Ceramsite aerated concrete blocks, known in the literature as CACB, have been spreading rapidly through construction markets because they solve two problems at once. The blocks are remarkably light, thanks to a porous internal structure produced by gas-forming reactions during manufacture, and their trapped air voids give them excellent thermal insulation. That combination lowers dead loads on foundations and cuts heating and cooling energy, making the blocks attractive for sustainable construction. But lightness and insulation say nothing about how a wall made from these blocks behaves when the ground beneath a building shakes. A team led by Li Ruige of Taizhou University, working with collaborators from construction and materials companies in Zhejiang Province, set out to answer that question with full-scale laboratory testing rather than assumptions.

The researchers built three reinforced concrete frame specimens. One was left bare, with no infill walls at all, serving as the reference structure. The other two were fitted with CACB infill walls, one configuration solid and one incorporating a window opening, reflecting the reality that most real walls contain doors or windows. Each specimen was then subjected to quasi-static cyclic loading, a laboratory technique in which horizontal forces are pushed back and forth across the structure in progressively larger excursions. This method mimics the repeated reversals a building experiences during an earthquake and allows engineers to measure bearing capacity, stiffness, ductility, and energy dissipation with precision that real seismic events can never provide.

The findings confirm that infill walls are anything but passive. Compared with the bare frame, the frames containing CACB walls carried substantially higher horizontal loads before failing. The walls acted as diagonal bracing elements within the frame, engaging the surrounding beams and columns in compression and fundamentally altering the load path through the structure. Crucially, the walls also changed how the structure failed. Instead of concentrating damage at discrete plastic hinge zones in the beams and columns, the classic ductile mechanism that seismic design codes try to cultivate, the infilled frames developed a more uniform distribution of cracks across their members. Whether that redistribution is beneficial or hazardous depends on the design intent, but it demonstrates that ignoring infill walls in analysis means misjudging the entire failure sequence.

Stiffness and ductility told a trade-off story. The CACB infill walls increased the initial lateral stiffness of the frames, meaning the structures deflected less under a given load. That sounds desirable, and for serviceability it is, but the added stiffness came at the price of reduced ductility, the capacity to deform far beyond yield without losing strength. Ductility is the property that lets a building absorb earthquake energy through controlled damage rather than sudden collapse. The frames with solid infill walls, without window openings, lost even more ductility than the frames with pierced walls, because the unbroken panel presents a stiffer, more rigid constraint to the frame. Meanwhile, as loading cycles intensified, the infilled frames degraded in stiffness significantly faster than the bare frame, as cracking spread through the lightweight block masonry and the wall gradually shed its share of the load back to the concrete members.

Energy dissipation, the ultimate measure of how much seismic shaking a structure can absorb, produced one of the study’s most nuanced results. The solid CACB infilled frames dissipated more energy than the bare frame, with friction between cracking block surfaces and the frame interfaces contributing to damping. The frames with window openings, however, dissipated slightly less energy than the bare frame. The opening interrupts the diagonal compression strut that a solid wall forms, concentrating damage around the window reveals and reducing the effective contact area available for frictional energy loss. For architects and engineers, this means that the seismic contribution of an infill wall cannot be assessed without accounting for its openings, a detail that simplified design models routinely overlook.

To extend the reach of the experiments, the team built finite element models of all three specimens in ABAQUS, a commercial simulation platform widely used in structural engineering. The models reproduced the hysteresis loops, the force-displacement fingerprints of cyclic loading, as well as the skeleton curves that trace peak capacity across loading stages. Simulated failure characteristics and the entire force process agreed well with the laboratory observations. This validation matters because validated models allow researchers to explore configurations that would be prohibitively expensive to test physically, and it gives practicing engineers a computational tool they can trust when assessing existing buildings or designing new ones with CACB infill.

The most forward-looking part of the study concerns a humble material more familiar from car door seals than from structural engineering: ethylene propylene diene monomer, or EPDM, a synthetic rubber prized for its durability and elasticity. The researchers analyzed what happens when EPDM is placed as a flexible buffer between the infill wall and the surrounding frame. The simulation results showed that this soft interface significantly increased structural deformation capacity, energy dissipation, and ductility. In effect, the rubber layer decouples the stiff wall from the deforming frame, allowing the frame to flex during shaking without the wall acting as an unintended brace that attracts forces and then shatters. The authors conclude that EPDM functions as an effective flexible connection capable of reducing earthquake damage.

