Evaluating Existing and Proposing New Seismic Design Provisions for Rigid Wall - Flexible Diaphragm Buildings

Buildings with heavy concrete on masonry walls supported by flexible wood or steel deck roof diaphragms are ubiquitour across the United States and the rest of North America. The current seismic design approach is based on the equivalent lateral force (ELF) method whose underlying assumptions significantly differ from the actual dynamic response of these buildings. The seismic behavior of rigid wall-flexible rood diaphragm (RWFD) Buildings is dominated by the diaphragm\u27s response instead of the wall\u27 in-plane response. Furthermore, the diaphragm\u27s ductility and overstrength capacity is unique to its own construction. Yet the current design methodology employed by practitioners directly ties the diaphragm shears and overstrength to the characteristics of the seismic force0resisting system\u27s (SFRS) vertical elements. Past problems in these buildings have been the repeated failures of the walls\u27 anchorage to the diaphragm, and through a series of trial and error iterations, the current design provisions have evolved. current wall anchorage forces for RWFD buildings are believed to now be near maximum expected force levels with litter necessary reliance on connector ductility; however, solving the wall anchorage issue may result in new failures within the diaphragm itself. Using a dedicated numerical modeling framework coupled with a FEMA P-695 collapse capacity evaluation process, a research study was conducted t evaluate performance for a variety of RWFD archetypes conforming to ASCE/SEI 7-10, as well as redesigned archetypes conforming to a new design methodology. Furthermore, a review of the predicted wall anchorage forces in FWFD buildings was also compared with existing design provisions. A new RWFD design methodology is proposed providing a rational approach to improve performance in these unique buildings

Effects of Cold-formed Steel Framed Gypsum Partition Walls on the Seismic Response of a Medical Facility

The first experimental phase of the NEES Nonstructural Grand Challenge Project: “Simulation of the Seismic Performance of Nonstructural Systems” investigated the in-plane hysteretic behaviors of thirty-six full-scale cold-formed steel framed gypsum partition walls. Results of quasi-static reverse cyclic and dynamic testing on sixteen wall configurations including walls with commercial and institutional construction details and innovative connection techniques are first briefly reviewed. Thereafter, six tri-linear hysteretic models of partition walls with pinching behavior and strength and stiffness degradation are developed based on the experimental data for use in a finite element analysis platform. The partition wall models, represented by shear spring elements at each floor level, are incorporated into a numerical model of a four story steel moment frame medical facility. Although nonstructural components are required to carry self-imposed loads and minimal external loads and are not required to be considered in the structural analysis and design of buildings, the addition of the partition walls are shown to increase the stiffness and strength of the building, reducing the natural period by more than 11%. Furthermore, partition walls are shown to introduce over 42% more damping into the building due to the continual energy dissipation through their pinched hysteretic behaviors. The effect of the nonstructural partition walls on the inter-story displacements and absolute accelerations is also examined

Seismic design of friction damped braced steel plane frames by energy methods

The investigation described in this thesis represents the first known attempt to develop a simplified method for the seismic design of structures equipped with a novel friction damping system. The system has been shown experimentally to perform very well and is an exciting development in earthquake resistant design. The design of a building equipped with the friction damping system is achieved by determining the optimum slip load distribution to minimize structural response. A new efficient numerical modelling approach for the analysis and design of Friction Damped Braced Frames (FDBF) is presented. The hysteretic properties of the friction devices are derived theoretically and included in a Friction Damped Braced Frame Analysis Program (FDBFAP), which is adaptable to a microcomputer environment. The optimum slip load distribution is determined by minimizing a Relative Performance Index (RPI) derived from energy concepts. The steady-state response of a single storey friction damped structure subjected to sinusoidal ground motion is investigated analytically. Basic design information on the optimum slip load for the friction device is obtained. The parameters governing the optimum slip load, which minimizes the amplitude for any forcing frequency, are derived. The study indicates that the optimum slip load depends on the characteristics of the ground motion and of the structure. Using variational principles on a shear beam analogy, an optimum slip load distribution along the height of the structure is derived when the total amount of slip load is specified. It is shown that the optimum slip load is proportional to the slope of the deflected shape of the structure. The results of the study reveal that only a small improvement in the response is obtained by using this optimum distribution compared to the response obtained with a uniform distribution. Therefore the use of an optimum uniform distribution seems adequate for the design of friction damped structures. Taking into account the analytical results obtained, FDBFAP is then used in a parametric study which leads to the construction of a design slip load spectrum. The spectrum depends on the properties of the structure and ground motion anticipated at the construction site. It is believed that the availability of this design slip load spectrum will lead to a greater acceptance by the engineering profession of this new and innovative structural concept.Applied Science, Faculty ofCivil Engineering, Department ofGraduat

Use of Building Information Modelling for the seismic design of non-structural elements

The damage observed during recent earthquakes demonstrated the high vulnerability of non-structural elements due to accelerations and displacements arising from the structure’s seismic response. Non-structural elements that do not incorporate any seismic design generally exhibit damage at low seismic intensities and can significantly affect the immediate functionality of buildings. This issue is of paramount importance for strategic facilities, such as hospitals and schools that must remain operational in the post-earthquake emergency response. Nowadays some impediments still hinder the introduction of seismic design of non-structural elements into practice. The introduction of the Building Information Modelling (BIM) technology has significantly enhanced several aspects of the planning, design and construction processes along with numerous aspects of the project management. The capability of BIM to organize and export information to external software could greatly increase the feasibility of conducting comprehensive and automatic seismic design and risk assessment. The use of BIM could represent a new frontier in the seismic design of non-structural elements by increasing the reliability of the seismic design. In this study, the effectiveness of using Building Information Models for the seismic design of non-structural elements is demonstrated. A conceptual framework to perform the automatic seismic design of non-structural elements using information available in Building Information Models is presented. A simple Excel based tool has been developed in order to perform the automatic seismic design of sprinkler piping systems. The design tool extracts the piping layout from Building Information Models and performs automatically the seismic design of sway bracings according to the seismic provisions of the NFPA13 standard in the United States. The effectiveness of the proposed conceptual framework, as well as of the developed design tool, is investigated via an illustrative example

