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This paper investigates the concrete breakout shear capacity of a single cast-in headed anchor embedded in steel fiber-reinforced concrete (SFRC). Experiments were carried out for anchors with a diameter of 30 mm, embedment depth of 240 mm, and edge distance of 150 mm. Fiber volume fractions of 0.33, 0.67, and 1.00% were examined. In addition to shear tests, four-point bending tests were carried out to evaluate the relationship between the material properties of SFRC and the shear capacity of anchors. The experimental results show that the current design formulas are valid for anchors in conventional plain concrete but not appropriate for the shear capacity of anchors in SFRC. Using the equivalent flexural strength ratio, a revised design equation is proposed to incorporate the effect of the steel fiber content on the concrete breakout shear capacity and provide reasonably similar safety for anchors in both un-reinforced and SFRC.

An experimental study was performed to examine the effects of concrete strength and fiber content ratio on the flexural capacity of steel fiber-reinforced concrete. Three fiber volume fractions, 0.25, 0.375, and 0.5%, and three concrete compressive strengths, 25, 35, and 45 MPa, were designed for the experiments. The stress and deflection relationship, first peak and post-cracking strength, and energy absorption capacity were evaluated with respect to the variance in the fiber volume fraction and concrete strength. The results showed that the equivalent flexural strength ratio, which is determined from the first peak strength and energy absorption capacity, increased with the increase in the fiber volume fraction but decreased with the increase in the concrete strength. Furthermore, the effects of the concrete strength and fiber content ratio are discussed in a steel fiber-reinforced concrete floor slab. The ultimate flexural capacity also required a consideration of the influence of the content ratio of steel fiber as well as the strength of cement composite matrix.

In this paper, an experimental study was performed to examine the flexural capacity of concrete reinforced with macro-type high strength polypropylene fiber. Four fiber volume fractions, 0.25, 0.5, 0.75, and 1.0%, and three concrete compressive strengths, 30, 40, and 60 MPa, were involved to determine the effects of the high strength polypropylene fiber on the flexural capacity of fiber-reinforced concrete. The stress and deflection curves, residual strength, and energy absorption capacity obtained from the experiment were used to investigate the flexural capacity of high strength polypropylene fiber-reinforced concrete, particularly in high strength concrete. High strength concrete reinforced with a 0.25% volume fraction of high strength polypropylene fiber showed a flexural capacity lower than normal strength concrete reinforced with the same volume fraction. The reinforcing effect of the high strength polypropylene fiber in the flexural capacity of high strength concrete was excellent at volume fractions more than 0.50%.

In this study, the seismic fragility curves of two reinforced concrete (RC) columns that were lap-spliced at the bottom and retrofitted with steel wrapping jackets were generated. Their seismic performance was probabilistically assessed in comparison to that of lap-spliced or continuous reinforcement RC columns. This study used two types of steel wrapping jackets, a full jacket and a split jacket. Analytical models of the four types of columns were developed based on the experimental results of the columns using OpenSEES, which is effective in conducting nonlinear time history analyses. A suite of ten artificial ground motions, modified from recorded ground motions, was used to perform nonlinear time history analyses of the analytical models with scaling of the peak ground acceleration from 0.1 g to 1.0 g in increments of 0.1 g. The steel wrapping jackets did not increase the medians for yield (slight damage state) of the lap-spiced column and did not exceed the corresponding median of the continuous reinforcement column. However, the two steel jackets increased the medians for failure by 1.872 and 2.017 times, respectively, and exceeded the corresponding median of the continuous reinforcement column by 11.8% and 20.5%, respectively.

Flexural strength of concrete ground slab reinforced with steel fiber is evaluated using the equivalent flexural strength ratio of steel fiber reinforced concrete based on the yield line theory. Recently, the European standard specifies that the tensile performance of the steel fiber reinforced concrete be evaluated directly from the residual flexural strength after the cracking of concrete. Thus, in the study, an experiment was carried out to evaluate the conventional equivalent flexural strength ratio and the residual flexural strength of the steel fiber reinforced concrete. Then the design flexural strength was investigated according to the location of a point load, based on the ratio of the radius of contact area of the load to the radius of relative stiffness. Design flexural capacity obtained from ACI 360R-10 was smaller than that from TR 34 (2003 & 2013). In addition, TR 34 (2013), which evaluates the design flexural capacity based on the residual flexural strength, showed slightly smaller value than TR 34 (2003).

