Objective -To develop a plan that details the engineering, research and implementation activities required to implement a new performance objective for the immediate occupancy of buildings following a natural hazard event.
What is the Technical Idea? The technical idea for this project is to improve resilience in buildings across the nation for natural hazard events by developing performance objective for “immediate occupancy” that can be used by designers, planners, and engineers in the design of buildings. By limiting damage to structures and their exterior envelope and interior equipment and elements, buildings could be immediately occupied following an event. An immediate occupancy performance objective would be a significant departure from current building code philosophies where life safety is the primary design goal that is achieved by minimizing the likelihood of building collapse. The current design goal addresses needs for occupant in-place refuge areas and evacuation. While collapse may be prevented, and the structural frame may be functional, buildings may incur other significant damage requiring costly, time-consuming repairs or even demolition. An immediate occupancy performance objective would reduce damage to the entire building and its contents to levels permitting immediate resumption of building occupancy and function.
Prescriptive building codes such as the International Building Code (IBC, 2012), ASCE/SEI 7-10 (ASCE 2010) and the NEHRP Recommended Seismic Provisions (FEMA 2015) have life safety as their core design philosophy. However, in the event of a strong hazard event such as an earthquake, tornado or hurricane, damage levels may require extensive repair to put the building back in service. An immediate occupancy performance objective would provide a framework for designers, planners, and engineers to address the desired performance of the entire building to function after an event.
At the present time, prescriptive building codes and standards adjust design loads for hazards based on the building occupancy, risk category, and/or hazard levels. In the case of earthquake, the Seismic Design Category (SDC) is identified based on the hazard level obtained from USGS, characterizing expected ground shaking, and structural risk category based on occupancy and soil classifications at the location. Fire stations and hospitals are categorized as SDC IV buildings and have an increased importance factor, resulting in increased design loads. However, increased loads for the design of the structural frame, while reduced the likelihood of structural frame damage, do not address the performance of the building envelope or interior systems. Building functionality is not explicitly addressed.
In the case of performance based seismic design (PBSD) there are specific performance objectives that are deemed to be implicitly achieved by satisfying Immediate Occupancy, Life Safety and Collapse Prevention performance levels at specified hazard levels depending on the risk category of the building, see Table 1. PBSD is a specialized area, that is addressed under ‘alternate methods’ provisions in building codes. Instead of prescriptive code provisions, this approach relies on increased engineering judgement and analyses together with peer review to verify anticipated performance. Recent work by Harris and Speicher (2015) has revealed that the correlation for Collapse Prevention performance level between ASCE 7 (a design standard for minimum design loads in new buildings and other structures) and ASCE 41 (a standard for evaluating the existing buildings) are not well correlated. Both standards use factored loads and risk categories to implicitly address the desired performance in buildings and other structures. Improved performance objectives for immediate occupancy that address the entire building can advance performance-based design practice and, ultimately, codes and standards.
Table1. Requirements for the performance objective equivalent to new buildings as a function of hazard level and risk category (Pekelnicky and Poland, 2012).
What is the Research Plan? The project has a focused goal of identifying the engineering research, both applied and basic, together with the implementation activities necessary to develop a new immediate occupancy performance objective. Thus, the effort is not to solve the problem itself but identify the necessary participants, research and activities necessary to lie out a comprehensive blueprint to develop the new performance objective. Accordingly, the following tasks will be addressed:
- Staffing of the effort, including internal NIST personnel and outside participants
- Identification of the stakeholders needed for engagement in this work - SDOs, hazard-specific expertise (e.g., wind engineers, flood experts, earthquake engineers, social scientists, and engineers from the lifelines community).
- Development of a strawman development needs document for comment and review by committee of outside experts.
- Holding of a workshop to discuss the strawman document and the overall effort involved in developing this performance objective.
- Writing of a draft report for stakeholder and NIST review.
- Writing of a final report to Congress.