Field behaviour of screw micropiles subjected to axial loading in cohesive soils

2018 ◽  
Vol 55 (1) ◽  
pp. 34-44 ◽  
Author(s):  
Zhengyang Guo ◽  
Lijun Deng
Keyword(s):  
Load Transfer ◽  
Limit State ◽  
Field Tests ◽  
Axial Loading ◽  
Cohesive Soils ◽  
Test Results ◽  
Cone Penetration ◽  
Load Transfer Mechanism ◽  
Theoretical Results ◽  
Field Behaviour

Field tests of full-scale screw micropiles with a diameter varying from 76 to 114 mm and a length varying from 1.6 to 3 m were undertaken to investigate the axial pile capacities, load-transfer mechanism, and end installation torques of the piles in cohesive soils. Forty tests were performed on piles subjected to axial compressive and tensile loads. Six tests were instrumented with strain gauges on the pile shaft. Results showed the piles reached the limit state before the displacement exceeded 10% of the shaft diameter. The majority of axial load was transferred to the threaded segment. The adhesion coefficient of the top smooth shaft at the limit state was less than 0.1. The failure mode along the cylindrical threaded shaft was cylindrical shearing along the edge of the threads; the threads increased the axial capacities of the segment. Axial capacities of the threaded tapered segment were 43% on average greater than that of a cylindrical segment with the equivalent volume. Compressive capacities of all test piles were estimated and the results agreed reasonably well with the measured capacities. A theoretical torque model was proposed to estimate the end installation torques based on the cone penetration test results; the theoretical results matched the measured end torques very well.

Geotechnical capacity of hollow-bar micropiles in cohesive soils

2014 ◽  
Vol 51 (10) ◽  
pp. 1123-1138 ◽  
Author(s):  
Ahmed Yehia Abd Elaziz ◽  
M. Hesham El Naggar
Keyword(s):  
Parametric Study ◽  
Load Transfer ◽  
Ground Improvement ◽  
Field Tests ◽  
Element Model ◽  
Cohesive Soils ◽  
Silty Clay ◽  
Test Results ◽  
Axial Capacity ◽  
Load Transfer Mechanism

Hollow-bar micropile construction, also known as self-drilled, is becoming a popular option because it allows faster installation processes and ground improvement at the same time. This paper presents a field study and numerical investigation on the behaviour of single hollow-bar micropiles embedded in a stiff silty clay deposit. Four hollow-bar micropiles were installed using an air-flushing technique employing large drilling carbide bits. Five axial tests were conducted on the four micropiles, comprising three compression and two tension monotonic axial tests. The results of the field tests are presented and analyzed in terms of load–displacement curves. A two-dimensional axisymmetric finite element model (FEM) was created and calibrated using the field test results. The calibrated FEM was utilized to select an appropriate failure criterion for hollow-bar micropiles depending on the load-transfer mechanism of the micropiles. In addition, the model was employed to carry out a parametric study to investigate the effect of the installation methodology, hollow-bar micropile geometry, and shear strength of the surrounding soils on the micropile capacity. Based on the outcomes of the parametric study, an equation is proposed to estimate the axial capacity of hollow-bar micropiles in cohesive soils.

Overlapped K Joints in Circular Hollow Sections Under Axial Loading (An Investigation of the Factors Affecting the Static Strength Using Numerical Modeling)

1996 ◽  
Vol 118 (1) ◽  
pp. 53-61 ◽  
Author(s):  
E. M. Dexter ◽  
M. M. K. Lee ◽  
M. G. Kirkwood
Keyword(s):  
Failure Modes ◽  
Load Transfer ◽  
Numerical Models ◽  
Axial Loading ◽  
Static Strength ◽  
Test Results ◽  
Factors Affecting ◽  
Current Design ◽  
The Relationship ◽  
Design Guidance

Overlapped joints are generally regarded as having higher strengths than otherwise identical, simple nonoverlapping joints because of the more efficient load transfer between braces. However, not only that relatively little research has been carried out on such joints, the few test data from which current design guidance was derived has also been recently rejected. This paper reports the first phase of a parametric finite element study into the strength of overlapping K joints under axial loading. The numerical models were validated and calibrated against existing gap and overlapped K joint test results, and various factors which affect the relationship between the strength and the overlap amount, such as boundary restraints, hidden welds, loading hierarchy, and failure modes, were investigated. The results of the work presented lay the foundation for a future parametric study.

