Passenger transport is an inseparable ingredient of public transport system for developing and developed nations. In present work design and analysis of state transport utility vehicle ~ bus is carried out. Present paper focuses on the design enhancements in structural features of sub and superstructure without any alterations on the chassis provided by OEMs. Limiting dimensions of bus as prescribed by automotive industry standard and central motor vehicle rules are the design constraints accounted in the present work. This work was commenced with the thorough study of sub and superstructure configurations, seat locations, passenger load patterns, locations of doors, windows & emergency exits and other relevant bus attributes. Hand calculations for evaluation gross section modulus of chassis and cross member combination are presented. Usage of shear force and bending moment diagrams to evaluate the stress and deflection for the proposed load patterns is made before proceeding for finite element analysis. Finite element modelling and analysis of the sub and super structure combination is carried using shell elements with the presumption that chassis of the bus is rigid. Roll-over analysis of bus for the present configuration is presented.

1. Deulgaonkar.et al. 2019. Int. J. Vehicle Structures & Systems, 11(2), 127-132
International Journal of
Vehicle Structures & Systems
Available online at www.maftree.org/eja
ISSN: 0975-3060 (Print), 0975-3540 (Online)
doi:10.4273/ijvss.11.2.02
© 2019. MechAero Foundation for Technical Research & Education Excellence
127
Design and Analysis of State Transport (S.T) Utility Vehicle ~ Bus
Vikas Radhakrishna Deulgaonkara,b
, Varun A Shitole c,d
Rohan M Panage e,f
a
Marathwada Mitra Mandal’s College of Engg., Karvenagar, Pune, Maharashtra, India
b
Corresponding author Email: vikasdeulgaonkar@gmail.com.
c
Equilibrium Solutions Pvt..Ltd Erandwane , Pune, Maharashtra, India , d
email:varunshitole@gmail.com
e
Veer Jijabai Technological Insitute, Matunga Mumbai Maharashtra, India f
rohanpanage007@gmail.com
ABSTRACT:
Passenger transport is an inseparable ingredient of public transport system for developing and developed nations. In
present work design and analysis of state transport utility vehicle ~ bus is carried out. Present paper focuses on the
design enhancements in structural features of sub and superstructure without any alterations on the chassis provided by
OEMs. Limiting dimensions of bus as prescribed by automotive industry standard and central motor vehicle rules are
the design constraints accounted in the present work. This work was commenced with the thorough study of sub and
superstructure configurations, seat locations, passenger load patterns, locations of doors, windows & emergency exits
and other relevant bus attributes. Hand calculations for evaluation gross section modulus of chassis and cross member
combination are presented. Usage of shear force and bending moment diagrams to evaluate the stress and deflection
for the proposed load patterns is made before proceeding for finite element analysis. Finite element modelling and
analysis of the sub and super structure combination is carried using shell elements with the presumption that chassis of
the bus is rigid. Roll-over analysis of bus for the present configuration is presented.
KEYWORDS:
Transport utility vehicles; Bus design; Stress analysis; Finite element analysis
CITATION:
V.R. Deulgaonkar, V.A. Shitole and R.M. Panage. 2019. Design and Analysis of State Transport (S.T) Utility Vehicle,
Int. J. Vehicle Structures & Systems, 11(2), 127-132. doi:10.4273/ijvss.11.2.02.
1. Introduction
History of public transport is one of the technological
innovations which are in continual improvement since its
inception from Stone Age. With the invention of wheel,
this transportation system has undergone several
developments with respect to the geographical situations,
nature of land and frequency of travel. Land transport
has progressed through various modes as walking,
palanquin (palkhis), animal powered transport as bullock
cart and horse carriage, hand-pulled rickshaw, bicycle,
cycle-rickshaw, auto-rickshaw, electric-rickshaw, taxi,
bus and bus rapid transit system (BRTS). Public
transport has been inseparable part of an individual
irrespective of environmental and geographical
situations, type of terrains and frequency of travel. With
the advancements in automobile realm, inclination
towards public transportation offered by state transport
agencies has been decreased due to many aspects
including but not limited to poor design of bus sub and
superstructures resulting in increased levels of vibration
to travelling passengers, noise resulting from the under
maintained doors, windows and the external appearance.
