Precast Segmental Concrete Columns Research Articles

Cyclic behavior of unbonded post-tensioned precast segmental concrete columns fabricated by 3D printed concrete permanent formwork

A 3D printed concrete permanent formwork of composite unbonded post-tensioned precast segmental concrete (3DPCPSC) column is proposed in this research. Its hysteresis performance and the failure mode are researched by quasi-static experiment and compared with the precast segmental reinforced concrete (PSRC) columns. Two interface enhancement methods, stainless-steel-nails internal shear bonds and prestressed steel-hoops external active confinement are proposed, and the enhancement effect and mechanism of 3DPCPSC columns with two interface enhancement methods are studied. Furthermore, the pouring and vibration load of 3D printing concrete formwork is analyzed using a three-dimensional solid finite element model finite element model. The results indicate that the energy dissipation capacity of 3DPCPSC columns is better than that of the PSRC column when the 3DPC formwork does not spall. The largest accumulated energy dissipation of the 3DPCPSC specimen is 1.14 times of the PSRC column. The 3DPCPSC column without interface enhancement has the phenomenon of formwork spalling, the bearing capacity is lower than the PSRC column, and the bearing capacity of the 3DPCPSC columns with two interface enhancement methods is close to or higher than the PSRC column. The initial stiffness of all the 3DPCPSC specimens is larger than the PSRC column. A comprehensive evaluation factor η is proposed to evaluate the hysteretic performance of precast segmental concrete columns. The comprehensive performance of the 3DPCPSC and PSRC is compared by the comprehensive evaluation factor η.

Numerical evaluation of the impact performance of precast concrete segmental columns and strengthening techniques

This paper numerically examines the influence of impact locations and the effectiveness of two strengthening techniques, i.e. energy dissipating (ED) bars and carbon fiber reinforced plastic (CFRP) wrapping at joints, on improving the performance of precast concrete segmental columns (PCSC) under lateral impacts. Mild steel and shape memory alloy (SMA) are used as ED bars. The numerical models are validated by test results available in literature. Different impact velocities and impact locations are considered in the parametric analysis. The impact performance of PCSC with different strengthening techniques is evaluated in terms of the effective plastic strain, deformation, and energy absorption. SMA ED bars are found more effective to reduce the residual displacement due to its super-elastic characteristic while the mild steel ED bars have better energy absorption ability. The response of PCSC is impact location dependent. When joint is impacted, segmental rotation is more pronounced, adding ED bars and CFRP wrapping at joints might not be effective to improve the column performance due to severe shear deformation of the segments. When a segment is impacted, the translational slippage of the segment is the primary response mode, the considered strengthening approaches can effectively reduce the slippage between adjacent segments of PCSC. Moreover, it is found that the deformation response of PCSC can be reduced by increasing the prestress force level, especially when CFRP wrapping is applied at segment joints. CFRP wrapping at joints is found outperforming ED bars on improving the impact resistance of PCSC.

Experimental testing of hybrid sliding‐rocking bridge columns under torsional and biaxial lateral loading

AbstractHybrid sliding‐rocking (HSR) bridge columns are precast concrete segmental columns with unbonded posttensioning, end rocking joints, and intermediate sliding joints. Having been developed for construction in seismic regions, HSR columns offer self‐centering, energy dissipation, and low damageability. Recent advances in the computational modeling of HSR columns have resulted in the proposal of a number of refinements to their original design, leading to the introduction of Second‐Generation HSR columns. Compared to First‐Generation HSR columns, Second‐Generation HSR columns use a reduced number of sliding joints made of high‐performance polytetrafluoroethylene (PTFE) materials to provide desirable levels of sliding and frictional energy dissipation. The seismic performance of Second‐Generation HSR columns was recently investigated through an extensive experimental study. The present paper discusses the major results of the tests performed on two half‐scale HSR column specimens under combined lateral‐torsional loading and biaxial lateral loading to demonstrate their performance under such loading scenarios. A variety of loading protocols were used to test each column specimen, including both cyclic and arbitrary paths. Both columns sustained minimal damage under displacement demands representing 975‐ and 2475‐year seismic hazards, meeting their design objectives. Because of the torsional sliding at sliding joints, the column subjected to lateral‐torsional loading did not exhibit any distinct torsional damage. The biaxial lateral loading was, however, found more damaging to HSR columns than torsional and uniaxial lateral loading.

