The proposed design combines the strength and plastic energy dissipation of steel with the flexibility and shear damping of rubber. Steel bars were welded between rigid upper and lower plates to form the principal load-bearing framework, while compounded recycled rubber filled the spaces around them. Before assembly, steel surfaces were treated with Chemlok 205 primer and Chemlok 220 rubber-to-metal adhesive.

Rubber sheets and the steel framework were then placed in a mould and joined by hot-compression vulcanization at 128–130 °C for 2–2.5 hours under pressure. The resulting continuous rubber core was intended to coordinate deformation among the bars and preserve a load path after local steel fracture, unlike a conventional steel bar damper whose response can be abruptly interrupted by fracture. The experimental matrix contained nine specimens: three steel bar dampers, designated BD; three rubber-only dampers, designated RD; and three recycled rubber–steel bar composites, designated RBD.

Each steel and composite specimen contained eight bars, each 10 mm in diameter, arranged in a 2 × 4 layout. The rubber and composite cores had a projected area of 26,250 mm², and the connection plates measured 200 × 250 mm and were 10 mm thick. Core heights of 75, 100 and 125 mm allowed configuration type and height to be evaluated separately.

The selected rubber contained 20% devulcanized rubber from truck-tread powder and 80% Standard Malaysian Rubber Constant Viscosity 60. Material tests gave it a tensile strength of 21.5 MPa, elongation at break of 530%, compressive modulus of 6.0 MPa at 20% strain and damping ratio of 6.31%. Each specimen underwent 13 displacement-controlled loading steps with three complete cycles at each step, allowing as many as 39 cycles.

Displacement amplitude increased from 2 to 50 mm, and loading rates ranged from 0.25 to 0.80 mm/s. Testing stopped when severe visible damage occurred or the maximum resisting force in the current cycle fell below 85% of the peak resisting force. The vertical arrangement generated cyclic shear deformation in each energy-dissipation core.

Because the loading path kept the distance between the connection plates essentially constant, geometric elongation of the steel bars could produce secondary axial tension at large displacements, although axial force was not independently applied or measured. All three configurations were tested with the same installation and boundary conditions. Damage observations showed a pronounced change in failure evolution.

Steel-only specimens fractured after pronounced bending of their bars: BD8–75 failed on cycle 19 at about 14 mm displacement, while the 100 and 125 mm versions failed on cycles 28 and 31 at amplitudes of 27.5 and 35 mm. The longer core increased the effective bending length and delayed fracture. Rubber-only specimens completed all 39 cycles and reached 50 mm, although they developed varying degrees of interface debonding and edge warping without through-thickness tearing of the rubber core.

The composites combined bar yielding and fracture with rubber shear deformation and interfacial debonding. Their continuous rubber core continued to connect the upper and lower plates after local bar fracture, limiting the sudden load degradation seen in the steel-only devices. The largest benefit occurred in the shortest composite core.

RBD8–75 reached its major failure on cycle 25 at approximately 22.5 mm, compared with cycle 19 and 14 mm for BD8–75. Its peak load was 33.12 kN, 35.2% above the steel specimen’s 24.49 kN. Peak loads for the 100 and 125 mm composites were respectively 30.5% and 43.0% higher than those of their steel-only counterparts.

After local steel damage, the taller composites retained residual load capacity and overall connectivity, and no through-thickness tearing occurred in their rubber cores. Numerical results showed that the height of the composite core reduced bar curvature and end plastic-strain concentration; at peak load, maximum equivalent plastic strains in the 100 and 125 mm models were 12.5% and 15.8% lower than in the 75 mm model. Stiffness declined as cyclic deformation accumulated, but the steel framework continued to support the composite after the bars began yielding.

Across displacement amplitudes of approximately 2–50 mm, effective stiffness decreased by about 62–64% for the rubber-only dampers and 73.3–82.6% for the steel dampers. Increasing the height from 75 to 125 mm reduced the rubber-only device’s maximum load by 40.2% while leaving its maximum displacement near 50 mm. For the steel damper, the same change reduced maximum load by 41.8% but increased maximum displacement by about 150%, from 14.01 to 35.02 mm.

The results expose a design trade-off: a taller steel core accommodates more distortion but generally develops less peak force because the bars bend over a longer length. Energy measurements showed that the composite produced more than a modest increase in resistance. Final cumulative dissipation by RBD8–75 was 217.5% higher than that of BD8–75, while RBD8–100 exceeded its steel counterpart by 29.0%.

At 125 mm, the final cumulative difference was only 0.4%, although the composite dissipated more over most of the displacement range shared by the two specimens. Maximum single-cycle energy dissipation was respectively 104.8%, 21.9% and 2.3% higher for the 75, 100 and 125 mm composites than for their steel counterparts. The rubber therefore made its largest contribution when short bars were especially vulnerable to concentrated deformation.

RBD8–100 provided the best balance among the tested composites, combining a peak load of 25.14 kN with the highest single-cycle and cumulative dissipation values. The researchers also developed a three-dimensional ABAQUS model with geometric nonlinearity, bilinear elastoplastic steel, ductile steel damage and a Neo-Hookean hyperelastic rubber. The model was validated against the three RBD specimens, not all nine experimental specimens.

Numerical-to-experimental peak-force ratios ranged from 0.941 to 1.095. Predicted stiffness degradation differed from the measurements by 0.30–2.10%, and errors for single-cycle energy dissipation ranged from 5.09% to 8.71%. The model was less accurate for the 75 mm composite’s cumulative energy dissipation and residual deformation, with errors of 37.07% and 34.52%, respectively.

It also omitted rubber viscoelasticity, the Mullins effect, rate dependence and progressive rubber damage, limiting its direct representation of dynamic or long-term behaviour. Separate numerical parameter studies indicated that increasing the steel-to-rubber area ratio from 1.53% to 4.69% raised the maximum absolute force at 10 mm displacement by about 249% and average energy dissipation per cycle by about 439%. The equivalent damping ratio increased more modestly, from 11.97% to 18.63%.

Raising steel yield strength from 250 to 500 MPa increased maximum absolute load at 22.5 mm by 42.9%, average single-cycle energy dissipation by 67.0% and equivalent damping ratio by 17.8%. Within the explored ranges, the researchers identified a 3.45% steel-to-rubber area ratio and yield strength near 400 MPa as balanced choices, not universal optimum values. A simplified bilinear backbone model based on the experiments and parametric models linked core height, area ratio and yield strength to initial stiffness, characteristic strength and post-yield stiffness; characteristic-parameter errors for the three experimental composites were below 5.1%, and backbone-curve errors ranged from 3.68% to 5.40%.

