Project Title/ID Number Improved IMs and EDPs for Acceleration Sensitive Nonstructural Components —5242003
Start/End Dates 10/1/03—9/30/04
Project Leader Eduardo Miranda (Stanford/F)
Team Members Shahram Taghavi (Stanford/GS)

F=faculty; GS=graduate student; US=undergraduate student; PD=post-doc; I=industrial collaborator; O=other

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1. Project Goals/Objectives:

The objective of this project is to identify and study alternative intensity measures (IM) and alternative engineering demand parameters that will result in improved estimates of the performance of acceleration sensitive components.

Previous research by the PI and other investigators at PEER has used peak floor acceleration (PFA) as the engineering demand parameter (EDP) to estimate the seismic performance of acceleration-sensitive nonstructural components. This study will investigate the possible use of floor response spectral ordinates (FRSO) as an improved EDP for flexible nonstructural components. The project will modify the current loss estimation methodology to make use of this EDP in addition to those currently being considered.

Current research at PEER has used the linear elastic spectral acceleration (Sa) at the fundamental period of vibration of the structure as a measure of ground motion intensity (i.e., as intensity measures, IM’s) in structures. This provides a simple and relatively efficient IM for drift related damage, particularly for structures in the velocity and displacement-sensitive regions. However, acceleration demands in buildings are strongly affected by higher modes, such that using Sa(T1) can lead to very large dispersions. This investigation will identify alternative IM’s that increase efficiency.

2. Role of this project in supporting PEER’s mission (vision):

This project provides vital information to PEER’s mission by providing improved demand assessment of acceleration-sensitive nonstructural components and contents. It is of great relevance for structures where a high percentage of the investment at risk is concentrated on acceleration-sensitive components, as is the case of laboratories, museums, hospitals, etc.

3. Methodology Employed:

This project provides vital information to PEER’s mission by providing improved demand assessment of acceleration-sensitive nonstructural components and contents. It is of great relevance for structures where a high percentage of the investment at risk is concentrated on acceleration-sensitive components, as is the case of laboratories, museums, hospitals, etc.The efforts toward identification of improved measures of ground motion intensity and demand characterization for acceleration-sensitive components are being tackled in two phases. The first phase involves intensity levels in which the structure remains elastic or nearly elastic. A parametric study was conducted on a continuum model proposed by PI and his team; to study different IM’s in different structural systems with various dynamic properties. The results shows that the performance of Sa(T1) is very poor for estimation of PFA’s while PGA performs much better specially in the lower portion of the structure. In general, a combination of PGA and Sa(T1) can be the best candidate.

Parametric studies conducted to date indicate that acceleration demands on flexible components can be significantly different from those of rigid of nearly rigid components, hence the use of PFA may not lead to good damage estimates of flexible components. The amplification or deamplification of PFA is strongly affected by the period of the components, the properties of the main structure, as well as by the location of the component within the structure. In contrast to the current code recommendations, the amplification can be much larger in the vicinity of the higher modes of the structure.

A first series of studies of the effect of structural nonlinearity on IM efficiency and EDP was conducted using the Van Nuys testbed structure. For investigating alternate IM’s a series of incremental dynamic analyses were conducted using 80 ground motions. Figures 1 and 2 show PFA at roof level as a function of Sa(T1) and as a function of PGA, respectively. The mean and mean ± one standard deviation are also plotted for the two intensity measures. It can be seen that the use of PGA leads to a smaller dispersion of peak floor acceleration demands compared to those that occur when using Sa(T1) as intensity measure.

Figure 1 – Roof acceleration demands vs. Sa(T1) in Van Nuys bldg.

figure 2
Figure 2 – Roof acceleration demands vs. PGA in Van Nuys bldg.

figure 3
Figure 3 – Ratio of nonlinear to linear of FRSO of Van Nuys bldg at roof level.

Figure 3 shows acceleration floor spectra ordinates computed when in nonlinear analyses normalized to those computed in elastic analyses of the Van Nuys building. Results indicate that the level of amplification/deamplification of acceleration demands strongly depend on the level of nonlinearity in the structure. In particular results indicate that FRSO’s tend to saturate and not increase with ground motion intensity, however saturation is stronger at periods corresponding to the modes of vibration of the structure.

4. Brief Description of past year’s accomplishments (Year 6) & more detail on expected Year 7 accomplishments:

Year 6 accomplishments:

  1. Extending the number of fragility curves and cost functions of nonstructural components in Van Nuys bldg.
  2. Developing simplified models to estimate FRSO
  3. Performing loss estimation of Van Nuys bldg. using PEER-developed fragility and cost functions.

Year 7 accomplishments:

  1. Comparison of the efficiency of different ground motion intensity measures in linear when the EDP of interest is acceleration.
  2. Study the effects of nonlinearity on efficiency of intensity measures.
  3. Study the effect of structural parameters such as fundamental period of the structure and lateral resisting system as well as damping of the secondary system on PFA and FRSO in linear structures.
  4. Study the difference of acceleration demands in nonlinear structures compare to linear structures as a function of structural nonlinearity using incremental dynamic analysis.

5. Other Similar Work Being Conducted Within and Outside PEER and How This Project Differs:

Some experimental work has been conducted at MCEER on ceiling and piping systems. This research has been conducted at SUNY Buffalo and U. of Nevada at Reno, respectively. That research is not investigating acceleration demands in the components, but rather their fragility.

6. Plans for Year 8 if project is expected to be continued:


7. Describe any actual instances where you are aware your results have been used in industry:

Some of the results of this investigation are being considered for the inclusion into the FEMA-sponsored ATC-58 Performance-Based Design project.

8. Expected Milestones & Deliverables:

The main milestones for the project will be the identification of efficient IM’s for acceleration sensitive nonstructural components and contents and the modification of the PEER loss estimation methodology to consider the alternative IM’s and to consider FRSO as one of the EDP’s in the seismic performance analysis. The deliverables of this project will be a report containing a step-by-step description of the improved loss PEER methodology. It is anticipated that one and possibly two journal papers will also be prepared during year 7 to disseminate the results of this investigation. Also one paper will be prepared to be presented at the 13th World Conference on Earthquake Engineering to be held on August 2004 in Vancouver.

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