Experimental study on seismic performance of precast segmental concrete columns after seawater freeze-thaw cycles

To accelerate construction speed, precast segmental concrete bridge columns are widely used in offshore bridge construction. Due to the cyclic action of the tide and the difference of temperature between seawater and atmosphere, offshore piers inevitably experience seawater freeze–thaw cycles in cold climates. The purpose of this paper is to study the seismic performance of precast segmental concrete columns after seawater freeze–thaw cycles through experimentation. Based on the low cyclic loading test on 12 specimens with different freeze–thaw cycles, stirrup spacing values, axial compression ratios, and longitudinal reinforcement diameters, the seismic performance of precast segmental concrete columns was evaluated through analyzing cracking and failure patterns, hysteresis characteristics, skeleton curves, stiffness degeneration, and energy dissipation capacity. The experimental results reveal that, for the specimens with the same design parameters, increasing the number of freeze–thaw cycles from 0 to 125 gradually reduces the peak value of the lateral load, the initial stiffness, and the cumulative energy dissipation but continuously increases the peak displacement. Moreover, for the specimens experiencing 125 freeze–thaw cycles, longitudinal reinforcement diameter, axial compression ratio, and stirrup spacing are the main factors affecting the seismic performance of precast segmental concrete columns.

Effect of Major Design Parameters on the Seismic Performance of Bridges with Hybrid Sliding–Rocking Columns

This paper explores the effects of major design variables on the seismic performance of the so-called hybrid sliding–rocking (HSR) bridge columns. The HSR bridge columns are precast concrete segmental columns with internal unbonded posttensioning, end rocking joints and intermediate sliding joints, which offer significant self-centering and energy dissipation capabilities. HSR columns introduce additional design variables, the effects of which on the seismic response of such columns have remained unclear. Using a recently developed robust computational modeling approach, this study identifies four major design variables, investigates their effects on the dynamic response of HSR columns, and proposes component-level design recommendations. The four design variables include the number of the sliding joints and their distribution over the column height, the incipient sliding base shear, the incipient bearing sliding amplitude, and the peak achievable sliding capacity. This study further investigates the effect of the vertical component of the earthquake excitation on the response of HSR columns and compares the seismic performance of an HSR column with that of a rocking-only column of the same strength. The findings indicate that HSR columns can be more damage resistant than rocking-only columns under earthquake excitations. The response of HSR columns was found to be insensitive to the vertical component of the earthquake excitation.

Stress Wave Propagation and Structural Response of Precast Concrete Segmental Columns under Simulated Blast Loads

Although a number of precast concrete segmental columns (PCSC) have been built and developed in recent years owing to their various advantages, the dynamic responses of the column under blast loads are not well investigated. The characteristics of stress wave propagation within the column and their effects on the response and failure of the PCSC are still unknown. Understanding blast load induced stress wave propagation and the subsequent dynamic structural responses of PCSC is essential for blast resistant design and protection of PCSC. In this study the dynamic behaviours of the PCSC under blast loads are numerically investigated by using the explicit finite element software LS-DYNA. The numerical models and modelling techniques are carefully validated by three experimental blast tests from three different studies. The stress wave propagation within the cross-section and along the column height caused by blast loads is examined. The effect of steel tubes in protecting the PCSC from the blast loads is also investigated. It is found that the deformation of the column section under blast loads consists of two main phases, i.e. compression phase and expansion phase, in which failure of the concrete segment mostly occurs in the latter phase. Besides, the use of steel tubes has a marginal influence during the compression phase on the concrete section, but it becomes crucial in the expansion phase that the local failure of concrete segment, i.e. spalling and scabbing, is prevented by the confining effect. Furthermore, confining all concrete segments by steel tubes shifts the response of the PCSC from the local failure of the concrete segment to the global flexural response with fracture of the post-tensioned tendon. The influence of the blast location on the response of the column is also investigated in this study.

Effects of steel confinement and shear keys on the impact responses of precast concrete segmental columns

The impact responses of three precast concrete segmental columns (PCSCs), i.e. a conventional PCSC, a PCSC with the two bottommost segments confined by steel tubes, and a PCSC with all the segments confined by steel tubes (PCSC-FST), are numerically investigated and compared in this study. The behaviours of the columns subjected to various impact loads at two different impact locations, i.e. at the top and at the centre of the first segment, are considered. It is found that the use of steel confinement does not only enhance the impact resistant capacity of the PCSC but also significantly change the impact behaviours of the PCSC. While the local failure of concrete at the impacted segment governs the response of the conventional PCSC, the failure of Column PCSC-FST is associated with the fracture of the prestress tendon. The confinement with steel tubes of the two bottommost segments shifts the failure mode of the PCSC from local to global failure. Steel shear keys (SSKs) are also integrated into the PCSC-FST to increase the column shear capacity. The numerical results show that the SSKs significantly reduce the lateral displacement and shear force in the tendon when the column response is dominated by shear slippages between segments.

