Chang-Soon Rha

Nonlinear Efficiency of Bored Pile Group under Lateral Loading

A 3×3 bored pile group consisting of nine cast-in-drilled-hole reinforced concrete shafts and a comparable single-shaft were subjected to reversed cyclic, lateral head loading to investigate group interaction effects across a wide range of lateral displacements. The piles had the same diameter of d=0.61 m and similar soil conditions; however, various equipment constraints led to two differences: (1) a fixed head (zero rotation) boundary condition for the single pile versus minor pile cap rotation in the vertical plane for the group and (2) shaft longitudinal reinforcement ratios of 1.8% for the single pile and 1% for the group piles. To enable comparisons between the test results, a calibrated model of the single pile (1.8% reinforcement) was developed and used to simulate the response of a single shaft with 1% reinforcement. Additional simulations of the pile group were performed to evaluate the effects of cap rotation on group response. By comparing the simulated responses for common conditions, i.e., 1...

Nonlinear Load-Deflection Behavior of Reinforced Concrete Drilled Piles in Stiff Clay

AbstractThe results of three full-scale lateral load tests of cast-in-drilled-hole RC piles are evaluated to provide insights into the soil-pile interaction behavior as represented by p-y curves (p = soil reaction/length; y = lateral pile deflection) spanning from elastic conditions to mobilization of the soil capacity. The test sequence enables evaluation of the diameter effects on the p-y behavior as a result of testing two otherwise similar specimens, but with different diameters (0.6 and 1.8 m), and evaluation of the head-fixity effects as a result of testing similar specimens (with a 0.6 m diameter) under flagpole and fixed-head conditions. A constrained exhaustive search procedure that facilitates data interpretation even in the presence of severe shaft nonlinearity is introduced, which was needed because the testing was performed to full structural failure conditions. The p-y curves obtained with the present test data differ from the predictions of a standard (American Petroleum Institute) model, i...

Finite Element Analysis of Gabled Hyperbolic Paraboloid Shells

In this study, mechanical role of edge beams in the gabled hyperbolic paraboloid shells was investigated through the comparisons of Finite element(FE) analysis results between the shells structures with and without edge beams. In addition, the effects of roof slope was studied. FE analysis showed that roof loads was directly transferred to the supports at corners by the arch action in the diagonal direction of the shells, thus, less member forces in the edge and ridge beams but higher stresses near supports were estimated than those from the membrane theory. When the edge beams were removed, stress concentration in the shells near the supports and the deflections along the shell edge were increased. Such phenomenon were intensified as the roof slope decrease. Thus, in gable hyperbolic paraboloid shell, the thickness of the shell near supports needs to be increased and careful investigation should be made in the cases when the roof height is low and/or the edge beams are removed.

Finite Element Analysis of Inverted Umbrella-type Hyperbolic Paraboloid Shell

This study presents the comparisons between the analysis results based on membrane theory and finite element analysis for the inverted umbrella-type hyperbolic paraboloid shell structure. The effects of the roof angle on the roof deflections, member forces of edge beams and ribs, and shell stress are also investigated with various roof angles. Results show that the membrane theory overestimates the member forces of edge beams and ribs. On the contrary, the shell stresses are underestimated in the membrane theory when compared to the results from the finite element analysis. The deflections of roof slabs by finite element analysis show drastic increasement as the roof angle decreases.

A Study on the Structural Behaviour of Staggered Truss System by the Shape of Truss

This paper analyzed structural behaviors of the staggered truss system, typically used in low seismicity regions, resisting the lateral loads such as wind and seismic load. A comparative study of cost and efficiency was carried out by analysing and designing the 10and 20-story buildings with various types of truss, including pratt, howe, warren, K-, and vierendeel, which may typically be used in staggered truss system. In design, column and truss members are selected in group, and the efficiency of the member design was judged by average demand capacity ratio of the all members in same group. And economic analysis of the system was investigated by the quantity of the structural members. As a result, staggered truss system with the pratt truss and warren truss showed the most economical and efficient performance for 10-story building, and 20-story building, respectively.

