Projekte

Projects

Pöhl dam – the smaller Thoßfell “pre-dam” - concrete repairs to the above and below the waterline

The purpose of the Thoßfell and Neuensalz “pre-dams” of the Pöhl dam is to eliminate
pollutants such as nitrates and phosphates, which are introduced by the high population
density in the catchment areas.

Another objective is the retention of sediments.
The “pre-dams” are continuously kept full.
A reduction in the water level or draining of the water is only done if necessary for repairs.

Preliminary investigations by the Planning Office revealed serious defects in the existing
concrete (alkali silica reactions)

This clearly identified the building contract, replacement of old concrete (high-pressure water jet removal) and application of anchored, reinforced shotcrete in the zones subject to alternating water levels above and below the waterline.
Due to the poor accessibility, the first step was the construction of a 350-metre-long construction site access, the preparation of a crane support surface and the laying of pipes for the drainage of inflows from the stilling basin.

After removal of the damaged concrete by high-pressure water jet robots, reinforced shotcrete with hollow microspheres was sprayed on. Then followed the formation of construction joints, which were then sealed with a compression profile.

Installation of new reinforced shotcrete arches for two railway overpasses in Erkrath

The Reconstruction Division of SCHACHTBAU NORDHAUSEN GmbH was commissioned by the REGIO-Bahn GmbH with the reconstruction of two railway overpasses in Erkrath as part of the railway line Mettmann-Düsseldorf reconditioning.

First step was the extensive removal of damaged brickwork up to 20 cm depth in one meter broad streaks by milling. To catch and remove leakage water, drainages were installed every two meter.

As replacement for the removed brickwork a new, 20 cm thick shotcrete layer of water-proof concrete was applied. The concrete got a reinforcement that was fixed by anchors against the original, undamaged brickwork. In doing so, the structural stability and watertightness of the overpasses was reestabilished again. in total 82 m³ brickwork was removed and 340 m injection tubes for grouting were installed. For the construction of the replacement layer 3400 anchors, 7 t reinforcement steel and 115 m³ shotcrete had to be processed.

During all stages of the construction works comprehensive safety precautions had to be taken, to avoid any danger for the onegoing pedestrain and bicycle traffic underneath the overpasses.

Water reservoir Pöhl - Dam repair

From September 2003 to July 2007 the Pöhl reservoir`s concrete dam was completely overhauled, commissioned by the State Office for Water Reservoir Management Saxony (District Zwickauer Mulde/Weiße Elster).

The complex work started with the repair of the overflow spillway as first construction section. After that, the part of the dam which is alternatively in contact with air and water was overhauled and so was the service building. Zhose works were finished in December 2004. Here for the very first time new technologies were applied, such as robot aided high pressure water blasting, operated from console scaffolding, as well as dry mix shotcrete with added micro hollow balls and maximum grain size of 16 mm.

From July 2006 to July 2007 finally the complete downsream dam face and the aluminium-glass-facade of the power house were overhauled.

In total 11,800 m² damaged concrete surface was removed up to 20 cm detpth from the damm structure and got replaced by reinforced shotcrete with special properties and a thickness up to 25 cm. For reinforcement 134.5 tons wiremesh were fixed with 63,000 anchors to the dam surface before the shotcrete was applied. For sealing the joints 2.5 km elastic joint tape were built in.

South Bridge Düsseldorf

SCHACHTBAU NORDHAUSEN GmbH was commissioned with the strengthening of the South Bridge Düsseldorf-Neuss in May 2004 (remark: the bridge was renamed in "Josef-Kardinal-Frings-Bridge" during construction period).

The bridge actually consists out of three separated structures, the main bridge crossing the river Thine and two foreshore bridges either on the Neuss side and the Düsseldorf side.

Within the three years of contract duration the strengthening was done by installation of 220tons steel beams (t-profile and standard I-profile) inside zhe box girder of the main bridge. For this the execution of 20 km welding seams was necessary. The bearing capacity of the foreshore bridges was improved by adding L-profile steel beams to the main and cross structure beams. Furthermore a 800 m long catwalk (covering 4.000 m² open mesh flooring) was attached to the bridge for easier maintenance and repair access.

Together with the ongoing construction work beneath the bridge surface, the joints between the road surface sections were overhauled, 1.600 m crash barrier were installed and the handrail was raised to 1.2 m in height. During all stages of the construction work the unobstructed traffic crossing the bridge had to be guaranteed.

