Precast High-strength Concrete Research Articles

Analytical solution for the horizontal dynamic response of strength composite piles in fractional viscoelastic unsaturated ground

The analytical representation of the dynamic interaction between a strength composite (SC) pile and unsaturated soil under lateral excitations at the pile head is studied using three-dimensional continuum modelling. The fractional standard line solid (FSLS) model is utilized in the governing equation of unsaturated soil to characterize the flow-independent viscosity of the soil skeleton. Timoshenko beam theory is employed to describe the horizontal dynamic behaviour of SC piles composed of cement-soil mixing (CM) piles and precast high-strength concrete (PHC) pipe piles. A closed series form solution of the horizontal dynamic behaviour for an SC pile embedded in unsaturated soil under lateral excitation at the pile head is deduced theoretically. The solutions of the proposed model are compared with those captured from existing solutions. Finally, the effects of physical parameters in the SC pile-unsaturated soil system on the horizontal dynamic behaviour of the SC pile are evaluated with analytical examples and parametric study. The results indicate that the radius and elastic modulus of the SC pile have a critical influence on the horizontal dynamic behaviour of the SC pile, the FSLS model parameters are the key factors influencing the horizontal dynamic behaviour of the SC pile, and the horizontal dynamic behaviour of the SC pile varies with the change in liquid saturation of unsaturated soil. The research results provide theoretical references for the anti-vibration design and safe operation of SC piles.

Prediction of axial load bearing capacity of PHC nodular pile using Bayesian regularization artificial neural network

Pre-stressed precast high strength concrete (PHC) nodular piles with hyper-MEGA construction method are favorably used in medium to high-rise building foundations. In this study, a feed-forward neural network (FFNN) was adopted to investigate the ultimate axial load bearing capacity of the PHC nodular pile. The network receives the composite pile and geotechnical conditions with eight input neurons and outputs the nodular pile's ultimate axial load bearing capacity. Among numerous possible FFNN network architectures, the most accurate one is determined by optimizing the hidden layer. Network training is conducted with Bayesian regularization backpropagation (BRB); the training datasets consist of static pile load test and standard penetration test index of soil profile collected from various projects in Vietnam. The significance of each input parameter is quantified with importance-based sensitivity analysis. An explicit function has been constructed from weights and bias values at each neuron in the FFNN to estimate the axial load bearing capacity. The excellent agreement of all output values by the proposed FFNN with the measured values proved the model’s robustness and reliability. The predictive capacity of the proposed FFNN model has significantly outperformed all current empirical formulas. The outcome of this study can be directly put into engineering practice to furnish an economically optimal design of the composite nodular pile.

Thermal performance analysis and assessment of PCM backfilled precast high-strength concrete energy pile under heating and cooling modes of building

Thermal behavior of the precast high-strength concrete (PHC) energy pile with phase change material backfill (PCMB) has been rarely reported. In this study, a three-dimensional heat transfer model of a PHC energy pile with PCMB was developed to investigate the thermal response of PCMB-PHC energy pile under heating and cooling modes of building. Moreover, the effects of different PCMB properties on heat extraction and injection performances of PCMB-PHC energy pile were comprehensively evaluated using Taguchi-Grey relational analysis (Taguchi-GRA) method. The results indicate that increasing the PCMB thermal conductivity facilitates an enhancement in the heat transfer capacity of PCMB-PHC energy pile, and the total exchanged energy can be improved by 258.8 % (heating mode) and 256.8 % (cooling mode) as the PCMB thermal conductivity increases by 1 W/(m K). Increasing and decreasing the PCMB melting temperature of 4 ℃, the heat transfer capacity of PCMB-PHC energy pile rises by 19.3 % and 14.2 % under heating and cooling modes. In terms of PCMB latent heat, the heat transfer capacity of PCMB-PHC energy pile can be enhanced by 17.7 % (heating mode) and 12.6 % (cooling mode) with a 200 kJ/kg increase in PCMB latent heat. Furthermore, higher melting temperature (heating mode), lower melting temperature (cooling mode), and larger latent heat of PCMB can alleviate the fluctuation amplitude of soil temperature around the PCMB-PHC energy pile. Based on the Taguchi-GRA method, PCMB thermal conductivity (occupies 94.36 % and 93.75 % contribution percentages) is the most significant factor to affect the heat extraction and injection capacities of PCMB-PHC energy pile under heating and cooling modes, followed by PCMB melting temperature and latent heat. The results are useful for the performance optimization of PCMB-PHC energy pile in practical applications.

