The target of the investigation was calcium silicate hydrate, or C-S-H, the binding phase that gives cement its strength. C-S-H is a layered material: stiff silicate chains form sheets that are stacked and held together by water molecules and calcium ions. That layered architecture is both a blessing and a curse. Within the sheets, the silicon-oxygen framework is extremely rigid, but between the sheets the material is comparatively soft and prone to sliding and separation. This anisotropy means that C-S-H — and therefore concrete — behaves very differently depending on the direction of the load, and it is precisely at these vulnerable interlayer regions that vibration damage tends to begin.

To probe how polymers could shore up these weak zones, the team built realistic atomistic models of C-S-H with a calcium-to-silicon ratio of 1.67, matching ordinary Portland cement, and inserted three representative polymers into the interlayer spaces: polyethylene (PE), polyvinyl alcohol (PVA), and polybutadiene (PB). These three were chosen deliberately because they differ in one crucial chemical respect. PE and PB are essentially nonpolar hydrocarbon chains, while PVA is decorated with abundant hydroxyl groups — the same -OH chemistry that makes water sticky. The polymer content was kept between roughly 1 and 5 percent by weight, consistent with what is used in real damping-modified concretes.

The simulations themselves were ambitious. Using the LAMMPS package with the ClayFF and CVFF force fields, the researchers first calibrated their model against known experimental and computational values, confirming that the tensile strength, elastic modulus, and shear modulus of their C-S-H matched earlier studies. They then subjected both pristine and polymer-modified C-S-H to two kinds of cyclic shear loading: constant strain-rate cycling and sinusoidal loading inspired by dynamic mechanical analysis, the standard laboratory technique for measuring viscoelastic damping. Each condition ran for 72 full loading cycles, with simulations lasting up to 46 nanoseconds — an enormous investment of computational time at the atomic scale.

The mechanical results were encouraging but nuanced. Adding polymers barely changed the tensile strength of C-S-H along its strong direction, and left shear strength along the stiff XY plane essentially untouched, because that direction is governed by the intrinsic silicate framework. But along the weak interlayer direction, the story changed dramatically. Polymer chains acted as molecular bridges spanning adjacent C-S-H sheets, raising shear strength in the XZ direction and — critically — providing residual strength after failure. When unmodified C-S-H was pulled apart along its weak axis, it fractured completely; when polymer was present, the broken pieces remained tethered together, delaying catastrophic failure and increasing the material’s ductility and toughness. Dosage mattered too: around 2.5 to 2.7 percent by weight gave the best tensile reinforcement, while 4.9 to 5.3 percent maximized shear enhancement.

The atomic-scale analysis explained why. Radial distribution functions showed that polymers sitting on the (010) surface of C-S-H readily form hydrogen bonds with interlayer water molecules at distances of roughly 2 to 3 angstroms, whereas polymers on the (001) surface form almost none. Hydrogen bond counting during deformation revealed that these bonds are the workhorses of interlayer cohesion: under tension along the weak direction, the hydrogen bond network collapses, but under shear it largely survives, allowing energy to be dissipated gradually through sliding and rearrangement rather than sudden breakage. Among the three polymers, PVA formed by far the most hydrogen bonds with C-S-H, thanks to its hydroxyl-rich chemistry, giving it the strongest interfacial grip.

When the team turned to damping — the heart of the study — the findings became genuinely striking. Under cyclic shear, plain C-S-H showed equivalent viscous damping of about 0.099 along the XY direction and 0.096 along XZ. After polymer modification, damping along the stiff XY direction rose only modestly, but along the weak XZ direction it jumped substantially: PE increased the loss factor by about 10.1 percent, PB by 11.3 percent, and PVA by 13.7 percent. Even more interesting, polymer modification flipped the anisotropy. Before modification, C-S-H dissipated more energy along its strong plane; after modification, the formerly weak interface became the better energy-dissipating interface. In effect, the polymers converted concrete’s structural liability into a functional asset.

The viscoelastic measurements reinforced this picture. Under sinusoidal loading, both the storage modulus, which measures elastic energy storage, and the loss modulus, which measures energy converted to heat, increased after polymer modification — with PVA again showing the largest gains. The non-zero phase shift between applied strain and resulting stress confirmed that C-S-H is genuinely viscoelastic, and the polymers widened that phase lag, particularly along the interlayer direction. The mechanism is elegant: hydrogen-bonded polymer bridges increase interlayer friction and enable controlled structural rearrangement during each cycle, so vibrational energy that would otherwise drive crack growth is instead bled away as heat, cycle after cycle.

The implications for infrastructure are considerable. A concrete that can dissipate vibration without sacrificing strength could extend the service life of bridges, tunnels, seismic-resistant buildings, and industrial facilities, while reducing maintenance costs and material consumption. The study is careful to acknowledge its limits: each simulation condition was run once, the nanosecond-scale loading frequencies far exceed real structural frequencies, and features like aggregates and heterogeneous hydration products are absent from the models. The authors frame their results as molecular-level guidance rather than engineering predictions, and call for experimental dynamic mechanical analysis and multiscale modeling to validate the mechanism at full scale. Still, the core insight stands: by choosing polymers with the right hydrogen-bonding chemistry — PVA chief among them — and orienting them within cement’s weakest layers, engineers may one day design concrete that doesn’t just resist vibration, but quietly swallows it.

Subject of Research: Molecular mechanisms of polymer-induced damping enhancement in calcium silicate hydrate

Article Title: Hydrogen-bond-mediated damping enhancement in polymer-modified calcium silicate hydrate

Article References: Hydrogen-bond-mediated damping enhancement in polymer-modified calcium silicate hydrate. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: calcium silicate hydrate, molecular dynamics, hydrogen bonds, polyvinyl alcohol, damping, cement, viscoelasticity, concrete, interlayer sliding, energy dissipation, C-S-H, infrastructure

In a study published in the Journal of Applied Physics, a journal of the American Institute of Physics, the researchers describe a metastructure built from water-filled aluminum eggshells arranged in an array and sandwiched between two aluminum impact plates. The work, authored by Yuxin Wang, Yuqing Liu, and Hao Li, was released on September 8, 2026, and presents both simulations and 3D-printed test articles subjected to hypervelocity impact conditions. The results suggest that the humble eggshell, when organized collectively, offers protection properties that individual shells could never deliver on their own.

