Results Of Static Load Tests Research Articles

Study on construction technology and bearing mechanism of pressure cast-in-situ pile with spray-expanded frustum

The pressure cast-in-situ pile with spray-expanded frustum (PCPSF) is a new type of pile developed by the last author, which is composed of pile body, ribbed plate and expanded body with double-frustum. This paper presents the equipment used to produce the PCPSF and the spray-expansion extrusion vibration and pressure method used for construction of the PCPSF. The PCPSF model of cement soil transition layer around pile is built with finite element software. The accuracy of the numerical calculations is verified through a comparison with the results of static load tests conducted on PCPSF. Furthermore, the impact of the expanding ratio, expanded body location, and ribbed plate length on the response of the PCPSF is investigated. The results show that: (1) the ultimate bearing capacity (UBC) of PCPSF single pile is proportional to the diameter expanding ratio and the length of the ribbed plate; (2) the improvement of the bearing capacity of single cubic concrete of PCPSF decreases with the increase of expanding ratio; (3) the bearing capacity of expanded body can be activated ahead of time as it advances up in position, and there is a trend toward a steady increase in the combined bearing capacity of the expanded body and pile end; (4) as the expanded body moves up, the vertical stress of the soil below pile tip decreases, the rate of decay of additional stress is accelerated; (5) under the identical circumstances, the PCPSF's bearing capacity is 1.5 times greater than the traditional cast-in-place pile's, and the presence of cement soil transition layer contributes 15 % of the lateral resistance of the PCPSF.

Salt-freeze resistance and life prediction of geopolymer recycled concrete mixed with rice husk ash and modified rubber particles

Rice husk ash (RHA) and Span-40 modified waste rubber particles (WRP) were mixed into geopolymer recycled concrete (GRC) to improve its frost resistance in normal and chlorine environment. The freeze-thaw and static loading test results show that GRC has the best freeze-resistance when 5 %RHA and 10 %WRP are added. The strength loss rate of GRC after 200 freeze-thaw cycles in normal environment and chlorine salt environment is 8.3 % and 8.8 % lower than that of GRC without RHA and modified WRP, respectively. Based on the test results, the material damage model and strength loss model of GRC doped with RHA and modified WRP were established. The failure probability and service life of GRC were predicted. The results showed that the failure probability of GRC mixed with 5 %RHA and 10 %WRP was reduced by more than 10 % compared with that of GRC mixed with no RHA and modified WRP at 200 freeze-thaw cycles under normal environment and chlorine salt environment, and the failure probability decreased with the increase of cycle times. The life prediction results showed that the service life of GRC mixed with 5 %RHA and 10 %WRP increased by 17.9 % and 21.6 %, respectively, compared with that of GRC mixed with no RHA and modified WRP under the freeze-thaw cycle of normal environment and chlorine salt environment.

Research on the Vibration Fatigue Characteristics of Ancient Building Wood Materials

In this study, we selected ancient building timber as the research object. A series of static load tests were conducted to analyze the different performances of timber under tensile and compressive loads. After that, vibration fatigue tests on ancient timber samples were carried out under different upper limit stress ratios. Finally, a dynamic constitutive model of ancient timber was established based on the Ramberg–Osgood model. The static load test results show that the tensile strength was approximately 80% of the compressive strength. Meanwhile, the samples that failed under compressive pressure had obvious residual strength, and their failure strains were also much larger than those under tensile stress. In the vibration fatigue tests, the stress–strain curves were analyzed and the results showed that the curves displayed a trend moving to sparse from dense during the loading process. Meanwhile, the curves moved right with the increase in the upper limit stress ratios. The relationship between axial strain and the number of cycles appeared to be characterized by a three-stage form, i.e., damage occurrence, damage expansion, and damage penetration, and this relationship was formulated by a nonlinear function model. Finally, a dynamic constitutive model with high accuracy in describing the vibration fatigue characteristics of ancient timber was established by converting constant parameters to the variable parameters of the Ramberg–Osgood model.

