Static Load Test Research Articles

Deflection function of a novel bolt-connected precast concrete floor

Owing to the post-cast procedure and relatively complex joint configuration, composite precast floors limit the full display of advantages of precast concrete systems. The development of fully assembled precast floors is of necessity; therefore, a novel bolt-connected precast concrete floor was proposed in this study to meet the increasing demand for quick assembly, lightweight, and good insulation in flooring systems. The proposed floors consist of precast sandwich unit slabs that are fully assembled to an integral floor with dry-type bolted connectors. Field static loading tests were conducted on four full-scale precast concrete floors. The test results indicate that the floors exhibited a two-way flexural ability due to the involvement of the bolted connectors. The restraining mechanism at anchorage and load-transferring mechanism at joints were investigated through a theoretical analysis. Based on the theory of plates and shells, a simplified theoretical method of solving the deflection function of the floors was established and validated to provide a reference for designing such fully assembled floors. The comparison between the theoretical and experimental results indicates that the arrangement of joint connectors could affect the theoretical calculation accuracy due to its influence on the performed continuity simplification. The application scope of the proposed theoretical method was evaluated through a finite element analysis.

Full-Scale Load Testing for Evaluating Crack Performance in Precast Prestressed Concrete Communication Towers with Annular Sections

Tall prestressed concrete poles with annular cross-sections are increasingly used as communication towers. The annular section subjected to bending moments has a smaller extreme tension area, resulting in higher stress increments in the materials within this region. As slender concrete structures, their bending behavior and crack resistance performance need to be critically examined. However, large-scale tower structures have rarely been experimentally investigated. Moreover, current code-specified crack width calculation methods are designed for square sections, so their applicability to concrete members with annular sections requires further investigation. To address these issues, this study conducted full-scale static loading tests on two 30-meter-high tower structures made of prestressed high-strength concrete and evaluated the accuracy of code methods for estimating the maximum crack width. During the static loading tests, displacement, cracking moments, crack widths, and crack spacings were meticulously recorded, and a theoretical methodology for calculating the stress in the extreme tension bars was developed. Four calculation methods specified in structural codes were compared: the Concrete Design Code of China (GB50010), Eurocode 2, ACI 224R, and the Concrete Design Guideline of Japan (JGC2007). The experimental results showed that diameter significantly affects the stiffness and displacement of the structure, with reloading stiffness of the full-scale tower reducing by up to 11% after exceeding the serviceability limit state. Regarding crack width prediction, substantial deviations were observed among the results of the four methods. On average, GB50010 underestimated crack widths, while JSCE, Eurocode 2, and ACI 224R overestimated them. Eurocode 2 and ACI 224R provided relatively conservative and accurate predictions. These findings highlight the need for improved and tailored code provisions for annular sections. It is also noted that the comparison was limited to crack widths less than 0.1 mm and a relatively small amount of data. Future research should focus on developing prediction methods specifically for prestressed concrete tower structures with annular sections.

Effect of the connection structure of zirconia dental implants on biomechanical properties

The connection structure of zirconia dental implants significantly influences their biomechanical behavior and plays a crucial role in the overall service performance of the implant system. This study aims to compare the stress distribution of zirconia implants featuring various internal connection structures under different working conditions. Four distinct types of connection structures were designed for zirconia dental implants: triangular, quadrilateral, hexagonal, and hexalobular plus connections. Additionally, the finite element method was employed to analyze these structures under three working conditions: a static load test model, a bone level model, and a torsion model. Results indicated that in the static load test model, the hexagonal structure experienced the highest stress value at 1284.9 MPa due to its thin neck wall, whereas the hexalobular plus connected implant exhibited the lowest stress value at 1252.9 MPa. In the bone level model, the triangular connection structure demonstrated poor stress distribution for cortical bone and cancellous bone at 69.606 MPa and 7.8191 MPa, respectively. Conversely, the hexalobular plus connection yielded superior stress results for cortical bone and cancellous bone, with values of 69.606 MPa and 7.8191 MPa, respectively. In the torsion model, the hexalobular plus-connected implant exhibits the highest stress value at 210.37 MPa, while maintaining the smallest force transmission angle. Therefore, given that the abutment necessitates a greater range of installation angles and improved torque transmission, the hexalobular plus connection structure may represent the optimal choice.

