The vulnerability of beam–column joints is one of the most sobering lessons of modern seismic engineering. When an earthquake shakes a reinforced concrete frame, the regions where beams meet columns become battlegrounds of shear. Diagonal cracking propagates through the joint core, concrete crumbles, and the reinforcement anchoring the beam bars can lose its grip. Once the joint fails, the entire load path of the building is compromised, and the frame can lose its ability to carry gravity loads even while the earthquake continues. Many existing buildings, particularly those designed before modern seismic codes mandated dense joint confinement, contain joints with little or no transverse reinforcement — a hidden deficiency that retrofit programs around the world have struggled to address economically.

Retrofitting joints conventionally involves jacketing with steel, concrete, or fiber-reinforced polymer wraps, often increasing member dimensions and requiring extensive labor. The new research explores a different philosophy entirely: rather than adding material around the joint, why not replace the weak material inside it? The team, led by Shuangcen Li of Sichuan University Jinjiang College, Hamed N. Harharah of King Khalid University in Saudi Arabia, and Jemshid Ismael and Kiyan Endalib of the University of Bartin in Turkey, developed and tested a material they call a steel-fiber-reinforced epoxy composite, or SFREC.

The SFREC is not a conventional cement-based concrete at all. It consists of an epoxy resin binder combined with silica sand as aggregate, a cement–microsilica blend as filler, and hooked-end steel fibers dispersed throughout the matrix. The choice of epoxy as the binder is significant. Unlike cement paste, which is brittle and develops fine cracks under tension at relatively low stress levels, epoxy is a polymer with substantial tensile capacity and excellent adhesion to both aggregate and embedded steel. The microsilica filler packs into the gaps between sand grains, densifying the matrix, while the hooked-end steel fibers act as microscopic reinforcement bridges. When a crack tries to open in the composite, the fibers spanning the crack resist its growth, and their hooked geometry means they must pull out or deform before the crack can widen — a mechanism that absorbs significant energy.

Before testing full joints, the researchers first characterized candidate SFREC mixtures through compressive, direct tensile, and flexural tests. Using a multi-criteria performance ranking, they selected a mixture designated F30-EB15-SF1.0 as the optimal formulation for the structural stage of the program. This two-stage approach ensured that the material entering the joint specimens had been vetted for the properties that matter most in seismic response: compressive strength to resist joint shear, tensile strength to control diagonal cracking, and flexural toughness to sustain deformation without brittle fracture.

The heart of the study was a series of three half-scale exterior beam–column joint specimens subjected to quasi-static reversed cyclic loading — the standard laboratory method for simulating the repeated oscillations a building experiences during an earthquake. The first specimen, BCJ-REF, served as a baseline: a conventional joint with no transverse reinforcement in the core, representing the deficient detailing found in many older buildings. The second, BCJ-TR, was a normal-concrete joint incorporating conventional joint-core transverse reinforcement, representing the code-compliant solution. The third, BCJ-SFREC, was identical in reinforcement detailing to the reference specimen but had a portion of the normal concrete within the joint core replaced with the selected SFREC mixture.

The results were striking. Under cyclic loading, the reference joint BCJ-REF behaved as expected for a deficient detail: pinched hysteresis loops, rapid strength degradation, and a displacement ductility factor of only 2.73, indicating limited capacity to deform beyond yield without losing strength. The conventionally detailed BCJ-TR improved matters considerably, reaching a ductility factor of 4.11 — the hoops within the joint core confining the concrete and holding the joint together as cracks formed. But the SFREC joint, BCJ-SFREC, outperformed both. It achieved a peak load of 6.23 kilonewtons, representing an increase of 55.4 percent over the reference joint and 39.4 percent over the conventionally confined joint. Its displacement ductility factor of 4.64 exceeded even the joint with transverse reinforcement.

Perhaps most remarkably, the SFREC joint accomplished this without any transverse reinforcement in the core whatsoever. The fibers within the epoxy composite appear to have taken over the role that steel hoops normally play: confining the joint, transferring shear across diagonal cracks, and preventing the catastrophic disintegration of the core. The hooked-end fibers, randomly oriented in three dimensions, are ideally positioned to bridge the diagonal tension cracks that form under cyclic joint shear — a task for which discrete fibers are naturally suited, since cracks in joints form in complex, changing orientations that fixed reinforcement hoops cannot fully intercept.