The work points toward a way to combine metal yielding with rubber shear deformation while reusing waste tyre rubber, but the evidence remains limited to laboratory-scale quasi-static component tests and numerical models. Repeated experiments over broader parameter ranges, full-scale and structural-subassembly tests, dynamic cyclic loading, realistic earthquake records, and evaluations of temperature, aging, environmental exposure and interface durability are still needed before the performance or practical deployment of the damper can be assessed beyond the studied conditions.

Subject of Research: Component-level cyclic performance of recycled-rubber–steel bar composite dampers

Article Title: Mechanical performance of novel recycled rubber–steel bar composite dampers: Experimental and numerical investigation

Article References: Alhokabi, A. A., Tan, C. G., Zou, C., Ibrahim, Z., Bunnori, N. M., El‑Shafie, A., Nazri, F. M., Ghaedi, K., & Gordan, M. (2026). Mechanical performance of novel recycled rubber–steel bar composite dampers: Experimental and numerical investigation. Case Studies in Construction Materials, 25, Article e06629. https://doi.org/10.1016/j.cscm.2026.e06629

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06629

Keywords: recycled rubber, steel–rubber composite, cyclic loading, energy dissipation, hysteretic response, damage tolerance, finite element analysis, seismic dampers, waste tyre rubber, structural resilience, Mechanical, performance

Composite concrete-filled shear walls combine steel plates and infilled concrete into a single structural element, exploiting the best properties of both materials. The steel provides tensile strength, ductility, and confinement, while the concrete contributes mass, stiffness, and compressive capacity, with the two materials working together to resist the lateral forces imposed by wind and earthquakes. These walls have earned a reputation for great strength, stiffness, and ductility, and they have found applications ranging from high-rise buildings to safety-related nuclear facilities. But almost all of that reputation rests on tests and analyses performed at ambient conditions, on walls that have never been damaged. What happens when one of these walls, cracked and yielded from a violent earthquake, is then engulfed by fire, is a question that has received far less attention.

That question is precisely what motivated Parisa Samiee and Gholamreza Ghodrati Amiri of the Iran University of Science and Technology, together with Shirin Esmaeili Niari and Vahid Akrami of the University of Mohaghegh Ardabili. Their approach was computational. The team developed a detailed finite element model of the problem in the commercial package ABAQUS, and, critically, they did not simply trust their model on faith. Before running any new simulations, they first verified the numerical procedure against previously published experimental data, a validation step that lends credibility to everything that follows. Only after the model demonstrated that it could reproduce known behavior did the researchers unleash it on a comprehensive parametric investigation of composite shear walls under sequential hazards.

The numerical procedure itself was a staged, multi-physics affair that mirrors the real sequence of a compound disaster. It began with a heat-transfer analysis to capture how thermal energy penetrates the wall and how temperatures evolve through the steel plates and the concrete core. Monotonic lateral loading was then applied to establish baseline strength and deformation characteristics. To evaluate hysteretic behavior, the response of the walls under the repeated, reversing displacements characteristic of earthquake shaking, the researchers ran cyclic analyses following the ATC-24 loading protocol, a widely used guideline for cyclic seismic testing of steel structural components. Finally, and most distinctively, they coupled the results of the seismic stage with a sequential post-earthquake fire analysis, in which a wall already damaged by simulated earthquake loading was subjected to simulated fire exposure and its remaining resistance tracked until failure.

One of the central design variables the team examined was the boundary element, a reinforced zone at the edges of the wall where flexural demands concentrate during lateral loading. The parametric study swept through wall configuration, the length of these boundary elements, the surfaces of the wall exposed to fire, and the ratio of lateral loading applied before the fire began. The results quantify just how much these edge zones matter. Boundary elements greatly improved the ambient lateral strength and deformation capacity of the walls, producing increases in peak load of 6.3 to 13.5 percent and increases in yield displacement of 26.5 to 42.9 percent. In plain terms, walls equipped with boundary elements could not only carry more lateral force but also deform significantly further before reaching their yield point, a valuable property in any seismic design philosophy that expects structures to endure large inelastic excursions.

The cyclic loading results reinforced that picture. When subjected to the reversing displacement histories of the ATC-24 protocol, the walls with boundary elements exhibited more saturated hysteresis loops, meaning the force-displacement curves enclosed more area and maintained their load-carrying capacity more consistently through repeated cycles. Fuller, more stable hysteresis loops translate directly into greater energy dissipation, the mechanism by which a structure absorbs and dissipates the kinetic energy delivered by an earthquake. The boundary-element walls also achieved higher peak strengths under cyclic loading, confirming that the benefit of these edge zones is not an artifact of monotonic testing but a robust feature of their behavior under realistic seismic demands.

The most striking findings, however, emerged from the post-earthquake fire stage, where the interplay between prior seismic damage and subsequent thermal attack came into sharp focus. Depending on the fire scenario and the level of damage the wall had accumulated before the fire began, a boundary element with a length of 0.15 times the wall dimension could extend the time to failure by up to 95.6 percent. In effect, this modest design enhancement nearly doubled the window of time that a damaged wall could continue to resist fire before collapsing. In a real post-earthquake environment, that additional time is not an abstract metric; it is the margin that allows occupants to evacuate, firefighters to operate, and search-and-rescue teams to work beneath and beside structures that have already been shaken to their limits.

If boundary elements emerged as the hero of the study, multi-sided fire exposure emerged as the villain. Among all the parameters examined, exposure to fire on multiple sides was identified as the most harmful factor, cutting the time to failure by up to 89.7 percent. The physics behind this result is intuitive once stated: a wall heated from one face retains a cooler, stronger core and a relatively undamaged back face to which loads can be transferred, whereas a wall heated on several faces loses structural capacity nearly everywhere at once, with its steel plates softening at elevated temperature and its concrete core degrading simultaneously across its section. The finding carries a direct lesson for building layout and fire protection strategy, since shear walls positioned at building perimeters or adjacent to open floor plans may be far more vulnerable in a post-earthquake fire than interior walls shielded on one or more faces.

Another layer of the investigation concerned the lateral loading ratio, the fraction of the wall’s capacity that had been mobilized by the earthquake before the fire began. This parameter matters because it encodes the severity of the preceding seismic event relative to the wall’s design capacity. A wall that survived the earthquake essentially undamaged enters the fire with its full material properties and geometry intact, while a wall pushed deep into its inelastic range brings cracked concrete, yielded steel, and possibly local buckling into the fire scenario. The study’s demonstration that failure time in the fire stage depends on the level of damage prior to the fire underscores the central premise of sequential hazard analysis: the fire resistance of a structure is not a fixed property stamped on its drawings, but a degraded and damage-dependent quantity that can only be assessed honestly by simulating the earthquake first.

