Local Failure Modes Research Articles

LITERATURE SURVEY OF WEB CRIPPLING EXPERIMENT ON CEE-SHAPED SPECIMENS WITHOUT PERFORATIONS

Cold-Formed Steel (CFS) products are widely used in the field of building construction due to their inherent characteristics such as high material strength and design versatility. Depending upon their application and loading configuration, these structures are prone to different types of failures. Web crippling is a type of localized failure mode observed in CFS beam structures due to concentrated loading over them. The web crippling behavior in CFS products are influences by various factors including geometric, material, loading and environmental properties, making it a complex failure phenomenon. This literature survey investigates ten research studies performed on Cee-shaped CFS specimen, focusing on various dimensions and loading configurations. By examining the experimental and analytical methodologies considered across various studies, the paper attempts to consolidate the key findings which could propose future researches. The survey offers an insight into discrepancies in the design practices for predicting the ultimate web crippling strength in Cee-shaped Cold-Formed Steel specimens.

On the Assessment of Reinforced Concrete (RC) Walls under Contact/Near-Contact Explosive Charges: A Deep Neural Network Approach

In recent years, the use of machine learning has been expanded to several fields, with promising advances in structural engineering applications. Deep neural network models have been implemented to predict the structural response of systems under conventional loading. Some of those neural network models are based on datasets containing images, test data, and/or data produced by using finite element models developed for a specific environment. While the accuracy of these models relies on the size and quality of the dataset, their use for blast analysis is rather limited, as publicly available data are scarce or restricted. Reinforced concrete (RC) walls or slabs under blast loading are commonly evaluated for flexural and shear behaviour, for which performance guidelines are widely available. While such response mechanisms are typically associated with the far-field range, the target response is controlled by local failure modes when blast loads are generated by contact or near-contact detonations. This paper introduces the implementation of a neural network model for the response prediction of RC walls subjected to contact and near-contact explosions. The model predicts the damage category (i.e., no damage, spall, and breach) associated with a given explosion scenario. The model is trained using experimental data from multiple test programmes available in open-source literature. It considers several parameters associated with the explosive charge (e.g., type, geometry, charge weight, and standoff) and RC target (e.g., material properties, geometry, and reinforcement). The model is able to accurately predict 81% of the total breached specimens, 66% of the total spalled specimens, and 71% of the full set of non-damaged specimens, with an overall accuracy of 72%, with precision and recall ranging from 60 to 76% and 66 to 81%, respectively. The current model is shown to be a significantly better predictor of the damage category than the semi-empirical approach outlined in UFC 3-340-02, making it a promising tool that can be improved with the inclusion of more experimental data.

Computational design of auxetic microstructures via stress-based topology optimization

Material design plays a pivotal role in industries dedicated to lightweight manufacturing. In response to the needs of such industries, topology optimization (TO) has evolved beyond structural optimization to include designing material microstructures for improved structural performance. While conventional approaches often prioritize stiffness-oriented designs as a foundational aspect of structural integrity, it is equally imperative to emphasize strength-based design principles to ensure robustness against localized stress concentrations and potential failure modes. This paper explores the application of stress-constrained topology optimization (SCTO) for designing auxetic microstructures. The study commences with a comprehensive parametric analysis to examine the influence of the P-norm parameter, variations in volume fraction, and initial design adjustments on the resulting microstructures. Several optimized structures, accompanied by stress contours, are generated to showcase how the optimization process responds to these parameters. The approach employs the density-based solid isotropic material with penalization material interpolation scheme, and it utilizes the stress penalization technique to mitigate the singularity phenomenon. The multi-constraint optimization employs the method of moving asymptotes algorithm to update design variables. The effectiveness of the proposed approach to utilize actual strain fields, derived from macroscopic finite element analysis under service loads, for TO of an auxetic microstructure according to strength requirements is demonstrated. The application of the designed microstructure is explored through its integration into an auxetic cushion pad. This analysis confirms the microstructure’s effectiveness in practical applications, demonstrating its potential for broader usage in similar applications.