It may seem counterintuitive to turn to eggshells as a blueprint for strength. A single eggshell breaks easily under a local force, which is precisely why the idea appears to defy intuition. Yet the researchers argue that natural biological structures have evolved, over long periods of adaptation, to demonstrate excellent energy absorption performance, and that the secret lies not in any individual shell but in how the shells behave as a group. When the water-filled aluminum eggshells are placed blunt side down in an array between two aluminum plates, the mechanical response to an impact changes fundamentally.

According to Wang, a single shell fails readily when a concentrated load is applied, but the array operates on an entirely different principle. The cooperative deformation of the eggshell units transforms a localized impact load into distributed energy dissipation across the entire metastructure. Rather than one point bearing the full brunt of a strike, the energy from an impact gradually spreads through the material, allowing each shell to sequentially collapse and deform in turn. This staged failure absorbs the kinetic energy of a projectile far more effectively than a monolithic plate, which must absorb the same energy across a much smaller effective volume of material.

The water inside each shell plays a critical supporting role. Under high-impact loading, the water sloshes violently within the shell cavity, and that internal motion suppresses the propagation of impact waves through the structure. The interaction between the fluid and the surrounding aluminum shell significantly reduces and dissipates the energy delivered by the strike, effectively turning the fill liquid into a dynamic damping medium. In effect, each eggshell is both a deformable crumple zone and a fluid-filled shock absorber, and the array multiplies those effects across the protected area.

To quantify the benefit, the team compared several configurations through 3D printing and computer simulations: bare aluminum plates, water-filled aluminum spheres sandwiched between aluminum plates, and the eggshell-based metastructures. The sandwiched, water-filled eggshell design performed best of all. It withstood high loads and reduced the velocity of an impact projectile by nearly 65 percent, a striking margin compared with the 51 percent reduction achieved by aluminum plates on their own. The gap between those figures represents, in practical terms, the difference between a projectile that still carries dangerous residual energy and one that has been largely robbed of its ability to penetrate.

Geometry mattered as much as composition. Among the various possible eggshell orientations tested, the metastructure patterns in which the eggs were placed upright, with their small end contacting the top plate, proved the most effective at defeating incoming projectiles. That orientation presumably optimizes the sequence of shell collapse and the distribution of loads through the array, though the researchers emphasize that the precise mechanics are still being mapped. The findings underline a broader principle in modern materials science: in architected or metamaterial structures, the arrangement of identical building blocks can be as decisive as the material they are made from.

The implications for spacecraft design are considerable. Traditional Whipple shields and multi-wall bumpers protect satellites and crewed vehicles by shattering incoming debris, but they add mass, and mass is the single most expensive commodity aboard any launch. A bio-inspired metastructure that dissipates energy through coordinated deformation and fluid damping could, once optimized, offer lightweight shielding panels with superior performance per kilogram. The researchers note that before such material can be flown, its geometry and filling must be further optimized and impact-tested under realistic conditions.

That optimization work is already underway. The team is currently refining the thickness of the aluminum eggshells, their aspect ratio, and their layout within the array to improve the material’s protective energy absorption. Each of these parameters influences how the shells buckle, how the water responds to the strike, and how efficiently the load is shared among neighboring units. The interplay is complex, which is why the combination of physical 3D printing and numerical simulation is central to the research program, allowing the group to explore design space far faster than testing alone would permit.

Beyond the immediate application, the study is part of a growing movement in engineering that treats evolution as a design consultant. Nature has spent hundreds of millions of years solving problems of impact, load distribution, and energy management in shells, bones, and honeycombs, and researchers are increasingly translating those solutions into synthetic architected materials. Wang expressed hope that the work will attract more attention to bio-inspired protective structures and demonstrate that bionic, lightweight metastructures are a promising route for hypervelocity-impact protection. If eggshell-inspired panels eventually ride into orbit on satellites, telescopes, or crewed vehicles, the shield that keeps them safe will owe its elegance to a design older than any civilization: the humble egg, reinterpreted in aluminum and water for the debris-strewn frontier of low Earth orbit.

Subject of Research: Eggshell-inspired water-filled aluminum metastructures for hypervelocity-impact spacecraft shielding

Article Title: Eggshells: Next-generation spacecraft protection

Article References: Eggshells: Next-generation spacecraft protection. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: space debris, eggshell metastructure, hypervelocity impact, bio-inspired materials, aluminum shielding, water-filled shells, energy dissipation, spacecraft protection, Journal of Applied Physics, Dalian University of Technology, architected materials, orbital debris mitigation

Precast concrete construction has become a cornerstone of building industrialization because it offers rapid assembly, easier quality control, and a smaller environmental footprint than conventional cast-in-place methods. Yet the beam-column joints that tie these structures together remain a persistent engineering challenge. These regions experience some of the most complex stress states in an entire frame, transferring and distributing internal forces while holding the structure together during violent ground shaking. In traditional precast joints, columns are typically spliced with grouted sleeves or grouted lap splices, techniques that demand exceptional workmanship on site. Incomplete grouting is a common defect, and the story-by-story assembly process requires extensive temporary shoring that consumes space, prolongs construction, and accumulates installation errors.

To overcome these shortcomings, the research team led by Xiao-Ran Wang and He-Tao Hou of Shandong University developed what they call a latticed steel-concrete composite, or LSCC, beam-column joint. The design builds on multi-story precast column technology, in which columns spanning two or three stories are cast as a single unit in the factory and hoisted into place, leaving the joint regions open for wet connections. The new joint fills these open regions with a latticed steel column connector fabricated from chords, batten plates, through-diaphragms, and welded cross stiffeners. Structurally, the chords behave like the longitudinal reinforcement of a conventional column, while the batten plates act as stirrups. Before the joint concrete is poured, the chords provide a continuous load-transfer path across the open joint zone, and the cross stiffeners restrain local distortion of the central latticed segment, giving the column temporary stiffness, integrity, and stability during transport and erection.

The connection to the beams is equally deliberate. Each precast beam end carries an embedded H-section steel connector, with the beam’s longitudinal reinforcing bars welded to the outer flange surfaces. During assembly, the H-section web is bolted to a connecting plate on the latticed column while the flanges are welded to the through-diaphragms. By substituting a latticed configuration for the solid-web steel components used in many earlier composite joints, the design cuts steel consumption substantially. The researchers calculated that an equivalent joint built with a solid-web steel tube would require roughly 103.7 kilograms of steel, whereas their latticed specimens needed only 84.6 and 79.8 kilograms, savings of 18.4 and 23.0 percent respectively.

