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Piping in seismic conditions.

Recent events around the world have shown that the threat of seismc activitiy is still a very real risk that needs to be taken into account in construction, maintenance and rehabilitation of all types of buildings.

An earthquake zone clearly presents problems for structures and piping alike. With forces and deflections well beyond normal static conditions, welded piping systems can prove lacking, and with only the ability to resist movement in a single direction they cannot protect pipes from earthquakes. The results may be costly - cracking, substantial leakage and associated damage.

At an 8-inch DN200 test assembly at Leigh University's ATLSS Lab there was no evidence of pipe joint leakage throughout testing

Testing has shown that grooved piping systems -- using a combination of flexible and rigid couplings -- have advantages over traditional joints. Rigid couplings provide the same strength and stiffness of a weld in protecting against forward movements from seismic shifts. Flexible couplings can bear deflection and move with the pipes, which reduces damage from vibration, sway, expansions and contractions.

When exposed to bending forces, grooved systems remain intact. A bending moment will occur when the joint deflects beyond its maximum allowable angular deflection. Where these deflections are anticipated, additional flexible couplings can be installed to accommodate this movement.

DETAILED RESEARCH Two major laboratory tests have established the advantages of grooved systems in seismic conditions.

The Bird's Nest Olympic Stadium in Beijing where the Victaulic piping system offers an infrastructure system that reduces damage and protects vital services during earthquakes

The first was carried out as part of a series of tests conducted by ANCO Engineers Inc, an independent laboratory that specialises in seismic evaluations of products. These tests were conducted to assess the structural and functional integrity of Victaulic products during seismic loading for a major electric utility considering the use of grooved piping at one of its nuclear plant sites.

The laboratory used computerised data monitoring control and acquisition systems, plus servo-hydraulic actuators and feedback controls to conduct the tests. Three test segments were constructed on a shake table that measured 13.7 m long by 4.3 m wide and 4.3 m high.

Post-test inspection by the laboratory of the Victaulic fittings and couplings revealed no abrasion, cracks, deformation, or damage of any kind, indicating it could continue to perform its intended function. Hydro-tests after the first also demonstrated that these Victaulic components maintained functionality during and after the simulation, thereby substantiating their reliability under seismic conditions.

Grooved performance in seismic conditions was found to be excellent in a seismic swing joint tested as part of Leigh University's ATLSS Lab

In addition, research carried out by Lehigh University's ATLSS Lab (Advanced Technology of Large Structural Systems), a member of the Network for Earthquake Engineering Simulation, has found performance of grooved couplings in seismic conditions to be excellent. These tests also featured couplings manufactured by Victaulic.

Tests were carried out on a range of pipe diameters with simulated accelerations equivalent to between 4.1g and 7.7 g. There was no evidence of any pipe joint leakage throughout all of the tests. A constant internal pressure was always maintained and piping and couplings exhibited very robust behaviour even after the failure of a large number of seismic bracing elements.

PROJECTS IN MOTION Grooved solutions have been employed to great effect in two recent showcase projects in China -- both in seismic risk zones.

Victaulic regional manager Rami Mahmoud in front of the Burj Khalifa, which features Victaulic grooved mechanical systems

A Victaulic grooved solution was installed in the 100,000 seater National Stadium in Beijing China, commonly known as the "Bird's Nest". This building hosted the opening and closing Olympic ceremonies. Minor earthquakes are common in the area, so the stadium had to be reinforced to withstand repeated seismic movements without significant damage.

The Victaulic piping system offers the Bird's Nest an infrastructure system that moves with the building to reduce damage and protect vital services during earthquakes.

The Jin Mao Tower in Shanghai is where another Victaulic solution was applied. At the time of construction it was the 4th tallest building in the world, built by the China Jin Mao Group and designed by American architect SOM Construction Group from Chicago. It stands at 420.5 m tall with 88 above-ground floors.

Victaulic flexible coupling image cut-away

Although the building's octagonal design, eight 340-m long mainstays and eight additional round pillars absorb some seismic movements, the incredible height of the Jin Mao Tower made it susceptible to seismic shifts. The Victaulic solution allowed the designers to connect pipes with mechanical couplings and gaskets without having to change the original design.

Victaulic provides reliable, durable pipe joints that are sufficiently robust for seismic applications. Installed in accordance with published requirements, grooved systems are easily asssembled with hand tools in a fraction of the time of welded systems. In addition, because they do not require welding, there is no costly fire watch or potentially harmful onsite emissions.

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Publication:Gulf Industry
Date:Mar 1, 2013
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