The broader significance of this work lies in its contribution to performance-based design, an evolving philosophy in structural engineering that asks not merely whether a building complies with prescriptive code provisions, but whether it actually achieves defined performance objectives under realistic multi-hazard scenarios. Fire researchers and earthquake engineers have increasingly converged on the view that designing for the two hazards in isolation can leave dangerous blind spots, because the fire that follows an earthquake strikes a fundamentally different structure than the one the fire code assumed. By delivering a validated finite element framework that chains heat transfer, monotonic and cyclic seismic loading, and post-earthquake fire analysis into a single coherent procedure, and by quantifying how boundary elements and fire exposure configuration govern survival time, the researchers have given designers both a tool and a set of design-relevant numbers. For concrete-filled composite shear walls, one of the most promising lateral systems in modern construction, the message is now backed by analysis: thoughtful detailing at the wall edges can buy precious minutes in the fire that follows the quake, while a fire burning on multiple faces can steal almost all of them away.

Subject of Research: Post-earthquake fire performance of concrete-filled composite shear walls analyzed with finite element simulation

Article Title: Post-earthquake fire performance of concrete-filled composite shear wall

Article References: Samiee, P., Ghodrati Amiri, G., Esmaeili Niari, S., & Akrami, V. (2026). Post-earthquake fire performance of concrete-filled composite shear wall. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02719-y

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02719-y

Keywords: post-earthquake fire, composite shear wall, concrete-filled, finite element analysis, boundary element, cyclic loading, ATC-24 protocol, fire resistance, sequential hazards, ABAQUS, seismic performance, hysteretic behavior

The research team, led by Nikolay V. Turbin, set out to answer a question that has lingered in the composite fatigue literature for decades: once an impact has seeded a delamination inside a laminate, how does that defect evolve when the structure is compressed over and over again? The question matters because modern airworthiness regulations, including the European Union Aviation Safety Agency’s CS 25.571 damage tolerance requirements and the Federal Aviation Administration’s Advisory Circular 20-107B on composite aircraft structure, demand that manufacturers demonstrate that damaged structure can sustain load until the damage is detected. For metals, fracture mechanics offers mature tools for predicting crack growth under fatigue. For composites, the picture has remained stubbornly incomplete, and the field has been searching for reliable slow-growth approaches for post-impact fatigue for years.

The experimental core of the study involved two test specimens fabricated from carbon-fiber reinforced laminate, a material class that dominates modern primary aircraft structures. Each specimen was first subjected to impact, creating the characteristic internal damage zone of delaminations at multiple depths through the thickness. The researchers then mapped the dimensions and depth of these internal delaminations before and after cyclic compression testing, using non-destructive inspection to build a before-and-after picture of the hidden damage architecture. This baseline-and-post-test comparison is what allowed the team to quantify how much the delaminations grew, in which directions, and at which interfaces between plies, rather than simply recording whether the specimen eventually failed.

Under cyclic compression, an impacted composite panel does not behave like a pristine one. The delaminated region behaves as a local zone of separated plies that can buckle outward or inward under compressive stress, and this local instability drives the interlaminar crack faces apart, pumping energy into the delamination front with every load cycle. The result is a distinctive damage evolution pattern: the delamination front advances through the laminate, the buckling zone enlarges, and the residual compressive capacity of the element declines. Previous studies by groups including Butler and Almond, Melin and Schön, and Uda and colleagues have documented aspects of this behavior, but the field still lacks a validated, practical framework that connects measured damage growth to a computational prediction that engineers could use in certification-oriented analysis.

The Moscow Aviation Institute team approached the problem with a two-pronged strategy. On the theoretical side, they developed a framework for describing specific damage growth in the impacted laminate, drawing on the classical foundations of fracture mechanics established by Griffith in 1921 and the crack propagation laws formalized by Paris and Erdogan in 1963, adapted to the particular geometry and mechanics of a delamination embedded in a compressed anisotropic plate. On the computational side, they built numerical simulations of the approximated damage growth, using finite element tools of the kind employed in commercial platforms such as Siemens Simcenter 3D, to reproduce the stress state around the delamination and the progression of the interlaminar crack. The theoretical predictions and the numerical model were then tested against the experimental observations from the cyclic compression tests.

One of the most striking findings from the cyclic testing was the appearance of a stage of unstable delamination growth followed by arrest. Rather than advancing smoothly and continuously with every cycle, the delamination in the tested specimens went through a period of rapid, unstable extension and then stopped growing, remaining arrested until the prescribed number of cycles expired. This behavior has important implications for how engineers think about post-impact fatigue life. It suggests that damage growth in these laminates is not a monotonically accelerating march toward failure but a more nuanced process in which the local mechanics of the buckled delamination zone, the changing geometry of the crack front, and the laminate’s resistance to interlaminar fracture interact to produce periods of dormancy as well as bursts of growth.

The study’s central claim is that this damage initiation and growth can be predicted. The researchers report that both their theoretical analysis and their numerical modeling captured the detected damage initiation and the subsequent growth observed in the experiments. In other words, the computational tools did not merely describe the damage after the fact; they anticipated where and when the delaminations would begin to extend and how far they would travel under the cyclic compression loading. The authors conclude that the possibility of a computational estimate of the damage tolerance of a composite element under cyclic loads is confirmed, which is precisely the kind of validated predictive capability that the slow-growth damage tolerance philosophy requires.

The significance of this confirmation reaches well beyond a single laboratory experiment. Certification practice for composite aircraft structures has traditionally leaned on conservative assumptions, treating barely visible impact damage as a strength knockdown rather than tracking its growth over time, because reliable slow-growth prediction has been elusive. As Pascoe and co-workers argued in a widely cited 2021 review, current research approaches had not yet delivered a workable slow-growth damage tolerance method for fatigue after impact in fiber-reinforced polymers. If computational frameworks of the kind demonstrated in this study can be refined and generalized, they could allow designers to quantify how a specific impact scar will behave under a specific service load spectrum, potentially reducing conservatism while maintaining or improving safety margins.

The work also illustrates a broader trend in composite structural mechanics: the convergence of high-fidelity simulation, fracture-mechanics theory, and advanced non-destructive inspection. Phased array ultrasonic scanning of impact damage in carbon-fiber composites, as documented in the inspection literature, provides the detailed three-dimensional damage maps that models need as input and validation data. Finite element analysis of composite materials, supported by dedicated modeling techniques for delamination and progressive damage, provides the predictive engine. And carefully designed cyclic compression-after-impact tests, following standards such as ASTM D7137 for compressive residual strength of damaged laminates and ASTM D7136 for damage resistance to drop-weight impact, provide the ground truth. The new study weaves all three strands together in a single, self-consistent methodology.

