Column Longitudinal Reinforcement Research Articles

Numerical Investigation on the Hysteretic Performance of Self-Centering Precast Steel–Concrete Hybrid Frame

To improve the construction performance and seismic resilience of precast reinforced-concrete frame structures, an innovative self-centering precast steel–concrete hybrid frame has been proposed and subjected to cyclic loading tests. In this paper, a comprehensive numerical analysis was conducted to further investigate the frame’s hysteretic behavior. Initially, a numerical model was developed using the finite element software OpenSees. Numerical analyses of two frame specimens were conducted, demonstrating good agreement between the numerical and experimental hysteretic characteristics, thus validating the model’s accuracy. Subsequently, based on the numerical simulations, a quantitative comparison of hysteretic performance between a novel frame and a traditional reinforced-concrete frame of the same scale was performed. While the proposed frame exhibited slightly lower initial stiffness and energy dissipation capacity than the traditional frame, it outperformed in terms of load-carrying capacity and self-centering ability. Finally, parametric analyses were carried out to assess the influence of various design parameters on the hysteretic performance, including friction force in the web frictions devices, initial post-tensioned force of the prefabricated steel–concrete hybrid beams, the steel arm length, and the column longitudinal reinforcement ratio. The results showed that increases in these four parameters improved the load-carrying capacity and initial stiffness of the proposed frame. Additionally, an increase in the friction force, steel arm length, or column longitudinal reinforcement ratio enhanced the frame’s energy dissipation capacity, while an increase in the initial post-tensioned force or a decrease in the friction force enhanced the frame’s self-centering capacity.

Finite element analysis of the seismic performance of PVC-CFRP confined concrete column-ring beam interior joints

This paper presents a finite element (FE) analysis of the seismic performance of PVC-CFRP confined concrete column-ring beam interior joints (PCCC-RBIJs) under low cyclic loading. Based on the constitutive relationship of materials, a FE model was established using ABAQUS and validated against the experimental results of ring beam joints found in the literature. Then, FE parametric analysis was performed to investigate the influence of studied parameters on the seismic performance of the PCCC-RBIJs. These studied parameters included the axial compression ratio, height-diameter ratio of the ring beam joint, column longitudinal reinforcement ratio, reinforcement ratio and stirrup ratio of ring beam, and joint concrete strength. The FE analysis showed that the seismic performance of PCCC-RBIJ specimens can be enhanced by increasing their axial compression ratio, column longitudinal reinforcement ratio, and ring beam reinforcement ratios or decreasing their height-diameter ratio of the ring beam joint. Although the joint concrete strength and ring beam stirrup ratio have little effect on the seismic performance of the joint, the ring beam stirrup ratio affects the stirrup utilization. The paper also provides design suggestions for PCCC-RBIJs.

Seismic behavior of eccentric new RCS joints with through columns

Architectural requirements often result in beam-column joints with eccentrically framing beams. However, the fabrication of eccentric through beam-type reinforced concrete column and steel beam (RCS) joint is extremely complex due to the presence of column longitudinal reinforcement and joint confinement reinforcement. To mitigate the constructability issues associated with through-beam type RCS eccentric joints, the current study proposed a through-column type New RCS joint. The proposed New RCS joint used joint cover plates and continuity plates as additional attachments while eliminating the need for joint confinement reinforcement. Two large-scale beam column subassembly specimens were tested to evaluate the seismic behavior. Both specimens had high-strength reinforced concrete columns (New RC columns) with a design concrete grade of 84 MPa and steel reinforcement of specified yield stress 690 MPa. The experimental results revealed the asymmetric shear stress development in the joint cover plates due to joint eccentricity. Based on experimental observations, a joint shear force-deformation model was presented, which was able to capture the joint shear response with reasonable accuracy. Finally, simplified expressions were presented, which were able to provide reliable estimates of joint shear strength, which is suitable for design purposes.