This finding places the study within a growing international research movement toward seismic isolation of infill walls. Conventional wisdom held that the stiffer the connection between wall and frame, the better the composite action. Earthquake after earthquake has exposed the flaw in that logic: rigidly connected infills create soft-story mechanisms when they fail on one floor but not another, and they shear off column ends by imposing concentrated contact forces. Flexible connections, whether rubber buffers, slotted details, or specially engineered joints, aim to let the wall ride along with the frame rather than fight it. The Taizhou results provide quantitative evidence that a simple, inexpensive elastomer strip can capture many of these benefits for lightweight aerated concrete construction.

The broader significance of the work lies at the intersection of two urgent agendas. Cities in seismic zones need buildings that protect their occupants during rare but devastating events, and the entire construction sector needs materials that cut embodied carbon and operational energy. Lightweight aerated blocks serve the second agenda beautifully, and this study shows that with informed structural design, and possibly a strip of rubber at the wall-frame interface, they can serve the first as well. The research, funded by the Zhejiang Provincial Natural Science Foundation under grant LGG20E080006 and supported by regional building materials companies, offers a template for how emerging sustainable materials should be vetted: not only for their thermal and weight advantages, but for the full, sometimes surprising, structural behavior they introduce when the ground begins to move.

Subject of Research: Seismic performance of reinforced concrete frames with ceramsite aerated concrete block infill walls

Article Title: Experimental study on seismic performance of reinforced concrete frame with ceramsite aerated concrete block infill wall

Article References: Ruige, L., Huadong, C., Yuhua, L., Jinfa, L., Yanru, W., Chongxin, L., & Lingchao, D. (2026). Experimental study on seismic performance of reinforced concrete frame with ceramsite aerated concrete block infill wall. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02642-2

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02642-2

Keywords: ceramsite aerated concrete block, infill wall, seismic performance, reinforced concrete frame, quasi-static cyclic loading, ductility, stiffness degradation, energy dissipation, EPDM flexible connection, ABAQUS finite element simulation, earthquake engineering, lightweight building materials

A new study published in the Bulletin of Earthquake Engineering proposes a way to resolve that trade-off, and its central idea is disarmingly simple: give the earthquake something cheap and expendable to break. Researchers Min Jae Park of Pukyong National University in Busan, Ali Ghamari, Imran Karimi of Tabriz University, and Radhika Sridhar of Walailak University in Thailand have developed a hybrid precast concrete beam-column connection built around a replaceable I-shaped steel ductile link that functions as a structural seismic fuse. Like the fuse in an electrical circuit, the device is designed to absorb damage on behalf of the more valuable components around it, concentrating plastic deformation in a sacrificial element that can be unbolted and swapped out after a major event.

The mechanics of the system reflect a deliberate strategy of controlled damage. The steel link is bolted inside a steel-jacketed joint region at the intersection of the precast beam and column. During an earthquake, as the frame sways and the joint demands rotational capacity from the connected members, the I-shaped link yields in a controlled fashion, dissipating seismic energy through plastic deformation. Crucially, the design ensures that yielding is confined exclusively to the fuse itself. The precast beams, the columns, and the joint region are all shielded from the inelastic demands that would otherwise crack concrete, buckle reinforcement, and leave a structure permanently weakened or economically unrepairable. Once the shaking stops, the damaged link can be removed with ordinary tools and a new one installed, restoring the connection to its original capacity.

To understand how such a fuse should be proportioned, the research team carried out an extensive parametric and numerical study, anchored against experimental data to ensure the models reflected real structural behavior rather than numerical artifacts. Four key design variables came under scrutiny. The first was the ratio between the strength of the steel link and the strength of the concrete beam, denoted by the Greek letter psi, which governs whether the fuse or the surrounding concrete yields first. The second was the rho factor, capturing the effect of the relative resistance distribution within the connection. The third and fourth were the geometric properties of the I-shaped link itself: the thickness of its flanges and the depth of its cross-section, the two dimensions that most directly control how much bending resistance and deformation capacity the fuse can deliver before it is exhausted.

