The adequacy of the requirements presented in current ROPS regulatory standards has been questioned by some researchers and more recently by Ho (1994), who used a simplified collapse load approach to study the energy absorption capability of a fixed base two post ROPS prior to encroachment of the DLV。 He examined a number of two post ROPS configurations with collapse loads equal to 100%, 124%, 150% and 200% of the minimum lateral load provision of SAE J1040 and concluded that a ROPS which had a collapse load greater than 150% of the minimum lateral load requirement would be able to absorb the necessary amount of energy prior to encroachment of the DLV。 Ho’s investigation is extended further in this paper by using finite element analysis to verify the adequacy of the K275 ROPS frame。 In this investigation the sectional geometry of the posts was varied to obtain a range of collapse loads。 The width and thickness of the post was kept constant, while the depth of the section was varied。 in order to limit the number of variables and minimise the number of numerical simulations。 The investigation involved assessing the

capacity of the ROPS to adequately fulfil the requirements of the standard and its energy absorption capacity prior to DLV infringement。 It is believed that such a study will provide meaningful results that may assist with the development of ROPS design guidelines。 In all the analyses the geometry of the ROPS model was proportioned carefully to ensure that the formation of plastic hinges required for energy dissipation took place at the top and base of each post during application of the lateral load。 In order to ensure this, the beam section size was adjusted to give a much higher plastic moment capacity than that of the posts

Plastic Analysis of ROPS under Lateral Load

As ROPS rely on the absorption of rollover impact energy through the permanent plastic deformation of their structural members, plastic design principles are appropriate to develop member sizes for ROPS。 Consider the 2 post ROPS shown in Figure 13, where the plastic moment capacity MP2 of the beam is larger than that of the posts。 Using the principles of virtual work for a rotation , the collapse load Fc for the ROPS is given by

FC = 4MP1 /Le where  MP1 = Zp1  y (1)

In the above equations Le represents the clear height from the base of the post to the underside of the beam, MP1 the plastic moment capacity of the post about its local Y-Y axis, Zp1 the plastic section modulus of the ROPS post and y the yield stress of the material。

Numerical Investigation of Full Scale K275 ROPS

The full scale FE model of the K275 ROPS that was treated in the previous section was subjected to further numerical investigation。 This involved varying the section geometry of the ROPS posts to study its influence on the structure’s ability to absorb energy prior to infringement of the DLV and in fulfilling the load and energy absorption requirements of the standard。 FE models of the K275 ROPS were developed using the same procedures as before。 The wall thickness of the beam linking the posts was increased to 12mm in all the

models to ensure that the plastic hinges developed within the posts of the ROPS。 Four different ROPS models were considered, having post section sizes of 120x250x10, 150x250x10, 200x250x10 and 240x250x10。 These section geometries corresponded  to ROPS collapse loads of 100%, 140%, 200% and 260% of the minimum lateral loading provision of the standard respectively。 These ROPS models were studied to evaluate the lateral loading and energy absorption provisions of the standard (AS2294。2-1997), which is the main focus of this paper and the ROPS standards。 The other two loading sequences are strength cases to ensure that a ROPS has adequate capacity in the vertical and longitudinal directions。 For this study, ROPS posts were proportioned to develop plastic hinges about their weak axis normal to the applied lateral load, however, in addition to this they were also proportioned to have sufficient capacity about the other axes to withstand the subsequent vertical and longitudinal loading stages。