Prestressed Concrete | Structural Engineering

Pakistan Private Limited

Prestressed Concrete | Structural Engineering
Company Brochure

STRONGHOLD PRESTRESSING SYSTEM

STRONGHOLD PAKISTAN

Specialist Sub-Contractor of Prestressing Works
And Structural Rehabilitation

TECHNICAL AND SERVICES BROCHURE

To engineers who, rather than blindly following the codes of practice, seek to apply the laws of nature.

T. Y. Lin, 1955.

Table of Contents

6. STRESSING & GROUTING PROCEDURE – GENERAL METHOD STATEMENT ....................3 0

8. SELECTION TABLES – TENDON, TRUMPET, JACK AND SHEATH ........................................3 6 9. TRUMPET & ANCHOR BLOCK- DESIGN DATA DIMENSIONS ...............................................4 0

Appendix A – Design Notes

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Appendix B – Selective List of PT Projects

Ebro River Bridge – Spain

Completed: 1979 Consultants: Fernandez Casado S.A PT Contractor: CTT Stronghold S.A Prestressing System: Stronghold Multi-Strand Stays: 35 Pairs of Stronghold Cable

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1. COMPANY HISTORY

Stronghold Pakistan was established in 1985 as a licensee of CTT Stronghold SA, a renowned Spanish company that has now been integrated into the VSL Group – a member of Bouygues Construction.

The company founder Tahir Karamat who holds Masters degree in Structural Engineering from the Massachusetts Institute of Technology (MIT), and is in the post-tensioning field since the 1960’s, pioneered the use of multi-strand post-tensioning system in the country with local manufacturing of anchorages under a license agreement with CTT Stronghold with the founding of Stronghold Pakistan. Under his leadership, the company grew rapidly within the early years of its founding and became market leader in the post-tensioning field. The company enjoyed near monopoly for over twenty years with almost 100% of the posttensioning market with us in Pakistan.

Stronghold pioneered local production of trumpets, anchor blocks and sheaths for its multistrand market. In our state-of-the-art production facility, we have developed innovative methods of production that have led to cost competitiveness of our products while maintaining highest industry standards meeting all relevant code requirements and specifications.

Stronghold introduced the incremental launching method (ILM) of bridge construction in Pakistan. As a joint venture partner with CTT, we helped Daewoo Engineering and Construction Co to construct six long span box girder bridges using ILM on the LahoreIslamabad Motorway Project, a 375 KM dual carriage motorway – the first project of its kind in the country. We locally fabricated steel nose, formwork and some other items that were required for launching the bridges to completion. The project was successfully completed within the set budget and time. The steel nose used in the project was later exported after modification carried out by us for launching a few other bridges in Portugal.

Pakistan Motorway- Two ILM bridges over River Soan at Chakri – 1x40m+7x50m+1x40m spans

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Motorway Project- Lifting and pushing equipment for an ILM bridge during launching.

On the Lahore-Islamabad Motorway Project Stronghold provided all post-tensioning related supplies and services single-handedly for all of its over 150 bridges to Daewoo. In fact, Stronghold has already been involved in over 10,000 bridges completed to date in Pakistan where our products and services have been used. Live and dead anchorages, and couplers for cable up to 37/0.5″ and 31/0.6" locally produced by Stronghold have been delivered successfully in these projects. In addition, the company has also supplied a large number of imported elastomeric bearings, pot bearings, and modular expansion joints capable of accommodating up to 510mm of movement.

Star Coupler produced by Stronghold Pakistan for the Motorway Project

Test in Barcelona of fabricated Star Coupler produced by Stronghold Pakistan – Test showing broken strands with no distress to coupler.

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Throughout our history, we have been at the forefront of providing prestressing services and supplies on almost all major projects completed across Pakistan. From the mega metro projects like the Lahore Metro and Green Line to power projects like the Gulpur Hydro Power in AJ&K, Stronghold has been a key sub-contractor for the prestressing works, and in most cases delivered all prestressing related services and supplies on the given projects.

New Khairabad Bridge Attock

Stronghold has successfully completed a range of projects requiring different methods of bridge construction – construction with pre-tensioned girders, post-tensioned cast-in-situ, segmental balanced cantilever method etc. For example, in the New Khairabad Bridge both segmental as well as conventional cast-in-situ construction method was employed. All the post-tensioning services and supplies were rendered by Stronghold.

Khushal Garh Bridge over River Indus

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Bridge Over River Indus, Islamabad – Peshawar Motorway

Stronghold has made several contributions to rehabilitation projects in Pakistan. We are the first local company to carryout external tensioning to strengthen an existing bridge super-structure.

Ghazi Ghat Bridge – External post- tensioning of cable in the deck recess.

We have also successfully completed a number of projects where we have lifted bridge decks for bearing replacements with our locally developed flat jacks. In some cases we have lifted bridge super-structure directly through the girders. In these projects diaphragms that are generally employed for lifting were found under-capacity for jacking the decks.

Chiniot Bridge – Three lifting jacks with lifting capacity of 70 Metric Tons each placed under bridge girder with over all height of only 45 mm.

Lastly, Stronghold has been pivotal in the development of the post-tensioning industry in Pakistan. From the production of PT supplies to providing stressing and grouting services, a number of companies in operation in this line are founded by former employees of Stronghold. While we take pride in our role as seen by many as an institution, we look forward to continuing with our ambition in the development of new sectors with introducing latest technologies to the construction industry in Pakistan.

