Vertical Load Tests Research Articles

New approach to predict load-displacement curves of bored piles in homogeneous sandy soils: numerical analyses

Large-diameter bored piles (LDBPs) are increasingly used as foundations elements for various structures such as tall buildings, highway bridges, retaining structures, and power transportation structures, among others. Stabilizing fluids like bentonite or polymers are commonly employed to maintain borehole integrity in soils with high water tables and low resistance. Previous research has highlighted the significant influence of stabilizing fluid and construction methods on the performance of bored piles. Due to the absence of routine design methods for bored piles with stabilizing fluids, full-scale instrumented load tests are regularly conducted to investigate load transfer mechanisms and predict bearing capacity. Alternatively, numerical modeling offers a cost-effective approach to analyze pile performance in layered soil with stabilizing fluids. However, the complexity of this problem, involving different soil layers, and the thin layer of soil-stabilizing fluids in the shear band, presents challenges for numerical analysis. In this study, a numerical model is proposed to analyze bored pile performance in sandy soil, considering different pile diameters and lengths. The model is calibrated using data from instrumented vertical load tests conducted on a 1 m diameter and 24.10 m long bored pile constructed with bentonite. Based on previous research findings, simplifications were made regarding soil layers and stabilizing fluids. Calibration involved utilizing Abaqus/CAE software and the Mohr-Coulomb failure criterion to describe granular material behavior. The soil model comprises a unique sand layer with 12.5 m in length and 36.15 m in depth and mean parameters derived from seven in-situ layers data. Load test simulations involve applying a vertical displacement equivalent to 10% of the pile 1m-diameter and analyzing load-displacement curves, load transfer mechanisms, interface behavior, and field stress-displacement. Initial findings show good agreement between experimental and numerical load results. Parametric analysis investigates the influence of pile geometry and soil properties on various resistances (Q_u,Q_b and Q_f) and coefficients (β,μ and K), proposing normalization expressions to estimate load capacities based on soil and pile properties. This study provides insights for developing supplementary methods to predict bored pile resistance and behavior and conducting future numerical analyses with stabilizing fluids and layered soils, thereby enhancing engineering practices in this field.

Vertical bearing behavior and pile group effect for cemented-soil composite pile groups based on on-site experiments

Bearing characteristics and interactions of a pile group are complex. and there is almost no on-site full-scale test data for cemented-soil composite pile group. In this research, vertical static load tests were conducted on two isolated pile, two-pile group and six-pile group for long-core SDCM pile. The bearing behavior of long-core SDCM pile and the interaction between pile groups have been studied. The results indicate that the long-core SDCM single pile is a typical friction type pile, and cemented soil provides most of the lateral friction resistance for the bearing capacity. In pile groups, pile spacing is the main factor affecting the pile group effect. The model calculation results based on the equivalent pier method are verified using on-site test data and the key parameters in the pile group for long-core SDCM pile including pile spacing Sij, cemented soil Elastic modulus Ec and PHC pipe pile Elastic modulus Ep are analyzed using a mathematical model. Parameter analysis results indicate that the pile group interaction for long-core SDCM pile is mainly reflected in settlement. Group effect is inapparent at pile spacing greater than 4 D. The appropriate value of Ec and Ep are taken in the range of 1.2–1.6 GPa and 30–40 GPa.

Study on the Ratio and Model Test of Similar Materials of Heavily Weathered Granite.

To study the bearing characteristics of rock-socketed single piles on the southeast coast of Fujian Province, we conducted similar material ratio tests and single pile model tests. Initially, based on the mechanical parameters of strongly weathered granite, 10 groups of similar material samples were prepared using iron concentrate powder, barite powder, and quartz sand as aggregates, with rosin and alcohol as the cementing agents and gypsum as the modulating agent. Through triaxial testing and range and variance analysis, it was determined that the binder concentration has the most significant impact on the material properties. Consequently, Specimen 1 was selected as the simulation material. In the model test, the strongly weathered granite stratum was simulated using the ratio of Specimen 1. A horizontal load was applied using a pulley weight system, and the displacement at the top of the pile was measured with a laser displacement meter, resulting in a horizontal load-displacement curve. The results indicated that the pile foundation remained in an elastic state until a displacement of 2.5 mm. Measurements of the horizontal displacement and bending moment of the pile revealed that the model pile behaves as a flexible pile; the bending moment initially increases along the pile length and then decreases, approaching zero at the pile's bottom. The vertical load test analyzed the relationship between vertical load and settlement of the single pile, as well as its variation patterns. This study provides an experimental basis for the design of single pile foundations in weathered granite formations on the southeast coast of Fujian Province and aids in optimizing offshore wind power engineering practices.

