• Structural Engineering and Mechanics
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• v.31 no.5
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• pp.545-566
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• 2009

Bridge columns are subjected to combined actions of axial force, shear force and bending moment during earthquakes, caused by spatially-complex earthquake motions, features of structural configurations and the interaction between input and response characteristics. Combined actions can have significant effects on the force and deformation capacity of RC columns, resulting in unexpected large deformations and extensive damage that in turn influences the performance of bridges as vital components of transportation systems. This paper evaluates the seismic response of three prototype reinforced concrete bridges using comprehensive numerical models that are capable of simulating the complex soil-structural interaction effects and nonlinear behavior of columns. An analytical approach that can capture the shear-flexural interacting behavior is developed to model the realistic nonlinear behavior of RC columns, including the pinching behavior, strength deterioration and stiffness softening due to combined actions of shear force, axial force and bending moment. Seismic response analyses were conducted on the prototype bridges under suites of ground motions. Response quantities of bridges (e.g., drift, acceleration, section force and section moment etc.) are compared and evaluated to identify the effects of vertical motion, structural characteristics and the shear-flexural interaction on seismic demand of bridges.

• International Journal of Concrete Structures and Materials
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• v.11 no.2
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• pp.365-375
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• 2017

An experimental evaluation of crack propagation and post-cracking behavior in steel fiber reinforced concrete (SFRC) beams, using full-field displacements obtained from the digital image correlation technique is presented. Surface displacements and strains during the fracture test of notched SFRC beams with volume fractions ($V_f$) of steel fibers equal to 0.5 and 0.75% are analyzed. An analysis procedure for determining the crack opening width over the depth of the beam during crack propagation in the flexure test is presented. The crack opening width is established as a function of the crack tip opening displacement and the residual flexural strength of SFRC beams. The softening in the post-peak load response is associated with the rapid surface crack propagation for small increases in crack tip opening displacement. The load recovery in the flexural response of SFRC is associated with a hinge-type behavior in the beam. For the stress gradient produced by flexure, the hinge is established before load recovery is initiated. The resistance provided by the fibers to the opening of the hinge produces the load recovery in the flexural response.

• Steel and Composite Structures
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• v.10 no.5
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• pp.373-383
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• 2010

This paper presents the experimental studies of the flexural behavior of steel-concrete composite beams. Herein, steel-concrete composite beams were constructed with a welded steel I section beam and concrete slab with different material strength. Four simply supported composite beams subjected to two-point concentrated loads were tested and compared to investigate the effect of high strength engineering materials on the overall flexural response, including failure modes, load deflection behavior, strain response and interface slip. The experimental results show that the moment capacity of composite beams has been improved effectively when high-strength steel and concrete are used. Comparisons of the ultimate flexural strength of beams tested are then made with the calculated results according to the methods specified in guideline Eurocode 4. The ultimate flexural strength based on current codes may be slightly unconservative for predicating the moment capacity of composite beams with high-strength steel or concrete.

• Computers and Concrete
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• v.7 no.2
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• pp.169-190
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• 2010

The focus of this research effort was characterization of the flexural and tensile properties of a specific ultra-high-strength, fiber-reinforced concrete material. The material exhibited a mean unconfined compressive strength of approximately 140 MPa and was reinforced with short, randomly distributed alkali resistant glass fibers. As a part of the study, coupled experimental, analytical and numerical investigations were performed. Flexural and direct tension tests were first conducted to experimentally characterize material behavior. Following experimentation, a micromechanically-based analytical model was utilized to calculate the material's tensile failure response, which was compared to the experimental results. Lastly, to investigate the relationship between the tensile failure and flexural response, a numerical analysis of the flexural experiments was performed utilizing the experimentally developed tensile failure function. Results of the experimental, analytical and numerical investigations are presented herein.

• Computers and Concrete
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• v.17 no.4
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• pp.477-488
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• 2016

This paper aims to model the effects of five different variables which includes: cement content (C), the steel fiber amount (F), the silica fume amount (SF), the superplasticizer (SP), the silica fume amount (SF), and the water to cementitious ratio (w/c) on 28 days flexural toughness of Ultra High Performance Concrete (UHPC) as well as, a study on the variable interactions and correlations by using analyze of variance (ANOVA) and response surface methodology (RSM). The variables were compared by fine aggregate mass. The model will be valid for the mixes with 0.18 to 0.32 w/c ratio, 4 to 8 percent steel fiber, 7 to 13 percent cement, 15 to 30 percent silica fume, and 4 to 8 percent superplasticizer by fine aggregate mass.

