Pretensioned Spun High Strength Concrete Research Articles

Comparative Investigation of Axial Bearing Performance and Mechanism of Continuous Flight Auger Pile in Weathered Granitic Soils

Axial bearing performance and mechanism of continuous flight auger (CFA) pile in weathered granitic soils, i.e., a widespread special soil in South China, were investigated by field test in this study. Load–settlement responses of four CFA piles were examined, and evolutions of shaft/base resistances were captured by ultra-weak fiber Bragg gratings (UWFBG) with a reflectivity ≤−40 dB. Performances of CFA piles were compared with those of a slurry displacement (SD) pile at the same site, thirteen pretensioned spun high-strength concrete (PHC) piles in the literature and empirical data in design code. Test results show that the ultimate bearing capacity of the CFA pile is highest among different pile types, and typically is twice that of the SD pile. Again, CFA pile produces the highest shaft resistances at 140 kPa and 153 kPa in two weathered granitic soils, while the base resistance of 3080 kPa is between those of the SD pile and the PHC pile. By field excavation, the superior mechanism of the CFA pile is suggested to avoid the formation of in-between bentonite layers and prevent preferential baseflow along fissures, both of which can weaken the soil–pile interface. Overall, this study provides fundamental data through UWFBG and explanations based on field observations which underpin the need for developing a design code specified for CFA piles in South China.

The Embodied Life Cycle Global Warming Potential of Off-Site Prefabricated Concrete Products: Precast Concrete and Concrete Pile Production in Korea

The impacts of concrete on global warming through its use in structures such as buildings and infrastructure must be identified and better understood, as concrete is known to have a very high global warming potential (GWP). However, in contrast with ordinary on-site constructed reinforced concrete, GWPs of off-site factory-made prefabricated concrete products such as precast concrete (PC) and concrete piles that are widely used in construction are rarely evaluated, owing to the complicated manufacturing processes that make the determination of greenhouse gas emission difficult. In this study, the embodied life cycle GWPs were derived for PC and pretensioned spun high-strength concrete (PHC) piles to enable precise assessment of the global warming impact of concrete structures and the concrete industry of Korea. The determined embodied GWPs of PC and PHC piles were 1.77 × 10−1 kg CO2 eq/kg and 1.87 × 10−1 kg CO2 eq/kg, respectively. As a result, both prefabricated concrete products were determined to have high GWP due to input materials, such as cement rebars, while the GWP contributions of the off-site prefabrication processes were low. Moreover, the embodied GWPs of both prefabricated concrete products were significantly higher than those of ordinary reinforced concrete, and the impact of both products on global warming was found to be approximately 4% of the impact of the Korean concrete industry. This indicates that it is necessary to consider the impacts of the PHC pile and PC industries when assessing the impacts of greenhouse gas occurring in the concrete industry at the national level. It is expected that these findings will be widely used to obtain a more accurate assessment of the impact of concrete structures and industry on global warming.

Full-scale experimental study of the seismic performance of pretensioned spun high-strength concrete piles

Pretensioned spun high-strength concrete (PHC) piles have been widely used in the pile foundations of buildings in soft soil areas due to their high axial bearing capacity and good economic benefit. However, the behavior of PHC piles under lateral loading is generally poor and this restricts their application in high-intensity seismic regions, especially for high-rise buildings. The existing research on the performance of PHC piles under cyclic lateral loading and with the presence of axial force is scarce. In this paper, the seismic performance of PHC piles is systematically evaluated through full-scale tests and numerical simulations. Lateral cyclic loading tests for two full-scale PHC pile specimens were conducted under different axial force ratios, and their performances were examined in terms of cracking pattern, failure mode, hysteretic characteristics, lateral bearing capacity, ductility, stiffness degradation and energy dissipation capacity. A dedicated finite element (FE) model was then developed using the software DIANA to compute the cyclic behavior of PHC piles, and the model was verified against the experimental results. Using the verified FE model, parametric analyses have been carried out to study the effects of axial force ratio, prestressing level of prestressing tendons, longitudinal reinforcement ratio, concrete wall thickness of the pile body and distributed pattern of prestressing tendons on the seismic performance of the PHC piles. The results show that the axial force ratio has a significant effect on the cyclic behavior and failure mode of PHC piles; an increase in the axial force ratio leads to an increase in the lateral bearing capacity but generally a decrease in the deformation capacity. The failure mode of the PHC piles is controlled by the rupture of prestressing tendons under lower axial force ratios (less than 0.15) but crushing of concrete under higher axial force ratios (greater than 0.15). Increasing the concrete wall thickness tends to improve the overall performance of the PHC piles, especially under higher axial force ratios.