To test the concept, the team fabricated three full-scale exterior joint specimens: a monolithic cast-in-place reference specimen and two precast LSCC specimens differing only in the width of the batten plates. The columns measured 450 by 350 millimeters in cross-section and stood 3,040 millimeters tall, while the beams were 350 by 250 millimeters and 1,780 millimeters long. All specimens used C30 concrete, Q355B steel plates, and HRB400 reinforcing bars, with weld lengths deliberately exceeding code minimums to improve reliability under cyclic loading. Each specimen was subjected to a constant axial load of about 1,050 kilonewtons on the column, representing a realistic design axial load ratio drawn from an actual multi-story precast frame project, while two hydraulic actuators pushed and pulled the beam tips in a low-cycle reversed cyclic protocol following Chinese seismic testing standards.

The differences in behavior were striking. The cast-in-place specimen developed dense diagonal cracks in the joint core, concrete spalling at the beam-column interface, and a pinched, inverse S-shaped hysteretic response caused by joint shear failure and bond-slip of the reinforcement. The two LSCC specimens, by contrast, showed minimal cracking in the joint core and plump, spindle-shaped hysteresis loops with negligible strength degradation. Their damage concentrated in the beam span, roughly 300 to 800 millimeters from the column face, rather than at the joint itself. In quantitative terms, the composite joints achieved peak loads 45.1 and 43.1 percent higher than the monolithic reference, ultimate displacements 56.6 and 50.8 percent greater, and cumulative energy dissipation at their ultimate states 135.8 and 115.6 percent higher. At a beam-tip displacement of 70 millimeters, their equivalent viscous damping coefficients exceeded the cast-in-place specimen’s by more than 80 percent.

Strain measurements and curvature analysis revealed the mechanism behind this superior performance. The embedded H-section steel stiffens the beam end so effectively that it relocates the plastic hinge, the zone of controlled flexural yielding where a structure is designed to absorb earthquake energy, away from the vulnerable joint region toward the beam span. In the cast-in-place specimen, the near-joint segment dominated flexural deformation, contributing up to 89 percent of the total displacement at large amplitudes. In the composite joints, once displacement exceeded 30 millimeters, the outer beam segments took over, with one segment alone contributing 54 percent of the deformation in a representative case. This more uniform curvature distribution allows a larger volume of material to participate in energy dissipation, which is precisely what seismic designers strive to achieve.

The team also built high-fidelity finite element models in ABAQUS, using the concrete damaged plasticity model and a reinforcement hysteretic constitutive law that accounts for bond-slip effects. The simulations reproduced the observed failure modes and damage evolution with peak-load errors below 7.1 percent, validating the modeling approach. A parametric study then explored design trade-offs. Thinning the latticed connector from 10 to 8 millimeters, a 7.4 percent steel saving, barely affected capacity, but reducing it to 4 millimeters cut peak load by 13.8 percent. Lengthening the embedded H-section steel increased capacity steadily, adding 6.9 to 13.5 kilonewtons of peak load for every 75 millimeters of additional length. Upgrading reinforcement from HRB400 to HRB500 or HRB600 raised peak capacity by 12.7 and 24.9 percent respectively, though the higher-strength bars showed slightly faster post-peak strength degradation due to their narrower plastic deformation margin.

The authors caution that their experimental conclusions rest on a single specimen per configuration, without repeated tests, so the reported improvements apply primarily to the dimensions, materials, and loading conditions investigated. Still, the implications are considerable. The study demonstrates that rational detailing, such as narrowing the batten plates in the joint core, can trim steel consumption by more than 5 percent with almost no loss of structural performance, and that a latticed connector can simultaneously solve the temporary-stability problems of multi-story precast columns and deliver seismic behavior that surpasses monolithic construction. If subsequent testing confirms these trends across a wider range of parameters, latticed steel-concrete composite joints could become an attractive option for resilient, rapidly assembled buildings in seismic zones worldwide.

Subject of Research: Seismic performance of novel prefabricated latticed steel-concrete composite beam-column joints

Article Title: Seismic performance of novel prefabricated latticed steel-concrete composite beam-column joints

Article References: Wang, X.-R., Hou, H.-T., Xia, H.-J., Zhang, B., Wang, D.-Y., & Liu, S.-Q. (2026). Seismic performance of novel prefabricated latticed steel-concrete composite beam-column joints. Results in Engineering, 32, Article 113355. https://doi.org/10.1016/j.rineng.2026.113355

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113355

Keywords: prefabricated concrete, beam-column joints, seismic performance, latticed steel connector, cyclic loading test, plastic hinge relocation, energy dissipation, finite element analysis, precast construction, steel-concrete composite, ductility, earthquake engineering

A new computational study by Nahid Mirizadeh and Mohammad Manafpour, published in Results in Engineering, offers the most systematic answer yet. Using high-resolution computational fluid dynamics simulations in the open-source OpenFOAM platform, the researchers modeled a classical hydraulic jump at an upstream Froude number of 7.5, a regime typical of high-velocity spillway flows, while systematically varying the inflow air concentration from zero to fifty percent. Crucially, unlike most previous investigations, which examined only a handful of aeration levels, the study anchored every aerated scenario against a rigorously validated non-aerated baseline, allowing the progressive influence of air to be isolated and quantified for the first time across the full practical spectrum.

The numerical framework itself represents a careful exercise in verification. The team solved the unsteady Reynolds-averaged Navier-Stokes equations for a two-phase air-water mixture, tracking the free surface with the Volume of Fluid method, in which a scalar indicator function defines the fractional volume of water in each computational cell. Three turbulence closures were tested against laboratory measurements from the University of Queensland, where a horizontal rectangular flume 3.2 meters long, half a meter wide, and 0.41 meters high produced a well-defined jump with a Reynolds number near 140,000. The standard k-epsilon model emerged as the clear winner, predicting the roller length with only a 3.7 percent deviation from experiment, while the SST k-omega and Realizable k-epsilon models erred by 20 and 30 percent respectively.

Validation extended well beyond a single metric. The simulated free-surface profile matched laboratory data with a coefficient of determination of 0.99 and a Kling-Gupta Efficiency of 0.94, a score classified as excellent. The predicted secondary flow depth agreed with the theoretical Bélanger equation to within two percent, and velocity fields reproduced the characteristic structure of the jump: a high-velocity jet hugging the bed, a recirculating roller of reverse flow above it, and a shear layer between the two where turbulence is generated most intensely. A grid convergence analysis using the Grid Convergence Index confirmed that results were mesh-independent, with roller length varying by less than 2.5 percent between medium and fine grids.