Cyclic test and numerical study of precast segmental concrete columns with BFRP and TEED

Previous studies on the seismic behaviour of precast segmental concrete column revealed that concrete crushing and spalling damages may occur at the toes of the segments due to rocking between segments at the joints. In addition, the energy dissipation capacity of segmental column is smaller than the conventional monolithic column. Energy dissipation bars therefore have been proposed to increase its energy dissipation capability, which, unfortunately, at the cost of also increasing the residual displacement of the column, hence degrades the most advantageous characteristic of precast segmental column. To solve these problems, this paper proposes wrapping the segments with basalt fibre-reinforced polymer (BFRP) to reduce the concrete compressive damage and tension-only external energy dissipation (TEED) devices to dissipate energy without substantially increasing the residual displacement. Experimental cyclic tests and numerical simulations are carried out to examine the effectiveness of the proposed method. The results show that the damage of the segments could be effectively reduced by using BFRP, and the columns show good ductility and almost no strength degradation. The TEED devices are effective to increase the energy dissipation capacity of the column without significantly increasing the residual displacement.

The response of precast concrete segmental columns subjected to near base impact

Precast concrete segmental column has attracted many attentions for the past decades due to its unique features especially in improving the construction quality and efficiency. However, the performance of precast segmental column under lateral impact loading has been less studied. Our previous studies performed laboratory pendulum impact tests on scaled segmental columns to investigate their behaviours when impacted at mid-span of the column. This article studies the response of segmental column when impacted near the column base, which generates different response modes and failure mechanisms compared to the columns subjected to the mid-span impact. Lateral impacts are applied either to segmental joint between the two bottom segments or directly onto the centre of the base concrete segment. A detailed three-dimensional numerical model is created and validated with laboratory impact testing results on scaled segmental columns. A full-scale 3-m tall segmental column is then numerically built to study the behaviour under near base impact. The column damage and failure modes are analysed. The influences of prestress level in the post-tensioning tendon and concrete strength on the performance of segmental column subjected to near base impacts are investigated through numerical simulations.

Multi-hazard resistance capacity of precast segmental columns under impact and cyclic loading

Using precast segmental concrete columns in structures improves the construction efficiency and site safety, leads to better construction quality, and reduces the construction cost, site disruption and environmental impact. The performance of segmental columns to resist earthquake and impact loads is not well studied yet. As a structure might be subjected to such loads during its service life, understanding its resistance capacities is essential for structural safety. This article reports the findings of our recent studies on the response of precast segmental columns with unbonded prestress tendons. Pendulum impact test and uniaxial cyclic test were conducted on quarter-scale segmental columns. The seismic performance and impact-resistant capacity were evaluated experimentally and compared with a reference conventional monolithic column. Test results showed that under cyclic loading, segmental columns exhibited better deformation ability and smaller residual drift; under impact loading, segmental columns also showed better self-centring capacity and less residual displacement. By introducing concrete shear key, the shear resistance at segmental joint could be improved; however, shear key would also result in more concrete segment damage owing to stress concentration.

Numerical investigation of the behavior of precast concrete segmental columns subjected to vehicle collision

This study numerically investigates the response of precast concrete segmental columns with unbonded prestress tendons subjected to vehicle collision. Numerical models are developed using LS-DYNA and validated against experimental tests. The validated model is then used to perform intensive numerical simulations to analyze the effectiveness of prestressing level, number of segments, concrete strength, and vehicle velocity on the behavior of precast segmental concrete columns. The numerical results have shown that the effect of the initial prestressing level and the number of segments are marginal on the impact force time history but significant on the residual displacement and the damage of the column. Better self-centering capacity as well as smaller lateral displacement can be achieved on segmental columns by reducing the number of column segments and increasing the prestress level. In addition, the height-to-depth ratio of a concrete segment should be smaller than two in order to minimize an undesirable local damage at the rear side opposite the impact point. Varying concrete strength from 20 MPa to 80 MPa shows an unnoticeable change of the impact force but its effects on mitigating the damage of the columns are considerable. Last but not least, increasing the impact velocity does not always increase the peak impact force of a segmental column. It is recommended that both the peak impact force and impulse should be taken into consideration in the analysis and design of segmental columns against vehicle impact.

