Glass failure in high-rises shocks experts

The result stunned and troubled emergency managers and building experts.

Hundreds of windows blew out in dozens of high-rises, causing extensive and expensive damage to such centers of public life as the Broward County Courthouse and heralded new Miami landmarks such as the Espirito Santo Plaza and Four Seasons Tower.

On Tuesday, panes were still falling from the posh Miami hotels, recently completed under the strictest building and wind codes. They posed such a public safety danger that Miami police closed five blocks of Brickell Avenue to traffic.

''This looks like Berlin after the war,'' said Miami Police Chief John Timoney, as he surveyed more than a half-dozen ravaged buildings on Brickell. ``I don't know what to make of it. These buildings are supposed to resist winds up to 150 miles per hour.''

The destruction perplexed structural engineers and contractors as well, who were groping for causes that may not be pinpointed until inspectors and engineers examine each structure.

Some pointed to one obvious suspect -- an assault of wind-driven debris, perhaps gravel from surrounding high-rise roofs or trash from surrounding construction sites -- but there were many possibilities.

In older buildings, it could be as simple as glass never designed to withstand hurricane winds. In newer ones, it might be anything from poor construction techniques to faulty materials to specific designs of some buildings to the dynamic of wind moving among buildings and possibly ''tunneling,'' or multiplying, its force.

`DUMBFOUNDED'

No less of a construction authority than Herb Saffir, a Coral Gables structural engineer who co-developed the Saffir-Simpson scale used to rate hurricane intensity, pronounced himself ''dumbfounded'' by the widespread window losses -- particularly to newer downtown Miami buildings such as the JW Marriott hotel, constructed after Miami-Dade beefed up its building codes following Hurricane Andrew in 1992.

Wilma, Saffir pointed out, wasn't even a major hurricane when it hit the Southeast coast, but a Category 2 or even 1. The highest reported gusts in downtown Fort Lauderdale barely topped 100 mph. Downtown Miami got off even lighter.

''Even if it had been the pre-Andrew code, I think those windows should have stayed in place,'' he said.

Most of the damage in Miami-Dade and Broward was the familiar kind -- damaged house and condo roof or tiles, downed trees, felled fences -- but few expected so many high-rise blowouts.

NOT ISOLATED CASES

In Miami, in addition to the newer JW Marriott, Four Seasons and Espirito Santo Plaza, there were dozens of other buildings that lost windows. The most notable damage: The southern side of the Colonial Bank building at 1200 Brickell was punched out, as were windows on the southern side of the Greenberg Traurig building at 1221 Brickell across the street.

In North Bay Village, Wilma blew through dozens of units at the Grand View Palace apartments, and the unoccupied South Shore Hospital in Miami Beach lost more than 100 panes.

While some of the newest apartments and condos seemed to survive intact, many of the tallest buildings in downtown Fort Lauderdale had damage.

Among the worst-hit were the Broward Financial Center, at U.S. 1 and Broward Boulevard, and the school district headquarters on Southeast Third Avenue at Southeast Sixth Street. Nearly all of the windows were blown out on the west faces of both buildings.

The Broward County Courthouse also suffered severe damage, as did one of the New River Village apartment buildings on Sixth Street west of U.S. 1. The Bank of America building, at Broward Boulevard and Northeast Third Avenue, had a large hole halfway up the south face.

The way many high-rises are built, with windows affixed to a strong building skeleton in what archtitects call ''a curtain wall,'' experts say window blowouts don't typically threaten the stability of building. But window failures can gut offices or living spaces and put them out of commission for months.

Before Andrew, Saffir said, a building's ''cladding,'' or outer shell, fell into a poorly regulated gray area. After Andrew, Miami-Dade and Broward adopted a tougher building code, adopted statewide for coastal areas in 2001.

Under that code, high-rises' windows are supposed to withstand not only the higher pressure of more powerful upper-level winds but some debris as well.

Like home windows, they also are supposed to withstand impact tests, including the two-by-four fired from a cannon. But windows above 60 feet are supposed to be designed to withstand small debris flying at Category 3 levels, or around 120 mph.

Still, because of the wide amount of damage to old and new buildings, several experts say some sort of debris remains the most plausible explanation.

Scott Schiff, a professor of civil engineering at Clemson University, said his chief suspect would be gravel used on some -- particularly older -- high-rise roofing systems. The rock, applied atop tar and paper to protect the waterproofing, can be easily blown off a roof into that building or surrounding ones.