Improving the seismic performance of non-structural elements using Building Information Modelling

The post-earthquake functionality of critical facilities, such as hospitals, relies on the continued operation of non-structural elements including piping systems, partitions, ceiling systems and other medical equipment. The damage observed during past earthquakes showed the poor seismic performance of nonstructural elements and the need to improve their design and installation strategies. The application of performance-based seismic design to the entire building environment could be the possible solution to achieve desirable performance objectives for various seismic hazard levels. In this context, the use of Building Information Modelling is a promising approach to apply the seismic design of non-structural elements into practice. The data available in Building Information Models could be used to perform automatically the seismic design of non-structural elements and then to identify the interferences (i.e. clash detection) between all structural and non-structural elements in the building. In this paper, a conceptual framework to perform the automatic seismic design of non-structural elements using the information available in Building Information Models is presented. The effectiveness of the procedure is demonstrated though a simple application in which the seismic design of pressurized fire suppressant sprinkler piping systems and of ceiling systems installed in a reinforced concrete building is performed. The bracing elements required by current seismic provisions for non-structural elements considered are automatically reintroduced in the original Building Information Model. The automatic updating of the Building Information Model allowed to perform the clash detection and to verify if the bracing positions needed to be modified in order to optimize efficiently the seismic design of the entire building environment

Floor Acceleration Demand on Steel Moment Resisting Frame Buildings Retrofitted with Linear and Nonlinear Viscous Dampers

An improvement of the seismic performance of a building can be achieved by adding supplemental damping through viscous dampers. In some cases, however, the incorporation of viscous dampers in the structure can cause an increment of the seismic demand on acceleration-sensitive nonstructural elements. Two steel moment resisting frame buildings of three and six stories were selected from the SAC Steel Project in California. These buildings were equipped with linear and nonlinear viscous dampers designed by following a uniform distribution design approach in which a unique damping coefficient is assigned to all dampers along the building’s height. Additionally, three target first modal damping ratios were used along with six different velocity coefficients of the fluid viscous dampers. Nonlinear time-history analysis was carried out with the FEMA P695 far-field ground motion record set. The records were scaled to two intensity levels and floor acceleration time histories and 5% damped floor acceleration response spectra were obtained. The results show that the implementation of viscous dampers generally reduces the seismic demand in terms of floor acceleration compared to the original (nonretrofitted) building in most cases. Nevertheless, the floor acceleration demand varies significantly when the damping ratio and the velocity coefficient of fluid viscous dampers are varied. In some cases, the peak floor accelerations and the floor spectral accelerations in certain non-structural period ranges can exceed that of the original building

Seismic performance of steel moment-resisting frame retrofitted with linear and nonlinear viscous dampers

The implementation of linear and nonlinear viscous dampers improves the seismic performance of a structure. The velocity coefficient which governs the hysteretic behavior of nonlinear viscous dampers modifies the seismic response and consequently the seismic performance of the structure. A six-story steel moment-resisting frame building was selected as an archetype structure to investigate the effect of nonlinear viscous dampers on its seismic performance. This building, incorporating brittle beam-column connections common in the pre-Northridge earthquake designs, was retrofitted with different configurations of viscous dampers to improve its seismic performance. Linear and nonlinear viscous dampers were designed by following two different design approach: 1) a uniform distribution design approach in which similar dampers are introduced at every level of the structure and 2) an equivalent lateral stiffness distribution design approach for which proportional damping is preserved. An incremental dynamic analysis was carried out with the FEMA P695 far-field ground motion set. The seismic performance of the archetype building was evaluated in terms of collapse capacity, median peak inter-story drifts, and median peak damper forces. The results showed a considerable improvement of the seismic performance with the implementation of fluid viscous dampers. However, the design approach and the velocity coefficient modified the seismic response, affecting the seismic demand on the structure

A Value Case for Seismic Isolation of Residential Buildings

Seismic isolation is an effective technology for significantly reducing damage to buildings and building contents. However, its application to light-frame wood buildings has so far been unable to overcome cost and technical barriers such as susceptibility to movement during high-wind loading. The precursor to research in the field of isolation of residential buildings was the 1994 Northridge Earthquake (6.7 MW) in the United States and the 1995 Kobe Earthquake (6.9 MW) in Japan. While only a small number of lives were lost in residential buildings in these events, the economic impact was significant with over half of earthquake recovery costs given to repair and reconstruction of residential building damage. A value case has been explored to highlight the benefits of seismically isolated residential buildings compared to a standard fixed-base dwellings for the Wellington region. Loss data generated by insurance claim information from the 2011 Christchurch Earthquake has been used by researchers to determine vulnerability functions for the current light-frame wood building stock. By further considering the loss attributed to drift and acceleration sensitive components, and a simplified single degree of freedom (SDOF) building model, a method for determining vulnerability functions for seismic isolated buildings was developed. Vulnerability functions were then applied directly in a loss assessment using the GNS developed software, RiskScape. Vulnerability was shown to dramatically reduce for isolated buildings compared to an equivalent fixed-base building and as a result, the monetary savings in a given earthquake scenario were significant. This work is expected to drive further interest for development of solutions for the seismic isolation of residential dwellings, of which one option is further considered and presented herein