The results of the numerical campaign were strikingly consistent. Across the range of parameters examined, every model exhibited stable hysteretic behavior, the looping force-deformation signatures that engineers read as evidence of a structure absorbing and releasing seismic energy cycle after cycle without rapid deterioration. All models achieved moment capacities exceeding the plastic moment of the beam, meaning the fuse could reliably mobilize the full strength of the connection, and the system displayed minimal stiffness degradation, indicating that the connection did not progressively soften and loosen as the shaking continued. In seismic engineering, where degrading hysteresis loops often signal a connection heading toward collapse, this combination of stable loops and preserved stiffness is precisely the behavior a resilient system should show.

Perhaps the most consequential finding concerned which of the four design variables actually mattered most. Intuition might suggest that the strength ratio between the fuse and the concrete beam, psi, would dominate the response, since it determines where yielding occurs. The study found otherwise. The depth of the I-shaped link, h, exerted the strongest influence on the system’s behavior, outweighing the strength ratio, the rho factor, and the flange thickness. That result carries practical weight for designers: it means that tuning the depth of the sacrificial element is the most powerful lever available for shaping how the connection performs, a conclusion that was not obvious before the parametric study was run and one that could redirect how future fuses are detailed.

Beyond identifying the dominant parameter, the researchers distilled their findings into proposed design equations for the system, giving practitioners a quantitative route from target performance to fuse dimensions. Design equations of this kind are the bridge between a promising laboratory concept and a buildable technology, because they allow engineers to size the link so that it yields before the surrounding precast elements, sustains the large deformations expected in a design-level earthquake, and retains enough residual capacity to protect the joint through the full duration of strong ground motion. The study’s grounding in established seismic frameworks, including references to modern minimum design load provisions and seismic provisions for structural steel buildings, situates the proposal within the codes that already govern practice.

The motivation for this line of research is written in the damage surveys of recent disasters. Investigations following the February 2023 Kahramanmaras earthquake sequence in Turkey documented widespread failures of reinforced concrete and precast construction, with brittle connections and inadequate detailing cited among the recurring deficiencies. Earlier events, notably the 2011 Christchurch earthquake in New Zealand, exposed how conventionally detailed reinforced concrete frames can suffer damage so extensive that repair becomes uneconomical, forcing demolition of buildings that technically did not collapse. Those experiences have pushed the international research community toward a resilience paradigm that goes beyond life safety: structures should not merely stand up during an earthquake but should emerge from it repairable, functional, and quickly returnable to service.

Replaceable fuse technology has become one of the most active fronts in that paradigm shift, with researchers developing damage-control joints, bio-inspired hinges, artificial controllable plastic hinges, and self-centering connections for both cast-in-place and precast frames. What distinguishes the new study is its integration of the fuse concept into a hybrid precast connection that preserves the construction speed advantages of precast systems while solving their historical connection problem. The bolted arrangement inside a steel-jacketed joint means the fuse is not cast into the concrete or welded into place, so replacement is a matter of unbolting rather than cutting, chipping, and recasting. For building owners and city planners, that distinction translates directly into downtime: a connection repaired in days rather than months keeps schools open, hospitals running, and businesses operating after a quake.

The work, supported by grants from the National Research Foundation of Korea and the Korea Agency for Infrastructure Technology Advancement, along with facilities provided by Walailak University, arrives at a moment when the global building stock in earthquake-prone regions is expanding fastest precisely where seismic risk is highest. Precast construction will remain attractive to developers for its speed and economy, and the question is not whether it will be used but whether it will be used safely. By demonstrating through validated numerical modeling that a bolted, replaceable, ductile steel fuse can deliver stable hysteretic performance, protect the primary structure, and be tuned through a single dominant geometric parameter, the researchers have offered the industry a concrete, and constructible, answer. The next steps toward widespread adoption will involve experimental validation at full scale and codification of the proposed design equations, but the study makes a compelling case that the weakest link in precast construction can be redesigned into its strongest feature: a sacrificial component that takes the hit so the building does not have to.

