Lap-spliced Column Research Articles

Impact of corrosion on risk assessment of shear-critical and short lap-spliced bridges

Increasing corrosion in aging reinforced concrete structures is increasing their vulnerability to failures. This is particularly true for bridges with low-ductility columns, including shear-critical columns and columns with short lap splices. This paper presents a methodology to assess the impact of corrosion on performance of these structures. The combined analytical and numerical modeling of shear-critical and lap-spliced columns is detailed, and outcomes are verified with previous experimental test data. Corrosion effects are accounted for through reduction of longitudinal and transverse reinforcement and bond deterioration between the steel and concrete through corrosion-induced cracking. The impact of corrosion on risk is assessed through conducting fragility analyses. Results quantify the increase in failure probabilities of these structures, measured by increasing probabilities of exceeding defined damage states, with increasing levels of corrosion. Corrosion is found to have a larger impact on increasing probabilities of exceeding more severe damage states. Twenty percent mass loss of reinforcement increases the probability of exceeding the complete damage state by up to 49% and 34% for a shear-critical and lap-spliced column, respectively. The effect is more pronounced at intermediate loading intensities, where there is uncertainty about the performance of the structure. Comparing between failure modes, bridges with columns of short lap splice are more vulnerable to collapse under the same degree of corrosion compared with shear-critical columns.

Seismic retrofit of circular RC columns through using tensioned GFRP wires winding

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.

Bond behaviour of substandard splices in RC beams externally confined with CFRP

Bond splitting failures of substandard lap-spliced columns have led to collapse of many RC buildings during recent earthquakes in developing countries. The strengthening of lap-spliced regions with CFRP confinement can reduce the seismic vulnerability of such buildings. This paper investigates bond splitting using flexural tests on twelve RC beams with substandard lap splices (25bar diameters) at midspan. Different confinement configurations (no confinement, internal stirrups or CFRP sheets), concrete covers and bar sizes are examined at the splice region. The results show that light CFRP confinement enhances the splice bond strength by up to 65% compared to unconfined specimens. Predictive equations from the literature are shown to yield a large scatter in results and to overestimate the strain developed in the CFRP confinement. An alternative approach to calculate the confinement strain and the additional bond strength provided by CFRP confinement is proposed and validated.

Seismic fragility analysis of lap-spliced reinforced concrete columns retrofitted by SMA wire jackets

The aim of this study is to provide seismic fragility curves of reinforced concrete columns retrofitted by shape memory alloy wire jackets and thus assess the seismic performance of the columns against earthquakes, comparing them with reinforced concrete columns with lap-spliced and continuous reinforcement. For that purpose, this study first developed analytical models of the experimental results of the three types of columns, (1) lap-spliced reinforcement, (2) continuous reinforcement and (3) lap-spliced reinforcement and retrofitted by SMA wire jackets, using the OpenSEES program, which is oriented to nonlinear dynamic analysis. Then, a suite of ten recorded ground motions was used to conduct dynamic analyses of the analytical models with scaling of the peak ground acceleration from 0.1g to 1.0g in steps of 0.1g. From the static experimental tests, the column retrofitted with SMA wire jackets had a larger displacement ductility by a factor of 2.3 times that of the lap-spliced column, which was 6% larger compared with the ductility of the continuous reinforcement column. From the fragility analyses, the SMA wire jacketed column had median values of 0.162g and 0.567g for yield and collapse, respectively. For the yield damage state, the SMA wire jacketed column had a median value similar to the continuous reinforcement column. However, for the complete damage state, the SMA wire jacketed column showed a 1.33 times larger median value than the continuously reinforcement column.

Effect of steel wrapping jackets on the bond strength of concrete and the lateral performance of circular RC columns

In this study, the bond behavior between steel reinforcing bars and concrete confined via steel wrapping jackets is estimated. Lateral bending tests are conducted for the reinforced concrete columns with continuous longitudinal reinforcement or lap-spliced longitudinal bars confined by the steel wrapping jackets. It is found that the jackets increase the bond strength and ductile behavior due to the transfer of splitting bonding failure to pull-out bonding failure. In the column tests, the steel wrapping jackets increase the flexural strength and ultimate drift for the lap-spliced column. However, the jacket for the column with continuous longitudinal reinforcement only increases the ultimate drift since the flexural strength depends on the yield of reinforcement. Finally, this study suggests a basic concept for determination of the thickness of the steel wrapping jackets which is different from the conventional method.