Several efforts have been made by researchers over
the globe to improve the passenger comfort in public
transport. Testing and experimentation of bus involves a
considerable amount of labour, time as well as economic
investment. Most of the state transport buses in India are
designed on the basis of past experience without much
technical considerations. The state transport workshops
have fabrication units in which the bus superstructure is
fabricated with the use of tooling and past experience.
The chassis along with necessary mounts is supplied by
OEM’s. The dimensions of bus are governed by
automotive industry standard (AIS 052) and central
motor vehicle rules. The superstructure influences
directly the life and health of travellers in case of
accidents. Rollover is one of the prominent tests which
the bus superstructures are required to pass before the
buses are put into service [12]. Rollover is exceptionally
hazardous as it results into significant deformation of
roof arch members and side walls. Reasons of rollover
occurrence include collisions and high speed cornering.
Intrusion of structure inside the passenger survival
space is the reason for injury and death of the
passengers. When the bus takes a turn, i.e. during
cornering three forces act on it viz, tire (centrifugal)
force, inertial (centrifugal) force and gravity force.
Cornering force creates thrust and pushes the vehicle
towards the curve centre as this force acts below the
centre of mass and at the ground level. Inertial force act
in horizontal direction through the centre of vehicle mass
and away from the turn. When the magnitude of these
forces increases more than force of gravity, the bus starts
to rollover.
2. Sub - Structure of bus
Floor of the bus is a composition of longitudinal and
cross members placed on chassis and attached with the
help of minimum 15 U-bolts from strength and rigidity

2. Deulgaonkar et al. 2019. Int. J. Vehicle Structures & Systems, 11(2), 127-132
128
considerations. Two types of bus compositions are
available viz, chassis and body manufactured into two
separate parts and the other is chassis and body produced
as single component. The former composition of
separate manufacturing of chassis and body is preferred
to achieve desired factor of safety [15]. The design
constraints of the bus include height, width, overall
length, front overhang distance, rear overhang distance,
location and dimensions of emergency exits viz doors
and windows. The dimensional constraints prescribed by
AIS 052 and central motor vehicle rules are summarized
in Table 1. The cross bearers used for the composition of
bus floor is symmetric C-sections. These C-sections are
interconnected with the aid of standard angle sections.
The desired interspacing between C-sections is
maintained with the suitable length of these angle
sections of 5050mm.
Table 1: Dimensional constraint for public transport bus
Parameter Allowable dimensions in mm
Maximum vehicle height 3800
Width of the vehicle 2600
Overall length of the vehicle 10370
Front overhung distance 1185
Rear overhung distance 3235
Door
Window
700500
1250550
Loads acting on the bus include but not limited to
static loads due to self-weight, passenger weight,
luggage allowed with passengers, load due to baggage
on roof luggage carrier, wind loads and loads due to
vertical acceleration resulting from tire road interaction.
The load transfer in bus begins from roof top of bus and
ends at vehicle chassis [6]. The computer aided model of
the combination of chassis, cross bearers and
longitudinal angle sections is shown in Fig. 1. Total
number of cross bearers used in public transport buses is
14 and varies according to requirement of gross vehicle
weight. The inter-spacing distance between the cross
bearers is governed by passenger seat locations, wheel
base and overall length of the bus.
Fig. 1: Computer aided model of the bus sub structure
3. Design and analysis of bus floor
The floor is as described is the combination of
longitudinal angle sections and rectangular cross bearers.
The load is transferred from seat locations to cross bears,
Cross bearers are attached to chassis and the left and
right overhung portions. Cantilever action is observed
during the load transfer. The longitudinal angle sections
and cross bearers are joined by using oxy-acetylene
welding. The new floor design includes 8 cross bearers
with overall reduced weight. A comparison of existing
and new design parameters is shown in Table 2. The
newly designed deck includes combination of chassis, C
section and cross bearers. This combination offers higher
value of section modulus during bending and further
reduces the stress value to which the floor is subjected
[17].
