Search

The reciprocal of the condition number of the stiffness matrix was determined to be Graph HT ht . The authors have conducted the same analysis and found that I the result for the MKR- i Graph HT ht I method in Figure 1(c) of the discussion paper is wrong i . The authors have conducted the same analysis and found that I the results for the MKR- i Graph HT ht I method in Figure 3 of the discussion paper are again wrong i . [Extracted from the article]

• Structure with variable dynamic properties is considered in ground motion selection; • A site-specific ground motion selection procedure using target UHS is proposed; • PBEE framework to relate hazard to structural response prediction is implemented; • Suites of ground motions at various hazard levels are selected for a paradigm site; • The probability distribution and variability of major EDPs are evaluated; With an emphasis on predictable performance, the paramount importance of performance-based earthquake engineering (PBEE) in quantifying earthquake risks and facilitating the better-informed design of the built environment to achieve earthquake resilience has been widely acknowledged. And the uses of damping systems, i.e., structures incorporated with supplemental damping devices, have been recognized as an effective structural development to increase the resilience of structures to earthquakes. This paper presents a uniform hazard spectrum (UHS) based site-specific ground motion selection procedure, to implement the PBEE framework to relate earthquake hazard to structural performance for structures with variable dynamic properties. This ground motion selection procedure accounts for the effect of variable structural dynamic properties on hazard characterization for structures with damping systems. A paradigm building site, on which the site-specific hazard from the probabilistic seismic hazard analysis (PSHA) is consistent with the risk-targeted hazard from the design maps of ASCE/SEI 7-10, is selected for the implementation of the procedure. Three suites of 40 ground motions representing various hazard intensities at the building site are selected for time history dynamic analysis of a prototype structure with nonlinear viscous damping system. Evaluated is the probability distribution of major engineering demand parameters (EDPs) including story drift, residual story drift, floor velocity, and floor acceleration. The results demonstrated that the major EDPs of a building structure with supplemental nonlinear viscous dampers at a paradigm site can be estimated using the lognormal probability distribution, and the proposed UHS-based site-specific ground motion selection procedure is critical to the performance assessment of structures with variable dynamic properties in the PBEE framework. [ABSTRACT FROM AUTHOR]

The 'model-based' algorithms available in the literature are primarily developed for the direct integration of the equations of motion for hybrid simulation in earthquake engineering, an experimental method where the system response is simulated by dividing it into a physical and an analytical domain. The term 'model-based' indicates that the algorithmic parameters are functions of the complete model of the system to enable unconditional stability to be achieved within the framework of an explicit formulation. These two features make the model-based algorithms also potential candidates for computations in structural dynamics. Based on the algorithmic difference equations, these algorithms can be classified as either explicit or semi-explicit, where the former refers to the algorithms with explicit difference equations for both displacement and velocity, while the latter for displacement only. The algorithms pertaining to each class are reviewed, and a new family of second-order unconditionally stable parametrically dissipative semi-explicit algorithms is presented. Numerical characteristics of these two classes of algorithms are assessed under linear and nonlinear structural behavior. Representative numerical examples are presented to complement the analytical findings. The analysis and numerical examples demonstrate the advantages and limitations of these two classes of model-based algorithms for applications in structural dynamics. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY This paper evaluates the seismic resistance of steel moment resisting frames (MRFs) with supplemental fluid viscous dampers against collapse. A simplified design procedure is used to design four different steel MRFs with fluid viscous dampers where the strength of the steel MRF and supplemental damping are varied. The combined systems are designed to achieve performance that is similar to or higher than that of conventional steel MRFs designed according to current seismic design codes. Based on the results of nonlinear time history analyses and incremental dynamic analyses, statistics of structural and non-structural response as well as probabilities of collapse of the steel MRFs with dampers are determined and compared with those of conventional steel MRFs. The analytical frame models used in this study are reliably capable to simulate global frame collapse by considering full geometric nonlinearities as well as the cyclic strength and stiffness deterioration in the plastic hinge regions of structural steel members. The results show that, with the aid of supplemental damping, the performance of a steel MRF with reduced design base shear can be improved and become similar to that of a conventional steel MRF with full design base shear. Incremental dynamic analyses show that supplemental damping reduces the probability of collapse of a steel MRF with a given strength. However, the paper highlights that a design base shear equal to 75% of the minimum design base shear along with supplemental damping to control story drift at 2% (i.e., design drift of a conventional steel MRF) would not guarantee a higher collapse resistance than that of a conventional MRF. At 75% design base shear, a tighter design drift (e.g., 1.5% as shown in this study) is needed to guarantee a higher collapse resistance than that of a conventional MRF. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Real-time hybrid simulation (RTHS) is a testing method by which a structural system is divided into analytical and experimental substructures. This paper proposes a methodology to conduct RTHS for structures that use passive nonlinear viscous dampers (NLVDs), some of which are physically tested in the experimental substructure and others that are in the analytical substructure via online model updating (OMU). The proposed methodology uses the response of a physically modelled NLVD to improve the response prediction of the numerically modelled NLVDs. An explicit solution of the constitutive relations of the Nonlinear Maxwell Model (NLMM) is proposed to perform a non-iterative real-time state determination of a damper modelled using the NLMM. The model updating is performed using the Unscented Kalman Filter (UKF). RTHS of a two-story reinforced concrete structure subjected to strong earthquake ground motions (including both near-field and far-field recorded earthquake records) are performed to validate the model updating procedure. • Explicit-based solution of nonlinear Maxwell model constitutive relations. • Formulation allows real-time updating of model parameters. • Real time hybrid simulations using explicit-based model with on-line model updating. [ABSTRACT FROM AUTHOR]

