Benchmarking Performance of New RC Frame Buildings - 1382005

Project Title—ID Number	Benchmarking Performance of New RC Frame Buildings - 1382005
Start/End Dates	10/1/05 – 9/30/06
Funding Source	PEER-NSF
Project Leader (boldface) and Other Team Members	Greg Deierlein (Stanford/F), Curt Haselton (Stanford/GS), Abbie Liel (Stanford/GS), Sarah Lange (UCD/US)

Project goals and objectives

The objective of this project is to assess the seismic performance provided by modern design provisions for reinforced-concrete buildings. By applying the PEER PBEE assessment methodology to a collection of building designs, the project will provide insight on how to extend the building-specific assessment methodology for individual buildings to assess building code provisions, which are used as the basis for design. Data from this research will serve a number of goals, including: (a) gage whether design standards provide the expected performance across the range of building configurations permitted by design codes, (b) contribute to establishing appropriate performance targets for performance-based design of new buildings, (c) provide a benchmark against which new innovative systems can be judged, (d) provide data for improved building fragility models as input for loss simulations of large geographic regions, and (e) demonstrate the benefits of the PEER PBEE assessment method as compared to the current state-of-art in engineering practice (e.g., FEMA 356). A related objective is to compare the collapse safety of modern (2003) buildings with ones designed according to the 1967 UBC code, which are viewed as seismically deficient according to modern codes.

Beyond the primary objective to benchmark current design provisions, the project will contribute to the packaging of these tools as part of the technology transfer to practice. Additionally, by evaluating the impact of alternative design parameters on performance, the project will provide improved understanding to develop appropriate design criteria to relate provisions for minimum strength, stiffness and ductility of the structural system to the resulting performance.

Role of this project in supporting PEER's mission (vision)

The goals and scope of this project are central to realizing the vision outlined in the strategic plan for Thrust Area (TA) I – Building Systems. Synthesis of the PBEE methodology components, models and criteria relates directly to the TA I need to package the PBEE methodology and make it accessible to the engineering community. The procedures and data from the RC building benchmarking studies are an integral part of the major unifying theme of the TA I research over Years 8-10.

Methodology employed

The overall research strategy is to conduct an in-depth PBEE assessment of prototypical buildings designed according to the seismic provisions of the 2003 edition of the International Building Code (and the associated standards included by reference). Input and review from practicing engineers has been solicited in formulating strategies for developing the benchmark building designs for various building occupancies. This includes, for example, guidance on typical constraints faced in layout of framing bays, proportioning beams and columns, foundation design, and other items necessary to fulfill the minimum building code requirements. The study is primarily focused on new buildings in high-seismic regions, although the project is examining how various design parameters, including changes in building code provisions from 1970 to the present, can affect building performance.

The benchmark building designs are assessed using the PEER-PBEE approach, where the structural response is evaluated through nonlinear time history analysis using OpenSees. The structural damage assessment is made using information developed both within and outside PEER on relationships between EDPs (primarily drift and inelastic deformations) and damage to the RC components. Damage to nonstructural components and loss models (DM-DV) is being provided by the collaboration with the Caltech research team.

Brief Description of previous year's achievements, with emphasis on accomplishments during last year (Year 8)

In prior years, detailed plans were developed to outline (a) key design, construction, and structural behavior considerations in the benchmark investigation, (b) details for implementing and applying the PBEE methodology to the benchmark buildings, (c) a matrix of descriptors for the initial benchmark building study. A four-story benchmark RC building was developed, including comprehensive specification of the structural system and major nonstructural components and contents. Models, criteria and simulation tools were assembled and validated (in collaboration with researchers at Caltech and UCLA) to conduct the performance assessment, including detailed nonlinear simulation models in OpenSees.

A detailed assessment of the four-story index building has been completed. Shown in Figure 1 (see below) is an example of the incremental dynamic analysis results OpenSees analyses to determine the peak interstory drift ratio as a function of the site hazard (expressed in terms of spectral acceleration). Preliminary findings are that this building performs very well and has collapse safety consistent with building-code expectations. Research is currently underway on a systematic investigation of alternative structural configurations.

Other similar work being conducted within and outside PEER and how this project differs

The PI is not aware of similar work of this type applied to reinforced concrete frames. The project shares some common aspects to a series of assessment studies of steel moment frame buildings conducted through the SAC joint venture; and these studies are being examined.

Synthesizing and "packaging" of the methodology and tools for this project is being done in collaboration with related PEER investigations, including: Beck/Porter (loss modeling); Miranda (loss modeling and non-structural components); May (articulation of performance metrics), Krawinkler (assessment and design methodology), Cornell (assessment methodology), Stewart (soil-structure interaction effects), Lehman/Lowes (damage assessment of RC components), Eberhard (simulation and performance of beam-columns), and others.

The initial benchmark study of the four story building has been conducted jointly between this project and two other TA 1 projects: Beck/Porter (Caltech) "Loss Modeling for Downtime, Deaths and Decision-Making" and Stewart (UCLA) "Implementation SFSI and Site Effect Models in PEER Methodology". The Caltech group has been instrumental in the loss modeling aspects (EDP-DV) and the UCLA team has contributed to developing foundation models, site hazard data, and input ground motions for the time history analyses.

Describe any instances where you are aware that your results have been used in industry

The performance-assessment process and specific results from this benchmarking study are of direct interest to technical organizations involved in the development of building code provisions for seismic design. FEMA is supporting two such efforts that will affect engineering practice – one concerning the development of provisions for performance-based seismic design (ATC 58) and a second (ATC 63) concerning the development of a rational procedure for substantiating seismic response parameters (e.g., R and Cd) of current building code provisions. The PI is involved in both of these projects, and his involvement is facilitating technology transfer of the procedures, technologies and data from the PEER research. Results of this research have also been show-cased in a technical seminar on the performance assessment of RC buildings that was jointly sponsored by PEER and EERI in 2006.

Expected milestones & deliverables

This project is a multi-year effort, which began in Year 7 with the detailed design and PBEE assessment of a 4-story code-complying RC office building. The Year 7 effort has culminated in a technical report (completed in April 2006, co-authored by the teams at Stanford, Caltech, and UCLA) on the benchmarking study. The following is a summary of future milestones and deliverables:

• - Periodic Status Reports - status reports and other requested contributions to PEER quarter coordination meetings, PEER Annual Meetings, and meetings with outreach efforts to FEMA-ATC projects.
• - Structural Modeling Guidelines – written guidelines to summarize OpenSees modeling techniques, assumptions and criteria to evaluate structural performance of code- complying buildings up through collapse (6/2006).
• - Detailed Planning Document on Strategy for Generalizing Results – documentation of research plan to generalize the benchmarking study to account for varying building configurations and design uncertainties. Plan to be presented and reviewed by TA I research team (6/2005).
• - Final Project Report – anticipated for completion at end of Year 9 (9/2006).

Member company benefits

This study is serving to refine and implement the PBEE methodology that is of interest to PEER's Business and Industry Partners who are involved in the seismic design and evaluation of buildings and in building code development.