There remain, of course, limits to what two specimens can establish. The authors are explicit that the aim of the work is to enhance the understanding of post-impact damage growth in order to refine the model used for composite material damage tolerance estimation, not to deliver a finished certification tool. Extending the approach across a wider range of layups, impact energies, load levels, and environmental conditions will be the necessary next step, and the statistical variability inherent in both impact damage and fatigue behavior will demand larger datasets. The study was carried out under a grant from the Russian Ministry of Science and Higher Education for large scientific projects in priority areas of scientific and technological development, reflecting the strategic weight that aviation nations place on composite damage tolerance. But the core message is clear and consequential: the hidden damage left by an impact need not remain an unquantified unknown. With the right combination of theory, simulation, and experiment, the life story of a delamination under cyclic compression can be read in advance, and that ability may reshape how the next generation of composite aircraft structures is designed, inspected, and certified.

Subject of Research: Post-impact delamination growth in carbon-fiber composite laminates under cyclic compression loading

Article Title: Computational and experimental analysis of the post-impact delamination growth in a composite structural element subjected to cyclic compression

Article References: Turbin, N. V., Kononov, N. O., Tatarintsev, N. S., Shramko, K. K., Lutoshkina, A. E., & Kutdusov, R. R. (2026). Computational and experimental analysis of the post-impact delamination growth in a composite structural element subjected to cyclic compression. Aerospace Systems. https://doi.org/10.1007/s42401-026-00547-1

Image Credits: AI Generated

DOI: 10.1007/s42401-026-00547-1

Keywords: composite structures, damage tolerance, delamination, compression fatigue after impact, carbon-fiber reinforced laminate, cyclic loading, fracture mechanics, finite element analysis, non-destructive inspection, aerospace structures, impact damage, fatigue life prediction

The study, published in Polymer Bulletin by Yuanwen Liu, Jianlei Qi, Zheng Pan, Yu Qiao, Lei Dong, Jianyu Wu, and Yanping Wang, focuses on the ratcheting response of nitrile butadiene rubber, commonly abbreviated NBR. Ratcheting is a phenomenon engineers have studied intensively in metals, where cyclic stressing of pipelines, rails, and weld joints produces progressive plastic deformation that can ultimately trigger fatigue failure. In metals, sophisticated constitutive models exist to predict how quickly this deformation accumulates. Rubber, however, is a fundamentally different beast. It is a highly elastic material capable of enormous reversible deformation, often several hundred percent strain, and the models that work so well for steel and titanium simply do not transfer to elastomers without serious modification.

To understand why rubber ratcheting matters, it helps to picture what happens inside a rubber seal on an engine mount. Every vibration applies a stress pulse. If the peak stress is high enough, the polymer network and its reinforcing filler particles begin to rearrange. Some of that rearrangement is recovered when the load is removed, but some is not. The unrecovered portion is the ratcheting strain. In practical terms, a seal that ratchets will gradually change shape, lose its preload, and eventually leak or crack. Because NBR is the workhorse elastomer for oil-resistant applications, from O-rings to fuel line hoses, predicting its ratcheting behavior is directly relevant to product lifetime and safety.

The researchers designed a systematic experimental program to isolate the influence of each loading parameter. They varied the mean stress, which is the average stress level around which the cycle oscillates; the stress amplitude, which is how far the stress swings above and below that average; the stress loading rate, which is how quickly the stress is applied during each cycle; and the loading history, meaning the order in which different stress levels were applied. This kind of parametric study is essential because in real service, a rubber component rarely experiences a single, constant loading condition. It sees a messy combination of amplitudes, frequencies, and stress levels that change over its lifetime.

The results revealed a clear hierarchy of influence. Within the tested parameter range, the stress amplitude and the stress loading rate turned out to be the dominant factors controlling ratcheting strain. Higher stress amplitudes drove markedly more cumulative deformation, and so did slower loading rates. That second finding may seem counterintuitive at first glance, but it makes physical sense for a viscoelastic material. Rubber deforms through a combination of instantaneous elastic response and time-dependent viscous flow. When the stress is applied slowly, the polymer chains and filler networks have more time to flow and rearrange, so more of the deformation becomes permanent. When the stress is applied rapidly, the material behaves more stiffly and elastically, and less strain accumulates per cycle.

Mean stress, meanwhile, played a subtler but still critical role. When the peak stress of the cycle was held constant, or when the sequence of loading levels was considered, the mean stress had a more significant effect on the ratcheting behavior than the other parameters. This matters because two loading programs with the same peak stress can produce very different amounts of accumulated strain depending on where the cycle is centered. For designers, the practical implication is that specifying only a maximum operating stress is not enough to guarantee long-term dimensional stability; the entire stress waveform, including its baseline, must be considered.

The team also examined loading history, testing whether prior exposure to one stress level changed the material’s response to a subsequent level. This question is important because of the Mullins effect, a well-documented phenomenon in filled rubbers in which the first stretching of the material causes internal damage and softening, making the response to later loading history-dependent. The literature on filled elastomers shows that this induced softening and anisotropy can persist and interact with other inelastic mechanisms such as creep and stress relaxation. Understanding how loading sequence interacts with ratcheting is therefore a step toward more realistic lifetime predictions for components that experience variable duty cycles.

On the modeling side, the researchers confronted a fundamental problem: standard metal ratcheting models assume small deformations and are not applicable to large-deformation materials like rubber. Their solution was to introduce a deformation correction parameter, denoted as gamma, into the existing ratcheting framework. This parameter extends the applicability of the metal ratcheting model into the large-strain regime, allowing the model to successfully fit the ratcheting evolution of NBR under mean stress control. The resulting framework is phenomenological, meaning it captures the observed macroscopic behavior with fitted parameters rather than deriving it from molecular physics, but phenomenological models of this kind are exactly what engineering practice needs: compact, calibrated equations that can be implemented in finite element simulations of real components.

The significance of this work lies in bridging two research communities that have historically operated separately. The ratcheting literature is rich with studies of structural metals, including carbon steels, stainless steels, zirconium alloy tubes, magnesium alloys, and titanium, where ratcheting-fatigue interaction governs the life of pressurized pipes and welded joints. A parallel literature has documented ratcheting in polymers such as polycarbonate, PTFE, polyethylene, and PEEK, and in various filled rubbers including vulcanized natural rubber and its cerium-oxide-filled variants. By systematically quantifying how stress amplitude, loading rate, and mean stress shape the ratcheting of NBR, and by providing a corrected model tailored to highly elastic materials, the new study gives elastomer engineers a tool that metal engineers have enjoyed for decades.

The broader payoff could be substantial. Rubber components fail in service far more often through slow, cumulative degradation than through sudden overload, and ratcheting is a central mechanism in that degradation. A validated predictive model means manufacturers can simulate years of vibration and pressure cycling in software before a single seal is molded, screening designs for ratcheting resistance and optimizing compound formulations accordingly. It also means maintenance intervals can be set on a rational basis rather than conservative guesswork. The authors note that their framework could inform future analysis of highly elastic materials more generally, suggesting the correction-parameter approach may extend beyond NBR to other elastomers. As industries from aerospace to renewable energy push rubber components into harsher, longer-duty applications, understanding and predicting this quiet creep of matter under repeated stress becomes not just an academic exercise but a foundation for safer, longer-lasting machines.

