A new study published in Case Studies in Construction Materials by Seon Yeol Lee, Seoung Ik Choi, Taek Hee Han, and Jun Kil Park tackles this gap by asking a deceptively simple question: what happens when polyethylene fiber-reinforced mortar is exposed to real seawater while it is still curing? The researchers focused on ultra-high-molecular-weight polyethylene fibers, which, unlike steel fibers, are immune to corrosion and chemically robust in marine conditions. Polymer fibers of this kind are the backbone of engineered cementitious composites, materials famous for their ability to hold cracks below roughly 60 micrometers in width, a scale fine enough to slow chloride ingress dramatically. Recent variants have even embraced seawater and sea sand as mixing ingredients to conserve freshwater and terrestrial aggregates, making the question of seawater’s influence on mechanical development all the more urgent.

What distinguishes this work from earlier research is its attention to timing. Previous studies had either mixed seawater directly into the concrete, submerged specimens immediately after demolding, or exposed them to seawater only after 28 days of standard curing. Each approach interacts with cement hydration at a different stage, and prior work on cement pastes had shown that the age of first seawater exposure significantly alters which hydration products form. The Korean team designed their experiment around the practical scenario facing precast marine elements: mortar cured in tap water for 0, 3, 7, or 14 days, then transferred to natural seawater collected from Busan, with a total curing period of 28 days for every condition. They compared these against control specimens cured entirely in tap water or entirely in seawater.

The material itself was engineered for high performance. The mortar used Type I ordinary Portland cement, Australian silica sand, a water-to-cement ratio of just 0.25, and a polycarboxylate superplasticizer to keep the mix workable at that low water content. The polyethylene fibers were remarkably slender, with an average diameter of 23.5 micrometers and a length of 12 millimeters, giving an aspect ratio above 500, an elastic modulus of 100 gigapascals, and a tensile strength of 3000 megapascals. Three fiber contents were tested: zero, one, and two percent by volume. The team targeted a compressive strength of at least 80 megapascals, placing the material at the lower bound of the high-strength engineered cementitious composite range considered suitable for harsh marine loading including earthquakes, typhoons, and tsunamis.

The results, drawn from flexural, compressive, and length-change tests on hundreds of specimens, revealed a strikingly nuanced picture. Every series showed improved first-crack behavior, quantified as the Limit of Proportionality, as seawater exposure lengthened. For the unreinforced mortar, the first-crack toughness rose by up to 132.8 percent under full seawater curing compared with tap-water curing. But the peak flexural performance, the Modulus of Rupture, split the fiber-reinforced series in opposite directions. The one-percent fiber mortar grew stronger and tougher with seawater, while the two-percent fiber mortar grew weaker, with its peak toughness falling by 34.9 percent under full seawater exposure relative to its tap-water counterpart.

The best overall performer was the one-percent fiber mortar cured in tap water for seven days and then exposed to seawater for 21 days. Compared with the same mix cured entirely in tap water, its first-crack strength, deflection, and toughness increased by 94.2, 66.7, and 174.2 percent respectively, while its peak strength, deflection, and toughness rose by 5.6, 23, and 42.8 percent. This mix also achieved the highest compressive strength of the entire study, 98.3 megapascals. The findings suggest that a brief freshwater pre-cure followed by seawater exposure may actually be an ideal sequence for precast marine elements, turning an unavoidable logistical constraint into a performance advantage.

The mechanism behind these gains lies in cement chemistry. When chloride ions from seawater react with tricalcium aluminate phases and calcium hydroxide in the cement paste, they form Friedel’s salt, a chloride-bearing aluminate phase that fills capillary pores and accelerates hydration. Seawater also promotes the formation of a high-surface-area calcium silicate hydrate gel, the glue of concrete, refining the pore structure. Earlier studies cited by the authors reported that seawater-mixed pastes showed a 12 percent reduction in 28-day porosity and finer pore networks. The result is a denser microstructure and, crucially, a strengthened interfacial transition zone, the porous region surrounding each fiber where cracks preferentially begin. Because flexural and tensile behavior are far more sensitive to this zone than compressive behavior, the improvements showed up most dramatically in the bending tests, and the measured expansion of the specimens tracked neatly with the strength gains.