Concrete edge failure of a single anchor in concrete is strongly dependent on the tensile performance of the concrete, which can be greatly improved by the addition of steel fibers. This study investigated the effect of steel fibers on the shear failure mode and edge breakout resistance of anchors installed in steel fiber-reinforced concrete (SFRC) with fiber volume percentages of 0.33, 0.67, and 1.00%. The anchor used in the study was 30 mm in diameter, with an edge distance of 75 mm and embedment depth of 240 mm. In addition to the anchor specimens, beam specimens were prepared to assess the relationship between the tensile performance of SFRC beams and the shear resistance of SFRC anchors. The ultimate flexural strength of the beam and the breakout shear resistance of the anchor increased almost linearly with increasing volume fractions of fiber. Therefore, based on the ACI 318 design equation, a term was proposed using the ultimate flexural strength of concrete instead of the compressive strength to determine the concrete breakout shear resistance of an anchor in the SFRC. The calculated shear resistance of anchors in both the plain concrete and SFRC were in good agreement with the measurements. In addition to the load capacity of the SFRC anchors, the energy absorption capacity showed a linear increase with that of the SFRC beam.

The aim of this paper is to suggest a jacketing method using glass fiber reinforced polymer (GFRP) wires for reinforced concrete (RC) columns with lap splice of longitudinal reinforcement. For this study, four RC columns were prepared of 400 mm in diameter and 1400 mm in height with an aspect ratio of 3.5; two were lap spliced and the other two had continuous longitudinal reinforcement. One specimen of each of the two types was jacketed by GFRP wires that had a diameter of 1.0 mm. The GFRP wires were tensioned with small force during winding each column. The jacket comprised stepped layers along the variation of bending moment of the column. Cyclic lateral force was applied at the top of the columns, and the top displacement of the columns as well as corresponding force was measured during the bending tests. This study considered the failure of the four tested columns and analyzed their later force–displacement behavior. Additionally, the effective stiffnesses of the force–displacement curves were evaluated. The GFRP wire winding jacket prevented splitting of the lap-spliced reinforcement in the lap-spliced column and delayed buckling of the longitudinal reinforcement. The jacket protected the continuous reinforcement column against steel buckling and concrete spalling off and, thus, induced shear failure in the column. The GFRP wire winding jacket increased the failure drifts of both jacketed columns compared with those of the references.

This study provides experimental results of bond tests for concrete confined by FRP wire jackets and investigates bond behavior. The used FRP wire jackets are newly introduced and found to be more effective in wrapping around concrete members than conventional FRP sheet jackets. Bond–slip tests were conducted by push-out tests using concrete cylinders with an embedded rebar at the center of the cylinders. Two parameters of concrete strength and amount of confinement were chosen. Bond strength and radial strain of concrete are discussed with the stiffness ratio of confinement. A method to estimate the increment of bond strength due to confinement is suggested. The bond strength of confined concrete shows a logarithmic relationship to the stiffness ratio of confinement and, thus, there is a limit on how to increase the bond strength by external confinement. It is found that radial strain at bond strength or the corresponding lateral confining pressure is a critical factor to increase bond strength.

The goal of this study is to investigate the prestressing effect of shape memory alloy bars in reinforced concrete beams; bars are prestressed by external force or recovery stress due to shape memory effect. The shape memory alloy bars are heated by hydration heat of concrete during curing to induce the shape memory effect. To achieve this goal, this study conducts bending tests of concrete beams reinforced by shape memory alloy bars as well as those reinforced by steel bars. The beams with shape memory alloy bars with recovery stress show the same or slightly larger flexural strength than those with shape memory alloy bars prestressed with external force. Thus, this study indicates that the recovery stress of shape memory alloy bars plays the same role as the prestressing force, and that the shape memory effect can be induced by hydration heat of concrete instead of heating by electronic resistance.