Subject of Research: Ratcheting deformation behavior of nitrile rubber under cyclic stress loading

Article Title: Influences of stress amplitude and stress loading rate on the ratcheting response of nitrile rubber: experimental and numerical modeling

Article References: Liu, Y., Qi, J., Pan, Z., Qiao, Y., Dong, L., Wu, J., & Wang, Y. (2026). Influences of stress amplitude and stress loading rate on the ratcheting response of nitrile rubber: experimental and numerical modeling. Polymer Bulletin, 83(11), Article 621. https://doi.org/10.1007/s00289-026-06675-0

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06675-0

Keywords: nitrile rubber, ratcheting effect, cyclic loading, stress amplitude, mean stress, loading rate, elastomers, constitutive modeling, polymer mechanics, fatigue, Mullins effect, deformation correction parameter

A team of researchers led by Jie Wang and Kunfeng Kong collected mixed demolition waste from a recycling source in Zhengzhou, Henan Province, China. The material, derived from demolished brick-concrete buildings, was crushed, screened, and cleaned of impurities before testing. Particle-by-particle analysis showed that recycled crushed stone, recycled concrete, and recycled clay brick together accounted for more than 95 percent of the mass in every size fraction examined, with impurities below 3.5 percent. Because demolition waste from brick-concrete structures naturally contains all three components mixed together rather than separated, the researchers argue this composition is representative of what recycling plants actually supply, making large-scale reuse more practical than processes demanding careful component sorting.

The material’s physical properties reveal why it behaves so differently from natural aggregates. Its water absorption of 8.5 to 9.8 percent and crushing value of 29.5 percent are far higher than those of conventional fill materials, reflecting the porous, weaker nature of recycled concrete and clay brick particles. Its optimum moisture content of roughly 13.5 percent is considerably higher than that of natural granular fills of similar gradation, while its maximum dry density of 1.827 grams per cubic centimeter is markedly lower. In practical terms, this means field crews must control moisture carefully during compaction, allow time for water to redistribute within the absorbent particles, and accept a lighter but more void-rich skeleton that is more sensitive to drainage conditions.

To characterize the material’s static strength, the team prepared cylindrical specimens 150 millimeters in diameter and 300 millimeters tall, compacted at three degrees of compaction representing well-compacted, insufficiently compacted, and relatively loose states, and tested them in a large-scale triaxial apparatus under confining pressures of 50, 100, and 150 kilopascals. The saturated drained shear tests showed clear strain-softening behavior: specimens reached a peak deviatoric stress and then weakened as shearing continued. Both peak strength and residual strength rose substantially with confining pressure and compaction. When confining pressure increased from 50 to 150 kilopascals, residual strength climbed by 106.8 percent, 87.3 percent, and 121.0 percent for specimens compacted to 96, 92, and 88 percent, respectively, demonstrating that even loosely packed waste fill gains considerable post-peak capacity when laterally confined.

The stiffness results carried a subtler message. The secant modulus at 50 percent of peak stress, a standard measure of deformation stiffness, was far more sensitive to compaction at low confining pressure than at high. At 50 kilopascals, the modulus of 96-percent-compacted specimens exceeded that of 88-percent-compacted specimens by more than 111 percent. Yet raising confining pressure from 50 to 150 kilopascals improved the modulus by only 6.8 percent for the densest specimens, compared with 77.3 percent for those at 92 percent compaction. The implication is that loosely compacted waste fill benefits enormously from lateral confinement, making it best suited to subgrade zones where surrounding material can provide strong restraint, such as well-compacted internal fill layers or track-supporting layers.

Volumetric behavior added another dimension. Under shear, the specimens first contracted slightly and then dilated, with the maximum dilation exceeding that of conventional natural subgrade fills. Denser specimens dilated more because their tight initial contacts left little room for further compression, forcing deformation to proceed through particle rotation and interlocking. Looser specimens contracted instead, densifying progressively. The researchers note that this contraction-dilation response matters for railway engineering: contraction signals ongoing settlement accumulation, while dilation indicates a well-interlocked skeleton but, near critical stress levels, may disturb interfaces with overlying ballast or track layers.

The heart of the study, however, lay in its long-term cyclic triaxial tests, which subjected specimens to 10,000 loading cycles at 1 hertz under saturated drained conditions. Here the team introduced the shear stress ratio, or SSR, defined as the applied cyclic deviatoric stress divided by the material’s static peak strength measured under identical compaction and confinement. This strength-normalized measure proved decisive. When SSR remained below roughly 0.5, cumulative plastic deformation grew slowly and stabilized as the particle skeleton compacted and rearranged. Once SSR exceeded about 0.5, the fitted curves steepened sharply and deformation accelerated toward incremental failure. Grey relational analysis confirmed SSR as the single most influential variable, ranking ahead of confining pressure and degree of compaction.

Perhaps the most striking finding concerned densely compacted specimens under high stress. At an SSR of 0.8, the final cumulative deformation of the 96-percent-compacted specimens was about 3.7 times that of the 92-percent specimens, the largest relative increase among all compaction states. The explanation lies in the dense skeleton’s limited remaining void space: once cyclic stress approaches the mobilized strength capacity, particle sliding, abrasion, and breakage are repeatedly activated, and with no room left for gradual compaction, the structure responds through dilation and abrupt loss of interlocking. Looser fills, by contrast, can still absorb cyclic deformation through progressive densification. In other words, compaction alone does not guarantee stability if the traffic-induced stress level creeps too close to the material’s strength reserve.

The resilient modulus, which quantifies the recoverable elastic stiffness under repeated loading, generally increased with compaction, confining pressure, and cyclic deviatoric stress. Dropping compaction from 96 to 88 percent reduced the modulus by roughly 13 to 25 percent across the tested stress states. But the researchers caution against a tempting misreading: a rising resilient modulus does not necessarily indicate a healthy structure. Correlation analysis across 21 matched loading conditions found only a moderate linear association between modulus evolution and final cumulative plastic deformation, meaning the recoverable and irreversible components of deformation can evolve independently. A subgrade may appear stiff while quietly accumulating permanent settlement.

From these results the authors distill a preliminary design framework: compaction near 96 percent is preferred when cyclic stresses stay within the stable range; an SSR at or below 0.30 offers a conservative reference for long-term service; the range between 0.30 and 0.50 warrants caution; and SSR at or above 0.50, associated with accelerated deformation, should be avoided under conditions comparable to those tested. The team stresses that these thresholds are laboratory observations specific to the tested gradation, moisture state, and loading regime, not universal design limits, and that field-scale and in-situ verification remain necessary. Unresolved questions include the effects of wetting-drying cycles, freeze-thaw weathering, particle breakage quantification, and varying train speeds. Still, the study offers railway engineers a concrete, stress-based recipe for turning demolition debris into dependable subgrade, a step that could simultaneously ease landfill pressure and relieve the aggregate shortage confronting infrastructure construction worldwide.

