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

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 study, published in the Bulletin of Earthquake Engineering, focused on the Guangyue Tower, a traditional hybrid pavilion-style timber structure located in Liaocheng, Shandong Province, in northern China. Led by Xian-Cai Ren of Xi’an University of Architecture and Technology, together with colleagues from Liaocheng University and Qingdao University of Technology, the research team fabricated a 1/4.5-scale model of the tower and mounted it on a shaking table, a laboratory platform capable of reproducing the ground motions of real earthquakes. Three ground motion records of increasing intensity were applied to the model, allowing the researchers to track how the structure’s behavior evolved from mild tremors to rare, severe shaking.

Shaking table tests are among the most demanding experiments in earthquake engineering. The platform must replicate not only the peak acceleration of a seismic event but also its frequency content and duration, all while the instrumented model records accelerations, displacements, and dynamic properties at every level. For heritage timber structures, the challenge is compounded by the need to faithfully reproduce traditional joinery. The Guangyue Tower model incorporated the characteristic features of Chinese pavilion-style construction, including mortise-tenon joints, dou-gong bracket sets, and column feet that rest on stone plinths without rigid anchorage. These connections are deliberately loose by modern standards, and that looseness turned out to be central to the structure’s survival strategy.

Under strong seismic excitation, the model displayed exactly the kind of damage that conservators might fear: significant loosening at the joints and visible cracking in members. Yet the structural consequences were remarkably contained. The fundamental frequency of the model, a measure of its stiffness, dropped by 22.8 percent as the joints worked loose and energy was absorbed through friction and slippage. At the same time, the corresponding damping ratio increased by 59.3 percent, meaning the structure became far more effective at dissipating vibrational energy. In effect, the damage itself acted as a protective mechanism, softening the building and damping its response before deformations could grow dangerous.

Perhaps the most striking finding concerned acceleration. At every story of the model, the acceleration amplification factor, the ratio of the acceleration at that level to the acceleration at the base, remained below 1.0, and the factors decreased as seismic intensity increased. In conventional stiff buildings, accelerations typically amplify toward the roof, imposing large inertial forces on upper levels. The Guangyue Tower model did the opposite: the ground shaking was largely filtered out before it reached the upper stories. This behavior stems from the sliding and rocking of column feet and the energy dissipation at semi-rigid joints, which decouple the superstructure from the most violent components of ground motion.

Deformation capacity proved equally impressive. Under the rarely met earthquake, the most severe shaking level considered, the maximum interstory drift, the relative horizontal displacement between adjacent floors normalized by story height, reached 1/29. For many modern structural systems, drift ratios of this magnitude would raise concerns about collapse or permanent damage. Yet the timber model showed no obvious residual inclination after the shaking stopped. The structure simply returned to its original plumb position, its joints re-seating themselves as the motion subsided. This self-centering behavior, driven by gravity acting on rocking columns and the elastic recovery of timber, is a hallmark of traditional Chinese timber construction and a property that modern engineers often struggle to replicate with rigid connections.

To extend the experimental findings beyond the laboratory, the team developed a simplified numerical model of the structure and validated it against the shaking table measurements. The finite element model reproduced the dynamic responses of the test specimen with good agreement, capturing the frequency shifts, damping changes, and story-level accelerations observed experimentally. With a trustworthy computational surrogate in hand, the researchers could then ask a question that no ethical test program could answer directly: what would happen if the column feet were rigidly fixed to their foundations instead of resting freely on stone plinths?

The numerical comparison delivered a clear verdict. A model with rigid ground-story column foot connections did reduce the maximum interstory drift, making the structure nominally stiffer and less deformable. But this apparent benefit came at a steep price: the roof acceleration response increased significantly, exposing the upper levels of the building to much larger inertial forces. In other words, fixing the columns would trade controlled flexibility for amplified shaking at the top of the tower, potentially overloading roofs, brackets, and upper-story joints. The flexible, sliding column foot, so often dismissed as primitive, is in fact a deliberate seismic fuse that protects the entire building above it.

The implications reach well beyond a single tower in Shandong. Thousands of multi-story traditional timber structures across China, Japan, and Korea face seismic risk, and many have already been damaged in recent events, including the Ms 6.0 Luxian earthquake of 2022, which harmed numerous cultural heritage buildings. Rehabilitation programs guided by modern strengthening instincts, such as anchoring columns or stiffening joints, could inadvertently destroy the very mechanisms that have preserved these buildings for centuries. The study’s authors emphasize that their findings can serve as a reference for the rehabilitation of multi-story traditional hybrid pavilion-style timber structures, and the message for conservation engineers is unambiguous: preserve the flexible behavior of column foot connections if seismic resilience is the goal.

