InTrans / Aug 14, 2018

National cost study of timber bridges

A study is underway to determine the initial cost of
timber bridges compared to those of steel, concrete,
and prestressed concrete bridges. This report
discusses the early results of the timber bridge
portion of the data set. To this end, timber bridge
owners, as identified in the June 1994 National
Bridge Inventory (NBI), were sent a specially
designed questionnaire to survey cost information
on timber bridges under their ownership. In order
to establish a comparative basis, timber bridges
were selected under the requirements that they be
built no earlier than 1980 and be load rated
according to American Association of State
Highway and Transportation Officials (AASHTO)
specifications. No private or government
demonstration bridges were included in this study,
Given these requirements, 1604 timber bridges
were identified as survey bridges. This paper
summarizes the analysis of data collected on the
cost of timber bridge superstructures throughout the
country. The results of such analysis suggest that
unit costs were highest for both the longest and
shortest bridges considered and tend to increase
with higher load ratings. Additionally, it was noted
that questionnaire responses were lower than
expected for shorter, narrower bridges that were
designed to carry lighter loads.