Earthquake in Venezuela: Why do some buildings collapse and others don't?

After a major seismic event, the urban landscape often presents a bewildering image to the untrained eye: a completely collapsed building next to a seemingly similar structure that remains intact. In such a scenario, public opinion often blames "bad luck" or the quality of the blocks.

However, for structural engineers and geologists, chance has no place in this equation. The answer to this destructive selectivity lies in wave physics, the dynamic interaction between the subsurface and the superstructure, and the ability of materials to absorb energy.

Below, we will analyze from a strictly geophysical and forensic approach what dictates the survival of a building, demystifying structural damage through the behavior of materials and the COVENIN 1756 standard.

The Physics of Destruction: Site Effect and Resonance Frequency

To understand why some towers fall and others don't, we must analyze how seismic waves interact with the local terrain. The key lies in two inseparable phenomena in the seismic microzonation of sedimentary valleys: the site effect and resonance frequency.

When shear waves travel through bedrock and enter a soft, deep soil layer (such as the more than 300 meters of sediment in areas of the Caracas valley), their velocity dramatically decreases. To conserve energy, the wave responds by increasing its amplitude. This is the site effect, a natural amplifier of ground motion.

But selective destruction is defined by the resonance frequency. Every structure has a fundamental period of vibration (the time it takes to complete a full oscillation cycle). As a general rule in practical engineering, the period S of a building can be estimated as T \approx 0.1N, where N is the number of stories.

• The Case Study (1967 and 2026): During the historic Caracas earthquake of 1967, and similarly in the recent seismic event of 2026, we observed an identical forensic pattern. Long-period waves generated by deep sediments in areas like Los Palos Grandes oscillated in the 1.0 to 1.2 second range.

• Buildings of 10 to 12 stories: Their fundamental periods oscillated exactly between 1.0 and 1.2 seconds. When the ground frequency matched that of the structure, the phenomenon of resonance occurred. Lateral displacements multiplied cycle after cycle until they exceeded the structure's capacity, leading to their collapse.

• Low-rise buildings (1 to 3 stories): With periods of 0.1 to 0.3 seconds, these structures vibrated quickly and rigidly, but did not resonate with the ground. Therefore, despite being on the same street as the collapse, they remained unscathed.

Ductility: The True Structural Life Insurance

When elastic design is surpassed by the demands of a severe earthquake (and resonance is unavoidable), the survival of the structure depends on a single factor: ductility.

Ductility is the ability of a structural system to enter the inelastic range, deforming severely without losing its capacity to support vertical (gravity) loads. The regulatory objective is not for the building to be crack-free; the objective is to dissipate seismic energy through controlled damage (plastic hinges) to safeguard human life.

A rigid but brittle structure will fail suddenly and catastrophically. A ductile structure will "dance" with the earthquake, absorb the impact, and remain standing.

Hot-Rolled Steel: Dynamic Superiority

When evaluating inelastic behavior, we must be objective about material selection. Reinforced concrete structures can be excellent if they have impeccable rebar detailing (strict confinement, stirrups at minimum distances). However, poorly detailed concrete under high dynamic demands suffers a brittle and explosive failure, rapidly losing its confined section.

This is where hot-rolled steel demonstrates its indisputable dynamic superiority against seismic forces:

• Isotropic and Ductile Behavior: Materials such as W, IPE, HEB profiles and structural tubular sections (heavy conduit) possess intrinsic ductility. Steel can deform in yield far beyond its elastic limit before fracture.

• Strength/Weight Ratio: Steel provides very high strength with much less weight than concrete. Since seismic force is proportional to the mass of the building (F = m \cdot a), a lighter building attracts considerably lower seismic forces (lower base shear).

• Control of Collapse Mechanism: Using hot-rolled profiles and pre-qualified connections, structural engineers can ensure the "Strong Column - Weak Beam" philosophy, ensuring that plastic hinges form in the beams and never in the columns, preventing floor collapse.

Design with Precision and Without Improvisation: Descargaplanos.com

Understanding the geophysical behavior of the soil and the dynamic demands of the superstructure is only 50% of the job. The other 50% is ensuring that this knowledge translates into error-free plans and construction details. In earthquake-resistant engineering, a poorly detailed joint is a structural sentence.

As design professionals, we cannot afford to improvise in the CAD room. I invite you to optimize your projects and reinforce your structural calculations by visiting Descargaplanos.com.

On our platform, you will find a specialized library of construction details, pre-qualified connections, DWG blocks, and parameterized structural plans, prepared in strict adherence to regulations for hot-rolled steel structures. Streamline your workflow, elevate the technical quality of your deliverables, and design buildings that respect (and resist) Venezuela's tectonic pulse.