Subject of Research: Seismic-resilient precast concrete beam-column connections with replaceable ductile steel fuses

Article Title: Towards resilient precast concrete frame featuring a hybrid system with replaceable ductile steel fuses

Article References: Park, M. J., Ghamari, A., Karimi, I., & Sridhar, R. (2026). Towards resilient precast concrete frame featuring a hybrid system with replaceable ductile steel fuses. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02668-6

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02668-6

Keywords: precast concrete, seismic fuse, ductile steel link, beam-column connection, earthquake engineering, hysteretic behavior, replaceable plastic hinge, structural resilience, parametric study, stiffness degradation, repairable structures, Bulletin of Earthquake Engineering

The method, called IOPER, short for Inverse-Optimized Pushover with Energy Redistribution, was developed by Jose Mendoza, Alfredo Canelas, and Berardi Sensale. Its central idea is deceptively simple: instead of guessing how seismic demand should be distributed over the height of a building, let the structure itself reveal the answer. In the first stage, the analysts run a conventional displacement-controlled pushover using a modal force pattern, usually based on the dominant mode shape, which in their benchmark buildings accounted for roughly 78 percent of the effective modal mass. As the structure is pushed, the software records the hysteretic energy dissipated at every node, obtained by numerically integrating the enclosed area of each force-deformation loop. That energy is then aggregated story by story, producing a vertical profile of where the building actually absorbed its inelastic demand.

What happens next is the methodological heart of IOPER. The dissipated energy at each level is multiplied by a residual rigidity coefficient, computed through a logarithmic scheme that penalizes stories with high cumulative hysteretic demand. The logarithmic form is deliberately sublinear: it compresses peak energy values while preserving the contrast between stories, mirroring the saturation behavior seen in dynamic analyses, where stiffness loss slows even as energy demand keeps climbing. Damaged stories therefore retain residual capacity and continue participating in the global response rather than being artificially erased. The resulting weighted vector is normalized and exported as the lateral force pattern for a second pushover run on the original, undegraded model. A third iteration repeats the process using the energy traces of the second run, tracing progressively advanced redistribution scenarios. The output is not a single curve but a triplet of capacity curves, each representing a distinct interpretive layer: modal response, energy-induced redistribution at an initial degraded state, and redistribution at a final degraded state.

This architecture is deliberately external to the simulation engine. Where fully adaptive pushover methods, such as the Force-Based Adaptive Pushover procedure of Antoniou and Pinho, recalibrate the load pattern at every analysis step inside the solver using updated mode shapes and spectral accelerations, IOPER performs its adaptivity outside, through MATLAB scripting that reads SeismoStruct output files, integrates hysteretic loops, computes degradation coefficients, and writes new force vectors back into the model. The authors argue that this decoupling is a feature rather than a compromise. Many commercial platforms restrict access to internal state data, lack restart capabilities, or bury their adaptive logic in undocumented code. By making every redistribution decision explicit, auditable, and reproducible through plain text files, IOPER offers a quasi-adaptive alternative that practitioners can inspect, modify, and trust, without iterative eigenvalue calculations at every step.

The validation campaign is substantial. The team tested the framework on two benchmark steel moment-resisting frames originally developed for the ASCE structural control problem: a nine-story building with a square footprint 45.73 meters per side and a first-mode period of 2.28 seconds, and a twenty-story tower rising 80.77 meters with a fundamental period of 3.89 seconds. Both frames qualify as vertically irregular. The nine-story structure shows a stiffness drop at the second level to less than 25 percent of the base value, a classic soft-story condition, while the twenty-story building combines a stiffness reduction below 21 percent at the third floor with a mass jump exceeding 150 percent of the floor below. These irregularities matter because they are precisely the conditions under which fixed load patterns fail, and where elevation-sensitive redistribution strategies earn their keep.

The dynamic benchmark comprised seven real ground motion records, including El Centro, Kobe, Northridge, Landers, Hollister, Loma Prieta, and Imperial Valley, spectrally matched to the Eurocode 8 design spectrum for Ground Type B and scaled to four intensity levels ranging from 0.45 g to 0.90 g. Nonlinear time history analyses used a fiber-based distributed plasticity model with 150 fibers per section, force-based elements, a co-rotational formulation for geometric nonlinearity, and the implicit Hilber-Hughes-Taylor integration scheme. Against this demanding reference, IOPER held its own. In the elastic range, all static methods converged on similar stiffness, but beyond it the differences emerged. The ASCE 41 uniform-load procedure rose monotonically to 7182 kilonewtons on the nine-story frame, blind to degradation, while FAP and IOPER saturated near 6479 and 6518 kilonewtons respectively, closer to the physically plausible post-elastic behavior of the dynamic envelope, which peaked at 7509 kilonewtons. Notably, both adaptive-family methods exhibited a capacity recovery phase beyond 0.6 meters of roof displacement, with IOPER closely following the shape of the incremental dynamic analysis mean curve.