Dynamic response of rock sheds to successive rockfall impacts using lightweight expanded clay aggregate (LECA) cushions: An experimental and numerical study

This study investigates the effectiveness of Lightweight Expanded Clay Aggregate (LECA) as a novel cushion material mitigating repeated rockfall impacts on reinforced concrete (RC) slabs in rock sheds. Small-scale impact tests and finite element simulations analyze LECA particle size, cushioning material, block shape, and impact energy level influence on the dynamic response and damage. Results show LECA outperforms sand in attenuating impact forces and transmitted loads under successive impacts, which indicates a better protection effect on the substructure. Smaller LECA particles lead to wider stress distribution angles, longer impact durations, and lower peak forces. Block shape significantly influences impact force, with higher unified nose factors increasing forces. LECA cushions exhibit a dynamic amplification factor less than 1, indicating reduced transmitted loads compared to sand. Under high-impact energy conditions, the LECA cushion limits RC slab deflection within the elastic limit across all block shapes, while sand exceeds the elastic limit, potentially leading to structural failure. LECA mitigates flexural cracking and redistributes loads more uniformly, reducing overall RC slab damage compared to sand. However, localized failure modes require further optimization. This study highlights LECA's potential for enhancing rock shed structural safety and resilience against severe rockfall events, providing insights for optimal mitigation strategies.

Behavior of Cofferdam Using Non-uniform Geotextile Mats on Soft-overlying-stiff Foundation

Non-uniform geotextile mats are employed as soft foundations in cofferdams. However, investigations on the influence of complicated geological conditions on the mechanical behavior of cofferdams are limited. We investigated the behavior of a cofferdam using non-uniform geotextile mats to explore the failure mechanism of non-uniform geotextile mats over a soft overlying stiff foundation and quantify its stability. The two typical failure modes, global and local failure modes, differed distinctly in the velocity field and sliding surface shape. Geometric factors may partially affect the failure mode, whereas a higher soil strength can enhance the stability of the cofferdam, especially when stiff soil is involved. The failure mechanisms of cofferdams using non-uniform geotextile mats on soft overlying stiff clay and a corresponding stability prediction method are proposed to guide the design of cofferdams using non-uniform geotextile mats.

Experimental investigation of the mode I fracture toughness behaviour of timber adhesive joints: The synergistic effect of the adhesive type and the bondline thickness

Timber is a construction material widely used for structural applications. In the last decades, the improvements of both the bonding techniques and the quality of the adhesives enabled to overcome the intrinsic limitations of sawn timber, resulting in a wide spread of engineered wood products (EWPs). Understanding and assessing the bonding quality of structural EWPs has become nowadays a crucial point to assure their load-bearing capacity and even to increase their performance. One of the most revealing properties to assess the bonding quality and behavior is the fracture energy (or toughness), which could be estimated by performing suitable tests. In the present work, the results of an experimental campaign aimed to define the mode I fracture toughness of timber-to-timber adhesive bonding are presented and discussed. The fracture toughness behavior of three different categories of adhesives for structural applications was investigated, namely melamine-urea-formaldehyde (MUF), polyurethane (PU) and phenol-resorcinol-formaldehyde (PRF). In addition, the effect of the adhesive bondline and precrack thickness (0.15 and 0.30 mm) was also investigated. The results revealed different fracture toughness behaviour between the various adhesives and bond line thickness, in terms of both crack initiation and propagation. In fact, the mode-I fracture toughness appears to be highly dependent on the adhesive type, as also seen by the related analysis of variance. The fractured surfaces are also characterized by means of optical microscopy, giving insights about the local failure modes.