The bridge approach slabs (BAS) to provide a transitional roadway between a roadway pavement and a bridge structure have not performed adequately due to various factors. The current Korean Roadway Design Guidelines treat the BAS as a simply supported beam with 70% of the span length and do not consider settlement and void development underneath the slab. To investigate the effect of soil settlements on the bending moment of BAS, a beam on elastic support (BAS-ES) was used in the present study. The parameters used in this study were span length, washout length, washout location, and soil modulus. It was shown from the parametric study that washout regions closer to the midspan exhibit maximum moment in the slab. Since voids under the BAS have typically been observed to be closer to bridge abutments, the springs from the abutment were removed to simulate settlement and void development in the model. The design moments based on AASHTO LRFD Bridge Design Specifications were compared to those of Korean Standard Specifications for Highway Bridge and Design Trucks for Highway Bridges. Even if the design moment from BAS-ES was used to incorporate the effect of the potential washout, significant savings could still be achieved compared to the current BAS design.

This study conducts a series of compressive tests of concrete cylinders confined by shape-memory alloy (SMA) rings to provide lateral confinement for reinforced concrete columns. Ni50Ti41Nb9 (at. %) SMA bars with a diameter of 3 mm and a length of 446 mm were prepared and strained to 7% before welding. Three of the six confined cylinders were heated to 200 ◦ C to introduce recovery stress in the SMA rings, which was predicted to provide active confinement of concrete. The behavior of two welded bars with a resulting diameter of 6 mm were tested and compared with that of the continuous SMA bars without welding. The continuous SMA bars showed the typical behavior of martensitic SMAs, such as an elastic range, a transformed state, and hardening behavior due to austenite. However, the welded bars were fractured at the welding point at or just after elastic range. The concrete cylinders confined by the SMA rings showed greater peak strength and larger failure strain compared to the plain concrete cylinders. However, the stress-strain curves of the confined cylinders showed stepping behavior due to the sequential fracturing of the SMA rings. The heated SMA ring cylinders did not show greater peak strength than the unheated SMA ring cylinders, indicating that active confining was not effective. © 2012 Elsevier B.V. All rights reserved.

This study investigates the effectiveness of FRP wire to confine concrete. For this purpose, axial compressive tests are conducted with three parameters, peak strength of concrete, confining amount of FRP wire, and epoxy application. The behavior of the FRP-wire confined concrete is examined in the axial and circumferential directions as well as in terms of volumetric strain. Each behavior is discussed according to the stiffness ratio of the confining FRP wire to concrete. Moreover, the confinement effectiveness of the FRP wire is estimated using the actual rupture strain of the FRP wire as well as the ultimate tensile strain. Both cases show slightly larger effectiveness than that of FRP sheet confined concrete. The external jacket of the FRP wire increases the peak strength satisfactory and restrains volumetric expansion when the stiffness ratio of the jacket is sufficiently large. The failure of the FRP wire confined concrete occurs at the mid-height of the cylinder. Furthermore, this study investigates the behavior of partially confined concrete exhibiting smaller peak strength compared to the corresponding fully confined specimen, as it appears to have a smaller stiffness ratio.

This study suggests a dense lateral reinforcement for a Reinforced Concrete (RC) column whose spacing is smaller than the maximum gravel size. This study conducts axial compressive tests of concrete cylinders confined by dense reinforcement to verify the effectiveness of the dense lateral reinforcement. Stainless steel rings are used for the reinforcement since they are corrosion resistant. The dense reinforcing method with stainless steel rings successfully increases the peak strength of the concrete. The strains at the peak strength are much larger than those for the concrete confined by a conventional method with steel reinforcing bars. The failure mode of concrete densely confined by steel rings is due to the gradual fracture of each ring; the fracture of each ring reduces the stress on the concrete. The cyclic behavior of the densely confined concrete is similar to that of concrete confined by conventional steel reinforcement.