Damage – Permeability analysis of pretensioned spun high strength concrete pipe piles based on stochastic damage model

In off-shore zones, the pretensioned spun high strength concrete (PHC) pipe piles are widely applied for its ability to provide high permeability resistance. However, one of the most applied pile-driving method of the PHC pipe piles is the hammer pile-driving method, and the piles are usually damaged due to the cyclical impact from the hammer. The damage in concrete will remarkably increase the permeability of the material, which will cause an early durability failure in the piles. By this means, a model that comprehensively relates the damage and permeability is firstly proposed under the framework of stochastic damage model in this study. By comparison to the experimental results, the proposed model is verified for its accuracy. And based on the proposed model, the engineering problem of damage - permeability performance of the PHC pipe piles of a construction site in Guangdong province is evaluated.

Flexural performance of pretensioned spun concrete piles reinforced with steel strands

The application of pretensioned spun high-strength concrete (PHC) piles in high-intensity seismic areas has been limited by insufficient horizontal load resistance and poor deformation capacity. A new type of pretensioned spun concrete pile with high-strength and high-elongation steel strands instead of steel bars has been developed. This paper presents a flexural performance evaluation of the new centrifugal spun concrete pile with steel strands (hereafter referred to as a PSC pile). An experimental study is presented first, including bending tests on six full-scale pile test specimens with three different pile diameters. The flexural performances of PHC and PSC piles are comparatively assessed. The results show that the new PSC piles have similar crack resistance, but higher ultimate bearing capacity and better deformation capacity under a flexural condition. Compared with PHC piles, which exhibit a brittle bending failure, PSC piles demonstrate a ductile bending failure. Following the experimental study, a theoretical model is developed to evaluate the flexural strength of the piles, and a simplified calculation equation for ultimate bending moment is proposed. Finally, a finite-element model is established to simulate the flexural performance of the piles; the modelling results are found to be in good agreement with the experimental results.

Experimental shear test of deep PHC piles reinforced by infilled concrete and shear rings

This paper presents experimental shear tests of pretensioned spun high-strength concrete (PHC) piles reinforced by infilled concrete and shear rings with shear span-to-depth ratio of less than 2.0. Seven specimens are designed and fabricated, where the longitudinal reinforcement ratio and presence of shear rings and sludge are set as key variables. The load–deflection responses and crack patterns of the specimens, strain behavior of shear rings, and composite action between the PHC pile and infilled concrete are measured and analyzed comprehensively. Based on the experimental results, this study examined whether the current design codes, which are section-based models, are appropriate for designing PHC piles with infilled concrete. In addition, a strut and tie model is proposed to estimate the shear strengths of PHC piles with circular cross-sections and different material properties. The analysis results show that the code equations can be used for the shear design of deep PHC piles reinforced by infilled concrete and shear rings in a conservative manner, and that the proposed strut and tie model considering different material characteristics of the PHC piles and infilled concrete provides good evaluation results.

Flexural performance of pretensioned centrifugal spun concrete piles with combined steel strands and reinforcing bars

Pretensioned spun high-strength concrete (PHC) piles have been widely used in building foundations in many parts of the world. However, PHC piles are also known to have poor lateral deformation and ductility capacity and hence are not suitable for seismic regions. To improve the horizontal load bearing and deformation capacities, pretensioned centrifugal spun concrete piles with steel strands alone (hereafter referred to as PSC piles) or a combination of steel strands and mild steel deformed rebars (referred to as PSRC piles) have been developed. PSRC piles are expected to benefit on the one hand from steel strands with high deformation capacity, and on the other hand from deformed steel bars with good bond with concrete and hence better control of cracks. This paper presents a comprehensive study on the comparative flexural performance of PSC and PSRC piles. The bending tests of PSC piles and PSRC piles were firstly conducted on six full-scale pile specimens with three different pile diameters, respectively. The flexural performances are evaluated in terms of crack resistance, flexural and deformation capacities, as well as crack distribution. The results show that the cracking bending moment of PSRC piles is similar to that of PSC piles, but the ultimate bending moment is about 55% higher due to the addition of deformed rebars. The general cracking behavior of PSRC piles exhibit remarkable improvement comparing to PSC piles, with an extended crack region, denser distribution of cracks, and much reduced maximum crack width. Following the experimental study, a theoretical method is proposed for the calculation of the flexural strength and flexural stiffness of prestressed concrete piles considering the presence of both steel strands and deformed rebars. Furthermore, a finite element (FE) model has been developed to simulate the flexural performance of the piles. The accuracy of the FE model is validated through comparing with the experimental results, and subsequently parametric analyses are conducted to explore the influences of three parameters, including the prestressing level of the prestressing strands, prestressing strand ratio and deformed steel bar ratio, on the flexural performance of PSRC piles.