Table 2: Existing and new floor design specifications
Parameter New deck (mm)
Existing deck
(mm)
Floor dimensions 85352440 85352440
No. of cross bearers 8 14
Length of each bearer 2440 2440
Stool Height 100 200
Spacing between bearers 1250 Variable
Width of door 885 690
Weight of floor 415 489
Cross bearer dimension 100505 100506
Longitudinal bearer 75405 75406
Angle section 50505 50506
Stool C channel 100505 Not used
Dimensions of the cross and longitudinal bearers are
selected from IS 808. Out-rigger brackets are used to
combine the cross-bearers with vehicle chassis. Floor
runners are the structural members that connect the cross
bearers. Fig. 2 depicts the diagrams indicating the
combination of chassis, cross bearer and stool for
existing and proposed design. The section modulus value
offered by the combination comprising stool is more as
compared with the value of existing composition.
Location of centroid for both combinations, moment of
inertia of individual and combined sections are evaluated
using the method presented by Deulgaonkar et.al [1].
The values of section moduli from all four locations and
centroid location of both the sections are given in Table
3.
Fig. 2: Existing (Left) and proposed design (Right) combined
sections
Table 3: Section properties of existing and proposed configuration
Parameter With stool (mm3
) Without stool (mm3
)
Section modulus
form left
207369.94 102105.8669
Section modulus
form right
168391.2765 51536.3153
Section modulus
form bottom
598738.6577 404334.9183
Section modulus
form top
783081.34 502633.557
C.G location (X,Y) (44.703, 297.519) (21.803, 80.112)

3. Deulgaonkar et al. 2019. Int. J. Vehicle Structures & Systems, 11(2), 127-132
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This value of increased section modulus reduces the
stress induced in every cross bearer and offers more
bending resistance. This increases the passenger comfort
with reduced levels of vibrations transferring from
ground to roof of bus. Combination of longitudinal and
cross bearers is made such that the seat locations across
the entire space, gangway for standee passengers and
entry door space constraints were satisfied as AIS052
[7]. Computer aided model of both configurations is
prepared considering the loading condition (static and
dynamic) on the deck. The deck acts as a single unit
during loading as they are welded to each other. Surface
modelling technique is used for preparation of the
computer model using CATIA V5.
Two computer models of the floor composition are
prepared viz existing and stool configuration. Fig. 3
depicts both the configurations. Limiting dimensions of
floor are decided using Central Motor Vehicle Rules and
automotive industry standard. For finite element analysis
the computer aided model is verified for surface
connectivity errors of geometric modelling technique.
Finite element analysis of the present and stool
configurations is carried in two phases viz pre-
processing which includes meshing of the longitudinal
and cross bearers, applying the boundary conditions and
solving the finite element model. Meshing phase
includes element selection, mesh quality verification and
verification of interconnectivity of the elements used in
mesh [14].
Fig. 3: Computer models of existing and stool floor configurations
Element selection for floor constituents has been
carried out by accounting the complexities in geometries
of floor after welding, variations in cross-sections,
profiles and geometries of all attachments and
constituents. Two dimensional (2-D) quadrilateral shell
elements are selected to simulate the floor behaviour
under different load situations of the bus. All the
components of the floor are made of structural steel;
density of 7850 kg/m3
, Poisson’s ratio of 0.3 and
modulus of elasticity as 250MPa. Intense loads are
applied over the nodes on seat locations. Complex
geometries are meshed using 2-D triangular elements
ensuring node connectivity. Node coincidence and
common nodes at all the continuous and discontinuous
sections of the floor sections is ensured for proper
element connectivity. Element connectivity is needed for
efficient load transfer at all sections for finite element
analysis. All elements (quads & trias) are assigned with
5mm thickness. This meshed model is verified for
meshing errors such as warpage, aspect ratio, skewness,
taper and interior angle before applying constraints on
the meshed floor structure. Meshed model of existing
configuration is depicted in Fig. 4.
