Source: Radio New Zealand
siwakorn / 123RF
Bridge engineers say the NZ Transport Agency’s work to update how bridges are designed and assessed should at most have a “minor positive” impact.
Two trucking groups have expressed worries that NZTA is missing an opportunity to make more highway bridges able to carry heavier trucks in future, especially if that applies to the Roads of National Significance.
The agency said its new measures were “not anticipated to have a significant impact on existing bridge stock or the construction of new ones”.
The recently formed Bridge Engineering Technical Society at Engineering NZ agreed, based on what NZTA had said.
“It is our understanding that the update to the design (vehicle) loading model, to be applied to new bridge designs, has been done to address risks associated with accommodating heavy vehicles on our roads,” the society told RNZ.
“These have arisen from evolutions in the heavy vehicle fleet make-up, as well as bridge design and construction practice in recent times.
“Our understanding is that the risk relates to maintaining the standard margin between evaluation (day-to-day) loadings and design capacity for longer, continuous span bridge construction that has become more common.”
It also captured the effects due to multiple heavy vehicles following each other (“platooning”), which was more likely to occur with longer span bridges compared to shorter spans, it said.
NZTA has said the “effects of platoons of vehicle travelling at minimum spacings” in the same lane could be “substantially greater than those resulting from the previous evaluation loading”, so it had caught its bridge rules up to account for it.
However, Transporting NZ said “platooning” was not a factor as New Zealand roads were not the sort that allowed for it much if at all, so bridges should not be designed as if it was.
“Platooning trucks is highly unlikely to happen in New Zealand for the sheer reason that we don’t have enough multi-lane highways to do that,” it said.
“This is our concern, [that] they’re worrying about something that will likely never happen here.”
The society made the point it was not uncommon that design standards were revised periodically to take into account increased knowledge and understanding, improvements in technology and changes in demands such as traffic loading, “especially heavy vehicle configurations”.
“Based on available information, we concur in principle with NZTA’s response that any cost implications of the changes in the design loading model will not have a significant impact on new bridge designs.
“While any implications depend on the bridge type and/or material, in many cases the marginal increase due to the updated design (vehicle) loading, taken as a portion of the overall total weight of the structure, would not require significant additional material.”
The evaluation loading for existing bridges was amended some in mid-2022 and the updates for new bridge designs ensured consistency.
“It appears that the changes which NZTA have introduced should not have a significant impact on the industry, or a minor positive one.”
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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand
