The severity of the earthquake that rocked the central Italian town of L’Aquila last April was underlined by the damage to centuries-old buildings which had survived numerous previous tremors. But there was still shock that so many relatively modern buildings suffered so severely, some collapsing completely. The media
focused in particular on the San Salvatore hospital, built just 18 years ago. It was so badly damaged, medical staff had to evacuate and set up temporary facilities in the hospital courtyard to treat quake victims.
Subsequent investigation revealed that many newer buildings which totally or partially collapsed used
substandard concrete. Builders were accused of mixing cement with ordinary beach sand rather than the refined building variety. And, according to a civil engineer working with the government technology and environment agency ENEA, in the hospital this combined with defective steel reinforcement.
In total, the quake, which registered 6.4 on the Richter scale, damaged or destroyed an estimated 500,000 buildings in L’Aquila and the surrounding area. It killed 294 people and made 40,000 homeless. So the massive challenge facing the community and, indeed, the country was not only to build thousands of new dwellings rapidly, but also to come up with structures that would last and withstand future quakes in one of the world’s most seismically active hotspots.
This is where Binderholz of Austria and its prefabricated BBS cross-laminated timber (CLT) panels came in. The company was one of 63 that entered the initial government-monitored reconstruction tendering process launched last May. In total, 150 apartment blocks of up to 1,800m2 each were put out for quotation.
Eventually 15 companies were selected for the work, Binderholz among them, with its initial contract comprising two developments, L'Aquila Projects 1 and 2, for housing 1,200 people. The contract stipulated that the buildings were proven earthquake resistant, environmentally sustainable, had a service life of 30 years and scored on aesthetics too.
“They didn’t want transient, interim solutions that were worthless in architectural quality,” said Helmut Spiehs, Binderholz managing director. “The tendering procedure awarded points for energy efficiency, sustainability architectural quality, interior work, spatial efficiency and occupation density.”
Making the project more demanding still, given the need to rehouse quake victims before the winter, was the deadline. “Stipulated construction time was 80 days from start to key handover,” said Spiehs. “In other words, all buildings had to be completed by fall.”
On L’Aquila Project 1, Binderholz worked with timber construction specialist Wood Beton Spa. The development comprised a total of 192 apartments divided between eight ‘estates’, each of which is made up of four blocks connected by stairways.
The prefabricated walls of these buildings comprised 163mm-thick CLT panels, with 100mm of Rockwool insulation and interior plasterboard skin ready fitted, while the floors and ceiling panels are in 147mm BBS.
“Service ducts and openings for the timber windows and doors were all pre-cut in the factory,” said Spiehs. “On site the panels were erected by Wood Beton, with our personnel advising. As in all the L’Aquila developments, the foundations combine a concrete platform and piles and the buildings are finished with aluminium roofs and exterior render.”
Interior walls, he added, were standard lightweight timber frame construction, comprising timber studding, insulation and plasterboard.
Project 2, built with Sistem Costruzioni, comprised 189 apartments in seven bigger three-storey units. BBS was again used for all the structural elements, but in this case the external wall panels are 110mm, and ceilings and floors 181mm, with 110mm panels also used for the interior walls.
“The designer, Strutture di Legno, wanted a different look,” said Spiehs. “The building is externally finished in tiles, so they specified a thinner panel for the outer walls, with additional structural support and sound insulation provided by the BBS internal walls.”
In total the two buildings used 11,000m3 of CLT and transport from Binderholz’s factory in Tamsweg to site in about 250 truckloads was a major logistical challenge, but the material was produced, despatched and delivered on time. Construction also went to schedule. The first fix stage was completed in 55 days and the buildings were ready for residents to move into about three weeks later.
Because of the thickness and density of CLT, the L’Aquila buildings meet the REI 60-90 fire safety standard with no specific timber fire resistant treatment. According to Binderholz, they will also withstand even major tremors.
As in all the L’Aquila rebuild developments, the Binderholz blocks’ foundation pillars are topped by anti-seismic bearings, with the concrete slab effectively ‘swimming’ on these. And the CLT structure itself adds inherent quake resilience.
“The individual BBS panels are 1.25m wide,” said Spiehs. “In themselves, these are very resilient to any building movement. They are also connected by mechanical fasteners, comprising metal plates, nails with improved adhesion and self-drilling screws, which help dissipate the shock in a quake. They add to the ductility of the building, effectively acting as shock absorbers and contributing to a sizable reduction of seismic force affecting the structure.”
Underlining the company’s confidence in cross-laminated performance, Binderholz has put a video on its website of a seven-storey block undergoing a quake test. It’s not for the faint-hearted, with one shot showing furniture being hurled across a room on the seventh floor by the force of a 7.2 Richter scale tremor; but the building survives intact and structurally sound (www.binderholz-bausysteme.com).
The L’Aquila blocks also push all the right green buttons, said Spiehs. “The panels combine insulation performance with thermal mass, so the buildings will be energy efficient, but not overheat in the summer. Each 1m3 of timber stores 0.8 of a tonne of CO2, so the L’Aquila project locks up 8,800 tonnes and, in addition, of course, it is renewable. Austria’s forests are growing at an estimated 52m3 per minute, so the 11,000m3 of material used will be replaced in just 3.5 hours!”
As a result of its work on the apartment blocks, Binderholz also secured the contract to provide CLT panels for the restoration of L’Aquila’s abbey walls and roof.
The company now anticipates doing further housing projects in the town as the reconstruction work continues and it sees its work there boosting the use of BBS elsewhere in Italy.
“We’ve already had numerous follow-up orders for homes, schools and public halls,” said Spiehs. “It’s persuasive evidence that L’Aquila has given BBS fresh impetus in Italian social construction sector generally.”
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The two Binderholz developments sit on quake-resistant foundations. These comprise piles topped with anti-seismic bearings and the slab ‘swimming’ above |
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In total, the two developments used 11,000m3 of CLT |