Analysis of the heat exchange performance of PHC energy pile under cooling condition

To investigate the influence sequence of different factors on the heat exchange performance of precast high-strength concrete （PHC） energy pile， a three-dimensional numerical simulation model of PHC energy pile was established and the effects of various thermal conductivities of grout backfill material， inlet temperatures of heat exchange pipe， thermal conductivities and backfill diameters of PHC pile on the heat exchange performance of PHC energy pile were analyzed. The results show that the heat exchange amount of PHC energy pile increases with the increase of the thermal conductivity of grout backfill material. In the cooling condition， increasing the inlet temperature of heat exchange pipe is beneficial to improving the heat exchange amount of PHC energy pile. Increase of thermal conductivity of PHC pile can enhance the heat exchange behavior of PHC energy pile. Moreover， the heat exchange amount of PHC energy pile gradually increases with increasing backfill diameter of PHC pile. On this basis， the Taguchi method was used to analyze the influence sequence of four different factors on the heat exchange performance of PHC energy pile. The impact of the inlet temperature of heat exchange pipe is the greatest， followed by the thermal conductivity of grout backfill material and backfill diameter of PHC pile， and the impact of thermal conductivity of PHC pile is the least. The results can provide a technical support and guidance for the design and application of the PHC energy piles in practical engineering. <fig fig-type="abstract-image" id="F1" orientation="portrait" position="float"><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="SP.J.1249-2022-39-1-51/A363044C-8B03-42d6-B755-DE9E707AD29F-F001.jpg"/></fig>

Influence of backfilling phase change material on thermal performance of precast high-strength concrete energy pile

The use of phase change materials (PCMs) within the precast high-strength concrete (PHC) energy pile is relatively rare. A study concerning the thermal performance of the PHC energy pile backfilled with PCMs were performed to compare with conventional backfill materials. Field tests of the PHC energy pile were conducted. Then, different types of heat transfer numerical models for the PHC energy pile backfilled with water, ordinary grout, and PCMs were established, and the validities of models were confirmed by the field test data and other published studies. The following results are obtained from this study: (1) the thermal performances of the PHC energy pile backfilled with ordinary grout and PCM-type backfill materials (i.e., PCM, enhanced-PCM, and enhanced-PCM-1) are significantly greater than that backfilled with water under continuous operation; (2) intermittent operation has a larger influence on the heat exchange rate of PCM-type backfilled PHC energy pile than ordinary grout backfill material, and enhanced-PCM and enhanced-PCM-1 backfill materials generate higher heat exchange rates for the PHC energy pile than the ordinary grout under intermittent operation; (3) enhancements in the thermal properties of PCMs and intermittent operation both are important to improve the heat transfer performance of the PHC energy pile backfilled with PCMs, and the lower melting temperature of PCMs helps to enhance the thermal performance of PCM-type backfilled PHC energy pile in the cooling mode; and (4) under higher velocity of groundwater flow, ordinary grout backfill material is more suitable for the PHC energy pile compared with PCM-type backfill materials.

Investigation of the thermal response of PHC energy pile backfilled with phase change material

The influence of phase change material (PCM) backfill material within precast high-strength concrete (PHC) pile on the thermal behavior of the energy pile is rarely studied. This paper develops a numerical model to investigate the thermal response of the PHC energy pile backfilled with PCM. The results show that the higher latent heat and thermal conductivity of PCM backfill material inside the PHC pile can effectively improve the heat transfer capacity of PHC energy pile. Besides, the intermittent operation mode is beneficial to the enhancement in heat transfer behavior of PCM-backfilled PHC energy pile. For PCM and improved PCM backfill material, the heat exchange rates of PHC energy pile at 6:18 intermittent mode rise by 57.11% and 64.06% compared with continuous mode. Finally, because the improved PCM backfill material has higher latent heat and thermal conductivity, the ground temperature around the improved PCM-backfilled PHC energy pile shows a faster growth trend than PCM backfill material. Additionally, the intermittent operation mode produces a slower growth rate of ground temperature around the pile.