So why did the two-percent fiber mix falter? The answer lies in a phenomenon known as the group effect. When fibers are packed too closely together, they interfere with one another, concentrating stress in the matrix and reducing the reinforcing efficiency of each individual fiber. Using a constitutive model developed for steel fiber-reinforced concrete, the team calculated that fiber spacing in the two-percent mix, 171.2 micrometers, sat uncomfortably close to the fiber effect distance of 141 micrometers, the threshold at which the group effect activates. Seawater exposure strengthens the fiber-matrix bond, which extends that effect distance, pushing the crowded two-percent mix over the edge. Image analysis of polished cross-sections confirmed the story: while the overall fiber distribution appeared more uniform at higher dosage, the count of distinct fiber objects dropped by about 14 percent, indicating local clustering, and crack surfaces of the two-percent specimens showed visible clumps of fibers where uniform dispersion was expected.

The practical implications are considerable. For engineers designing precast elements for offshore wind platforms, submerged tunnels, and coastal defenses, the study suggests that one percent polyethylene fiber offers the sweet spot, and that seven days of tap-water curing before seawater exposure yields the best flexural performance under the tested conditions. It also adds momentum to the broader movement toward seawater and sea-sand concrete, which could relieve pressure on freshwater supplies and river aggregates in coastal construction booms. Because polymer fibers cannot corrode, they sidestep the classic failure mode of steel-reinforced marine concrete entirely, and the microcrack-control ability of these composites further delays chloride penetration.

The authors are careful to note the limits of their work. The study covers only the first 28 days of strength development, and the formation of Friedel’s salt and high-surface-area calcium silicate hydrate was inferred from the literature and from expansion measurements rather than directly verified with microscopy or spectroscopy. Fiber orientation was not quantitatively evaluated, the seawater’s chemistry was not analyzed, and seasonal temperature variations were not considered. Future work involving X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, three-dimensional fiber imaging, and pull-out tests should pin down the mechanisms more firmly. Long-term exposure studies will be essential before these findings translate into design codes. Still, the central message stands: the ocean, so often cast as concrete’s enemy, can under the right curing schedule and fiber dosage become an unexpected ally in building tougher, more durable marine infrastructure.

Subject of Research: Effects of seawater exposure timing during curing on the flexural behavior of polyethylene fiber-reinforced mortar for marine precast concrete

Article Title: Effects of seawater exposure during curing on the flexural behavior of polyethylene fiber-reinforced mortar

Article References: Lee, S. Y., Choi, S. I., Han, T. H., & Park, J. K. (2026). Effects of seawater exposure during curing on the flexural behavior of polyethylene fiber-reinforced mortar. Case Studies in Construction Materials, 25, Article e06591. https://doi.org/10.1016/j.cscm.2026.e06591

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06591

Keywords: polyethylene fibers, seawater curing, fiber-reinforced mortar, marine concrete, precast concrete, Friedel's salt, flexural behavior, engineered cementitious composites, chloride ingress, fiber-matrix bond, group effect, durability

The research team, led by Wenting Yuan and colleagues including Yiwei Zuo, Long Ma, Xiangtong Wu and Anxin Guo, set out to close a critical gap in the engineering literature. Previous studies had characterized how corroded sleeve splices behave under monotonic, steadily increasing tension, but almost nothing was known about their performance under cyclic loading, the kind of repeated stress that earthquakes and traffic impose on real structures. Because the seismic performance of an entire precast pier depends on the cyclic stress-strain relationship of its sleeve connections, this missing constitutive knowledge left engineers without a reliable tool for assessing aging precast bridges in corrosive environments, particularly coastal and marine settings where chloride ions steadily penetrate the concrete cover.