With the model proven trustworthy, the researchers turned to the central question, and the answer they found is strikingly nonlinear. For aeration levels up to thirty percent, the free-surface profile of the jump barely budges, with normalized water depths changing by less than 1.5 percent. But at forty and fifty percent air concentration, the surface elevation at the beginning of the transition zone rises by roughly six to nine percent compared with the non-aerated case. The mechanism is physical rather than mysterious: the entrained air increases the volume of the air-water mixture and locally reduces its bulk density, forcing the flow to occupy a greater depth. For dam designers, this means that heavily aerated spillways may demand deeper tailwater to keep the jump anchored in its stilling basin.

The roller, the churning recirculation zone that gives the hydraulic jump its characteristic white-water appearance, responds even more dramatically. Low to moderate aeration of up to twenty percent lengthened the roller by 11.6 percent, but at forty and fifty percent aeration the roller stretched by 26.9 and 34.9 percent respectively. The authors attribute this elongation to two-phase flow mechanisms that slow the decay of turbulence: compressible air bubbles temporarily store turbulent energy and release it gradually, while buoyancy-driven secondary currents disrupt the main vortical structures. Because the mean streamwise velocity remains largely unchanged, the turbulence simply lingers longer, and the roller must extend downstream to complete the dissipation of kinetic energy. Since roller length often dictates the required basin length and the placement of baffle blocks, this finding carries direct consequences for structural design.

The most reassuring result concerns cavitation protection, the original motivation for pre-aeration in the first place. In the non-aerated simulation, the void fraction near the channel bed within the jump body remains essentially zero, leaving the boundary vulnerable to cavitation erosion. At forty and fifty percent inflow aeration, however, near-bed air concentrations reach approximately seven and twelve percent, with the higher value comfortably exceeding the eight percent threshold long associated with cavitation mitigation in the classic experimental literature. The study also confirms that peak air entrainment occurs in the initial portion of the shear layer, where the violent vortices at the jump toe drag air bubbles downward and transport them along the high-shear interface, in agreement with decades of experimental observation.

The velocity and turbulence fields reveal further subtleties. High aeration levels increased near-bed streamwise velocity by three to six percent, apparently because bubble penetration and slip effects reduce effective friction at the wall. While moderate, this change implies altered shear stresses that could shift scour patterns within and downstream of the stilling basin. Turbulent kinetic energy, meanwhile, peaked at the jump toe and concentrated in the shear layer, climbing by 18.3 percent at fifty percent aeration to reach approximately 2.76 square meters per second squared. Intriguingly, the normalized turbulence intensity first held steady, then rose sharply at thirty to forty percent aeration, and finally dropped at fifty percent, because the increase in maximum velocity outpaced the growth in turbulent fluctuations. The authors caution that RANS closures may underrepresent large-scale rotational eddies in highly aerated regions, suggesting that large-eddy simulation will be needed to fully resolve these structures.

Perhaps the most counterintuitive finding is what did not change: overall energy dissipation. Across the entire range of inflow air concentrations from zero to fifty percent, computed energy losses varied only between 63 and 64 percent, compared with 64.8 percent for the laboratory reference case. Because most of the entrained air is released downstream of the jump, the tailwater depth and velocity remain nearly identical to the non-aerated case, and the small residual differences stem mainly from variations in initial flow depth. This echoes earlier experimental work reporting less than two percent variation in dissipation between moderate aeration levels, and it means that pre-aeration delivers cavitation protection without sacrificing the jump’s core job of destroying excess kinetic energy.

Taken together, the results sketch a threshold-type picture of aerated hydraulic jumps that engineers can act on directly. Aeration up to twenty percent produces only minor hydraulic modifications, making it a low-cost, low-risk option. At forty percent and above, the benefits of robust cavitation protection arrive alongside measurable costs: deeper flow, rollers up to a third longer, higher near-bed velocities, and elevated turbulence that could increase dynamic loads on basin linings. The authors argue that these trade-offs should be explicitly built into tailwater calculations, basin dimensioning, and scour assessments for chute spillways and stilling basins operating at high Froude numbers. They also acknowledge the study’s limitations, including its reliance on RANS turbulence modeling, a two-dimensional idealization, and a single Froude number, and they call for future work spanning wider flow regimes, prototype-scale field validation, and design aids that translate these quantitative trends into practical engineering guidelines. For the dams that hold back the world’s rivers, even a few well-placed bubbles may prove to be the difference between a structure that endures and one that slowly crumbles.

Subject of Research: Effects of upstream flow aeration on two-phase hydraulic jump dynamics in rectangular channels using CFD simulation

Article Title: Progressive effects of upstream flow aeration on two-phase hydraulic jump dynamics in rectangular channels: a CFD investigation

Article References: Mirizadeh, N., & Manafpour, M. (2026). Progressive effects of upstream flow aeration on two-phase hydraulic jump dynamics in rectangular channels: a CFD investigation. Results in Engineering, 32, Article 113234. https://doi.org/10.1016/j.rineng.2026.113234

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113234

Keywords: hydraulic jump, CFD, OpenFOAM, pre-aeration, cavitation, stilling basin, spillway, two-phase flow, Volume of Fluid, turbulence, roller length, energy dissipation

The material at the center of the research is the thin spray-on liner, or TSL, a flexible support layer sprayed onto rock surfaces in layers typically 5 to 20 millimeters thick. Unlike rigid shotcrete, a well-designed TSL penetrates micro-fractures in the rock during application, binds fragmented rock into a continuous load-bearing composite, and forms a shallow load-bearing arch in partnership with the surrounding ground. Commercial TSLs fall into two families: latex-based products, which are highly ductile but prohibitively expensive, and polymer-modified cementitious liners, which are cost-effective but historically too stiff and brittle for the demands of deep tunnels with large deformation. The research team, led by Xing Gao and Jinlong Teng, set out to close that performance gap with fiber reinforcement.

The researchers formulated a two-component cementitious TSL from white cement, fine quartz sand, vinyl acetate-ethylene copolymer powder, and various admixtures, then added chopped glass fibers at four dosage levels: 0, 0.5, 1.0, and 1.5 percent of the powder mass. The fibers themselves were slender, 6-millimeter strands with a tensile strength of 555 megapascals and an aspect ratio of nearly 484. Specimens were cast, cured for seven days under controlled temperature and humidity, and then subjected to uniaxial compression and three-point bending tests, each group run with six parallel samples to ensure statistical reliability.

