Abstract:
The thesis is concerned with the theoretical determination of the overall
and local effects on the collapse behaviour of bus structures in a roll
over situation. The aim is to enable an early selection of structural
components, so that the finished body can absorb enough energy and
preserve sufficient strength to meet the roll over safety requirements.
Chapter 1 gives an introduction into the bus roll over problem, discusses
the present safety legislation and reveals that there is very little
information on the performance of buses in real accidents and that no
collapse analysis of the complete structure or bending collapse of its
details had been undertaken.
The investigation into 21 bus roll over accidents, summarised in Chapter
2, showed that structural safety relies on both the overall collapse
modes and hinge properties. Theoretical determination of the overall
collapse mechanism and maximum strength of a typical British coach is
carried out in Chapter 3 using the CRASHD collapse program. Some
peculiarities of the finite element modelling are demonstrated and the
analysis indicates that the collapse mechanism can be controlled by
careful selection of various structural components. Chapter 4 emphasises
the importance of a better understanding of the hinge behaviour in
vehicle structures.
Bending collapse of rectangular section tubes is investigated in Chapter
5 for hinge rotation angles up to 30-50 degrees. The analysis starts
with determination of the maximum strength of sections which may buckle
within elastic range. Repeatability of local collapse mechanisms
enabled the definition of the appropriate theoretical model. Kinematic
theorem of the limit analysis is then applied to derive the formula for
the hinge moment-rotation curve. Particular attention is paid to the
selection of the appropriate material properties. The agreement with
experimental evidence (Chapter 6) was very good for the complete range
of tubes tested. This range includes practically all the standard
sections that are used in the general structural design.
The theory is used in Chapter 7 to optimise sections from the safety
point of view and, in combination with the CRASHD program, to predict
the collapse behaviour of beams, bus rings and complete structure entirely
on the theoretical basis. Static and dynamic tests of bus rings gave
good agreement with theory.
The practical aspects of the work have been emphasised throughout the
thesis. Detailed explanation of all the major decisions has increased
the volume of the text, but the author believes that this will prove
useful for practicing engineers. People interested in essentials only
are referred to Chapter 8 where all the most important conclusions are
given.