Use of High Performance Reinforced Concrete Systems Located in Seismic Regions

Abstract eng:
In the past decade, reinforced concrete became the most popular building material for tall buildings [1]. According to the Council of Tall Buildings and Urban Habitat, in 2013, 63% of the buildings 200 m or taller were built out of reinforced concrete. Shear demand on the core wall is one of the key parameters that govern the seismic design of reinforced concrete high-rise building systems. Higher mode affects that are not prominent in the design of regular buildings further amplify these demands controlling the core wall dimensions and wall thicknesses over the building height. For core wall systems with or without backing moment frame, the wall thicknesses required to resist these shear demands could be substantial. Increased wall thicknesses not only increase the material costs and reduce the efficiency of the floor plate by increasing the ratio of the core wall area to the floor area but also result in increased foundation forces and seismic forces due to increased weight. Primary inelastic energy dissipation mechanism of core wall systems, is the flexural or shear yielding of coupling beams connecting the core wall pier together. Rotation and shear demands on these elements are generally substantial. These demands could lead design that require too much reinforcing steel creating constructability problems as well as substantial damage and repair time for the building during and after an earthquake. High force and deformation demands controlling the core wall thicknesses and coupling beam design led us to investigate the feasibility of using High-Performance Fiber-Reinforced Cementitious Composites (HPFRCCs) as an alternative to the normal to high strength concrete that is currently the common construction practice for high rise buildings in seismic zones. As part of the study, four case study buildings were analyzed. Case study lateral load resisting systems consisted of a) core only, (b) dual system (core + backing moment frame), (c) core with outriggers at mid-height, and (d) core with outriggers at mid-height and roof. Construction cost and seismic performance of each structural system was compared. The use of HPFRCC’s enabled the relaxation of confinement reinforcement in columns and boundary elements of shear walls. In addition, reinforcement quantities in coupling beams were reduced using HPFRCC’s. Savings in reinforcement quantities by using fiber reinforced concrete is calculated to be considerably less than the additional cost of using HPFRCC’s. Seismic performance was measured in terms of expected loss. Incremental dynamic analysis (IDA) results were used with ATC 58 methodology and PACT program to assess the expected loss due to seismic activity. Considering the improved performance of the structural members and reduced cost, results of the study suggested that use of HPFRCC elements should be seriously considered for the design of tall buildings in seismic regions.

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