The energy dissipation results underscore the point. The SFREC joint accumulated approximately 470 joules of cumulative hysteretic energy dissipation over the loading history — an increase of 128.2 percent over the reference joint and 62.6 percent over the conventionally confined joint. Energy dissipation is among the most important metrics in seismic design: a structure that dissipates more energy through stable, repeated inelastic cycles absorbs more of the earthquake’s input energy, limiting the demands transmitted to the rest of the building and reducing the risk of collapse. The substantially fuller and more stable hysteresis loops observed for the SFREC joint indicate that the composite core maintained its integrity and its load-carrying capacity through repeated cycles of cracking and reopening, with the steel fibers continuously working to restrain crack growth.

The implications for practice are significant. A localized material substitution at the joint core offers a targeted strategy for improving the seismic performance of deficient exterior joints, whether in new construction — where the SFREC could be cast into the joint region while conventional concrete fills the members — or potentially in retrofit applications, where damaged or weak joint concrete could be removed and replaced with the composite. Because the improvement is confined to the joint itself, the approach avoids the dimensional increases, weight additions, and architectural disruption associated with jacketing schemes. The epoxy binder’s rapid curing characteristics, relative to conventional concrete, could also shorten construction timelines.

The researchers are careful to frame the work as exploratory. The experimental program involved three half-scale specimens under one loading protocol, and questions of long-term durability, fire behavior of epoxy-based materials, bond between the SFREC core and surrounding normal concrete, and performance at larger scales remain open. Epoxy resins can soften at elevated temperatures, and any field application would need to account for fire protection requirements. The bond between the new composite and the existing concrete substrate, in retrofit scenarios, would also require careful detailing to ensure composite action.

Nevertheless, the study provides compelling experimental evidence that the material within a joint core, and not merely the reinforcement within it, governs how that joint performs under seismic demands. Decades of seismic engineering have focused on detailing — hoops, anchors, confinement — as the path to joint robustness. This work suggests that a carefully engineered composite material, with steel fibers doing the work of crack control in three dimensions and an epoxy matrix providing tensile capacity far beyond that of cement paste, can deliver comparable or superior performance with a fundamentally simpler reinforcement arrangement.

As cities worldwide continue to grapple with vast inventories of pre-modern-code reinforced concrete buildings, strategies that combine effectiveness with constructability will be essential. A fiber-strengthened epoxy joint core that raises strength by more than half and nearly triples energy dissipation — using no joint hoops at all — offers a provocative glimpse of where that search may lead. The next steps, scaling the concept from the laboratory to real frames, will determine whether this clever material substitution becomes a practical tool in the global effort to make existing buildings safer when the ground begins to shake.

Behind the new procedure lies a deceptively simple question that stands behind every rigorous seismic simulation: when an engineer runs a nonlinear response-history analysis — the most demanding tool in earthquake engineering, in which a detailed computer model of a structure is marched through a recorded earthquake second by second — which ground-motion records should be used, and by how much should each be amplified or attenuated? Because no two earthquakes are alike, engineers must select a handful of recorded accelerograms and scale them so that each represents the hazard level under study. The problem has spawned an entire research subfield, spanning spectral-matching algorithms, conditional-mean-spectrum methods, and generalized conditional intensity measures, all wrestling with the same challenge. Design codes such as ASCE/SEI 7-16 typically anchor scaling to a single spectral quantity at the building’s fundamental period. For a symmetric building, whose dominant mode of vibration is a simple side-to-side sway, that anchor works reasonably well. For an asymmetric-plan building, whose fundamental mode blends translation with torsion, a single spectral ordinate cannot characterize the incoming motion, and demand estimates drawn from the scaled records can be badly skewed.