Research on the vertical compressive bearing characteristics of offshore wind power steel pipe piles

In the absence of a comparison of static load test results for large-diameter steel pipe piles at home and abroad, optimize the design parameters based on the test pile results to guide later construction. This paper is based on the pile foundation design calculation method of API specification, as well as the relationship between the t-z, Q-z, p-y curve modes suggested by this specification, vertical ultimate bearing capacity, and stratum parameters. The conclusions and results obtained are limited to pile foundation calculations using API specifications. Analyze and back-analyze the results of static load tests on large-diameter steel pipe piles, and verify the pile foundation parameters. Combined with the data obtained from the test pile tests, analyze the stratum parameters to guide the optimization design of pile foundations in the construction drawing design stage of the offshore wind farm expansion project.

Pile–Soil Interaction during Static Load Test

Abstract This study highlights the possibility of determining the shear stress distribution along the skin of a pile, which represents skin resistance. Geotechnical engineering is plagued by the challenge of designing appropriate piles as a sufficient foundation construction while being economically justified solution. Static load testing facilitates verification if the pile satisfies these requirements. In most cases, the pile skin resistance is undervalued. This study first introduces the general approach based on static load test results using an appropriate mathematical approach in the presence of linear, vertical shear stress distribution boundary conditions as well as phenomena such as pile shortening and Kirchhoff's principle. Moreover, a scientific approach for pile compression and shear stress distribution is presented. Further, the study expands upon previous work by applying mathematical calculus to displacement piles. The promising results indicate that further work on greater number of piles may lead to a better understanding of pile–soil interaction and a more accurate design process.

Influence of precast microbial reinforcement on lateral responses of monopiles

Microbially Induced Calcium Carbonate Precipitation (MICP) provides an environmentally friendly solution for reinforcing large diameter monopiles for offshore wind turbines (OWTs). This study presents an investigation into the lateral responses of monopiles with precast microbial reinforcement using a low-pH one-phase method. Both static and cyclic loading tests were carried out. The results of static loading tests show that the failure mode of the bio-reinforced monopile was an overall overturn failure. The lateral bearing capacity was increased by 50% and the bending moment was reduced by about 25% with the bio-reinforcement. Further investigation was conducted on the secant stiffness, damping ratio, and accumulated deformation of the bio-reinforced monopile under various cyclic loadings. With the bio-reinforcement, the accumulated deformation under one-way cyclic loading can be reduced by 30%–60%. The influences of cyclic loading parameters and loading sequence on pile stiffness were clarified. The growth ratio of pile stiffness due to bio-reinforcement under one-way loading was between 1.65 and 2.82, and decreased with increasing load amplitude. The ratio was smaller under two-way loading. Three competing factors on pile stiffness were identified: cyclic compaction of the unreinforced sandy soil, weakening of the bio-reinforced soil and soil subsidence around the bio-reinforced soil.

Prediction of bridge structure deformation and strain based on dynamic testing and intelligent algorithms

The field load test is a direct and effective method for evaluating the performance of bridge structures. However, existing bridge field static load tests are costly and inefficient; moreover, they obstruct traffic and cause unavoidable damage to the bridge structure. As an alternative the the static load test, a random model update method based on bridge dynamic load tests and the Bayesian inference is proposed in this paper. The bridge static load test results were predicted with a high accuracy. To speed up the Bayesian method to infer the posterior probability density of the updated parameters, the Gaussian process was used in place of the finite element model, and the Bayesian inference used the Markov chain Monte Carlo method based on the delayed rejection adaptive Metropolis algorithm. First, the parameters to be modified for the bridge structure analysis model were determined based on the global sensitivity analysis method. Second, a uniform design sampling method was used to establish the Gaussian process optimization model to update the random model of the bridge structure. Finally, a reinforced concrete truss arch bridge was used to verify the correctness of the static load results of the bridge predicted by the random model update method based on dynamic load testing and Bayesian inference. The research results reveal that the prediction results of the bridge static load test based on the dynamic load test and Bayesian inference method agree with the actual test results.