Compressive Strength Testing of Hybrid Concrete-Filled Fiber-Reinforced Plastic Tubes Confined by Filament Winding

In this study, an experiment on compressive strength of the hybrid concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) confined by filament winding was conducted to improve the longitudinal strength while considering the thickness of filament winding as a variable. A maximum error of 17% was observed when the results of performing the finite element analysis (FEA) by applying the mechanical properties of the fiber-reinforced polymer (FRP) materials suggested in previous studies were compared to those of the compressive strength experiment on the hybrid-CFFT. Moreover, a maximum error of 15% was exhibited when the results derived from the strength equation proposed by analyzing the compressive strength experiment were compared. Furthermore, the compressive strength of the hybrid-CFFT increased by up to 14% when the longitudinal compressive strength of the pre-tensioned spun high strength concrete (PHC) pile and concrete-filled tube (CFT) were compared.

Final detailed design of an all-in-one attachment-based PHC pile head cutting robot and its structural stability analysis

ABSTRACT Conventional pretensioned spun, high-strength concrete (PHC), pile head cutting process is associated with safety, quality uniformity, and labor productivity problems. However, trend analysis has revealed that no technology has been developed to address these problems as these pertain to specific Korean construction site situations. This study aims to derive the final detailed design for an all-in-one attachment-based PHC pile head cutting robot, and analyzes its structural stability. To this end, the key functions of an all-in-one attachment-based PHC pile head cutting robot have been defined, and the related core element technologies have been analyzed. This has led to the presentation of two detailed design alternatives. Both of these were then subjected to an analytical hierarchal process (AHP) and trade-off analysis that led to the final selection of the diamond wheel saw-based detailed design. In a structural stability analysis of the final detailed design, all tested parts did not surpass the threshold yield strengths of 230 MPa (SS400) and 255 MPa (AL6061 T6). If a prototype is developed based on the final detailed design derived in this study, it is expected to have improved work safety, quality uniformity, and work efficiency characteristics compared with the conventional PHC pile head cutting process.

Pile Foundation Design Through the Increased Bearing Capacity of Extended End Pile

Pretensioned spun high strength concrete (PHC) piles are a commonly used type of pile, while approximately 60% of the pile′s strength is only used in the design bearing capacity. Because of the limited support capacities of PHC piles, applying PHC piles to high-rise buildings or soft ground is inefficient. Extended end (EXT) piles are a new type of pile that can reduce the waste of pile strength and increase the ground bearing capacity. This study investigated the behavior of EXT piles through a field test and it was confirmed that the bearing capacity of the EXT pile is better than the PHC pile. The increased bearing capacity of EXT piles also influenced work duration and project cost.