Seismic protection of lap-spliced RC columns using SMA wire jackets

This study used two forms of shape memory alloy (SMA) wires, nickel–titanium–niobium (NiTiNb) and nickle–titatanium (NiTi), to retrofit reinforced concrete (RC) columns with lap splices. NiTiNb shape memory alloys are considered to show a wider temperature window compared with NiTi shape memory alloys and thus may be beneficial for applications in the area of civil structures. The goals of this study are to assess the mechanical behaviour of the two shape memory alloy wires and investigate the seismic performance of the shape memory alloy wire jackets for reinforced concrete columns with lap splices. First, the study investigates the recovery and the residual stress of NiTiNb and NiTi shape memory alloy wires. This study also evaluates the behaviour of the NiTiNb shape memory alloy wire under residual stresses. The results indicate that the shape memory alloy wire jackets show good performance for reinforced concrete columns with lap splices. The shape memory alloy wire jackets increase the ductile behaviour of the lap-spliced columns without strength degradation. The results show that their performance is superior to that of the RC column with continuous reinforcements. The study shows that the NiTiNb shape memory alloy wire jackets are more adaptive for retrofit of RC columns than the NiTi shape memory alloy wire jackets since the NiTiNb shape memory alloy shows more appropriate temperature windows for the applications of shape memory alloys in civil structures.

Seismic performance of lap-spliced columns with glass FRP

The present paper represents experimental studies on the seismic performance of reinforced concrete circular columns with lap-splice details using glass fibre reinforced polymer (FRP) wrapping. Five full-scale model columns of 1200 mm diameter and 6550 mm height were classified into one column with no lap-splice, one column with lap-splice and three glass FRP retrofitted columns with lap-splice; those models were conducted by quasi-static cyclic loading test. The prototype structure is an existing circular reinforced concrete bridge pier designed by the following pre-seismic codes and constructed in South Korea in 1979. The lap-spliced column was expected to have a brittle failure owing to the bond-slip of lap-spliced longitudinal reinforcement. The retrofitted columns using glass FRP wrapping showed a significant improvement of seismic performance and developed the stable hysteretic loops. However, from the strain gauge readings, the unyieldingness of lap-spliced longitudinal bars was observed regardless of glass FRP thickness. It is concluded that the displacement ductility factor cannot be defined owing to the unyieldingness of longitudinal bar and the estimated displacement ductility factor should be introduced in order to evaluate the performance of the columns with lap-spliced longitudinal bars. Glass FRP retrofit design methods suggested by other researchers were verified in the experiment and a new modified design method was proposed.

Seismic retrofitting of R/C columns having plain rebars using CFRP sheets for improved strength and ductility

This experimental work focuses on the retrofitting of reinforced concrete columns using carbon fiber reinforced polymer (CFRP) sheets to improve their strength and ductility capacities. Plain rebars, inadequate splicing lengths and insufficient stirrup spacing were the main parameters to reflect the old construction practice. The effectiveness of CFRP strengthening technique was studied. The test results showed that retrofitting with CFRP sheets was effective for columns with continuous rebars. However, only a slight improvement in performance was obtained for the retrofitted lap-spliced column. When the column was retrofitted by welding of dowel rebars with longitudinal rebars near splicing region and then wrapped with CFRP sheets, its strength, ductility and energy dissipation capacity improved significantly.

Cyclic behavior of HPFRC-repaired reinforced concrete interior beam-column joints

A large number of old buildings have been identified as having potentially critical detailing to resist earthquakes. The main reinforcement of lap-spliced columns just above the joint region, discontinuous bottom beam reinforcement, and little or no joint transverse reinforcement are the most critical details of interior beam column joints in such buildings. Five 1/3-scale interior beam column joints representing these critical reinforcement details under seismic loads were constructed and tested under cyclic lateral loading simulating seismic excitation. These specimens behaved weakly such that they attained low load carrying capacity, small energy dissipation, and failed in diagonal shear in the joint region. After testing, the specimens were repaired using high performance fiber reinforced concrete (HPFRC) jacket, all around the joint column regions, and retested up to failure. Higher load levels were attained, more ductile behavior was achieved, substantial energy dissipation was observed, slower stiffness degradation was also noted. Failure modes were transformed from brittle shear in the joint diagonals to a ductile one in the beam region through plastic hinge formation in the beam maximum moment sections. Based on the findings of this study, the strengthening technique used promises to provide a cost effective, long-term repair and retrofit solution that can be implemented in the field.