Analysis and Design of Cross Laminated Timber (CLT) High-Rise Buildings

Abstract

The demand for the sustainable high-rise building is increasing day by day. Using mass timber in place of traditional building materials like steel and concrete for the structures would allow the construction of such a sustainable high-rise building. The usage of mass timber in construction reduces the CO2 footprint as compared to traditional reinforced concrete high-rise buildings. Moreover, wood’s low weight reduces the loads on the foundation and allows for the use of wood as an architectural element. The height boundaries for timber buildings are currently extending. At present, the tallest timber building in the world is the Ascent MKE in Wisconsin, USA with the total height of 87 m consisting of 25 floors. Tall timber buildings are more vulnerable to dynamic wind loading because of their lighter weight. Additionally, the current trend of designing slender high-rise structures increases the dynamic response of the structure due to wind. There are various design issues for high-rise timber structures like fire safety, floor slab vibrations and uplifting forces. The structural timber connection is also an important part as it should provide sufficient structural strength to transfer the loads. Various types of connections are glued connection, nailed connection, dowel connection, epoxied connection, and screwed connection. The effect of lateral loading on building should be checked for three aspects: strength, stiffness and serviceability. The main objective of the present study is to explore structural application of cross laminated timber (CLT) as a high-rise building material in alternate of Reinforced Cement Concrete (RC) building. The present study analyses and designs the CLT and RC buildings with foundation for a building having 15 stories with different lateral load resisting system such as Moment Resting (MR) Frame, StructuralWall-Moment Frame, MR Frame with Dampers at Centre and at Corners. Static & Dynamic analysis using site specific response spectrum & time history for both CLT and RC building are carried out in this project. The location of the buildings is considered to be in Ahmedabad (Seismic Zone III and basic wind speed of 39 m/s). The equivalent static analysis and response spectrum analysis is carried out in accordance with IS 1893 (Part 1): 2016 for seismic analysis. The static and dynamic wind loads are in accordance with IS 875 (Part 3): 2015. All the buildings are modeled, analyzed and designed in accordance to applicable Indian stanXII dards including IS 456:2000, IS 875 (Part 3): 2015, IS 1893 (Part 10: 2016), IS 13920, IS 16700: 2023 using ETABS software while the design of CLT building is performed in accordance to EN 1995-1-1: 2004: Eurocode 5. Excel sheets are developed for the design of CLT structural elements like CLT Beam, CLT Column and CLT floor slab. The modelling, analysis and design of isolated footing and raft footing are carried out in accordance to relevant IS Codes using SAFE software. Comparison of analysis results of CLT and RC building with different structural systems is carried out in terms of sizes of structural elements, deal load, natural time period and modal mass participation ratio, base shear, story shear, top storey displacement and interstory drift ratio. The comparison of foundation design for all the buildings is carried out in terms of type of foundation, volume of concrete, weight of steel. Based on the analysis and design of buildings with different structural system, it is found that the structural wall-moment frame building has minimum cross section sizes of structural members. By replacing shear walls with dampers, the response of the building remains similar. Dampers placed at the corners of the buildings shows better performance as compared to damper placed near the center. From the foundation design, it is observed that the all CLT buildings require Isolated Footing while the RC buildings require Raft Footing. Hence the CLT building greatly reduces foundation cost. From the present study, it is found that CLT building is cost effective as compared to RC building.