Suchart Limkatanyu

Responses of Reinforced Concrete Members Including Bond-Slip Effects

This paper discusses the importance of modeling bond-slip in the response of reinforced concrete (RC) members. A displacement-based, RC beam fiber model with bond-slip is presented. The formulation is general and applies to both monotonic and cyclic loads. It also extends to shallow beams strengthened in flexure by externally bonded thin plates. Two main applications are presented to illustrate the model characteristics and to show the importance of including bond-slip in modeling RC members. The first application considers a RC column experimentally tested under cyclic loads and previously modeled with a fiber element without bond-slip. The second application considers a shallow beam strengthened with a fiber reinforced plastic plate. In both cases, the model realistically predicts not only the strength of the members, but also their stiffness and, in the case of the column, the hysteretic energy dissipated during the loading cycles.

Behavior and Performance of GFRP Reinforced Concrete Columns with Various Types of Stirrups

Fiber reinforced polymer (FRP) composites are gaining acceptance in concrete structural applications due to their high ratio of strength/stiffness to self-weight and corrosion resistance. This study focused on the structural behavior and the performance of concrete columns internally reinforced with glass fiber reinforced plastic (GFRP) rebars. Twelve series of concrete columns with varied longitudinal reinforcement, cross section, concrete cover, and type of lateral reinforcement were tested under compression loading. The results show that the amount of GFRP longitudinal and lateral reinforcement slightly affects the column strength. The lateral reinforcement affects the confining pressure and inelastic deformation, and its contribution to the confined compressive strength increases with the GFRP reinforcement ratio. In addition, the confining pressure increases both concrete strength and deformability in the inelastic range. The confinement effectiveness coefficient varied from 3.0 to 7.0 with longitudinal reinforcement. The average deformability factors were 4.2 and 2.8 with spirals and ties, respectively. Lateral reinforcement had a more pronounced effect on deformability than on column strength.

Parametric Study on Dynamic Response of Fiber Reinforced Polymer Composite Bridges

Because of high strength and stiffness to low self-weight ratio and ease of field installation, fiber reinforced polymer (FRP) composite materials are gaining popularity as the materials of choice to replace deteriorated concrete bridge decks. FRP bridge deck systems with lower damping compared to conventional bridge decks can lead to higher amplitudes of vibration causing dynamically active bridge deck leading serviceability problems. The FRP bridge models with different bridge configurations and loading patterns were simulated using finite element method. The dynamic response results under varying FRP deck system parameters were discussed and compared with standard specifications of bridge deck designs under dynamic loads. In addition, the dynamic load allowance equation as a function of natural frequency, span length, and vehicle speed was proposed in this study. The proposed dynamic load allowance related to the first flexural frequency was presented herein. The upper and lower bounds’ limits were established to provide design guidance in selecting suitable dynamic load allowance for FRP bridge systems.

Modeling of axially loaded nanowires embedded in elastic substrate media with inclusion of nonlocal and surface effects

Nonlocal and surface effects are incorporated into a bar-elastic substrate element to account for small-scale and size-dependent effects on axial responses of nanowires embedded in elastic substrate media. The virtual displacement principle, employed to consistently derive the governing differential equation as well as the boundary conditions, forms the core of the displacementbased finite element formulation of the nanowire-elastic substrate element. The element displacement shape functions, analytically derived based on homogeneous solution to the governing differential equilibrium equation of the problem, result in the exact element stiffness matrix and equivalent load vector. Two numerical simulations employing the proposed model are performed to study characteristics and behavior of the nanowire-substrate system. The first simulation involves investigation of responses of the wire embedded in elastic substrate. Thesecond examines influences of several system parameters on the contact stiffness and reveals the size-dependent effect on the effective Youngs modulus of the system.

Exact Stiffness for Beams on Kerr-Type Foundation: The Virtual Force Approach

This paper alternatively derives the exact element stiffness equation for a beam on Kerr-type foundation. The shear coupling between the individual Winkler-spring components and the peripheral discontinuity at the boundaries between the loaded and the unloaded soil surfaces are taken into account in this proposed model. The element flexibility matrix is derived based on the virtual force principle and forms the core of the exact element stiffness matrix. The sixth-order governing differential compatibility of the problem is revealed using the virtual force principle and solved analytically to obtain the exact force interpolation functions. The matrix virtual force equation is employed to obtain the exact element flexibility matrix based on the exact force interpolation functions. The so-called “natural” element stiffness matrix is obtained by inverting the exact element flexibility matrix. One numerical example is utilized to confirm the accuracy and the efficiency of the proposed beam element on Kerr-type foundation and to show a more realistic distribution of interactive foundation force.

