Barry J. Goodno

TESTING OF ENERGY DISSIPATING CLADDING CONNECTIONS

Properly designed precast concrete cladding could potentially provide lateral stiffness, ductility, and energy dissipation for an overall building structure, especially during earthquakes. This paper describes a set of advanced connections that take advantage of the interaction between facade panels and structure (mainly due to horizontal interstorey drift) to dissipate energy, thereby reducing the response of the main structure. The results of an experimental program to characterize the hysteretic behaviour of advanced connections are presented. Design equations for the advanced connections are then calibrated against the test results, and the corresponding design charts are presented. It is anticipated that this research will lead to innovative ways of viewing the entire cladding system of a building.

Passive Control of Building Response Using Energy Dissipating Cladding Connections

Ductile cladding connections take advantage of the cladding-structure interaction during an earthquake to dissipate energy. An experimental test program studied the behavior of the different components of a connection system. Analytical models of the connection were incorporated into a 2D model of a six story building with cladding. Time histories of the energy demand and supply to the building, both with and without cladding, trace the response of the structure to earthquake excitations. Results show that properly designed energy dissipative connector elements can be responsible for the total hysteretic energy dissipated in the structural system. A design criterion for the connection that is formulated in terms of energy provides the optimal balance of stiffness and strength to be added to the structure by the dissipators. It results in maximum energy dissipation in the connectors, no plastification in the structural members, and reduced structural response. This approach could be applicable to both new and retrofitted buildings.

Effects of the January 2010 Haitian Earthquake on Selected Electrical Equipment

The focus of this survey was to collect data on the performance of mechanical and electrical systems at selected critical facilities in Haiti. First-hand observations confirmed that nonstructural elements that are well anchored and/or laterally restrained will perform well during a moderate seismic event. However, the investigation also revealed that many critical institutions in Haiti did not utilize state-of-the-art engineering design or construction practices when installing nonstructural equipment that turned out to be crucial to their post-earthquake operations. The survey team believes that absent or poorly implemented seismic anchorage of nonstructural elements hampered the ability to restore essential systems to operation after the event.

Building seismic response attenuation using robust control and architectural cladding

Robust control methods are used to design a hybrid control system that includes an active tensioning (bracing) system and a passive control system consisting of rigid cladding panels connected to the building with ductile (hysteretic) connection elements. Mu-synthesis control design methods are shown to yield controllers that remain stable and effective in the presence of significant stiffness changes in the structure (plant) introduced by the addition of the passive hysteretic damping. Controller stability is achieved in exchange for reduced nominal performance and increased controller complexity. The result is an overall 84% reduction in the peak response from the uncontrolled, undamped system.

Seismic evaluation of a low rise steel building

Abstract Most low rise building structures (four storeys or less) in the US today have received little, if any, design for lateral forces due to earthquakes, except in those few areas in which seismic analysis is mandated by local building codes. Infrequent but damaging earthquakes in areas of low to moderate seismicity may pose a substantial threat to structures not specifically designed for earthquake resistance. A well designed two storey steel office building located in Atlanta, Georgia, proportioned for gravity and wind loads only, was selected for detailed seismic evaluation. The dynamic properties of the building were obtained from analyses of three-dimensional computer models. The effective shear stiffness of diaphragms was used to study the influence of diaphragm flexibility on model response. The lateral force resisting capability of the building was evaluated using seismic load provisions of the Uniform Building Code and the tentative provisions of ATC-3. Elastic and inelastic responses of the analytical models to moderate earthquake motions were also determined. The inelastic response spectrum force levels were in good agreement with code values. Seismic resistance was found to be satisfactory for both the code and inelastic response spectrum force levels which were larger than the actual design wind loads.

Memory management in structural analysis on microcomputers

Abstract In the development of large and/or complex structural analysis programs on microcomputers, such as those for dynamic analysis of buildings, the size of the in-core memory is the primary limitation. In this paper, different ways of handling large matrices, which may arise in dynamics or other applications are discussed. Some techniques such as the use of ‘ram buffers’ in conjunction with hard disk or the use of unidimensional arrays with pointers and modular programming, are presented as an effective alternative to cope with memory limitations. The use of these techniques in a program for response spectrum dynamic analysis of R/C buildings is described.

