Stuart S. Chen

FUNDAMENTAL CONSIDERATIONS FOR THE DESIGN OF NON-LINEAR VISCOUS DAMPERS

An Erratum has been published for this article in Earthquake Engineering and Structural Dynamics 2000; 29(7):1076. Two interrelated issues related to the design of non-linear viscous dampers are considered in this paper: structural velocities and equivalent viscous damping. As the effectiveness of non-linear viscous dampers is highly dependent on operating velocities, it is important to have reliable estimates of the true velocity in the device. This should be based on the actual relative structural velocity and not the commonly misused spectral pseudo-velocity. This is because if spectral pseudo-velocities (PSV) are used, they are based on design displacements (Sv=ω0Sd) and are thus fundamentally different from the actual relative structural velocity. This paper examines the difference between these two velocities, and based on an extensive study of historical earthquake motions proposes empirical relations that permit the designer to transform the well-known spectral pseudo-velocity to an actual relative structural velocity for use in design. Non-linear static analysis procedures recommended in current guidelines for the design of structural systems with supplement damping devices are based on converting rate-dependent device properties into equivalent viscous damping properties based on an equivalent energy consumption approach. Owing to the non-linear velocity dependence of supplemental devices, an alternative approach for converting energy dissipation into equivalent viscous damping is advanced in this paper that is based upon power consumption considerations. The concept of a normalized damper capacity (ϵ) is then introduced and a simple design procedure which incorporates power equivalent linear damping based on actual structural velocities is presented. Copyright

The Seismic Response of a 1:3 Scale Model R.C. Structure with Elastomeric Spring Dampers

In this experimental study, elastomeric spring dampers, which have a distinct re-centering characteristic, are used to retrofit a non-ductile, previously damaged 1/3 scale model reinforced concrete building frame structure which is subjected to a variety of ground motions in shaking table tests. A velocity dependent analytical model is developed and verified for the elastomeric spring dampers. This model is implemented in the widely available non-linear dynamic time history analysis computer program DRAIN-2DX to produce response predictions which are in good agreement with experimental observations. The elastomeric spring damper devices significantly attenuate the seismic response of the structure and provide a considerable amount of energy dissipation while the main non-ductile reinforced concrete structural load carrying elements remain elastic. The effect of varying the damper configuration on the structural response was also investigated.

Automated Signal Monitoring Using Neural Networks in a Smart Structural System

Automated health monitoring of instrumented structures will require an appropriate suite of information processing techniques. One such technique, involving Quickprop neural networks, is developed to identify and locate structural damage in a 3D steel truss-type structure instrumented with accelerometers and strain gauges. In experiments conducted in a structural testing laboratory, transient vibration tests caused by impact hammer strikes were conducted on the instrumented structure which was subjected to various damage scenarios. Results of the investigation indicate that neural networks provide a promising approach as one component of the computational tool kit required for on-line autonomous health monitoring of instrumented structures. Anticipating the need for such a comprehensive tool kit, a computational framework for automated signal monitoring is proposed and introduced as well. This framework incorporates signal processors based on neural networks in an object-oriented model for structural monitoring and diagnosis.

Integration of Information and Automation Technologies in Bridge Engineering and Management: Extending the State of the Art

The current U.S. practice of information transfer during the bridge design, fabrication, construction, and operation processes is fragmented. These processes involve repeated manual transcription of data, which is error prone; approvals (e.g., of shop drawings) that are time-consuming; and formats that beg for standardization to facilitate electronic information transfer. Without such standards, electronic information exchange is impossible. This paper surveys the shortcomings of current piecemeal applications of information and automation technologies. It then explores the promise of parametric three-dimensional bridge information modeling as an enabling technology for accelerating the design and delivery of bridges and articulates aspects of the envisioned accelerated bridge delivery process for two purposes: to provide a glimpse of current technologies available to streamline the process of bridge delivery and to articulate anticipated advances that can be expected to facilitate accelerated bridge deli...

Component-based building representation for design and construction

Abstract This paper challenges the current limited use of computers in design and proposes the Component-Based Paradigm as an all encompassing model for building representation. The paradigm introduces the concept of a single three-dimensional computer-based model for the design process and explores the development of reasoning tools in a component modeling environment.

