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INSTRUCTOR:  John Lawson, C.E., S.E., M.ASCE 

Course Length:  1 hour

Sponsored by ASCE's Structural Engineering Institute and ASCE Continuing Education.

Purpose and Background

Buildings with large wood diaphragms supporting heavy concrete or masonry walls are very common in seismically active portions of the United States. 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 roof diaphragm (RWFD) buildings is dominated by the wood diaphragm's response instead of the walls' in-plane response. Furthermore, the diaphragm's ductility and overstrength capacity is unique to its own construction. Yet the current design methodology employed by practitioners directly ties the wood diaphragm shears and overstrength to the characteristics of the seismic force-resisting system's (SFRS) concrete or masonry vertical elements. This webinar evaluates the shortcomings of past practices in both the seismic design of the main diaphragm as well as the out-of-plane anchorage of the perimeter heavy walls to the diaphragm. It also discusses a proposal for a new design methodology, providing a rational approach to improving performance in these wood diaphragms.

Primary Discussion Topics

• Past performance issues
• Origins of current building code provisions
• Actual diaphragm and building behavior
• Ideas to improve performance
• Implications for future building code provisions

Learning Outcomes

• Learn the historical seismic performance problems of this building type
• Become familiar with the origins of anchoring heavy walls to wood diaphragms
• Know how to apply the various code provisions to diaphragm and wall anchorage design
• Understand the limitations of current diaphragm design practices
• Learn a new approach to increase diaphragm performance

Webinar Benefits

• Gain an appreciation for the origins of current code provisions
• Find out the latest understanding in wood diaphragm seismic behavior
• Get a glimpse of the possible direction of the seismic code provisions
• Obtain a variety of tools to evaluate the seismic performance of wood diaphragms

Intended Audience

• Structural engineers
• Civil engineers
• Building officials
• Building code developers
• Seismic hazard mitigation specialists

Webinar Outline

• Characteristics of Rigid Wall - Flexible Diaphragm (RWFD) buildings
• Past performance of wood diaphragms in RWFD buildings
• Evaluation of past and current building design practices
• Development of a new diaphragm design methodology
• Evaluation of a new design methodology
• Conclusions
• Questions