Performance of SRC unequal-depth beam-column irregular joint in NPP under progressive collapse

The prototype structure of this study is taken from the main shield building of nuclear power plant (NPP) conventional island facilities. Emphasis is on steel reinforced concrete (SRC) unequal-depth beam-column irregular joints, studying their resistance to progressive collapse via analysis of two 1/5 scale irregular joints. Vertical monotonic loading tests were conducted on the joints, followed by numerical simulations to analyze their mechanical properties, failure modes, and progressive collapse resistance. Experimental analyses focused on irregular joint failure modes, central column load changes with displacement, beam deformations, strain variations in critical sections, and resistance mechanism development. Finite element (FE) software modeled these behaviors and was validated against experimental data. Then, according to the various beam section depths of the connected beams, this research applied the validated numerical models to examine the load-bearing capacity of the irregular joints. The results indicate that the damage of the unequal-depth beam-column irregular joint exhibits significant asymmetric characteristics. In terms of load performance, the performance of the irregular joint depends on the component performance of the shallow beam section. Within a certain range, the greater the height difference between the various beams, the greater the joint bearing capacity, but the stability of the bearing performance deteriorates. The fracture yield of H-shaped steel significantly reduces the bearing capacity, and it is recommended to reinforce shallow beams. Providing data reference for the design of the irregular joints has important practical significance.

Evaluation of sensor-enabled piezoelectric geoelectric cable in cyclic shear tests of subgrade soil under vertical cyclic loads

Of late, deformation of subgrade soil has led to an increasing number of road subsidence diseases. Real-time monitoring of subgrade deformation is critical to ensure the safety of subgrade operations. In this paper, a sensor-enabled piezoelectric geoelectric cable (SPGC) with impedance strain effect and piezoelectric effect is tested. The SPGC impedance and voltage signals obtained by cyclic shear test under vertical static load and cyclic shear test under vertical cyclic load are used to evaluate the monitoring effect. The results showed that normal stress had the greatest effect on the shear strength of the soil, whereas the normal stress and horizontal shear displacement amplitude significantly influenced the strain in the soil. Varying the normal and horizontal shear frequencies had little effect on the shear strength and strain of the soil. The normalized impedance and voltage of the SPGC, respectively, decreased and increased rapidly during the initial stage of the shear cycle; these changes were relatively small during the middle and late stages of the shear cycle. The SPGC voltage waveform revealed the changes in the shear stress and vertical displacement under different normal and horizontal shear frequencies, from which the stability of the subgrade soil under the aforementioned conditions could be evaluated. The variations in the SPGC impedance and effective voltage from the cyclic shear tests under both vertical static and vertical cyclic loads remained essentially consistent with the number of cycles. However, there was a difference in that the trough of the SPGC impedance under the vertical cyclic load was larger than that under the vertical static load; likewise, the effective SPGC voltage under the cyclic load was larger than that under the static load. Through an analysis of the SPGC impedance and voltage signals in the subgrade soil, the consistency of the SPGC-normalized impedance and effective voltage with shear stress was clarified; this helped us evaluate the health of the subgrade and monitor the characteristics of the precursor signals before a slide were to occur, thereby affording us an opportunity to issue timely warnings.

Plate fixation of inferior ramus in pubis-ischium ramus improves mechanical stability in Tile B pelvic injures: a cadaveric biomechanical analysis and early clinical experience

