Analyzing the collapse of bridges in Indonesia<\/p>\n
Sohei Matsuno, Palembang<\/p>\n
It was Dec. 5, 1995 when the Air Beliti Bridge along the
\nTrans-Sumatra Highway collapsed in South Sumatra, some eight and
\na-half years before Cipunagara Bridge along the North Coast
\nHighway of West Java collapsed on July 23.<\/p>\n
The two bridges are of the same Callendar-Hamilton (C-H)
\ndesign with steel pony trusses. The loads the bridges carried at
\nthe time of collapse (six trucks on the Air Beliti Bridge and
\nseven trucks on the Cipunagara bridge) are also similar.<\/p>\n
The probable reason given for the most recent collapse is also
\nsimilar to the one initially given in 1995: An aging bridge
\noverloaded with heavy trucks.<\/p>\n
The C-H type bridge was designed to meet engineering
\nconditions in Indonesia, and played an important role in the
\n1970s and 1980s, with hundreds built throughout the country.<\/p>\n
Many adjustments to the bridges have also been made since
\ntheir initial construction, including efforts to widen the C-H
\nbridge's applicable span with minimum adjustments in parts and
\ncomponents.<\/p>\n
One of the enduring qualities of the C-H bridge is that it is
\nwell-designed, manufactured and assembled. Hence, it is suppposed
\nto be stable, workable and bankable. The bridges are designed to
\nbe durable, with a life span of more than 100 years under current
\ntraffic conditions, and all the parts and components of the
\nbridge are galvanized. The structures are also covered layers of
\nzinc that prevent them from rusting.<\/p>\n
When reviewing the investigation into the bridge collapse,
\nseveral important questions should be asked:<\/p>\n
If the collapse was caused by aging, why didn't other similar
\nbridges which are even older also collapse?<\/p>\n
If overloading was cited as the cause, why didn't other
\nbridges the trucks pass along the North Coast Highway also
\ncollapse?<\/p>\n
Why was there no warning of the dangers?<\/p>\n
If any of the above causes are proven, who should the victims
\nof the accident claim compensation from?<\/p>\n
None of the these answers can exclusively explain the
\naccident.<\/p>\n
If the accident was caused by aging, there must have been
\nsignificant warning signs, known in the trade as ominous
\ndeflection, and these could have been detected and a warning
\ncould have been issued.<\/p>\n
The investigation into the 1995 collapse focussed on corrosion
\nand metal fatigue as these are known to be common causes of
\nbridge collapse.<\/p>\n
It was confirmed the bridge had shown insignificant ominous
\ndeflection before the collapse. It was also found the bridge was
\nfully galvanized. Hence, there was little indication of corrosion
\nand consequential sectional loss throughout the structure.<\/p>\n
After these discoveries, corrosion was deleted from the list
\nof possible causes. Aging as a cause of the collapse disappeared
\nat this stage of the investigation.<\/p>\n
However, what was observed were apparent beach marks (evidence
\nof fatigue) on a sheared section of the bridge, which proved a
\nbridge support, or member, had broken because of fatigue.
\nHowever, this kind of fatigue occurrs only when a member is
\nsubjected to alternating deformation -- repetitious bending up
\nand down, expanding and contracting.<\/p>\n
And alternating deformation does not occur as a rule in this
\nkind of truss design. Therefore it was essential to determine how
\nthis sheared member was subjected to the deformation.<\/p>\n
The puzzle was solved when it was discovered that the bridge
\nwas erroneously supported by fixed shoes (hinges) at both ends.
\nIt should have been commonsense to support one end by a hinge and
\nthe other end with a movable shoe (rollers). In this way, changes
\nof size due to temperature variations could have been
\naccommodated.<\/p>\n
Because of the erroneous shoe arrangement, the upper part of
\nthe hinge (upper shoe) nodded up and down due to the longitudinal
\nthermal expansion and contraction of the bridge. After a certain
\nnumber of cycles, the bridge developed a fatigue crack at a point
\nwhere it was connected to the upper shoe. The crack gradually
\ngrew as a result of the alternating deformation until the member
\nbroke. It was subjected to a deformation angle of about plus or
\nminus 1.15 degrees and took an estimated 30,000 cycles to fail.<\/p>\n
The next question was to identify if the erroneous shoe
\narrangement was a design flaw or merely an implementation flaw.<\/p>\n
In studying the bridge construction manuals, it was found that
\ninstructions in the manual dated Aug. 9, 1977, identified the
\nneed to support one end by a hinge and the other with rollers.
\nHowever in bridge drawings dated Jan. 25, 1977, it was indicated
\nthat both ends could use a hinged shoe arrangement.<\/p>\n
As it is, it is reasonable to suppose the construction of the
\nbridge -- which began in 1976 -- used the January drawings.<\/p>\n
Future corrections in the scheme of the bridge did not take
\neffect after it was completed in 1978.<\/p>\n
Investigation of some of the 22 other C-H type bridges in the
\nSouth Sumatra Province and on the North Coast Highway between
\nJakarta and Surabaya found similar errors in construction.<\/p>\n
While overloading may have been a factor in triggering the
\nbridges' collapse, there is a strong likelihood the cause of the
\ncollapse of the Cipunagara Bridge is similar to that of the Air
\nBeliti Bridge, given its similarity of construction and type.<\/p>\n
The writer (ypnt@indo.net.id) was a leader of the ad hoc team
\nat the Regional Improvements Office II (RBO-II), Bina Marga that
\nconducted the investigation into the collapse of the Air Beliti
\nBridge in December 1995. He is currently a senior lecturer at
\nTridinanti University, Palembang.<\/p>",
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