Comparison of methods for determination the bearing capacity of piles in punched holes with broadening using the results of static load tests

In recent years, due to the increasing of urban construction extent, there has been a tendency to exhaust of territorial reserves, suitable for construction in large cities. Increasingly, it is necessary to use territories with unfavorable soil conditions for the construction of civil and industrial buildings. In such cases, various pile foundations are used, which have significant technical and economic advantages compared to foundations on a natural bases. Among the progressive designs of pile foundations, a special place is occupied by piles in punched holes with broadening (SPSu), which ensure the improvement of the physical and mechanical properties of the foundation during the production of works, as well as the reduction of material, energy and labor costs during their installation. Piles of this type are designed using the developed regulatory framework ISO 36554501-018-2009 "Design and installation of pile foundations and reinforced foundations from packed piles in punched holes". At the same time, the task of improving the quality of work on the design, arrangement, as well as the assessment and prediction of the bearing capacity of piles becomes particularly relevant. This task is solved with a high degree of accuracy by conducting large-scale tests of piles with a static load tests. These tests are carried out in real conditions of the construction site and allow to observe the changes pile`s settlement under load. The article is devoted to solving the problem of increasing the efficiency of assessing the bearing capacity of piles according to static load tests. Using the example of the test results of single SPSu, the authors of the article assess the effectiveness of the existing domestic and foreign methods for determining the bearing capacity of piles. As part of the solution of this issue, the results of the bearing capacity determining according to SP 24.13330.2021 were compared with the data obtained during the use of Davisson, Chin, De Beer, Hansen, Decourt and Eurocode 7 methods. The advantages and disadvantages of this approaches used are noted. Based on the accumulated practical experience of testing the SPSu in various ground conditions, the authors of the article proposed an alternative method of interpreting the "settlement - load" graph.

Considerations on an embedded pile’s effective length in an analytical calculation according to the commentary on the STN 73 1002 standard

The analytical model for calculating the bearing capacity of a pile, presented in the commentary to STN 73 1002 – Pile Foundations, gives a recommendation to reduce the pile’s length in the calculation of the shaft resistance. The recommendation is based on Caquot-Kérisel’s theory. Especially in the case of embedded piles, reducing a pile’s length in the calculation can cause the shaft friction of the embedded pile to be neglected, and the calculated resistance of the pile is thus significantly lower. The results of instrumented static load tests of embedded piles were analysed. The main aim of the study was to verify the validity of reducing the pile’s length in the analytical calculation of the shaft resistance. The results of the static load tests analysed did not show any reduction in the shaft friction on the embedded part of the pile. In the form of a parametric study, the effect of reducing the pile’s length in the calculation of shaft friction was analysed for different dimensions of embedded piles.

Verification of the Design Parameters Based on the Control Diagnostic of the Deformation Resistance of the Sub-Ballast Upper Surface

Abstract Based on the quality control diagnostics of the used base layers on the interstation railway section Palárikovo - Nové Zámky, the article analyzes the achieved results of static load tests that were carried out on the plane of the sub-ballast upper surface. The verification of the values is based on the project documentation, in which, on the basis of a previously performed geotechnical survey, the designer proposed a suitable type of structural sub-ballast layers. The design of the structural sub-ballast layers reflects the expected deformation resistance of the subgrade surface, its water regime, the railway line characteristic (speed zone), the type of construction work (reconstruction) and also takes into account the principle of conservation of natural resources (recycling of recovered ballast bed material).