Quantitative metrics reinforced the visual comparisons. At mid- and upper-story nodes, the researchers measured the mean absolute deviation of the IOPER curve from the pointwise median of the NLTHA ensemble and the proportion of drift points at which IOPER fell inside the absolute dynamic envelope. Deviations stayed below 0.05 in normalized base shear across all examined nodes, and the ensemble inclusion ratio ranged from about 71 to 91 percent, peaking at 90.8 percent for the mid-story node of the twenty-story frame. For total drift, root-mean-square errors against NLTHA dropped below 11 percent at the highest intensities, with FAP reaching 1.62 percent on the nine-story frame at 0.90 g. The study also found a meaningful correlation between the energy content of the scaled accelerograms and IOPER’s accuracy: records with high displacement and velocity demand, such as Loma Prieta and Imperial Valley, gave the redistribution logic richer energy traces to work with, improving predictions at severe intensities.

The framework is not without honest limitations, which the authors state plainly. Because the structural model is reset at each iteration, plasticity is not accumulated inside the solver; degradation lives entirely in the external energy metrics and rigidity coefficients. IOPER therefore cannot capture transient amplification, record-to-record variability, or instantaneous modal reshaping, and its accuracy degrades for interstory drift, particularly in upper stories of tall frames, where global errors exceeded 40 percent at 0.90 g on the nine-story building and 60 percent on the twenty-story tower. A refined metric restricted to stories meeting a 15 percent agreement threshold revealed that static methods perform well at lower elevations, with errors as low as 2.8 to 6.4 percent, but diverge near the roof, a persistent dynamic amplification phenomenon that the authors flag as a priority for future work through height-dependent corrections and transient-sensitive formulations.

Those caveats aside, the significance of the work lies in what it demonstrates about the philosophy of seismic assessment. IOPER treats a building’s response not as a geometric abstraction but as an accumulated energy narrative, in which the history of hysteretic dissipation shapes the forces applied next. It recontextualizes modal information as a baseline rather than a straitjacket, and shows that externally scripted control can emulate adaptive behavior without internal feedback loops, challenging the assumption that realism requires embedding adaptivity deep inside the solver. The authors position the framework for preliminary fragility assessment, redistribution-sensitive detailing, and comparative evaluation of modal activation, and note its compatibility with the spirit of ASCE 41 and Eurocode 8, both of which acknowledge stiffness degradation and force redistribution even though neither prescribes energy-based load patterns. Future extensions outlined in the paper include element-wise degradation models, calibration against experimental data for reinforced concrete and composite systems, integration with site-specific hazard spectra, extension to three-dimensional frames with torsional coupling, and evaluation under near-fault pulse-type motions. For a discipline caught between the fidelity of dynamic simulation and the tractability of static methods, IOPER offers a transparent middle path, one in which every force applied to the structure carries the memory of the energy it has already dissipated.

Subject of Research: A quasi-adaptive pushover framework using hysteretic energy redistribution for seismic assessment of steel moment-resisting frames

Article Title: IOPER: Inverse-optimized pushover with energy redistribution: A framework for enhanced control and degraded stiffness-aware seismic analysis

Article References: Mendoza, J., Canelas, A., & Sensale, B. (2026). IOPER: Inverse-optimized pushover with energy redistribution: A framework for enhanced control and degraded stiffness-aware seismic analysis. Results in Engineering, 32, Article 113209. https://doi.org/10.1016/j.rineng.2026.113209

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113209

Keywords: pushover analysis, seismic assessment, hysteretic energy, steel moment frames, nonlinear static analysis, stiffness degradation, NLTHA, ASCE 41, Eurocode 8, adaptive load patterns, structural engineering, earthquake engineering

The two materials at the heart of the study could hardly be more different in character. Burnt clay bricks, or BCB, are the conventional workhorse of masonry construction in South Asia and much of the developing world, fired in kilns at high temperature and prized for their compressive strength. Unburnt sandcrete blocks, or USB, made from a sand-cement mix and cured without firing, represent a greener alternative because they avoid the energy intensity and emissions of brick kilns. In many rapidly urbanizing countries, both materials sit side by side in the same neighborhoods, often in the same buildings, yet their influence on how a frame behaves in an earthquake has rarely been compared head to head under controlled laboratory conditions. That gap is precisely what the Bangladeshi team set out to close.

The experimental program involved three small-scale multi-story, multi-bay reinforced concrete frames, each partially infilled with a different masonry unit, subjected to quasi-static cyclic loading that mimics the back-and-forth demands of a strong earthquake. The researchers evaluated seismic performance through hysteretic behavior, the looped force-displacement curves that encode a structure’s strength, stiffness, ductility and capacity to dissipate energy. These four quantities are the currency of earthquake engineering: strength determines the load a frame can carry, stiffness governs how much it sways, ductility measures how far it can deform before collapse, and energy dissipation reflects how effectively the structure absorbs the earthquake’s input rather than passing it on to its occupants.

The headline finding is that the type of infill masonry matters far more than many design codes assume. The frames with burnt clay brick infills delivered the highest lateral load capacity of the three specimens, confirming the material’s reputation for stiffness and strength. But that strength came at a cost. The BCB-infilled frames showed sudden degradation of their initial stiffness and a brittle post-peak response, meaning that once the infill panels began to fail, the loss of strength and stiffness was abrupt rather than gradual. In seismic terms, brittleness is dangerous because it gives occupants and structures little warning and little reserve capacity after the peak demand has passed.

The unburnt sandcrete block infills told a different and arguably more nuanced story. Although the USB-infilled frames reached a slightly lower maximum lateral capacity, they exhibited improved ductility and the highest post-peak cumulative energy dissipation of the studied frames. In other words, the greener material did not simply lose to the conventional one; it traded a modest amount of peak strength for a more forgiving failure mode, deforming further and absorbing more cumulative energy after its peak load had been exceeded. For engineers weighing sustainability against safety, the study suggests that the trade-off is not one-sided, and that softer, weaker infills may actually enhance the survivability of a frame in a severe event, provided the reduced strength is accounted for in design.

Beyond the material comparison, the study examined failure mechanisms in detail and found extensive damage concentrated in the frame members and infill panels near the exterior beam-column joints. This observation matters because exterior joints are precisely the locations where infill frames are most vulnerable in real earthquakes: the panels interact with the surrounding columns and beams, transferring forces that the bare frame was never designed to resist. The concentration of damage near these joints echoes a long-standing concern in the literature, dating back decades to pioneering work on infilled frames, that infills can create unintended load paths, short columns and local failure concentrations that compromise an entire building even when the code-designed frame itself is adequate.

The second half of the study turned from the laboratory to the computer. The team evaluated two available macro-models of masonry infilled reinforced concrete frames, assessing how reliably they could predict the measured seismic performance. Macro-models, typically built from equivalent diagonal struts that stand in for the infill panel, are the workhorses of seismic assessment because modeling every brick individually is computationally prohibitive for whole buildings. The verdict, however, was sobering. Implementing the two macro-models proved difficult, and neither reproduced the experimental behavior with acceptable accuracy. One model depended on substantial empirical calibration, effectively requiring test data to be tuned before it could predict test data, while the other tended to overestimate both stiffness and energy dissipation, painting an optimistic picture that real structures may not match.

These modeling shortcomings have practical consequences. Nonlinear static and dynamic analyses of infilled buildings underpin seismic retrofit decisions, loss estimates and code provisions worldwide, from FEMA guidelines to Eurocode 8 and national codes such as the Bangladesh National Building Code. If a macro-model overestimates energy dissipation, it will underpredict displacements and could lead engineers to conclude a building is safer than it is. If it requires extensive calibration, its predictive value for buildings that have never been tested, which is to say nearly all of them, is limited. The study’s experimental dataset, generated with support from the Housing and Building Research Institute and Chittagong University of Engineering and Technology, therefore serves a dual purpose: it documents how two common infill materials behave, and it provides a benchmark against which future models can be honestly judged.

