A Test Rig for Jetted Conductors in Soft Clays

A reliability analysis of the axial compressive load bearing capacity of postfire reinforced concrete (RC) columns strengthened with carbon fiber reinforced polymer (CFRP) sheets was presented. A 3D finite element (FE) model was built for heat transfer analysis using software ABAQUS. Based on the temperature distribution obtained from the FE analysis, the residual axial compressive load bearing capacity of RC columns was worked out using the section method. Formulas for calculating the residual axial compressive load bearing capacity of the columns after fire exposure and the axial compressive load bearing capacity of postfire columns retrofitted with CFRP sheets were developed. Then the Monte Carlo method was used to analyze the reliability of the axial compressive load bearing capacity of the RC columns retrofitted with CFRP sheets using a code developed in MATLAB. The effects of fire exposure time, load ratio, number of CFRP layers, concrete cover thickness, and longitudinal reinforcement ratio on the reliability of the axial compressive load bearing capacity of the columns after fire were investigated. The results show that within 60 minutes of fire exposure time, the reliability index of the RC columns after retrofitting with two layers of CFRPs can meet the requirements of Chinese code GB 50068 (GB 2001) for safety level II. This method is effective and accurate for the reliability analysis of the axial load bearing capacity of postfire reinforced concrete columns retrofitted with CFRP.

The sea reclamation is one of the efficient ways to alleviate the shortage of land resources due to population growth, and the corresponding axial ultimate bearing capacity of piles has become one of the critical factors for evaluating the performance of the soil layer reclamation work. Many models are used to analyze the testing data. However, these models cannot describe the mean population bearing capacity and unit-to-unit variation simultaneously, and they cannot give the reliability of predicting the axial ultimate bearing capacity of piles. Thus, they are rarely used in practice. In this article, we propose a mixed-effects model, which could overcome the drawback of the models in the literature. A hierarchical Bayesian framework is developed to estimate the model parameters using Gibbs sampling. The proposed model is applied to a real pile dataset collected in silt-rock layer area, and we predict the mean axial bearing capacities under different reliability levels.

Under the influence of material defects, structural grooving, environmental corrosion, and other factors in engineering, concrete-filled steel tubes incur local defects on their external surfaces that affect their structural integrity and service life. This work conducts axial compression tests on 10 grooving-damaged square hollow concrete-filled steel tube (SHCFST) columns to investigate the effect of grooving damage on their axial compressive ultimate bearing capacity and the effect of steel tubes on concrete confinement. It explores the effects of three parameters, namely, the length of grooves, presence of slots in internal and external steel tubes, and orientation of grooves, on structural static performance. This study analyzes the loading, failure mechanisms, and axial compressive ultimate bearing capacity of grooving-damaged SHCFST columns. Results indicate that grooving weakens the steel tube’s confinement effect on the concrete core, reducing the axial compressive ultimate bearing capacity of specimens. On the basis of this experimental research, a method for calculating the axial compressive ultimate bearing capacity and axial compressive stiffness of grooving-damaged SHCFST columns is proposed. The calculation results closely align with experimental outcomes, providing valuable insights for related scientific research and engineering applications.

Oil and its derivatives such as gasoline, gasoil and ‎kerosene are the main sources of energy in the transport and industry sectors, and also the most common ‎soil contaminants. Oil contamination of the soils as a serious geoenvironmental problem not only affects soil quality ‎but also changes its geotechnical properties. Any changes in the geotechnical properties of the soils affect the axial bearing capacity of pile. The main objective of the current study is to determine the effects of various concentrations of different oil ‎products, as well as different soil relative densities, and thickness of the contaminated sand layer on the load–displacement (axial compressive) behaviour of two ‎instrumented, close-ended steel pipe piles with different diameters and slenderness ratios implemented in an oil-contaminated sandy soil through physical modelling. Tests results were compared with the CFEM ‎analytical method of calculating pile axial bearing capacities. Results showed that increasing the percentage of the oil in the soil reduces the values of net total, toe and shaft bearing ‎capacity of the pile. The type of the oil had a remarkable effect on the bearing capacities of the pile. The higher the kinematic ‎viscosity, the lower the amount of bearing capacities. ‎Comparing the measured and predicted values of bearing capacity based on modified CFEM ‎method concluded that, although a good agreement can be seen between the results of shaft capacity, the ‎CFEM method with modified bearing capacity factors could not predict the effects of oil contamination ‎on the toe bearing capacities of piles precisely.