Numerical study on the seismic performance of precast segmental concrete columns under cyclic loading

To accelerate construction speed, precast segmental column is becoming more and more popular in recent years due to its obvious advantages in saving construction time, reducing site disruption and controlling construction quality. However, the applications are still limited primarily in low seismic areas because its performance under earthquake loading is not well known yet. Many experimental studies have been carried out to investigate the seismic performance of segmental columns under cyclic loading. Due to the complexity in modelling such structures, numerical study of precast segmental columns subjected to seismic loads is limited. In this paper, three dimensional (3D) finite element (FE) models for two precast segmental columns are developed to predict the responses of such columns under lateral cyclic loading. The numerical models are first validated against the cyclic test results and then used to perform parametric studies. The influences of five parameters including bonding condition of the tendon, total initial axial forces level, confinement of the segments, number of segments, and energy dissipation (ED) bars on the performance of segmental columns are systematically investigated. Moreover, columns with shape memory alloy (SMA) bars are also investigated to increase the energy dissipation capacity and reduce the residual drift of the segmental columns. It is found that both mild steel and SMA bars can increase the energy absorption capacity of the column, but the SMA bars can minimize the residual drift due to its innate mechanical property. This study clearly identifies the influences of different factors on the performance of segmental columns. The developed numerical model can be used in the future studies to predict the seismic responses of structures with segmental columns.

Experimental investigation of the response of precast segmental columns subjected to impact loading

Although precast concrete segmental columns have been more and more widely used in constructions, there is a lack of study on its behaviour under dynamic loading especially impact loading. In this paper, the fundamental behaviour of precast segmental columns under impact loading is investigated through laboratory tests. Scaled precast segmental columns with unbonded posttensioning tendon were constructed and tested using pendulum impact system. Two segmental columns of the same height, but with different numbers of precast segments were designed and tested. A conventional monolithic reinforced concrete (RC) column was also casted and tested as a reference column to compare the performance with segmental columns under impact loading. The impact load time history and column displacement time histories at column top, mid-height and column base were recorded. The deformation-to-failure processes of the columns were monitored by a high-speed camera, and used to investigate the response of different columns under impact loads. The test results showed the segmental column is more flexible than monolithic column, which leads to lower peak impact force, but longer duration compared to those on the monolithic RC column. It was also found that compared with monolithic columns, segmental columns show better performance against impact load with better self-centring capability, similar energy dissipation capability and less residual displacement and concrete damage.

Experimental Study of Precast Bridge Columns with Built-In Elastomer

Two one-third-scale precast concrete segmental column models with energy-dissipating plastic hinges were designed and tested on a shake table at the University of Nevada, Reno. Conventional reinforced concrete was used in the plastic hinge of one column (SC-2). In the other model, a built-in elastomeric pad integrated with the footing and a concrete segment constituted the plastic hinge (SBR-1). The purpose of using the pad was to minimize damage while dissipating energy through yielding of the longitudinal bars and deformation of the pad. Both columns were subjected to the same ground motion as was recorded at the Sylmar station during the 1994 Northridge, California, earthquake with increasing amplitudes until failure. Compared with conventional precast concrete segmental columns, both SC-2 and SBR-1 showed superior performance, such as minimal residual displacement and larger energy dissipation. SBR-1 with the elastomeric bearing pad dissipated more energy and was free from damage in the plastic hinge zone.

Seismic tests on precast segmental concrete columns with unbonded tendons

Four unbonded post-tensioned precast segmental concrete columns were subjected to pseudostatic simulated lateral seismic loading in the Charles Lee Powell Structural Research Laboratories at the University of California at San Diego. The influence of parameters including steel jacket confinement, prestress level, and column aspect ratio on column force – deformation characteristics, energy dissipation, damage level, and failure mode was studied. To investigate prestress influence and damage repairability, each column was tested twice: the first test with a given prestress level and a second test, subsequent to column repair, with higher initial prestressing. Shear keys were not provided at segment interfaces, and thus shear was transferred by a friction mechanism. Ductile flexural response was observed in all tests, and maximum column drift levels of 4 – 6% were achieved. Damage included minor concrete crushing at the interface of column and footing, steel jacket inelastic straining, and residual drift on...