The purpose of this study is to estimate the compressive strength according to the age of the concrete structure using ultrasonic pulse velocity method. If the correlation between the ultrasonic pulse velocity and the compressive strength according to the age is derived, the compressive strength of the early age of the concrete structure can be estimated at the new construction site and the compressive strength of the existing structure can be estimated at the remodeling construction site. Concrete structural specimens were constructed with 123 specimens by setting 9 parameters based on the design compressive strength of 24, 30, 40 MPa at 16, 20, 24, 48, 72, 120, 168, 360, 672 h. For the calculation of the average ultrasonic velocity according to the age of concrete, it is carried out according to KS F 2731, ASTM C597 and ACI 228-2R, and the concrete compressive strength is carried out according to KS F 2405. From correlation between ultrasonic pulse velocity and compressive strength, this experiment suggests compressive strength estimation equation. The proposed estimation equation confirmed that it is possible to estimate the compressive strength of concrete according to its age using nondestructive test methods.
A finite element (FE) analysis with three-dimensional solid elements has been performed for estimating the structural behaviors of single shear bolted connections fabricated with cold-formed austenitic stainless steel by utilizing the existing test data for calibration. Failure and curling (out-of-plane deformation perpendicular to the direction of loading) criteria were proposed. Therefore, the failure mode and ultimate strength, predicted by FE analysis method, showed good agreements with those of experimental results. In this study, FE analyses for 10 test specimens fabricated with cold-formed carbon steel as well as stainless steel including failure mode of bolt shear fracture are carried out and the validity of numerical prediction for ultimate behaviors in cold-formed carbon steel bolted connections is also verified, based on the applicability of FE method for predicting the mechanical behaviors of bolted connections in cold-formed stainless steel. It is known from the coupon test results of steel materials that austenitic stainless (SUS304) steel has a higher tensile strength of material due to the effect of strength enhancements (considerable strain hardening) by means of cold-working process and much lower yield stress when compared to carbon steel. The influence of curling on the strength reduction of bolted connections is estimated quantitatively. In addition, characteristics of mechanical behaviors and the influence of curling in bolted connections between two different steel materials are compared through detailed investigation of FE analysis results.KEY WORDS: carbon steel; austenitic stainless steel; cold-formed steel; bolted connection; ultimate behavior; curling; finite element analysis.
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The increase of well-being culture of problem related to environmental depletion of resource is not the growing interest in timber the natural material of construction markets. Also, the perception for historic preservation has been increased in respond to heightened interest. However, it is fairly difficult for architectural properties to maintain their durability because it was made by timber construction. Preventing traditional structure from damage and structural performance reduction is paramount in maintenance problem. A number of studies of reinforced method have been conducted in order to solve such a problem. In this paper, external bonded reinforcement and near-surface mounted was used as a way to reinforce timber structure's durability. Bond strength for specimens with different bond length was investigated. As a result showed, maximum bond strength in bond length 300 mm from all method, was found to be not increased of bond strength over the certain bond length.
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