Fig. 4: Meshed model of bus
Imposing boundary conditions pertinent to the actual
load situations on the meshed model needs to be
addressed. The floor is attached with the aid of U-bolts
and hence constraints are applied to chassis [11]. All six
degrees of freedom of the nodes on the chassis are
arrested. Loads are applied at the seat locations and
corresponding cross bearer portion. Magnitude of load is
selected as 65kg per person. The load application on the
finite element model is done by accounting for number
of nodes in the area of loading. Loads and boundary
conditions applied on the meshed model are shown in
Fig. 5. Both the models were solved for stress and
deflection. The plots of the same are shown in Figs. 6 to
9 respectively.
Fig. 5: Boundary conditions applied on the floor configurations
Fig. 6: Stress plot for the existing floor
Fig. 7: Stress plot for the proposed floor

4. Deulgaonkar et al. 2019. Int. J. Vehicle Structures & Systems, 11(2), 127-132
130
Fig. 8: Deflection plot for the existing floor
Fig. 9: Deflection plot for the proposed floor
4. Design & analysis of bus superstructure
The superstructure of bus is a combination of vertical
and horizontal pillars. The elements of bus super
structure are vertical pillars, roof-arch members, can’t
rails, waist rails, sole bars, seat rails, roof runners, out-
rigger brackets and pillars. Present work for
superstructure includes reduction in overall weight of the
vehicle by reducing the total number of skeletal
members and further improves power utilization of the
bus without compromise in overall passenger safety. Fig.
10 depict the three dimensional details of superstructure
along with the detailed nomenclature. The weight
distribution of bus is governed by norms of weight
specified by transportation engineering department and
automotive industry standard. The weight on front axle
is 5080 kg and on the rear axle is 10160 kg and the gross
vehicle weight is 15240 kg. Keeping these values as
design constraints, a combination of skeletal members
mentioned above along with mild steel sheet is made.
Bus design economics needs balance between strength,
weight and cost.
Present bus structure includes combination of two
materials as mild steel for driver cabin and lightweight
aluminium for rest of the bus body. Rollover analysis of
the bus simulation needs detailed address to the
boundary conditions. During the simulation of rollover
process in present work the unladen kerb mass, centre of
gravity, distribution of mass, tire inflation pressure,
upright position of seats and closed situation of doors &
windows for bus are taken into account and boundary
conditions are applied
Fig. 10: 3-D representation of bus body structure
Though this combination results in weight reduction
of the structure, the strength of the structure is
compromised. The material for whole bus body under
consideration in present work is mild steel. Rollover
criteria according to AIS 052 specify that no displaced
parts must intrude into residual space. Residual space is
the space that is needed to be preserved in passenger
compartment during and after the rollover. The residual
space limiting dimensions for bus along with computer
model of the same are shown in Fig. 11. To evaluate the
force an angular velocity of 0.087 rad/sec for impact of
0.20 sec was considered. The magnitude of force applied
at 1050 on the bend of the pillars and roof sticks of the
structure is 1.26 times g force. This force acts along with
all the loads present on the respective load locations on
the bus and is shown in Fig. 12. This meshed model
along with the boundary conditions is further solved
using ANSYS solver. Results of analysis are depicted in
Figs. 13 & 14.
Fig. 11: Limiting dimensions and CAD model of residual space
Fig. 12: Forces and boundary conditions for rollover analysis
Fig. 13: Deflection plot for rollover analysis
Fig. 14: Stress plot for rollover analysis

5. Deulgaonkar et al. 2019. Int. J. Vehicle Structures & Systems, 11(2), 127-132
131
5. Results and discussion
Results of stress and deflection obtained from the finite
element analysis of existing and new design are in good
agreement with those of experimental results reflected in
literature [18]. The proposed combination of stool, floor
and superstructure shows reduced levels of stress and
deflection as compared with the existing bus model. The
stress and deflection values for existing and proposed
model are shown in Table 4.
Table 4: Stress and deflection magnitudes
Bus model Stress (MPa) Deflection (mm)
Existing model 89.55 2.45
Proposed model 68.59 1.63
Permissible values 250 5
From the above values it is inferred that the stool
box and hat configuration increases the section modulus
value and further reduces the stresses induced in the bus
body. Overall vehicle height is increased due to the stool
combination in floor design due to which the level of
vibrations to which the passenger is subjected is
drastically reduced. Rollover analysis of the bus carried
shows results far less those acceptable limits, wherein in
passenger safety is of concern.
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