The 365 km tunnels assessment along ASPI Motorways Network – Key findings addressing risk analysis procedures and structural conditions evaluation and strategy of interventions

An extraordinary assessment plan, performed on 365 km of motorway tunnels, has been carried out in Italy since 2020 starting with detailed inspections and testing. Hundreds of laser scanning kilometres and ground-penetrating radargrams, thousands of concrete compressive strength tests, endoscope inspections and flat-jack tests have been performed so far. Tens of thousands structural defects were detected and several square meters of temporary safety measures installed as well. This allowed to acquire a significant amount of knowledges about the current condition of the asset. According to the process defined by the new Italian Regulations, the dataset analysis provides an insight into the condition of the asset, guiding the entire maintenance process. The visual and detailed inspections frequency is driven by the simplified risk analysis outcome and further safety evaluation are designed based on multidisciplinary criticality. A comprehensive approach, based on in-depth knowledge of the characteristics of the existing tunnel, has been engineered for structural risk, with a focus on tunnel “history” (excavation stages and techniques, construction materials, etc.), design and dimensioning approaches (e.g. Kommerel’s graphical method), identified as standard methods for the tunnel construction period from literature review. Additional analyses are carried out for likely local structural failure modes of tunnel lining (punching and flexural strength of residual concrete layers, spalling hazard of concrete thickness anomalies due to temperature variations). When re-lining is needed, the design of a new shell aimed to ensure at least the same structural performance of the original one is addressed, including seismic loads that were neglected in the original design. The tunnel assessment, from inspections to re-lining works passing through risk analysis, is an on-going process open to be improved in the upcoming years within a wider asset management strategy.

An Improved Approach of Classical Upper Bound Theory for Stability Analysis of Layered Slopes

The equations for the critical height of layered slope were derived by a related researcher, but they lack details and do not agree with the method of limit equilibrium. So this topic was reinvestigated. Considering the possible global or local failure modes of the layered slope, the equations for the critical height of the above modes are derived based on the upper limit theorem by using rotational failure mechanisms or rotational and translational failure mechanisms. Based on the above theory, the stability coefficients of layered slope are investigated. The results show that the presented upper bound approach has better performance than other methods mentioned in the literature and is consistent with the limit equilibrium method. In combination with the strength reduction method, the global and local stability of the layered slope are analyzed using the several examples. The high-calculation accuracy of presented method and the specific measures to improve the smoothness of the sliding surface are reviewed. From the perspective of the combination of sliding surfaces, the dimensionless parameter vector of the layered slope is introduced. The possible limitations of the upper bound limit approach with log spirals are pointed out and the conditions which must be fulfilled in order to achieve a higher computational accuracy are mentioned.

Design of steel-concrete composite panels under low-velocity impact: Local punching failure

Steel-concrete composite panels (SC panels), consisting of two layers of steel plates and one layer of in-filled concrete, have excellent impact resistance. Currently, the proposed impact-resistant design methods of SC panels under low-velocity impact only consider the overall bending failure mode, but are unsuitable for the more common local punching failure mode. This study establishes an ideal tri-fold line resistance function and theoretically derives the stiffness and resistance of SC panels for the local punching failure mode. Furthermore, from the energy perspective, a design method is proposed in the study with impact-side steel plate tearing and SC panel penetration as safety criteria, and a design process covering two types of failure modes is provided. The design process is applied to the SC panel of the AP1000 nuclear station, and its practicality is validated, providing a simple tool for researchers and engineers.

Experimental recognition of seismic performance of simple bolt-connected precast frame by comparing with equal stiffness cast-in-situ frame

Multi-story industry buildings composed of precast concrete members and simple bolt-type connections are widely constructed in the world, and there is enormous need for future construction market. Based on the equal stiffness and stiffness distribution along the height, a 1/5-scale precast RC frame utilizing simple bolt-type connections and a reference cast-in-situ monolithic RC frame were designed and constructed to conduct shaking table tests. According to the test results, the seismic responses, failure modes and energy dissipation behaviors of the two models were analyzed and compared. The vibration modes of the precast frame performed bending deformation pattern, while the cast-in-situ one presented shear deformation pattern. The damage and inter-story drift of the precast frame was comparatively uniformly distributed along the stories, whereas that of the cast-in-situ frame was concentrated in the first story. The energy dissipation capacity of the precast frame was inferior to that of the reference frame, as the bolt-type connections couldn't have plastic damages and plastic hinges that occurred in the cast-in-situ joint zones. In general, the global seismic performance of the precast frame was close to the reference frame and its collapse resisting capacity under severe earthquakes was reliable. Some serious local failure modes and less of energy dissipation capacity of the precast frame should be concerned in high seismic regions.