SUMMARY Real-time hybrid simulation is a viable experiment technique to evaluate the performance of structures equipped with rate-dependent seismic devices when subject to dynamic loading. The integration algorithm used to solve the equations of motion has to be stable and accurate to achieve a successful real-time hybrid simulation. The implicit HHT α-algorithm is a popular integration algorithm for conducting structural dynamic time history analysis because of its desirable properties of unconditional stability for linear elastic structures and controllable numerical damping for high frequencies. The implicit form of the algorithm, however, requires iterations for nonlinear structures, which is undesirable for real-time hybrid simulation. Consequently, the HHT α-algorithm has been implemented for real-time hybrid simulation using a fixed number of substep iterations. The resulting HHT α-algorithm with a fixed number of substep iterations is believed to be unconditionally stable for linear elastic structures, but research on its stability and accuracy for nonlinear structures is quite limited. In this paper, a discrete transfer function approach is utilized to analyze the HHT α-algorithm with a fixed number of substep iterations. The algorithm is shown to be unconditionally stable for linear elastic structures, but only conditionally stable for nonlinear softening or hardening structures. The equivalent damping of the algorithm is shown to be almost the same as that of the original HHT α-algorithm, while the period elongation varies depending on the structural nonlinearity and the size of the integration time-step. A modified form of the algorithm is proposed to improve its stability for use in nonlinear structures. The stability of the modified algorithm is demonstrated to be enhanced and have an accuracy that is comparable to that of the existing HHT α-algorithm with a fixed number of substep iterations. Both numerical and real-time hybrid simulations are conducted to verify the modified algorithm. The experimental results demonstrate the effectiveness of the modified algorithm for real-time testing. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY Real-time hybrid simulation provides a viable method to experimentally evaluate the performance of structural systems subjected to earthquakes. The structural system is divided into substructures, where part of the system is modeled by experimental substructures, whereas the remaining part is modeled analytically. The displacements in a real-time hybrid simulation are imposed by servo-hydraulic actuators to the experimental substructures. Actuator delay compensation has been shown by numerous researchers to vitally achieve reliable real-time hybrid simulation results. Several studies have been performed on servo-hydraulic actuator delay compensation involving single experimental substructure with single actuator. Research on real-time hybrid simulation involving multiple experimental substructures, however, is limited. The effect of actuator delay during a real-time hybrid simulation with multiple experimental substructures presents challenges. The restoring forces from experimental substructures may be coupled to two or more degrees of freedom (DOF) of the structural system, and the delay in each actuator must be adequately compensated. This paper first presents a stability analysis of actuator delay for real-time hybrid simulation of a multiple-DOF linear elastic structure to illustrate the effect of coupled DOFs on the stability of the simulation. An adaptive compensation method then proposed for the stable and accurate control of multiple actuators for a real-time hybrid simulation. Real-time hybrid simulation of a two-story four-bay steel moment-resisting frame with large-scale magneto-rheological dampers in passive-on mode subjected to the design basis earthquake is used to experimentally demonstrate the effectiveness of the compensation method in minimizing actuator delay in multiple experimental substructures. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A building may suffer damage during an earthquake as a result of inelastic deformations developed in the members or connections. It is important that the structural integrity of the building be assessed to ensure the safety of the occupants. This assessment includes evaluating the ability of the structure to resist the demand from subsequent aftershocks and a major earthquake. In this paper a practical methodology to determine the low-cycle fatigue life of welded structural steel connections subject to inelastic cyclic loading is presented. The methodology is based on concepts of low-cycle fatigue and micromechanics, where an accumulated crack length based on a time history of strain and the corresponding triaxiality stress condition that develops in the structural component is calculated and used to establish the fatigue life. The methodology was used to predict the fatigue life of welded beam-to-column connection test specimens subjected to inelastic loading. A comparison with test results indicates that the methodology predicts reasonably well the relationship between number of cycles to fracture and the plastic rotation range observed in the test specimens. [ABSTRACT FROM AUTHOR]