Flexural behavior of open-web composite slab with I-shaped steel bottom chord and vertical flat webs

Traditional composite floor truss systems with top and bottom chords and web trusses have encountered difficulties in system erection, installation, and the passage of utilities. In order to address these challenges, this study introduces a novel open-web composite floor system that only consists of a bottom chord and vertically placed flat web elements. These vertical web members are essentially short I-shaped steel elements and are connected to the I-shaped steel beam bottom chord and concrete slab through steel top plates and shear connectors, forming an innovative composite floor system. This paper presents the results of static loading tests conducted on two specimens with distinct web members, evaluating deformation, cracking characteristics, ultimate bearing capacity, failure mode, and stress and strain distributions. The findings indicate that the new composite floor system offers good flexural performance. Furthermore, finite element models of the composite floor system have been developed to analyze the influence of the web element’s geometry on the composite slab’s ultimate bearing capacity. This study also develops a theoretical calculation method for determining the internal force, elastic deflection, and ultimate bearing capacity of the composite floor system. The theoretical calculation results regarding the failure mode and ultimate load capacity align closely with the experimental values, and the deformation calculation formula can be used to estimate the deformation curve shape and elastic deflection of the floor system.

Experimental study on axial compression monitoring of pile foundation based on sensor-enabled piezoelectric geocable

In concealed underground projects, pile foundations may cause severe engineering accidents owing to factors such as construction technology, geological conditions, and material properties. Accordingly, the construction industry has invariably focused on developing high-precision, distributed, and low-cost monitoring and disaster warning methods. Therefore, a new sensing material, sensor-enabled piezoelectric geocable (SPGC), was developed to monitor the deformation and failure of a pile foundation. Three model piles were constructed, and packaging and layout processes for the SPGC sensing material were proposed. Moreover, a fiber Bragg grating (FBG) sensor and resistance strain gauge were installed for comparison. Pile foundation failure and static load tests were performed using a large servo hydraulic press. The monitored effect was evaluated by obtaining the impedance and voltage signals of the SPGC. Pile foundation failure test results show that the mutation of impedance and voltage signals can be used as combined monitoring data, and the electrical signal of the SPGC can be used in three stages of early warning response. These findings ensure that pile foundation damage can be located, damage precursors can be identified, and timely warning can be provided. The static load test results indicate that the SPGC data are in good agreement with the FBG sensor and strain gauge data. The impedance of the SPGC increases linearly with the load. Accordingly, a linear calculation formula relating impedance and strain is derived. The research results are expected to provide a new technical method for pile foundation construction and long-term operation and maintenance monitoring.

Static Behavior Prediction of Concrete Truss Arch Bridge Based on Dynamic Test Data and Bayesian Inference

The field load test is a direct and effective method for evaluating the performance of bridge structures. However, the existing bridge static load tests on site are costly, inefficient, and obstruct traffic; moreover, improper loading may also cause some damage to the bridge structure. This paper proposes a random model update method based on bridge dynamic load tests and the Bayesian inference as an alternative to the static load test. The Gaussian process model was used instead of the finite element model to reduce the cost of model calculation. Furthermore, choose the Markov Chain Monte Carlo (MCMC) method based on delay rejection adaptive Metropolis algorithm for Bayesian inference to improve the speed of the Bayesian method inferring the posterior probability density of updated parameters. First, the parameters to be updated for the bridge structure analysis model were determined based on the global sensitivity analysis method. Second, a uniform design sampling method was used to establish the Gaussian process optimization model to update the random model of the bridge structure. Finally, a reinforced concrete truss arch bridge was used to verify the correctness of the static load results of the bridge predicted by the random model update method based on dynamic load testing and Bayesian inference. The results show that the predicted results of the bridge static load test based on the dynamic load test and Bayesian reasoning method have an excellent agreement with the measured results, and this method can effectively overcome the adverse effects of the existing bridge static load test.