What distinguishes this study from earlier work is its insistence on measuring toughness across the entire loading-to-failure process, not just at the peak. Using an energy-based framework rooted in the first law of thermodynamics, the team partitioned the compressive response of each specimen into four stages: compaction, elastic deformation, stable crack expansion, and post-peak accelerated crack growth. By integrating the stress-strain curves, they separated the total input energy into stored elastic energy and dissipated energy, the latter consumed by crack closure, crack propagation, and frictional sliding on fracture surfaces. From this accounting they derived a pre-peak toughness index, a post-peak toughness index normalized against the unreinforced material, and a coupled comprehensive compressive toughness index formed by their product.

The results traced a clear arc of improvement followed by decline. Compressive strength rose from 12.64 megapascals in the unreinforced liner to a peak of 14.75 megapascals at 1 percent fiber content, then fell back to 12.85 megapascals at 1.5 percent. Energy absorption followed the same pattern, peaking at 317.9 kilojoules per cubic meter at the 1 percent dosage. Failure modes evolved in parallel: the unreinforced material split with two longitudinal tensile cracks and shed fragments, the 0.5 percent mix developed a combined tension-shear crack pattern, the 1 percent mix failed through a single diagonal shear band while remaining intact, and the 1.5 percent mix displayed a complex tri-directional shear crack network with pronounced ductile dilation. The comprehensive compressive toughness index nearly doubled, climbing from about 0.48 to 0.93 across the fiber range.

Flexural testing told an equally striking story. Flexural strength peaked at 8.47 megapascals at 1 percent fiber content, a 77.2 percent gain over the unreinforced matrix, while fracture energy surged more than fivefold, from 408.53 newtons per meter to 2189.69 newtons per meter at the highest fiber dosage. The flexural toughness ratio climbed steadily from 0.22 to nearly 0.68. Crack lengths in bending shrank progressively from 37.5 millimeters in the unreinforced beams to 27 millimeters in the most heavily reinforced ones, and the post-peak load response shifted from a cliff-like brittle drop to a gentle stress-tailing curve sustained by the dense fiber network bridging the main crack.

To unify these findings, the team constructed a comprehensive toughness index R that multiplies the pre-peak compressive index, the post-peak compressive index, and the flexural toughness ratio. The multiplicative, non-compensatory design ensures that weakness in any single dimension drags down the overall score. The index rose from roughly 0.10 to 0.63 as fiber content increased, and unlike the flexural-to-compressive strength ratio, which peaked at 1 percent and then declined, R kept rising because it captured the continuously improving post-peak energy dissipation. Independent validation against failure modes and crack patterns confirmed that R tracked actual toughness evolution more faithfully than strength-based measures alone.

Beneath the macroscopic numbers lies a more complicated microscopic story, one the authors describe as a competition between positive toughening and negative damage. Microscopy of fracture surfaces and helium pycnometry revealed that fibers hinder the migration and escape of air bubbles during mixing and compaction, a cofferdam effect that traps pores near fiber intersections and, at high dosages, produces fiber agglomeration and continuous defect zones. Porosity fluctuated in a rise-fall-rise pattern, reaching its lowest value of 10.54 percent at the 1 percent dosage, where the fiber network achieved its optimal spatial arrangement. This pore evolution explained the ladder-like drop in elastic modulus and the sharper strength penalty under bending, which is far more defect-sensitive than compression: flexural strength fell 25.9 percent at 1.5 percent fiber content, against only 13.2 percent for compressive strength.

Field-emission scanning electron microscopy exposed the three-stage energy dissipation mechanism that gives the material its resilience. First, hydration products, including calcium silicate hydrate gel, calcium hydroxide platelets, and polymer films, tightly encapsulate the fiber surface, forming a dense interfacial transition zone that debonds under load and converts mechanical energy into debonding work. Second, the debonded fiber slides against rough matrix pore walls, dissipating energy as frictional heat during crack opening. Third, when the stress on a bridging fiber exceeds its ultimate tensile strength, the fiber fractures in a flush, brittle break, completing the final stage of energy absorption. Crucially, the team found that this positive toughening mechanism dominates over the pore-related damage, which mainly erodes strength rather than toughness.

The practical upshot is a clear design recommendation: 1 percent glass fiber content delivers the best overall balance of strength, toughness, cost, and pumpability, since higher dosages raise the risk of pipe clogging during spraying. The authors caution that their results come from laboratory-cast specimens, and that fiber orientation, moisture migration, and substrate constraint in real sprayed layers may shift performance, so field validation on rock surfaces remains necessary. Even so, the study delivers something the field has lacked: a quantitative, multi-scale framework that links fiber dosage, pore structure, interfacial micromechanics, and full-process energy dissipation. For engineers contending with squeezing ground and violent rockbursts in ever-deeper tunnels, that framework turns a promising flexible liner into a rationally designed one.

Subject of Research: Multi-scale toughness evaluation and fiber toughening mechanisms in cementitious thin spray-on liners for deep tunnel support

Article Title: Study on multi-scale toughness evaluation and toughening mechanism of fiber-reinforced cementitious thin spray-on liner

Article References: Gao, X., Teng, J., Feng, J., Liu, Y., Ma, L., Bu, X., & Cheng, L. (2026). Study on multi-scale toughness evaluation and toughening mechanism of fiber-reinforced cementitious thin spray-on liner. Case Studies in Construction Materials, 25, Article e06593. https://doi.org/10.1016/j.cscm.2026.e06593

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06593

Keywords: thin spray-on liner, glass fiber reinforcement, cementitious composites, tunnel support, toughness evaluation, energy dissipation, fracture energy, porosity, fiber-matrix interface, deep underground engineering, polymer-modified cement, flexural strength

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

The research team, led by Teng Li and Yongqiang Hou of Anhui University of Science and Technology, prepared cylindrical specimens from a mixture of crushed coal gangue, Class II fly ash, and ordinary Portland cement in a mass ratio of 5:2:1:2, yielding a slurry with a solid mass concentration of 80 percent. The gangue came from the Xieqiao Coal Mine operated by Huaihe Energy Group and was graded into coarse, medium, and fine aggregate fractions of 35, 35, and 30 percent respectively. After 24 hours of initial setting, the specimens were demoulded and cured for 28 days in a programmable chamber held at 95 percent relative humidity and one of four temperatures: 20, 30, 40, or 50 degrees Celsius. Three parallel specimens were tested per condition to average out experimental scatter.