Methods of improving the performance of drilled piers in weak rock

1983 ◽  
Vol 20 (4) ◽  
pp. 758-772 ◽  
Author(s):  
R. G. Horvath ◽  
T. C. Kenney ◽  
P. Kozicki
Keyword(s):  
Load Transfer ◽  
Limit State ◽  
Elastic Behaviour ◽  
Weak Rock ◽  
Test Results ◽  
Shaft Resistance ◽  
Load Tests ◽  
Rock Interface ◽  
Load Displacement ◽  
State Analysis

Investigations were made of two methods to improve the load–displacement performance of concrete piers socketed into very weak rock. Results of load tests on six full-size piers are reported.One method involved cutting grooves into the socket wall to roughen the pier–rock interface and thus increase the shaft resistance component of load support. Two types of piers were tested: piers with a void at the base (shaft resistance only) and piers having both shaft resistance and end-bearing resistance. In the latter case, flatjack load cells were installed to measure base loads. The test results indicated that increasing the roughness of the socket wall can cause important increases in shaft resistance.The second method involved the application of preload to the socket base to increase the end-bearing component of load support at small displacements. The test results showed that preloading the socket base resulted in a stiffer load–displacement behaviour of the pier–socket system.The initial portions of the load–displacement curves from all the tests were linear, reflecting elastic behaviour of the pier–socket system. This elastic behaviour did not appear to rely on socket roughness. Beyond the limit of proportionality, the load–displacement behaviour of each pier departed from that of an elastic system, and this departure was more rapid for the piers with smooth sockets than for those with roughened socket walls. Preloading the socket base caused the elastic range of loading to be extended.Two design approaches, limit-state analysis and elastic-state analysis, are discussed. Keywords: drilled piers and caissons, large-bored piles, shaft resistance, grooved shaft, load transfer, preload, shale, weak rock.

Load transfer mechanism of a load distributive compression anchor installed in weathered rock layer

2021 ◽  
Author(s):  
Gyu-Beom Shin ◽  
Bum-Hee Jo ◽  
Sung-Ha Baek ◽  
Sung-Ryul Kim ◽  
Choong-Ki Chung
Keyword(s):  
Shear Stress ◽  
Interference Effect ◽  
Load Transfer ◽  
Field Tests ◽  
Transfer Mechanism ◽  
Efficient Design ◽  
High Concentration ◽  
Construction Sites ◽  
Pull Out ◽  
Load Transfer Mechanism

The demand for a load distributive compression anchor (LDCA) in construction sites has been increasing, owing to its high bearing capacity and removable steel strand. As an LDCA comprises multiple anchor bodies and unbonded steel strands, the load applied to the strand generates a distributive compressive stress in the grout, preventing high concentration of grout–ground shear stress. Unlike in the conventional anchors, in an LDCA, independent load transfer of each anchor body induces interference effect between adjacent anchor bodies. Therefore, for an efficient design of an LDCA, it is necessary to investigate the load transfer mechanism considering the effect of multiple anchor bodies. In this study, a series of anchor pull-out field tests were conducted for LDCAs consisting of single, double, and triple anchor bodies spaced by 1, 2, and 3 m for all cases. According to the test results, the LDCA showed a stiffer load–displacement behavior with an increase in the number and spacing of the anchor body. The multiple anchor bodies of the LDCA generated an overlapping of the grout axial load and induced its rapid dissipation, increasing the grout–ground shear stress. This interference effect was more clearly observed with a decrease in the anchor body spacing.

Research on Load Transfer Mechanism of Steel-Concrete Joint Section of Hybrid Beam Cable-Stayed Bridge

2013 ◽  
Vol 639-640 ◽  
pp. 216-219
Author(s):  
Da Li Zhang ◽  
Yu Wen Bao ◽  
Jian Hui Gao ◽  
Lin Xiao ◽  
Xiao Zhen Li
Keyword(s):  
Load Transfer ◽  
Limit State ◽  
Transfer Mechanism ◽  
Test Model ◽  
Element Analysis ◽  
Cable Stayed Bridge ◽  
Hybrid Beam ◽  
Composite Joint ◽  
Load Transfer Mechanism ◽  
Joint Section

The WuSu Bridge of HeiXiaZi Island is a hybrid girder cable-stayed bridge with one pylons and single cable plane. Based on the similarity principle, a 1:3 reduced scale test model of steel-concrete joint section was designed to study the load transfer mechanism and verify the rationality. The test model was loaded according to the serviceability limit state, and the stress distribution of control sections and main members were obtained. The finite element analysis on the test model was carried out and the load transfer mechanism was studied by the way of combining the test results and the FEA results. As shown in the results, the load from steel is smoothly delivered to concrete through steel-concrete joint section, and the load distribution of the components of steel-concrete joint section is rational. It is proved that the steel-concrete composite joint section is reasonably designed.

