrete Beams Reinforced Concrete Column Joint Earthquake Resistant On Frame Structure Building

Floor Building that requires a large space such as for the meeting room, so it must remove the column in the middle of the room, then the span beam above the room will be long. If the beam of structural element with a span length reaches 15.00 m, then it is less effective and efficient using a regular Reinforced Concrete Beam because it requires a large section dimension, and will reduce the beauty of the view in terms of aesthetics of Architecture. In order to meet these criteria, in this design will use partial prestressing method with 400/600 mm section dimension, assuming the partial Prestressed Beam structure is still able to resist the lateral force of the earthquake. The design of the reinforcement has taken into account to resist the moment due to the gravitational load and lateral forces. The earthquake occurring on the frame structure of the building. In accordance with the provisions, the flexural moment capacity of the tendon is permitted only by 25% of the total bending moment on support of the beam, while the 75% will be charged to the reinforcing steel.Based on the analysis result, bring ini 1 (one) tendon contains 6 strand with diameter 15,2 mm. On the beam pedestal, requires 5D25 tensile reinforcement and 3D25 for the compression reinforcement, for shear reinforcement on the pedestal using Ø10-100 mm. Dimensional column section are 600/600 mm with longitudinal main reinforcement of 12D25, and transverse reinforcement Ø10-150. At the core of the beam-column joint, use the transversal reinforcement Ø10-100 mm. The moment of Column versus Beam Moment ∑Me > 1.2 Mg, with a value of 906.99 kNm > 832.25 kNm, qualify for ductility and Strong Columns-weak beam. Capacity of contribution bending moment of Strand Tendon’s is 23.95% from the total bending moment capacity of the beam, meaning in accordance with the provisions. Thus, the stability and ductility structure of Beam-Column joint is satisfy the requirements of SNI 2847: 2013 and ACI 318-11.

Flexural behaviour prediction for RC beams in consideration of compressive stress distribution of concrete with electric arc furnace oxidising slag aggregates

Research on the efficient utilisation of electric arc furnace oxidising slag, a by-product of the steel industry, is necessary as it is similar to natural aggregates in terms of chemical composition. The slag is also being produced in increasing amounts every year. This study performed flexural experiments on simply support beams with aggregate type and examined their concrete compressive strength, tension reinforcement ratio and compressive reinforcement ratio as variables to assess the effects of compressive stress distribution of concrete with electric arc furnace oxidising slag aggregates on the flexural behaviour of reinforced concrete beams. Compared to specimens with natural aggregates, electric arc furnace oxidising slag aggregates showed a smaller deflection before the yielding of tension reinforcement and ductile behaviour after yielding due to differences in compressive stress distribution. In addition, the proposed equations for the equivalent rectangular stress block parameter were found to provide more accurate predictions than the criterion used by other countries.

Numerical study of ultra-high-performance steel fibre–reinforced concrete columns under monotonic push loading

A finite element model is developed to investigate the behaviour of ultra-high-performance steel fibre–reinforced concrete columns under combined axial compression and horizontal monotonic push loading. The effects of steel fibre content, axial compression ratio, reinforcement ratio (or rebar ratio), stirrup ratio and shear span ratio on the structural behaviour of ultra-high-performance steel fibre–reinforced concrete columns are investigated in detail. The numerical model shows good agreement in bond–slip behaviour of specimens based on CEB model results and numerical results, and such behaviour should be taken into consideration in engineering practice. The results indicate that the developed finite element model could predict the structural behaviour and failure mode of ultra-high-performance steel fibre–reinforced concrete columns effectively. It is found that the reinforcement ratio, axial compression ratio, shear span ratio and volume fraction of steel fibre have a great influence on both the structural behaviour and failure modes of specimens.

Buckling of steel and Ni-Ti reinforcements in very high performance concrete (VHPC) elements

Nowadays, the use of new materials is becoming increasingly common in the construction world due to their improved properties. High or Very High Performance Concrete (HPC or VHPC) and Shape Memory Alloys (SMA), specifically those composed of nickel and titanium (Ni-Ti), are some of these new materials. The low austenitic modulus of Ni-Ti as regards the elasticity modulus of steel (40–65 GPa instead of 200 GPa) can cause local buckling. In order to replace steel bars with Ni-Ti bars in reinforced concrete elements, it is convenient to use concrete with a high steel fibre content to delay local bar buckling. Hence employing either High Performance Concrete or VHPC may be appropriate, due to its composition with a high steel fibre content.For all these reasons, VHPC elements with Ni-Ti reinforcements were studied. The results of an experimental campaign of VHPC columns are shown in this article. The VHPC columns were subjected to monotonic loading where the main goal was to study compressed steel reinforcement buckling. The results of these tests were also used to extend the mixed model proposed by Pereiro-Barceló and Bonet (2017), which determines the buckling critical stress for any transverse reinforcement separation and considers the effect of the concrete cover (with and without steel fibres). This model was recalibrated to consider elements made of VHPC. Besides, specimens made of either High Performance Concrete (HPC) or VHPC, and with Ni-Ti reinforcements, were also tested to study the behaviour of compressed Ni-Ti reinforcements in elements made of high strength fibre-reinforced concrete.