Up-tempo number

Sept. 15, 2009

The Sumatra-Andaman earthquake and resulting tsunami of 2004 claimed more than 230,000 lives and left 1 million homeless.

Especially hard hit was the northwest coast of the Aceh Province on the island of Sumatra in Indonesia, where the human toll was 167,700 (130,700 fatalities; 37,000 missing and assumed dead).

The Sumatra-Andaman earthquake and resulting tsunami of 2004 claimed more than 230,000 lives and left 1 million homeless.

Especially hard hit was the northwest coast of the Aceh Province on the island of Sumatra in Indonesia, where the human toll was 167,700 (130,700 fatalities; 37,000 missing and assumed dead).

Along the Aceh coast, from the cities of Banda Aceh in the north to Meulaboh 190 km south, 12 towns were washed away as well as long segments of the north-south coastal highway including 90 bridges. Travel on the route, normally a four-hour drive from Banda Aceh to Meulaboh, became a 20-plus-hour ordeal by four-wheel-drive vehicle. Depending on rain, the highway was impassable at times. The loss of the highway crippled the region’s transportation system, hampered post-tsunami reconstruction and created great social and economic hardships.

The U.S. through USAID committed $900 million in tsunami relief aid, with $245 million going toward the reconstruction of the Banda Aceh-to-Meulaboh Road. This article discusses the tsunami’s impact and the emergency response and covers how structure type selection was made based on local construction practice, site accessibility and material availability. It tells of the construction means and methods and of the programmatic design process instituted by Parsons, Chicago, the lead engineering firm on the job.

A year after the tsunami, the Parsons engineering team drove the 240-km route between Meulaboh and Banda Aceh and observed first-hand the emergency bridge constructions.

At some waterways, temporary panel bridges had been constructed. These bridges were holding up well for the most part, except for the timber decks, which were becoming worn and had occasional missing planks. Other bridges seemed to be of local design and construction from materials that could be obtained locally. Many bridges were made of tree trunks and logs. The nicer variety of these had timber plank decks.

Non-American ingenuity

At the Lambeso River an individual started his own ferry service. Originally he collected tolls, but eventually he was paid a monthly stipend to provide free service to travelers. Cars boarded the ferry by timber planks spanning to the dock. Boarding was a risky operation that shut down the ferry at times when cars drove off the planks and became wedged between the ferry and the dock.

Parsons’ contract with USAID allowed nine months for design and to prepare construction documents for 165 km of roadway and 90 structures. Following the design phase Parsons’ contract continued in the form of providing construction management services. To meet the schedule, structural design needed to begin immediately without geotechnical data, roadway geometry, structure locations or required structure lengths. The first step was to understand the local conditions and practices. This came first-hand in meetings with the Indonesian Ministry of Public Works (MPW), Indonesian fabricators and contractors and site visits to the structure locations.

The next step was to mobilize a large design staff. For the structural design effort, Parsons staff in four U.S. design offices, from Washington, D.C., to Seattle, Wash., worked together on the project and had to coordinate with the Parsons staff in Jakarta and Banda Aceh, Indonesia.

To facilitate coordination, project-specific design criteria (PSDC) were written. Such a document is common practice at Parsons for projects with large staffs and is invaluable when work is spread over several offices. The PSDC specified which sections of the AASHTO 17th Ed. bridge code were to be replaced by the Indonesian bridge design code (Bina Marga). It detailed bridge cross sections specifying lane, shoulder and sidewalk widths. Typical details for traffic barrier and pedestrian railing were given. Design loads were given as well as provisional loads such as future utility and resurfacing loads. It also specified material strengths for concrete, steel, reinforcing bars, prestressing strand and bolts.

The PSDC proved to be very important in the design coordination with USAID and the U.S. Army Corps of Engineers (USACE), who were retained by USAID to review Parsons’ work. The Indonesian MPW also provided comment on the designs. Prior to beginning design work, all of these stakeholders agreed to the PSDC.

