Yoo Jae Kim

BOND OF SURFACE-MOUNTED FIBER-REINFORCED POLYMER REINFORCEMENT FOR CONCRETE STRUCTURES

The aim of this paper is to show that the properties of the resin layer between surface-mounted fiber-reinforced polymer (FRP) materials and a concrete substrate are key facters in determining bond strength. Theoretical models for FRP delamination and cover delamination are presented. Results of bond characterization tests and beam tests are provided to verify the models. It is concluded that significant improvement in bond strength can be achieved with proper design of the bond layer. The models can be used for design of surface-mounted FRP reinforcement.

Cyclic Shear-Friction Constitutive Model for Finite Element Analysis of Reinforced Concrete Membrane Elements

This paper develops a shear-friction membrane model that is able to limit the shear strength of concrete crack surfaces according to the shear-friction theory so that concrete can fail in shear. The proposed shear-friction model is developed for membrane elements with one-directional cracks and is validated with experimental results available in the literature. Based on experimental observations, this paper introduces the concept of the friction coefficient relative to the “crack opening path,” which is the relationship between the crack slip and the crack separation when the cracks are in contact and slipping without developing normal or shear stresses on the sliding concrete crack surface. The shear friction model rationally predicts failure due to shear transfer across cracks and is able to capture the fundamental behavior of crack slip and separation associated with shear transfer across cracks in reinforced concrete.

High Performance Precast Wall Panels with Shear Transfer Provided by Carbon Fiber Grid

Composite insulated wall panels using carbon fiber grid in combination with expanded polystyrene (EPS) insulation have been produced for over 5 years. The carbon fiber grid and the EPS act together to provide shear transfer between the wythes of the composite panel. A design procedure has been developed, based on testing at Washington University and North Carolina State University. The approach discussed here is to ensure that the flexural strength, the cracking moment, and the deflection are all within acceptable limits. This paper first discusses the testing that has been performed to develop the material properties used in the design procedure. Then methods for computing the flexural strength, the cracking moment and the deflection are also presented. Deflections are not often an issue and cracking moments can be easily controlled by the amount of prestress. Therefore, the most important concern is providing adequate shear transfer. The design procedures discussed here were later verified by full scale testing at North Carolina State University.

Investigation of Rheological Properties of Blended Cement Pastes Using Rotational Viscometer and Dynamic Shear Rheometer

To successfully process concrete, it is necessary to predict and control its flow behavior. However, the workability of concrete is not completely measured or specified by current standard tests. Furthermore, it is only with a clear picture of cement hydration and setting that full prediction and control of concrete performance can be generalized. In order to investigate the rheological properties of blended cement pastes, a rotational viscometer (RV) was used to determine the flow characteristics of ordinary and blended pastes to provide assurance that it can be pumped and handled. Additionally, a dynamic shear rheometer (DSR) was used to characterize both the viscous and elastic components of pastes. Ordinary Portland cement paste and blended pastes (slag, fly ash, and silica fume) were investigated in this study. The stress and strain of the blended specimens were measured by the DSR, which characterizes both viscous and elastic behaviors by measuring the complex shear modulus (the ratio of total shear stress to total shear strain) and phase angle (an indicator of the relative amounts of recoverable and nonrecoverable deformation) of materials. Cement pastes generally exhibit different rheological behaviors with respect to age, mineral admixture type, and cement replacement level.

Analysis of Acoustic Characteristics of a Car Cabin Using Computer-Aided Engineering

A computer-aided engineering (CAE) model was developed to analyze the acoustic characteristics of a car cabin. Pro/Engineer Wildfire 4.0 was used to three-dimensionally represent the geometry of the cabin. The CAE, using COMSOL Multiphysics 4.2a, was performed to investigate the distribution of sound pressure fields at natural frequencies. The principle mode indices were (2, 1, 1), (2, 1, 1), (1, 1, 1), and (2, 2, 2), corresponding to the modal coefficients 1, 2, 3, and 4 and the natural frequencies of 179.691, 139.276, 221.620, and 231.386 Hz, respectively. The results of the analysis provided insight into the car cabin design to suppress exterior and interior noise.

Prediction of Compressive Strength of Aerated Lightweight Aggregate Concrete by Artificial Neural Network

This paper presents artificial neural network techniques for predicting the compressive strength of Aerated Lightweight Aggregate Concrete (ALAC) based on the effects of the concrete mix parameters. The compressive strength of sixty different concretes with densities ranging from 551 to 1948 kg/m3 was used and trained. The primary mix design variables studied included amount of cement, water, coarse aggregate, fine aggregate, surfactant, the volume percentage of air in the matrix (A/M), and the volume percentage of matrix of the total mix (M/T). The training and testing results indicate that the model explains 0.984 and 0.979 of the variability in compressive strength for the single aggregate used in the study, respectively.