Performance of stirrup-confined concrete-filled steel tubular stub columns under axial loading: A further investigation

Axial compressive behavior of corroded double-steel-plate composite shear wall with binding bars

This study aims to employ machine learning algorithms to analyze the axial bearing capacity of rubberized alkali-activated concrete filled steel tubes. A dataset encompassing 327 synthesized instances and seven input features is adopted for training and testing six machine learning models, including Decision Tree, Random Forest, Extremely Randomized Trees, Adaptive Boosting, Gradient Boosting Decision Trees (GBDT), and eXtreme Gradient Boosting Trees (XGBoost). The SHapley Additive exPlanation algorithm is employed to elucidate the prediction process of machine learning models and to analyze the influence of each parameter on axial bearing capacity. Comparison of evaluating metrics shows that GBDT and XGBoost models achieve highest accuracy and generalization capabilities when their Coefficient of Determination values surpassing 0.98 and Mean Absolute Percent Error remaining below 3%. Moreover, the explanation analysis of machine learning models reveals that diameter/width of the cross section, rubber content, yielding strength and thickness of steel tubes are critical variables that affect the axial bearing capacity, while compressive strength of alkali-activated concrete, specimen height, and shape of cross section show negligible impact. Besides, GBDT model overemphasizes the effect of specimen height and might lead a conservative prediction for specimens with smaller heights. Finally, compressive strength of alkali-activated concrete and diameter/width, thickness, and yielding strength of steel tubes are positively correlated with axial bearing capacity, and the increase of rubber content in alkali-activated concrete leads to the decrease of capacity.

Cold-formed steel framing walls with infilled lightweight FGD gypsum Part II: Axial compression tests

Post-blast performance and residual capacity of CFDST columns subjected to contact explosions

Surface casing jet-in and drill-ahead have become a common practice for deepwater drilling operation around the world. The main objective of the jet-in and drill-ahead operation is to set the surface conductor casing which is typically 36-inch in size and drill ahead the next hole section with the same bottomhole assembly (BHA). This paper reviewed 25 jet-in and drill-ahead BHA runs for deepwater drilling operations in Malaysia, with the intention to share the experience and findings. It is aimed to highlight the pertinent operating procedures needed for a successful jet-in and drill-ahead operation for future deepwater drilling operations, both in Malaysia and in other parts of the world. Multiple designs of BHAs in various sizes were imperative to achieve an optimum outcome for the jet-in and drill-ahead operation. The bit size, jet-in procedures, jetting speed, bit extension (stick out), assembly type, flow rate, formation and survey procedures are among other key aspects for a successful deepwater jet-in and drill-ahead operation. While all the deepwater jet-in and drill-ahead operations in Malaysia were performed with a mud motor BHA, a recent deployment of a rotary steerable system BHA in an ultra deepwater drilling operation had achieved a faster, verticality improvement to ±1°, a value-added outcome.

The Helix Stiffened Cement Mixing (HSCM) pile is a new type of composite pile. In order to investigate the effects of construction machinery and the one‐time pile construction process on the axial bearing performance of HSCM piles, field pile driving tests and axial loading tests were carried out. The pile diameter and bearing deformation characteristics of helical piles, hollow bar micropiles, and HSCM piles were compared and analyzed. The enhancement effect of the one‐time pile construction process on the frictional resistance of HSCM piles was discussed. The load transfer mechanism of HSCM piles under different load levels during one‐time pile construction was revealed. The test results showed that the one‐time pile construction process could form a cement‐soil column around the pile core, and an appro‐priate increase in the helix plates was beneficial to forming the cement‐soil column. When applied in marine soft clay, the bond diameter of HSCM piles could be conservatively estimated to equal the diameter of the helix plates. The axial bearing capacity of HSCM piles is about twice that of helical piles. The one‐time pile construction process increased the pile‐soil contact area and improved the axial bearing capacity. During loading, the load of HSCM piles was transferred from the helical pile core to the ce‐ment‐soil and further to the pile‐soil contact surface, and its load transfer mechanism was the failure of the pile‐soil contact surface.

