Influence of considering Malaysia National Annex for seismic design of reinforced concrete building

Abstract

The current practice for reinforced concrete building design in Malaysia using BS 8110 does not include seismic design provision since Malaysia is not located in active fault zones. The urgency of seismic design in Malaysia started when several tremors from neighbouring countries were felt and slightly damaged some structures especially after a recent earthquake in Sabah which hit Ranau in 2015 with 5.9-magnitude. In 2017, Malaysia has recently published its own National Annex (NA) for seismic design according to Eurocode 8 (EC 8) to include seismic provision into account. This study focuses on the estimation of the required reinforcement for conventional design (BS 8110) and seismic design (Malaysia NA to EC 8); and the seismic performance of the buildings when such codes are used for design. In this study, buildings have been designed based on different parameters such as number of storey (3 and 6 storey), ductility class (low and medium ductility) and soil type (stiff and soft soil). One Peak Ground Acceleration (PGA) has been selected which is 0.1g based on condition in Peninsular Malaysia. The results show low ductility class with soft soil buildings have 95% to 173% higher reinforcement percentage difference when compared to the with conventional design This indicates higher additional reinforcement is needed for low ductility class with soft soil buildings to withstand the seismic load in such condition. Furthermore, the seismic capacity curves of the buildings are established by using non-linear static pushover analysis. The maximum displacements are obtained for all load cases of 3-storey and 6-storey buildings and have been compared to the conventional design. The results indicate the maximum displacement for conventional design is less than buildings that are designed with seismic provision. This shows under the earthquake event, building with conventional design will form plastic hinges and proceed to failure stage earlier than seismic designed buildings. In addition, the seismic performance points are obtained for all types of buildings. The results showed for all load cases conventional designed 3-storey building and 6 storey building considered safe under 0.1g ground motion if they were designed under stiff soil ground condition (type A) as plastic hinges formed only reached to IO state. However, if they were designed under soft soil (type D), the buildings were not safe as the hinges formed beyond CP state at the target displacement. For seismic designed of 3-storey buildings, only buildings with soft soil regardless of ductility class were not safe even though the seismic provisions were included in the design. Meanwhile, for seismic designed of 6-storey buildings, all types of buildings were safe under 0.1g ground motion as plastic hinges formed only reached to IO to LS states. The results obtained for 6-storey seismic designed buildings were different with 3-storey seismic designed buildings due to additional structure element that were added in the 6-storey buildings which was shear walls that been designed from bottom to the top of building. The shear wall made the structure become stiffer thus can cater the earthquake load applied to the building.