APPLICATION OF PROBABILISTIC DECISION MODELS FOR SEISMIC REHABILITATION OF STRUCTURES

This paper outlines a decision framework that incorporates state-of-the-art earthquake engineering information and decision maker preferences into multicriteria decision models to support earthquake risk mitigation decisions. Seismic risk analysis of a structure is utilized for probabilistic estimation of the anticipated seismic losses, which in turn is used as inputs to the decision analysis for seismic rehabilitation of the structure. Three decision models are used to provide insight into the value of system interventions to reduce earthquake risks: (1) an equivalent cost model, (2) multi-attribute utility theory, and (3) joint probability decision making. Guidelines for selecting and applying multicriteria decision models for seismic rehabilitation of building structures are derived based on preferences for including risk attitudes and for measuring values. The detailed procedures for the selection and application of the decision models for seismic rehabilitation of building structures are demonstrated through a case study, where a collection of hospitals in a metropolitan area is examined.

Performance evaluation of robust controllers in earthquake structural dynamics problems with large hysteretic nonlinearities

Hybrid passive-active systems for controlling building seismic response offer the promise of combining the best features of each to achieve superior performance. Analytical investigations of building hybrid control systems designed to combine robust active control systems with passive damping provided by structural hysteresis are described. The passive control forces were introduced through hysteretic interaction between heavy architectural cladding and the supporting structure, while the active control forces were assumed to be generated by an active tendon system. Results presented for a case study structure show that the hybrid control system was more effective in reducing peak drift compared with the cases of either the passive or active systems acting alone. Moreover, it is shown that a practical robust control system of reduced order can be designed with sufficient and robust stability to tolerate as much as a 50% change in the nominal structural stiffness. At the same time, the presence of passive damping yielded reduction in peak force requirements for the active system.

EFFECTS OF THE JANUARY 2010 HAITIAN EARTHQUAKE ON SELECTED EQUIPMENT AND THE IMPLICATIONS FOR THE SEISMIC DESIGN OF CRITICAL NON-STRUCTURAL COMPONENTS REQUIRED FOR POST-EARTHQUAKE RECOVERY OPERATIONS IN DEVELOPING COUNTRIES

Director and Chief of Technology, ABS Consulting, 77 Westport Plaza, Suite 210, St. Louis, MO 63146; Ph (314) 819-1550; email: ngould@absconsulting.com Professor, School of Civil & Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, 30332-0355, Ph (404) 894-2227, email:bg6@ce.gatech.edu Harold D. Jolley Professor, MEMS Department, Washington University, St. Louis, MO; Ph (314) 935 6383; email: pgoul@seas.wustl.edu Schneider Electric Codes & Standards, 1990 Sandifer Blvd., Seneca, South Carolina 29678, Ph (864) 886-1471; email: philip.caldwell@us.schneider-electric.com

Hybrid Control of Buildings with Hysteretic Cladding Connection Elements

Publisher Summary This chapter describes analytical investigations of hybrid control systems for buildings designed to combine passive damping provided by cladding-structure interaction with robust active control systems. Hybrid passive–active systems for controlling building seismic response offer combines the best features of each to achieve superior performance. A hybrid control system, consisting of passive cladding and active tendon systems, was found to be an effective means of reducing building seismic response for a broad range of input motion levels. The passive system consisted of heavy cladding combined with specially designed advanced connector elements which dissipate energy at low excitation levels and yet retain structural integrity under larger motion. The passive control forces were introduced through hysteretic interaction between heavy architectural cladding and the supporting structure, while the active control forces were assumed to be generated by an active tendon system. The active tendon system was designed to operate at higher excitation levels. To illustrate the role of hybrid control applications in the seismic response of building structures, simulation studies were performed on a 1/4 scale 6-story steel space frame. When used together, the resulting hybrid system was shown to yield reduced demands on either the passive or active systems acting alone, while at the same time lowering building interstory drift response. Analytical results remain to be verified with laboratory experiments on the case study structure to complete the validation of the concept of heavy cladding systems as part of an economical hybrid control system for buildings in seismic regions.