Seismic behavior of precast 100 MPa grade HSC frames under reversed cyclic loading

This paper concerns characterizing the seismic behavior of precast high-strength concrete (HSC) frames. A half-scale, two-story, and two-bay precast HSC frame and a corresponding cast-in-place (CIP) frame were designed, constructed, and tested under reversed cyclic loading according to a prescribed history. The precast HSC frame consisted of precast column, composite beam, and CIP beam-column connection. HSC used had a nominal compressive strength of 100 MPa. Results demonstrate that both frames failed by crushing of concrete at the column bases, exhibiting a mixed sidesway failure mechanism. The hysteresis curves of both frames are arch-shaped without an evident pinching effect, and the energy dissipation capacity of two test frames is close. Also, the precast HSC frame and CIP frame show similar load-carrying capacity, with a difference of less than 1%. Global displacement ductility of the precast HSC frame is 3.75, which increases by 20.9% than that of the CIP frame. Moreover, a degenerated four-linear restoring forcing model for CIP and precast 100 MPa grade HSC frames is proposed.

Field Test and Numerical Simulation on the Long-Term Thermal Response of PHC Energy Pile in Layered Foundation.

Investigation on the long-term thermal response of precast high-strength concrete (PHC) energy pile is relatively rare. This paper combines field experiments and numerical simulations to investigate the long-term thermal properties of a PHC energy pile in a layered foundation. The major findings obtained from the experimental and numerical studies are as follows: First, the thermophysical ground properties gradually produce an influence on the long-term temperature variation. For the soil layers with relatively higher thermal conductivity, the ground temperature near to the energy pile presents a slowly increasing trend, and the ground temperature response at a longer distance from the center of the PHC pile appears to be delayed. Second, the short- and long-term thermal performance of the PHC energy pile can be enhanced by increasing the thermal conductivity of backfill soil. When the thermal conductivities of backfill soil in the PHC pile increase from 1 to 4 W/(m K), the heat exchange amounts of energy pile can be enhanced by approximately 30%, 79%, 105%, and 122% at 1 day and 20%, 47%, 59%, and 66% at 90 days compared with the backfill water used in the site. However, the influence of specific heat capacity of the backfill soil in the PHC pile on the short-term or long-term thermal response can be ignored. Furthermore, the variation of the initial ground temperature is also an important factor to affect the short-and-long-term heat transfer capacity and ground temperature variation. Finally, the thermal conductivity of the ground has a significant effect on the long-term thermal response compared with the short-term condition, and the heat exchange rates rise by about 5% and 9% at 1 day and 21% and 37% at 90 days as the thermal conductivities of the ground increase by 0.5 and 1 W/(m K), respectively.

Temperature effects on the in-situ mechanical response of clayey soils around an energy pile evaluated by CPTU

Thermomechanical behaviour of clay has been widely investigated by well-controlled laboratory experiments, while in-situ test of thermal effects on soil is rare. The piezocone penetration test (CPTU) is first used in this study to directly evaluate the temperature effects under in-situ stress condition. A full-scale precast high strength concrete (PHC) pile was utilized as the heat source and a series of CPTU were conducted in adjacent layered clays after monotonic heating and thermal cycle. The results show that unprecedented temperature elevation leads to an apparent reduction of soil strength in all soil layers; this degradation was alleviated after the thermal cycle. After exposure to a higher temperature, the normally consolidated soil was improved even when tested at a lower elevated temperature; whereas, the overconsolidated soil could nearly recovered to the pre-heated value. The measured pore pressure (u2) also decreased after heating indicating a more overconsolidated or dilatant behaviour during shearing. By comprehensively considering the in-situ responses, the in-situ soils were believed to be unloaded by the thermally induced pore fluid pressurization and densified after cyclic thermal loading. Finally, a hypothesis is proposed to qualitatively explain the thermomechanical responses of in-situ soil in the framework of critical state soil mechanics theory.