Experimental Study on Structural Performance of Cast-in-Place Frame Printed Concrete Wall

A growing number of nations and regions have printed concrete structures thanks to the application of 3D printing technology in the field of civil engineering. However, the houses built with printed concrete are mostly printed concrete wall structures with composite load-bearing walls and cast-in-place frames. This structure solely takes into account the performance of the structure under vertical loads, which does not address its ability to withstand horizontal loads. In this paper, wall specimens were designed and tested under horizontal reciprocal loads in order to investigate the structural performance of this cast-in-place border-frame printed concrete wall structure under horizontal loads. Four factors are examined in order to determine how well the cast-in-place frame printed concrete wall structure performs when subjected to horizontal loads: column longitudinal reinforcement strain, hysteresis curve, skeleton curve, and energy dissipation capacity. According to the test results, the addition of the wall increased the bearing capacity and accumulated energy dissipation of the specimen, but the increase in stiffness also caused the structural ductility to decrease. As a result, cracks were more likely to generate at the wall–column joints, so the stiffness matching between the printed concrete wall and the cast-in-place side frame needed to be further coordinated to obtain a higher ductility. It turns out that the wall sections have little impact on the seismic performance of the members.

Experimental investigation and numerical modelling of the seismic performance of corroded T-shaped reinforced concrete shear walls

Six T-shaped reinforced concrete (RC) shear wall specimens were subjected to constant-current and drying-wetting cycle accelerated corrosion tests and pseudostatic loading tests in this paper. The corrosion appearance, failure mode, and mechanical properties of each specimen were compared, and the impact of the corrosion degree and axial compression ratio on the seismic performance of the T-shaped RC shear wall was analysed. The experimental outcomes illustrate that the seismic behaviour of the specimens under positive and negative loading was conspicuously different because of the asymmetric section of the specimens. Under positive loading, the bearing capacity of the specimens was higher, and the deformation capacity was poor, while the negative loading was the opposite. As the corrosion degree increased, the bearing capacity, deformability, stiffness degradation degree, cumulative energy dissipation capacity, and proportion of shear deformation in the total deformation of the specimens all showed a downwards trend. With increasing axial compression ratio, the bearing capacity of the specimen increased, the cumulative energy dissipation capacity, ultimate displacement and the proportion of shear deformation in the total deformation decreased, and the degradation rate of stiffness accelerated. Subsequently, considering the correction of corroded materials, a numerical model of the corroded T-shaped RC shear wall based on the ShellMITC4 multilayer shell element was established, and the exactitude of the numerical model was validated based on test data. Finally, based on the established numerical model, the effects of the concrete strength, boundary column longitudinal reinforcement ratio and vertical distribution reinforcement rate on the seismic behaviour of corroded T-shaped RC shear walls were studied. These research outcomes can offer supporting theories for numerical modelling analysis and seismic capacity assessment of existing RC shear wall structures in coastal environments.

Seismic shear behavior of new high-strength reinforced concrete column and steel beam (New RCS) joints

New high-strength reinforced concrete column and steel beam (New RCS) joints were developed in this research. Two-way, through-beam New RCS joint details with beams concentrically or eccentrically connected to the joint were proposed. The beam in one direction was continuous through the joint (continuous beam). The beam in the other direction was connected to the continuous beam by complete joint penetration (CJP) groove welds. Five-spiral reinforcement was used for joint transverse reinforcement. A method to calculate the amount of five-spiral reinforcement was proposed considering the confinement effect from the face-bearing plates (FBPs). Doubler plates were used to strengthen the eccentric beam flanges with predrilled holes to allow the passage of column longitudinal reinforcement. A method was proposed for the design of the doubler plates. Large-scale New RCS joint specimens designed to fail in joint shear were tested. Test results showed that the proposed joint details and design methods effectively avoided failure in undesirable locations. All the specimens failed in joint shear but still reached high drift ratios. The eccentric joint specimens (IDEHS and ISEHS) exhibited peak joint shears higher than the concentric beam specimen (IHS). The 1994 ASCE and 2015 ASCE shear strength models produced conservative predictions of the peak joint shear and the joint shear at 0.5% joint shear deformation for all the specimens. The predictions by the 2015 ASCE method were more reasonable with less scatter than the 1994 ASCE method because the former recognizes the shear strength contribution from the outer joint panel even without the use of shear keys and allows a longer steel web in shear strength calculation.