Study on bearing characteristics of single pile in heterogeneous layered foundation

Based on a project in Lanzhou City, Gansu Province, China, the bearing and internal force characteristics of 2 piles of different lengths under vertical load were tested and analyzed by using BOFDA technology and anchor pile method static load test. The results show that long pile has higher vertical bearing capacity and greater elastic working range, but the axial force of long pile and short pile has the same trend. The lateral friction resistance of the soil layer around the pile plays a role earlier than the pile tip resistance, and the lateral friction resistance of the upper soil layer plays a role earlier than the lower soil layer. The increasing amplitude of lateral friction resistance in different soil layers is also different. The settlement of short pile top is mostly caused by the displacement of pile bottom, and the pile tip resistance is more affected by the pile tip sediments. The relationship between pile end resistance and displacement under the influence of sediments can be analyzed by three-fold line model.

BI-DIRECTIONAL STATIC LOAD TESTING

A full-scale static load testing program can optimise many of the requirements in terms of costs and remove uncertainties. The bi-directional load testing method, by eliminating the reaction structures of the traditional top-down testing methodology, opens up unseen possibilities of the testing program in the most efficient, safe, and cost-effective manner for all types of foundations, particularly for larger test loads. The benefits of using bi-directional load tests and how effective they are will be described in the paper. The revolutionary bi-directional static load testing method has also a significant side effect of reducing CO2 emissions for such tests by up to 80%.

Experimental and numerical analysis of instrumented caissons in tropical soil

This paper presents an experimental and numerical study on the behavior of three (3) instrumented caissons in a tropical laterite soil in the Planalto Central, DF, Brazil. The concrete caissons have a shaft diameter of 0.6 m, a bell diameter of 1.2 m and 1.3 m and lengths of 8.9 to 14.4 m. Static load tests were conducted out to investigate the behavior of the caissons. The results of load vs displacement and their interactions with the tropical soil were measured and evaluated using the methodology of Camapum de Carvalho et al. (2008, 2010) and numerical modeling with back-calculation of static load tests in the Plaxis 3D software. The paper presents the analysis of the load transfer lines and the comparison with the proposed methods. The results pointed to a constant load transfer along the shaft, with a significant contribution from the skin friction, developed for a fraction of the displacement necessary for its mobilization. The accuracy of using the Camapum de Carvalho et al. methodology stands out (2008, 2010), identifying the region dominated by skin friction, tip and plasticization of the foundation, confirming the authors’ predictions for a tropical soil in the Distrito Federal/DF, Brazil. The numerical method using the Plaxis 3D software, proves that for the limit test load there was a significant contribution from skin friction, which must be consider in the analysis of the behaviour of caissons.

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.

Study on the bending mechanical properties of composite tube and metal joint bonding structure

Abstract The study of the mechanical properties of composite adhesively bonded joints is a very important issue, which directly affects the safety and reliability of the structure. This article studies the bending performance of carbon fiber composite tubes and metal joint bonding structures, as well as obtains the structural bearing capacity, influencing factors, and structural failure modes. Through mechanical analysis and static bending load tests, it is shown that the failure model of composite tube adhesively bonded metal joints under bending load is manifested as the first layer peeling or interlayer failure of the composite material in the bonding area between the tube and the joint, leading to local crushing at the end of the tube. There is no gap between the tube and the joint, which has little effect on the bending bearing capacity. The thickness gradient treatment at the end of the joint does not help improve the bending bearing capacity. The adhesive layer is at a 90 ° angle, which makes it easy for the first layer to peel off; it should be avoided. Other angle layers have little impact on load-bearing capacity. The longer the bonding length is, the stronger the bending capacity is. The adhesive J133 or 420 has a similar load-bearing. Wrapping a carbon fiber unidirectional layer around the ends of tubes and joints is helpful in improving their bending load-bearing capacity.

