Segmental Columns Research Articles

Seismic performance of precast CFDST segmental column with hybrid energy dissipation devices

Precast segmental column has various advantages as compared to traditional cast in-situ monolithic column. The major issues of such column are the concrete compressive damages at the toes of the segments and limited energy dissipation due to the rocking mechanism. This study explores a new design of precast segmental column with damage resistant features and hybrid energy absorption system. Super elastic shape memory alloy (SMA), external energy dissipation devices and concrete-filled double-skin steel tubes (CFDST) segments are used to form a seismic resilient precast segmental column. Specifically, the SMA rebars provide the column with good self-centring ability; the external replaceable energy dissipation devices provide extra energy dissipation capacity; the use of CFDST segments mitigates the concrete damage. It is found that the proposed column performs well with small residual displacement, satisfying energy dissipation and minor damage.

Numerical studies on the seismic responses of precast segmental columns-supported bridge structures subjected to near-fault ground motions

Precast segmental columns have attracted wide attentions in bridge construction industry recently due to its ability to accelerate construction speed, improve construction quality and reduce environmental impact. It is of great practical importance to study the seismic performances of segmental columns, and many experimental and numerical studies have been performed. However, most previous studies focused on segmental column itself, the research on the seismic performance of a whole bridge structure supported by precast segmental columns is very limited. In particular, no systematic studies have been performed to investigate the seismic performances of segmental columns-supported bridges subjected to near-fault (N-F) ground motions (GMs). To bridge this research gap, the seismic responses of three bridge structures (i.e. a segmental columns-supported bridge, a bridge supported by segmental columns with internal energy dissipation bars, and a conventional bridge supported by monolithic columns) subjected to four types of earthquake ground motions (i.e. a N-F GM with fling-step (F-S) effect, a N-F GM with forward-directivity (F-D) effect, a non-pulse-like N-F GM, and a typical far-field (F-F) GM are investigated and compared in the present study based on the validated numerical models developed in ABAQUS. The influences of permanent ground displacement in the F-S ground motion and pulse period are also systematically investigated. The numerical results demonstrate that the permanent ground displacement in the N-F ground motions has very different effects on the segmental-columns supported bridge and monolithic columns supported bridge.

Time-Varying System Identification of Precast Segmental Columns Subjected to Seismic Excitations

Precast segmental columns, as one structures, have attracted increasing attention in bridge and building construction. To understand the performance and dynamic characteristics of precast segmental columns subjected to earthquake excitations, this paper develops a novel approach for time-varying system stiffness identification of precast segmental columns under seismic excitations, based on the adaptive unscented Kalman filtering (AUKF) method. In the proposed approach, a precast segmental column model is considered as an equivalent single-degree-of-freedom (SDOF) system with time-varying system parameters. The AUKF method is employed to identify the time-varying stiffness parameters by using measured acceleration responses and then calculate dynamic displacement responses of the SDOF system to verify the accuracy of the identified stiffness parameters. Since the system parameter identification process and measurement noise covariance matrices are updated at each time step, the estimated results can be reliably obtained to evaluate the conditions of segmental columns subjected to seismic excitations. To verify the feasibility and effectiveness of using the proposed approach for time-varying system stiffness identification of segmental columns, numerical studies on a planar precast segmental column subjected to different intensities of ground motion excitations are conducted. Shake table tests on a scaled precast segmental column and a scaled monolithic column subjected to earthquake excitations are conducted in the laboratory to further verify the performance of the proposed approach. Measured acceleration responses are used for time-varying system identification. Both numerical and experimental results demonstrate that the proposed approach can successfully identify the time-varying stiffness values of precast segmental columns subjected to earthquake excitations, and the displacement responses of these columns are predicted accurately as compared with the measured ones.

