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 pulse period, usually written as Tp, governs the dominant timescale of a velocity pulse and wields an outsize influence on how structures respond. Whether a pulse is short and sharp or long and rolling can determine whether a frame sways mildly or lurches into its inelastic range, and the relationship between Tp and a building’s fundamental period can swing structural demands dramatically. Pulse period also feeds directly into ground-motion simulation, pulse-consistent spectral models, and probabilistic seismic hazard analysis, which means that getting Tp wrong can quietly distort downstream estimates of earthquake risk.

Yet despite decades of research, no single method for determining Tp has achieved universal acceptance. Wavelet analysis, peak-point measurements on velocity time histories, analytical pulse-model fitting, and response-spectrum-based techniques all identify the period in different ways. The most popular family of approaches reads Tp directly off a response spectrum, taking the period at the peak of the spectral velocity (the SV method) or at the peak of the product of spectral velocity and spectral displacement (the SV·SD method). These methods are attractively simple, but they hinge on picking one local maximum out of a spectrum that may be jagged, multi-peaked, or contaminated by high-frequency content, and that dependence can produce badly underestimated or overestimated pulse periods for certain records.

The new study takes a fundamentally different route. Instead of hunting for a spectral peak, the researchers define the pulse period using the relative elastic input energy spectrum, EI,r, a quantity from energy-based seismic design that reflects not only the amplitude and frequency content of a ground motion but also its duration and total energy. The rule is elegant: the pulse period is the oscillator period that bisects the area enclosed by the EI,r spectrum and the period axis, leaving exactly half of the spectral energy on each side. Rather than asking where the spectrum peaks, the equal-area criterion asks where the cumulative input energy is balanced, producing a globally representative characteristic period for the record.

To make the integration interval robust, the team devised an adaptive termination criterion. The energy spectrum is computed from 0.01 seconds in steps of 0.01 seconds, and the calculation continues until the spectral tail has decayed sufficiently: the most recent twenty consecutive ordinates must all fall below either one percent of the running spectral peak or an absolute tolerance, with tightly constrained variation between adjacent ordinates. A hard cap of 40 seconds prevents runaway extension for records with persistent long-period content. Sensitivity analyses reported in the paper confirm that the identified pulse periods are essentially insensitive to reasonable variations in these parameters.

Crucially, the authors did not simply assert that their equal-area period is physically meaningful; they tested it. The EI,r-based Tp is prescribed in the analytical pulse model of Mavroeidis and Papageorgiou, while the remaining four pulse parameters, amplitude, phase, number of oscillations, and timing, are optimized with a genetic algorithm that minimizes the squared difference between the extracted pulse and the original velocity time history. Because the pulse period is held fixed during optimization, any agreement between the extracted wavelet and the actual record must flow from the identified period itself. Across the records examined, the optimized pulses reproduced the dominant velocity features and matched the principal range of the 5-percent-damped spectral velocity, supporting the physical reasonableness of the new definition.

The method was then benchmarked against six established techniques: the continuous wavelet transform classification of Baker, a wavelet packet transform approach, variational mode decomposition combined with genetic-algorithm pulse fitting, a signal-only optimization parameterization, and the SV and SV·SD spectrum methods. Across 311 representative pulse-like records, correlation coefficients between the new method and the reference approaches ranged from 0.87 to 0.98, with most above 0.90, indicating strong overall consistency. Detailed case comparisons revealed instructive differences. On some records the SV method seized on a short-period local peak and produced a far too narrow pulse, while the SV·SD method occasionally drifted toward very long periods. The equal-area energy criterion typically landed between the two, capturing the main velocity-pulse scale without the extremes of either peak-chasing approach.

To demonstrate engineering relevance, the researchers classified pulse-like motions into short-, medium-, and long-period groups and assessed the collapse fragility of a four-story, three-bay reinforced concrete frame modeled in OpenSees. The fiber-section model, validated against shake-table test data from the European Laboratory for Structural Assessment, reproduced measured drift profiles, displacement histories, and story shears with satisfactory accuracy. Cloud analyses using the geometric-mean spectral acceleration as intensity measure and the maximum inter-story drift ratio as demand parameter showed that pulse period matters enormously: records with pulses longer than two seconds produced markedly higher collapse fragility, while the short-period group shifted fragility curves toward higher ground-motion intensities and thus more favorable collapse performance. Comparable trends emerged when records were grouped using the CWT and SV·SD methods, reinforcing the conclusion that the observed pulse-period effect is genuine rather than an artifact of one identification technique.

The authors are careful to position the new criterion as a complement rather than a replacement. Different identification methods emphasize different characteristics of complex pulse-like motions, and no single definition suits every record. What the equal-area EI,r approach offers is a measure that is less hostage to a particular local spectral peak, is grounded in the cumulative distribution of input energy that energy-based design frameworks already prize, and carries a clear physical interpretation as an energy-balanced characteristic period. The study also confirms that pulse period is a critical parameter for interpreting the collapse potential of near-fault motions and for building pulse-period-dependent fragility models.

Limitations remain, and the authors flag them candidly. The structural application covered only a four-story bare reinforced concrete frame, so the quantitative fragility results depend on that building’s dynamic properties and its 0.711-second fundamental period. Future work, they write, should extend the framework to structures with different heights, periods, and response mechanisms to probe the interaction between pulse period and structural period more deeply. Even so, the method arrives at a moment when near-fault seismic risk assessment increasingly demands pulse-aware tools, and it provides engineers and hazard analysts with a computationally light, physically grounded way to extract one of the most consequential numbers in earthquake engineering from any velocity record.

Subject of Research: An energy-based method for identifying velocity-pulse periods of near-fault ground motions

Article Title: An efficient energy-based approach for identification of velocity-pulse periods

Article References: Gao, Q., Chang, Z., Monti, G., & Mollaioli, F. (2026). An efficient energy-based approach for identification of velocity-pulse periods. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02677-5

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02677-5

Keywords: pulse period, near-fault ground motions, input energy spectrum, velocity pulse, seismic fragility, reinforced concrete frame, genetic algorithm, M&P wavelet, probabilistic seismic hazard analysis, earthquake engineering, response spectrum, collapse vulnerability