Arch Truss Structure, Enns Bridge in Ternberg

Ternberg (Upper Austria)

Arch Truss Structure
Enns Bridge, Ternberg

In 1996, the capabilities of engineered timber construction amazed the bridge-building community. An 80-meter span glulam arch truss was erected as a scaffolding structure for a reinforced concrete construction over the Enns River, 25 meters below. Timber proved to be competitive against steel. Unfortunately, nothing of this "temporary structure" can be seen today, as it was removed after the concrete cured.

The insights and developments from WIEHAG's in-house engineering office represent another pioneering achievement for the company.

Project Scope and Implementation

A Structure with
an 80-Meter Span

Based on the load specifications and geometric requirements, WIEHAG engineers developed custom designs for an arched box girder.

The construction was carried out in four sections, each with individual arch lengths of 23.0 m and 22.0 m. The approximately 2,600 kNm moment connection in the quarter joints was achieved with integrated tension rods. The connection for approximately 164 kN shear forces was made using 20 ring wedge dowels as end-grain connections. At the apex, the precise assembly of the entire arch involved a moment connection of about 2,800 kNm, also with integrated tension rods.

The quarter arches were transported to the construction site by truck and assembled into half-arches on site. These half-arches were floated on pontoons to the assembly position on the dammed Enns River. After being positioned in the abutments, they were lifted with tension cables and connected at the apex joints with moment connections.

Since two concrete structures needed to be built, the scaffolding was simply moved and used a second time.