Field investigations on the thermo-mechanical behavior of a partially activated energy pile in Miocene sediments

The City of Vienna, as one of the largest public clients in Austria, initiated a research project to determine the load-bearing behavior of various foundation elements in typical Viennese soils. Numerous large-scale tests were carried out on bored piles, micro piles, anchors, and jet grouted columns. In addition, two energy piles were installed in different soil layers to investigate their behavior under mechanical and thermal loading in each soil layer separately. This paper discusses the energy pile in the Miocene sediments, which consist mainly of silty fine sand and some sandy silt. The energy pile – fully instrumented with strain gauges, extensometers, heat gauges and optical fiber sensors – was loaded for two and a half months. The mechanical load was kept constant throughout the thermal cycles to determine the response of the pile to thermal loads. The measured temperature data were used in numerical back-calculations to determine the thermal parameters of the soil layers and the concrete. Based on the measured strain and deformation data, the deformation behavior of the energy pile due to the thermal load was investigated. Finally, a static pile load test was carried out on the energy pile and the results are compared with those of the conventional reference piles installed in the vicinity, which have not been subjected to thermal loading. The test demonstrated that, after several weeks of cyclic thermal loading, the energy pile exhibited more favorable load-deformation behavior compared to conventional reference piles.

Experimental Study on the Time-Dependent Resistance of Open-Ended Steel Piles in Sand

Open-ended steel piles are commonly used as the foundation for offshore structures. Numerous model and field tests have demonstrated a time-dependent increase in the resistance of these piles, a phenomenon referred to as pile ageing or pile setup. Additionally, for open-ended steel piles with comparably small diameters, soil plugging enhances the resistance against axial compressive loads. Realistically predicting these effects is necessary for their reliable incorporation into design practice. This contribution presents static compression and tension pile load testing conducted in an experimental pit filled with wet, uniformly graded silica sand. In total, twelve piles (L= 5.5 m, Do= 325 mm) were driven into homogeneously compacted sand using a pneumatic impact hammer. Firstly, static compression pile load testing was executed at various times after installation. Subsequently, static tension pile load tests were carried out. The results of the static compression pile load tests indicate that the compressive resistance doubles over an ageing period of 64 weeks. The experimental investigations of the effect of soil plugging showed marginal soil plugging during pile installation, but a significant influence of the soil plug on the compressive resistance.

Analysis of the possibility of description the pile load-settlement curve based on the CPTu results

One of the field soil tests commonly used for pile design is CPTu static sounding. The load-bearing capacity of pile foundations is commonly verified in field experiments through static load tests. The result of this test is the load-settlement relationship of the pile which can be approximated by a curve named M-K. The main aim of the work is to check the possibility of determining the parameters of the M-K curve based on the results of field tests with the CPTu sounding. Experimental research leads to relationships between the parameters of the M-K curve and geotechnical parameters, including CPTu static sounding. The paper presents the possibilities of using the CPTu sounding to estimate the pile settlement curve. Knowledge of this relationship at the foundation design stage allows you to confirm whether the pile meets the load-bearing conditions and to determine the safety margin, which gives designers greater opportunities to correctly design the foundation

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.

Technological and Mechanical Studies on Additively Manufactured Cellular Structures Made of the Ultrafuse 316L Composite Filament

Regular cellular materials produced using additive manufacturing (AM) techniques represent a significant development trend in modern engineering materials. Depending on the applied elementary unit cell of topology, it is possible to define the course of the structure deformation process in order to obtain the highest possible energy absorption effectiveness. This feature makes regular cellular structural materials particularly attractive for a number of industrial branches. This paper presents the results of technological trials and the results of experimental studies on the mechanical properties of regular cellular structures made using 3D printing technology under compression test loading conditions. The material used for their production was the Ultrafuse 316L filament and the fused filament fabrication (FFF) technique. The proposed material is a polymer-metal composite with a manufacturing process similar to metal injection moulding (MIM). The adopted research methodology included a feasibility study aimed at achieving material homogeneity and compression tests of the developed and manufactured regular cellular structures under quasi-static loading conditions. Several structural topologies were analysed. Experimental results indicated that regular cellular structures made from 316L steel exhibit high mechanical strength and extensive plastic deformation capabilities. The utilized in this work manufacturing technology used combines the advantages of 3D printing process with the potential of powder metallurgy. The proposed technique of structure manufacturing process is much cheaper than other based on melting metallic powders.