The temperature distributions of concrete structures strongly depend on the value of thermal conductivity of concrete. However, the thermal conductivity of concrete varies according to the composition of the constituents and the temperature and moisture conditions of concrete, which cause difficulty in accurately predicting the thermal conductivity value in concrete. For this reason, in this study, back-propagation neural network models on the basis of experimental values carried out by previous researchers have been utilized to effectively account for the influence of these variables. The neural networks were trained by 124 data sets with eleven parameters: nine concrete composition parameters (the ratio of water-cement, the percentage of fine and coarse aggregate, and the unit weight of water, cement, fine aggregate, coarse aggregate, fly ash and silica fume) and two concrete state parameters (the temperature and water content of concrete). Finally, the trained neural network models were evaluated by applying to other 28 measured values not included in the training of the neural networks. The result indicated that the proposed method using a back-propagation neural algorithm was effective at predicting the thermal conductivity of concrete.

This study conducts two field tests of a steel railway bridge supported disk bearings to assess the long-term dynamic behavior of the steel railway bridge and a disk bearing in the service for 5.5 years; the length of the bridge is 12 m. Displacement and acceleration in vertical direction, deformation of disk bearings and natural frequency of the first mode are measured and analyzed. In addition, the vertical stiffness of the disk bearing is estimated, and the deformation of the disk bearing due to static loading is calculated using the estimated stiffness and compared to the measured dynamic response. Vertical displacement at mid-span, deformation of a fixed disk bearing, and the first natural frequency do not vary due to the 5.5 year service. However, deformation of an expansion disk bearing increases sharply comparing to other components.

This study suggests the utilization of heat of hydration of concrete to activate the shape memory effect (SME) of shape memory alloy (SMA) wires embedded in concrete and produce recovery and residual stress on the wires. This method is more convenient than the previous electronic resistance heating. For the purpose, this study prepares NiTiNb SMA wires that show appropriate temperature window for the use of heat of hydration. Axial compressive tests of concrete cylinders confined by the NiTiNb SMA wire jackets are used to prove that the utilization of heat of hydration is valid to generate recovery and residual stress in the SMA wires. The confined cylinders show increased peak strengths and much larger failure strains than those of the plain concrete. The general behavior of the SMA wire-confined specimens in this study is similar to that of specimens heated by electronic heating jacket. Also, this study explains two examples for the utilization of heat of hydration for the SME in reinforced concrete beams and columns.

This study is planed to solve the overturning problem and manifestation of tensile cracking of plain concrete piers of railroad bridges. For the overturning problem, earth anchors are used to fix the bottom of a pier to a rock-foundation using prestressing cables. Composite of Fiber Reinforced Polymer (FRP) and steel plates (FSP) are attached longitudinally on the surface of the pier to prevent cracking. Then, FRP band strips are wrapped onto the composite of FRP and steel plate to provide lateral confinement. Push-over tests in field show that the earth anchors are effective in preventing the overturning of the pier, and that the FSPs and the FRP strips prevent the cracking of concrete and increase the strength in bending.

This study proposed a new method to confine concrete cylinders or reinforced concrete columns using martensitic, Ti-49.7Ni (at %), or austenitic, Ti-50.3Ni (at %), shape-memory-alloy wires. Prestrained martensitic SMA wire was used to wrap a concrete cylinder and, then, was heated by a heating jacket. In the process, confining stress was developed around the cylinder by the SMA wire due to shape memory effect, which can increase the strength and ductility of the cylinder under axial compressive load. For austenitic shape memory wires, some prestraining was introduced in the wires during wrapping concrete cylinders on which post-tensioning stress was generated. In this study, 1.0 mm diameter of martensitic and austenitic SMA wire was used for confinement. Recovery tests were conducted for the martensitic and the austenitic shape memory wires to determine the recovery stress and superelastic behavior, respectively. The confinement by martensitic shape memory wires had increased the strength slightly and the ductility substantially. However, the austenitic shape memory wires only increased the ductility because the imposed prestress was too small. This study showed the potential of the proposed method to retrofit reinforced concrete columns using shape memory wires to protect themselves from earthquakes.