With little schedule it was evident that stand-alone construction plan sets could not be prepared for each structure. Early on it was agreed that Parsons would proceed with the preparation of standard plans for three types of structures: cast-in-place box culverts, prestressed concrete I-girder bridges and steel-truss bridges. These structure types satisfied the constraints of site accessibility, material availability and common construction practices.

With the standard plans providing the design, the only unique plan sheet for each bridge was the structure layout sheet, which presented the structure plan and elevation and gave key dimensions.

To aid in bidding, pay-item quantities for each structure were given in quantity tables categorized by structure type. As part of the construction work, the contractor was required to provide complete shop drawings specific to each structure. This confirmed that the standards were being applied correctly and that site-specific variations were being correctly incorporated into the structure’s construction.

Truckload of difference

An important difference between the Bina Marga bridge design specification and the AASHTO bridge design specification was the greater design live load specified by Bina Marga. The reason for the difference was greater truckloads in Indonesia, and from what was observed as a common occurrence of overloaded trucks. Overloaded trucks were the cause for the failure of one of the panel bridges and one of the log bridges. However, it must be admitted that the log bridge was built by local tradesmen, and the construction was not based on an engineered design.

It was ascertained in reviewing the Bina Marga code that it closely corresponded to the AASHTO 17th Ed. LFD code, but the live-load magnitude differed notably. Similar to AASHTO the Bina Marga live load has lane-load and truckload cases. Impact factors are variable and are based upon length of loaded span. AASHTO’s truckload is a three-axle vehicle with axle loads of 35.6 kN, 142.3 kN and 142.3 kN. The Bina Marga truckload also has three axles but with magnitudes of 50 kN, 200 kN and 200 kN—40% greater than AASHTO. The Bina Marga lane load has uniform-load and rider-load components as does AASHTO, but the magnitudes are much greater. The Bina Marga uses a uniform load of 8 kN/sq meter and a rider load of 44 kN/meter, compared with AASHTO’s uniform load of 3.1 kN/sq meter and rider load of 37.9 kN/meter. The culmination of the review of the Bina Marga code was to adopt the Bina Marga live-load, temperature-range and seismic-response spectrum. All other design criteria were based upon AASHTO 17th Ed., which was the preference of USAID.

A key constraint driving the structure-type selection was site accessibility. Construction equipment and material delivery would have to be made over dirt roads and temporary bridges that proved unreliable at times.

Another constraint was material availability. Precast concrete I-girders and piles were available from fabricators in Medan, Indonesia, located 300 km away by road. Steel girders would have to come from Jakarta, a 1,500-km trip by sea and land.

Another constraint was accepted design and construction practices. For example, jointless integral abutment bridges, proposed by Parsons, were rejected by the Indonesian MPW because they were not familiar with that construction method. Steel-bridge barrier railing, recommended by Parsons, was rejected in favor of cast-in-place concrete barrier over concerns that it would be stolen for steel scrap.

Sixty of the 90 structures were replaced by reinforced concrete-box culverts. Culverts were cast in place to eliminate the challenges associated with shipping precast boxes. Concrete was mixed at batch plants set up by the contractor at various locations along the project corridor.

The standard structural plans for single-cell and multi-cell box culverts provided tabulated designs for cells as large as 3 x 3 meters and cover depths ranging from 0 to 10 meters. The standard plans detailed the culvert headwalls, wingwalls and a unit length of the culvert barrel. Culvert locations were identified on the roadway plan sheets and quantities tabulated in a culvert schedule.

Culverts beyond the applicability of the standard plan tables were designed on a case-by-case basis.

The Indonesian MPW requested that the maximum prestressed concrete I-girder beam lengths be limited to 33 meters. Standard single-span bridge designs were prepared for girder lengths of 19, 22, 25, 28 and 33 meters. Thirty-nine-meter and 45-meter-long bridges were designed consisting of two equal simple spans each.

In response to shipping constraints and to facilitate erection, precast concrete I-beams were fabricated in approximately 6-meter-long segments.