Cost-effective post-tensioned bridge pier with internal dissipation

This paper presents the development and testing of a novel internal dissipation connection for the use of post-tensioned rocking columns. The solution is one of the many referring to the dissipative controlled rocking (DCR) bridge design philosophy. The internal dissipaters are carefully designed to be cost-effective and reduce the overall construction cost. The dissipaters are fully threaded, Grade 300 bars connected to the permanent column and foundation longitudinal reinforcement with threaded couplers. In this research, a DCR column is subjected to subsequent earthquake events, and the dissipaters' strain design limits are chosen such that there is no need for replacing after a significant seismic event. The result is a recommended design strain limit of 1.5% for the dissipaters that guarantees the structural integrity of the DCR column after a seismic event. Additionally, a cumulated strain of 5% is recommended for the dissipaters before replacement is suggested. The proposed connection detailing with replaceable internal dissipaters, combined with post-tensioned high strength bars and well-confined concrete, provided self-centring capabilities (no residual displacement), dissipation capacity and significantly less damage in the bridge column than a traditional reinforced concrete solution.

Influence of reinforcement on the performance of non-seismically detailed RC beam-column joints

Beam-column connections play an important role in the seismic behavior of reinforced concrete structures. Among various factors that can affect the performance of beam-column joints, reinforcement detailing has attracted researchers' attention because of its undeniable impact on the behavior of RC joints and structures under seismic loads. In this study, the influence of reinforcement detailing (including beam longitudinal reinforcement, beam transverse reinforcement, the angle of beam stirrups and column longitudinal reinforcement) on the displacement ductility and curvature ductility is numerically investigated. To achieve the study's objective, 25 RC beam-column joint models were developed in non-linear Finite Element software; three of them were verified by a similar experimental study conducted by Li et al. The reinforcement detailing was then changed to evaluate response of the joints. Results show that by increasing the longitudinal reinforcement of beam or decreasing the size of beam stirrup, both displacement ductility and curvature ductility decrease. Another notable conclusion is that decreasing the angle of beam stirrup or increasing the longitudinal reinforcement of a column can lead to an increase in curvature ductility and displacement ductility.

Seismic behavior of precast columns with large-spacing and high-strength longitudinal rebars spliced by epoxy mortar-filled threaded couplers

An innovative precast concrete column system, which is expected to be emulative to conventional cast-in-situ columns, is proposed in this paper. In this system, short novel epoxy mortar-filled threaded couplers (MTCs) provide column longitudinal reinforcement with continuity; large-spacing and high-strength longitudinal rebars are used to replace the conventional normal-strength rebars for simplified rebar splices; labor-saving spiral hoops combined with crossties provide core concrete with enhanced confinement. The effectiveness of the innovative construction details was investigated by individual connector tests and column tests. Test results showed that precast columns exhibited global behavior, damage state, cracking distribution, energy-dissipation, and deformation capacity comparable to those of cast-in-situ columns, validating the reliability of the innovative construction details. The short MTCs had little effect on the plastic hinge formation, and could enable precast columns to exhibit stable load-carrying capacity through extensive deformations. Eventually, an approximate method based on a modified plastic hinge length was developed to evaluate the deformation capacity of spliced columns, and the evaluated results agreed well with the measured ultimate drifts.

Artificial neural network based multi-dimensional fragility development of skewed concrete bridge classes

Recent researches are directed towards the regional seismic risk assessment of structures based on a bridge inventory analysis. The framework for traditional regional risk assessments consists of grouping the bridge classes and generating fragility relationships for each bridge class. However, identifying the bridge attributes that dictate the statistically different performances of bridges is often challenging. These attributes also vary depending on the demand parameter under consideration. This paper suggests a multi-parameter fragility methodology using artificial neural network to generate bridge-specific fragility curves without grouping the bridge classes. The proposed methodology helps identify the relative importance of each uncertain parameter on the fragility curves. Results from the case study of skewed box-girder bridges reveal that the ground motion intensity measure, span length, and column longitudinal reinforcement ratio have a significant influence on the seismic fragility of this bridge class.

Numerical Study of Bond and Development of Column Longitudinal Reinforcement Extended into Oversized Pile Shafts

AbstractThis paper presents a numerical investigation to examine the bond-slip behavior of column longitudinal reinforcing bars embedded in oversized pile shafts and to determine the minimum embedm...

