Assessment of Floor Accelerations in Yielding Buildings
By Joseph D. Wieser, Gokhan Pekcan, Arash E. Zaghi, Ahmad M. Itani and Emmanuel “Manos” Maragakis
Abstract: The large investment in nonstructural components in buildings and severe damage to these components in recent earthquakes necessitates improved design provisions for these components. This study uses the OpenSees finite element framework to develop full three-dimensional models of four steel moment frame buildings. The incremental dynamic analysis method is employed to evaluate the floor response of inelastic steel moment frame buildings subjected to all three components of a suite of 21 ground motions.
To better understand the acceleration demands on nonstructural components, this study focuses on the influence of structural period, level of ductility of the structure, and relative height in the building on the horizontal and vertical floor acceleration response. As a result of this study, a more realistic formulation of the peak floor acceleration response accounting for the effect of structural period and ductility is proposed and may be used to improve current code estimations. In addition, a direct method for developing an envelope horizontal floor response spectrum is presented.
A Numerical Model for Capturing the In-Plane Seismic Response of
Interior Metal Stud Partition Walls
By Richard L. Wood and Tara C. Hutchinson
Abstract: A commonly used nonstructural system representing significant investment in building construction is the ceiling-piping-partition (CPP) system. In this work, one of the subsystems within the CPP is given particular attention, namely the partition wall subsystem. Using data from experiments conducted at the University at Buffalo within the NEES Nonstructural project, a numerical model is developed to capture the inplane seismic response of full-height gypsum board on cold-formed steel framed partition walls. The behavior of the partition wall is captured using a lumped model localized within a zero-length element in the OpenSees platform.
The model’s predictive capabilities are demonstrated via simulation of individual walls. In particular, a fully connected partition wall, a normalized mean model is shown to capture the experimental hysteresis behavior with reasonable accuracy. The partition element is then integrated into numerical models of representative building types and the sensitivity of the building dynamic characteristics due to the presence of the partition wall is evaluated. At most, a period shift of 14% is noted for the shortest example building considered.
Bayesian Fragility for Nonstructural Systems
By Chang Hoon Lee and Mircea D. Grigoriu
ABSTRACT: A method is developed for calculating the fragility of a nonstructural system supported by a structure subjected to earthquakes. The nonstructural system consists of a collection of nominally identical components. The input to these components depends on properties of the supporting structure and of site seismicity. It is assumed that the seismic load can be described by 22 ground acceleration records and the components of the nonstructural systems have uncertain properties.
A Bayesian framework is developed for fragility analysis. The report also includes a manual that describes the MATLAB code used in the Bayesian fragility computation. A two-story perimeter concrete steel moment resisting frame is used to illustrate the use of the code.
Experimental Seismic Evaluation, Model Parameterization, and Effects of Cold-Formed Steel-Framed Gypsum Partition Walls on the Seismic Performance of an Essential Facility
By R. Davies, R. Retamales, G. Mosqueda and A. Filiatrault
Abstract: The first phase of the NEES Nonstructural Grand Challenge Project tested full-scale cold-formed steel-framed gypsum partition walls using the University at Buffalo Nonstructural Component Simulator (UB-NCS). A description and experimental results for 22 different partition wall configurations is given. The experimental data are used to populate an extensive seismic fragility database for cold-formed steel-framed gypsum partition walls. Parameters for a tri-linear hysteretic model, aimed at reproducing the in-plane mechanical behavior of partition walls, are determined from the experimentally obtained force-displacement curves.
Recommended parameters for in-plane walls are given for individual configurations and cold-formed steel-framed nonstructural partition walls. The calibrated partition wall models are combined with the structural model of an existing four-story steel moment-resisting frame medical facility to demonstrate the effect on dynamic properties. As the period of the structure reduces due to the increased stiffness from partition wall systems, reductions in drift and absolute floor accelerations are observed. The assumption that these wall systems have negligible impact is disproven by the use of incremental dynamic analyses performed according to the FEMA P695 methodology. The analyses show that including the contribution of steel stud gypsum partition walls to the lateral force-resisting system increases the building collapse safety margin by 32 percent.
Modeling and Seismic Evaluation of Nonstructural Components: Testing Frame for Experimental Evaluation of Suspended Ceiling Systems
By A.M. Reinhorn, K.P. Ryu and G. Maddaloni
Abstract: This report describes the development of a new testing facility for use with single or tandem shake tables to evaluate suspended ceilings and other nonstructural components. A large reconfigurable frame of 20 ft. by 50 ft. was developed to test a continuous suspended ceiling of up to 1,000 ft2. The frame has dynamic characteristics with variable frequencies to match those typical of floors and roofs with suspended ceilings. Analytical models were developed using the structural analysis program SAP2000 to estimate the dynamic properties and complete the design of the frame.
The combined designs of the physical frame and the shake table motion allow for testing of a variety of suspended systems while simulating more realistic floor motions and eliminating side effects caused by wall distortions. This study describes the design of the frame and introduces the procedure for motion design which can also be implemented in other experimental facilities.