연약지반에 적용된 변단면 연약지반보강기초의 거동분석

인천 <TEX>${\bigcirc}{\bigcirc}$</TEX>지역의 연약지반에 시공된 변단면 연약지반보강기초(Variable cross-section soft ground reinforced foundation)의 연직압축거동을 분석하였다. 변단면 연약지반보강기초는 원지반과 고화재를 혼합교반하여 형성되는 고형체의 높은 강성과 강도를 이용하여 상부구조물로부터 유발되는 연약하중을 효과적으로 저항하기 위하여 시공된다. 변단면 연약지반보강기초는 군말뚝 형식으로 시공이 되는데, 정확한 연직거동을 알기 위하여 1개소의 기초에 대한 연직재하시험을 수행하였다. 변단면 연약지반보강기초의 거동을 일반적인 깊은 기초의 거동과 비교하기 위하여 유사한 천층지반조건에 시공된 PHC 파일의 재하시험 결과와 비교하여 재하하중에 따른 침하량 및 하중전이 거동특성을 분석하였다. 연직재하시험결과를 비교분석하였다. 변단면 연약지반보강기초는 제한된 범위의 연직하중에 대하여 천층에서도 효율적으로 저항하는 것으로 분석되었다. Compressive axial behavior of the variable cross-section soft ground reinforced foundation is investigated from the field load test results at <TEX>${\bigcirc}{\bigcirc}$</TEX> construction site in Incheon city. Variable cross-section soft ground reinforced foundation is a type of partial-displacement pile formed by mixing bidding material with in situ soils to obtain a rigid and strong variable cross-section column in a relatively soft ground. The foundations are usually constructed as a group; however in this study, only single foundation was installed and tested under compressive axial load on foundation head. For the comparison of the variable cross-section soft ground reinforced foundation axial behavior, behavior of typical Pretensioned spun high strength concrete (PHC) pile constructed on a relatively soft ground near the surface was analyzed. It was concluded that variable cross-section soft ground reinforced foundation efficiently resists against axial load with sufficient stiffness and strength within a considerable range of axial load magnitude.

CPT-based method for toe resistance of driven piles in sand

This study proposes a cone penetration test (CPT)-based toe resistance method for predicting toe resistance of pre-tensioned spun high-strength concrete (PHC) piles driven into sand. In total, 82 CPTs and 190 pile-driving analyser test piles were conducted at a construction site Myoungji site in the Nakdong River deltaic area west of Busan City in South Korea. Based on the toe resistance results obtained from the pile-driving analyser test analysis, the reliability of which was verified by comparison with on-site O-cell tests, a new CPT-based method for predicting the toe resistance of the PHC driven pile is proposed based on a statistical rank index. The new method consists of the geometric average of the CPT cone resistance and the loose soil ratio within the influence zone of 8D above and 4D below the pile toe (where D is pile diameter). The new method is found to provide better toe resistance prediction than previously suggested CPT-based methods.

Field Evaluation of the Vertical Bearing Capacity of a Screw Pretensioned Spun High-Strength Concrete Pile

This study has evaluated the vertical bearing capacity by conducting static load tests for noise-free and vibration-free screw pretensioned spun high-strength concrete (PHC) piles installed using two different methods (end-squirting shoe and pre-boring methods). Vertical bearing capacity differences seem to occur due to the displacement of soils near the external circumference of a pile, depending on the installation method. A method by which to evaluate the bearing capacity of screw concrete piles is suggested by considering the equations that already have been used to calculate the bearing capacity of piles. Based on static load tests and analysis, the pile installed using the end-squirting shoe method was assumed to be a bored pile and it was reasonable to use the equation proposed by the Japanese Geotechnical Society. At the same time, the pile installed using the pre-boring method was deemed a low soil displacement pile and so it was reasonable to apply the equations proposed for calculating the bearing capacity of the driven pile suggested by the Architectural Institute of Japan.

Applicability of CPT-based methods in predicting toe bearing capacities of driven piles in sand

This paper presents a study on applicability of predicting toe bearing capacities from cone penetration test (CPT) for PHC (pretensioned spun high-strength concrete) driven piles into deep sandy deposits in the Nakdong River deltaic area west of Busan City in South Korea. Using toe bearing capacities obtained from pile driving analyzer (PDA) tests as reference values, which were reliably calibrated by on-site O-cell tests, the applicability of the CPT-based methods was evaluated using a statistical rank index (RI). A total of 82 piezocone penetration test soundings and 190 PDA test piles were used for reliability analysis in this study. Three correction steps were applied to obtain reliable PDA and CPT data sets before ranking is carried out. The RI index is combined from four criteria: (1) the best-fit line, (2) the arithmetic mean and standard deviation, (3) the cumulative probabilities, and (4) the log-normal and histogram distributions. Based on these criteria the performance of some SPT-based methods in the literature is evaluated.

A Comparative Study between Welding and High-Tensile Vertical Bolt Methods in PHC Pile Coupling Work

Few studies have been conducted on the constructability or economic feasibility of the coupling of Pre-tensioned Spun High Strength Concrete (hereinafter PHC pile). For this reason, before applying it to actual construction sites, an analysis of constructability and economic feasibility is necessary. Therefore, this study aims to compare the welding method with the high-tension vertical bolt method. It is found that the use of the high-tension vertical bolt method can reduce expenses by 25 percent on average compared with the welding method.