• Structural Engineering and Mechanics
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• v.15 no.6
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• pp.705-716
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• 2003

Gradient elastic flexural beams are dynamically analysed by analytic means. The governing equation of flexural beam motion is obtained by combining the Bernoulli-Euler beam theory and the simple gradient elasticity theory due to Aifantis. All possible boundary conditions (classical and non-classical or gradient type) are obtained with the aid of a variational statement. A wave propagation analysis reveals the existence of wave dispersion in gradient elastic beams. Free vibrations of gradient elastic beams are analysed and natural frequencies and modal shapes are obtained. Forced vibrations of these beams are also analysed with the aid of the Laplace transform with respect to time and their response to loads with any time variation is obtained. Numerical examples are presented for both free and forced vibrations of a simply supported and a cantilever beam, respectively, in order to assess the gradient effect on the natural frequencies, modal shapes and beam response.

• Structural Engineering and Mechanics
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• v.52 no.4
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• pp.787-813
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• 2014

Starting with Hamilton's variational principle, the governing field equations for the steady state response of thin-walled beams under harmonic forces are derived. The formulation captures shear deformation effects due to bending and warping, translational and rotary inertia effects and as well as torsional flexural coupling effects due to the cross section mono-symmetry. The equations of motion consist of four coupled differential equations in the unknown displacement field variables. A general closed form solution is then developed for the coupled system of equations. The solution is subsequently used to develop a family of shape functions which exactly satisfy the homogeneous form of the governing field equations. A super-convergent finite element is then formulated based on the exact shape functions. Key features of the element developed include its ability to (a) isolate the steady state response component of the response to make the solution amenable to fatigue design, (b) capture coupling effects arising as a result of section mono-symmetry, (c) eliminate spatial discretization arising in commonly used finite elements, (d) avoiding shear locking phenomena, and (e) eliminate the need for time discretization. The results based on the present solution are found to be in excellent agreement with those based on finite element solutions at a small fraction of the computational and modelling cost involved.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6D
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• pp.905-913
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• 2008

Recently, concrete tracks are introduced into high-speed railroads as an alternative to ballast tracks. Concrete tracks are superior to ballast tracks in the aspect of durability, maintenance and safety. However, deteriorated stiffness of railroad bed and settlement of soft ground induced by trapped or seepage water lead to problems in safety of train operation. In this research, flexural rigidity of concrete tracks was employed as an index of track displacement and a new seismic technique called FRACTAL (Flexural-Rigidity Assessment of Concrete Tracks by Antisymmetric Lamb Waves) method was proposed to delineate flexural rigidity of concrete tracks in a 2-D image. In this paper, to establish theoretical background, parametric research was performed using numerical simulations of stress-wave tests at concrete tracks. Feasibility of the FRACTAL technique was proved at a real concrete track for Korean high-speed trains. Validity of the FRACTAL technique was also verified by comparing the results of impulse-response tests performed at the same measurement array and the results of DC resistivity survey performed at a shoulder nearby the track.

• Computers and Concrete
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• v.18 no.6
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• pp.1213-1234
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• 2016

This paper describes a deformation-based strut-and-tie model for the flexural members at post-yield state. Boundary deformation conditions by flexural post-yield response are chosen in terms of the flexural bar strains as the main factor influenced on the shear strength. The main purpose of the proposed model is to predict the shear capacities of the flexural members associated with the given flexural deformation conditions. To verify the proposed strut-and-tie model, the estimated shear strengths depending on the flexural deformation are compared with the experimental results. The experimental data are in good agreement with the values obtained by the proposed model.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.170-177
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• 2000

Recently many high-rise apartment buildings are constructed using the box system which is composed only of concrete walls and slabs. Commercial softwares such as ETABS used for the analysis of high-rise apartment buildings are employing the rigid diaphragm assumption for simplicity in the analysis procedure. In general the flexural stiffness of floor slabs are ignored in the analysis, This assumption may be reasonable for the estimation of seismic response of framed structures. But in the case of the box system used in the apartment buildings floor slabs has major effects on the lateral stiffness of the structure. So if the flexural stiffness of slabs in the box system is ignored the lateral stiffness may be significantly underestimated, For these reasons it is recommended to use plate elements to represent the floor slabs. In the study A typical frame structure and a box system structure are chosen as the example structure. When a 20 story frame structure is subjected to the static lateral loads the displacements of the roof are 15.33cm and 17.52cm for the cases with and without the flexural stiffness of the floor slabs. And in case of box system the roof displacement was reduced from 16.18cm to 8.61cm The model without the flexural stiffness of floor slabs turned out to elongate the natural periods of vibration accordingly.