Since the last four decades, the behavior of concrete contains of steel fiber, or often called steel fiber concrete, with a wide range of compressive strength has been carried out. Generally, the results of the experimental program produced a material which has a more ductile compared with normal concrete or concrete without fiber. Due to the ductility properties of the material, it is very suitable for use as an earthquake-resistant structural material. At the same time, the behavior of high-strength steel-fiber concrete has also investigated, one of which is about confined high-strength steel-fiber concrete. Analytical models of confined high-strength steel fiber concrete have been developed in various preliminary studies, with their characteristics derived based on the experimental results. Therefore, this research evaluated the models of confined high-strength steel-fiber concrete proposed by Mansur et al., Hsu and Hsu, and Paultre et al. The evaluation includes stress-strain behavior, strength enhancement of confined concrete (f'cc/f'co) or K value, the increase in confined concrete strain (ε'cc/ε'co), and strain of confined concrete when the stress has dropped by 50 percent against its unconfined strain (εcc50/εc50). The comparison method was carried out using a statistical approach and stress-strain simulation. Evaluation results showed significant predictive differences in confinement models in terms of post-peak behavior and parameters ε'cc/ε’co and εcc50/εc50. Prediction of confinement models on the value of f'cc/f’co to the experimental results has a coefficient of variation above 10%. The result further showed that a modified model of confined high-strength steel-fiber concrete was proposed and able to simulate the stress-strain behavior.

In reinforced concrete columns design, P-M interaction diagram is used as axial load control and column bending without taking into account the effect of lateral reinforcement bars. Design principles that ignore the effect of reinforcement bars will result in low value of actual axial capacity of column. This paper presents the effect of lateral reinforcement with a case study of square-sectional columns on high-strength concrete. The equation of unconfined concrete strength enhancement is based on Mander, Legeron, Imran, Antonius and Muguruma models. The reviewed parameters include compressive strength of concrete, reinforcement configuration, and spacings of confinement. The result of the analysis is a comparison of P-M diagram based on confinement models. It shows that confinement significantly influences axial capacity of column, yet it has a certain collapse point at point P = 0 in all models. This is caused by longitudinal reinforcement system. Configuration of reinforcement, spacing and confinement models greatly affects the collapse behavior of column, whether the collapse is classified as compressive collapse or tensile collapse based on the P-M diagram.

This paper presents the results of an assessment of the existing 5-storey building built in 1980, which aims to determine the level of safety against the most recent standards. The method used is non-destructive testing, collecting planning data in the form of as built drawings and implementation data. The assessment of the existing structure consists of an evaluation of the condition of the material, structural system, and analysis of the structure using the latest load standards. The test results of the existing structural material show that the compressive strength of the concrete still meets the requirements based on SNI-2847-2019. The results of the evaluation of the structure against earthquake loads show that the performance of the structure has a mass participation of 100% and the dynamic base shear force (V) reaches 100% of Vstatic therefore it meets the requirements in SNI 1726-2019. The results of the evaluation of the performance of the structure show that the lateral drift and P-delta effects still meet the requirements of the most recent standards. Horizontal and vertical structural irregularities are found in the existing structural system. The structure's overall performance level (X and Y direction earthquakes) is Damage Control. These results are still permitted for structures with a priority factor (Ie) 1.50, with an earthquake return period of 2500 years.

Gunny sack fiber concrete has not been explored especially the behavior under high temperatures. This paper presents the results of an experimental investigation of gunny sack fibrous concrete (percentage of 0.5% of volume) given a monotonic- compressive load. A number of cylindrical test specimens were made which consisted of control specimens and which were incinerated at temperatures of 300oC, 600oC and 900oC. The concrete -compressive strength was designed with three variations of the cement water ratio to get the compressive strength of a standard cylinder with normal, medium and high -quality compressive strength categories. Experimental results show that normal to high quality concrete can be produced with gunny sack fiber substitution. The compressive strength of the gunny sack fiber concrete decreased significantly from the control specimen to the specimen which was burned at 300oC. The loss of compressive strength from the control specimens to the post-burn specimens of medium quality and high -quality of gunny sack fiber concrete was the same compared with the loss of compressive strength of normal- quality concrete. This study also carried out a comparison of the degradation of the compressive strength of steel fibrous concrete with gunny sack fiber in post-burn conditions.