Transformation behavior and shape memory characteristics of temperature gradient anneal (TGA) treated and thermo-mechanically treated (TMT) Ti–47Ni–3Cu(at.%) alloys were investigated by means of differential scanning calorimetry and thermal cycling tests under constant load. Both TGA treated and TMT Ti–47Ni–3Cu alloys showed B2–B19' transformation behavior. The change in Ms * by 23 K was developed in the TGA treated Ti–47Ni–3Cu alloy along the length of the sample (150 mm). TGA treated Ti–47Ni–3Cu alloy showed perfect shape memory effects. The temperature dependence of elongation (de/dT) of a TGA treated specimen was in the range of 0.02–0.09% K−1 depending on the amount of applied stress, which was small compared to that of a TMT specimen (0.01–0.18% K−1). The temperature dependence of elongation (de/dT) of the TGA treated specimen on cooling is almost the same as that on heating, while de/dT of the TMT specimen on cooling is much smaller than that on heating (0.68% K−1).

Transformation behaviour, shape memory characteristics and superelasticity of Ti?(45 ? x)Ni?5Cu?xV(at.%) (x= 0.5?2.0) alloys were investigated using different techniques. The B2?B19' transformation occurs when V content is less than 1.0?at.%, above which the B2?B19?B19' transformation occurs. The temperature gap between (the B2?B19 transformation start temperature) and Ms (the B19?B19' transformation start temperature) increased from 8 to 22?K with increasing V content from 1.0 to 2.0?at.%. V content dependence of (the B2?B19 transformation start temperature) was 20?K?at.% ?1. One-stage elongation occurred in Ti?44.5Ni?5.0Cu?0.5?V and Ti?44.0Ni?5.0Cu?1.0?V alloys, while two-stage elongation occurred in Ti?43.5Ni?5.0Cu?1.5?V and Ti?43.0Ni?5.0Cu?2.0?V alloys. Transformation hysteresis decreased from 16 to 12?K with increasing V content from 0.5 to 2.0%. The superelastic recovery ratio increased from 65.0 to 86.1% with increasing V content from 0.5 to 2.0%.

Conventional lead-rubber bearings may have a problem of instability and unrecovered deformation with a strong ground motion. As a way of solving the problem, this study proposes a new concept of an isolation device in which shape memory alloy wires are incorporated in an elastomeric bearing. A three-span continuous steel bridge was used for seismic analyses to compare the performance of lead-rubber and the proposed bearings. The proposed bearings limit the deck relative displacement effectively with strong ground motions and recover almost original undeformed shape.

Conventional lead–rubber bearings (LRB) may have a problem of instability and unrecovered deformation with a strong ground motion. To improve the problems, this study proposed a new concept of an isolation device in which shape memory alloy wires were incorporated in an elastomeric bearing. This study illustrated the behavior of shape memory alloy in tension and discussed the variation of stiffness and stress on the hyteresis curves. A three-span continuous steel bridge was used for seismic analyses to compare the performance of lead–rubber bearings with the proposed bearings. This study showed that large residual deformation of LRB occurred even with a weak ground motion of peak ground acceleration (PGA) of 0.2g. The proposed bearings effectively limited the relative displacement of the deck when tested for the strong ground motions and almost recovered the original undeformed shape. However, the proposed bearing increases the demand on bridge columns compared with the LRB.Key words: shape memory alloy, lead–rubber bearings, seismic bridge analysis, isolation device, residual deformation.

A study was carried out to evaluate the use of recycled fibres from carpet industrial waste for reinforcement of concrete at 1 and 2 vol% fractions. Compressive, flexural, splitting tensile and shrinkage tests were performed. Significant increases in shatter resistance, energy absorption and ductility were observed. This paper reports on the experimental programme and compares the effectiveness of such recycled fibres with that of virgin polypropylene fibres specially made for fibre reinforced concrete (FRC). The paper also discusses the benefits of using such FRC for construction applications and possible ways to further enhance the performance of such FRC.