Seismic Investigation of Steel Pile Bents: II. Retrofit and Vulnerability Analysis

This paper is the second of a two-part study on the seismic vulnerability of deck bridges supported on steel pile bents. A conceptual elastic cap/elasto-plastic steel pile retrofit strategy is proposed in this part with the aim of strengthening the connection and ensuring plastification takes place only in the steel pile. An experimental program was carried out to assess the retrofit strategy. On the basis of the experimental results for existing as well as retrofitted connections, a seismic vulnerability analysis for bridges supported by steel pile bents was performed. Fragility curves for such structures were developed using a simplified fundamental mechanics-based approach. The study showed that the retrofitted connections exhibited superior energy absorptions with respect to the existing connections. Fragility curves also demonstrated the effectiveness of the retrofit strategy proposed.

Computer-Aided Design of Passive Snow Control Measures

Control of blowing and drifting snow on the nations highways is important to reducing maintenance costs and closure times and to improving crash incidence by improving visibility, preventing drifting on the road, and reducing road icing. Means of engineered mitigation using road design and snow fences have been incorporated into a software tool, SnowMan (for Snow Management), that has been deployed for use statewide within the New York State Department of Transportation. The software has been developed as a MicroStation Development Language application to run within the Bentley Micro-Station CAD software environment used in highway design projects. The scope of SnowMan includes drift prediction (mitigated and unmitigated), evaluation of roadway cross sections and determination of trial fence solutions subject to combinations of height, setback, porosity constraints, and prescription of upwind earthwork solutions. This paper describes the development and implementation of this software tool for mitigation of blowing and drifting snow problems and illustrates its usage, while also providing an overview of the relevant data, underlying algorithms, and engineering approaches to blowing and drifting snow mitigation as implemented in SnowMan.

Cyclic Performance of Precast Concrete Segmental Bridge Columns: Simplified Analytical and Finite Element Studies

The cyclic performance of an unbonded precast concrete segmental bridge column system is examined in this paper. This system uses unbonded posttensioning to enhance the self-centering capability and mild steel reinforcement extended across the segment joints to enhance the energy dissipation capability. A simplified analytical method for the system under lateral load is established, and the simplified analytical results are compared with those obtained from the three-dimensional (3-D) finite element method (FEM). On the basis of the simplified analytical method, suggestions are made about both the height of the column to which the mild steel should be continued from the foundation and the limitation of the steel ratio to minimize residual displacement. With the steel ratio varied, the correlation between the energy dissipation capability and the self-centering capability of this system is investigated by means of the 3-D FEM. From simulation results, it was found that both the energy dissipation and the r...

Neural-network-based signal monitoring in a smart structural system

This paper focuses on the signal processing aspect of a smart structure computational support environment for health monitoring, investigating the use of neural networks to identify and locate structural damage in a steel truss structure instrumented with accelerometers and strain gauges. Cracking damage is simulated by introducing sawcuts into the main members of the structure. Results using accelerometer data alone indicate that Quickprop backpropagation neural networks constitute a promising tool for these purposes, although network performance in locating damage should be improved by use of strain data as well.

Three-Dimensional Parametric Data Exchange for Curved Steel Bridges

Improved software interoperability is key to realizing more fully the potential benefits of integrated and accelerated project delivery in a way that also somehow ensures product quality. The increasing appeal of three-dimensional (3-D) building information modeling (BIM) notions applied to bridges [known as bridge information modeling (BrIM)] motivates the need for principled prescriptions of associated electronic data exchanges between various project stakeholders and the various software applications that they use. Such data exchanges must be sufficiently precise to facilitate detailing for fabrication and construction while being sufficiently concise to facilitate parametric modeling and thereby avoid needless data duplication. The highway geometry to which bridges must conform distinguishes BrIM from the building column grid orientation of BIM at the outset of the bridge life cycle. In contrast to the over defined highway geometry in the LandXML data exchange standard, a 3-D control curve is defined, presented, illustrated, and recommended as the basis for parametric data exchange suitable through the life cycle of steel I-girder bridges on (straight and) curved alignments. This 3-D control curve combines in a single curve the traditional horizontal control line and profile grade line that bridge structural engineers receive from highway designers to define bridge geometry. Data exchanges associated with three distinct stages in the life cycle of a steel bridge are defined and illustrated: analysis and design, detailing for fabrication, and erection and construction. The data exchange based on a 3-D control curve provides the data integrity required through the life cycle of a steel bridge.