Dynamic Analysis and Experimental Research of Laser Cutting Machines

2014 ◽  
Vol 915-916 ◽  
pp. 31-34
Author(s):  
Qing Ping Zhang ◽  
Zheng Ru Wang ◽  
Yan Fang Wang
Keyword(s):  
Machine Tool ◽  
Modal Analysis ◽  
Laser Cutting ◽  
Machining Accuracy ◽  
Dynamics Analysis ◽  
Theoretical Base ◽  
Test Results ◽  
Cutting Machine ◽  
Manufacturing Errors ◽  
Theoretical Results

Vibration is one of the most important problems in laser cutting machine tool, which causes the manufacturing errors, also influences the machining accuracy of the parts. Modal analysis can calculate vibration type of structures. The paper presents how to use the powerful FEA software ANSYS to do the modal analysis on laser cutting machine tool and also studies the undamped free vibration on laser cutting machine tool. Finally, the test results and theoretical results were compared to verify the rationality of the modal, these provide theoretical base and conditions for dynamics analysis and optimal design.

scholarly journals Estimation of Outdoor PM2.5 Infiltration into Multifamily Homes Depending on Building Characteristics Using Regression Models

2021 ◽  
Vol 13 (10) ◽  
pp. 5708
Author(s):  
Bo-Ram Park ◽  
Ye-Seul Eom ◽  
Dong-Hee Choi ◽  
Dong-Hwa Kang
Keyword(s):  
Regression Analysis ◽  
Correlation Analysis ◽  
Field Test ◽  
Outer Surface ◽  
Regression Models ◽  
Field Tests ◽  
Test Results ◽  
Correlation And Regression Analysis ◽  
Building Characteristics ◽  
Pm2.5 Concentration

The purpose of this study was to evaluate outdoor PM2.5 infiltration into multifamily homes according to the building characteristics using regression models. Field test results from 23 multifamily homes were analyzed to investigate the infiltration factor and building characteristics including floor area, volume, outer surface area, building age, and airtightness. Correlation and regression analysis were then conducted to identify the building factor that is most strongly associated with the infiltration of outdoor PM2.5. The field tests revealed that the average PM2.5 infiltration factor was 0.71 (±0.19). The correlation analysis of the building characteristics and PM2.5 infiltration factor revealed that building airtightness metrics (ACH50, ELA/FA, and NL) had a statistically significant (p < 0.05) positive correlation (r = 0.70, 0.69, and 0.68, respectively) with the infiltration factor. Following the correlation analysis, a regression model for predicting PM2.5 infiltration based on the ACH50 airtightness index was proposed. The study confirmed that the outdoor-origin PM2.5 concentration in highly leaky units could be up to 1.59 times higher than that in airtight units.

scholarly journals Verification of Brittle Fracture Criteria for Bimaterial Structures

2014 ◽  
Vol 8 (1) ◽  
pp. 44-48
Author(s):  
Grzegorz Mieczkowski ◽  
Krzysztof Molski
Keyword(s):  
Experimental Data ◽  
Composite Materials ◽  
Cyclic Loading ◽  
Brittle Fracture ◽  
Axial Loading ◽  
Loading Conditions ◽  
Fracture Criteria ◽  
Interfacial Cracks ◽  
Theoretical Results ◽  
Brittle Fracture Criteria

Abstract The increasing application of composite materials in the construction of machines causes strong need for modelling and evaluating their strength. There are many well known hypotheses used for homogeneous materials subjected to monotone and cyclic loading conditions, which have been verified experimentally by various authors. These hypotheses should be verified also for composite materials. This paper provides experimental and theoretical results of such verifications for bimaterial structures with interfacial cracks. Three well known fracture hypotheses of: Griffith, McClintock and Novozhilov were chosen. The theoretical critical load values arising from each hypotheses were compared with the experimental data including uni and multi-axial loading conditions. All tests were carried out with using specially prepared specimens of steel and PMMA.

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