This paper provides an overview of methods to detect, locate, and characterize damage in structural and mechanical systems by examining changes in measured vibration response. Research in vibration-based damage identification has been rapidly expanding over the last few years. The basic idea behind this technology is that modal parameters (notably frequencies, mode shapes, and modal damping) are functions of the physical properties of the structure (mass, damping, and stiffness). Therefore, changes in the physical properties will cause detectable changes in the modal properties. The motivation for the development of this technology is presented. The methods are categorized according to various criteria such as the level of damage detection provided, model-based versus non-model-based methods, and linear versus nonlinear methods. The methods are also described in general terms including difficulties associated with their implementation and their fidelity. Past, current, and future-planned applications of this technology to actual engineering systems are summarized. The paper concludes with a discussion of critical issues for future research in the area of vibration-based damage identification.

A summary review of vibration-based damage identification methods

Dynamics of structures

Vibration based condition monitoring refers to the use of in situ non-destructive sensing and analysis of system characteristics –in the time, frequency or modal domains –for the purpose of detecting changes, which may indicate damage or degradation. In the field of civil engineering, monitoring systems have the potential to facilitate the more economical management and maintenance of modern infrastructure. This paper reviews the state of the art in vibration based condition monitoring with particular emphasis on structural engineering applications.

Vibration Based Condition Monitoring: A Review:

Design-oriented stress–strain model for FRP-confined concrete

Minimum Design Loads for Buildings and Other Structures provides requirements for general structural design and includes means for determining dead, live, soil, flood, wind, snow, rain, atmospheric ice, and earthquake loads, as well as their combinations, which are suitable for inclusion in building codes and other documents. This Standard, a revision of ASCE/SEI 7-05, offers a complete update and reorganization of the wind load provisions, expanding them from one chapter into six. The Standard contains new ultimate event wind maps with corresponding reductions in load factors, so that the loads are not affected, and updates the seismic loads with new risk-targeted seismic maps. The snow, live, and atmospheric icing provisions are updated as well. In addition, the Standard includes a detailed Commentary with explanatory and supplementary information designed to assist building code committees and regulatory authorities. Standard ASCE/SEI 7 is an integral part of building codes in the United States. Many of the load provisions are substantially adopted by reference in the International Building Code and the NFPA 5000 Building Construction and Safety Code. Structural engineers, architects, and those engaged in preparing and administering local building codes will find this Standard an essential reference in their practice. Note: New orders are fulfilled from the second printing, which incorporates the errata to the first printing.

Minimum Design Loads for Buildings and Other Structures

Steel moment-resisting frames (MRFs) with posttensioned connections are constructed by posttensioning beams to columns using high strength strands. Top and seat angles are added to provide energy dissipation and redundancy under seismic loading. This new type of connection has several advantages, including the following: (1) field welding is not required; (2) the connection stiffness is similar to that of a welded connection; (3) the connection is self-centering; and (4) significant damage to the MRF is confined to the angles of the connection. An analytical model based on fiber elements was developed for these connections. Experimental test results were used to calibrate the model. The model was used for inelastic static analyses of interior connection subassembages as well as dynamic time history analyses of a six-story steel MRF. A self-centering capability and adequate stiffness, strength, and ductility were observed in the results of these analyses. Time history analysis results show that the seismic...

Posttensioned Seismic-Resistant Connections for Steel Frames

This paper presents the results of an experimental investigation of the axial behavior of small-scale circular and square plain concrete specimens and large-scale circular and square reinforced concrete columns confined with fiber reinforced polymer (FRP) composite jackets, subject to monotonic, concentric axial loads. Improvements in the axial load-carrying and deformation capacities of FRP jacketed concrete members over unjacketed members are reported. Factors influencing the axial stress-strain behavior of FRP confined concrete, such as transverse dilation and effectively confined regions and their relationship to jacket properties, are identified and discussed. Factors necessary to calibrate in situ jacket behavior and reported or measured FRP material properties are proposed and their interrelationships discussed.

Axial Behavior of Reinforced Concrete Columns Confined with FRP Jackets

As buckling-restrained braced frames (BRBFs) have been used increasingly in the United States, the need for knowledge about BRBF behavior has grown. In particular, large-scale experimental evaluations of BRBFs are necessary to demonstrate the seismic performance of the system. Although tests of buckling-restrained braces (BRBs) have demonstrated their ability to withstand significant ductility demands, large-scale BRBF tests have exhibited poor performance at story drifts between 0.02 and 0.025 rad. These tests indicate that the large stiffness of the typical beam-column-brace connection detail leads to large flexural demands that cause undesirable failure modes. As part of a research program composed of numerical and experimental simulations, a large-scale BRBF with improved connection details was tested at the ATLSS Center, Lehigh University. During multiple earthquake simulations, which were conducted using a hybrid pseudodynamic testing method, the test frame sustained story drifts of close to 0.05 rad and BRB maximum ductility demands of over 25 with minimal damage and no stiffness or strength degradation. The testing program demonstrated that a properly detailed BRBF can withstand severe seismic input and maintain its full load-carrying capacity.

Experimental Evaluation of a Large-Scale Buckling-Restrained Braced Frame

Nine large-scale subassembly tests were conducted to investigate the behavior of an innovative posttensioned wide flange beam-to-column connection for steel moment resisting frames subjected to seismic loading conditions. The connection includes top and seat angles bolted to the beam and column. Strands are placed along the length of the beam, passing through the column and posttensioned to provide a precompression of the beam against the column. The parameters investigated in the study include the angle thickness, angle gage length, beam flange reinforcing plates, connection shim plates, and posttensioning force. The test results demonstrate that posttensioned connections provide excellent elastic stiffness, strength, and ductility under cyclic loading, with energy dissipation occurring primarily in the angles. The connection initial elastic stiffness is comparable to that of a fully restrained welded connection. In addition, the connection has essentially no residual deformation following several cycles...

Experimental Evaluation of Earthquake Resistant Posttensioned Steel Connections

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.

James M. Ricles

Papers

Posttensioned Seismic-Resistant Connections for Steel Frames

Axial Behavior of Reinforced Concrete Columns Confined with FRP Jackets

Experimental Evaluation of a Large-Scale Buckling-Restrained Braced Frame

Experimental Evaluation of Earthquake Resistant Posttensioned Steel Connections

Experimental studies of full-scale posttensioned steel connections