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2. OUR SERVICES

We offer a range of services that include the following:

••

Stressing and grouting of post-tensioned structures e.g. bridges, buildings, dams, etc. Supply and installation of post-tensioning sheaths and anchorage set – wedges, trumpets and anchor blocks

•••••

Stressing of pre-tensioned structures including cable installation Stressing and grouting of ground anchors Design and consulting services for temporary structures e.g. pre-tensioning yard Structural rehabilitation and heavy load lifting Supply of imported ground anchors, bridge bearings and expansion joints

We are a strong team with many of our staff with 25 plus years of diversified experience gained on major infrastructure projects. Given our large staff strength and equipment inventory we are by far the biggest company in Pakistan offering prestressing services and are capable of handling multiple projects simultaneously anywhere across the country.

Post-tensioning 31/0.6″ Cable – DHA Karachi. Pre-tensioning Mono-Strand – Gulpur
Hydro Power Project, AJ&K.

Stressing in progress – Karachi Green Line.

Deck lifting – Bridge on Islamabad Muree

Highway undergoing rehabilitation

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3. PRESTRESSING PRODUCTS

We offer the following products for mono-strand and multi-strand applications.
1. Trumpets 2. Anchor Blocks 3. Couplers 4. Wedges 5. Sheaths both flattened and round 6. Ground Anchors

Some of our product samples are shown below.

Trumpet and Anchor Block for post-tensioned slabs and other multistrand flat cable applications.

Trumpet and Anchor Block for post-tensioned multistrand cable applications.

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Coupler for multi-strand cable

Imported wedges for 0.5″ and 0.6″strand

Flat sheath for post-tensioned slab cable

Round sheath for multi-strand cable

We manufacture our products under strict quality control program in our facility in Karachi and Lahore that has a combined working space of over 20,000 square feet. We regularly get our raw material tested in nationally recognized laboratories like the University of Engineering and Technology Lahore, Peoples Steel Mills Karachi, Delta Laboratories Karachi etc. All our products satisfy relevant requirements of major international codes and standards such as the AASHTO and EN., and have been successfully used since 1985 in over 10,000 bridges to date across Pakistan.

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4. PRESTRESSING EQUIPMENT

Our prestressing equipment includes hydraulic jacks, pumps, grouting machines and some ancillary equipment. Prestressing jack ranges from mono-strand jacks that are typically used in post-tensioned slabs and in pre-tensioning applications to multistrand jacks that are generally employed for post-tensioning in bridges and other heavy civil structures.

4.1. Hydraulic Jacks

We have a large selection of hydraulic jacks to stress a range of different cable sizes. Our jacks possess the universal ability to stress any form of cable composed of wires or strands that is individually anchored by means of wedges. Whatever the pattern or angular disposition assumed by the cable, Stronghold jacks can stress a given strand with only 30cm of end projection irrespective of the strand orientation.

Stronghold jacks are designed to seat wedges forcibly by means of hydraulic lock-off that ensures uniform draw-in when transferring load to the cable. The draw-in limit for the Stronghold system is 7mm.

Operating sequence of Stronghold Jack

Locate temporary bearing plate over anchor plate. Position indexing template on projecting end of cable and advance the Jack.

In this position the cable is ready for stressing with all its elements separately and simultaneously gripped by the Jack’s internal wedges

The cable is extended to specified load and elongation.

The anchorage wedges are advanced by the template which also seats them forcibly,

under pressure from the Jack’s lock-off

mechanism. The Jack is retracted, automatically releasing the stressing wedges. It is then removed from the cable end.

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Mono-Strand Alevin Jacks:

A range of mono-stressing jacks of different strokes and force range has been developed and thoroughly tested, incorporating the Stronghold features of front-gripping and hydraulic lock-off. These jacks have multiple applications such as in prestressing yards, for ground/rock anchors, circular stressing of plastic-coated unbonded strands, etc. The following details relate only to the post-tensioning applications of the Alevin jacks which are commonly used in conjunction with the Stronghold multi-stressing equipment.

Multi-Strand Jacks:

Stronghold system was officially launched in 1974 at the FIP Convention in New York, USA. It was among the leading few systems in the world at the time that was developed for multi-strand prestressing. Since its launch it has been incorporated in innumerable projects world-wide with many notable structures including cable-stay bridges being built on

G-800 Stronghold Jack

the Stronghold system.

CTT Project – Barrios de Luna Bridge, Spain. Stronghold Stays used.

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CTT Projects – Weirton-Steubenville Bridge, USA and Water Towers, Kuwait

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Stronghold multi-strand system has been developed for a range of jacks that are capable of delivering a maximum jacking force ranging from 60 metric tonnes to 1600 metric tonnes. These jacks are classified as G series jacks and labelled as G-60 to G-1600 respectively. Their dimensional details are provided in Table 4-1.

Table 4-1: Jack dimensional details

Note: From time to time, we update our equipment inventory based on the market needs. Therefore, in addition to our Stronghold jacks we also carry stressing equipment from other vendors that are custom made and compatible with our Stronghold system. Accordingly, we are in a position to take on any prestressing related work without requiring any third party assistance/equipment.

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De-tensioning Jacks:

De-tensioning jacks are employed in pre-tensioning applications when the strands projecting beyond the precast section that has attained its desired concrete strength have to be de-tensioned. Our inventory includes such jacks with de-tensioning capability upto 1000 metric tonnes and 300mm stroke.

De-tensioning jack in operation during casting of pre-tensioned bridge girders

4.2. Hydraulic Pumps

Stronghold pump Type-B are the commonly used pumps to operate the Stronghold prestressing jacks. These pumps operate at high pressure for stressing and low pressure for retracting. A double control valve separates stressing and lock-off operations, the latter being preset before delivery. A manual relief valve enables pressure to be gradually reduced, so ensuring uniform transfer of jacking force to the tendon. A large capacity oil tank is incorporated fitted with a tubular indicator gauge. The pump is mounted on a pair of wheels for maximum mobility.

Table 4-2: Type-B Pumps – Capacity

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4.3. Grouting Machines