CESP Building 2, São Paulo — a Concrete Office Tower That Fully Collapsed in Fire

Summary

CESP Building 2 (Sede II), a 21-storey cast-in-place reinforced-concrete office tower on Avenida Paulista in São Paulo, suffered a fire-induced collapse of its central structural core on the evening of 21 May 1987, roughly two hours after the fire reached the building, killing one company employee and injuring some 300 people. The proximate cause was not the loss of concrete strength alone but a mechanism that designers of the period rarely considered: the thermal expansion of fire-heated T-beams, which drove the spanning floor system outward against an asymmetrically stiffened frame and overloaded its vertical members in shear until the core failed and pancaked through the full height of the building.

This is one of the few documented cases in the engineering literature of a complete fire-induced collapse of a reinforced concrete office structure, and it failed in a way that contradicted the assumption that concrete buildings simply "burn out" rather than fall. The central region — the bay containing the elevator shafts — lost its vertical support and dropped as if imploded, splitting the tower into a front and a rear portion; the front section was so damaged it had to be demolished days later.

Sede II was a building of conventional 1960s design: parallel reinforced-concrete frames carrying T-beams of 8 to 11 metre span at roughly 8 metre spacing, with ribbed floor slabs, in a tower paired with the 19-storey Sede I. On paper it was an ordinary structural solution. Its fatal characteristics were the absence of vertical fire compartmentation, inadequate horizontal separation, and a stiffness asymmetry — stiff columns clustered at the elevator core on one side of each frame — that concentrated the expansion forces where the frame was least able to resist them.

The forensic literature did not treat the collapse as bad luck. Studies of São Paulo's concrete-structure fires, published alongside analyses of the earlier Andraus (1972) and Joelma (1974) towers, concluded that this structural solution "from the point of view of fire safety must be avoided." The CESP case became a demonstration that a reinforced-concrete frame is not automatically a fireproof frame: heated to large thermal dilation, with no compartmentation to limit the fire's reach and an asymmetric load path to amplify the strain, even concrete can be made to collapse.

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Timeline

1960s

Towers designed and built on Avenida Paulista

CESP, the São Paulo state power company, builds its headquarters complex: Sede I (19 storeys) and Sede II (21 storeys), both cast-in-place reinforced-concrete office towers, above a podium and the Shopping Center 3 retail level.

As designed

Conventional frame, no fire separation

Sede II is framed as multiple parallel reinforced-concrete gantries carrying T-beams of 8–11 metre span at ~8 metre spacing with ribbed slabs. Stiff columns form the elevator shaft on one side of each frame. No vertical fire compartmentation is provided between floors.

1972 & 1974

Andraus and Joelma fires kill 200+

Two earlier São Paulo high-rise fires together cause more than 200 deaths and prompt the city's first fire-safety regulations in 1974 — focused on egress and evacuation, not on the structural fire performance of concrete frames.

21 May 1987, evening

Fire breaks out in the CESP complex

A fire ignites in the buildings and spreads, eventually involving over 20,000 m² of floor area across the complex more or less simultaneously. Many floors of Sede II burn at once, with the fire most intense on the upper and middle floors.

21 May 1987, +~1 hr

No compartmentation lets fire dominate the tower

With no vertical separation, the fire engulfs multiple storeys of Sede II concurrently, heating the long-span T-beams over a large fraction of the building's height.

21 May 1987, +~2 hr

Heated T-beams expand; core fails in shear

Thermal expansion of the fire-exposed T-beams thrusts outward; the asymmetric stiffness forces the less-stiff frame portions to absorb the dilation, generating critical shear in the central-bay columns. They fail, the elevator-shaft region drops through the full height "as if imploded," killing one CESP employee and splitting the tower in two.

21 May–22 May 1987

Fire burns on into the next day

The conflagration continues until late the following afternoon, gutting the surviving floors of both Sede I and Sede II.

Days later

Damaged front section deliberately demolished

The front portion of Sede II, structurally compromised, is brought down in a controlled demolition, damaging much of the Shopping Center 3 podium beneath it.