Under uniaxial compression in a displacement-controlled electronic universal testing machine, every specimen told the same four-part story: an initial compaction stage in which pre-existing pores and microcracks close, an approximately linear elastic stage, a concave-down yield stage where irreversible deformation accumulates, and a post-peak failure stage marked by flaking and blocky spalling. But the numbers behind those stages shifted dramatically with temperature. Compaction stress climbed from 0.4219 megapascals at 20 degrees to 1.4195 megapascals at 40 degrees, an increase of roughly 236.5 percent, before falling back to 0.9605 megapascals at 50 degrees. Peak stress followed the same arc, rising from 1.6645 megapascals at 20 degrees to a maximum of 5.682 megapascals at 40 degrees, then dropping 32.4 percent to 3.841 megapascals at 50 degrees.

The elastic modulus, a measure of the material’s stiffness, traced the same non-monotonic curve with an even tighter fit to a quadratic function. It rose from 239.86 megapascals at 20 degrees to 609.99 megapascals at 40 degrees, a gain of 154.4 percent, then fell 31.2 percent at 50 degrees. Interestingly, stiffness and strength did not respond to temperature in perfect lockstep. The modulus gained less than strength during the warming phase but lost about the same proportion during the overheating phase, suggesting that stiffness reflects the initial rigidity of the material skeleton and responds sluggishly to pore filling, while strength depends more directly on the cementitious bonds formed by hydration products and is therefore more sensitive to accelerated hydration.

The mechanism behind the reversal at 50 degrees is a classic case of too much of a good thing. Below 40 degrees, elevated temperature accelerates cement hydration, generating more calcium silicate hydrate gel and needle-like ettringite crystals that fill pores, bind the gangue aggregate, and densify the structure. Above that threshold, hydration races ahead so quickly that products cluster unevenly, encapsulating aggregates in some regions while thermal stresses from the exothermic reaction spawn fresh microcracks. Scanning electron microscopy at 5000 times magnification made the contrast vivid: at 20 and 30 degrees the 28-day microstructure remained loose and porous, with intact spherical fly ash particles showing limited pozzolanic activity, while at 50 degrees the fly ash was tightly enveloped in a thick hydration layer that looked dense but lacked strong chemical bonding, producing what the authors call a dense-but-not-strong weak interfacial structure.

Energy analysis added a thermodynamic dimension to the picture. Applying the first law of thermodynamics, the team split the mechanical work done on each specimen into releasable elastic strain energy and dissipated energy consumed by crack growth and friction. At the peak stress point, total strain energy density peaked at 40 degrees with 36.2804 kilojoules per cubic meter, alongside 26.4641 kilojoules per cubic meter of elastic energy and 9.8163 kilojoules per cubic meter of dissipated energy. All three indices rose and then fell with temperature, confirming that the 40-degree material could both store and dissipate the most energy. Beyond that point, brittleness increased, crack propagation shifted from gradual to sudden coalescence, and the dissipated energy at the peak collapsed to 2.7745 kilojoules per cubic meter, nearly the same as the room-temperature value.

The failure modes themselves transformed with heat. At 20 degrees, specimens failed in tension along semi-penetrating axial cracks with limited secondary fracturing. At 30 and 40 degrees, the failure shifted to a tensile-shear mixed pattern with dense, interconnected crack networks that broke the material into bulking blocks. At 50 degrees the fragmentation was most severe, with pronounced lateral dilatancy and intense bulking. In practical terms, hotter-cured backfill does not merely weaken; it fails more suddenly and more violently, a distinction that matters for engineers assessing the load-bearing stability of pillars of waste backfill supporting deep mine roofs.

Perhaps the study’s most technically ambitious contribution is a new piecewise damage constitutive model. Building on the Drucker-Prager strength criterion and assuming a power-law statistical distribution of micro-element strength, the model treats the initial compaction stage as a defect-closing phase without damage propagation and captures the elastic and yield stages with a statistical damage variable corrected by a coefficient accounting for the residual load-bearing capacity of failed elements. When fitted to the experimental curves, the model tracked the pre-peak stress-strain behavior closely at all four temperatures. Its shape parameter told a striking story of its own: it stayed relatively stable from 20 to 40 degrees but jumped sharply at 50 degrees, indicating that thermal microcracks had prematurely eliminated the weakest elements and left the survivors with a homogenized strength distribution, the statistical fingerprint of thermally induced embrittlement.

For the mining industry, the implications are concrete. As backfill operations descend into hot deep seams, the ambient rock temperature becomes a design variable rather than a background detail. The study identifies 40 degrees as the optimal curing temperature for this gangue-fly ash-cement system, where a structural strengthening mechanism gives way to a thermal damage deterioration mechanism. Curing regimes and mix proportions can now be tuned to the geothermal conditions of a specific mine, and the temperature-sensitive model parameters offer a way to predict pre-peak mechanical behavior without waiting for field failures. The authors note that their model covers only the pre-peak regime, since post-peak behavior is dominated by frictional sliding along macroscopic fracture surfaces, and they plan to extend the framework with discrete element methods and acoustic emission monitoring.

There is also a broader environmental resonance. Gangue cemented backfill simultaneously disposes of coal waste and restores structural integrity to mined-out voids, making it a cornerstone of green mining initiatives. Understanding exactly how temperature governs its long-term stability means that the mountains of gangue stacked around coal mines can be converted into reliable underground support even in the hottest, deepest workings. What this study makes clear is that the relationship between heat and strength is not a straight line but a curve with a summit, and knowing where that summit lies could determine whether the backfill holding up a kilometer of rock endures or crumbles.

Subject of Research: Effect of curing temperature on the mechanical properties, energy evolution, and damage behavior of gangue cemented backfill for deep coal mine backfilling

Article Title: Mechanical properties, energy evolution, damage characteristics of gangue cemented backfill under different curing temperatures

Article References: Li, T., Hou, Y., Yu, X., Xionggang, Z., Du, H., Wang, Y., & Zhang, X. Y. (2026). Mechanical properties, energy evolution, damage characteristics of gangue cemented backfill under different curing temperatures. Case Studies in Construction Materials, 25, Article e06589. https://doi.org/10.1016/j.cscm.2026.e06589

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06589

Keywords: gangue cemented backfill, curing temperature, coal mining, thermal damage, uniaxial compression, energy dissipation, damage constitutive model, hydration, fly ash, deep mines, brittle failure, elastic modulus

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 central idea is deceptively simple. In a force-displacement plot, one complete cycle of motion traces a loop through four quadrants: two where displacement and force share the same sign, and two where they oppose each other. The ENSFD is engineered to deliver substantial damping force only in the second and fourth quadrants, the unloading phases of the cycle, while remaining nearly passive during loading. Because the device never pushes back hard against the structure as it moves in the direction of the driving force, it does not increase the maximum damping force transmitted to the building. At the same time, the asymmetric resistance mimics the effect of negative stiffness, a property that, in structural dynamics, effectively lengthens the period of a structure and softens its response to ground motion. The result is a damper that reshapes the hysteresis loop rather than simply enlarging it, concentrating energy absorption where it does the most good and least harm.