To anchor their experiments in realistic service conditions, the researchers first developed a theoretical framework for predicting how deeply a sleeve corrodes over time. Using Fick’s second law of diffusion, they modeled how long chlorides take to breach the concrete cover and reach a critical concentration at the sleeve surface, then applied Faraday-based relationships to track the time-variant corrosion depth of the steel wall. The calculations produced striking numbers: increasing the concrete cover from 30 to 70 millimeters delays corrosion initiation from just 3.3 years to 47.4 years, while at a 100-year service life the predicted sleeve corrosion depth ranges from 1.8 to 3.4 millimeters. Because the sleeve is a hollow section, such losses can approach full wall penetration, a scenario the experiments were designed to probe.

The experimental program involved twenty-four commercial sleeve specimens, each 310 millimeters long with a 41.4 millimeter outer diameter and a 3.2 millimeter wall, connecting 16 millimeter reinforcing bars with an effective anchorage length of roughly 150 millimeters. The sleeves themselves yielded at 381 megapascals and ultimately carried 669 megapascals, while the grout achieved a compressive strength of 70.8 megapascals. Six target corrosion ratios were chosen, from 0 to 50 percent, with four replicate specimens at each level. To corrode the sleeve without corroding the rebars, the team sealed the exposed bars and immersed the specimens in a 3.5 percent sodium chloride solution, applying an accelerated current density of 800 microamperes per square centimeter and calculating the required exposure time from Faraday’s law of electrolysis.

After corrosion, the specimens were scanned with a high-resolution 3D scanner, and the reconstructed models revealed a crucial and previously underappreciated feature: corrosion was markedly non-uniform, both around the circumference and along the length of each sleeve. The most severe damage concentrated at the sleeve ends, a pattern the authors attribute to residual welding stresses at the ends and to the shorter, more accessible transport pathways for chloride ions and dissolved oxygen near the vent openings. Maximum local corrosion depths reached approximately 4 millimeters, indicating localized wall penetration in the most aggressive cases. The team is careful to note that accelerated corrosion at such high current densities does not perfectly replicate decades of natural exposure, but it remains an effective method for reproducing the non-uniform deterioration that governs mechanical response.

Under cyclic tensile loading, the specimens told a clear story of thresholds. Below roughly 30 percent corrosion, the connections behaved almost identically to intact ones, sustaining peak loads near 120 kilonewtons and ultimate displacements of about 100 millimeters, with failure dominated by rebar fracture, the desirable ductile mode. As corrosion deepened and sleeve walls began to penetrate, the confinement the sleeve provides to the internal grout weakened and the effective anchorage length shortened, shifting failure toward grout crushing, rebar pull-out and grout pull-out. Strength ratios held near 1.4 for corrosion below 30 percent, then collapsed in the heaviest group, where three specimens dropped to values of 1.16, 0.35 and 0.89, all below the 1.25 threshold that design codes require for adequate bearing capacity.

Deformation capacity degraded along a parallel track. Intact specimens achieved an average deformation ratio of 9.4, which barely changed at 30 percent corrosion but fell to 4.6 at 50 percent. Two heavily corroded specimens failed before even yielding, their deformation ratios falling below 1.0. The hysteretic loops painted the same picture from an energy perspective: below 30 percent corrosion the loading-unloading cycles remained stable with little degradation, at around 40 percent the loops grew erratic and post-peak strength loss intensified, and at 50 percent premature pull-out produced narrow, incompletely developed loops signaling a substantial collapse in energy dissipation, precisely the property that protects structures during earthquakes.

