• Steel and Composite Structures
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• v.45 no.5
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• pp.665-682
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• 2022

In the current study, punching behavior of Reinforced concrete (RC) isolated footings was experimentally and numerically investigated. The experimental program consisted of four half-scale RC isolated footing specimens. The test matrix was proposed to show effect of footing area, reinforcement mesh ratio, adding internal longitudinal reinforcement bars and stirrups on the punching response of RC isolated footings. Footings area varied from 1200×1200 mm2 to 1500×1500 mm2 while the mesh reinforcement ratio was in the range from 0.36 to 0.45%. On the other hand, a 3D non-linear finite element model was constructed using ABAQUS/standard program and verified against the experimental program. The numerical results agreed well with the experimental records. The validated numerical model was used to study effect of concrete compressive strength; longitudinal reinforcement bars ratio and stirrups concentration along one or two directions on the ultimate load, deflection, stiffness and failure patterns of RC isolated footings. Results concluded that adding longitudinal reinforcement bars did not significantly affect the punching response of RC isolated footings even high steel ratios were used. On the contrary, as the stirrups ratio increased, the ultimate load of RC isolated footings increased. Footing with stirrups ratio of 1.5% had ultimate load equal to 1331 kN, 19.6% higher than the bare footing. Moreover, adding stirrups along two directions with lower ratio (0.5 and 0.7%) significantly enhanced the ultimate load of RC isolated footings compared to their counterparts with higher stirrups ratio (1.0 and 1.5%).

• Steel and Composite Structures
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• v.50 no.2
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• pp.217-235
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• 2024

Concrete-filled steel tubes (CFSTs) nowadays are widely used as the main parts of momentous structures, and its connection has gained increasing attention as the complexity in configuration and load transfer mechanism. This paper proposes a novel CFST pier-to-footing incorporating tube-confined RC encasement. Such an innovative approach offers several benefits, including expedited on-site assembly, effective confinement, and collision resistance and corrosion resistance. The seismic behavior of such CFST pier-to-footing connection was studied by testing eight specimens under quasi-static cyclic lateral load. In the experimental research, the influences on the seismic behavior and the order of plastic hinge formation were discussed in detail by changing the footing height, axial compression ratio, number and length of anchored bars, and type of confining tube. All the specimens showed sufficient ductility and energy dissipation, without significant strength degradation. There is no obvious failure in the confined footing, while local buckling can be found in the critical section of the pier. It suggests that the footing provides satisfactory strength protection for the connection.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.1
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• pp.183-192
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• 2008

Generally, application of steel pipe pile as deep foundation member needs special requirement for the connection method between steel pipe pile and concrete footing. Even though two types of connection method are suggested in the korea highway bridge code, type-B method is prevalent. In this study, vertical, lateral, and tension loading test are done for two types of type B connection to review stress concentration, formation and behavior of imaginary RC column in the footing. Welding type and hook type as the connection method are considered in this study. Test results show that welding type have the more reserve capacity than hook type and the specimens connected by the welding type behave as the imaginary RC column in the footing. However, the specimens connected by the hook type did not behave as the imaginary RC column in the footing but behave as the hinge.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.476-485
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• 2006

The connection system of steel pile and RC footing is an important structure, because the total load of upper construction should be transferred through this joint construction of different two materials-steel and RC-with strongly changed section area. Although many connection systems have been developed, their structural and economical efficiency and workability are often insufficient. Therefore, a new connecting system was developed to improve the problems of current systems. The divided arc plate could improve the workability and economical efficiency, structural efficiency could be reached by welding construction. The main purpose of the research is to evaluate the structural behavior of the new designed connection system through experiments and numerical analysis.

• Earthquakes and Structures
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• v.7 no.6
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• pp.1001-1024
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• 2014

The size of spread footings was found to be unnecessarily large from some actual engineering practices constructed in Taiwan, due to the strict design provisions related to footing uplift. According to the earlier design code in Taiwan, the footing uplift involving separation of footing from subsoil was permitted to be only up to one-half of the foundation base area, as the applied moment reaches the value of plastic moment capacity of the column. The reason for this provision was that rocking of spread footings was not a favorable mechanism. However, recent research has indicated that rocking itself may not be detrimental to seismic performance and, in fact, may act as a form of seismic isolation mechanism. In order to clarify the effects of the relative strength between column and foundation on the rocking behavior of a column, six circular reinforced concrete (RC) columns were designed and constructed and a series of rocking experiments were performed. During the tests, columns rested on a rubber pad to allow rocking to take place. Experimental variables included the dimensions of the footings, the strength and ductility capacity of the columns and the intensity of the applied earthquake. Experimental data for the six circular RC columns subjected to quasi-static and pseudo-dynamic loading are presented. Results of each cyclic loading test are compared against the benchmark test with fixed-base conditions. By comparing the experimental responses of the specimens with different design details, a key parameter of rocking behavior related to footing size and column strength is identified. For a properly designed column with the parameter higher than 1, the beneficial effects of rocking in reducing ductility and the strength demand of columns is verified.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1607-1614
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• 2011

