Prefabricated reinforced concrete construction occupies a distinctive place in structural engineering. Unlike cast-in-place buildings, whose columns and beams are monolithically poured, precast structures are assembled from factory-produced elements joined on site. This makes them fast and economical to build, but it concentrates seismic vulnerability in the connections. In the classic Turkish precast industrial building, roof girders rest on column corbels, typically through dowel bars and elastomeric bearing pads, and the entire lateral load path depends on how well these joints hold together when the ground lurches. The 2023 Kahramanmaraş earthquake sequence, with its pulse-like near-fault motions and unusually high vertical accelerations, tested those joints as severely as any event in Turkish history.

The research team began with field investigations in the affected region, documenting damage patterns across prefabricated buildings exposed to the twin shocks. Their reconnaissance identified a recurring catalogue of construction deficiencies: inadequate dowel detailing at girder-corbel connections, missing elastomeric bearing pads, substandard grout applications, and insufficient confinement reinforcement in columns and joints. Each of these defects, individually modest in appearance, proved capable of triggering or accelerating structural failure. Where bearing pads were absent, girders pounded directly against concrete corbels, crushing the bearing surfaces and losing their ability to accommodate the relative displacements that near-fault shaking imposes. Where dowels were poorly anchored or under-reinforced, the connections that should have tied roof girders to columns simply gave way.

These observations align with a long history of lessons from Turkish earthquakes. Precast structures were damaged in the 1998 Ceyhan earthquake, the 1999 Kocaeli earthquake, the 2011 Van earthquake, and the 2020 Sivrice earthquake, and in each event the same weak points surfaced: connections, corbels, and the detailing that modern codes require but field practice does not always deliver. What distinguishes the new study is that it does not stop at cataloguing damage. It converts the field evidence into quantitative fragility models, the statistical machinery that engineers use to estimate the probability that a structure will exceed a given damage state at a given level of ground shaking intensity.

Fragility analysis works by subjecting numerical models of a structure to suites of ground motion records and tracking how often a governing limit state, such as the onset of significant connection damage or loss of lateral load capacity, is exceeded as shaking intensity increases. The team built detailed nonlinear models of representative reinforced concrete prefabricated buildings and ran them through ground motions representative of the Kahramanmaraş sequence, including records with the velocity pulses and strong vertical components characteristic of near-fault sites. The resulting fragility curves provide a probabilistic portrait of vulnerability, allowing engineers to compare design variants on a common, defensible footing rather than relying on anecdote alone.

The single most striking quantitative finding concerns the roof girder-to-corbel connection. When the dowels connecting girders to columns were bolted, the seismic resilience of the structure improved dramatically: the median ground motion intensity at which the governing limit state was exceeded nearly doubled compared with structures relying on unbolted dowel connections. In practical terms, a building with bolted dowel connections could withstand roughly twice the shaking intensity before reaching its critical damage threshold. That is not an incremental improvement; it is the difference between a structure that survives a near-fault event and one that does not, achieved through a connection detail that costs comparatively little to implement.

The study also examined the role of infill walls, the masonry or precast panels that fill the bays between columns. In general, infill walls improved seismic resistance, stiffening the frames and sharing lateral load that would otherwise concentrate entirely on the columns. But the analysis revealed a crucial caveat: the benefit depended heavily on the integrity of the connections between the walls and the surrounding frame. Where those connections were robust, the walls acted as effective seismic fuses and load-sharing elements. Where the connections were poor, the walls detached early, their contribution vanished, and in some scenarios the falling panels introduced additional hazards. The lesson is that infill walls are not a passive benefit that can be assumed; they are only as good as the detailing that ties them into the structural system.

Near-fault effects emerged as a decisive amplifier of all these vulnerabilities. Earthquakes that rupture directly beneath or very close to a site produce ground motions with forward directivity, meaning a long-period velocity pulse arrives with much of the fault’s slip concentrated in a single large cycle of motion. The Kahramanmaraş events, including documented episodes of supershear rupture, delivered exactly this kind of pulse-like loading, along with vertical accelerations strong enough to degrade the friction and bearing capacity of simply supported precast elements. For connections already weakened by missing pads or deficient dowels, the combination of horizontal pulses and vertical acceleration was punishing. The study’s numerical results make clear that fragility assessments for precast buildings in near-fault zones must explicitly account for these motion characteristics rather than relying on generic record sets.

