Plastic Hinge Zone Research Articles

Partially corroded reinforced concrete piers under axial compression and cyclic loading: An experimental study

Twelve reinforced concrete (RC) pier specimens were developed and partially corroded to simulate severe corrosion in splash and tidal zones. Six target corrosion levels were applied to rebars and stirrups using an electrochemical accelerated corrosion technique. Axial compression loading and cyclic loading tests were carried out with six specimens per group. The test results showed that mechanical parameters of pier specimens degraded with an increase in corrosion. The ultimate load, ductility factor, energy dissipation decreased by 29.96%, 9.26%, 67.44% for axial compression specimen with 15.82% rebar mass loss compared to those of intact specimen; for cyclic loading specimens, they decreased by 10.69%, 21.47%, 57.46% with 15.71% rebar mass loss, respectively. Comparative analysis showed that the difference for the degradation level of dimensionless parameters was not obvious between axial compression loading and cyclic loading tests. Findings also showed that for severely corroded specimens, the plastic hinge zone transferred from the bottom of RC piers to the splash and tidal zones. Although the extent of the degradation of the results between the published paper and this test shows significant variations; degradation of dimensionless energy dissipation was always the most serious one.

Seismic evaluation of precast bridge columns with built-in elastomeric pads

A novel built-in elastomeric pad was incorporated into the plastic hinge zone of precast bridge columns with grouted corrugated duct connection to improve its seismic performance. Appropriate energy dissipation and minimal local concrete damage are expected in the innovative precast reinforced concrete (RC) columns. Four 1/4-scaled bridge column specimens were designed and tested under constant axial compression force and cyclic lateral loads to evaluate the feasibility and effectiveness of the proposed concept. Detailed experiment results were compared and discussed. The testing results showed that the main seismic index of precast RC bridge columns with grouted metal corrugated duct connection was similar to that of the cast-in-place bridge columns. It was also found that the precast RC column with a built-in elastomeric pad in the plastic hinge zone effectively minimized local concrete damage at the bottom of bridge columns and increased the energy dissipation capacity. The laminated elastomeric pad is recommended to be applied in the precast bridge column to maintain necessary initial stiffness and energy dissipation capacity and to avoid lateral bulge of single thick rubber. Excessive buckling and shear deformations of longitudinal rebars should be prevented by inserting a rectangular or square steel tube at the center of the elastomeric pad.

Experimental study on seismic behaviours of hybrid FRP–steel-reinforced ECC–concrete composite columns

Owing to the high strength, noncorrosive property, and linear stress–strain relationship of fibre-reinforced polymers (FRPs), hybrid FRP–steel-reinforced concrete members exhibit higher strength, superior durability, and lesser residual deformation compared to steel-reinforced concrete members and higher ductility compared to FRP-reinforced concrete members. Hybrid-reinforced members have been widely used as flexural-dominated members rather than compression-dominated members owing to the poor compression performance of the FRP reinforcement. This paper proposes a novel approach for improving the seismic behaviour of such members through the use of high-ductility engineered cementitious composites (ECCs) in the plastic hinge zone. Numerous hybrid FRP–steel-reinforced ECC–concrete columns were tested under reversed cyclic loading. The effects of the matrix type, reinforcement type, axial force ratio, and reinforcement ratio on the seismic behaviours, including the failure mode, crack pattern, load-carrying capacity, residual deformation, ductility, and energy-dissipation capacity, of the columns were systematically investigated. The replacement of concrete with ECC in the plastic hinge zone efficiently eliminated the local buckling of the FRP bars and significantly improved the seismic performance of the column. Compared with the steel-reinforced ECC–concrete composite column, the hybrid-reinforced composite column exhibited significantly less residual deformation and higher post-yielding stiffness. With an increase in the axial force ratio, the ultimate strength increased, while the deformation capacity decreased.