Numerous devices exist for reducing or eliminating seismic damage to structures. These include passive dampers, semi-active dampers, and active control devices. The performance of structural systems with these devices has often been evaluated using numerical simulations. Experiments on structural systems with these devices, particularly at large-scale, are lacking. This paper describes a real-time hybrid testing facility that has been developed at the Lehigh University NEES Equipment Site. The facility enables real-time large-scale experiments to be performed on structural systems with rate-dependent devices, thereby permitting a more complete evaluation of the seismic performance of the devices and their effectiveness in seismic hazard reduction. The hardware and integrated control architecture for hybrid testing developed at the facility are presented. An application involving the use of passive elastomeric dampers in a three story moment resisting frame subjected to earthquake ground motions is presented. The experiment focused on a test structure consisting of the damper and diagonal bracing, which was coupled to a nonlinear analytical model of the remaining part of the structure (i.e., the moment resisting frame). A tracking indictor is used to track the actuator's ability to achieve the command displacement during a test, enabling the quality of the test results to be assessed. An extension of the testbed to the real-time hybrid testing of smart structures with semi-active dampers is described. [ABSTRACT FROM AUTHOR]

Large-scale laboratory experiments are carried out to evaluate and improve the performance of structural members, connections, and assemblies. The information related to these large-scale structural laboratory experiments, such as pseudo-dynamic tests and hybrid pseudo-dynamic tests, is often complicated and stored in various documents, drawings, photos, and other computer-based files. A data model is needed to organize this information and the related data from the structural experiments, so that this information and data can be accessed, shared, and used efficiently. This paper describes a data model for large-scale structural laboratory experiments developed at the Real-Time Multi-Directional (RTMD) testing facility at the ATLSS Center at Lehigh University. The RTMD facility is an equipment site within the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES). The data model is called the Lehigh Model. For typical structural experiments, the Lehigh Model has a class hierarchy consisting of the project, experimental task, test condition, and test classes to organize and represent information about structural laboratory experiments. For hybrid pseudo-dynamic tests, the model also has the hybrid experimental task class and related classes to represent the communications among the simulation coordinator at a site, the analytical substructures at one or more sites, and the physical substructures at one or more sites. The test condition class provides more detailed information on the setup of a structural experiment including the geometries, materials, and locations of the components of the specimen. An application of the classes of the Lehigh Model is presented using steel moment connection tests as an example. [ABSTRACT FROM AUTHOR]

An analytical study was conducted to investigate the seismic behavior of reduced beam section (RBS) moment connections to a deep wide flange column. Calibrated three-dimensional finite element models of RBS connections in perimeter special moment resisting frames with deep columns were used to perform parametric studies under inelastic monotonic and cyclic loading. The parameters in the study included: beam-to-column connection type, column section, composite floor slab, panel zone strength, and beam web slenderness. The results from the parametric study show that a composite floor slab provides restraint to the top flange of the beams, reducing the magnitude of beam top and bottom flange lateral movement in the RBS, column twist, and strength degradation due to beam instability in the RBS. The effect of beam web slenderness contributing to an increase in the lateral movement of the beam flange in the RBS and column flange is significantly reduced when a composite floor slab is present. A weaker panel zone results in higher potential for ductile fracture in the connection region. An RBS connection to a deep column is shown to have less potential for ductile fracture in the connection region than a welded unreinforced flange connection. The potential for fracture is increased in RBS connections when the column section properties are reduced, leading to larger stress and strain. [ABSTRACT FROM AUTHOR]

Six full-scale interior connection subassemblies of posttensioned wide flange beam-to-column moment connections were subjected to inelastic cyclic loading up to 4% story drift to simulate earthquake loading effects. Bolted top and seat angles are used in the connection, along with posttensioned high strength strands that run parallel to the beam. These strands compress the beam flanges against the column flange to develop the resisting moment to service loading and to provide a restoring force that returns the structure to its initial position following an earthquake. The parameters studied in these experiments were the initial posttensioning force, the number of posttensioning strands, and the length of the reinforcing plates. The experimental results demonstrate that the posttensioned connection possesses good energy dissipation and ductility. Under drift levels of 4%, the beams and columns remain elastic, while only the top and seat angles are damaged and dissipate energy. The lack of damage to the beams, columns, and the posttensioning enable the system to return to its plumb position (i.e., it self-centers). Closed-form expressions are presented to predict the connection response and the results from these expressions compare well with the experimental results. [ABSTRACT FROM AUTHOR]

The behavior of square concrete-filled steel tube (CFT) beam–columns made from high-strength materials was investigated experimentally. The effects of the width-to-thickness ratio, yield stress of the steel tube and the axial load level on the stiffness, strength and ductility of high-strength CFT beam–columns were studied. Sixteen three-quarter scale CFT specimens, which included eight monotonic beam–column specimens and eight cyclic beam–column specimens, were tested. The experimental results indicate that cyclic loading does not have a significant influence on the stiffness or strength of CFT beam–columns. However, it causes a more rapid decrease of the post-peak moment resistance. The moment capacity of high-strength CFT beam–columns can be predicted with reasonable accuracy using the American Concrete Institute (ACI) code provisions for composite columns.Fiber-based models were developed for the CFT beam–column specimens. The uniaxial stress–strain curves for the fibers were derived from three-dimensional nonlinear finite element analyses of the CFTs. The results from the fiber analyses of the monotonic and cyclic beam–column specimens compare favorably with the experimental results. [Copyright &y& Elsevier]

A response by Cheng Chen and James M. Ricles to a letter to the editor about their article "Real-time hybrid testing using the unconditionally stable explicit CR integration algorithm," that was published in the 2009 issue.