The difficulty is rooted in structural dynamics. When a building’s plan is asymmetric along one direction — what the researchers call one-way asymmetry — lateral translation couples with rotation about the vertical center of stiffness. The coupled mode shapes mean the building does not merely lean with the ground; it pivots, and the flexible edge of the plan swings through larger displacements than the motion of the center of mass alone would suggest. Demand parameters such as interstory drift ratios and edge-frame deformations therefore scatter far more widely for irregular structures than for regular ones, and the choice of intensity measure becomes critical. A good intensity measure correlates tightly with the engineering demand parameters — the drifts, displacements, and force demands that designers care about — reducing the dispersion that otherwise forces analysts to run more records to reach the same level of confidence. Researchers have explored richer scalar measures, including spectral-shape indicators such as the parameter epsilon, and, most relevant here, spectra computed for oscillators that are allowed to yield rather than held elastic: the inelastic deformation spectrum.

The new procedure descends from a distinguished lineage. In 2011, researchers Erik Kalkan and Anil Chopra introduced the modal pushover-based scaling procedure, known as MPS, which scales each ground motion so that the inelastic displacement of a single-degree-of-freedom oscillator tuned to the building’s fundamental mode approaches a target derived from the structure’s own nonlinear pushover behavior. Later work extended MPS to multistory unsymmetric-plan buildings. Meanwhile, study co-author Mohammad Sadegh Birzhandi and colleague A. M. Halabian had developed the two-degree-of-freedom modal pushover analysis, or 2DMPA, which represents a plan-asymmetric building with a pair of coupled oscillators — one translational, one torsional — and applied it to fragility analysis of such structures. First author Hamid Hojaji, together with Birzhandi and Mohammad Mahdi Zafarani, fused these two threads into what they call the two-degree-of-freedom modal pushover-based scaling procedure, 2DMPS. In essence, they rebuilt the MPS philosophy on the 2DMPA skeleton, producing a scaling method whose idealized model finally matches the physics of the buildings it is meant to interrogate.

At the heart of 2DMPS lies what the authors call the inelastic 2DOF modal stick: an idealized two-degree-of-freedom system standing in for the building’s fundamental coupled lateral-torsional mode. Instead of scaling records to match an elastic spectral ordinate, the optimized procedure adjusts each candidate ground motion iteratively until the inelastic displacement of this first-mode 2DOF modal stick approaches a target value drawn from an inelastic deformation spectrum computed for the two-degree-of-freedom system. Because that target encapsulates the yielding behavior of the coupled system — its strength, its post-yield characteristics, its deformation capacity — the scaled records arrive at the full structural model already tuned to the nonlinear regime in which a real building must survive a design-level earthquake. For taller structures in which higher modes contribute significantly, the authors extend the procedure to reflect those modes, so the scaling does not blind itself to the higher-mode demands that frequently govern damage in the upper stories of taller moment frames. The payoff sought is twofold: unbiased median demand estimates, and reduced record-to-record dispersion.

To determine whether the added sophistication pays for itself, the researchers mounted a disciplined head-to-head trial. They selected three reinforced-concrete special moment-resisting frame buildings — 4, 6, and 13 stories tall — and subjected detailed nonlinear models of each to ground motions scaled three different ways: by the new 2DMPS procedure, by the original single-degree-of-freedom MPS, and by the scaling provisions of ASCE/SEI 7-16. Special moment-resisting frames are among the most ductile concrete systems in modern practice, and their response under severe shaking is governed by the controlled flexural yielding of beams and columns — precisely the nonlinear behavior that a scaling procedure must respect. A set of 21 unscaled ground-motion records served as the benchmark, providing reference distributions of engineering demand parameters against which every scaled group could be judged. The nonlinear dynamic analyses were carried out on a commercial performance-based design platform, and the team tracked how closely the median demands from each scaled set reproduced the benchmark medians, and how tightly the individual demands clustered around them.

The verdict was unambiguous. Median values of the engineering demand parameters computed from records scaled with 2DMPS closely matched the benchmark results for the buildings studied. More strikingly, the bias in demand estimates within each group of scaled records — the systematic deviation from the group median that scaling can inject — proved lower than the dispersion observed across the 21 unscaled records themselves. In practical terms, scaling the records did not distort the answer; it refined it. That a scaled subset can land within the envelope of variability of the raw records is the central test of any scaling scheme, and the authors report that it held across the buildings studied. The comparison also delivered a conceptual conclusion: the inelastic response spectra of the two-degree-of-freedom modal stick are better suited to calculating seismic demands for one-way asymmetric-plan structures than the single-degree-of-freedom inelastic spectra that underpin the older methods — an advantage that held for the small 4-story frame, the mid-rise 6-story building, and the 13-story tower where higher-mode response intrudes.

