Abstract Roll Over Protective Structures (ROPS) are safety devices fitted to heavy vehicles to provide protection to the operator during an accidental roll over。 At present, ROPS design standards require full scale destructive testing which can be expensive, time consuming and unsuitable for small companies。 More economical analytical methods would require an understanding on post yield behaviour and energy absorption capacity of ROPS。 With this in mind, this paper treats a bulldozer ROPS using experimental and analytical techniques to generate research information which will enable development of analytical design guidance and enhance safety。82309

Key words: Roll Over Protective Structure, Impact, Energy Absorption, Safety,

Introduction

Heavy vehicles used in the rural, mining and construction industries are susceptible to rollovers as they have a high centre of gravity and commonly operate on sloping and uneven terrain。 A steel moment resisting frame with either two or four posts is usually attached to these vehicles above the operator’s cabin for protection during rollovers。 This safety  device is called a Rollover Protective Structure (ROPS) and its role is to absorb some of the kinetic energy of the rollover, whilst maintaining a survival zone for the operator。 The design and analysis of ROPS is complex and require dual criteria of adequate flexibility to absorb energy and yet, enough stiffness to maintain a survival zone around the operator。

Evaluation techniques used in the current Australian standard for earth moving machinery protective structures AS2294–1997 are simplified and involve full scale destructive testing of ROPS subjected to static loads along their lateral, vertical and longitudinal axes。 The standard is performance based, with certain force and energy absorption criteria which are derived from empirical formulae related to the type of machine and operating mass。 Deflection restrictions are also employed to enable a survival space known as the dynamic limiting volume (DLV) to be maintained for the vehicle operator。 These simplified provisions provide design guidelines intended to substantially improve the operator’s chances of survival during an accidental rollover。 This form of certification can be time consuming and extremely expensive as establishing the force and energy criteria can involve large loads which may therefore require the use of a specialized testing facility。 In addition to this, the nature of the testing procedure is destructive which means that the ROPS will incur irrecoverable permanent deformation。 Consequently, failure of a ROPS to meet the requirements of the standard will mean that another improved prototype will have to be fabricated and re-tested。 This process can be avoided by most fabricators through  providing

additional strength and stiffness to the ROPS。 The addition of increased stiffness to the ROPS to avoid premature failure may not be the most desirable solution for the operator’s chances of survival, as a ROPS is an energy absorption device that requires a balance between strength and stiffness to be maintained。 Safety may be compromised by the ROPS manufacturers who avoid the expenses associated with repetitive experimental testing。

Preliminary research has shown promise for the use of analytical techniques to model the nonlinear response of ROPS。 These analytical methods have been very simplified and have primarily involved the use of elasto-plastic beam elements to simulate the behaviour of a ROPS subjected to a static lateral load。 In recent years, substantial advances have been made in both computational power and the implementation of advanced element types in Finite Element (FE) techniques that can accurately model and predict the nonlinear response of structures, particularly in the post yield region。 Research carried out on ROPS behaviour using analytical and experimental techniques include those of Clark et al。 (2006 and 2005), Kim and Reid (2001), Tomas et al。 (1997), Swan (1988) and Huckler et al。 (1985)。