Heavyweights brought into shape in a safe and economic manner

PPL Holtwood Hydroelectric Station, Holtwood, PA, USA

(lifePR) ( Weißenhorn, )
Since 2009, work has been progressing to expand the 100-year-old Holtwood hydroelectric power station on the Susquehanna River with the aim of increasing the generating capacity by 125 megawatts. After carefully reviewing proposals from numerous vendors, PERI USA was commissioned to supply a wide variety of formwork and shoring solutions for this complex project. In addition to other PERI products, VARIOKIT heavy duty shoring towers serve to safely transfer the enormously heavy loads from the slabs of the intake structure. An outstanding advantage for the contractor, Walsh Construction, is that the planning and supply of the formwork and scaffolding is from a single source so that the systems used are perfectly matched to one another.

The expansion facilities include an intake structure as well as a powerhouse. Most of the new facilities' structural components are characterized by their large dimensions resulting in high loads being imposed on the formwork and shoring systems. For the concrete work, various PERI systems are being used - each optimally adapted to suit both geometry and loads.

Among other products, PERI supplied its proven TRIO panel formwork system for the north wall of the powerhouse. TRIO was also used for the pier walls of the six bays of the two turbine units. CB 240 climbing brackets were used to support the panel formwork at the two sided climbing conditions of the project. The high loadbearing capacity of the CB brackets allow greater bracket spacing and therefore larger climbing formwork units, while at the same time having the ability to carry very high loads. Walsh Construction also utilized CB 240 climbing units for the over 30 m high south wall of the powerhouse. The external walls of the powerhouse were poured against rock and utilized the versatile VARIO GT 24 wall formwork elements support by SKS single-sided climbing scaffold platforms. The SKS climbing scaffold system transfers the loads resulting from the fresh concrete pressure by means of walers, compression spindles, strongbacks and the brackets themselves into the SKS anchors placed in the previous pour. In this way formwork ties are not required for the one sided pours.

Heavy-duty shoring for metre thick slabs

During construction of the intake structure roof, extremely high loads had to be carried to the ground. The slab thickness ranging from 4.60 m to around 13.20 m, require heavy-duty loadbearing shoring. PERI VARIOKIT shoring towers were provided which transfer maximum leg loads of 660 kN into the ground. Three separate towers were aligned in a single row in each of the bays. The 6- and 4-legged towers were positioned on HDT main beams with a corresponding special wedge connection component compensating for the 34 % bottom slab slope. For height adjustment at the top of the towers, VST head spindles were utilized which allow hydraulic lowering and lifting under full load.

SLS heavy-duty spindles are used for bracing of the approx. 12.20 m high by 3.25 m wide shoring towers. Thanks to the high rigidity of the towers, the construction team can pre-assemble the units on the ground and then quickly position them between the intake walls with the crane. PERI delivered the shoring tower bents to the jobsite as pre-assembled so assembly times were kept to an absolute minimum thereby ensuring the demanding timeline of the project could be met.

The compatibility of the VARIOKIT engineering construction kit with the PERI UP modular scaffold system allowed fast installation of all the required working platforms. Thus, system components are used at key connection points along the tower in order to fix the safe and secure working platforms for the construction crew to work from. Up to 100 ft tall PERI UP stair towers serve as the means to provide extremely safe access to all areas of the project. The generous width of the stair towers enable site personnel to easily climb and descend in both directions simultaneously.

The intake slab formwork elements also consisted of PERI system components featuring GT 24 lattice girders, SRU steel walers and RCS rails. The 5.80 m wide formwork elements were pre-assembled on the ground and then flown into place with the crane. After the concrete hardened, the slab formwork was lowered hydraulically ensuring that the complete striking procedure is carried out easily, safely and efficiently. Subsequently, the construction team lowered the towers onto roller bearings and pulled them out of the intake structure.

Formwork and scaffolding from one source - optimally planned and perfectly implemented

One of the biggest challenges for the contractor is maintaining the tight schedule required to complete the power plant expansion on time. A particularly important issue is therefore a smooth execution of all working operations and processes associated with the formwork and shoring operations. Thanks to its comprehensive product range and vast experience, PERI offers the contractor optimized solutions for all the work to be carried out. Apart from materials, the PERI overall solution includes all technical documents such as structural calculations, assembly drawings as well as assembly support and site assistance for the contractor.

In addition, the VARIOKIT solution primarily consists of rentable standard components which provided an extremely economical solution for Walsh Construction. The optimized, well balanced design of the systems in use supports the contractor in meeting the challenging time schedule of the project.
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