Perforate-Wash-Cement (P/W/C) is a well plugging technique extensively used by ConocoPhillips in the Greater Ekofisk Area over the last ten years. In Jet-type P/W/C, Tubing Conveyed Perforating (TCP) guns perforate casing in the target interval before the zone is washed and a cross-sectional cement plug is installed using a specialized Bottom Hole Assembly (BHA). The goal is to maximize the cement plug quality through optimizing the BHA and operational process parameters within constraints imposed by the operating conditions. This paper describes application of Computational Fluid Dynamics (CFD) to achieve this objective. CFD is well suited for modeling wash and cement processes including the associated non-Newtonian fluids. A CFD model of these processes employs unsteady multiphase Reynolds Averaged Navier Stokes (RANS) based Volume of Fluid (VOF) approach with a Shear Stress Transport (SST) K-omega turbulence model. BHA translation and rotation are simulated using moving deforming-layering mesh with interface approach. Physical properties of non-Newtonian fluids selected are based on in-situ conditions and derived via lab tests. CFD-specific considerations such as domain size, turbulence model, mesh type and size, and computational timestep are discussed in this paper. The magnitude and duration of the jet-induced "pressure pulse" in the annular space between the formation wall and the casing are a key to efficient displacement during the wash and cementing processes. Displacement efficiency, in terms of the percentage of mud or cement in a control volume as a function of time, depends on perforation size and density, nozzle size/number, flow rate, fluid properties, as the ROP/BHA pulling speed and tool RPM. Key findings from a parametric study to optimize these parameters are presented. To validate CFD nozzle flow predictions and to rule out potential for false results due to cavitation, laboratory tests were performed under pressurized conditions. A comparison of results from CFD simulations using traditional versus optimized parameters are presented, demonstrating significant efficiency improvement achieved. The study initially focused on North Sea application. Encouraged by substantial improvement in process efficiency through parametric optimization, the technique was extended to UK operations and is planned for the Bayu-Undan field. Cementing simulation results for Bayu-Undan specific well configurations are presented, showing how CFD modeling helped reveal less than ideal cementing efficiency. Ultimately, this work provides significant time savings and quality improvement for P&A projects while maintaining a high safety standard.

Solid steel tubular concrete members have excellent axial compression capacity. In terms of the calculation method of their axial compression bearing capacity, the current ten domestic standards all provide specific provisions. On the basis of main structure provisions such as diameter-thickness ratio and confinement factor, the formula differences in axial-force compression capability of domestic and international standards are compared and analyzed. First, the difference value of bearing capacities reach up to 62.79% according to current standards when diameter-thickness ratio range from 4 to 30. Second, concrete-filled steel tube members with diameter-thickness ratio greater than 20 and diameter less than 200, the current specifications cannot calculate the axial compressive bearing capacity.

A new type of square concrete-filled steel tubular (SCFST) column is proposed, which is characterized by transverse stiffened bars inside the steel tube to improve the effective constraint performance of the concrete core. The experiment of this kind of composite material under axial compression was carried out. The results showed that the bearing capacity of the SCFST column reinforced by internal transverse stiffened bars increased by 4.5%-15% than that of the ordinary SCFST column. The transverse strain is smaller than the SCFST column. As the diameter of the reinforcement increases and decreases the spacing of bars, the axial load bearing capacity increased. The transverse strain of the member decreased obviously. It is noted that the confinement performance of the concrete core of this type was improved to some extent. At the same time, based on the unified theory, the simplified calculation formula of axial compression bearing capacity is derived.

To study the axial compression performance of high-strength recycled concrete columns with built-in square steel tubes, ABAQUS software was used to model and analyze two existing test specimens, verifying the accuracy of the model. On the basis of a reliable model, parameter analysis was conducted on 13 specimens, with variable parameters including square steel tube thickness, square steel tube strength, and slenderness ratio. The results showed that the established finite element model exhibited longitudinal reinforcement buckling and steel tube tearing deformation consistent with the experimental results, and the height of the load axial displacement curve was consistent. The average error of the ultimate bearing capacity was within 5%; The increase in steel tube thickness has little effect on the axial compression bearing capacity and stiffness, while the increase in steel tube yield strength has a significant impact on the axial compression bearing capacity and residual bearing capacity; With the increase of slenderness ratio, the axial compression stiffness and ultimate bearing capacity of composite columns are obviously degraded. A numerical calculation method between the axial compression stability coefficient and slenderness ratio is fitted, which can be used as a reference for the design of composite columns.