Subject of Research: Strength and deformation behavior of brick-concrete construction waste used as railway subgrade fill

Article Title: Analysis of the strength and deformation characteristics of brick-concrete construction waste used as subgrade fill

Article References: Wang, J., Kong, K., Li, Y., Lin, L., Wang, Z., Chen, F., Yao, J., Wang, M., & Xiao, Y. (2026). Analysis of the strength and deformation characteristics of brick-concrete construction waste used as subgrade fill. Case Studies in Construction Materials, 25, Article e06565. https://doi.org/10.1016/j.cscm.2026.e06565

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06565

Keywords: construction waste, railway subgrade, recycled aggregates, triaxial testing, shear stress ratio, cumulative deformation, resilient modulus, strain softening, compaction, cyclic loading, geotechnical engineering, sustainable materials

The study, published in the Bulletin of Earthquake Engineering by Ju-Seong Jung of Chungwoon University and colleagues at Hanyang University’s Innovative Durable Building and Infrastructure Research Center, proposes a hybrid system the authors call BFC-FRP: a combination of prefabricated basalt fiber sheets and fiber-reinforced polymer panels applied to the surface of reinforced concrete columns. Basalt fiber, drawn by melting volcanic rock at high temperature, has attracted growing attention in structural engineering because it offers a favorable balance of mechanical performance, chemical stability, and cost compared with the glass and carbon fibers that have traditionally dominated the retrofit market.

To test the concept, the team fabricated seven large-scale columns, each with a square cross section of 350 by 350 millimeters and a clear height of 1.5 meters, dimensions representative of real building columns rather than miniature laboratory proxies. Three of the specimens were detailed to fail in shear, the most dangerous failure mode because it is sudden and brittle, while four were designed to be flexure-controlled, meaning their response is governed by bending and tends to be more ductile. Every column was then pushed sideways under reversed cyclic lateral loading, the laboratory equivalent of the back-and-forth motion an earthquake imposes, while a constant axial load corresponding to a ratio of 0.10 pressed down from above.

The strengthening scheme varied along two experimental axes. The first was coverage: some columns received strengthening only in the end regions, where damage typically concentrates, while others were wrapped over their full surface. The second was the arrangement of the prefabricated basalt fiber sheets and the FRP panels, allowing the researchers to compare how different configurations of the composite layers influenced confinement of the concrete and restraint of the longitudinal reinforcement. This systematic variation is what gives the study its practical value, because retrofit budgets rarely allow blanket coverage, and engineers need to know whether partial wrapping is enough.

The results for the shear-critical columns were striking. Full-surface BFC-FRP strengthening increased the ultimate strength by approximately 1.5 times compared with the unstrengthened control specimen, but the more important gain was in deformation: the displacement reached at ultimate strength grew by a factor of 2.0 to 2.6. In seismic terms, that transformation matters more than raw strength. A column that can keep carrying load while being pushed far sideways gives occupants time to evacuate and prevents the soft-story collapse mechanism that has killed thousands of people in recent earthquakes worldwide, from Turkey and Syria to Morocco and Japan.

For the flexure-controlled columns, which started from a more forgiving baseline, the retrofit delivered different but equally consequential improvements. The ultimate displacement increased by roughly 1.4 times, and the ductility ratio, a normalized measure of how much inelastic deformation a member can sustain before losing capacity, nearly doubled. Most notably, the energy dissipation capacity, which quantifies how much seismic energy the column can absorb and dissipate through hysteretic behavior in each loading cycle, rose by approximately 2.4 to 2.5 times. Since earthquake-resistant design fundamentally relies on structures dissipating energy rather than simply resisting force, this multiplication of dissipative capacity is arguably the study’s headline finding.

Alongside the physical tests, the researchers built nonlinear quasi-static cyclic finite element models of the columns using the disturbed stress field model, a mechanics-based formulation for reinforced concrete developed at the University of Toronto and implemented in analysis software widely used for shear-dominated members. The modeling work serves a purpose beyond reproducing the experiments: if a numerical framework can reliably predict how a wrapped column will deform and dissipate energy, engineers can extend the findings to configurations that were never tested, and design codes can eventually incorporate the strengthening system with confidence.

The models performed well. They reproduced both the load-displacement envelopes and the energy-dissipation responses of the tested columns with average deviations of approximately 10 percent, a level of accuracy that is respectable for nonlinear analysis of reinforced concrete, a material whose cracking, crushing, and bond-slip behavior is notoriously difficult to capture. The authors note that these results demonstrate the proposed BFC-FRP system can improve the deformation and energy-dissipation capacities of both shear- and flexure-controlled columns within the tested conditions, a carefully scoped conclusion that reflects the bounded nature of laboratory evidence.

The work sits within a broader and urgent engineering challenge: seismic strengthening of existing buildings. International guidelines, including documents from the American Concrete Institute and the Japan Building Disaster Prevention Association, already recognize externally bonded FRP systems as a legitimate retrofit strategy, but the field continues to search for materials that lower cost and improve sustainability. Basalt fiber fits that agenda well because its raw material is abundant volcanic rock, requiring no energy-intensive precursor chemistry of the kind needed for carbon fiber. Recent studies have explored basalt composites for repairing earthquake-damaged and corroded beam-column joints, for strengthening precast bridge piers, and even for confining columns built with recycled brick aggregates, suggesting a rapidly maturing research ecosystem.

For practitioners, the Korean team’s findings offer a concrete, quantified case for considering basalt-based wrapping when assessing older building stock, particularly in regions where shear-critical columns from pre-modern-code construction remain common. The demonstration that full-surface wrapping can more than double the deformability of brittle shear-critical columns, while partial schemes remain available where budgets constrain coverage, gives retrofit designers a tested menu of options. As with any laboratory campaign, the caveats are real: the tests covered a single axial load ratio, one column size, and specific composite arrangements, and fire performance of FRP-strengthened members remains a recognized consideration in practice. But the combination of large-scale testing, systematic parameter variation, and validated numerical modeling makes a persuasive case that volcanic rock, spun into fiber and bonded onto concrete, can help the world’s aging buildings stand up to the next big shake.