From these findings the authors draw a clear retrofitting agenda for the existing stock of reinforced concrete prefabricated structures. Priority measures include upgrading connection details, particularly bolting dowel connections at girder-corbel joints; adding elastomeric bearing pads where they are missing; and installing properly designed precast infill walls with reliable connections. Beyond the physical interventions, the study emphasizes the need for clear design guidelines and rigorous field assessment protocols so that existing buildings, especially in regions exposed to near-fault seismicity, can be systematically evaluated and reinforced before the next earthquake rather than after. The authors note that implementing these strategies would substantially enhance the seismic resilience of the precast building stock, reducing potential future human and economic losses.

The broader significance of the work extends beyond Türkiye. Precast industrial construction is common across seismic regions worldwide, from the Mediterranean to the Americas, and the failure modes documented after Kahramanmaraş echo those observed after the 2012 Emilia earthquakes in Italy, the 1994 Northridge earthquake in California, and the 1995 Kobe earthquake in Japan. The Turkish study adds a quantitative dimension to that international record, demonstrating with fragility curves just how much performance hinges on a handful of connection details. For engineers, the message is disarmingly simple: in prefabricated construction, the earthquake finds the joints. Bolting a dowel, seating a bearing pad, or grouting a connection properly may look like minor line items in a construction budget, but the difference they make, roughly a doubling of the shaking a building can survive, is the kind of margin on which lives and livelihoods depend when the fault finally slips.

Subject of Research: Seismic fragility and construction deficiencies of reinforced concrete prefabricated buildings in the 2023 Kahramanmaraş earthquakes

Article Title: Seismic performance assessment of reinforced concrete prefabricated structures during the 2023 Kahramanmaraş earthquakes: fragility analysis and construction deficiency evaluation

Article References: Seismic performance assessment of reinforced concrete prefabricated structures during the 2023 Kahramanmaraş earthquakes: fragility analysis and construction deficiency evaluation. (n.d.). https://doi.org/10.1007/s10518-026-02712-5

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02712-5

Keywords: prefabricated concrete, Kahramanmaraş earthquakes, fragility analysis, seismic performance, dowel connections, corbel connection, elastomeric bearing pads, infill walls, near-fault ground motion, retrofitting, East Anatolian Fault, Bulletin of Earthquake Engineering

Flashover is the dividing line between a fire that can be escaped and suppressed and one that consumes the building. In the fire dynamics of enclosed spaces, hot gases accumulate beneath the ceiling, radiate heat downward, and progressively heat all exposed combustible materials. When the upper layer reaches temperatures in the range of roughly 500 to 600 degrees Celsius, or when the heat flux radiated to the floor exceeds approximately 20 kilowatts per square metre, ignition of items throughout the compartment becomes essentially inevitable. In modern buildings, engineers estimate this threshold using decades of compartment-fire experiments. In ancient dwellings, where timber members are massive, ventilation is asymmetric, and ceiling geometries vary from flat smoke lobbies to tall skywell shafts, the standard correlations were never validated, and this is precisely the gap the new work set out to fill.

The study focused on the two most distinctive features of Huizhou vernacular architecture as they are modified during contemporary retrofitting: the partition walls, typically brick or timber panels that subdivide the open halls into rooms and separate storeys, and the skywell, the open vertical courtyard that draws daylight and air into the deep interior of the house. Both features are frequently altered in conservation projects, with additional partitions inserted to create usable rooms and skywells glazed or partially covered to improve thermal comfort. Each change, the researchers found, redistributes airflows and heat in ways that fundamentally reshape when and how flashover occurs.

Using computational fluid dynamics modelling of fire-driven flows, calibrated against the geometry and material properties of representative Huizhou dwellings, the team simulated fire growth in compartments with varying partition configurations and skywell conditions. The simulations tracked the temperature of the hot upper layer, the oxygen concentration, the velocities of air entering and exiting the openings, and the radiative feedback onto the timber surfaces. Across dozens of scenarios, a consistent picture emerged: the timing of flashover is governed by a competition between the rate at which the fire entrains fresh air through the skywell and the rate at which the growing smoke layer is confined by partition walls.

In the original, relatively open configurations, the skywell behaved as a natural chimney. Buoyant gases rose through the vertical shaft and vented to the atmosphere, while cooler air was drawn in at lower levels. This stack-effect ventilation slowed the growth of the upper layer and delayed the onset of flashover, in some scenarios pushing the critical moment well beyond the time available for occupants of a single room to escape. The traditional courtyard house, in this sense, embodies an intuitive, if unintentional, fire-safety design: the same opening that admits light and rain also bleeds away the heat that drives flashover.