BackgroundManagement of inferior ramus of the pubis-ischium ramus remains controversial, and related research is sparse. The main intention of this study is to describe the biomechanical and clinical outcomes of pubis-ischium ramus fractures in Tile B pelvic injuries and to identify the feasibility and necessity of fixation of the inferior ramus of the pubis-ischium ramus.MethodsThis study comprised two parts: a biomechanical test and a retrospective clinical study. For the biomechanical tests, Tile B-type pelvic injuries were modeled in six cadaver specimens by performing pubis-ischium osteotomies and disruption of the anterior and interosseous sacroiliac ligaments. The superior and/or inferior rami of the pubis-ischium ramus were repaired with reconstruction plates and separated into three groups (A, B, and C). Specimens were placed in the standing position and were loaded axially with two-leg support for three cycles at 500 N. The displacements of sacroiliac joints at osteotomy were measured with Vernier calipers and compared using statistical software. To investigate the clinical outcomes of this technique, 26 patients were retrospectively analyzed and divided into a superior ramus fixation group (Group D) and a combined superior and inferior ramus of the pubis-ischium ramus fixation group (Group E). The main outcome measures were time of operation, blood loss, postoperative radiographic reduction grading, and functional outcomes.ResultsIn the vertical loading test, Group E showed better pelvic ring stability than Group D (P < 0.05). However, the shift of the sacroiliac joints was almost identical among the three groups. In our clinical case series, all fractures in Group E achieved bony union. Group E demonstrated earlier weight-bearing functional exercise (2.54 ± 1.45 vs 4.77 ± 2.09; P = 0.004), earlier bony union (13.23 ± 2.89 vs 16.55 ± 3.11; P = 0.013), and better functional outcomes (89.77 ± 7.27 vs 82.38 ± 8.81; P = 0.028) than Group D. The incidence of sexual dysfunction was significantly lower in Group E than that in Group D (2/13 vs 7/13; P = 0.039). Bone nonunion occurred in two patients in Group D, and two patients in Group E had heterotopic ossification. None of the patients exhibited wound complications, infections, implant failures, or bone–implant interface failures.ConclusionsFixation of the inferior ramus of a pubis-ischium ramus fracture based on conventional fixation of the anterior pelvic ring is mechanically superior in cadaveric Tile B pelvic injury and shows rapid recovery, good functional outcomes, and low incidence of complications.

The vertical loading tests of single and group piles by centrifuge modelling

ABSTRACT Pile foundations are widely used for tall buildings, but determining their capacity and behavior under load often involves expensive and lengthy field tests or imprecise numerical models. This research employed a centrifuge to perform vertical loading tests on single and grouped piles in dry sand, subjected to 100 times gravitational acceleration, to investigate pile capacity and load transfer mechanisms. The results from centrifuge modeling, numerical simulations, and field tests were consistent. The total pile capacity for a single pile was 5800 kN/m², while short and long pile groups had capacities of 6800 kN/m² and 9200 kN/m², respectively. End-bearing accounted for 40% of the capacity in single and short pile groups, and 13% in long pile groups. Surface friction was 95 kN/m² for single piles and 140 kN/m² for grouped piles. A method for estimating total pile capacity based on soil properties showed good agreement with empirical results.

Analysis of influencing factors of penetration mechanism and vertical bearing characteristics of monopile in calcareous sand: Laboratory model testing and in-situ testing

The construction of islands and reef engineering structures in marine environments has been a hot topic in recent years, and calcareous sand, which possesses unique physical properties, is widely distributed on islands and reefs. Due to the properties of calcareous sand, engineering problems such as pile slipping while driving and a low bearing capacity during service can occur. To address the key problem of pile‒soil interactions in calcareous sand foundations, laboratory model and in situ tests were conducted, accounting for factors such as impact energy, relative density, pile-forming method, and pile aspect ratio. First, the penetration mechanism of hammered piles in calcareous sand was studied. Then, the differences in vertical bearing characteristics between hammered and pre-embedded piles under different conditions were explored. The pile driving test results showed that a higher impact energy and lower relative density are more conducive to pile sinking. Moreover, as the number of hammer drops and dynamic penetration resistance increase with increasing burial depth, the pile tip resistance is the main factor limiting pile penetration in calcareous sand. The vertical static loading test revealed that particle breakage accelerates soil redistribution around the pile and that compaction enhances the bearing capacity of the pile. The pile aspect ratio, relative density and pile-forming method also play major roles in the vertical bearing capacity of piles in calcareous sand. In addition, the skin friction of a pile rapidly increases to the ultimate value along a multisegment trend of polyline functions. Similarly, the pile tip resistance rapidly increases at the initial loading stage, exhibiting the behavior of an end-bearing pile. The in situ test results indicated that the pile penetration depth in coral calcareous sand is an important factor affecting the bearing capacity.