Durable Bridge Columns using Stay-In-Place UHPC Shells for Accelerated Bridge Construction

Ultra-high performance concrete (UHPC) is a durable material that allows the construction of innovative structural elements and conforms with accelerated bridge construction (ABC) goals. The main idea of this research is to utilize UHPC to prefabricate a shell that acts as a stay-in-place form for bridge columns. The prefabricated shell eliminates the conventional formwork while reducing the on-site construction time and acting as a durable protective layer for the normal concrete inside the shell against environmental attacks. In addition, the UHPC shell provides additional confinement to the column concrete, which improves the column’s structural performance. During construction and after completing the column reinforcement work onsite, based on the conventional construction methods, the prefabricated UHPC shell is placed around the column reinforcement, followed by casting a portion of UHPC for a column-to-footing connection, which improves the capacity of the connection and shifts the plastic hinge zone above the connection. Once the UHPC portion hardens, normal concrete is placed inside the shell, forming a permanent concrete-filled UHPC shell. The construction process is finalized by placing and connecting a prefabricated cap beam to the column through the same developed connection as that in this research. This technical note presents the development of two test specimens using an UHPC shell in lieu of a conventional formwork with the advantage of improving the column performance and durability.

Experimental and numerical study on low-velocity lateral impact behaviors of RC, UHPFRC and UHPFRC-strengthened columns

This paper aims to develop a strengthening method based on ultra-high performance fiber reinforced concrete (UHPFRC) to improve the performance of a column under impact loading. Impact performances of UHPFRC columns were first examined by using the drop-hammer impact test system. The impact-resistant performance of an axially-loaded UHPFRC column was experimentally confirmed to be superior to that of the conventional RC column. The importance of exerting an axial load was highlighted and addressed by comparing the experimental data of UHPFRC columns with and without axial loads. Subsequently, three different types of UHPFRC-strengthened RC columns were experimentally investigated in detail. Superior performances were observed for the strengthened column with two-end (i.e., potential plastic hinge zone) UHPFRC jackets in comparisons with the other strengthening schemes. Impact strengths could be improved when adding a UHPFRC jacket in the contact zone, but significant increases in impact forces would be induced simultaneously. The column with UHPFRC jackets in both the contact zone and the two ends was shown to be the worst configuration because shear (or punching) failure is prone to occur in the remaining RC portions. A finite element (FE) modeling method was proposed and demonstrated as being capable of reasonably predicting impact responses of UHPFRC columns and UHPFRC-strengthened columns. The findings drawn from the experimental and numerical studies can facilitate the strategic application of UHPFRC for improving the impact-resistant performance of bridge and building columns.

Seismic behavior of masonry-infilled precast concrete frames considering effects of opening

Abstract It is commonly accepted that addition of infilled masonry walls (IMW) could enhance the in-plane strength and stiffness of RC frame buildings subjected to seismic loads. However, once the IMW walls failed, the shear force initially resisted by the IMW has to be transferred to the surrounding frames and may incur shear failure to the frames. Despite the extensive studies carried out in the past decades, studies on the structural performance of masonry infilled precast concrete (PC) frames are few. In this study, eight half-scaled single-story one bay frame were tested subjected to seismic loading, including three reinforced concrete (RC) frames and five PC frames. The investigated PC frames deviates the beam potential plastic hinge zone away from beam-to-beam connection region. The variables investigated in the tests included the types of opening in masonry infill walls and the types of cast-in-place concrete at the connections (normal concrete or steel fiber reinforced concrete). Results indicated that the investigated PC construction method has minimal effects on inelastic behavior and ductility of bare and infilled frames. However, the PC construction method may affect the crack development, especially at the interfaces in between precast and cast-in-place concrete surfaces in the region of the connection. However, the load resisting capacity and ductility was insensitive to the usage of steel fiber reinforced concrete at the connections, especially for bare frames.

Seismic performance of precast RC and RC/ECC composite columns with grouted sleeve connections

Grouted Sleeve Connections are commonly applied in precast columns for enhanced construction efficiency. In this paper, a precast RC/ECC composite column with grouted sleeve connections was proposed by substituting concrete with ECC in the plastic hinge zone of columns to improve its seismic performance. Cyclic loading was applied to a precast RC column, a precast RC/ECC composite column and a cast-in-place RC column to compare their seismic performance. According to the test results, both the two precast columns show a similar ductility and load-carrying capacity as the cast-in-place RC column. The precast RC/ECC composite column shows a better energy dissipation capacity and a better damage resistance than the precast RC column and the cast-in-place column. Therefore, application of ECC in the plastic hinge zone of precast column can effectively enhance its seismic performance.