Shear friction performance between high strength concrete (HSC) and ultra high performance concrete (UHPC) for bridge connection applications

Ultra high performance concrete (UHPC) has been typically used as grout material in the bridge connections or as a repairing material in the bridge deck applications due to outstanding mechanical properties, especially, superior bond strength with precast concrete. However, shear stresses due to mechanical, shrinkage, environmental loads, or any combination, usually develop at the interface between the two materials. Therefore, the interface should have enough capacity for these stresses at both early ages and during the service life. In this study, the interface bond performance between precast high strength concrete (HSC) and cast in place (UHPC) was examined under direct shear using the push-off test. The contribution of the shear reinforcement (SR) to the load transfer, before and after interface failure, was investigated. Results from this study were also compared with the predicted values from codes provisions. The test results indicate that UHPC has superior adhesion to the precast concrete, which exceeded the adhesion value of the monolithic surface specified by the provisions. A bond strength versus displacement model is proposed based on data analysis and could be used in the modeling of HSC-UHPC interface under a shear stress state. The shear reinforcement placed across the interface played a key role in reducing the slip at the interface before interface failure. The shear capacity from standard codes is highly conservative and could be used in the design.

Investigation on the thermal response of full-scale PHC energy pile and ground temperature in multi-layer strata

A thermal response test (TRT) was conducted on a full-scale precast high strength concrete (PHC) pipe pile installed in multi-layered ground, in order to investigate the thermal response of the pile and soils in inhomogeneous ground. The thermal properties of each layer were tested in the laboratory and compared to the estimation from the TRT. The ground temperature evolution was monitored using 4 boreholes around the pile, and the pile temperature distribution was captured from transducers prefabricated in the pile wall. The system thermal conductivity estimated from TRT results was 2.11 W/(m K) which is about 2 times that from the lab test (1.15–1.71 W/(m K)). The comparison with other TRTs suggests that fitting time and heating power may influence the estimated results. The ground temperature response varied along the depth. Comparing the layers, more conductive soil was cooler near the pile but warmer at a distance. Up to 23% difference of temperature increment (1.1 °C) was found. The pile temperature was less influenced by soil stratification but was evidently affected by end effects, which caused a maximum difference of 16% (3.2 °C) from the average temperature increment. The average ground and pile temperature increased by 1.1 °C and 1.5 °C respectively at 37 days after heating. This suggests that an accumulated temperature increase could happen in a cooling-dominated district.

Evaluation of the thermal efficiency and a cost analysis of different types of ground heat exchangers in energy piles

This paper presents an experimental and numerical study of the results of a thermal performance test using precast high-strength concrete (PHC) energy piles with W and coil-type ground heat exchangers (GHEs). In-situ thermal performance tests (TPTs) were conducted for four days under an intermittent operation condition (8h on; 16h off) on W and coil-type PHC energy piles installed in a partially saturated weathered granite soil deposit. In addition, three-dimensional finite element analyses were conducted and the results were compared with the four-day experimental results. The heat exchange rates were also predicted for three months using the numerical analysis. The heat exchange rate of the coil-type GHE showed 10–15% higher efficiency compared to the W-type GHE in the energy pile. However, in considering the cost for the installation of the heat exchanger and cement grouting the additional cost of W-type GHE in energy pile was 200–250% cheaper than coil-type GHE under the condition providing equivalent thermal performance. Furthermore, the required lengths of the W, 3U and coil-type GHEs in the energy piles were calculated based on the design process of Kavanaugh and Rafferty. The additional cost for the W and 3U types of GHEs were also 200–250% lower than that of the coil-type GHE. However, the required number of piles was much less with the coil-type GHE as compared to the W and 3U types of GHEs. They are advantageous in terms of the construction period, and further, selecting the coil-type GHE could be a viable option when there is a limitation in the number of piles in consideration of the scale of the building.