Hybrid Evaluation Method of Bridge Bearing Capacity

This study proposes a new method to assess the bearing capacity of similar bridges while avoiding the disadvantages of costly static loading tests. First, we present a detailed evaluation of the bearing capacity for a repaired pre-stressed concrete continuous-beam bridge following a ship collision. We have developed a finite element model, modified it, and combined with two other methods to evaluate its bearing capacity. The first method proposed is the bridge design code-based method, where the bearing capacity is assessed using specified design parameters. The second is the field test-based method, where the bearing capacity is evaluated using field tests combined with structural appearance observation. Considering the relative merits of these two methods, a new and improved method for bearing capacity evaluation is proposed and implemented by combining the design code, finite element model, and field loading tests. The innovation and contribution of this paper lie in obtaining modal parameters through a convenient dynamic load test to predict the static behaviour of the bridge structure based on the modified finite element model. Based on the dynamic test results, the static behaviour of the bridge, predicted by the modified finite element analysis, and the appearance test data of the bridge structure, the bearing capacity of the bridge structure is evaluated.

Experimental study on mechanical properties of pin-trunnion connection nodes of temporary steel brackets for elevated bridges

Currently, the pin connection test exists mainly for unidirectional force loading, while the pin connection of a temporary steel bracket applied to elevated bridges is for bi-directional force. The damage mechanism of the pin connection with bi-directional force is not yet fully understood in research. The effect of the loading direction, single-hole plate end distance and unilateral width ratio a/b, ear plate thickness ratio t1/2 t2, and ear plate shape on the mechanical properties of the pin connection need to be considered. In this study, destructive static loading tests were conducted on eight groups of double-hole pin connections, and the damage mode, bearing capacity, deformation, and strain of the pin connections were determined. The results show that the thickness of the trunnion plate primarily controls the damage mode of the pinned connection and the ratio is smaller for single-trunnion plate damage, which can achieve larger bearing capacity and deformation. The ratio of the end distance of the monocore plate to the width of the single side primarily controls the damage location of the monocore plate, and the ratio varies from large to small, gradually causing tensile damage to the side section, end cleavage damage, and end shear damage. The loading direction has a minor effect on the mechanical properties of the pin connection; however, the tensile deformation is significantly larger than the compressive deformation. By chamfering, the M shape is properly adjusted to optimize the shape of the double trunnion plate, which does not reduce the load-carrying capacity and deformation of the pin connection and can reduce the amount of steel used by 10 %. A comparative analysis of the change in the ear-plate shape before and after the open ear-plate test, determination of the cross-sectional damage location and effective calculation distance b1, and improvement and derivation of a practical method for calculating the load-carrying capacity for engineering are performed, at the same time, it can be applied to projects of different spans, which can greatly improve construction efficiency and reduce labor costs.

Bayesian Inference and Condition Assessment Based on the Deflection of Aging Reinforced Concrete Hollow Slab Bridges

This paper presents a Bayesian inference framework for updating the structural rigidity ratio of aging hollow slab RC bridges using deflection measurements. The framework models the structural rigidity ratio as a stochastic field along the hollow RC slabs, using the Karhunen–Loeve (KL) transform to capture spatial correlation and variation. Bayesian inference is then applied using deflection data from static loading tests, supported by a finite element model (FEM) and a Kriging surrogate model to enhance computational efficiency. The posterior distribution of the structural rigidity ratio is derived using a Markov chain Monte Carlo (MCMC) sampler. The proposed method was tested on an RC bridge with hollow slabs, using deflection measurements taken before and after reinforcement. The Bayesian updates indicated increased structural rigidity ratios after reinforcement, validating the effectiveness of the reinforcement. The deflection predictions from the updated models closely matched the measurements, with the 95% confidence bounds encompassing most of the data. This demonstrates the method’s validity and robustness in capturing the structural improvements post-reinforcement.