The work also adds to a growing body of experimental evidence on traditional timber engineering, from shaking table studies of Forbidden City palaces and Japanese pagodas to laboratory investigations of dou-gong brackets and mortise-tenon joints. Together, these studies sketch a coherent picture of an ancient building system that achieves earthquake resistance through energy dissipation, joint loosening, rocking, and self-centering rather than through the strength and stiffness that dominate modern codes. As China continues to invest in the protection of its timber heritage, validated numerical models like the one developed in this study offer a practical tool: they allow engineers to test rehabilitation strategies computationally, predict how a real tower will respond to future earthquakes, and ensure that interventions enhance rather than undermine the ingenious flexibility that has kept these wooden giants upright through the centuries.

Subject of Research: Seismic performance of multi-story traditional Chinese pavilion-style timber structures evaluated through shaking table tests and numerical modeling

Article Title: Seismic performance of multi-story traditional hybrid pavilion-style timber structures: shaking table tests and numerical analysis

Article References: Ren, X.-C., Meng, Z.-B., Wang, S.-W., & Cao, Y. (2026). Seismic performance of multi-story traditional hybrid pavilion-style timber structures: shaking table tests and numerical analysis. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02643-1

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02643-1

Keywords: timber structures, seismic performance, shaking table test, Guangyue Tower, mortise-tenon joints, dou-gong brackets, column foot connections, interstory drift, damping ratio, finite element model, heritage conservation, earthquake engineering

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

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

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

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

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

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

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

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

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

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

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

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

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02670-y

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

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

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

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

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

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

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

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

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

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

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

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

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

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02712-5

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

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

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

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

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

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

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

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

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

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

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

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

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06453

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

A study published in the Bulletin of Earthquake Engineering by Qi Cao of Dalian University of Technology and colleagues offers a way to resolve that compromise. The research team fabricated and tested seven full-scale concrete beam-column joint specimens reinforced with a hybrid combination of glass fiber reinforced polymer, or GFRP, bars and highly ductile stainless steel bars. Both materials are corrosion resistant, so the assembly can in principle survive aggressive environments, while the pairing of a brittle, linear-elastic composite with a ductile, strain-hardening metal restores the energy-dissipating behavior that pure FRP reinforcement notoriously lacks. Beam-column joints are the critical nodes where columns and beams meet in reinforced concrete frames, and their behavior under cyclic loading often determines whether a building sways and recovers during an earthquake or collapses outright.

The core problem the researchers set out to address is well known in the seismic engineering community. FRP bars are extraordinarily strong in tension, immune to electrochemical corrosion, and much lighter than steel, which makes them attractive for structures built with seawater and sea sand concrete in regions where fresh water and sound aggregates are scarce. But unlike steel, GFRP does not yield. Its stress-strain relationship is essentially a straight line until sudden, brittle rupture. Conventional seismic design of concrete frames relies on steel yielding in the beams near the joints, forming plastic hinges that absorb earthquake energy through controlled inelastic deformation. A structure reinforced entirely with FRP has no such mechanism, which is why design codes have historically restricted FRP-reinforced concrete in high seismic zones.

Hybrid reinforcement offers an elegant workaround. By placing GFRP bars and stainless steel bars together in the same cross-section, the composite bars contribute their high strength and corrosion immunity, while the stainless steel provides a genuine yield plateau and a long, ductile post-yield response. Highly ductile stainless steel alloys are particularly suitable for this role because, unlike many high-strength steels, they combine substantial elongation capacity with strength that continues to rise as strain accumulates. The result is a member that can crack, deflect, and dissipate energy like a well-detailed steel-reinforced element, while resisting the chloride attack that would cripple ordinary reinforcement within a few decades of coastal exposure.

To find out how this concept performs at the joint level, the team varied three experimental parameters across the seven specimens. The first was the type of longitudinal reinforcement used in the columns. The second was the GFRP bar replacement rate in the beams, meaning the proportion of the beam’s tension reinforcement provided by GFRP rather than stainless steel. The third was the ratio of GFRP stirrups in the joint core region, the confined zone at the intersection of beam and column where shear demands during an earthquake are most severe. Each specimen was then subjected to reversed cyclic loading, the standard laboratory proxy for the back-and-forth shaking a frame experiences during an earthquake, while researchers recorded load, displacement, and deformation patterns.