From the full dataset, the researchers distilled an equivalent stress-strain constitutive model for corroded sleeve splices, expressing yield stress, peak stress, yield strain, peak strain and ultimate strain as functions of the measured corrosion ratio. The trends are distinctive: yield and peak stresses hold steady until corrosion exceeds roughly 33.6 percent and then decline, peak and ultimate strains rise before falling, and yield strain climbs continuously as interfacial slippage accumulates, collectively eroding the connection’s effective elastic modulus. To prove the model’s usefulness beyond the coupon scale, the team embedded it in a finite element simulation of corroded precast bridge piers previously tested under cyclic loading, using the OpenSees platform with fiber-based cross-sections and bond-slip elements. The predicted hysteretic curves matched the experiments well, with peak force errors of 10 to 11 percent for one pier and an average of 5 percent for the more heavily corroded one.

The implications reach well beyond the laboratory. Prefabricated bridges in coastal and deicing-salt environments are aging into precisely the corrosion regimes this study maps, and seismic assessments of such structures have until now relied on constitutive relationships that ignore sleeve deterioration. By quantifying where the safe plateau ends, below 30 percent corrosion for deformation capacity and below 50 percent for strength, and by supplying a validated stress-strain model that captures the transition, the researchers have given engineers a quantitative bridge between field corrosion surveys and structural-level seismic evaluation. The authors caution that their experiments corroded the sleeve in isolation, whereas real sleeves and rebars may deteriorate concurrently, and that validation so far rests on two pier specimens. Future work will address combined corrosion, natural exposure, additional sleeve geometries and variable-amplitude loading, but the present findings already mark a decisive step toward keeping the joints that hold prefabricated cities together honestly accounted for in the face of rust.

Subject of Research: Effect of chloride-induced corrosion damage on the cyclic tensile mechanical behavior and constitutive modeling of grouted sleeve connections in prefabricated concrete bridges

Article Title: Effect of corrosion damage on cyclic tensile mechanical behavior of grouted sleeve connections

Article References: Yuan, W., Zuo, Y., Ma, L., Wu, X., & Guo, A. (2026). Effect of corrosion damage on cyclic tensile mechanical behavior of grouted sleeve connections. Case Studies in Construction Materials, 25, Article e06620. https://doi.org/10.1016/j.cscm.2026.e06620

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06620

Keywords: grouted sleeve connections, corrosion, prefabricated bridges, cyclic tensile loading, chloride-induced corrosion, stress-strain model, seismic performance, precast concrete, bond degradation, accelerated corrosion testing, finite element validation, structural durability

The research, led by Azlan Adnan of Universiti Teknologi Malaysia together with Yuyun Tajunnisa and colleagues at Institut Teknologi Sepuluh Nopember in Surabaya, Indonesia, combines full-scale laboratory testing with advanced computer simulation to trace the entire chain of seismic damage, from the first hairline crack in a joint to the collapse of an entire frame. The work was funded by the Indonesian Endowment Fund for Education under the EQUITY Program and supported by Malaysia’s Public Works Department, which supplied technical data for the connection details studied.

At the heart of the study is a deceptively simple structural element. In many precast industrial buildings, particularly in Southeast Asia, beams are not cast monolithically with columns. Instead, they are supported on nibs, short cantilevered projections that carry the beam’s reaction through a combination of bearing pressure, dowel action of any projecting reinforcement, and friction. This arrangement speeds up construction enormously, but it also creates a discontinuity in the load path precisely where seismic forces concentrate. When a frame sways during an earthquake, the beam-to-column interface must transfer alternating moments and shears through a joint that was never designed as a continuous monolithic element.

To understand how such a joint actually deforms, the team built a full-scale specimen of a nib connection and subjected it to cyclic loading, the laboratory equivalent of the back-and-forth shaking an earthquake delivers. The test followed internationally recognized protocols for cyclic seismic testing of components, applying progressively larger displacement cycles while measuring the force resisted by the joint. The resulting load-deformation loops, known as hysteresis curves, revealed how stiffness degrades and energy is dissipated as cracking, bond slip, and concrete crushing accumulate at the nib. These experimental curves are the gold standard for characterizing connection behavior, but they describe only a single joint, not a whole building.

That is where the hybrid modeling strategy of the study becomes significant. The researchers first constructed a detailed three-dimensional nonlinear finite element model of the tested joint in ABAQUS, using plastic-damage constitutive models for concrete that capture the material’s degradation under cyclic loading. By calibrating this micro-scale model against the full-scale test data, they ensured the simulation reproduced the real joint’s stiffness, strength, and hysteretic shape. From the validated model, they extracted a moment-rotation relationship for the connection, a curve describing how much rotational resistance the joint provides as it is progressively damaged. Because this curve was synthesized from both experiment and simulation, the authors describe it as a hybrid moment-rotation curve, and it forms the critical bridge between component-level physics and building-level analysis.

The hybrid curve was then imported into SAP2000, a structural analysis platform widely used in engineering practice, as a custom nonlinear hinge placed at each beam-to-column interface of a complete precast frame. This allowed the global model to reproduce the complex, pinching hysteretic behavior observed in the laboratory rather than assuming an idealized elastic or perfectly plastic joint. With the frame model in place, the team ran two complementary forms of nonlinear analysis. The first, nonlinear static pushover analysis, pushes the structure laterally with a monotonically increasing force pattern to identify the sequence of damage states and the governing collapse mechanism. The second, incremental dynamic analysis, subjects the frame to a suite of earthquake ground motion records scaled to ever-higher intensities, tracking how drift demands and damage accumulate as shaking intensifies.

The output of these analyses is a set of fragility curves, probabilistic functions that express the likelihood of reaching a defined damage state at a given level of ground shaking, here quantified by peak ground acceleration. Fragility curves are the workhorses of modern seismic risk assessment: they allow engineers, insurers, and code writers to translate a hazard forecast into an expected probability of damage. For the precast frame with nib connections resting on rock sites, the results are encouraging. The probability of first cracking, corresponding to the Immediate Occupancy performance level at which a building remains safe to use without significant repair, begins to rise at a peak ground acceleration of about 0.20 g. More strikingly, the probability of reaching the Collapse Prevention threshold, the point beyond which the structure is on the verge of partial or total collapse, remains a negligible one percent even at 0.30 g, a level of shaking that would be destructive in many regions.

Those favorable numbers, however, come with an important caveat that the authors emphasize through parametric variation. When the same frame is assumed to stand on softer soils, local site amplification magnifies the ground motion transmitted to the structure, and the damage probabilities climb substantially. The finding underscores that soil-structure interaction is not a secondary refinement but a first-order control on seismic risk for precast buildings. Two identical frames on the same street can face materially different fragilities depending on what lies beneath their foundations, a fact with direct consequences for site selection, foundation design, and retrofit prioritization in moderate-seismicity zones.

The study’s broader significance lies in its methodology as much as its results. In regions of low to moderate seismicity, such as much of Malaysia and Indonesia outside the great subduction zones, large destructive earthquakes are rare enough that extensive experimental databases do not exist, yet frequent enough that vulnerability assessment matters for schools, hospitals, and industrial facilities built with precast technology. By anchoring a numerical model to a full-scale test and then propagating that validated connection behavior through pushover and incremental dynamic analyses to fragility curves, the researchers have demonstrated a transferable framework. Other connection types, from dapped-end beams to grouted duct and post-tensioned joints, could be assessed with the same pipeline, filling a persistent gap between idealized code assumptions and the idiosyncratic behavior of real precast interfaces.

For the precast industry, the message is cautiously optimistic. Nib connections, when properly detailed and founded on competent ground, appear capable of delivering adequate seismic safety in moderate seismic zones, with cracking initiating only at shaking levels that would already alarm occupants and collapse probabilities remaining vanishingly small at 0.30 g on rock. But the same analysis shows that the margin evaporates as soil softens, and that the connection, not the member, is the component that governs the whole frame’s fate. As cities across Southeast Asia and beyond continue to expand with factory-built construction, studies of this kind provide the quantitative evidence base that codes and practitioners need to ensure that speed of assembly never comes at the cost of resilience when the ground finally moves.