To make this concept usable in engineering practice, the researchers needed a way to represent the nonlinear, half-cycle behavior of the damper with parameters that standard analysis tools can handle. They built a nonlinear single-degree-of-freedom model of the ENSFD and applied the method of slowly varying parameters, an analytical technique for deriving the steady-state response of systems whose properties change gradually over a cycle of motion. From this treatment they extracted equivalent linearization parameters, essentially a stiffness and a damping coefficient that capture the averaged effect of the device over a full oscillation. These equivalent parameters were then checked against direct time-history analysis, in which the full nonlinear equations are integrated step by step under recorded ground motions. The comparison confirmed that the simplified parameters reproduce the response accurately enough for design-level seismic analysis, giving engineers a practical bridge between an exotic nonlinear device and the linearized calculation methods embedded in building codes.

Turning the mathematics into hardware required a control system capable of recognizing, in real time, which phase of the motion cycle the structure is in. The team designed a semi-active ENSFD built around an STM32 microprocessor, a widely used embedded controller with enough speed and reliability for structural applications. The complete system has three cooperating subsystems: a signal acquisition system that measures the structural response, a control system that processes those signals and decides the operating state, and a variable friction execution system that adjusts the friction force accordingly. The controller must distinguish among loading, unloading, and the transitional moments when the direction of motion reverses, because the damper’s behavior differs fundamentally in each state. Getting this logic right is the difference between a device that dissipates energy selectively and one that degenerates into an ordinary friction damper.

The experimental program consisted of low-cycle reciprocating tests, the standard laboratory protocol for seismic devices, in which the damper is pushed back and forth through many cycles at controlled displacement amplitudes and frequencies. The measured hysteresis curves matched the theoretical expectations: the device provided substantial damping force during unloading while contributing little resistance during loading, producing the characteristic asymmetric loop that defines equivalent negative stiffness behavior. The three subsystems worked together effectively, with the controller making accurate judgments during loading, unloading, and the transitions between them. This is a notable achievement for a semi-active device, since misclassification of the motion state would corrupt the force profile and undermine the entire design rationale.

Beyond confirming the basic behavior, the tests revealed how the damper’s energy dissipation capacity depends on its operating conditions and internal parameters. The researchers found that energy dissipation is positively correlated with the loading displacement amplitude, which is intuitive, since larger strokes sweep out larger hysteresis loops, and positively correlated with the spring stiffness of the device’s internal components. It is negatively correlated with the loading frequency, meaning the damper absorbs somewhat less energy per cycle when driven faster. When the team ranked the influencing factors by their impact, the ordering was clear: loading amplitude mattered most, spring stiffness came second, and loading frequency had the least effect. For designers, this hierarchy is valuable because it indicates that the device’s performance is governed primarily by the seismic demand itself, with the tunable mechanical properties offering a secondary but meaningful degree of control.

The equivalent negative stiffness damping characteristics of the ENSFD serve two complementary functions. First, by effectively extending the structural period, the device shifts the building’s response away from the frequency content of the earthquake, reducing the accelerations transmitted into the superstructure. This is the same principle that underlies base isolation, but achieved here through a supplementary damping device rather than by modifying the isolation system itself. Second, the concentrated unloading-phase dissipation controls seismic responses without the penalty of increased maximum damping force that accompanies conventional dampers. The authors report that the equivalent parameters derived from their analytical treatment are suitable for engineering analysis, which means the device can be incorporated into standard response-spectrum and time-history workflows without requiring bespoke nonlinear modeling of every installation.

The study situates itself within a growing body of research on negative stiffness and semi-active seismic protection. Negative stiffness devices, including the well-known device developed by Sarlis, Pasala, Constantinou, Reinhorn, Nagarajaiah, and Taylor, and various quasi-zero-stiffness and magnetic spring concepts, aim to reduce apparent structural stiffness and amplify damping effectiveness. Semi-active resettable devices, explored by Chase, Mulligan, and colleagues and by Bobrow, Jabbari, and Thai, demonstrated that reshaping hysteretic behavior with controllable hardware can outperform passive damping. Earlier work by members of the present team, including half-cycle friction damping devices and double triangular damping devices with equivalent negative stiffness for base-isolated buildings, laid the groundwork for the current ENSFD. The new study advances this lineage by closing the loop: a full analytical model, an equivalent linearization scheme validated by time-history analysis, a working electronic control system, and experimental verification in a single coherent program.

The practical significance of the frequency and amplitude findings deserves emphasis. Real earthquakes are broadband, nonstationary signals, and a damper whose output varies strongly with excitation frequency could behave unpredictably across different ground motions. The ENSFD’s weakest sensitivity being to frequency suggests a degree of robustness that bodes well for real-world deployment, while the strong dependence on displacement amplitude means the device naturally scales its energy absorption with the severity of the response, dissipating more when the structure moves more and less when the motion is mild. That self-scaling behavior is characteristic of well-behaved seismic protective systems and simplifies the task of designing the device for a target performance objective.

Challenges remain before such devices appear in buildings. The laboratory tests were conducted under controlled low-cycle reciprocating loading rather than full-scale shaking table conditions, and long-term reliability of the variable friction mechanism, along with the durability of the sensing and control electronics during years of dormancy punctuated by rare earthquakes, will need further study. Nevertheless, the demonstration that an STM32-based control system can reliably identify loading states in real time, and that the resulting hysteresis behaves as theory predicts, moves the equivalent negative stiffness friction damper from concept toward practice. For a field searching for ways to add damping without adding force, a device that works only half the cycle, and works best when the shaking is worst, is an idea whose time may have come.