Structural Assessment of a Post‐Tensioned Box Girder Bridge affected by Concrete Creep

AbstractThe behavior of post‐tensioned concrete bridges is often influenced by time‐dependent phenomena, such as relaxation of prestressing steel, creep and shrinkage of concrete. For bridges built using the balanced cantilever method, the evolution of time‐dependent phenomena during the construction phase must be carefully considered. In common practice, the assessment of the structural safety of this bridge typology is a complex task due to the numerous factors and uncertainties involved in the evaluation process. Numerical models can be adopted to perform structural analyses at successive phases over bridges' lifetime, while destructive and non‐destructive evaluation methods are used to gather information to ensure that the numerical model matches the actual behavior of the bridge. In this context, this paper presents the structural behavior assessment of a multi‐span post‐tensioned box girder bridge with vertically prestressed internal joints. A numerical model was constructed to investigate on the effect of creep and construction phases on the actual stress/strain conditions of the bridge. To reduce model‐based uncertainties, compression tests were carried out on concrete cores extracted from the structure and the results of static load tests were used for model validation purposes.

Study on Load Transfer Mechanism of Local Curved Prestressed Hollow-Core Slab Bridge

The assembled hollow-core slab bridge is the most widely used beam bridge in China. With the increasing traffic volume and traffic load in China, the joints of the hollow-core slab bridge are prone to damage. In this paper, a hollow-core slab bridge with locally curved prestressed tendons is proposed. Based on the static load test of a beam with joints taken from the cross section of a hollow-core slab bridge in practical engineering, a finite element nonlinear analysis is used to simulate the test, and the concrete and interface parameters under the correct analysis results are obtained. Finally, the parameters are applied to the three-beam and two-joint hollow-core slab bridge with a span of 10 m and a finite element analysis is carried out to explore the total failure process and performance improvement effect of the prestressed hollow-core slab bridge. The results show that the interface unit method can successfully simulate the new-to-old concrete interface where the joint is in contact with the precast beam segment. Compared with the static load test results, the analysis error of each finite element model is basically within 15%. Compared with the traditional hollow-core slab bridge, the cracking load, through-joint load, and ultimate load of the prestressed hollow-core slab bridge are increased by 50.0%, 91.7%, and 66.7%, respectively. Under the same load, the stress of the U-bar, the relative deflection of both sides of the joint, and the maximum width of the joint of the prestressed hollow-core slab bridge are lower than those of the traditional hollow-core slab bridge. When the ultimate load is reached, the longitudinal crack lengths of the traditional hollow-core slab bridge and the prestressed hollow-core slab bridge are 0.48 L and 0.4 L, respectively, and the damage degree of the prestressed hollow-core slab bridge is lower than that of the traditional hollow-core slab bridge.

Mechanical behavior analysis and bearing capacity calculation of CFG pile composite foundation on coral sand site

Coral sand foundation formed by hydraulic fill often faces the problem of poor bearing capacity. This paper proposed for the first time to apply CFG pile composite foundation to coral sand sites to verify the feasibility of this scheme and understand its mechanical characteristics. Firstly, taking on-site coral sand as the research object, a pile sand interface shear test was conducted to clarify the mechanism of pile side friction. At the same time, the ultimate bearing capacity of CFG pile and its composite foundation was measured through in-situ static load tests. Then, based on the strength parameters of the pile sand interface revealed by indoor tests, numerical simulations were conducted to analyze the bearing characteristics of CFG piles and their composite foundations. Finally, a method for calculating the vertical bearing capacity of rigid piles in composite foundation considering interface parameters was proposed. The results showed that the bearing capacity characteristic values of single pile and composite foundation meet the design requirements; The interface friction angle and cohesion together increased the ultimate side friction by 64.41%; The load is mainly borne by the pile tip resistance, and the increase of the interface friction angle will make the proportion of the side friction load first increase and then decrease more obviously; The pile soil stress ratio first increased and then tended to stabilize as the interface strength increased. Compared with the field static load test results, the rationality of the calculation method for composite foundation rigid piles was verified. This study may have reference significance for the design and construction of coral sand foundation treatment in offshore island and reef projects.