Subject of Research: Seismic retrofit of reinforced concrete columns using basalt fiber-reinforced polymer composites

Article Title: Experimental and numerical investigation on the seismic performance of reinforced concrete columns retrofitted with basalt FRP composites

Article References: Jung, J.-S., Lee, B.-G., Kim, K., & Lee, K.-S. (2026). Experimental and numerical investigation on the seismic performance of reinforced concrete columns retrofitted with basalt FRP composites. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02653-z

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02653-z

Keywords: basalt fiber, FRP, seismic retrofit, reinforced concrete columns, cyclic loading, ductility, energy dissipation, finite element analysis, disturbed stress field model, shear-controlled columns, flexure-controlled columns, earthquake engineering

The idea behind recycled-component concrete is deceptively simple. Instead of crushing waste concrete down into small recycled aggregates, or even into mid-sized concrete lumps of 60 to 300 millimeters, the new approach salvages entire concrete members, such as columns recovered through selective dismantling, and gives them only minimal processing: stripping off the rendering layer, cutting to length, and roughening the surfaces. These chunky recycled components are then placed directly inside the formwork of a new member, and fresh self-compacting concrete is cast around them. The result is a hybrid column in which nearly half the cross-section is made of old, already-cured concrete, complete with its original reinforcing bars and stirrups still intact inside.

The advantages over conventional recycling are substantial. Crushing waste into recycled aggregates still demands all the cement of ordinary concrete, so the carbon penalty of clinker production remains untouched. Recycled lump concrete improves on that by replacing some of the new mix, but casting quality limits lump replacement to about 35 percent, and the crushing process generates fine powder that is difficult to use. Recycled-component concrete, by contrast, can replace more than 50 percent of the new concrete, produces far less waste powder, and preserves the old reinforcement in usable condition, potentially trimming the amount of new steel required. Earlier studies in Europe had reused cut concrete slabs directly in new buildings, with one prototype floor system showing embodied carbon 80 to 94 percent lower than conventional concrete floors. But direct reuse runs into a stubborn problem: salvaged members rarely match the dimensions or strength grades their new positions demand. Casting new concrete around a recycled component elegantly dissolves that mismatch, because the surrounding mix absorbs any dimensional discrepancy and a stronger new mix can compensate for weaker old concrete.

What had never been tested, until now, was whether this hybrid configuration could survive the two brutal trials that matter most for columns: crushing axial compression and repeated cyclic earthquake loading. The concern was real. In a recycled-component concrete column, the old concrete sits as a concentrated block in the center of the section, surrounded by new concrete, creating a large, regularly shaped interface between the two generations of material. If that interface were to delaminate or slip under load, the whole concept would collapse, figuratively and literally. There was also a puzzle for the engineers’ calculators: the column contains two overlapping systems of stirrups, the new outer hoops and the old hoops locked inside the recycled component, and existing strength-prediction models, built for a single confinement system, simply did not apply.

To find out, the team fabricated nine square column specimens, 400 millimeters on a side and 1200 millimeters tall, for axial compression testing, seven of them recycled-component columns with a replacement ratio of 46 percent and two conventional references. Each recycled component was a 270 by 270 millimeter column, cut and roughened from a prefabricated 300 by 300 millimeter old column, its eight 12-millimeter longitudinal bars and 6-millimeter stirrups retained. The specimens were squeezed in a 15,000-kilonewton machine under displacement control, with strain gauges glued to both old and new stirrups to reveal how the two confinement systems shared the work. Seven more specimens, cantilever columns with a shear-span ratio of 3.375, were subjected to low-cycle reversed lateral loading under a constant axial load ratio of 0.4, mimicking the demands of a major earthquake.

The axial results were encouraging. During testing, no large-area delamination or spalling of new concrete from the recycled components occurred, confirming that the bond between old and new material held firm all the way to failure. The recycled-component columns carried somewhat lower peak loads than the references, from 7571 to 8339 kilonewtons against 8445 to 8648 kilonewtons, but the shortfall traced cleanly to the weaker old concrete, not to any interfacial weakness. Crucially, when the team raised the strength of the new concrete, specimen CR6 reached 8339 kilonewtons, nearly matching the 8445-kilonewton conventional reference, proving that a stronger surrounding mix can compensate for weaker salvaged material. Inclined-crossed stirrups, arranged in an X-pattern instead of conventional rectangular hoops, slightly increased capacity at the same steel quantity, and strain measurements showed they mobilized their confinement more effectively.

The seismic tests delivered the headline finding. Under reversed cyclic loading, the recycled-component columns and the conventional reference failed in the same characteristic way, with flexural cracks forming at the base, evolving into diagonal flexural-shear cracks, and culminating in concrete crushing within the plastic hinge region. Their hysteretic loops were similarly full, indicating strong energy dissipation, and their skeleton curves were nearly indistinguishable. Ductility coefficients ranged from 3.43 to 3.80, comfortably above the minimum of 3 required for reinforced concrete columns, and all but one specimen exceeded the 2 percent ultimate drift ratio demanded by Chinese seismic design codes. Remarkably, the recycled-component columns actually developed higher peak lateral loads than the conventional reference, reaching up to 370.2 kilonewtons against 343.9 kilonewtons, thanks to the stronger old concrete and the higher yield strength of the retained reinforcement. Incorporating a recycled component while slimming the new longitudinal bars from 18 and 16 millimeters down to 12 millimeters cost only 4 percent of ductility.

The experiments also delivered practical verdicts on construction details. Drilling post-installed rebars into the recycled components proved counterproductive under axial load, reducing peak capacity by 4.2 percent, apparently because the drilling introduced internal defects, and offering no seismic benefit either. Welded connectors between new and old stirrups improved ductility by only 4.7 percent, a gain judged too small to justify the cumbersome installation. The team’s recommendation is refreshingly economical: skip both. On the other hand, widening the spacing of the new stirrups cut the equivalent viscous damping coefficient by 17.6 percent and dropped one specimen below the drift-ratio requirement, so the confinement steel in the plastic hinge zone must not be skimped. Inclined-crossed stirrups emerged as the preferred arrangement, boosting energy dissipation by up to 8.6 percent, and their orientation relative to the loading direction made virtually no difference, freeing contractors from fussy placement.

Finally, the researchers closed the analytical gap. They divided the hybrid cross-section into three regions: unconfined cover concrete, concrete confined by the new stirrups alone, and the central old concrete squeezed simultaneously by both stirrup systems, then summed the regional contributions along with the old and new longitudinal steel. The resulting formula predicted the measured axial capacities of all nine specimens with a maximum error of just 8 percent, and only 5 percent for the conventional columns, showing that the dual-confinement model works across the spectrum. Taken together, the study offers the first technical foundation for columns that swallow nearly half their volume in salvaged concrete and part of their steel in salvaged reinforcement, while standing up to earthquakes as reliably as their all-new counterparts. In a construction industry desperate to cut its carbon ledger, that is a result worth building on.