Post-tensioning system as a strengthening solution for masonry arch bridges: numerical and experimental results

One of the most common bridge typologies in roadway and railway networks in Italy is the masonry arch bridge, typically built more than a hundred years ago. To keep these structures operatives with increasing traffic load, strengthening interventions are required in some cases. The solution investigated in this work is the external post-tensioning system, which consists of applying external loads to the arch by means of tensioned cables, resulting in a better configuration of internal forces. An experimental campaign was conducted on pre-damaged single span masonry arches by anchoring the cables to the intrados of the arch. The results of cyclic eccentric vertical load tests show an increase in displacement and load-carrying capacity. Numerical tests were performed to validate the experimental results using the rigid-block analysis method. The comparison between the experimental and numerical results is reported in terms of limit load capacity.

Study on the behavior of short pile groups on soft soil with sand leveling using a smallscale physical model with schneebeli analog material

This paper examines the effectiveness of short piles on soft ground with leveling sand, using a 2D small model. The study focuses on the geology of the Mekong Delta, which consists of a thick layer of soft soil and a layer of leveling sand with a thickness of 2-5m. The use of small and short piles (less than 30x30 cm and 5m or less) is a viable option for low-rise buildings in such conditions. The model replaces the sandy soil with a Schneebeli analog material and the weak clay with EPS foam, while short reinforced concrete piles are replaced by steel bars of the square cross-section. The vertical load tests were conducted on groups of piles, with variable parameters such as pile spacing, s, and the distance from the pile tip to the boundary of two soil layers, H. The results show that when the pile spacing, s, is constant and the distance from the pile tip to the boundary of two soil layers, H, decreases, as well as the deformed soil area under the pile tip. Conversely, when the pile spacing, s, increases, the failure of the soil under the pile tip becomes more localized. The use of a footing increases the bearing capacity of the pile group but also increases the vertical strain of the foam layer in both vertical and horizontal directions. Overall, the study shows that reinforcing soil with short piles significantly improves bearing capacity, increasing it by 2.3 to 3.5 times compared to unreinforced soil.

Stability of the ‘Tensyudai’ of a Japanese castle under a long-term load

‘Tensyudai’ is the term used for the truncated masonry base that supports the main tower (Tensyukaku) of a Japanese castle. In response to concerns regarding the structural integrity and conservation of Tensyudai masonry walls, this study seeks to investigate the mechanism of their collapse and load capacity. A reduced-scale model of Tensyudai, based on Osaka Castle, was constructed and subjected to a vertical load test to evaluate its three-dimensional mechanical properties. This paper postulates a collapse mechanism, and the equilibrium of forces for the Sumiishi and Hiraishi sections of the Tensyudai is analysed, considering the arch effect. Experimental results are compared, using a series of equations to calculate the collapse burden (q c). Additionally, the safety factor is determined, based on the active earth pressures at various masses. The findings indicate that the safety factor of a standard Tensyukaku weight is approximately 25, which rises with increased Tensyukaku weight. Moreover, this study contributes to future research and preservation efforts for historical structures, by shedding light on the structural stability and safety of Tensyudai masonry walls. It can also provide basic data for considering the protection of other masonry wall structures from earthquakes.

Comparing and Evaluating the Effect of Different Thickness of Two Metal-Free Restoration on Fracture Resistance in Molar Implant Prosthesis

Aim: The objectives of this article was to determine the minimum thickness of two monolithic materials for a posterior implant prosthesis. Materials and methods sixty monolithic IPS E.MAX CAD and zirconia crowns with different occlusa l thicknesses were made with the use of a computer-aided design/computer-aided manufacturing technique was divided into 3 experimental groups: group (1) 0.5 mm group (2) 0.7mm group (3)1mm. A universal testing machine was used to determine the fracture load value. The restoration was loaded until fracture; the fracture resistance was registered. Two-way ANOVA has been used to examine the data., followed by the least significant difference LSD test. One-way ANOVA variance analysis was used to examine the differences in fracture load of monolithic zirconia or IPS E.MAX CAD at various thicknesses (p=0.05). Results vertical load test revealed that the fracture resistance of monolithic zirconia higher than the lithium disilicate crown (E.MAX CAD). The results showed that the highest mean value of fracture load test was obtained in the ice zirconia translucent with 1mm thickness group (1880N), while the lowest mean value was in the E.MAX CAD with thickness 0.5mm Group (223N). Conclusions: The fracture resistance of CAD-CAM monolithic crowns is influenced by the occlusal thickness. zirconia prosthesis with occlusal thickness 0.7mm,1mm had a high fracture resistance when compared with E.MAX CAD.