Subject of Research: Semi-active negative stiffness friction dampers for seismic response control of structures

Article Title: Experimental study and equivalent parameter analysis of a semi-active negative stiffness friction damper

Article References: Li, W., Peng, L., & Lai, Z. (2026). Experimental study and equivalent parameter analysis of a semi-active negative stiffness friction damper. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02647-x

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02647-x

Keywords: negative stiffness, friction damper, semi-active control, seismic protection, equivalent linearization, hysteresis, STM32 microcontroller, energy dissipation, base isolation, earthquake engineering, structural dynamics, low-cycle loading

The research team developed two distinct connection configurations, both designed to provide continuity and core reinforcement at the critical slab-to-beam interface. The first, designated Continuity and Core reinforcement – Combined (CC-C), integrates the continuity and core reinforcement within a combined arrangement, while the second, Continuity and Core reinforcement – Discrete (CC-D), separates these reinforcement functions into discrete elements. Both connections incorporate a 75 millimetre ledge width, a dimension chosen deliberately to comply with the minimum ledge support advised by New Zealand standards, which have long been regarded as among the most demanding seismic detailing provisions in the world following that country’s devastating earthquake experiences with precast flooring.

The significance of the ledge dimension cannot be overstated. In past earthquakes, most notably the Northridge earthquake of 1994 and the Canterbury earthquake sequence in New Zealand, hollow core floors suffered failures traced to insufficient bearing length and inadequate connection detailing. When a building sways laterally during strong ground shaking, the ends of precast slabs experience alternating positive and negative bending moments, and if the supporting ledge is too narrow or the reinforcement poorly arranged, the slab end can crack, lose its seating, and ultimately drop. The New Zealand requirement for minimal ledge support therefore represents a hard-won lesson from forensic investigations of real failures, and the Indian research team’s decision to adopt it signals a commitment to internationally recognized best practice.

To evaluate the seismic efficiency of the two novel connections, the researchers subjected full-scale specimens to reverse cyclic loading, the standard laboratory method for simulating the back-and-forth deformation demands that an earthquake imposes on a structure. The testing regime allowed the team to assess a comprehensive suite of performance indicators, including ductility, load capacity, energy dissipation capacity, damping characteristics, hysteretic response properties, stiffness degradation, load ratios, elastic stiffness, and strain distribution. Each of these parameters tells part of the story of how a connection behaves as damage accumulates: ductility measures how far the joint can deform beyond its elastic limit, energy dissipation reflects its capacity to absorb seismic energy, and stiffness degradation tracks how the connection softens through repeated cycles.

The headline result is striking. Both the CC-C and CC-D connections effectively sustained both positive and negative moments without losing support, even under lateral drift levels reaching ±5.36 per cent. To put that figure in perspective, modern seismic design codes typically expect structures to remain standing at drift levels of around 2 to 3 per cent, and acceptance criteria for moment frames tested under standards such as ACI 374.1-05 demand stable performance at considerably smaller deformations. A connection that retains its slab seating at more than five per cent drift has demonstrated a remarkable margin of safety, one that would translate directly into life-safety performance during a severe earthquake. The fact that neither configuration lost support at any point in the testing suggests that the ductile detailing successfully transformed a traditionally brittle failure mode into a ductile, energy-absorbing one.

Complementing the laboratory programme, the team carried out a thorough three-dimensional nonlinear finite element simulation using ABAQUS software, one of the most widely used platforms for advanced structural analysis. The numerical models employed the concrete damaged plasticity framework, a constitutive approach rooted in the plastic-damage theories developed by Lubliner and colleagues and later extended by Lee and Fenves, which captures both the crushing and cracking behaviour of concrete under cyclic loading. The simulations showed strong agreement with the experimental findings, with discrepancies remaining within 10 per cent, a level of correlation that validates the modelling approach and opens the door to using such models for future design studies without the expense of physical testing for every variant.

Beyond simply reproducing the test results, the numerical investigation yielded critical insights into the modelling aspects that govern the accuracy of finite element predictions for these assemblies. The researchers examined element size sensitivity, confirming that mesh resolution materially affects the computed response, a well-known but frequently underestimated issue in nonlinear concrete analysis. They also investigated material dilation properties, which control how concrete expands as it shears and which influence confinement effects within the connection zone, and the role of viscosity coefficients, the numerical regularization parameters that help convergence in softening materials without artificially stiffening the response. These findings provide practical guidance for other researchers and engineers seeking to model precast connections reliably, addressing pitfalls that can otherwise lead to misleading predictions.

The strain distribution measurements from the experiments added another layer of understanding, revealing how forces flow through the connection detailing and where the reinforcement is most heavily engaged. Such data are essential for confirming that the design philosophy behind the connections, namely that yielding should occur in the ductile reinforcement rather than through brittle concrete failure at the slab bearing, is actually realized in practice. The hysteretic loops recorded during cyclic testing, together with the damping characteristics derived from them, indicate how effectively each configuration dissipates seismic energy cycle after cycle, a property directly linked to how quickly a building’s vibrations decay during an earthquake.

The broader implications of this work extend well beyond the laboratory in Chennai. Precast and prestressed concrete construction is growing rapidly worldwide, driven by demands for speed, quality, and sustainability, and hollow core slabs remain a flagship product of the precast industry, supplied in this study by TEEMAGE PRECAST in Kancheepuram. In seismically active regions from India to the Mediterranean to the Americas, the vulnerability of slab-to-beam connections has been a persistent obstacle to confident adoption of precast flooring in high-seismic zones. Connection solutions that are both ductile and practical to construct, using conventional materials and detailing techniques compatible with codes such as IS 13920 for ductile detailing and IS 15916 for prefabricated concrete construction, could substantially expand the safe use of these efficient floor systems.

By pairing rigorous physical testing with validated high-fidelity simulation, the Anna University team has delivered a template for how connection research should be conducted: propose a detailing innovation grounded in lessons from past failures, verify it under realistic cyclic demands against international acceptance benchmarks, and then distil the behaviour into numerical models that designers can trust. The demonstration that hollow core slab-to-beam connections can survive drift levels exceeding five per cent without losing support marks a meaningful advance in precast seismic engineering, and the detailed modelling guidance ensures that the findings will ripple outward, informing future designs, code provisions, and the ongoing effort to make precast buildings as resilient as they are efficient.

Subject of Research: Seismic performance of ductile hollow core slab-to-beam connections in precast concrete buildings

Article Title: Seismic resilience of hollow core slab – beam connections with novel ductile detailing: experimental and numerical simulations

Article References: Vinutha, D., Vidjeapriya, R., & Jaya, K. P. (2026). Seismic resilience of hollow core slab – beam connections with novel ductile detailing: experimental and numerical simulations. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02681-9

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02681-9

Keywords: hollow core slabs, precast concrete, seismic resilience, ductile detailing, reverse cyclic loading, finite element analysis, ABAQUS, connection design, drift capacity, energy dissipation, New Zealand standards, earthquake engineering