Jacketing can be an effective way to improve the performance of the lap-spliced region of reinforced concrete (RC) columns. This paper introduces a new steel-jacketing method for RC columns that uses external pressure to attach the steel jackets to the column surface. The advantage of this method is that it does not require the application of grout between the steel jackets and the concrete surface to attach them together. Experimental tests of twelve concrete cylinders and four RC columns are performed to assess the effectiveness of the proposed method. Both single-layered and double-layered jackets are tested. The newly jacketed cylinders show good results in terms of increasing the compressive strength and ductility compared to plain cylinders. The double-layered jackets are estimated to show equal performance to that of a single steel jacket with the same thickness. The proposed steel-jacketing method increased the ductility of lap-spliced RC columns. The double-layered jacket appeared to perform better in terms of increasing ductility and energy dissipation capacity than the single-layered jacket.

Shape memory alloy (SMA) wire jackets for concrete are distinct from the conventional jackets of steel or FRP since they provide active confinement that can be easily archived due to the shape memory effect of SMAs. This study uses NiTiNb SMA wires of 1.0 mm diameter to confine concrete cylinder with the dimension of 300 mm × 150 mm (L × D). The NiTiNb SMAs have a relative wider temperature hysteresis than NiTi SMAs and, thus, are more applicable for severe temperature-variation environment which civil structures are exposed to. Steel jackets of passive confinement are also prepared to compare the cyclic behavior of active and passive confined concrete cylinders. For this purpose, monotonic and cyclic compressive loading tests are conducted to obtain axial and circumferential strain. The both of strains are used to estimate volumetric strains of concrete cylinders. Also, plastic strains from cyclic behavior are also estimated. For the NiTiNb SMA jacketed cylinders, the monotonic axial behavior differs from the envelope of cyclic behavior; this should be studied in future. The plastic strains of the active confined concrete show a similar trend to those of the passive confinement. The trend of plastic strain of this study does not match with that of CFRP (Carbon Fiber Reinforce Polymer) jackets. For the volumetric strain, the active jackets of the NiTiNb SMA wires provide more energy dissipation than the passive jacket of steel.

Transformation behavior, shape memory characteristrics and superelasticity of Ti-(45-x)Ni-5Cu-xV(at%)(x=0.5-2.0) alloys were investigated. The B2-B19-B19' transformation occurs when V content was more than 1.0 at%, while the B2-B19' transformation occurred when V content was 0.5 at% in solution treated specimens. However, the B2-B19 and B19-B19' transformations were not separated clearly in the thermo-mechanically treated specimens. A temperature gap between Ms'(the B2-B19 transformation start temperature) and Ms(the B19-B19' transformation start temperature) increased from 8 K to 22 K with increasing V content from 1.0at % to 2.0 at% in solution treated specimens. One-stage elongation associated with the B2-B19' transformation occurred in a Ti-44.5Ni-5.0Cu-0.5V alloy, while two-stage elongation associated with the B2-B19-B19' transformation occurred in a Ti-43.0Ni-5.0Cu-2.0V alloy. The superelastic recovery ratio increased from 65.0 % to 86.1 % with increasing V content from 0.5 % to 2.0 % in solution treated specimens. The thermo-mechanically treated specimens showed the superelastic recovery ratio more than 95 %.

The application of FRP wire as a mean of improving strength and ductility capacity of concrete cylinders under axial compressive load through confinement is investigated experimentally in this study. An experimental investigation involves axial compressive test of three confining amounts of FRP wire and three concrete compressive strengths. The effectiveness of FRP wire confinement on the concrete microstructure were examined by evaluating the internal concrete damage using axial, circumferential, and volumetric strains. The axial stress－strain relations of FRP wire confined concrete showed bilinear behavior with transition region. It showed strain-hardening behavior in the post-cracking region. The load carrying capacity was linearly increased with increasing of the amount of FRP wire. The ultimate strength of the 35 MPa specimen confined with 3 layer of FRP wire was increased by 286% compared to control one. When the concrete were effectively confined with FRP wire, horizontal cracks were formed by shearing. It was developed from sudden expansion of the concrete due to confinement ruptures at one side while the FRP wire was still working in hindering expansion of concrete at the other side of the crack. The FRP wire failure strains obtained from FRP wire confined concrete tests were 55∼90%, average 69.5%, of the FRP wire ultimate uniaxial tensile strain. It was as high as any other FRP confined method. The magnitude of FRP wire failure strain was related to the FRP wire effectiveness.