Title page for ETD etd-11022005-232019

Type of Document

Dissertation

Author

Avci, Onur

Author's Email Address

oavci@vt.edu

URN

etd-11022005-232019

Title

Effects of Bottom Chord Extensions on the Static and Dynamic Performance of Steel Joist Supported Floors

Degree

PhD

Department

Civil Engineering

Advisory Committee

Advisor Name	Title
Murray, Thomas M.	Committee Co-Chair
Setareh, Mehdi	Committee Co-Chair
Charney, Finley A.	Committee Member
Plaut, Raymond H.	Committee Member
Wicks, Alfred L.	Committee Member

Keywords

acceleration response
effective mass
damping
mode shape
natural frequency
vibration testing
digital signal processing
experimental modal analysis
finite element modeling
dynamic analysis
Floor vibrations
joist
resonance
stiffness testing
bottom chord extension
truss

Date of Defense

2005-09-08

Availability

unrestricted

Abstract

The purpose of this study was to examine the effect of bottom chord extensions on deflections and vibration characteristics of joist supported floor systems when joist bottom chord extensions are installed. To understand the effect of bottom chord extensions on deflections, natural frequency, damping, mode shape and effective mass, extensive analytical and experimental studies were conducted on single span and three span joist supported laboratory footbridges with different bottom chord extension configurations. Finite element computer models were created to simulate and compare the results of stiffness and vibration tests. Testing was done with a) the bottom chord extensions in-place before the concrete was placed, b) with all or part of the bottom chord extensions removed, and c) after the bottom chord extensions had been reinstalled with jacking for the single span footbridge and without jacking for the three-span footbridge.

Results from the stiffness tests indicate that re-installing the bottom chord extensions to the joists of the single span footbridge with cured concrete with the center of the span raised helps to reduce the uniform load deflections to some extent, but not as much as placing the bottom chord extensions before the concrete placement. Likewise, for the three span footbridge, placing the bottom chord extensions before the concrete placement is observed to be a better solution.

Results from the dynamic tests indicate that the effect of bottom chord extensions on the single span footbridge is consistent for natural frequency, 20 psf live load deflections, sinusoidal excitations with high amplitudes, quarter point heel drop excitations, walking excitations, and effective mass values. The effect of bottom chord extensions on the three span footbridge is consistent for the natural frequency and 20 psf deflections. However, the FRF (Frequency Response Function) peaks of chirp, heel drop, sinusoidal excitations, accelerations from walking data, and the MEScope and Finite Element model effective mass results do not follow a common trend.

It can be concluded that even though the footbridge was stiffened by the bottom chord extensions, that does not necessarily mean that the acceleration levels, and hence the frequency response function peaks, decrease. However, bottom chord extensions do increase the natural frequencies for all the three governing bending modes.

Files

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Filename		Size	28.8 Modem	56K Modem	ISDN (64 Kb)	ISDN (128 Kb)	Higher-speed Access
	Apx.A,B,C.pdf	826.48 Kb	00:03:49	00:01:58	00:01:43	00:00:51	00:00:04
	Apx.D.pdf	3.21 Mb	00:14:53	00:07:39	00:06:41	00:03:20	00:00:17
	Apx.E.pdf	11.09 Mb	00:51:19	00:26:23	00:23:05	00:11:32	00:00:59
	Thesis-Onur-AVCI.pdf	12.06 Mb	00:55:51	00:28:43	00:25:08	00:12:34	00:01:04
	VITA-Onur-AVCI.pdf	19.69 Kb	00:00:05	00:00:02	00:00:02	00:00:01	< 00:00:01