Lateral Load Analysis – Load Deflection Response

The lateral load deflection response which satisfied the requirements of AS2294。2-1997, is shown in Figure 17 for each ROPS model。 It can be seen that each model satisfied the minimum loading and energy absorption requirements of the standard without violation of the 500mm deflection limitation of the DLV。 The softening of the load deflection responses of the different ROPS models took place at lateral deflections in the region 35 mm- 45 mm, accompanied by shape distortions at plastic hinge locations at the top and base of the posts upon further loading。 This feature was also observed during the experimental testing。 The graphs indicate that the criteria established in the ROPS design standard may be satisfied  by

placing either a high force/low deflection demand, as observed with the two stiffer ROPS models or a low force/high deflection demand, as observed with the less stiff ROPS models。

Summary and Conclusions

Rollover Protective Structures have to date been seen as the most viable method for providing protection to occupants during the rollover of heavy vehicles on construction and mining sites。 These types of safety devices which are commonly fabricated from mild steel hollow sections rely predominantly on plastic deformation of their members in order to absorb some or all of the kinetic energy of the roll。 For the case of earthmoving vehicles, the current performance standards both in Australia and worldwide employ simplified static testing methods to assess the capabilities of a ROPS。 This form of ROPS certification is destructive and can be extremely expensive, particularly for the case of large vehicles。 To address this, a collaborative university – industry research project using analytical (FE) and experimental techniques, was undertaken to generate comprehensive research information that may be used to develop an analytical procedure for the design and assessment of ROPS。 This paper presented the research findings pertaining to a 2 post K275 bulldozer ROPS。

The experimental program involved the use of static testing to assess ROPS behaviour and to provide a base model for the establishment of an analytical method for ROPS evaluation。 Finite element analysis formed the basis for the analytical program and involved subjecting the established analytical models of the tested ROPS to code specified loadings。 The combined analytical and experimental approach enabled a validated analytical ROPS assessment procedure to be established that could lessen the need for expensive full scale testing。 The developed procedure was able to replicate the loading sequences required by the relevant Australian standard。 While it may de desirable to do some experimental testing of ROPS  (new  designs)  for  capturing physical  behaviour  and validating numerical   models,

computer simulations can later be used to investigate the influence of parameters。 The results of the present study clearly support the use of finite element techniques for ROPS evaluation and design。 The set of mutually-supporting experimental/analytical/numerical methods used in treating ROPS behaviour demonstrate that these methods support one another。

It was found that correlation between analytical and experimental results was excellent under the lateral loading phase which represents the most crucial loading condition of the standard。 For the other two loading phases namely those in the vertical and longitudinal directions, it was found that the finite element analysis under-predicted the resulting displacements。 Reasons for this lack of correlation were attributed to the inability of the FE plasticity material model to handle (i)  influence of load reversal effects such as the Baushinger  effect,

(ii)possible inherent residual stresses in the members from the heavy welding of the members during fabrication and (iii) residual stresses from the previous loading phase(s)。 Further detailed finite element analysis of full scale two posts ROPS subjected to static loads led to the development of simplified design guidelines that would enable ROPS designers to quickly proportion ROPS members to adequately meet the requirements of the standard。 For a set global ROPS geometry, a range of plastic moment capacities were assessed  by adjusting the section properties of each of the posts of the ROPS。 For the two post ROPS treated herein, a simple collapse load model which assumed the formation of plastic  hinges at the top and base of each post was able to be used to assess the maximum structural capacity of a ROPS。 This method was also tested analytically and it was discovered that a carefully proportioned two post ROPS was able to adequately meet the performance requirements of the Australian standard provided that it possessed a collapse load that was equivalent to that of the minimum lateral loading provision of the standard。 In addition to this,  it  was  also  discovered  that  the  energy  absorption  capability  of  a  ROPS  was    an