Why does this matter beyond the journal’s pages? The earthquake engineering community has long worried about the side effects of record scaling. Amplifying the record of a moderate earthquake to represent a rare, larger event distorts the frequency content and duration that a structure experiences, and studies have shown that such scaling can bias estimates of collapse probability derived from the analyses. Intensity measures that are more sufficient — that carry more of the information a structure actually responds to — shrink both that bias and the record-to-record variability that inflates design uncertainty. The 2DMPS approach attacks the problem at its source. By scaling to a target that already knows the building is asymmetric and nonlinear, it leaves the record’s idiosyncrasies less room to contaminate the demand estimates, delivering what the authors describe as both accuracy and efficiency: medians that land close to the truth, and scatter small enough that fewer analyses are needed for the same confidence.

The implications reach into everyday practice. Fragility curves — the probability statements that tell a hospital operator or a city planner how likely a class of buildings is to exceed a given damage state under shaking of a given intensity — are only as trustworthy as the demand estimates beneath them, and the authors’ earlier work applied the 2DMPA framework precisely to fragility analysis of plan-asymmetric structures. A scaling procedure that reproduces benchmark medians with lower dispersion feeds directly into sharper fragility estimates, and from there into retrofit prioritization for the irregular schools, L-shaped hospitals, and corner towers that populate seismic cities from Tehran to Tokyo to Los Angeles. The study also offers code committees a concrete alternative, having benchmarked its method directly against the ASCE/SEI 7-16 scaling procedures — the kind of head-to-head evidence that eventual revisions of seismic design provisions tend to demand.

None of this makes asymmetric buildings safe by decree; geometry remains unforgiving, and torsional response will always punish careless edge detailing. What the study changes is the fidelity of the microscope. For decades, engineers have viewed plan-asymmetric structures through analytical lenses ground for symmetric ones — single oscillators, elastic anchors, purely translational modes. Hojaji, Birzhandi, and Zafarani have ground a new lens, one that twists when the building twists. The next irregular tower on an engineer’s screen may owe its margin of safety not to extra concrete, but to a two-degree-of-freedom idealization quietly at work inside the scaling factor of every earthquake record on the desk.

The team’s research centers on prefabricated, assembled, and self-centering bridge piers. These piers are engineered to mitigate damage during seismic events while ensuring that the bridges themselves remain intact and functional. Traditional bridge design often leaves structures susceptible to significant damage or even collapse when faced with the forces of an earthquake. Conversely, the new design paradigm aims to provide a safety net against such catastrophic failures through innovative engineering solutions.

A key highlight of this research is the introduction of a damage transfer configuration within the bridge piers. Damage transfer is a strategic design method that allows for the controlled dissipation of seismic energy across the structure. By carefully distributing the forces exerted during an earthquake, these piers can prevent localized damage, which is often the precursor to failure in more conventional designs. This not only protects the bridge but also minimizes repair costs and downtime, making infrastructure more reliable and resilient.

Moreover, the self-centering feature of these bridge piers is significant. Traditional piers often experience permanent deformation post-event, necessitating extensive repairs. In contrast, the self-centering mechanism effectively restores the structure to its original position after the seismic forces subside. This capability is achieved through the integration of advanced materials and design techniques that enable the pier components to flexibly absorb and rebound from stress, akin to a spring. This functionality dramatically reduces the likelihood of severe structural damage and enhances the longevity of the infrastructure.

In addition to design innovations, the research incorporated rigorous testing methodologies to ascertain the efficacy of the prefabricated, self-centering bridge piers. The experimental setups included both static and dynamic testing, simulating various seismic conditions to evaluate how these piers behave under stress. The results were promising, revealing that the new piers outperformed conventional designs in key metrics of stability and resilience. Such findings underscore the necessity of adopting forward-thinking design philosophies in modern engineering practices.