THE SQUAIRE FRANKFURT – structural upgrading and restoration of welded seams

In the largest continental hub of international air traffic directly above the ICE railway station, the most mobile workplaces of our time – THE SQUAIRE centre Frankfurt. The building is located right in the middle of the B 43 and BAB 3.
The railway station completed in 1999 was designed as a superstructure with 5 floors.
However, the current design provided for a building of 9 floors. For this reason the so-called fish-bellied girders above the supports had to be reinforced.

The objective of the restoration approach.To increase the load-bearing capacity of the steel structure, it was necessary to restore faulty welded seams and weld in new steel plates into the junctions to upgrade the seams.
Repairs. All welded seams were examined after the fire protection lining of the support structure in the fish-bellied girder was removed. Faulty seams were grouted, burned out or grounded out and re-welded. The incorporated structural elements consisted of metal sheets up to 100 mm thick, each weighing up to 800 kg. Due to the high single loads, all the steel sections had to be manoeuvred into position by chain hoists and custom-made trolleys. To be installed, the massive steel sections had to be pre-warmed from 120°C to 150°C. In some sections, up to 60 beads per welded seam were drawn.
The gases emanating from the welding could be extracted over sophisticated extraction units.
Because the railway station remained operational and at the same time the smoke detectors were turned off, each welding job was manned by a full-time fire officer.
Main mass
A total of approx. 100 t steel was installed and approx. 25 t welding rod was used. The total project operated in two shifts with the use of 22 welders, 22 fire officers and 8 fitters. At some stages as many as 10 welding jobs per shift took place simultaneously. Up to 350 m pipelines were laid for air extraction. A total length of approx. 2,500 m of gas and oxygen pipelines was used.

Rhine River bridge Leverkusen BAB A 1 - reinforcement of the superstructure

The above-mentioned road bridge is where the federal motorway A1 crosses over the Rhine River. The actual steel bridge features a 700-metre long cable-stayed bridge with two box girders and orthotropic deck.
After detecting fillet-weld cracks between the longitudinal ribs and the deck plate, the client did a structural analysis of the existing bridge. The investigations revealed that the permissible stress at various components was exceeded and that the required safety against bulging was not met. This led to the commissioning of various reinforcement measures.

By welding in additional T-stiffeners on the existing longitudinal beam base plate section by section and by halving the existing bulges through the installation of additional T-stiffeners in the box girder bar section by section, the known defects of the structure were counteracted.
In addition, the staff of SCHACHTBAU NORD HAUSEN GmbH performed the following internal services in this regard:

•   Complete implementation planning according to the standard technical details of the structural eng.
•   Section by section reinforcement of the underside cover plate
•   Reinforcement of box girder support plates
•   Additional bridge exits in the bridge pier areas
•   Walkways in the bridge pier areas
•   Welded seam restoration to seams of longitudinal beams of orthotropic steel deck plate
•   Halving the existing bulges by installing additional T-stiffeners

Ahrtalbridge BAB A 61 repairs to underside and substructures of bridge

The federal motorway BAB 61 crosses the Ahr valley at a maximum height of 54 metres. The superstructures designed as a continuous girder per carriageway dating from 1976 are 1,521 metres long and consist of 22 sections with lengths of between 45 m and 106 m.
Broken out concrete areas with exposed reinforcement, exposed tendons, honeycombing and cracks on the coupling joints represent the damage symptoms.
To ensure the safety of traffic below the bridge all concrete defects had to be eliminated. By trimming the existing board structure and a subsequent protective coating of the outside surfaces of the superstructure and pier heads, should provide the structure the necessary durability.

The repairs on the piers and abutments were carried out from stationary scaffolding with safety nets. Concrete preservation measures on the pier shafts were limited to damaged areas.

An OS-C coating was only applied to the top 6 metres of the pier heads.
Repairs on the superstructure were carried out from two movable, water and wind-proof suspension scaffolds.

Work cycles:
- Expose damaged areas, remove formwork anchors
- Dismantle bridge drainage
- Grind down board structure and high-pressure water jets up to 1000 bar
- Re-profiling of individual damaged areas
- Repairs on the pier heads
- Apply an OS c coating to the bridge underside, abutments and pier heads
- Apply an OS B coating to the caps
- Dismantle bridge drainage

Main mass
About 100,000 square metres of concrete surface were examined as part of repair measures:
Service: 71,600 m² OS-C; 5,000 m² OS-B; re-profile 990 m² individual damaged areas, replace 500 m bridge drainage to the main pipeline, blast 167 pieces drainage pipe and apply corrosion protection.
Materials: 486 t fine filler, 20 800 l coating material; 160 t blasting media, 97 t shotcrete and 75 t of heavy mortar.