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.

The purpose of this paper is to investigate the flexural behavior of concrete beams with deformed steel bars and FRP bars for the reinforcement. From experimental and analytical works, stiffness, crack, strength, and deflection behavior was analyzed and compared with ACI318 and ACI440. The specimens were six, which were tested by the variables of reinforcement combination (steel-steel, steel-GFRP, steel-CFRP) and concrete strength (40MPa, 60MPa). Test results showed that specimens with steel-FRP reinforcements had more two times higher strength than the specimens with steel-steel reinforcements and that deflection of specimens were similar. Nominal flexural strengths of specimens by ACI318 and ACI440 were 113~142% of flexural strengths by the test. From finite element analysis, the reliability of the analysis was demonstrated by comparison between appropriate analysis model and test results.

This study conducted experiments to investigate the flexural behavior of steel–concrete composite beams with U-shaped sections, utilizing cold-formed lipped channels as web components. To enhance both flexural and shear performance, trapezoidal plates were added to the lower sides of the composite beams. A total of ten specimens were fabricated, with variables defined according to the following criteria: presence of bottom tension reinforcement and bottom studs, thickness of the trapezoidal side plates (6 mm and 8 mm), and the welding method. Four-point bending tests were conducted, and all specimens exhibited typical flexural failure at the ultimate state. Specimens with bottom tension reinforcement, specifically those in the H5-T6 and H5-T8 series, demonstrated increases in ultimate load of 28.8% and 33.5%, respectively, compared to specimens without tension reinforcement. The use of lipped channels enabled full composite action between the concrete and the steel web components, eliminating the need for stud anchors. Additionally, it was confirmed that the plastic neutral axis, reflecting the material test strengths, was located within the concrete slab as intended. This study also compared the design flexural strengths, calculated using the yield stress distribution method from structural steel design standards such as AISC 360 and KDS 14, with the experimental flexural strengths. The comparison was used to evaluate the applicability of current design standards.

Among fiber-reinforced composites, steel fiber has been widely-used for concrete infrastructure such as silos, tunnels, specifically aiming at reducing the weight of concrete and enhancing its strength by overcoming the brittleness. However, there is still little known about appropriate quality management and applicability assessment for steel fiber composites. This study fills this knowledge gap by testing the possibility of maintenance through steel fiber concrete thickness estimation and assessing the applicability of the quality management instrument. To this end, this study utilizes two different stress wave-driven non-destructive test methods: ultrasonic pulse velocity and impact-echo methods. The ultrasonic pulse velocity method was employed to estimate the compressive strength of steel fiber reinforced concrete, while the impact-echo method was applied to estimate the thickness of various steel fiber reinforced concrete members. As a quality management factor of concrete, correlations between steel fiber mixing ratios and compressive strengths were experimentally explored and validated by error ratios for twenty-four specimens. The reliability was relatively high overall. The average error rate of all the specimens with steel fiber mixing ratios of 0, 0.75 and 1% was 3.36%. Accordingly, the results prove the applicability of the non-destructive test methods for building quality management.

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.DOI: http://dx.doi.org/10.5755/j01.ms.21.4.9702