Subject of Research: Axial compressive and seismic performance of recycled-component concrete columns made from reused waste concrete members

Article Title: Axial compressive behavior and seismic performance of recycled-component concrete columns

Article References: Li, Y., Wu, B., Zhang, H., & Wang, F. (2026). Axial compressive behavior and seismic performance of recycled-component concrete columns. Case Studies in Construction Materials, 25, Article e06453. https://doi.org/10.1016/j.cscm.2026.e06453

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06453

Keywords: recycled-component concrete, recycled concrete, construction and demolition waste, seismic performance, axial compression, confinement, stirrups, carbon reduction, sustainable construction, cyclic loading, structural engineering, circular economy

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

Image Credits: AI Generated

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

The study, led by Zhaoxun Yuan of Guangdong Polytechnic of Water Resources and Electric Engineering together with Guiqiang Hao, Junxian Zhao of South China University of Technology, Wei Han, and Jiulin Bai of Chongqing University, focuses on a seismic-resilient connection for precast concrete moment frames that the same research group had previously proposed and tested. The concept is elegant: instead of allowing an earthquake to crack and crush the concrete beam itself, the design deliberately concentrates all the damage into sacrificial steel components that can be unbolted and swapped out after a quake, much like replacing a blown fuse in an electrical panel.

The connection is installed at the splice location along the beam — the point that corresponds to the inflection point of the beam under gravity loading, where bending demands are naturally lowest. At the top of the beam, vertical steel plates known as shear tabs are embedded across the splice section and extend into the adjacent precast beam segments. These tabs perform two simultaneous jobs: they act as the rotational center of the connection, allowing the beam ends to rock and rotate under seismic motion, and they transfer shear forces between the beam segments. Shear studs welded onto the embedded portions of the tabs help anchor the forces into the surrounding concrete. At the bottom of the beam, two buckling-restrained braces, or BRBs, serve as the replaceable fuse. A BRB is a steel yielding core wrapped in a restraining mechanism that prevents the brace from buckling in compression, allowing it to yield repeatedly in both tension and compression and dissipate seismic energy in a stable, predictable way — a technology with a well-documented track record in steel braced frames.

Previous experimental work by the team had validated the broader damage-control philosophy of the system: the fuses yield, the concrete stays essentially intact, and the building snaps back into service with only a quick component replacement required. But a critical question remained unanswered. The shear tabs are not simple elements — they simultaneously carry axial forces, shear forces and bending moments between the beam segments while themselves rotating as the connection rocks. If a designer sizes the tabs incorrectly, they can either fail to transmit the forces reliably or fracture prematurely under the relentless back-and-forth of cyclic earthquake loading. Before this new study, no systematic design criteria existed for these components, leaving the innovative connection without an engineering pathway from proof-of-concept into actual building codes and practice.

To close that gap, the researchers constructed detailed finite element models of the connection, carefully calibrated against the earlier test data so that the simulations reproduced the observed behavior with confidence. With a validated digital replica in hand, they used it as a virtual laboratory to dissect the force transfer mechanism inside the shear tabs — mapping how axial, shear and flexural demands flow through the steel plates and into the welded shear studs and surrounding concrete. Understanding this internal load path was the essential prerequisite for writing any rational design rule, because a design criterion is only trustworthy if it reflects what the component is actually experiencing, rather than what an idealized diagram suggests.

Informed by that mechanism, the team then formulated two complementary families of design criteria. The first are strength criteria, which ensure that the shear tabs and their stud groups are strong enough to transmit the full complement of forces demanded of them — including the capacity of the replaceable BRB fuses, which are intentionally sized to yield before anything else in the connection. The second are damage-control criteria, which protect the tabs themselves from premature fracture under cyclic loading, guaranteeing that the replaceable fuses remain the sacrificial elements while the permanent load-transfer hardware stays elastic and intact through the design earthquake. In other words, the design ensures the right components break — and only the ones that were meant to.

The researchers then put these proposed design methods through their paces. They generated families of finite element models in which the cross-sectional dimensions of the shear tabs, the height-to-thickness ratios of the plates, and the arrangements and diameters of the welded shear studs were varied systematically. The validation confirmed that the new design equations reliably bounded the behavior across this range of geometries, giving engineers a defensible basis for proportioning real connections rather than relying on trial and error or conservative guesswork. The numerical campaign, illustrated in the paper by more than twenty figures of stress distributions, failure modes and performance comparisons, effectively converts the earlier experimental proof-of-concept into a designable, code-ready structural system.

The broader context makes the work timely. Precast concrete construction — in which beams, columns and walls are factory-cast and assembled on site — offers speed, quality control and reduced labor costs, which is why it dominates industrial construction in many seismically active regions. Yet earthquake after earthquake has exposed the vulnerability of poorly detailed precast connections: the 2012 Emilia earthquake in Italy, the 1999 Turkey earthquake and the 1994 Northridge earthquake all produced characteristic connection failures in precast industrial and commercial buildings, often collapsing roofs even when the rest of the structure survived. Modern seismic design therefore treats the connection, not the member, as the critical link, and decades of research have produced a wide repertoire of alternatives — wet cast-in-place joints, prestressed self-centering systems, slit dampers, friction devices and replaceable energy-dissipation bars — each with its own trade-offs in cost, complexity and recoverability.

What distinguishes the shear-tab-plus-BRB-fuse concept is the way it decouples the two functions that conventional connections force into a single overloaded zone. The steel tabs handle the geometric and force-transfer duties while remaining elastic; the braces handle the energy dissipation and accept the damage. Because the fuses sit at the beam inflection point rather than at the column face, the connection also avoids stressing the critical beam-column joint region, which is notoriously difficult to repair. The result, validated in the team’s earlier experiments, is a frame that experiences minimal residual drift after a design-level earthquake — meaning doors still close, partitions stay uncracked, and the building can be occupied while a small crew bolts in new fuses over a weekend.

The new design methodology for the shear tabs removes what was arguably the last major obstacle to practical implementation of this system for precast concrete frames. With strength and damage-control criteria now validated numerically across a wide parameter space, structural engineers have a complete, documented design procedure for the connection’s every component. The research was funded by the National Natural Science Foundation of China, the Guangdong Basic and Applied Basic Research Foundation, and the Guangdong Provincial Key Laboratory of Modern Civil Engineering Technology. As cities in seismic regions continue to expand with precast construction, designs of this kind point toward a future in which the question after a major earthquake is no longer whether a building can be saved, but simply how quickly the spare parts can be installed.

Subject of Research: Design of shear tabs in seismic-resilient precast concrete moment connections with replaceable buckling-restrained brace fuses

Article Title: Seismic resilient precast concrete moment connections with top shear tabs and bottom replaceable fuses: numerical study on shear tabs detailing

Article References: Yuan, Z., Hao, G., Zhao, J., Han, W., & Bai, J. (2026). Seismic resilient precast concrete moment connections with top shear tabs and bottom replaceable fuses: numerical study on shear tabs detailing. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02666-8

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02666-8

Keywords: seismic resilience, precast concrete, moment frame, shear tabs, replaceable fuse, buckling-restrained brace, finite element analysis, damage-control design, beam-column connection, earthquake engineering, force transfer mechanism, cyclic loading