Seismic-improved reinforced-concrete composite column using a high-ductile fiber cementitious composite precast box

ABSTRACTThe purpose of this study is to investigate the applicability of the high-ductile fibre cementitious composite to develop seismically improved reinforced concrete columns. The high-ductile fibre cementitious composites were fabricated to exhibit high-ductile tensile strains as above 2.0% with sustaining the tensile stress after cracks and to develop multiple micro-cracks while avoiding crack localisation. In order to seismically improve the reinforced concrete column, the precast box made of the high-ductile fibre cementitious composite was locally used at the flexurally critical region in the column plastic hinge zone, and the construction process was also proposed. In seismic capacity evaluation of the developed column, cyclical loading tests were carried out by using four column specimens fabricated. It was revealed, from experiments, that the developed reinforced concrete and the high-ductile fibre cementitious composite columns showed an improvement of the seismic capacity of the column as well as a minimisation of flexural and shear cracks in the bending critical region of the column.

Experimental Study on Seismic Capacity of Reinforced Concrete Composite Columns Based on a High-ductile Fiber Cementitious Composite

The authors examined the application of a high-ductile fiber cementitious composite (HDFC) to develop seismic-improved reinforced-concrete columns. HDFC was manufactured to show high-ductile tensile strains above 2.0%, sustaining tensile stress after cracks and developing multiple micro-cracks while avoiding crack localization. To seismically improve a reinforced-concrete column, a precast box made of HDFC was applied locally at the flexural critical region in the column plastic hinge zone; a construction process is also proposed. In seismic performance evaluations of the developed column, a series of cyclic load tests was conducted by manufacturing four column specimens. It was shown from experiments that the developed reinforced concrete and HDFC composite columns showed not only improved seismic performances but also minimized bending and shear cracks in the flexural critical region of the column.

Experimental Investigation on the Usage of Steel Fibres and Carbon Fibre Mesh at Plastic Hinge Length of Slab

Abstract Plastic hinges are usually considered as the most severely damaged zone of the structural element which experience huge inelastic deformation. The performance of plastic hinge is critical for RC structural elements. Plastic hinge length is an essential parameter where severe confinement should be provided to improve the ductility of the RC structural element. This paper deals with an experimental investigation on the usage of steel fibres and carbon fibre mesh at plastic hinge length of slab. During the first stage of experiment, mechanical properties of concrete for both conventional and Steel Fibre Reinforced Concrete (SFRC) were determined. According to the results, addition of steel fibre increased the compressive, spilt tensile and flexural strength of concrete. Many expressions are available to calculate plastic hinge length. Priestley and Park expression was used in this study. Eight different types of slabs were casted to determine the influence of steel fibres and carbon fibre mesh at plastic hinge zone. It is found from the result that providing steel fibres at plastic hinge length is more efficient and results in a better ductile behavior.

Experimental Study on Novel Energy‐Dissipating Prefabricated Beam‐Column Joints

A new dapped‐end beam to column connection is designed in this paper. Its assembly connection zone changes from inside the joint to midspan of the beam. The proposed connection can not only provide good structural integrity but also ensure that the plastic hinge moves away from the column edge. The rotational capacity of the plastic hinge determines the internal force redistribution of the joint and the energy dissipation capacity. The high‐strength bolts and steel plates are used to realize connection, further enhancing the rotation of the plastic hinge and minimizing the cast‐in‐place concrete volume. Three full‐scale exterior beam to column joints are casted and then subjected to reversal cyclic loading. The finite element (FE) analyses are carried out to compare with experimental results and study the effect of connection position on the structural behaviours. The obtained results show that the plastic hinges of all three specimens are firstly developed to a distance from the column edge, thus revealing that this kind of joint can achieve beam hinge mechanism and prevent joint shear failure. And the connection position is the most disadvantaged when coinciding with the plastic hinge zone, which would result in the excessive deformation and the early failure of the steel bar anchor system. The new type of joint shows good seismic performance during earthquake if the connection can be properly designed, and thus this kind of structural form can be applied to actual engineering structures in seismic regions.

Behaviour of Hybrid Steel and FRP-Reinforced Concrete-ECC Composite Columns under Reversed Cyclic Loading.