The broader significance of the work lies in the collision between sustainability goals and seismic safety. As countries seek to phase out energy-hungry brick kilns, unburnt alternatives such as sandcrete blocks are being promoted on environmental grounds, sometimes with little attention to their structural implications. This study suggests that such a transition need not be seismically harmful and could even improve post-peak performance, but it also warns that the two materials produce measurably different frame responses in stiffness degradation, strength, ductility and energy dissipation. Codes and assessment procedures that treat all masonry infills as equivalent, or that ignore infills altogether, are missing behavior that the experiments show to be significant and, in the case of brittle burnt brick panels, potentially hazardous.

For a region that sits near the active boundaries of the Indian and Eurasian plates and carries the memory of devastating earthquakes, research of this kind is not academic. The study’s combination of physical testing and critical numerical evaluation offers engineers a clearer picture of what actually happens inside an infilled frame when the ground shakes, and a candid reminder that the computational tools used to certify safety still lag behind the messy reality of masonry-concrete interaction. As Mukhlis and his colleagues demonstrate, the humble brick in the wall may be the most important structural element nobody designed.

Subject of Research: Seismic performance of reinforced concrete frames infilled with burnt clay brick and unburnt sandcrete masonry

Article Title: Seismic performance of RC frames with burnt and unburnt brickwork masonry infills: experimental and macro-model evaluation

Article References: Seismic performance of RC frames with burnt and unburnt brickwork masonry infills: experimental and macro-model evaluation. (n.d.). https://doi.org/10.1007/s10518-026-02670-y

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02670-y

Keywords: reinforced concrete frames, masonry infill, burnt clay bricks, sandcrete blocks, seismic performance, hysteretic behavior, stiffness degradation, ductility, energy dissipation, macro-modeling, earthquake engineering, Bangladesh

The research, conducted by Hessam Atghaee and Farhang Farahbod of Islamic Azad University’s West Tehran Branch together with Fayaz R. Rofooei of Sharif University of Technology, was published in the Bulletin of Earthquake Engineering. The team set out to answer a deceptively simple question: what happens to the in-plane seismic behavior of a concrete-filled steel deck diaphragm when it is simultaneously squeezed by out-of-plane gravity loading? Despite decades of use in commercial and industrial construction around the world, the coupled influence of sustained gravity loads and connection detailing on diaphragm response has remained insufficiently quantified, leaving a gap between how these systems are tested in laboratories and how they actually perform in buildings.

To close that gap, the researchers built and tested three full-scale diaphragm specimens, each measuring 2.5 by 5.0 meters, under reversed cyclic in-plane loading that mimics the back-and-forth shearing an earthquake imposes. The first specimen served as a control, carrying no gravity load and containing no mechanical connectors between the steel deck and the concrete. The second was subjected to a sustained gravity load of 600 kilograms per square meter, a realistic service-level loading, but likewise lacked mechanical connectors. The third combined the same gravity loading with self-drilling screws installed to enforce composite action between the steel deck and the concrete fill. This three-way comparison allowed the team to isolate the effect of gravity loading alone and then to evaluate whether mechanical fasteners could compensate for the degradation it causes.

The experimental program captured a rich set of response measurements, including hysteretic load-displacement loops, stiffness degradation from cycle to cycle, slip at the steel-concrete interface, and the progression of visible damage through to failure. The results were striking. Sustained gravity loading reduced the in-plane diaphragm capacity by approximately 20 percent compared with the unloaded control specimen. Just as importantly, gravity loading accelerated the development of damage under cyclic loading, meaning the diaphragm not only lost strength but also deteriorated faster as the simulated earthquake continued. In seismic terms, that combination is doubly concerning: a weaker diaphragm that degrades more quickly offers less protection precisely during the strongest and longest phases of ground shaking.