EXPERIMENTAL RESEARCH ON SEISMIC PEFORMANCE OF FRAME PIERS OF DOUBLE-DECK VIADUCTS

Based on a double-deck viaduct, two double-deck viaduct piers with different column longitudinal reinforcement ratios are designed and the influence of the longitudinal reinforcement ratio on the seismic performance of double-deck viaducts is investigated with pseudo-static test and numerical analysis. The experiment results show that the beam and lower-level beam-column joints of the high reinforced pier suffer severe damage. When the reinforcement ratio is reduced, damage mainly appears on the column, and the level of damage on the beam and the joint is mitigated effectively. Based on the experiment results, a finite element model of the pier is built and used for parametric analysis. The analysis results indicate that when the column longitudinal reinforcement ratio increases, the ductility capacity of double-deck viaducts decreases and the beam would collapse before the column, which disobeys the performance objective of strong beam and weak column.

Experimental Research on T-Shaped Beam-Column Joints at Top Floor with Mechanically Anchored Reinforcement

Abstract Mechanical anchorage becomes popular for recent reinforced concrete construction because of the ease-to-install at congested connections. Column longitudinal reinforcement is anchored at T-shaped beam-column joints at top floor where the anchorage may be positioned beyond the beam core because columns typically have larger dimensions than beams. Thus premature failure can be caused at the anchorage; however, no design details have been provided in previous studies. Therefore, this study proposes a theoretical method to evaluate the minimal requirement for reinforcement to prevent anchorage failure of column longitudinal rebar. Static cyclic loading tests were conducted on three 1/2 scale T-shaped partial frame specimens representing a beam-column joint at top floor to examine the effectiveness of the proposed quantity of anchorage-reinforcing bars. The anchorage-reinforcing bars were intensively arranged at the ends of the anchor plates in all the specimens, while different amounts of joint shear reinforcement were applied to the specimens. Consequently, all the specimens failed with beam flexural yielding, and none obvious strength deterioration was observed until a drift ratio of 1/25rad. The theoretical requirement for anchorage-reinforcing bars proposed in this study is effective to prevent premature anchorage failure in T-shaped beam-column joints.

Development of Bridge Column Longitudinal Reinforcement in Oversized Pile Shafts

AbstractThis paper presents an experimental investigation to determine the embedment length required for longitudinal reinforcement in a bridge column extending into an oversized pile shaft, and the amount of transverse reinforcement required for the pile shaft to prevent premature bar anchorage failure due to concrete splitting induced by bar slip. Four full-scale column–oversized pile assemblies were tested under quasi-static cyclic lateral loading. The test specimens had different embedment lengths for the column reinforcement, different amounts of transverse reinforcement in the piles, different sizes of longitudinal bars, ranging from No. 8 to No. 18 (25 to 57 mm) bars, and different column-to-pile diameter ratios. All column–pile assemblies behaved in a ductile manner with plastic deformation occurring near the base of the columns despite some cone-shaped fractures and tensile splitting cracks occurring in the top portion of the piles. The test results show that the embedment length for the column r...