Fibre-reinforced polymer (FRP) is used widely in concrete structures owing to its noncorrosive, light-weight, nonmagnetic, and high tensile-strength properties. However, the FRP-reinforced concrete flexural member exhibits low ductility owing to the linear–elastic property of FRP reinforcement. Hybrid steel—FRP-reinforced concrete members exhibit good strength and ductility under flexure owing to the inelastic deformation of steel reinforcement. The existing investigations have focused on the mechanical behaviours of the hybrid steel—FRP-reinforced flexural members. Only few studies have been reported on the members under combined flexural and compression loads, such as columns, owing to the poor compressive behaviour of FRP bars. We herein propose a new type of hybrid steel—FRP-reinforced concrete—engineered cementitious composite (ECC) composite column with ECC applied to the plastic hinge region and tested it under reversed cyclic loading. The hybrid steel—FRP-reinforced concrete column was also tested for comparison. The influence of matrix type in the plastic hinge region on the failure mode, crack pattern, ultimate strength, ductility, and energy dissipation capacity, of the columns were evaluated systematically. We found that the substitution of concrete with ECC in the plastic hinge zone can prevent the local buckling of FRP bars efficiently, and subsequently improve the strength and ductility of the column substantially.

Evaluation of load–deformation behavior of reinforced concrete shear walls with continuous or lap-spliced bars in plastic hinge zone

This article presents an analysis procedure for evaluation of load–deformation behavior of reinforced concrete shear walls with continuous or lap-spliced bar connections in plastic hinge zones under horizontal loads. For the shear walls with continuous bars, the lateral deformations caused by flexure, shear, and reinforcement slip are evaluated by considering their interaction. The flexural deformation is calculated by conventional fiber model. The shear mechanism is based on modified compression field theory with a softened smeared cracked reinforced concrete membrane element. Both the flexural and shear deformations are estimated separately in the plastic hinge and non-plastic hinge regions. In addition, an approach is proposed for analysis of plastic hinge length based on fracture energies of materials. For the shear walls with lap-spliced bars, due to its complicated behavior and mechanism, a simple way to deal with the lap splice is proposed. The equations regarding bond-slip of the lap splice with minimum spliced length are established and the stress and strain states of lap splices with different spliced lengths are analyzed on the basis of equilibrium of forces with a mean bond stress model. Finally, the validity of the proposed analysis procedure is confirmed by comparing the analytical results with previous experimental data.

Tensile Behavior of Single Cast-in Anchors in Plastic Hinge Zones

Tensile Behavior of Single Cast-in Anchors in Plastic Hinge Zones

Effects of postcast connection locations on the seismic performance of precast concrete frame joints

SummaryFor the precast structure with postcast connections, the location of the connection is usually the midspan of the beam, joint core, and beam end. However, the postcast connections located at the midspan of the beam or the joint core would increase the difficulty of construction because of the large dimension of the precast components or reinforcement congestion at joint core, respectively. A connection located at the beam end could decrease the seismic performance the energy dissipation mechanism being disturbed. To balance the requirements on the transportation, construction, and seismic performance, the connection is proposed to be located at one plastic hinge length from the beam end. A quasi‐static test was conducted on three 6 m × 3 m beam‐column joints, including two precast joints and a monolithic joint. The results show that the joint with connections located outside the plastic hinge zone had good seismic performance. When the connection located at the beam end, the ductility, strength, and energy dissipation reduced 8%, 10%, and 30%, respectively. To optimize the postcast location, finite element analysis was conducted and 2h was suggested for the postcast location according to the analysis results.

Shear Strength Behaviour of Steel Truss Embedded in Flexural Plastic Hinge Zone of Reinforced Concrete Beam Subjected to Reversed Cyclic Loading

Shear Strength Behaviour of Steel Truss Embedded in Flexural Plastic Hinge Zone of Reinforced Concrete Beam Subjected to Reversed Cyclic Loading

Shake Table Studies and Analysis of a Precast Two-Column Bent with Advanced Materials and Pocket Connections