An experimental and numerical approach to derive ground thermal conductivity in spiral coil type ground heat exchanger

This paper presents an experimental and numerical study on the evaluation of thermal response test (TRT) results observed in a precast high-strength concrete (PHC) pile and a general conventional vertical type borehole with spiral coil type ground heat exchangers (GHEs). Field TRTs were carried out on a PHC energy pile and a general vertical type borehole, and an equivalent ground thermal conductivity was estimated using the spiral coil source model. The PHC energy pile and conventional vertical type borehole were numerically modeled using a three dimensional finite element method for the estimation of borehole thermal resistance and the comparison with the TRT results. Based on the results, this paper suggested a method to evaluate the ground thermal conductivity using the infinite line source model and the results were compared with those of the spiral coil source model.

Design of spiral coil PHC energy pile considering effective borehole thermal resistance and groundwater advection effects

This study presents experimental and numerical research results in determining an effective borehole thermal resistance of a spiral coil energy pile. A precast high-strength concrete (PHC) energy pile with a spiral coil GHE was installed and thermal response test was carried out to evaluate the thermal behavior of the energy pile and to validate the effective borehole thermal resistance. Besides, parametric studies using a numerical analysis were carried out to suggest a multiple regression equation for the effective borehole thermal resistance of spiral coil energy piles. The adjusted coefficient of determination (adjR2) of the regression equation was 92.4%, which was also verified by comparison with experimental results. Furthermore, using current analytical models, this paper examined the effect of groundwater advection on the long-term ground temperatures. In the long-term period operation, groundwater advection attenuates the average temperature rise in the ground compared to the case with the absence of groundwater advection, and this phenomenon ultimately causes a decrease of the temperature penalty value. The temperature penalty value, considering the effect of groundwater advection, was calculated and compared for various groundwater advection velocity values in different pile arrays.

Thermal transfer behavior in two types of W-shape ground heat exchangers installed in multilayer soils

This paper presents an experimental and numerical study on the evaluation of a thermal response test using a precast high-strength concrete (PHC) energy pile and a closed vertical system with W-type ground heat exchangers (GHEs). Field thermal response tests (TRTs) were conducted on a PHC energy pile and on a general vertical GHE installed in a multiple layered soil ground. The equivalent ground thermal conductivity was determined by using the results from TRTs. A simple analytical solution is suggested in this research to derive an equivalent ground thermal conductivity of the multilayered soils for vertically buried GHEs. The PHC energy pile and general vertical system were numerically modeled using a three dimensional finite element method to compare the results with TRTs'. Borehole thermal resistance values were also obtained from the numerical results, and they were compared with various analytical solutions. Additionally, the effect of ground thermal conductivity on the borehole thermal resistance was analyzed.

Evaluation of thermal response and performance of PHC energy pile: Field experiments and numerical simulation

This paper presents an experimental and numerical study on evaluation of thermal response and performance of prototype precast-high strength concrete (PHC) energy pile. Short-term field thermal response tests (TRTs) were conducted for the PHC energy piles installed in partially saturated weathered granite soil deposit, in which two types of heat exchangers were considered: W and 3U-shaped heat exchangers. The TRTs were successfully simulated by three-dimensional finite element analyses employing quasi-steady-state convective heat transfer boundary condition. The numerical model was applied to simulate 3-day TRTs, and the simulation results were used for assessing effective thermal conductivity and thermal resistance. Besides, continuous and intermittent operation simulations of the energy piles were performed, and for the results of performance analyses, discussion was made to evaluate energy efficiency of the prototype PHC piles.

Case Study of a High-Performance Concrete Bridge in Tennessee

This paper presents a case study on a high-performance concrete (HPC) bridge in Tennessee. The bridge is a twin bridge with high-strength concrete (HSC) beams in one bridge lane and normal-strength concrete (NSC) beams in the other bridge lane. The compressive strength of HSC and NSC were 92 and 49 MPa, respectively. The bridge was instrumented for strains and temperatures in precast beams, cast-in-place decks, and diaphragms during various construction stages. Test results presented in this paper include temperature changes in the concrete, time-dependent strains and cambers of precast HSC and NSC beams, and strain changes of deck and diaphragm. It was observed that the HSC members exhibited rapidly developed early-age creep and shrinkage strains, rapidly developed time-dependent cambers, and apparent differential shrinkage relative to the deck concrete. Recommendations for design and construction of HSC bridges are also presented in the paper.