The main problem facing structural engineer Nabih Youseff & Associates was, of course, earthquakes. In particular, “the big one when the state slides into the sea”, as structural engineer Bryan Smith puts it. The trick has been to create foundations that will move with the ground in an earthquake but are insulated from the cathedral, so it will not move with them.
One part of the answer was to build the cathedral on a single base-isolated slab. The other was to put in sliding steel and Teflon plates under the central columns to allow movement of 600 mm in any direction. These plates will be restrained by giant rubber and steel springs that connect the sidewalls of the basement to the ground slab. A British firm is supplying the springs, four of which are used to support a 52 m bell tower. A space nearly 2 m high has been created below the base slab so that quake isolators can be changed. The base-isolated structure reduced the amount of steel needed by 70%, says Smith.
Even so, reinforcement is still on a Titanic scale. “Californian earthquake codes stipulated that the walls had to be 600 mm thick,” said Smith. As it happened, the architectural, not structural, design demanded walls up to 1.4 m thick.
If the foundations move, gas, electricity and water pipes must move with them. “Pipes go through a complex 3D flexible bend linked by several ball joints,” said John Gautrey of Ove Arup & Partners, the M&E specialist on the project. “For the electrical power lines, we had to think out the cable loop paths very carefully.”
The cathedral, Our Lady of the Angels, started on site in May 1999, on a prime site in the city’s theatre district, surrounded by skyscrapers. The design brief given to the architect, José Rafael Moneo of Spain, insisted that the building echo European traditions. And, in fact, the high-vaulted, thick-walled structure is highly reminiscent of the gothic bulk and spaces of medieval giants such as Notre Dame. But the architect has chosen to install some of the most sensitive material imaginable for decor. Thin sheets of translucent alabaster will be used in the 20 m tall windows, to allow light to stream in through the delicate veining to give the impression of stained glass.
Unfortunately, Spanish alabaster is only found in nodules, allowing sheets no bigger than 1 m2 to be cut. It also breaks easily and, worst of all, is heat-sensitive – a worry in a city with a Mediterranean climate. “Above 48°C, the alabaster turns to ordinary gypsum, completely opaque” says Gautrey.
Rather than abandon the material, the team took up the challenge. The alabaster panels will now sit 2 m behind the outer, glazed windows, and Gautrey has taken advantage of the building’s high thermal mass and lofty interior to create a thermal funnel in which cool air from the building’s interior replaces air heated by sunlight. To limit the effect of direct sunlight, low-light-transmitting outer glazing will be used.
Church services
Services must cope with the centuries, too. In the main, the solution has been to go for accessible, easily replaceable plant, rather than to try to give each component a long life. The services design also has an impact on the architecture, demanding a variety of non-public galleries, walkways and stairwells to allow access for maintenance.
As far as possible, energy-conscious sustainable solutions for air-conditioning and other services are being used. “We have employed techniques from time immemorial, using the high thermal mass of the thick cathedral walls,” says Gautrey. A strong stack effect allows a good draft in the high space. “We considered a forced system of dedicated fans, but in several decades’ time they could be removed because their purpose is not known”, he explains. Instead, the body heat from “up to 2800 worshippers” will cause the air to rise in the 32 m high nave. This air flow will draw cooled displacement air through custom-made grilles beneath the pews.
Interior fans are limited to areas such as saints’ altars, where large numbers of candles burn in the outward-facing side-chapels. “The building’s thermal mass is so high that, ironically, keeping worshippers cool at midnight mass was the biggest problem,” says Gautrey.
The cathedral will welcome its first worshippers at the end of 2002.