The insertion of partition walls changed that calculus dramatically. Because the walls subdivide the interior into smaller, more tightly bounded compartments, the smoke layer within each room reaches ceiling-level confinement much sooner, and the volume of hot gas needed to reach critical temperatures shrinks accordingly. The simulations showed that fires in partitioned rooms could achieve flashover conditions in a markedly shorter time than equivalent fires in open halls, because radiative feedback is concentrated in a smaller enclosure and the combustible timber linings of the room are exposed sooner to intense heating. Yet the walls also play a protective role at the scale of the whole building: once a partitioned room flashed over, the walls acted as thermal barriers, delaying fire spread to adjacent compartments and to the timber structural frame. The trade-off is stark and counterintuitive: retrofitting partitions makes the first room burn faster but may buy the rest of the house critical minutes.

Skywell retrofitting produced the opposite asymmetry. When the courtyard was glazed or covered, the chimney effect was suppressed. Smoke and hot gases that would previously have escaped accumulated instead beneath the new covering, heated it, and spread laterally along the upper storeys of the dwelling. In several scenarios the covering itself, if combustible, became an additional fuel and radiation source. The simulations indicated that covering the skywell could transform a configuration in which flashover remained localized into one in which the entire hall complex approached critical conditions, with the upper layer spilling across partition tops and igniting timber galleries on multiple floors. For conservation authorities weighing the comfort benefits of closing skywells against fire risk, the result offers a quantitative argument for restraint, or at least for ventilated designs that preserve some smoke exhaust capacity.

The researchers distilled these observations into a description of how the critical mechanisms evolve through the fire. In the early growth phase, ventilation dominates: open skywells limit upper-layer development, while partitions do little to impede the initial plume. In the middle phase, confinement dominates: partitions accelerate compartment-level flashover by shrinking the hot-gas volume, while a covered skywell accelerates building-level hazard by trapping effluent. In the late phase, the roles reverse: partitions slow inter-compartment spread and the remaining ventilation paths determine whether the fire becomes ventilation-limited or continues to grow. Flashover, in other words, is not a single threshold but a cascade whose controlling mechanism shifts as geometry and ventilation conditions change, and any retrofit that alters geometry shifts the cascade.

For heritage fire engineering, the practical implications are immediate. The study suggests that retrofit guidelines for vernacular timber dwellings should treat partitions and skywells as a coupled ventilation-fuel system rather than as independent design elements. Inserting partitions without ensuring that each new compartment retains adequate smoke exhaust, for example through high-level vents connected to the skywell shaft, could compress escape times in a way that existing evacuation assumptions do not capture. Conversely, preserving or restoring skywell ventilation may be one of the most effective passive fire protections available in these buildings, requiring no intervention on historic fabric. The work also underscores the value of fire dynamics simulation as a conservation tool, allowing authorities to test candidate retrofits numerically before committing to changes that cannot easily be undone in protected structures.

Beyond Huizhou, the findings speak to a global problem. Vernacular timber architecture across southern China, Japan, the Himalayas and much of Europe shares the same basic ingredients: combustible frames, deep plans, internal courtyards and centuries of accumulated retrofits. Fire remains one of the leading causes of loss of built heritage worldwide, and the pace of climate-driven heatwaves and densifying historic centres is only increasing the exposure. What the Huizhou study demonstrates is that heritage fire safety cannot be imported wholesale from modern codes, because the physics of these buildings is distinctive. It must instead be derived from the buildings themselves, in which the very features that give them their identity may hold the key to their survival, provided that identity is not erased by well-intentioned but fire-illiterate renovation.

Subject of Research: Flashover critical mechanisms under partition-wall and skywell retrofitting in Huizhou ancient dwellings

Article Title: Evolution of flashover critical mechanisms under partition-wall and skywell retrofitting in Huizhou ancient dwellings

Article References: Wu, Y., Li, L., Chen, S., & Zhao, M. (2026). Evolution of flashover critical mechanisms under partition-wall and skywell retrofitting in Huizhou ancient dwellings. npj Heritage Science. https://doi.org/10.1038/s40494-026-03005-5

Image Credits: AI Generated

DOI: 10.1038/s40494-026-03005-5

Keywords: flashover, Huizhou ancient dwellings, fire safety, heritage buildings, partition walls, skywell, timber structures, retrofitting, fire dynamics simulation, cultural heritage, Evolution, critical