A comprehensive research project was carried out at the Queensland University of technology (QUT) with the objective of establishing the feasibility of using analytical methods for (i) design and evaluation of ROPS and (ii) investigating the influence of parameters for enhancing ROPS performance。 Limited experimental testing is required, both to capture physical behaviour and to use the results to validate the finite elements models, which could then be used in further investigation。 As it is difficult to carry out full scale testing on ROPS, ½ scale models were designed based on the principles of similitude modelling and Buckingham Pi theorem was used to develop the relationships between the prototype and the model。 Three different types of ROPS were considered in the project。 This paper treats ROPS models for a K275 bulldozer using experimental testing of a ½ scale

ROPS model and extensive computer simulations first on ½ scale and then full scale FE ROPS models。 The FE analysis was validated through comparison of results for the ½ scale models and then extended to full scale ROPS models through similitude verification。 This project aims to (i) enhance our understanding on ROPS behaviour, (ii) improve energy absorption and safety and (iii) generate research information which will contribute towards the development of analytical techniques for design and evaluation that may lessen the need for destructive full scale testing。

ROPS for K275 Bulldozer

The K275 bulldozer is a crawler type dozer with a gross vehicle weight of approximately 50 tonnes。 This type of dozer is commonly used in the construction and mining industries for earthmoving purposes。 Rollover protection for the occupant is afforded through a two post rollbar type ROPS, which is shown in Figure 1。 This ROPS is primarily a fixed base portal frame, consisting of two posts and a beam, rigidly connected to the chassis of the vehicle。 In addition to the ROPS, a roof canopy section known as the FOPS (Falling Object Protective Structure), is incorporated to provide protection to the operator under falling objects。 In this study, the FOPS, which is a separate detachable structure, was omitted。 The  overall geometry of the full scale K275 ROPS model was established from site measurements taken at the manufacturer’s storage yard。

Design of ½ scale ROPS model

Previous research by Srivastava et al (1978) has shown that principles of similitude modelling could be successfully applied to ROPS testing techniques, and could lead to large scale economic savings。 Based on the research findings of these authors the principles of similitude were applied to the K275 bulldozer ROPS in order to lessen fabrication costs and reduce  the  magnitudes  of  the  test  loads  to  be  applied  to  the  ROPS。  Reduction  in  the

magnitudes of the loads was essential as a full scale test of a ROPS for a vehicle such as this were extremely large and would require the use of an extensive laboratory testing facility。

Buckingham Pi theorem was employed to determine the number of independent dimensionless parameters that would influence the behaviour of the system。 Once the independent Pi terms were determined, they were equated between the model and prototype ROPS to establish the model design conditions。 A scaling factor of ½ (for size) was then selected between the model and prototype which gave rise to the scaling factors of 1/8 for the energy absorbed under lateral load, ¼ for loads and ½ for deflections。 A 1/2 scale model of the K275 ROPS with length 1000mm and height 900mm, using hollow tube sections, was designed and fabricated and subjected to the loading and energy requirements of AS2294- 1997。 The cross- sectional dimensions of the posts and beam in the ROPS model were 125x75x5mm, as shown in Table 1 and conformed to the required similitude relationship for the second moment of area I of the model and prototype in the form IM = IP/16, where the subscripts M and P denote the model and prototype respectively (Clark 2005)。 The member types used for the ROPS consisted of 350 grade RHS with full penetration butt welded moment resisting connections。