Study on model test of the new O-cell load test method with two loading directions

Aiming at the possible problems of the new O-cell load test method with two loading directions in engineering practice, the operability and feasibility of this new method is studied by using indoor model tests and finite element numerical simulations. According to the similar principle, three groups of the traditional static load test, the O-cell load test and the updated O-cell load test under the same working conditions are designed and poured to obtain the pile ultimate compressive bearing capacity for comparison. Strain gauges and optical fibers are also used to detect the strain of the outer surface of the pile and the soil layer around the pile. The research results show that based on the bearing capacity results of the traditional static load test, the results of the physical model under the updated O-cell load test are compared with the results under the O-cell load test. The deviation is reduced by 3.54%-7.34%. At the same time, based on the physical test, the finite element analysis shows that the longer the pile length, the greater the deviation reduction. When the pile length is twice the physical model test, the contrast deviation reduction value is 9.15 %-15.71%. The strain results in the physical test also reflect the mechanism of pile-soil interaction well, and there is also a deficiency that the position of the equilibrium point needs to be determined.

Prediction of mechanical behavior of reinforced concrete bridges following a fire based on the fire dynamics simulator–kriging model

AbstractThe performance degradation and degree of damage of bridge materials are more extensive at the fire source compared to other bridge locations. The traditional finite‐element model (FEM) modification method leads to a large error and is unable to achieve a good correction effect. In addition, as the traditional static load test method is used to evaluate the bearing capacities of bridges postfire, the risk of bridge damage, or collapse‐induced by secondary loading—remains unaddressed. To solve these problems, this paper proposes a modified FEM of a bridge following a fire based on the fire dynamics simulator (FDS)–artificial intelligence algorithm. The static behavior of a bridge is predicted using the modified FEM. First, a numerical simulation of a bridge fire is conducted using the FDS to obtain the temperature field distribution and determine the influence ranges of local design parameters of the bridge at the fire source. Second, a response surface model with a high fitting accuracy is constructed to modify the initial FEM by using the artificial intelligence algorithm proxy model together with dynamic load test results for the bridge postfire. Finally, the static behavior is predicted using the updated model. In this study, an actual hollow girder bridge postfire is taken as the research object, and the static behavior prediction results obtained via the proposed method are compared with the static loading test results. The results indicate that the response‐predicted value of the modified FEM is close to the measured value of the bridge postfire.

Cast‐in‐place deep foundations in Myanmar

AbstractThis article is a summary of the available research works of cast‐in‐place deep‐seated bored piles in Myanmar. Instrumented static pile load test results are analyzed, discussed, and updated. The information contained in the article is mainly from the construction projects of private sectors constructed in Yangon and extended study of previous work on current practices of deep foundations and deep excavation Works in Myanmar.

Final-State Structural Behavior of the Long-Span Kömürhan Cable-Stayed Bridge under Torsional and Bending Loadings

Final-state field load testing is an effective method for understanding the real behavior of a bridge before it opens to traffic. The paper presents the procedure and the results of final-state static field tests on the new long span Kömürhan cable-stayed bridge with a single pylon and back span anchorage block under torsional and bending loadings. A total of six static loading cases were conducted to investigate real structural behavior of the bridge having a back span anchorage block and main span deck connected to the pylon with 42 tensioned cables in the deck center. Measured results have been obtained from the surveys and sensors while theoretical results have been calculated from the three-dimensional finite element model of the bridge final-state geometry. The results of final-state static load tests include the main span deck deflections, pylon horizontal displacements, the strains of the main span deck and the pylon, and the cable forces. A good agreement has been achieved between the experimental and theoretical results. Both experimental and theoretical results have shown that the real bridge behavior is in the elastic state under the planned test loads and supplies the design requirements. It is also observed that the results from the torsional and bending load cases positioned in the same sections are close to each other.