2方向水平力を受ける鉄筋コンクリート造立体隅柱梁接合部の耐震性能および立体破壊モデルに基づく曲げ終局耐力の評価

Static loading tests to reinforced concrete (R/C) three-dimensional (3D) corner column-beam subassemblage specimens were carried out by Katae and Kitayama (2014) to investigate the effect of column compressive axial load on failure mechanics of joint-hinging proposed by Shiohara. The Shiohara's proposal pointed out that failure mode of a R/C beam-column-joint frame depends greatly on a column-to-beam capacity ratio and joint-hinging failure tends to develop when a column-to-beam capacity ratio is close to unity. Note that a column-to-beam capacity ratio can be varied by changing not only the magnitude of column axial load but also the amount of column longitudinal reinforcement. Therefore three 3D corner column-beam subassemblage specimens (two without slabs and one with a slab having a thickness of 70 mm) were tested under bi-lateral loading and constant column axial load where a column-to-beam capacity ratio of 1.5 and 2.6 was set by placing column longitudinal reinforcement of 8-D16 and 8-D19 respectively. All 3D subassemblage specimens failed in joint-hinging with an increase in story drift. It is revealed by Katae and Kitayama (2014) that the ultimate flexural capacity of corner column-beam joints under bi-lateral loading can be estimated based on the new mechanism of joint-hinging by assuming that the orbit on the rectangular coordinates plane defined by joint-hinging capacities in both directions orthogonal to each other traces an ellipse curve under bi-lateral loading. Three-dimensional (3D) failure surfaces and stress flow conditions in a corner column-beam joint under bi-lateral loading, however, are not clarified yet. Then a 3D joint-hinging failure model was constructed for a corner joint based on test results referring to a plane joint-hinging failure model proposed by Kusuhara and Shiohara. A quick evaluation method for the ultimate joint-hinging capacity was proposed based on the 3D failure model in a corner column-beam joint under bi-lateral loading. General conclusions are drawn from the study as follows. (1) When a column-to-beam capacity ratio increased from 1.5 to 2.6, the ultimate joint-hinging capacity computed as a resultant force of two orthogonal story shear forces under bi-lateral loading increased to 1.19 times by large amount of column longitudinal reinforcement. This indicates that the ultimate joint-hinging capacity was enhanced by the increase in a column-to-beam capacity ratio due to increasing the amount of column longitudinal reinforcement. (2) When a column-to-beam capacity ratio was changed from 1.5 to 2.6 by the increase in the column compressive axial load in past tests or the amount of column longitudinal reinforcement in this tests, the column compressive axial load had a greater influence on enhancement of the ultimate joint-hinging capacity under bi-lateral loading than the amount of column longitudinal reinforcement. (3) A slab contributed to enhancing the ultimate joint-hinging capacity by 1.07 times that without a slab for 3D corner column-beam subassemblages with a column-to-beam capacity ratio of 1.5, failing in joint-hinging. Torsional moment at the end of a transverse beam caused by tensile force of slab reinforcing bars in the longitudinal direction, whose rotating direction is counter to that of upper and lower columns, is carried to a beam-column joint and restrains rotation of the upper and lower columns. This is the reason for enhancement of the ultimate joint-hinging capacity due to a slab. (4) Proposed method based on 3D failure model herein can adequately evaluate the ultimate joint-hinging capacity of a corner column-beam joint under bi-lateral loading since there is a discrepancy within 10 % between predicted ultimate capacity and test result.

Reliability Analysis of RC Columns and Frame with FRP Strengthening Subjected to Explosive Loads

Some structures, both military and civilian, might experience explosive loads during their service life. Owing to high uncertainties in blast load predictions and structural parameters, accurate assessment of the performances of structures under explosion loads is a challenging task. For example, a number of experimental studies using fiber-reinforced plastic (FRP) strengthening of RC structures have been reported in the literature. Most of these studies demonstrate that FRP strengthening is effective in increasing the blast load–carrying capacities of RC structures. However, significant variations in the effectiveness of FRP strengthening have also been observed owing to the large uncertainties in blast loading, RC and FRP material properties, and workmanship in preparing the test specimens and conducting experimental tests. Very few studies that take into consideration these uncertainties in analyzing the effectiveness of FRP strengthening of RC structures on blast loading resistance can be found in the literature. This study performs a reliability analysis to assess the performance of RC columns with or without FRP strengthening in resisting blast loads. Statistical variations of blast loading predictions derived in a previous study are adopted in this study. To define structural performance, pressure-impulse (P-I) curves with a damage criterion on the basis of axial load-carrying capacity that were developed in previous studies for RC columns without strengthening or with FRP strip, FRP wrap, or both FRP strip and wrap strengthening are used. Considering the uncertainties in blast loading predictions and RC column and FRP material properties and dimensions, limit-state functions corresponding to different damage levels of RC columns with or without FRP strengthening are formulated. The statistical variations of blast loading, RC column dimension, longitudinal and transverse reinforcement ratio, and concrete, steel, and FRP material strength and FRP thickness are considered. The failure probabilities of RC columns corresponding to different damage levels with or without FRP strengthening are calculated. The effectiveness of FRP strengthening on the RC column’s blast loading resistance capacities is discussed. The importance of considering the random fluctuations on blast loading and RC column parameters in assessing the blast loading effect on RC columns is demonstrated. A structural system reliability analysis is also carried out to examine the probability of structural collapse as a result of blast loading applied to the front of an example two-span multistory RC frame. The results obtained in this study demonstrate the effectiveness of FRP strengthening on structure protection and can also be used to assess RC structure performance under blast loadings.