Seismic behavior of precast segmental column bridges under near-fault forward-directivity ground motions

Seismic behavior of precast segmental column bridges under near-fault forward-directivity ground motions

VIS camera studies of the combustion process of pyrotechnic retarders of NGP-76 underwater fifle grenades

Abstract The study presents the combustion process of the multi-segment, low-gas pyrotechnic column of the warhead retarder of the NGP-76 underwater rifle grenade, designed to combat divers with an underwater shock wave. The combustion process, i.e. process from the ignition of the first segment of the retarder to the completion of combustion of its last segment, was recorded with a VIS camera filming at 30 frames per second. The rapid, short combustion of these outermost segments containing zirconium and Pb3O4 (minium) was accompanied by a blinding plume of brightly glowing particles of zirconium dioxide and lead vapor. The combustion of the middle segments formed from the MGS-54 pyrotechnic mixture containing BaCrO4, KClO4 and Sb2S5, determining the duration of the delay, i.e. the delay produced by the retarder, was much slower and longer than that of the outermost segments. During the combustion of each MGS-54 segment, the combustion front took the form of a flat section in the initial part of the segment, i.e. in the area of higher density, while in the further part of the segment (with lower density) the shape of the front became irregular. At the MGS-54 segment boundary, the combustion front halted briefly. Behind the combustion front, a conical tail of luminous solid combustion products became clearly visible at the MGS-54 segment boundary. The gaseous combustion products of the MGS-54 segments, formed in small amounts and revealed as white plumes, were probably KCl vapor and/or sulfur dioxide. After combustion, the retarder column of the MGS-54 segments was green in color due to the presence of chromium compounds, possibly Ba(CrO2)2.

Shaking table test on a low-damage controlled multiple-rocking-column steel frame

Ancient timber structures represented by the Shaka Pagoda can remain intact after strong seismic actions. Inspired by the rocking and energy dissipation mechanisms of ancient timber structures, a multiple-rocking-column steel frame (MRCSF) system was proposed in this study. The proposed system consists of continuous beams, segmented columns and self-centering friction connections. Friction joints are employed at the beam-column and column base connections to dissipate energy, and the self-centering capacity is mainly provided by the gravity load and additional springs at the connections. A 1/3-scale model of a three-story MRCSF was designed, fabricated and tested on a shaking table at Tongji University. Test results showed that the columns started to rock when subjected to excitations beyond the frequent earthquake level, as expected. The tested frame successfully underwent a series of strong excitations and exhibited excellent low-damage characteristics. Negligible residual drifts and structural damage were measured after the tests. Finally, a feasible design process for the newly proposed MRCSF system was proposed.

Experimental study of durable low-friction concrete contacts for precast segmental columns with resettable sliding joints

Planar sliding joints have been introduced to precast segmental bridge columns to alleviate the detrimental effects of earthquakes. However, residual sliding movements may result from strong shaking. Resettable sliding joints comprising V-shaped or W-shaped interfaces of gentle inclinations have been proposed to achieve better resilience against seismic actions in regions of moderate to high seismicity. However, possible deterioration of the frictional performance at the concrete contact surfaces may affect the resetting performance of these joints. In this regard, the tribological features, performance and durability at the interface of resettable sliding joints in precast segmental bridge columns were investigated experimentally utilizing 3D printed moulds and computed tomography scanning technology. Various surface treatment and lubrication methods were evaluated monthly up to 360 days after casting based on a modified cyclic direct shear apparatus at high loading pressure. Results show that high-performance PTFE grease lubricant is useful in achieving and maintaining favourable coefficients of friction as low as 0.05.

Seismic Performance of Precast Segmental Concrete-Filled Steel-Tube Bridge Columns with Internal and External Energy Dissipaters

Abstract The prefabricated segmental column using posttensioning technology has become an ideal candidate for rapid and environmentally friendly construction. To avoid damage to the segment joint d...