One of the study’s co-authors emphasized the crucial role that collaboration among civil engineers, material scientists, and urban planners must play in advancing these designs from theory to practical application. Specific focus on how these new piers integrate with existing infrastructure is vital for engineering teams aiming to enhance urban resilience comprehensively. A holistic approach that considers not only the structural integrity of individual bridges but also their interaction with surrounding infrastructure is essential for sustained community safety.

The implications of this research extend beyond mere engineering improvements; they touch upon urban planning and policy. With the looming threat of climate change and the increasing unpredictability of natural disasters, cities must adapt their infrastructure development strategies. By adopting self-centering and prefabricated technologies, municipalities can significantly enhance their resilience against emergencies, ultimately safeguarding citizens and reducing economic losses.

Importantly, this innovative bridge design is aligned with global sustainability goals. The incorporation of prefabricated components can lead to reduced construction waste and shorter building timelines, supporting both environmental and economic objectives. Fast-tracked construction means fewer resources consumed and a quicker return to normalcy in the wake of disaster. For local governments looking to bolster their climate resilience efforts, these findings present a viable path forward.

As cities increasingly embrace smart technologies and data analytics, the adaptability of these new bridge designs can dovetail with digital infrastructure. Incorporating sensors and real-time data collection into the self-centering piers could provide continuous monitoring during seismic events. Such integration would empower engineers and city planners to make informed decisions regarding emergency responses and maintenance protocols.

On the research front, the study opens numerous avenues for exploration. Future investigations may delve deeper into optimizing materials for even lighter and more resilient designs or adapting the core principles of the self-centering concept for other types of infrastructures, such as buildings and retaining walls. As researchers build on this foundation, the potential for transformative breakthroughs in earthquake engineering appears limitless.

The results of this research are set to be published in a forthcoming issue of the journal “Earthquake Engineering and Engineering Vibration.” The team anticipates that their findings will not only contribute to scholarly discourse but also inform policy and best practices in civil engineering, particularly within earthquake-prone regions across the globe. While the study itself is a monumental step forward, the broader conversation about building resilient urban environments is just warming up.

In conclusion, the pioneering work of Zhang, Wu, Qian, and their colleagues represents a significant leap toward ensuring that infrastructure can withstand the rigors of natural disasters. Given the increasing unpredictability of seismic activity worldwide, the urgency of implementing more resilient designs cannot be overstated. The self-centering, prefabricated bridge piers explored in this research showcase how innovation in engineering can effectively address the challenges posed by environmental change and urbanization. The future of bridge design is here, and it holds the promise of saving lives and resources in the face of adversity.

Through collaborations, continued research, and adaptation of innovative technologies, the civil engineering community shows great potential in reshaping the infrastructure landscape. The journey towards resilient urban environments has just begun, and studies like this one are crucial milestones along the way. As advancements continue to emerge, it is imperative that the lessons learned from research translate into practical applications to build a safer, more resilient future for all.

Subject of Research: Seismic behavior of prefabricated, assembled, self-centering bridge piers with a damage transfer configuration.

Article Title: Seismic behavior of prefabricated, assembled, self-centering bridge piers with a damage transfer configuration.

Article References: Zhang, J., Wu, J., Qian, Y. et al. Seismic behavior of prefabricated, assembled, self-centering bridge piers with a damage transfer configuration. Earthq. Eng. Eng. Vib. 24, 861–874 (2025). https://doi.org/10.1007/s11803-025-2341-5

Image Credits: AI Generated

DOI: July 2025

Keywords: seismic resilience, bridge design, prefabricated structures, self-centering technology, damage transfer, civil engineering

The vulnerability of slopes during earthquakes has long posed a critical challenge to engineers, urban planners, and safety officials worldwide. Steep terrains, especially those adjacent to urban settlements or infrastructure, are particularly susceptible to failure when shaken by seismic waves. Historically, seismic intensity measures have focused predominantly on flat terrains and horizontal ground motions, often neglecting the vertical component and the nuanced behaviors of slopes at different elevations. This research addresses that gap by systematically investigating how seismic waves impact slopes of varied heights under the combined influences of vertical and horizontal shaking.