Assembly required

At the bridge site, segments were assembled and post-tensioned into a continuous beam. Epoxy was applied to the keyed mating surfaces prior to post-tensioning. The preferred erection method was to launch the individual girder segments across temporary supports. They were post-tensioned after the segments were in position from one bridge pier to another.

Another erection method was to stage the girder assembly and doing post-tensioning on the embankment behind the abutment before launching the girder as one piece instead of as individual segments. Once girders were in place, a two-course deck was constructed. The deck consisted of 70-mm-thick precast deck panels with a 130-mm reinforced concrete topping.

During construction the contractor requested that precast deck panels be no larger than 1,510 mm by 500 mm to keep the piece weight below 1,250 kN. This request was to facilitate their placement in the field by hand.

For bridges longer than 45 meters, steel-truss bridges were the contractor’s bridge type of choice, especially if this eliminated pier work in the river. Steel-truss spans ranged from 40 to 80 meters in length. Beyond 80 meters, truss bridges comprised multiple spans.

The longest truss bridges consisted of two spans of 60-meter trusses. All steel-truss bridges, except the 80-meter single-span truss bridge, had a common panel length of five meters. The standard panel length permitted a typical floor system to be used for all truss bridges.

The floor system consisted of 6-mm-thick corrugated steel decking, which has adequate strength to support the full live load. This was desired by the contractor since the steel decking supported crane loads during truss erection. Upon the decking a reinforced concrete deck was cast.

The contractor elected to perform deck casting under a shade shelter to control shrinkage cracking. Trusses were fabricated in Jakarta and fully assembled in the factory to check fit-up prior to shipping. Truss-bridge erection was performed on temporary shoring constructed of palm tree trunks. All steel members and hardware were hot-dip galvanized for corrosion protection.

Measure for geology

For most of its length, the highway hugs the west coast at an elevation just above sea level between the beach and the steep volcanic hills. Site-specific geotechnical data was not available during design for most of the structures. But the general geology was known. At most bridge locations the geology consists of underlying rock with 10 to 15 meters of soft-soil overburden. At locations where there is no beach, the road rises into the rocky hills, and structures are founded directly on rock.

Standard plans were developed for two foundation cases: piles driven to rock and spread footings on rock. For each of the bridges an estimate of the rock elevation was made and judgment was used to select the foundation type for the purposes of bidding.

Construction contract documents required the contractor to obtain borings at each bridge location to verify the applicability of the foundation assumptions made during design. Pile driving was governed by a variation of the Hiley formula.

Based upon input from contractors and material availability, two pile types were used in construction: 400-mm square precast, prestressed concrete piles for lightly loaded foundations and 600-mm-diam. spun, precast, prestressed hollow piles for heavily loaded foundations.

Piles were fabricated in Medan and trucked to the bridge sites in 15-meter lengths. Pile splicing was accomplished by casting steel plates into the pile segment ends and welding the plates together in the field.

WiKA, an Indonesian contractor, was awarded a one-year road maintenance contract in September 2005 to maintain an 80-km segment of the emergency road. As construction contracts were let for sections of roadway, the selected contractors took over the road maintenance of the corresponding sections of the entire emergency road between Banda Aceh and Calang.

In order to expedite construction of the highly traveled northern section near Banda Aceh while the remaining contracts were being tendered, USAID expanded the scope of WiKA’s contract to include 40.2 km of roadway and 14 bridges in March and October of 2006.

The work on these contracts was to be completed within 15 months. However, due to slow progress caused in part by community obstructions and the unavailability of the full right-of-way, USAID elected to de-scope the partially completed southernmost section of WiKA’s contract to enable it to focus on the remaining 28.3 km of roadway and 10 bridges. Issues with the community that had obstructed progress have since been resolved and the remaining work is expected to continue later this year with a different contractor.

The balance of the construction work, which consists of approximately 105 km of new and rehabilitated road and 13 bridges, was awarded to SSangyong-Hutama Karaya, a South Korean-Indonesian joint venture, in June 2007. Their work is to be completed by March 2010.

About The Author: Magliola is with Parsons, Chicago.

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