PFAS treatment with granular activated carbon and ion exchange resin: Comparing chain length, empty bed contact time, and cost

Per- and polyfluoroalkyl substances (PFASs) are among the most recalcitrant chemicals ever manufactured and are associated with substantial global environmental challenges. PFAS removal performance of granular activated carbon (GAC) and ion exchange resin (IX) was evaluated and compared using a segmented column system with full scale media under continuous flow conditions. Results from the PFAS breakthrough analysis established via column operation under different empty bed contact times (EBCTs) was used to characterize the mass transfer zone (MTZ) of multiple PFASs and evaluate optimum EBCTs for GAC and IX treatment. The height of the MTZ corresponded to PFAS chain length and functional group, where the poorly removed short chain perfluoro-carboxylic acids exhibited the longest MTZ. Elongated PFAS MTZs justified longer EBCTs required for treatment of short chain PFAAs compared to long chain PFAAs for GAC and IX. In addition, a cost sensitivity analysis was employed to demonstrate how unit media cost, changeout frequency, and treatment goal feasibility dictated annual operation and maintenance (O&M) costs associated with GAC and IX installations. IX was found to the most cost-effective adsorbent for the removal of long and short chain PFASs compared to GAC. Results from the cost analysis indicated that adsorbent selection was the most critical factor dictating treatment cost with marginal impact from unit media cost or expected changeout frequency.

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.

Innovative resilient system of precast segmental RC hollow bridge columns

This study introduces an innovative resilient system for precast segmental reinforced concrete (RC) bridge columns. The proposed system consists of a typical precast hollow core RC segmental column and an energy dissipation (ED) element. The ED element is a precast RC column partially filling the hollow core of the segmental column. As a new damage control component, the ED element (the inner column) is adopted to provide the system with adequate ED capacity. Using commercial finite element (FE) software, a three-dimensional (3D) model of experimentally tested precast segmental columns was developed. After validating the results of the FE model, the model was used to systematically investigate the behavior of the proposed system under lateral cyclic loads. The parameters studied are related to the design details of the inner column with respect to the main column (the precast segmental column): column height ratio, and cross-sectional area ratio. In addition, concrete compressive strength, main reinforcement yield strength, and longitudinal reinforcement ratio were examined. Moreover, under the influence of successive earthquakes, repeated cyclic loading scenarios were applied to the proposed system. The FE results show that, the new system with a well-designed inner column can ensure limited damage, controlled increase in the lateral resistance, acceptable ED capacity and the required resilience after successive earthquakes.

Increased number of activated microglia in rat spinal cord during early stage of diabetic induction.

Diabetic neuropathy is a common chronic complication in diabetes mellitus. Such neuropathy associates with chronic inflammation and immune system activation. Microglia, a type of neuroglia, are involved in the immune system and are found in grey and white matter of the central nervous system, such as the brain and spinal cord. The spinal cord connects the peripheral nervous system and the higher brain centre. Hyperglycaemia during diabetes mellitus has been found to activate and increase number of microglia in the dorsal grey horn or column of the lumbar segments in spinal cord, which release several cytokines in the development of hypersensitivity in diabetic neuropathic pain. Therefore, in this study, anatomical alterations of rat spinal microglia in all areas (dorsal, intermediate and ventral columns of grey matter and dorsal, lateral and ventral funiculi of white matter) in cervical enlargement, thoracic level and lumbosacral enlargement were observed in early stage of diabetic conditions by using light and transmission electron microscopies. The numbers of microglia in all parts of grey and white matter of all spinal levels significantly increased in the diabetic group. The structures and ultrastructures of microglia in grey and white matter at cervical enlargement, thoracic level and lumbosacral enlargement similarly changed in diabetes. In diabetic rats, microglia became hypertrophied with a pale nucleus. Moreover, short fragments of rough endoplasmic reticulum, elevated numbers of lysosomes and numerous actin filaments in the cytoplasm were examined. Microglial phagocytosis of myelin and axonal debris were also observed. In this investigation, the morphology of spinal microglia during short-term diabetes became activated during hyperglycaemia. It is suggested that these changes may be involved in the development of diabetic neuropathic pain in the spinal cord.

Characterization of seminal parameters, sperm morphometry, micromorphology, and ultrastructure in gray brocket deer (Mazama gouazoubira, Fischer, 1814).