Seismic Performance Evaluation of Staggered Truss System by the Shape of Truss

The purpose of this study is to evaluate the seismic performance of Staggered Truss Frame(STF) system while changing a shape of truss. The model of this project is a office building of ten floors with Pratt, Howe, Warren, K and Vierendeel truss system applied on each model. Next step is to select the section of elements which satisfy the highest demand capacity ratio by structure design considering gravity load, earthquake load and wind load and then calculate natural period, base shear and story drifts. On the basis of these values, Capacity Spectrum Method(CSM) shows the plastic behavior of STF system such as performance point of Design Earthquake(DE) and Maximum Considered Earthquake(MCE), yield state, plastic hinge etc. to be compared with other truss systems. As a result, Vierendeel STF system especially was found to have the highest strength and stiffness to the corresponding earthquake and all the models for each truss shape fulfilled the target performance level.

Buckling Behaviors of Single-Layered Lattice Dome under Radial Uniform Loads

This paper presented the nonlinear behaviors of the single-layered lattice dome, which is widely used for the long-span structure system. The behaviors were analysed through the classical shell buckling theory as the single-layered lattice dome behaves like continum thin shell due to its geometric characteristics, and finite element analysis method using the software program Nastran. Shell buckling theory provides two types of buckling loads, the global- and member buckling, and finite element analysis provides the ultimate load of geometric nonlinear analysis as well as the buckling load of Eigen value solution. Two types of models for the lattice dome were analysed, that is rigid- and pin-jointed structure. Buckling load using the shell buckling theory for each type of lattice dome, governed by the minimum value of global buckling or member buckling load, resulted better estimation than the buckling load with Eigen value analysis. And it is useful to predict the buckling pattern, that is global buckling or member buckling.

Behavior of Gabled Hyperbolic Paraboloid Shells

Abstract Previous studies on gabled hyperbolic paraboloid shells (gabled hypar) revealed that shell loads are transferred to the supports mainly through diagonal arch action, and the contribution of edge beams, which have been traditionally included based on the assumptions of membrane theory, is actually very limited. This finding introduced a new shape of gabled hypars in which the edge beams are removed. This paper investigated the behaviors of gabled hypars with and without edge beams for various cases considering the effects of rise-to-span ratio (RSR) and lateral support movement. The FE analyses results indicated that, when the RSR was low, distribution of shell stress showed large variations. Lateral support movement caused an increase of tensile stresses, a decrease of compressive stresses, and intensified stress variation. When edge beams were not used, deflections were increased substantially, and local fluctuation of stress in the vicinity of the supports was intensified. Such behaviors were aggravated when RSR was low and proper constraints against the lateral support movement were not provided, thus resulting in inefficient systems. As such, gabled hypars without edge beams should be designed with caution.

Finite Element Analysis of Gabled Hyperbolic Paraboloid Shells Subjected to Support Movements

This study investigated the behaviors of the gabled hyperbolic paraboloid shell structure subjected to differential settlement and the horizontal displacement due to the elongation of tie rod/beam on supports. Two types of shell structure with different roof slopes are used in study; conventional type which has perimeter beams around the shell panel, and simple type which removes the edge beams along the slab edge line. The effect of the removal of edge beam under vertical or horizontal displacement on supports, and the roof slope was compared using the finite element analysis.

Field-testing and Modeling of Soil-Structure Interaction for Highway Support Structures

The focus of this study is the development of analytical and numerical models of soil-structure interaction in support structures that are frequently used in highway construction in urban settings. In a series of field tests, we have collected detailed and high-resolution data involving small and large-diameter reinforced concrete piles, and pile groups. The data were used to develop and validate simplified (macroelement), as well as detailed 3-dimensional finite element models of these support structures. Our findings indicate that pre-existing analysis methods and design guidelines do not accurately address the need to capture the broad variety of responses that are encountered in seismic regions due to different boundary conditions and structural geometries. Our newly developed models aim to close this perceived void, and are amenable to be routinely used in common design and analysis software used by practicing engineers.