Late 1980s–1990s

Ruins stand, then are cleared

The burned shells remain as ruins for roughly a decade before the site is redeveloped.

1990s–2000s

Forensic studies codify the case

Brazilian and international fire-engineering studies analyse the collapse mechanism and cite CESP Sede II, alongside Andraus and Joelma, as a defining case study of fire in São Paulo concrete structures.

The Build: A Conventional Concrete Frame With a Hidden Asymmetry

CESP Building 2 was, structurally, an unremarkable product of its era: a 21-storey office tower of cast-in-place reinforced concrete, one of a pair — Sede II beside the 19-storey Sede I — forming the headquarters of the Companhia Energética de São Paulo on Avenida Paulista, above the Shopping Center 3 podium. Its floor plates measured roughly 12 by 60 metres, framed by parallel reinforced-concrete gantries carrying T-beams of 8 to 11 metre span at about 8 metre spacing, with ribbed slabs between them. This is an efficient solution for column-free office space, and nothing about it was negligent by the gravity-and-wind standards of its design; the building carried its loads competently for two decades.

Two features, invisible in normal service, made it fragile in fire. The first was an absence: no vertical fire compartmentation between floors and inadequate horizontal separation, so a fire on one level could grow into a fire on many with nothing to confine it. The second was a geometry: within each frame, the columns forming the elevator shaft on one side were far stiffer than those on the other. Under ordinary loads this asymmetry was benign. Under the lateral thrust of thermally expanding beams it would prove decisive — because a stiff element does not yield to absorb deformation; it forces the deformation, and the force producing it, onto its weaker neighbours.

The Failure: Expansion, Not Just Softening, Brought It Down

The fire broke out on the evening of 21 May 1987 and, with no vertical compartmentation to stop it, spread to dominate an enormous floor area — over 20,000 square metres burned more or less at once — with the most intense burning on the upper and middle floors of Sede II. Many storeys were involved simultaneously, so the heating was not a localised event but a near-uniform thermal insult across a large fraction of the frame.

The collapse mechanism is the instructive part, because it is not the one most people imagine for a concrete fire. Concrete loses strength when heated and its reinforcement softens, but Sede II did not simply crumble from loss of material strength — it was destroyed by thermal expansion. The long-span T-beams, fixed between supporting frames and heated over much of their length, grew; restrained at their ends, that growth converted into large outward forces driving against the columns that held them.

Here the asymmetry turned fatal. The rigid elevator-core columns would not give, so the dilation forced the less-stiff portions of the gantries to take "greater efforts," generating critical shear forces in those vertical elements. Shear is the brittle, sudden failure mode for a reinforced-concrete column — far less forgiving than bending. Roughly two hours after the fire reached the building, the central bay's columns failed in shear, the elevator-shaft region lost its vertical support, and the core dropped through the full height of the tower in a progressive collapse, falling, witnesses said, as though it were being imploded. One CESP employee was killed. The tower was left split in two, and the damaged front half was demolished in the days that followed.

The Reckoning: A Structural Solution Judged Unsafe in Fire

What makes CESP Sede II valuable in the forensic record is that the engineering analysis did not stop at "there was a fire." Studies of São Paulo's concrete-structure fires traced the collapse to a specific, named chain: a fire allowed to dominate many floors at once for want of compartmentation; long-span T-beams heated until their thermal expansion produced large restraint forces; and an asymmetric frame that funnelled those forces into shear failure of the weaker columns and then progressive collapse of the core.

The verdict on the design was explicit. The literature concluded that this structural solution — long-span T-beams in an asymmetrically stiffened reinforced-concrete frame, without compartmentation to limit the heated length of the members — "from the point of view of fire safety must be avoided." The contributing deficiencies were itemised: absent vertical compartmentation, inadequate horizontal compartmentation, long T-beam spans without barriers to limit how much structure a single fire could heat, and undersized ribbed-slab beams in the companion structures.