Improved nonlinear displacement-based beam element on a two-parameter foundation

This paper presents a nonlinear beam element on a two-parameter foundation. A set of governing differential equations of the problem (strong form) is first derived. The displacement-based beam-foundation element with improved displacement shape functions (weak form) is then formulated based on virtual displacement principle. The improved functions are analytically derived based on homogeneous solution to the governing differential equilibrium equation of the problem and are employed to enhance the model accuracy. Tonti’s diagrams are used to conveniently represent the equations that govern both the strong and weak forms of the problem. An averaging technique previously proposed by the authors is employed to determine system parameters needed in evaluating the displacement shape functions. Finally, two numerical simulations are used to verify the accuracy and the efficiency of the proposed beam model. The first simulation is used to perform convergence studies of the proposed model and to show its accuracy in representing both global and local responses. The second simulation is used to address effects of the two-parameter foundation model on system responses when compared to the Winkler foundation model.

A Thermo-Hygro-Coupled Model for Chloride Penetration in Concrete Structures

Corrosion damage due to chloride attack is one of the most concerning issues for long term durability of reinforced concrete structures. By developing the reliable mathematical model of chloride penetration into concrete structures, it can help structural engineers and management agencies with predicting the service life of reinforced concrete structures in order to effectively schedule the maintenance, repair, and rehabilitation program. This paper presents a theoretical and computational model for chloride diffusion in concrete structures. The governing equations are taking into account the coupled transport process of chloride ions, moisture, and temperature. This represents the actual condition of concrete structures which are always found in nonsaturated and nonisothermal conditions. The fully coupled effects among chloride, moisture, and heat diffusion are considered and included in the model. The coupling parameters evaluated based on the available material models and test data are proposed and explicitly incorporated in the governing equations. The numerical analysis of coupled transport equations is performed using the finite element method. The model is validated by comparing the numerical results against the available experimental data and a good agreement is observed.

Unification of Mixed Euler-Bernoulli-Von Karman Planar Frame Model and Corotational Approach

This article presents an efficient and accurate frame element for small-strain but large-displacement/rotation analyses of elastic planar frames. The element formulation is based on the unification of the corotational concept and the Euler-Bernoulli-von Karman beam theory. The Hellinger-Reissner mixed functional is used to construct the locking-free Euler-Bernoulli-von Karman frame element. The directional derivative operator is used to linearize the Hellinger-Reissner mixed functional, thus resulting in the incremental element equations. The derived element stiffness matrix is symmetric and variationally consistent. The standard displacement interpolation functions for a linear frame element are used. With these assumed displacements, the force interpolation functions are derived such that the equilibrium equations in the deformed configuration are strictly satisfied. In the present study, the distributed loads along the element are assumed to be absent and only initially straight prismatic beams are considered. The validity of the proposed nonlinear frame element is confirmed by analyzing five benchmark examples exhibiting two types of critical points, namely snap-through and snap-back and comparing these results with analytical results available in literatures. The efficiency of the proposed nonlinear frame element is also assessed by comparing the numerical results obtained with the proposed model to those obtained with other nonlinear frame models.

Baseline Moisture Resistance of PWP Cement Composite Boards Reinforced with Internal Glass Fiber Reinforcement under Accelerated Wet-Dry Aging

∘ /90 ∘ ]. The board properties were evaluated under accelerated aging with wet-dry cycles to establish the durability and moisture resistance and the effect on flexural strength of the composite boards. The mechanical characteristics determined were the equivalent modulus of rupture (eMOR), the equivalent modulus of elasticity (eMOE), and the deformability factor (DF). The experimental results suggest that the strength and stiffness of the PWP composite boards with internal reinforcement are four times higher than those of the original PWP composite boards under accelerated aging based on 100 wet-dry cycles, implying better durability of the boards in outdoor use. The results provide a baseline to which improved formulations and reinforcements or designs can be compared using the same measurement methodology.

Parawood particle cement composite boards under accelerated wet/dry cycling and natural aging

The aim of this study is to investigate the potential use of Parawood particle waste (PWP) and cement to produce PWP cement composites for use as construction and decorative boards. Strength effects of the PWP–cement composites prepared, with respect to PWP/cement ratio and the type and amount of admixtures, were studied and discussed. Mixture M0-35-1 emerged as a suitable compromise between good practical strength and desirable high usage of PWP. For durability study, wet/dry accelerated, and natural aging, were imposed on the board prior to flexural testing. Mechanical properties were evaluated in terms of the equivalent modulus of rupture, equivalent modulus of elasticity, and toughness index. Significant deterioration of properties was found after 100 cycles of accelerated wet–dry aging, equivalent to 609 days under natural exposure. Poor durability infers that the created board needs to be further engineered to withstand rigorous outdoor applications.