Assessment of First Generation PBSD Methods Project

The project supports two critical problem-focused studies in Performance Based Seismic Engineering (PBSE). The applicability and accuracy of adopting first-generation PBSE analysis methods for existing reinforced concrete buildings and existing structural steel buildings in the design of new structures. The goal of this project is to evaluate the results and identify necessary changes to present model building codes and standards provisions. Project completion is to be in the third quarter of FY 2012.

Objective: The project supports two critical issues identified in Performance Based Seismic Engineering (PBSE): the use of PBSE analysis methods that were developed for existing buildings in the design and analysis of (a) new reinforced concrete buildings and (b) new structural steel buildings. A number of candidate buildings, designed using rules for new buildings will be compared with those same buildings evaluated under PBSE rules for existing buildings. The results will be compared to identify inconsistencies and provisions needing to be modified. The project is scheduled to be completed in Q3 of FY2012.                          

What is the new technical idea?  The project will benchmark current PBSE methodologies by assessing ASCE 41[1] existing building analysis procedures when they are used for the design of new buildings, and analyzing unresolved inconsistencies in predicted seismic performance when compared with designs using ASCE 7 [2]. A number of archetypical structurally regular [3] buildings of varying numbers of stories will be designed using current design procedures (i.e., ASCE/SEI 7-10) for new buildings located in areas of high seismicity. The designs will then be assessed using current ASCE 41 PBSE procedures for seismic rehabilitation. The predicted seismic performance using ASCE 41 will be compared with the design using the prescriptive procedures in ASCE 7. Project personnel have previous industry seismic design experience, and they are well-versed in linear and nonlinear dynamic analysis.  

An extramural peer review team consisting of leading practitioners and researchers, retained under task order with the NEHRP Consultants Joint Venture (NCJV), will assist in refining reliability studies of analysis results, to correlate ASCE 41 Performance Levels with ASCE 7 Occupancy Categories. The project has the added benefit of providing a series of peer-reviewed archetypical building designs that can be used by EL/NEHRP in future analytical research projects that support other aspects of PBSE. These building designs form the beginning of the NEHRP Building Models Library and will be used by other FY2012 projects.                      

What is the research plan?  Both steel (braced frames and moment frames) and reinforced concrete (shear walls and moment frames) Seismic Force Resisting Systems (SFRS) will be designed in accordance with ASCE 7-10 for three different heights up through 16 stories to capture the effects of higher response modes, P-Delta influence, and the degree of concentrated inelastic regions. Each SFRS will be designed for two target seismic hazard levels representing regions of high seismicity and will be modeled in detail, including material and geometric nonlinearities, and analyzed using nonlinear finite element analysis programs. The SFRS will be evaluated by each of the four methods developed in ASCE 41 to judge compliance with predefined seismic performance objectives. Based on the ASCE 41 assessment and comparison with the ASCE 7 design, the applicability of using ASCE 41 performance-based seismic engineering (PBSE) for the design of new structures will be quantified, indicating under what conditions the ASCE 41 methodology does not meet the design intent of the ASCE 7 code. This assessment is the first of its kind, and will be disseminated through NIST publications and peer reviewed journal articles. The PI and co-PI also are members of the current ASCE 31/41 and ASCE 7 code committees, respectively, and will disseminate findings there.  

In support of the work at NIST, an extramural peer review team will be engaged through the NCJV during the course of the work. Should changes in the project be recommended by the peer review team, further detailed project tasks and direction will be undertaken.

[2] Minimum Design Loads for Buildings and Other Structures, ASCE 7-10, American Society of Civil Engineers, Reston, VA 2010

[3] Regular buildings are defined here as buildings whose seismic force-resisting systems (SFRS) do not contain any horizontal or vertical irregularities as defined in modern seismic code provisions (e.g., ASCE 7-10).

Recent Results: NISTIR 7766 Evaluation of Contemporary Design of Reinforced Concrete Lateral Resisting Systems Using Current Performance Objective Assessment Criteria was produced in August 2010, which performed an ASCE 41/7 comparison for a single reinforced concrete moment frame and shear wall structure. It was carried out to feasibility of the analysis methodology, which was successful.

For the steel portion of the project, a conference paper on design of SMRF was presented at SEAOC 2009. Additionally, abstracts were submitted to SEAOC 2011 and STESSA 2012 on the results of the research, and they have been accepted.                        

Standards and Codes: The project will be formulated to facilitate incorporating its products into the next cycle of ASCE 31/41, ASCE 7, The International Existing Building Code (code equivalence table), and 2014 NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, which will be the basis for future model building code advances. The PI is on the current ASCE 31/41 standards committee. The Co-PI Jay Harris is on the ASCE 7 Seismic Subcommittee (TC-2).