Shake table experiments and analyses of a large-scale precast two-column bent with advanced materials in plastic hinge zones were conducted to develop bridge bents for use in accelerated bridge construction (ABC) in moderate and high seismic zones. Ultrahigh performance concrete (UHPC) and engineered cementitious composite (ECC) were used in column plastic hinge zones to reduce earthquake damage. Precast square columns were connected to a precast footing and a cap beam using pocket (also known as socket) connections. The primary objectives of this investigation were to evaluate the seismic response of the precast bent and the pocket connections and to assess the effectiveness of UHPC and ECC in reducing damage in the plastic hinge zones. The bent was subjected to successive motions simulating scaled versions of the 1994 Northridge-Sylmar earthquake until failure. The experimental results showed that the pocket connections performed well, and the structural integrity was maintained up to a drift ratio of 9.6% and displacement ductility of 12. UHPC and ECC effectively reduced the column plastic hinge damage, although the extent and location of damage for the two materials were different. Another finding of the study was that a relatively simple computational model of the bent in OpenSees led to close correlation between the measured and calculated responses.

Hysteretic behavior and modified design of square TSRC columns with shear studs

The tubed steel reinforced concrete (TSRC) column is a composite member consisting of the concrete core reinforced by a steel shape and the outer thin-walled steel tube which is made slightly shorter than the column to avoid direct axial loading and acts as a confining steel for the concrete. In this paper, the hysteretic behavior of square TSRC columns was investigated experimentally and analytically. Five square TSRC columns, in which high-strength concrete with fcu,150 = 85.4 MPa was used and the thin-walled steel tube in potential plastic hinge zones was stiffened by steel plates, were tested under constant axial compression and cyclic lateral loads. The influences of shear studs on the steel shape, axial load ratio, width to thickness (D/t) ratio were also considered in the test. The test results indicated that the confinement from steel tubes effectively improved the ductility and plastic deformation ability of the specimens, while the shear studs on the steel shape effected little on the co-working behavior between the concrete and the steel shape. A fiber-based element model using OpenSEES software was developed and a good agreement was achieved between the test and predicted results. Utilizing the numerical model, the limiting axial load ratio was analyzed to ensure that the square TSRC columns had the sufficient ultimate deformation capacity. To account for the improvement of strength and ultimate strain in the concrete core resulting from the tube confinement, relevant development methods for N-M interaction diagrams, such as those in the ACI and EC4, were modified for square TSRC columns.

Cyclic response analysis of high-strength self-compacting concrete beam-column joints

In this paper, finite element analysis software “DIANA” is implemented to simulate quasi-static cyclic loading test results of three full-scale beam-column joints cast with high-strength self-compacting concrete (HSSCC). The specimens were designed according to the New Zealand concrete standard (NZS3101 2006). Material models for concrete and steel were calibrated based on the physical characteristics of the materials derived either from laboratory tests or using expressions available in literature. Two-dimensional curved-shell elements were used in modelling the specimens. As the specimens were designed following the code requirements for seismic actions, bond between the reinforcement and concrete was assumed as perfect. In order to obtain a more representative prediction, both the longitudinal and transverse reinforcement were modelled in their actual locations. Pushover analyses were first conducted to check the mesh sensitivity; after which the modelled specimens were subjected to reversed cyclic loading histories applied in the experimental tests. Seismically important response parameters such as damping, stiffness, concrete and steel contributions in the joint shear resistance, joint shear deformation, strain development in the joint stirrups, elongation of the plastic hinge zone, development of compressive stress, and cracking pattern were extracted from the analytical predictions and compared to the experimental results. It was found that the adopted modelling and analysis approach was capable of predicting cyclic performance of HSSCC beam-column subassemblies with reasonable accuracy.

Shear Behavior of Single Cast-in Anchors in Plastic Hinge Zones

This paper presents two shear tests of ¾-in. diameter cast-in anchors embedded in the plastic hinge zone of reinforced concrete columns. Design codes, such as ACI 318-14, require special reinforcement for concrete anchors in concrete that could be substantially damaged during an earthquake. The test anchors in this study were equipped with the anchor reinforcement recommended and verified in the literature. The column specimens were subjected to quasi-static cyclic loading before the test anchors were loaded in shear. Steel fracture was achieved in both test anchors despite cracks and concrete spalling occurred to the concrete within the plastic hinge zones. Meanwhile, the measured anchor capacities were smaller than the code-specified capacity, especially for the anchors subjected to cyclic shear. Concrete cover spalling was found critical to the observed capacity reduction, which caused combined bending and shear action in the anchor bolts. Measures should be developed to mitigate such adverse impact. In addition, further studies are needed for post-installed anchors before practical applications.