Selim Günay

PEER Performance-Based Earthquake Engineering Methodology, Revisited

A performance-based earthquake engineering (PBEE) methodology was developed at the Pacific Earthquake Engineering Research (PEER) Center. The method is based on explicit determination of performance, e.g., monetary losses, in a probabilistic manner where uncertainties in earthquake ground motion, structural response, damage, and losses are explicitly considered. There is an increasing trend towards use of probabilistic performance-based design (PPBD) methods in practice. Therefore, the International Federation for Structural Concrete (fib) initiated a task group to disseminate PPBD methods. This article is a contribution to this task group summarizing and demonstrating the PEER PBEE methodology in a useful manner to practicing engineers.

Progressive Collapse Analysis of Reinforced Concrete Frames with Unreinforced Masonry Infill Walls Considering In-Plane/Out-of-Plane Interaction

Reinforced concrete (RC) frames with unreinforced masonry (URM) infill walls are commonly used in seismic regions around the world. It is recognized that many buildings of this type perform poorly during earthquakes. Therefore, proper modeling of the infill walls and their effect on RC frames is essential to evaluate the seismic performance of such buildings and to select adequate retrofit methods. Using damage observations of RC buildings with URM infill walls from recent earthquakes, this paper presents a new approach to consider in-plane/out-of-plane interaction of URM infill walls in progressive collapse simulations. In addition, the infill wall effect to induce shear failure of columns is simulated with a nonlinear shear spring modeling approach. The research endeavor is accompanied by implementation of the developed modeling aspects in the publicly available open-source computational platform OpenSees for immediate access by structural engineers and researchers.

INFILL WALLS AS A SPINE TO ENHANCE THE SEISMIC PERFORMANCE OF NON-DUCTILE REINFORCED CONCRETE FRAMES

This paper reports the results of an investigation on the efficacy of using rocking spines of strengthened infill walls as a retrofit measure for non-ductile reinforced concrete (RC) frames with unreinforced masonry (URM) infill walls. The study examines the effects of spines of strengthened URM infill walls on the behavior of the RC frame, with particular emphasis on whether spines could reduce the tendency to form a soft story mechanism. For this purpose, a nine story frame with five bays is selected to represent complex multi-story behavior, where the collapse of stiff infill walls may lead to the formation of a soft story mechanism. The effect of the proposed retrofit is investigated through nonlinear static and dynamic analyses. Fragility relationships are obtained for the frames using pseudo-acceleration corresponding to the first mode as the intensity measure and maximum interstory drift ratio as the response variable. For the analyses, a progressive collapse algorithm, previously developed and implemented into the object-oriented open system for earthquake engineering simulation (OpenSees) is utilized and the interaction between the inplane strength of the infill wall and its out-of-plane strength is taken into consideration. Analyses show that infill retrofit with rocking spines provides significant improvement in the seismic performance of non-ductile RC frames.

Hybrid Simulations: Theory, Applications, and Future Directions

Hybrid simulation is a testing method for examining the seismic response of structures using a hybrid model comprised of both physical and numerical substructures. Because of the unique feature of the method to combine physical testing with numerical simulations, it provides an opportunity to investigate the seismic response of structures in an efficient and economically feasible manner. It is this feature of the method which made it gain widespread use in recent years. This paper presents the theory of the method including an overview of the previous research related to various aspects of the method, an overview of two hybrid simulation applications, and the future directions for transforming the method to its next generation.

ALTERNATIVE INTEGRATORS AND PARALLEL COMPUTING FOR EFFICIENT NONLINEAR RESPONSE HISTORY ANALYSES

This paper is an attempt to address solutions to two common problems associated with nonlinear response history analysis (NRHA). The first is the convergence problems that occur at high levels of nonlinearity, while the second is the computational time which can be prohibitively excessive in certain cases. To overcome the first problem, suitability of the use of alternative integration methods in NRHA instead of the commonly used implicit Newmark integration is investigated. These alternative methods are Explicit Newmark and OperatorSplitting methods, which do not require iterations and convergence checks. NRHA conducted on highway overpass bridges with multiple-column bents showed that the Operator-Splitting method provides very close results to those from the Implicit Newmark method for some of the considered models even for high levels of nonlinearity. The Explicit Newmark method was not successful for the investigated bridge system because of the stability limits which were not feasible to satisfy. However, explicit methods, when applicable, can be useful since they eliminate the convergence problems and reduce the simulation time. Means to improve convergence are also investigated for the implicit Newmark integration method, especially when the use of alternative integration methods is not possible. To address the second problem, parallel and cloud computing resources are utilized together with the alternative time integration methods. Particularly, the parallel version of OpenSees (OpenSees MP) running on NEEShub, currently providing access to up to 4232 processors, is used where significant computing time savings are achieved.