Effect of Active versus Passive Confinement on Seismic Response of Wide RC Columns with Lap Splices

AbstractThe results of an experimental study on seismic bond strengthening of spliced reinforcement in wide RC columns using external confinement are presented. Two types of confinement techniques were evaluated and compared, as follows: (1) a combination of external carbon fiber-reinforced polymer (CFRP) jacket and CFRP anchors, and (2) active confinement by means of pretensioned steel anchor rods. The effectiveness of the different strengthening techniques was evaluated by comparing with test results of companion as-built columns, and earthquake-designed columns which were detailed in accordance with the seismic provisions of a national building code. The columns were subjected to a quasi-static cyclic loading, simulating regions of high seismic hazard. In addition to the type of the strengthening system used, the test variables included area and diameter of the column longitudinal reinforcement. The as-built columns suffered bond and load degradation immediately after yielding of the spliced reinforcem...

Anchorage of Longitudinal Column Reinforcement in Bridge Monolithic Connections

Most of the existing mechanical models for shear strength and strain calculation of beam-column joints do not explicitly account for bond conditions of the longitudinal reinforcement of the connected members that are anchored inside the joint region. When considered, bond is accounted for through empirical parameters. In this paper, an analytical method for the definition of the strain distribution along the anchorage of the column longitudinal reinforcement inside a bridge monolithic connection is proposed. The anchorage capacity of the main column reinforcement is considered to be affected by two independent mechanisms. The capacity of the first mechanism depends on the average bond stress along the elastic part of the anchorage that is calculated by a mathematical solution without taking into account the beneficial effect of the transverse reinforcement. The capacity of the second mechanism depends on the coefficient of friction arising between main column bars and transverse reinforcement that encloses and restrains the anchorage. The coefficient of friction is empirically set in relation to the position of the transverse bar; either along the elastic part of the anchorage or in the part where yielding penetrates inside the joint. A parametric evaluation of the main design parameters affecting the anchorage capacity is conducted next. The proposed model is finally used in calculating the joint shear response of selected bridge connection specimens for which reported data of strain distribution along anchorages exist. The calculated values correlate successfully with the associated experimental data.

An Experimental Study on Effectiveness of Reinforcing Methods on L-Shaped Prestressed Concrete Beam-Column Joints

This paper presents experimental results of cyclic loading tests carried out on three L-shaped prestressed concrete beam-column corner joints. Three types of reinforcing methods to enhance the anchorage performance of beam and column longitudinal reinforcing bars were studied based on the experimental results such as the load-displacement relation curves, deformation capacity, prestressing force variation, and strain measurements of the beam and column reinforcing bars. The test specimens were KPCL1 with the column longitudinal reinforcement with 180-degree hooks at their ends, KPCL2 with the column longitudinal reinforcement bent in a U-shape, and KPCL3 with U-shaped column longitudinal reinforcement and additional transverse reinforcement on the beam longitudinal reinforcement. It can be concluded that the anchorage performance was somehow enhanced by the three reinforcing methods in the positive direction of loading (closing direction), while in the negative direction of loading (opening direction) there was no remarkable improvement.

Effects of beam—column depth ratio on joint seismic behaviour

Full-scale reinforced concrete (RC) exterior beam–column joints, which are fabricated to simulate those in as-built RC frame buildings designed to BS 8110, are tested under reversed cyclic loading. The seismic behaviour of these non-seismically designed joints is investigated. Particular emphasis is given to the effects of the beam–column depth ratio, column longitudinal reinforcement and stirrups in joints on the seismic performance and shear strength of the joints. It is shown that beam–column depth ratio has a significant effect on the shear strength and ductility of beam–column joints, while intermediate longitudinal reinforcement may be used to enhance the shear capacity and improve the hysteretic behaviour of beam–column joints, and links placed in beam–column joint cores can effectively improve the seismic behaviour and enhance the joint shear strength. Test results are compared with those predicted by three seismic design codes (ACI-318, NZS 3101 and Eurocode 8) and two non-seismic design codes (BS 8110 and Eurocode 2). It has been shown that member sizing and reinforcement detailing have significant effects on the shear capacity and seismic behaviour of exterior beam–column joints. In general, present seismic and non-seismic design codes do not accurately predict the shear strength of the non-seismically detailed joints, while BS 8110 may provide relatively better predictions than others in these particular cases.