The historical irony is sharp. São Paulo had already learned, expensively, about high-rise fire: the Andraus (1972) and Joelma (1974) tower fires together killed more than 200 people and drove the city to adopt its first fire-safety regulations in 1974. But those rules addressed the lessons of those fires — egress, evacuation, occupant survival — not the structural fire performance of concrete frames, which the profession still presumed safe. CESP Sede II exposed the gap. No one had broken a rule; the relevant rule, governing how a concrete frame behaves when heated, had not yet been written into practice.

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Contributing Factors

01

Thermal expansion of restrained long-span beams

The governing mechanism was not loss of concrete strength but the outward thrust of T-beams spanning 8–11 metres as they heated against fixed ends. Restraint forces can exceed the demands a structure was designed for; a fire need not weaken concrete to its failure point if it can make the beams push their supports apart.

02

Asymmetric frame stiffness

Rigid elevator-core columns on one side would not yield to the beam dilation, so the expansion forces were dumped onto the less-stiff columns opposite, generating critical, brittle shear there. A symmetric or deliberately detailed frame would have shared and relieved the thermal strain instead of concentrating it.

03

No vertical or adequate horizontal compartmentation

With nothing to confine the fire, it dominated over 20,000 m² and many storeys at once. Compartmentation limits not just smoke spread but the heated length of structural members — the very quantity that controls how much thermal expansion a frame must absorb.

04

Shear-governed brittle column failure

The vertical members failed in shear, the least ductile failure mode for reinforced concrete. A column that fails in bending sags and redistributes; one that fails in shear lets go suddenly, with no margin and no time — which is why the core dropped through the full height rather than settling.

05

Design code blind to structural fire performance

São Paulo's post-Joelma 1974 fire rules addressed evacuation, not the behaviour of concrete frames in fire. The profession assumed reinforced concrete was inherently fire-safe, so no one analysed restraint, expansion or stiffness asymmetry under heating. The deficiency was a missing question, not a violated rule. ---

Aftermath

The collapse of CESP Sede II killed one employee and injured roughly 300, and destroyed a 21-storey headquarters tower along with much of its companion Sede I and the podium beneath. Its lasting significance is not its toll, low because the fire developed outside peak occupancy, but its standing as one of the few clearly documented total fire-induced collapses of a reinforced-concrete office building. It punctured the assumption that concrete frames cannot fall in fire and named the mechanism that fells them: thermal expansion of restrained beams driving asymmetric frames into shear failure. Brazilian fire-engineering research thereafter treated CESP Sede II as a defining case study, ranked beside Andraus and Joelma, feeding the broader shift in structural fire engineering away from "concrete burns out" toward explicit analysis of restraint, expansion and continuity under heating that later performance-based methods would demand. It became the standing counter-example to the belief that a concrete building cannot collapse in a fire.

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Lessons

Treat thermal expansion, not just strength loss, as a primary fire action on a frame — restrained long-span beams can push their supports to failure long before the concrete itself is "burned through."
Never let stiffness asymmetry go unexamined in a structure that may see fire; a rigid core that will not yield simply forces the deformation, and the failure, onto its weaker neighbours.
Provide real vertical and horizontal compartmentation in any concrete high-rise — it limits not only smoke and flame but the heated length of the members that controls how much expansion the frame must survive.
Detail columns and connections for ductile, bending-governed failure rather than brittle shear, so that an overloaded element warns and redistributes instead of dropping the structure without notice.
Do not assume a material is fireproof because it does not burn; ask explicitly how the frame behaves when heated, because the question a code never asks is the one a fire will. ---

References

Fires in concrete structures — significant case studies in São Paulo (A. F. Berto) Revista ALCONPAT, vol. 10 no. 1 (2020)
Fires in concrete structures — significant case studies in São Paulo (SciELO mirror) Revista ALCONPAT (SciELO México)
Incêndio nos edifícios da Companhia Energética de São Paulo Wikipédia (Portuguese)
Recent Developments on Structural Fire Performance Engineering — a State-of-the-Art Report ResearchGate (HUMAN CHECK: returns HTTP 403 to automated fetch; confirm it loads in a browser or replace with the primary source)
Category: CESP buildings fire Wikimedia Commons