Research – Henry V. Burton, Ph.D., S.E.

Henry Burton’s research group website ( http://www.henryburtonjr.com/research/)

Collapse Simulation of Concrete Frame Buildings with Infills

Concrete frame buildings with infills are commonly used throughout the world, both in developing and industrialized countries. Experience with past earthquakes has shown that frames with infills, particularly those with non-ductile concrete frames, are prone to collapse under earthquakes. In densely populated urban centers, the prevalence of non-ductile infill frame buildings presents a significant seismic risk. Effective mitigation of this risk requires reliable methods to assess the collapse behavior of these buildings. Analysis tools and guidelines have been developed to simulate the seismic collapse of non-ductile concrete frame buildings with masonry infills, incorporating important mechanisms related to frame-infill interaction and foundation rocking.

A Rocking Spine System for Concrete Frames with Infills

A rocking spine system is currently being developed as a cost-effective solution to achieving seismic collapse safety in reinforced concrete frame buildings with infills. The proposed technique uses structural spines constructed using strong, stiff infill frames or concrete walls that resist earthquake effects through rocking action. The system is applicable to both retrofit and new design. Relying on uplift of the foundation as a primary yielding mechanism reduces the required level of detailing that is needed to achieve ductility in the frames leading to substantial cost savings. Additional material and labor cost savings is realized for taller buildings since deep foundations are not required for the spine system. The primary behavioral goal of the rocking spine is to impose uniform deformations over the height of the structure. This reduces the tendency for concentrated drift demands that would typically occur at the lower levels of traditional infill frames. It also redistributes the yielding that would typically occur in the lower level columns to the adjacent beams and infill throughout the height of the structure.

Assessing the Post-Earthquake Structural Safety of Buildings

Recent initiatives like the San Francisco’s Resilient City Project have highlighted the growing need for analytical methods for assessing the post-earthquake structural safety of buildings. For example, the shelter-in-place limit state as defined by the San Francisco Planning and Urban Research Association refers to the ability of residents to remain in their home while it is being repaired after an earthquake. This is directly linked to the post-earthquake structural safety of these buildings. Assessing this limit state for residential buildings was a key step in evaluating the overall resilience of the San Francisco Bay Area. A performance-based methodology has been developed for assessing the post-earthquake occupiability of buildings. The new approach combines key elements from earlier work including component-level damage assessment, virtual inspection and aftershock collapse safety.

Community Resilience Assessment

A performance-based framework has been developed that explicitly incorporates functionality-based building limit states in the assessment of community resilience to earthquakes. These limit states are defined based on their implications to post-earthquake functionality and recovery. They include damage triggering inspection, occupiable damage with loss of functionality, unoccupiable damage, irreparable damage and collapse. The framework has been developed with a specific focus on modeling the post-earthquake shelter-in-place housing capacity of an inventory of residential buildings. This type of assessment can inform planning and policy decisions to manage the earthquake risk to residential housing capacity of communities. It can also be used to measure the impact of various resilience-building strategies such as enhanced seismic performance.