Seismic intensity measures act as pivotal indicators in earthquake engineering—they represent quantifiable parameters such as peak ground acceleration, velocity, or displacement that encapsulate the severity of seismic shaking at a site. However, the optimal choice of these measures varies depending on terrain characteristics and structural vulnerabilities. The present study highlights the importance of considering both the vertical and horizontal ground motion components to accurately characterize the seismic demand on slopes—a paradigm shift from traditional methods that largely isolated horizontal effects.

The researchers applied advanced computational models to simulate seismic events on slopes of various heights, meticulously analyzing the resulting stress distributions and potential failure mechanisms. By integrating vertical ground motion data alongside the conventional horizontal inputs, the models revealed complex interactions that substantially influence slope stability. These interactions, previously underestimated, underscore the necessity of a holistic approach to seismic intensity assessment.

One of the most compelling findings centers on the height dependence of seismic response. Slopes at different elevations do not uniformly react to seismic waves; instead, their dynamic behavior varies considerably, influencing the initiation and propagation of landslides or slope failures. The study provides detailed quantifications of how seismic intensities should be adjusted or interpreted based on height, which could transform hazard maps and risk assessments used in engineering practice.

Moreover, this research draws attention to the vertical component’s critical role—which is often overlooked—in inducing additional stresses within slopes. Vertical ground motions can exacerbate shear stresses and trigger failures in layered soil or rock formations, which are common in natural hillsides and embankments. Recognizing and incorporating this vertical shaking effect into seismic intensity measures allow for a more realistic and potentially life-saving assessment of landslide risks.

The implications for infrastructure design and disaster preparedness are profound. Engineering guidelines and building codes traditionally rely on seismic intensity measures that may not fully capture the risk posed to slopes, potentially leaving communities vulnerable. The study advocates for incorporating these refined intensity measures into the regulatory framework, advocating for adaptive engineering solutions that account for complex ground motion scenarios.

Furthermore, the research emphasizes the importance of site-specific seismic analysis, especially in mountainous or hilly regions where slope stability is a critical concern. It provides a robust methodological framework that engineers can employ to evaluate slope hazards more reliably, integrating seismic data in a way that factors in the three-dimensional nature of ground motions.

This pioneering work also has significant ramifications for early warning systems and real-time disaster monitoring. By understanding the multifaceted impact of seismic intensities across slope heights and motion components, seismic networks could be calibrated to deliver more precise warnings, potentially reducing casualties and economic losses associated with landslides triggered by earthquakes.

The interdisciplinary approach taken by the team—blending geotechnical engineering, seismology, and computational modeling—stands out as a model for tackling complex natural hazards. Their integration of empirical data and advanced simulations showcases how modern technology can push the boundaries of disaster risk science, ensuring that future landscapes are better safeguarded against nature’s unpredictable forces.

Media outlets and the broader scientific community have already noted the potential for this research to reshape earthquake resilience strategies globally. Regions with predominant hilly terrains—ranging from the seismic hotspots along the Pacific Ring of Fire to the mountainous belts in Asia and South America—are set to benefit the most as engineers and policymakers translate these findings into practice.

Looking ahead, the study’s authors call for further experimental verification through field studies and scaled physical models to validate their computational predictions. They also highlight the need for developing user-friendly tools that implement these seismic intensity measures in everyday engineering workflows, ensuring accessibility alongside scientific rigor.

In conclusion, this profound advancement in understanding seismic intensity measures for slopes under combined vertical and horizontal ground motion marks a crucial leap towards mitigating earthquake-induced slope failures. As our planet grapples with growing urbanization in seismic zones, adopting these refined measures will be instrumental in safeguarding communities and infrastructure, ultimately moving us closer to a future where the devastation wrought by earthquakes on vulnerable terrains is substantially diminished.

Subject of Research: Optimal Seismic Intensity Measures for Slopes at Various Heights Under Vertical and Horizontal Ground Motions

Article Title: Optimal Seismic Intensity Measures for Slopes at Various Heights Under Vertical and Horizontal Ground Motions

Article References:
Tran, D.T.P., Nguyen, H.D., Fei, J. et al. Optimal Seismic Intensity Measures for Slopes at Various Heights Under Vertical and Horizontal Ground Motions. Int J Disaster Risk Sci (2026). https://doi.org/10.1007/s13753-026-00696-z

Image Credits: AI Generated