Course on analysis, behavior, and design of
Earthquake Resilient Buildings at Near-fault Sites
Seismic design of most buildings to modern code-minimum requirements aims to life-safety and a low probability of collapse. Such buildings, especially at near-fault regions, are prone to significant post-earthquake damage and downtime, cost-prohibitive repairs or demolition. Analytical and experimental research in earthquake and structural engineering has provided with analysis, design methods, and technology that allow construction of cost-effective structures that sustain strong earthquake shaking and recover their functionality in reasonable time and cost. In United States, earthquake resilience is receiving increased attention with various relevant efforts. These actions were initiated because of Public Law 115-307 (NEHRP Reauthorization Act of 2018) and legislation efforts in the State of California (Assembly Bill 393, 2019-2020, functional recovery standard). The online school published an article on the earthquake resilience and functional recovery of buildings in U.S.
The course develops a comprehensive understanding of analysis, behavior, and design of earthquake resilient buildings (5- to 20-story tall) at near-fault sites and their performance comparison with conventional fixed-base RC wall and frame buildings. Three classes of earthquake resilient building structural systems are studied: (a) base-isolated (b) low-damage rocking walls; and (c) ductile RC walls of increased strength and stiffness. The need for earthquake-resilient buildings, at near-fault sites, is justified based on the poor seismic performance and the loss of functional recovery of fixed-base RC wall and frame buildings designed following minimum requirements of ASCE 7. The seismic hazard, historical damage, and characteristics of ground motions at near-fault sites is covered thoroughly. The course combines the state-of-the-art of the theoretical seismic response, the experimental testing behavior, the 3D nonlinear response history analysis (in ETABS Ultimate) of buildings at near-fault sites as well as the advanced seismic analysis and damage calculation of buildings with methods that go significantly beyond the tools used in best current practice.
Achievements and Deliverables
1. Comprehensive understanding of seismic performance and loss of functional recovery of RC buildings, at near-fault
sites, designed with modern code-minimum requirements.
2. Seismic design of buildings, at near-fault sites, via increased strength and stiffness to achieve prompt post-earthquake
3. Advanced seismic analysis of RC buildings, at near-fault sites, using the nonlinear beam-truss-model approach for
capturing shear failures and shear-related damage.
4. Analysis and design of earthquake-resilient buildings, at near-fault sites, with low-damage rocking walls.
5. Analysis and design of earthquake resilient buildings, at near fault-sites, using seismic isolation.
6. Three-dimensional nonlinear response history analysis (3D NLRHA) of buildings in ETABS and calibration (based on 3D NLRHA) of simplified analysis and design procedures.
Table 1 describes the topical coverage of each of the seven lectures. The course has five parts (Table 1). Part I, which consists of Lecture 1, reviews the fundamentals of earthquake shallow-fault-rupture-process and the basis of seismic design at near-fault sites according to ASCE 7-10 code provisions as well as according to performance-based guidelines. The fault characteristics and the seismic hazard of the cities of Los Angeles, San Francisco, and Seattle are compared. The lecture discusses the fault rupture process, ground motion and spectral characteristics as well as the near-fault earthquake damage occurred in six earthquakes: Christchurch-2011-M6.3, Imperial Valley-1979-M6.5, Northridge-1994-M6.7, Kobe-1995-M6.9, Loma Prieta-1989-M6.9, Chi-Chi-1999-M7.6. The engineering characterization of 49 near-fault pulse-type ground motions recorded in eleven earthquakes is presented in detail including the characteristics of strong pulses and how these affect spectral properties and seismic hazard.
Part II, which consists of Lectures 2 and 3, develops a comprehensive understanding of the seismic behavior, analysis, and design of fixed-base reinforced concrete (RC) wall and RC frame buildings at near-fault sites. Lecture 2 presents the nonlinear response of SDOF oscillators approximating the fundamental mode of response of buildings. The nonlinear SDOF analysis is used to estimate displacement demands of buildings. The second half of Lecture 2 discusses the fundamentals of the nonlinear mechanics of RC walls and the displacement-based analysis of them including the relation between displacements, plastic rotations and material strains. Lecture 3 consists of five parts. The first part compares the ASCE 7-10 code minimum analysis versus 3D nonlinear response history analysis (3DNLRHA) of five RC buildings. The 3DNLRHA is conducted both at the Design Earthquake and the Risk-targeted Maximum Considered Earthquake seismic hazard levels. The buildings range from 5- to 20-story tall including both RC wall and RC special moment frame buildings. The reasons that ASCE 7-10 code minimum analysis underestimates significantly displacement, force, and floor acceleration demands are presented. The second part presents the key results from the landmark 7-story full-scale shake table test and the main experimental observations validate key results of the nonlinear analysis of the buildings case studies. The third part presents the enhanced response spectrum analysis, implemented in ETABS, method which improves significantly the calculation of design forces compared with conventional response spectrum analysis. Part IV discusses how the seismic performance of fixed-base RC buildings can be enhanced by increasing the strength and the effective stiffness of the building. The last part covers the modeling and nonlinear response history analysis of RC buildings in ETABS Ultimate.