Populations of gray brocket deer (Mazama gouazoubira) are declining; yet, knowledge on the reproductive biology of this species remains limited. Therefore, this study aimed to describe morphology, viability, membrane integrity, mitochondrial activity, morphometry, micromorphology, and ultrastructure of the gray brocket deer sperm. Three adult male gray brocket deer were used in the study. Semen collection was performed using electroejaculation. Semen were analyzed by evaluating pH, motilities, vigor, mass movement, volume, concentration, viability, membrane integrity, mitochondrial activity, morphology, and morphometry. Micromorphology and ultrastructure of sperm were analyzed using scanning and transmission electron microscopy (SEM and TEM), respectively. There was no significant difference among males regarding on pH, motilities, vigor, mass movement, volume, concentration, viability. High values for membrane integrity, mitochondrial activity, and normal sperm were observed. The most frequent defects were simple bent tail and bowed midpiece. The head length, and width, midpiece, and tail length were 8.5, 4.4, 11.5, and 41.3 μm, respectively. SEM sperm showed paddle-shaped heads, with apical ridge and serrated band on the equatorial segment. TEM revealed the nucleus, acrosome, plasma membrane, mitochondria sheath, proximal centrioles, segmented columns, axoneme, outer dense fibers, and fibrous sheath. SEM and TEM showed the presence of some abnormalities. These results are expected to provide baseline values of diverse semen parameters, contributing toward the development of reproductive biotechnologies for gray brocket deer and, other deer species at risk of extinction.

Composite Enhancement Polyether-Ether-Ketone for Long Segmental Spinal Column Deformity Orthopedic Treatment

Polyether-ether-ketone (PEEK) anterior intervertebral fusion combined with posterior long segment orthopedic surgery is a common method for the therapy of orthopedic deformity of the spine. PEEK material plays an important role in the effect of surgery. Graphene on copper substrate was transferred to the surface of carbon-fiber reinforced polyether-ether-ketone (CFR-PEEK) material by ferric chloride (FeCl3) chemical erosion and physical adsorption, hence the compound enhancement polyether-ether-ketone (Ge-PEEK) was achieved. In terms of characterization, Raman spectrometer was used to analyze the characteristics of the product generation, the scanning electron microscope (SEM) was used to analyze the morphology of the product, and the hydrophilicity of the material was analyzed by the droplet contact Angle. From the perspective of intervertebral fusion, Ge-PEEK material was used in the intervertebral fusion device to analyze the effect of the fusion device in the correction of spinal deformity, such as displacement, convex Angle, and collapse. In the characterization test, Raman spectrum analysis showed that Ge-PEEK material had the characteristic peaks of graphene, and SEM analysis showed that CFR-PEEK material was covered on a large scale by graphene. In the droplet contact angle test, the contact angle of the graphene-modified CFR-PEEK material was significantly reduced (P < 0.05). The material had good hydrophilicity. In the analysis of lumbar interfusion, the anterior intervertebral fusion rate based on Ge-PEEK material was 95.8% (P < 0.05), and the vertebral deposition rate based on Ge-PEEK fusion device was 7.2% (P < 0.05). At the same time, the distance between the leading edge of the cone after operation and the last follow-up was compared, and it was found that the displacement distance of different segments was smaller (P < 0.05). This study proved that the proposed Ge-PEEK material was feasible for anterior intervertebral fusion in the correction of long-segment spinal deformity.

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.

The blast resistant performance of concrete-filled steel-tube segmental columns

Prefabricated segmental concrete column has seen an increased rate of adoption in the construction industry. Much effort has been paid to investigate the performance of segmental column under seismic and impact loadings. The study of its blast resistant performance is very limited. In the meanwhile, field blast tests and numerical simulations have demonstrated that concrete-filled steel-tube (CFST) columns exhibit outstanding blast resistant capacity. This study aims to investigate the blast performance of segmental column with CFST segments. A detailed 3D model of segmental CFST columns are generated using LS-DYNA. The model is validated with field blast testing data on CFST column and laboratory impact test on segmental column. The blast resistant performance of segmental CFST column is compared with conventional monolithic column and monolithic column with prestress. Parametric study is then conducted to investigate the influences of infill concrete strength, steel skin thickness, pre-stress ratio, and number of segments on the blast resistance of the segmental column. It is found that increasing the steel skin thickness could most effectively improve the blast resistance of a segmental CFST column, while increasing the concrete strength, prestress force, and the number of segments, also improve the capacity of segmental CFST column to resist blast loading.

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.