As the connection between spread footing and pile is very important structural connection, it acts as the inter-loading medium to transfer the rail loads applied by superstructure to ground through the body pile of foundation. The experimental study is the method how to reinforce the pile cap between steel pile and footing utilizing perfobond plate with protruding keys. It were experimented on the compression punching tests and bending moment tests against the vertical loading and horizontal loadings acting on head of steel tube pipe. As a result, the tension capacity of the perfobond plate exhibited the superior performance due to the interlocking or dowel effects by the sheared keys of perfobond plate, and there were showing the sufficient strength and ductile capacity against the bending moment of horizontal loading tests. Therefore, it is judged that "the embedded method of perfobond plate in pile cap and footing" which is utilizing the shear connection of perfobond plate with protruding keys has a sufficient structural stability enough to be replaced with the current specification of reinforced method of pile cap with vertically deformed rebar against the vertical compression loads and bending moments that are able to occur in the combination structure of steel pile and the footing foundation.

• Geomechanics and Engineering
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• v.13 no.2
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• pp.255-267
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• 2017

Soft clay strata can suffer significant settlement or stability problems under building loads. Among the methods proposed to strengthen weak soils is the application of a stone masonry trench (SMT) beneath RC strip foundations (as a masonry pad-stone). Although, SMTs are frequently employed in engineering practice; however, the effectiveness of SMTs on the ultimate bearing capacity improvement of a strip footing rested on a weak clay stratum has not been investigated quantitatively, yet. Therefore, the expected increase of bearing capacity of strip footings reinforced with SMTs is of interest and needs to be evaluated. This study presents a two-dimensional numerical model using the discrete element method (DEM) to capture the ultimate load-bearing capacity of a strip footing on a soft clay reinforced with a SMT. The developed DEM model was then used to perform a parametric study to investigate the effects of SMT geometry and properties on the footing bearing capacity with and without the presence of surcharge. The dimensions of the SMTs were varied to determine the optimum trench relative depth. The study showed that inclusion of a SMT of optimum dimension in a soft clay can improve the bearing capacity of a strip footing up to a factor of 3.5.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.823-828
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• 2002

Lap splice in plastic hinge region of RC bridge piers is inevitable because of the constructional joint between footing and column. RC circular columns with lap-splice in plastic hinge region are widely used in Korean highway bridges. It is, however, believed that there we not many experimental research works for nonlinear behavior of these columns subjected to earthquake motions. This study has been peformed to verify the effect of lap splice and confinement steel ratio for the seismic behaviour of reinforced concrete bridge piers. Quasi-static test have been done to investigate the physical seismic performance of RC bridge piers, such as displacement ductility.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.877-882
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• 2001

Lap splice in plastic hinge region of RC bridge piers is inevitable because of the constructional joint between footing and column. RC circular columns with lap-splice in plastic hinge region are widely used in Korean highway bridges. It is, however, believed that there are not many experimental research works for nonlinear behavior of these columns subjected to earthquake motions. This study has been performed to verify the effect of axial force, lap splice and confinement steel ratio for the seismic behaviour of reinforced concrete bridge piers. Quasi-static test have been done to investigate the physical seismic performance of RC bridge piers, such as displacement ductility and enemy absorption.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.288-296
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• 2003

Generally, application of steel pipe pile as deep foundation member needs special requirement for the connection method between steel pipe pile and concrete footing. Even though two types of connection method are suggested in the related specification, type B-method is provident. To investigate real structural behavior of type B connection, several load tests are done with carefully designed experimental system. The purpose of this experiment is mainly focused on the understanding of actual behavior which can be predicted by design theory. At this research stage, vertical and lateral loading test are done for three types of specimen to review stress concentration, formation and behavior of imaginary RC column in the footing and effect of non-slip device installed in the steel pipe pile. The load resistance mechanism in these specific connection method is predicted based on both experimental results. The three-dimensional finite element modeling is also done for the purpose of comparison between numerical and experimental result. With all the results gained from experiment the structural behavior of imaginary RC column in the design concept is confirmed. The role of non-slip device is very important and it affects the resistance capacity with help of composite action of concrete and steel pipe pile.