Mechanical behavior of Dou-Gong brackets in Chinese traditional timber structures: An experimental study

This study investigated the mechanical behaviour of Dou-Gong brackets with different structural forms, including Jixinzao and Touxinzao. Scaled Dou-Gong models were designed and fabricated at a 1:3.4 geometrical ratio. Vertical load tests were conducted to determine the failure modes, load-displacement response, stiffness degradation, and deformation capacity of the Dou-Gong models. Under vertical load, the primary failure modes of the Dou-Gong models were observed at the Lu-Dou, Nidao-Gong, and Hua-Gong component. The specimens demonstrated excellent load-bearing capacity and high deformation resistance. The Jixinzao Dou-Gong model exhibited a 15.0% higher ultimate load-carrying capacity than the Touxinzao Dou-Gong due to the presence of transverse arches. The number of transverse arches in the Dou-Gong models positively correlated with the compression stiffness, while their presence had a negligible effect on stiffness degradation rates. The Touxinzao Dou-Gong model exhibited superior ductility, characterized by a ductility coefficient 8.57% higher than that of the Jixinzao Dou-Gong model. Although the regular layering of the Dou-Gong models was disrupted by Ang component, the models remained stable in both the vertical and horizontal directions. The bi-linear model can effectively simulate the deformation behaviour of the Dou-Gong model under vertical load.

Vertical compressive bearing performance and optimization design method of large-diameter manually-excavated rock-socketed cast-in-place piles

To study the vertical compressive bearing characteristics of large-diameter rock-socketed cast-in-place piles, eight manually-excavated rock-socketed cast-in-place piles were subjected to vertical compressive on-site load and pile stress tests. The test results showed that the load–displacement (Q-s) curves of the eight test piles were all slow-varying, and the settlement of the piles was less than 11 mm, which met the minimum engineering requirements. The unloading rebound rate was between 55 and 75%, and the elastic working properties of the piles were apparent. The pile axial force gradually decreased with depth, and the slope of the axial force distribution curve reached a minimum in the moderately weathered muddy siltstone layer while the pile side friction resistance reached its maximum value. Pile end friction increases with the increase of load. But the pile end resistance was inversely proportional to the single pile length-to-diameter (L/D) ratio and the depth of rock embedment for the pile. The percentage of pile side friction resistance under maximum load was 86%, indicating that these were characteristic friction piles. Based on the test results and the current Chinese code, the friction coefficient of the pile side soil layer η and the total resistance coefficient of the rock-socketed section ζ were introduced. A revision to the calculation equation for the vertical bearing capacity of the rock-socketed cast-in-place pile in the code was proposed, together with an optimization design method for large-diameter rock-socketed cast-in-place piles.

Bearing characteristics of model piled raft foundations supported by sheet piles

Recently, with the development of new piling methods, steel sheet piles can be penetrated into various types of ground with high quality and precision. Although pipe piles are used for piled raft foundations, sheet piles could become an alternative. Thus, the aim of this research study is to demonstrate the possibility of using sheet piles for piled raft foundations. In this study, a series of model tests was carried out first to investigate the load transfer behaviours of model piled raft foundations supported by three types of piles in an air-dried sand ground. Two of them were composed of sheet piles, called plate piles and box piles, respectively, and the other was composed of conventional pipe piles for comparison. Both vertical and horizontal load tests were carried out, and the load sharing between the raft and piles was carefully investigated. As the plate pile foundation (PPF) exhibited outstanding behaviours, numerical analyses were carried out using finite-element methods to investigate the foundation–soil interaction in PPFs. According to test and calculated results, a piled raft foundation supported by sheet piles would be a promising alternative to a conventional pipe pile foundation, especially in highly seismic areas.

Biomechanical Comparison between Inverted Triangle and Vertical Configurations of Three Kirschner Wires for Femoral Neck Fracture Fixation in Dogs: A Cadaveric Study.