Direct Integration Algorithms for Efficient Nonlinear Seismic Response of Reinforced Concrete Highway Bridges

AbstractReinforced concrete (RC) highway bridges are essential lifeline structures, especially in California, which has numerous active faults at which earthquakes are common occurrences. Accurate seismic structural analysis is important to ensure their safety. The most suitable analytical simulation method for this purpose is nonlinear time-history analysis (NTHA). However, one of the main challenges for NTHA is related to the convergence of the numerical solution, which usually arises at high levels of nonlinearity. Inherent lack of high degrees of redundancy of the bridge systems and the need for their continuous functioning in the aftermath of an earthquake require accurate modeling and robust numerical solutions for the response investigation of these important structures. This paper presents solutions to the problems of convergence encountered in NTHA of RC highway bridges during the use of direct integration algorithms. The considered numerical integration algorithms include two that are explicit, ...

Rocking Spine for Enhanced Seismic Performance of Reinforced Concrete Frames with Infills

AbstractA rocking spine system is introduced as an alternative to more conventional approaches to improve the seismic collapse safety of concrete frames with masonry infills. Although infill frames are not formally recognized in ASCE 7 or other current U.S. building codes for new buildings, infills are present in many existing buildings, and infill frames are still a prevalent type of new construction that is permitted in many parts of the world. The proposed technique uses structural spines, constructed using either strong infill panels or concrete walls, to resist earthquake effects through controlled rocking action. The primary sources of overturning resistance are gravity loads on the spine and the restraint provided by beams and infill panels in framing bays adjacent to the spine. Equations are developed to describe the rocking response of the spine, relating the rigid-body kinematics to the internal deformations, forces and limit states in beams, columns, and infill panels. The main aspects of the d...

Towards Faster Computations and Accurate Execution of Real-Time Hybrid Simulation

This chapter reports three recent developments aimed towards faster computations and more accurate execution of real-time hybrid simulations (RTHS). The first of these developments is a standalone RTHS system which can accommodate integration time steps as small as 1 ms. The fast execution feature eliminates the approximations that would be introduced by the application of a predictor-corrector smoothing technique and increases the applicability range of explicit integration methods. The second development is the use of an efficient equation solver in RTHS which reduces computation time. This efficient solver, which decreases the computation time by factorizing the Jacobian of the system of linear algebraic equations only once at the beginning of the simulation, is especially beneficial in RTHS which involves analytical substructures with large number of degrees of freedom (DOF). The third development is a novel use of a three-variable control (TVC) for RTHS on a shaking table configuration. Although the TVC, which employs velocity and acceleration control in addition to the typical displacement control, is commonly used in conventional shaking table tests, this development is the first application of TVC in RTHS.

Teaching Innovation through Hands-on-Experience Case Studies Combined with Hybrid Simulation

AbstractTeaching innovations in earthquake engineering with special attention to Bloom’s taxonomy is explored utilizing the versatility introduced by the hybrid simulation (HS) testing method. Such innovations focus on developing a variety of case studies with integrated earthquake and structural engineering concepts tailored for high school and first-year undergraduate students. The goal is to effectively guide students to understand the intricacies of real structural systems by visualizing their complex behavior when subjected to earthquake loading. A teaching activity involving theoretical and hands-on-experience components, in which a HS testing demonstration is used as a part of the activity, is described, and the results of this activity are presented. The experiences gathered from this activity and the developed HS experience at various laboratories are used to create new instructional case studies making use of HS.

Progressive Collapse Simulation of Vulnerable Reinforced Concrete Buildings

There are many vulnerable reinforced concrete (RC) buildings located in earthquake-prone areas around the world. These buildings are characterized by the lack of seismic details and corresponding non-ductile behavior and significant potential of partial and global collapse. One of the current challenges of the earthquake engineering profession and research communities is the identification of such buildings and determination of effective and economical retrofit methods for response enhancement. Identification of these buildings is not a trivial task due to the various sources of non-ductile behavior and the large number of involved sources of uncertainty. Furthermore, accurate determination of collapse-prone buildings is important from an economical perspective. Unfortunately, there are not enough economical resources to retrofit all the non-ductile buildings that have the symptoms for collapse potential. In order to use the available monetary resources in an effective manner, these buildings should be accurately and reliably ranked to identify those that are most vulnerable to collapse. This chapter intends to provide a contribution to the accurate determination of the most collapse-vulnerable non-ductile RC buildings by discussing the methods from existing literature and exploring the research needs related to (a) gravity load failure modeling and (b) consideration of different uncertainty sources in an efficient manner.