Subject of Research: Seismic fragility assessment of precast concrete frames with nib beam-to-column connections

Article Title: Seismic performance and fragility analysis of precast concrete frames with nib connections

Article References: Adnan, A., Tajunnisa, Y., Ramli, M. Z., Falahi Abdul Halim, N. H., Ab Kadir, M. A., Nurhadi, H., Yudoprasetyo, K., & Hariyanto, I. R. (2026). Seismic performance and fragility analysis of precast concrete frames with nib connections. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02700-9

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02700-9

Keywords: precast concrete, nib connections, seismic fragility, cyclic testing, incremental dynamic analysis, pushover analysis, soil-structure interaction, finite element modeling, earthquake engineering, beam-to-column joints, moment-rotation curves, ABAQUS

The research matters because sandwich panels—two thin concrete wythes or steel sheets bonded around a lightweight insulating core—have become a dominant technology in energy-efficient construction. Their popularity stems from fast installation, excellent thermal performance, and reduced lifecycle costs, and building codes increasingly favor them as energy regulations tighten. But the insulation core is not merely filler. It transfers load between the outer layers, maintains composite action, and keeps the wall structurally stable. If heat from a fire passes through the concrete faces and softens the core, the panel’s entire load-transfer mechanism can be quietly undermined long before any visible failure occurs. Despite this, most prior research has focused on fire-resistance ratings and thermal conductivity rather than on how the mechanical properties of the core itself degrade.

The experimental program was unusually comprehensive. The team, led by Abhinav Anand with supervision from Vaibhav Singhal, cut specimens from commercially manufactured blocks of the three materials and subjected them to controlled heating followed by four types of mechanical testing at ambient conditions: compression, three-point flexure, double shear, and tension, all performed on a universal testing machine under displacement-controlled loading according to relevant international standards including EN 826, ASTM C203, EN 12090, and EN 1608. EPS specimens, with a density of 16 kilograms per cubic meter, were heated in a laboratory oven at temperatures from 50 to 80 degrees Celsius. The denser XPS, at 34 kilograms per cubic meter, was tested from 60 to 90 degrees Celsius. Rockwool, at 150 kilograms per cubic meter, was heated in a muffle furnace from 200 all the way to 800 degrees Celsius.

The first striking finding concerned geometry. Beyond 80 degrees Celsius for EPS and 90 degrees Celsius for XPS—temperatures associated with the glass transition of polystyrene, where polymer chains gain mobility and the material loses rigidity—the foams physically warped and bulged. EPS contracted dramatically, shrinking 28 percent in thickness, while XPS deformed anisotropically, expanding on some faces by more than 11 percent while contracting on others. At that point the materials could no longer sustain mechanical loading at all, making further testing impractical. Rockwool, by contrast, showed no melting or distortion even at 800 degrees Celsius, though specimens became noticeably softer, fluffier, and slightly discolored above 200 degrees Celsius—early signs that the organic binder gluing its basaltic fibers together was beginning to break down.

The compression results revealed a subtle hierarchy. EPS lost compressive strength progressively, dropping about 13 percent at 50 degrees Celsius and roughly 32 percent at 80 degrees Celsius, while its initial elastic modulus fell by nearly 48 percent. XPS proved remarkably resilient in compression, losing under 1 percent of compressive strength even at 70 degrees Celsius and only about 9 percent at 90 degrees—yet its elastic modulus still collapsed by 47 percent at the highest temperature, signaling irreversible damage to the closed-cell structure even when peak strength appeared intact. Rockwool told the most dramatic story: minor losses up to 400 degrees Celsius, then a catastrophic 78 percent strength reduction at 600 degrees and over 90 percent at 800 degrees, where the response was governed by loose fiber compaction rather than any true structural resistance, following near-complete burnout of the organic binder.