The findings carry practical weight for designers. Perhaps the most consequential observation is that the type of reinforcement placed in the columns did not change the failure mode of the joint under the conditions of this study. Instead, the GFRP replacement rate in the beams emerged as the dominant factor controlling how the joints ultimately failed. Joints with lower GFRP proportions failed in flexure within the beams, the most desirable mechanism in seismic design because beam bending is ductile and keeps damage away from the joint itself. As the GFRP share increased, failure shifted first to a combined bending-shear mechanism and, at still higher replacement rates, to brittle shear failure in the joint core, the least favorable outcome because core shear damage compromises the entire frame connection.

Ductility, the measure of how much deformation a joint can sustain beyond first yield, told a nuanced story. Hybrid reinforcement in the beams significantly improved joint ductility compared with configurations lacking that ductile steel component, confirming the central premise of the hybrid concept. But the rate of improvement depended critically on the governing failure mode. When specimens transitioned from beam bending failure to combined bending-shear failure, the growth rate of the ductility coefficient dropped, and it dropped again as specimens moved from combined failure to joint core shear failure. In other words, simply swapping more steel for GFRP does not proportionally erode performance; instead, ductility is preserved across regimes until a threshold is crossed, after which the benefit of the ductile component is increasingly throttled by brittle shear mechanisms.

The deformation results were equally revealing. Increasing the GFRP replacement rate in the beams enhanced the ultimate drift ratio overall, a metric of how far a structure can sway before losing capacity, conventionally taken as the point at which load falls to 85 percent of its peak value. And within any single failure mode, the deformation concentrated in the beam plastic hinge zone remained roughly constant. That regularity suggests that once a designer knows the failure mode, the plastic hinge behavior can be anticipated with reasonable confidence, a valuable property for performance-based seismic design, in which engineers target specific deformation and damage states rather than relying on prescriptive rules alone.

Energy dissipation, the ultimate currency of seismic resilience, followed the same logic as ductility and failure mode. The study found that the GFRP replacement rate in the beams was the main factor influencing how much energy the joints could absorb through repeated cycles. Configurations that preserved beam flexural failure dissipated the most energy, while those drifting toward core shear failure lost that capacity. This aligns with a foundational principle of earthquake engineering: the best structure is one whose beams, not its columns or joints, take the damage, because beams are comparatively easy to inspect and repair after an event, whereas joint core damage can be effectively unrepairable.

Beyond the laboratory findings, the study contributes analytical machinery for design. The researchers developed deformation and strength relationships parameterized in terms of the GFRP and stainless steel reinforcement areas, replacement rates, stirrup ratios, and plastic hinge dimensions, calibrated through regression analysis of the test data. Such tools allow practitioners to estimate yield and ultimate displacements, ductility coefficients, and drift capacities for hybrid joints without testing each configuration, which is essential if hybrid FRP-steel reinforcement is to move from promising research to routine specification. The work was supported by the National Natural Science Foundation of China and the Science and Technology Plan Project of Transportation of Henan Province.

The broader significance extends to infrastructure policy. Coastal and marine structures, from port facilities to bridges, face a well-documented corrosion crisis that costs economies billions in repairs annually, while seismic regions cannot accept the brittle behavior of pure FRP reinforcement. A reinforcement scheme that satisfies both demands simultaneously opens the door to concrete frames built with seawater and sea sand in earthquake-prone coastlines, structures that are durable over their full service life and dependable on the day the ground shakes. The seven joints tested here will not be the last word; further studies across scales, loading histories, and environmental exposure will be needed before codes fully embrace the approach. But the study demonstrates with clarity that the failure mode, governed primarily by how much ductile stainless steel remains in the beam, is the master variable for hybrid joints, and that gives designers a clear, actionable rule: preserve beam flexural yielding, and the hybrid system rewards the structure with ductility, drift capacity, and energy dissipation worthy of seismic regions.

Subject of Research: Seismic performance of corrosion-resistant concrete beam-column joints reinforced with hybrid GFRP and stainless steel bars

Article Title: Seismic performance of corrosion-resistant concrete beam-column joints reinforced with hybrid FRP and stainless steel bars

Article References: Cao, Q., Zhang, T., Luo, T., & Zeng, Z. (2026). Seismic performance of corrosion-resistant concrete beam-column joints reinforced with hybrid FRP and stainless steel bars. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02674-8

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02674-8

Keywords: GFRP bars, stainless steel reinforcement, hybrid reinforcement, beam-column joints, seismic performance, ductility, energy dissipation, plastic hinge, concrete structures, failure mode, earthquake engineering, corrosion resistance