The third specimen told a more encouraging story. Adding self-drilling screws to enforce composite action between the deck and the concrete effectively suppressed interface slip, the relative sliding that undermines the ability of the two materials to work as a single structural unit. With slip controlled, the fastened diaphragm exhibited significantly reduced in-plane deformations and enhanced post-elastic stiffness, retaining its shape and load path integrity at displacement levels where the unfastened specimens had softened considerably. Interestingly, however, the mechanical fasteners did not raise the ultimate in-plane capacity. Their benefit lies in deformation control and stiffness preservation rather than in raw strength, a distinction that matters for performance-based seismic design, where limiting drift and damage is often as important as preventing collapse.

Complementing the laboratory work, the researchers developed a detailed three-dimensional finite element model of the diaphragms and validated it against the experimental measurements. With the model proven reliable, they used monotonic numerical analyses to reproduce the seismic backbone, or envelope, response of the specimens and to run parametric investigations that would have been impractical experimentally. One parameter stood out: reducing the concrete compressive strength decreased both diaphragm stiffness and strength, though it did not alter the underlying failure modes. In other words, weaker concrete produces a weaker, more flexible diaphragm, but the same mechanisms govern its failure. By contrast, the orientation of the applied in-plane loading relative to the deck corrugations had only a minor influence on seismic diaphragm response, a finding that simplifies design considerations for decks loaded in different directions.

The implications ripple through seismic design practice. Modern codes and design guides, including documents from the American Concrete Institute, the American Institute of Steel Construction, and the Steel Deck Institute, provide procedures for diaphragm design, but the new results highlight the importance of explicitly considering sustained gravity effects rather than treating in-plane and out-of-plane demands as independent. A diaphragm designed without accounting for gravity-induced degradation could enter an earthquake with substantially less reserve capacity than its calculations suggest. The 20 percent capacity reduction measured here is not a marginal correction; it is the kind of systematic bias that can erode safety margins across an entire building stock, particularly in regions where composite steel deck floors dominate mid-rise construction.

The study also carries a practical prescription. Because self-drilling screws suppressed interface slip and dramatically reduced in-plane deformations without adding ultimate capacity, they represent a relatively inexpensive retrofit and detailing measure that improves seismic performance where it often matters most: controlling damage and maintaining functional stiffness during shaking. For new construction, specifying mechanical fasteners to enforce composite action offers a straightforward way to build in that resilience. For existing buildings, the findings give engineers a quantitative basis for assessing whether unreinforced diaphragms under significant gravity load warrant strengthening, especially in seismic retrofit projects evaluated under standards such as ASCE 41.

Methodologically, the work demonstrates the value of pairing full-scale cyclic testing with validated finite element simulation. Physical tests of 2.5 by 5.0 meter diaphragms under simultaneous gravity and cyclic in-plane loading are expensive and logistically demanding, and only a handful of configurations can realistically be examined. The validated numerical model extends the reach of the three experiments, allowing the team to explore how material properties and loading orientations shape the backbone response across a much broader design space. The researchers note that the experimental measurements and simulation results are available from the corresponding author upon reasonable request, given the large volume of data and the project-specific nature of the models.

Ultimately, the study delivers new quantitative insight into gravity-influenced diaphragm behavior at a moment when earthquake engineering is increasingly focused on realistic, coupled loading conditions rather than idealized single-demand tests. Buildings do not experience earthquakes in isolation from the loads they carry every day, and the structures that connect those loads to the lateral system should not be designed as if they did. By showing exactly how much capacity sustained gravity loading can consume, and by demonstrating a simple fastening strategy that claw back much of the lost performance, the researchers have given the seismic engineering community both a warning and a workable solution. For the countless composite steel deck floors overhead in offices, hospitals, and warehouses worldwide, the message is clear: the weight they carry shapes how well they can protect the people below when the ground begins to move.

Subject of Research: Experimental and numerical investigation of gravity load effects on the in-plane seismic behavior of composite steel deck diaphragms.

Article Title: Investigation of gravity load effects on in-plane behavior of composite steel decks

Article References: Atghaee, H., Farahbod, F., & Rofooei, F. R. (2026). Investigation of gravity load effects on in-plane behavior of composite steel decks. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02692-6

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DOI: 10.1007/s10518-026-02692-6

Keywords: composite steel deck, seismic diaphragm behavior, gravity load effects, cyclic loading, self-drilling screws, interface slip, finite element modeling, stiffness degradation, in-plane shear, earthquake engineering, concrete-filled steel deck, structural design