Part III, which consists of Lectures 4 and 5, develops a comprehensive understanding of advanced seismic analysis, design, and experimental testing behavior of base-isolated buildings located near major faults (earthquake magnitude M6.2 to M8.0). The lectures use an end-to-end approach extending from nonlinear response of SDOF systems representing seismic isolation and experimental testing of devices and base-isolated buildings up to 3D nonlinear response history analysis (NLRHA), in ETABS Ultimate, of 20-story tall base isolated buildings. Lecture 4 presents the fundamentals of the nonlinear dynamic behavior of various seismic isolation systems including the following devices: friction bearings, rubber bearings, and nonlinear viscous dampers. Using nonlinear SDOF analysis the response of seismic isolation systems to strong near-fault pule-like ground motions is studied and their equivalent linear analysis is presented. The theoretical as well as the experimental mechanical behavior of various isolation systems is presented. Lecture 05 presents the 3D NLRHA and seismic design of two base isolated buildings, 10- and 20-story tall. The response and design of the of the base isolated buildings is compared with the corresponding fixed-base designs presented in detail in Lecture 3. The buildings use a RC core-wall above the isolation plane. The incremental cost of base-isolated earthquake-resilient buildings is calculated. This lecture also presents examples of constructed base-isolated tall buildings (up to 45-story tall) as well as the effect of inelastic behavior of the superstructure of base-isolated buildings.
Part IV, which consists of Lecture 6, presents the advanced seismic analysis and damage calculation of RC buildings using the Beam-Truss-Model (BTM). The lecture consists of two parts. The first part, presents the observed damage of RC buildings in recent earthquakes including local bar buckling and fracture of reinforcing steel, global buckling of walls, diagonal shear failures as well as the effect of framing between vertical members and slabs in RC buildings. This part reviews experimental large-scale testing results of reinforcing steel, RC components, and RC buildings. The modeling of cyclic inelastic buckling and rupture of reinforcing steel in ETABS is presented. The second part, presents the advanced seismic analysis of RC components (walls, slabs, beams, columns) and buildings using the BTM (Figure 3). The BTM is a design-oriented analysis method developed, in the software Opensees, to model efficiently entire RC buildings and computing accurately their force and deformation capacity affected significantly by flexure-shear interaction. The BTM has been validated using experimental testing results of individual RC walls, coupled RC walls, slabs, and columns including cases where the components experienced shear failures. It has been successfully used to model entire RC core-wall buildings as well as the collapse simulation of the Alto Rio building. The lecture also covers how the BTM can be used in a simplified manner in ETABS Ultimate.
Part V, which consists of Lecture 7, presents the seismic analysis, design, and experimental testing behavior of low-damage rocking wall buildings. The special detailing of rocking components designed to develop low-damage is discussed. The design concepts are validated via 3D NLRHA using robust and practical modeling of rocking planes (Figure 2). The lecture first reviews the nonlinear mechanical behavior of conventional (fixed-base) ductile RC walls including their damage and failure modes as well as their force and displacement limits considering experimental testing data. Based on the limitations of ductile RC walls, the need for improved seismic behavior and damage resistance of concrete walls at regions of high seismic hazard is established. The nonlinear mechanical behavior of rocking concrete (with and without post-tension) is presented. The advances in the design of rocking walls in terms of type, layout, and detailing of reinforcement that enhance the capacity and damage resistance, compared to ductile walls, are covered. Experimental testing results of individual rocking walls and structures validate the theoretical approaches. The modeling and nonlinear analysis of rocking walls using the simplified beam-truss-model in ETABS Ultimate is covered. The concept of rocking planar walls is extended to the case of low-damage rocking core walls for tall buildings and computational simulations of entire buildings are presented. At the end, the experimental testing results of low-damage rocking fiber reinforced concrete columns is presented.
Figure 1. Landmark seismic experiments discussed in the course and links to videos. (a) Shake-table test of a full-scale 7-story RC wall building slice tested by Panagiotou et al.; (b) shake-table-test of a 5-story RC frame building with base-isolated and fixed-base conditions (Courtesy of M. Chen, Pantoli et al. 2016, PI: Hutchinson T.C.); (c) shake-table-test of a 3-story parking structure with low-damage post-tensioned RC rocking walls (Belleri et al. 2014, PI: Fleischman R.B.).
Figure 2. Left: Nonlinear analysis, in ETABS, of 20-story fixed-base and base-isolated core-wall buildings, for the Los Angeles MCE hazard. Right: Nonlinear analysis, in ETABS, of a 20-story rocking low-damage core-wall building for the Los Angeles MCE hazard level.
Figure 3. Left: shear failure analysis using the beam-truss-model of a RC wall specimen; Right: nonlinear analysis, in ETABS, of a 20-story core-wall building with the bottom four stories modeled with the beam-truss-model to capture shear failure of wall piers.