The purpose of this study was to compare single-cycle axial load and stiffness between inverted triangle and vertical configurations of three Kirschner wires (K-wires) for femoral neck fracture fixation in small dog cadaveric models. In each of the eight cadavers, the basilar femoral neck fracture model was prepared on both sides of the femur. One side of the femur was stabilized with three 1.0 mm K-wires of an inverted triangle configuration (group T), and the other femur was stabilized with a vertical configuration (group V). Postoperatively, the placement of the K-wires was evaluated with radiographic and computed tomography (CT) images, and static vertical compressive loading tests were performed. The mean yield load and the lateral spread were significantly higher in group T compared to group V (p = 0.023 and <0.001). On the cross-section of femoral neck at the level of the fracture line, the surface area between K-wires was significantly larger (p < 0.001) and the mean number of cortical supports was significantly higher in group T (p = 0.007). In this experimental comparison, the inverted triangle configuration of three K-wires was more resistant to failure under axial loading than the vertical configuration for canine femoral neck fracture fixation.

Experimental study on seismic behaviour of an unreinforced precast wall-slab structure based on UHPC sandwich panels

Heavy prefabricated components and complex reinforcement arrangements are regarded as main problems affecting the construction efficiency of traditional precast concrete structures. This study proposes a new wall-slab structure based on prefabricated ultra-high performance concrete (UHPC) sandwich panels, which features with light weight, no reinforcement, fast bolt-based dry connection and insulation system integrated. A large-scale two-story substructure is prefabricated and assembled, which consists of eight sandwich walls and four sandwich slabs. Vertical load test and lateral cyclic load test are conducted to investigate the mechanical behavior of the wall-slab structure. The cracking patterns, failure modes, bearing capacity, stiffness, energy dissipation capacity, and strain distribution are analyzed. Test results demonstrate that the maximum and cracking base shear forces are about 10 and 7 times the sum of gravity and live load of the specimen, respectively. The various connections between precast panels are all reliable without obvious damage during the test. Therefore, the new wall-slab structure has excellent seismic performance, which can even avoid cracking under severe earthquake. In addition, design suggestions are proposed based on the test results, regarding the design principle, inter-story drift ratio limit and panel connections.

Investigations of piles by bidirectional static loading test in Astana soils

The article presents the results of vertical static load tests of diametral and deep bored piles specially conducted at the construction site of EXPO-2017 in Astana, Kazakhstan. The methodology for determining the bearing capacity of the pile is summarized. Bored piles with a length of 31.5 m and a diameter of 1000 mm were tested. Vertical static load tests were conducted for the following load configurations: Bidirectional Static Loading Test (according to ASTM D8169), Static Compression Loading Test according to ASTM D1143-07 and Static Loading Test according to GOST 5686-12. The method presented in the paper can serve as practical guidelines to assess the capacities of bored piles installed in the field. This geotechnical investigation is important for understanding the soil-structures interaction on difficult soil ground conditions related to the construction sites.

国宝法起寺三重塔の最上層の構造特性に関する模型実験

In this study, a static vertical load test was conducted on the uppermost layer of the 1/10 model of the Hokiji three-storied pagoda.

Mechanical behaviors of Tou-Kung in historic timber structures subjected to vertical load

This paper investigates the mechanical behaviors of Tou-Kung under the action of vertical loads. A 1/3.52 scaled model of intact Tou-Kung fabricated according to the Building Standards of the Qing Dynasty was carried out on vertical loading test. The failure modes, vertical load–displacement curves, and vertical stiffness analysis are analyzed. The results show that the main failure modes of Tou-Kung are the compressive splitting of Da-Tou and plastic compressive deformation of Qiao’s middle part along the radial direction. The vertical load–displacement curves of intact Tou-Kung can be divided into three stages: elastic, plastic, and hardening. In general, the vertical load and displacement of Tou-Kung increases as the loading progresses. And the vertical stiffness increases first, then decreases, and finally increases. On this basis, numerical simulation is used to investigate the effect of overall tilting on Tou-Kung’s mechanical behaviors. It can be found that the tilting of Tou-Kung significantly changes the load transferring path in Tou-Kung, and the stress distribution of Da-Tou and Qiao gradually changes from symmetry to asymmetry as the tilting angle increases. Furthermore, the stress in the embedded area between the Da-Tou and Qiao is the highest, which is consistent with the test results. The vertical load–displacement curves of all damaged FEMs show the same change trend. However, with the increase of tilting angle, the initial stiffness, ultimate load and ultimate stiffness decrease.