Experimental and numerical analysis of single piled raft unit in unconventional soil

ABSTRACT This article explores the behaviour of single piled raft units and their components (raft and pile) under axial compression through experimental and numerical analysis. Prototypes were constructed and subjected to static load tests in silty-clayey sand subsoil. Piles were instrumented at different depths to analyse load distribution and transfer, showing improved load transfer along the pile length. Compared to single piles and rafts, single piled raft units in tropical soil exhibited approximately 10% and 62% higher bearing capacity, respectively. Experimental data validated a numerical model, indicating a stress bulb behaviour reaching 1.5 to 2 times the raft diameter in the pile region, reducing skin friction along the shaft. The pile-raft connection enhanced structural rigidity, increasing bearing capacity and reducing settlements. These findings underscore the significance of pile-raft interaction for foundation performance and efficiency under axial compression.

Multiple impact tests on precast reinforced concrete beams with pressed sleeve connections

Buildings may experience impact loads or even multiple impacts during their service life. Precast concrete (PC) structures have been widely used in engineering, with PC beams serving as the primary load-bearing components in these structures. In this study, six PC beams and two cast-in-place reinforced concrete (RC) beams were designed and manufactured, and drop hammer impact tests were conducted. Additionally, static load tests were conducted on two corresponding PC and RC beams. The experimental study provided benchmark data examining the influence of varying drop hammer mass, impact velocity, and level of pre-damage on the dynamic response of the PC beams, including their failure mode, mid-span deflection, impact force, deflection recovery ratio, and deformation energy consumption. The experimental results confirmed the reliability of using pressure sleeve connection as the assembly and connection form of PC beams. Under equivalent energy conditions, an increase in impact mass simultaneously leads to a decrease in peak and residual deflection of PC beams. This reduction is accompanied by an increase in their average impact force. Under the same impact mass and velocity conditions, the peak deflection of beams exhibiting different degrees of damage exceeded that of undamaged beams, although their residual deflection was relatively lower. In addition, the deflection recovery rate of damaged beams is slightly higher than that of undamaged beams.

Evaluation of retrofitting effect of concrete filling in hollow RC columns using XFEM

Hollow RC columns are widely utilized in the construction of high piers in mountainous regions. Recently, precast hollow RC columns have been increasingly used to enhance transportability and ease of handling, aiding Accelerated Bridge Construction. This paper evaluated the effectiveness of concrete-filling retrofitting measures for hollow RC columns using eXtended Finite Element Method (X-FEM). Our focus was particularly on instances where original hollow sections and post-filled concrete sections don't behave as unified structures. The proposed X-FEM model's reliability was validated through simulations replicating compressive strength tests on molded concrete specimens and previous static loading tests on hollow RC columns conducted to evaluate the efficacy of concrete-filling retrofitting for hollow RC columns. The proposed X-FEM model successfully represents the compressive softening and fracture behavior of concrete under uniaxial compression. It also successfully replicated the lateral load capacity and the crack patterns of hollow RC columns observed in the previous experiments. When comparing the component ratios of bending and shear deformation of the columns, the shear deformation component of the hollow RC column retrofitted with the concrete filling was about 1.5 times larger than that of the solid RC column at each displacement. This result indicates that concrete-filling retrofitting might not enhance the shear capacity of hollow RC columns to the anticipated level in scenarios where the pre-existing hollow portion and the post-filled concrete portion fail to function as unified structures. Based on these findings, this study investigated the efficacy of anchor reinforcement in hollow RC columns filled with concrete to enhance the structural unity of existing and filled portions. The results indicate that anchor reinforcement improved the shear resistance properties by enhancing the structural unity between the pre-existing hollow portion and the post-filled concrete portion.

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.