Structural Performance Evaluation of Reinforced Concrete Beams After Reinforcement Specification Reduction in The SMK Karya Bhakti Brebes Building

Abstract

Specification changes in reinforced concrete structural members may occur during construction and can affect the conformity, strength, and serviceability of structural elements. This study evaluates the structural performance of the reinforced concrete beam at Grid E of the SMK Karya Bhakti Brebes building under the as-built reinforcement specifications based on the requirements of SNI 2847:2019. The study employed secondary data obtained from the Detail Engineering Design (DED), field implementation data, and structural analysis using SAP2000. The evaluation focused on the beam’s flexural, shear, torsional, and reinforcement detailing performance by comparing the internal forces obtained from structural analysis with the capacity of the as-built beam section. The results show that the beam experienced specification changes, particularly in the longitudinal reinforcement, while the beam dimensions and concrete strength remained consistent with the design specifications. The as-built beam uses 3D16 longitudinal reinforcement, with an installed reinforcement area of 603.19 mm². The analysis produced a maximum negative bending moment of 32.74 kN·m at the support, while the design flexural capacity was 108.80 kN·m, indicating that the flexural capacity remained adequate. The maximum shear force at the support was 90.12 kN, while the calculated shear capacity ratio reached 3.47, indicating that the nominal shear strength was sufficient. The beam was also subjected to a torsional moment of 0.2029 kN·m, which was evaluated in accordance with SNI 2847:2019 and did not govern the structural capacity assessment. The maximum calculated deflection remained within the allowable limit, indicating acceptable serviceability performance. However, despite the beam satisfying the strength requirements for flexure and shear, the provided stirrup spacing did not comply with the required detailing provisions, with 100 mm spacing at the support exceeding the allowable 63 mm and 150 mm spacing at the span exceeding the allowable 126 mm. Therefore, the as-built beam retains adequate nominal structural capacity, but its transverse reinforcement detailing does not fully comply with SNI 2847:2019. These findings indicate that structural specification changes should be accompanied by comprehensive strength, serviceability, and detailing verification before being accepted as an alternative to the original design.