경골형 교량거더의 비틀림에 의한 말뚝연결부 응력저감기법

조립식지그재그 형태의 단일거더시스템이 적용되는 경골형 교량은 비틀림에 취약한 구조이다. 특히 거더와 PHC(Pretensioned spun High strength Concrete) 말뚝의 고정 연결부는 비틀림 하중에 의한 과도한 응력이 집중되는 취약부이므로 이를 저감시키기 위한 방안이 요구된다. 본 연구에서는 연결부에 발생하는 과도한 응력을 저감시키기 위한 다양한 보강재 형식의 효율성을 수치해석적으로 평가하였다. A fish-bone type bridge is vulnerable to the torsional behavior due to the single girder system with planar zigzag conformation. The fixed connecting area between the girder and pier is the special weak point because the torsional load creates excessive stress concentration. Therefore, the method to reduce the stress concentration is required. In this study, the reduction efficiency of various reinforcing types to reduce the excessive stress occurring at the connecting area is evaluated by using numerical analyses.

Implementation of Noise-Free and Vibration-Free PHC Screw Piles on the Basis of Full-Scale Tests

AbstractNoise and vibration caused by pile driving may disturb surrounding areas to the extent that nearby residents and businesses may file civil complaints, which can bring construction to a halt. To overcome these issues, construction engineers have worked diligently to develop low-noise and low-vibration pile driving methods. One such method, involving noise-free and vibration-free pretensioned spun high-strength concrete (PHC) screw piles, is proposed in this paper. This pile driving method penetrates the ground by rotating and compressing the pile to minimize noise and vibration in addition to maximizing capacity. A noise-free and vibration-free PHC screw pile prototype, the first of its kind, was manufactured and subjected to two pilot tests to determine its production and construction requirements in addition to its performance. In pilot tests, the new noise-free and vibration-free PHC screw pile driving method was found to successfully reduce noise and vibration compared with pile driving involvi...

내부충전 콘크리트와 횡보강 및 축방향 철근으로 보강된 PHC 말뚝의 휨강도

PHC 말뚝은 우수한 축하중 저항 능력에 비해 상대적으로 전단 및 휨 저항 성능이 낮은 단점을 가지고 있다. 이 연구의 목적은 기존 PHC 말뚝의 단점을 개선할 목적으로 개발된 중공부에 내부충전 콘크리트, 축방향 철근과 전단 철근으로 보강한 합성 PHC 말뚝(ICP 말뚝)의 휨성능을 평가하는 것이다. 이를 위하여 기존의 교대 설계사례로 부터 말뚝에 발생하는 축력과 휨모멘트를 조사한 후, ICP 말뚝 계산을 위하여 개발한 축력-휨모멘트 상관관계 프로그램을 이용하여 허용 축력과 휨모멘트가 발생하는 부재력을 만족하도록 ICP 말뚝을 설계하였다. 설계에 따라 ICP 말뚝을 제작하였으며, 휨실험을 수행하였다. 실험 결과 ICP 말뚝은 PHC 말뚝에 비하여 약 45% 큰 휨내력을 나타내었다. 또한 계산에 의해 예측한 ICP 말뚝 휨강도의 25%를 허용 휨모멘트로 취할 경우, 약 4.5의 안전율을 갖는 것으로 평가되었다.

Performance Evaluation of the Pretensioned Spun High Strength Concrete Piles (PHC) Using Recycled Concrete Aggregate

Performance Evaluation of the Pretensioned Spun High Strength Concrete Piles (PHC) Using Recycled Concrete Aggregate

내부충전 콘크리트와 전단철근을 이용한 중공 PHC말뚝의 전단보강 효과

In order to improve the shear strength of conventional pre-tensioned spun high strength concrete (PHC) pile, concrete-infilled composite PHC (ICP) pile, a PHC pile reinforced by means of shear reinforcement and infilled concrete, is proposed. Two types of specimens were cast and tested according to KS (Korean Standards) to verify the shear strength enhancement of ICP pile. Based on the test results, it was found that the KS method was not suitable due to causing shear failure of ICP pile. However, shear strength enhancement was clearly verified. The obtained shear strength of the ICP pile was more than twice that of conventional PHC pile. In addition, the shear strength of ICP pile reinforced with longitudinal reinforcement was estimated to be more than 2.5 times greater than that of conventional PHC pile. The allowable shear force of ICP pile, which was determined by the allowable stress design process, indicated a large safety factor of more than 2.9 compared to the test results.