Flexural and shear tests exposed even greater vulnerabilities. EPS flexural strength fell by 20 percent at 80 degrees Celsius, with stiffness plummeting 55 percent. XPS lost about 22 percent of flexural strength and 15 percent of stiffness at 90 degrees. Rockwool, however, could barely be tested in bending after 400 degrees Celsius: the fibrous matrix delaminated into a loose, fluffy mass that could not support its own weight, with residual flexural strength estimated at a mere 1.57 kilopascals—a 99 percent loss. In shear, the pattern repeated. EPS shear strength dropped 38 percent and its shear modulus 50 percent at 80 degrees; XPS lost 47 percent of shear strength and a striking 73 percent of shear modulus at 90 degrees; and rockwool’s shear capacity fell by more than half at just 200 degrees, reaching an estimated 0.34 kilopascals at 400 degrees, when specimens could no longer even hold the steel loading plates of the test apparatus.

Tensile behavior followed suit, with an important nuance about failure modes. EPS failed brittlely through its core, with cracks propagating along weak inter-bead boundaries, losing 27 percent of tensile strength at 80 degrees Celsius. XPS showed a mixed-mode failure dominated by interfacial debonding near the steel plate boundary, losing about 23 percent of tensile strength at 90 degrees. Rockwool failed progressively through fiber pull-out, rupture, and interlayer delamination—a ductile, distributed damage process—but its tensile strength collapsed by more than 90 percent at 400 degrees, at which point a specimen failed immediately under the self-weight of the test assembly alone. Across all four loading modes, tensile and shear properties consistently deteriorated faster than compressive ones, indicating that heat attacks interfacial bonding and cellular connectivity before it destroys bulk load-bearing capacity.

The overall comparison upends conventional fire-safety intuition. Within their survivable temperature ranges, the polymeric foams kept strength losses below 50 percent, because they were tested below their glass transition points where softening occurs but cellular geometry survives. Rockwool, despite never distorting, suffered strength and stiffness reductions exceeding 90 percent in most loading modes because its mechanical integrity depends almost entirely on an organic binder that burns away between 300 and 400 degrees Celsius. In other words, the material that best resists fire in the visible sense—no melting, no dripping, no combustible gases—is also the one whose structural contribution vanishes most completely. EPS and XPS, meanwhile, released combustible gases and warped at relatively modest temperatures, yet retained a larger fraction of their mechanical function within the ranges they could tolerate.

The authors emphasize that these residual-property datasets fill a critical gap for engineers and modelers. The measurements can support post-fire performance assessment, inform the selection of insulation cores for precast concrete sandwich panels, and provide calibration data for numerical models predicting how panel structures behave under thermal loading. The team also notes an important limitation: only a single commercial density of each material was tested, and since density strongly influences stiffness, strength, and thermal response, broader parametric studies will be needed to develop generalized design equations. For now, the message for the construction industry is clear and slightly uncomfortable—fire resistance and residual structural performance are not the same property, and the non-combustible hero of building insulation may be the first to quietly stop doing its structural job when the heat rises.

Subject of Research: Residual mechanical properties of EPS, XPS, and rockwool insulation materials after elevated temperature exposure

Article Title: Residual mechanical properties of EPS, XPS, and rockwool insulation materials after elevated temperature exposure

Article References: Anand, A., & Singhal, V. (2026). Residual mechanical properties of EPS, XPS, and rockwool insulation materials after elevated temperature exposure. Results in Engineering, 32, Article 113053. https://doi.org/10.1016/j.rineng.2026.113053

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113053

Keywords: EPS, XPS, rockwool, insulation materials, sandwich panels, elevated temperature, fire safety, compressive strength, shear modulus, precast concrete, thermal degradation, structural engineering

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

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

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

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

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

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

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

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

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

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

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

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

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02668-6

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

The 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

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