1 |
The structural response of industrial portal frame structures in fireWong, Shao Young January 2001 (has links)
A number of recent fires in single-storey warehouses have drawn attention to a current lack of understanding about the structural response of industrial portal frame structures to elevated temperatures. This research project has investigated the subject by conducting fire tests on a scaled model and by computer modelling using the non-linear finite element program VULCAN. This program has been developed in-house by the University of Sheffield and is capable of modelling the behaviour of three-dimensional steel and composite frames at elevated temperatures. It has been validated throughout its development. An initial investigation was conducted to validate the program for analysing inclined members, which form part of a pitched- roof portal frame, but for which it was not initially developed. Additional features were implemented into the program where necessary. A series of indicative fire tests was conducted at the Health and Safety Laboratories, Buxton. A scaled portal frame model was designed and built, and three major fire tests were conducted in this structure. In the third of these tests the heated rafters experienced a snap-through failure mechanism, in which fire hinges could clearly be identified. The experimental results were then used for validating the numerical results produced by VULCAN analyses. The correlations were relatively close, both for predictions of displacements and failure temperatures. This gave increased confidence in using VULCAN to conduct a series of parametric studies. The parametric studies included two- and three-dimensional analyses, and a number of parameters were investigated, including the effects of vertical and horizontal load, frame geometry, heating profiles and base rotational stiffness. The influence of secondary members was investigated in the three-dimensional studies using different fire scenarios. A simplified calculation method has been developed for estimating the critical temperatures of portal frames in fire. The results compare well with predictions from VULCAN. The current guidance document for portal frames in boundary conditions has been reviewed, and the concept of performance-based design for portal frame structures has been discussed.
|
2 |
Seismic performance evaluations and analyses for composite moment frames with smart SMA PR-CFT connectionsHu, Jong Wan 01 April 2008 (has links)
This thesis investigates the performance of composite frame structures with smart
partially-restrained (PR) concrete filled tube (CFT) column connections through
simplified 2D and advanced 3D computational simulations. It also provides a design
methodology for new types of innovative connections based on achieving a beam hinging
mechanism. These types of connections intend to utilize the recentering properties of
super-elastic SMA tension bars, the energy dissipation capacity of low-carbon steel bars,
and the robustness of CFT columns.
In the first part of this study, three different PR-CFT connection prototypes were
designed based on a hierarchy of strength models for each connection component.
Numerical simulations with refined three dimensional (3D) solid elements were
conducted on full scale PR-CFT connection models in order to verify the strength models
and evaluate the system performance under static loading. Based on system information
obtained from these analyses, simplified connection models were formulated by replacing
the individual connection components with spring elements and condensing their
contributions. Connection behavior under cyclic loads was extrapolated and then
compared with the monotonic behavior.
In the second part of this study, the application of these connections to low-rise
composite frames was illustrated by designing both 2D and 3D, 4 and 6 story buildings
for the Los Angeles region. A total of 36 frames were studied. Pushover curves plotted
as the normalized shear force versus inter story drift ratio (ISDR) showed significant
transition points: elastic range or proportional limit, full yielding of the cross-section,
strength hardening, ultimate strength, and strength degradation or stability limit. Based
on the transition points in the monotonic pushover curves, three performance levels were
defined: Design Point, Yield Point, and Ultimate Point. All frames were stable up to the
yield point level. For all fames, after reaching the ultimate point, plastic rotation
increased significantly and concentrated on the lower levels. These observations were
quantified through the use of elastic strength ratios and inelastic curvature ductility ratios.
The composite frames showed superior performance over traditional welded ones in
terms of ductility and stability, and validated the premises of this research.
|
Page generated in 0.0443 seconds