Evaluation of impact response of thermal-damaged FRP-RC slabs: Effects of FRP bar type and concrete cover thickness

The purpose of present study is to investigate the impact response of FRP-RC slabs under elevated temperatures. Considering the high-temperature degradation effect and strain rate enhancement effect of FRP bars and concrete materials, a numerical model for studying the fire and impact resistance of FRP-RC slabs was established and verified. The impact failure mechanism of in-fire thermal-damaged FRP-RC slabs was analyzed. The influence of the type of FRP bars, concrete cover thickness and fire duration on the in-fire impact resistance of FRP-RC slabs was revealed. Ultimately, the post-fire residual bearing capacity of the slabs after elevated temperature and impact was obtained. The results show that the typical local punching failure mode is not affected by thermal damage while energy dissipated by concrete accounts for most of the impact energy absorbed by the slabs. When exposed to fire for 60 min, the elevated temperature significantly deteriorates the impact resistance of FRP-RC slabs with a cover thickness of 15 mm. At this time, the greater the concrete cover thickness, the better the impact resistance of FRP-RC slabs. Under the combined action of elevated temperature and impact, Carbon FRP-RC slabs have greater stiffness, lower deflection, greater impact plateau value, less impact duration and lower energy consumption than Aramid FRP, Basalt FRP and Glass FRP-RC slabs. Moreover, the damage index of the slab based on residual bearing capacity and peak displacement is approximately linearly positively correlated. The influence of the concrete cover thickness is more prominent on the damage index based on the peak displacement.

Nonlinear Inelastic Stability Behavior of High-Strength Stainless Steel I-Beams with Sinusoidal Web Openings

Perforated beams can bring countless benefits compared to traditional plain-webbed beams. However, steel beams with sequential web openings are more susceptible to instabilities, and special care must be taken in a design concerning the failure modes these structures can present. The study presented herein explicitly dealt with the stability behavior of perforated beams with sinusoidal openings. This type of perforated member features smooth-lined openings constructed from a single thermal cut in conventional plain-webbed steel profiles. A broad study was carried out through numerical simulation using the ABAQUS software, in which perforated profiles manufactured with S600E high-strength stainless steel were studied. The use of high-strength steels in perforated profiles is a little explored topic in the literature, despite having a significant impact on the behavior of these elements. With the study carried out, a broad overview of the stability behavior of these members was obtained, especially concerning global stability. A total of 5940 FE models were developed, considering the application of different types of loads. In these models, linear buckling analysis (LBA) and geometrically and materially nonlinear analysis with imperfections (GMNIA) were performed. The results obtained were compared with international design codes, and it was found that some codes fail to represent the behavior of members that present lateral-distortional buckling (LDB) and interactions between local and global failure modes. This behavior is a significant design concern since the studied members had high yield strength, making them more susceptible to interaction-governed failure modes than usual-yield strength members. Additionally, the study found that some design codes do not accurately represent the behavior of members loaded outside the shear center due to the destabilizing effect of loading on these structures.

Minimum longitudinal reinforcement in rectangular and flanged reinforced concrete walls

The amount of longitudinal steel in reinforced concrete walls is a key point in the damage distribution along the wall, although it is usually associated mainly with the prevention of temperature and shrinkage problems. A recent earthquake in New Zealand pointed out its relevance after the observation of a localized failure mode found in walls due to insufficient longitudinal steel reinforcement. Low amounts of longitudinal steel reinforcement prevent the correct distribution of the damage and can even lead to an early fracture of the reinforcement. The following study analyzes walls with different sections, such as T, L, and C-shaped walls, among others, subjected to pushover analysis, where the amount of longitudinal boundary reinforcement is varied, using values close to the minimum provided by ACI 318-19 code. The main parameter under analysis was the strain at the boundaries, revealing different behavior depending on the amount of boundary steel. When using steel amounts less than the minimum provided by the code, a greater growth for the tensile strain is observed, which in turn localizes the damage in a few zones along the wall height at low drift levels. This is overcome when using the recommended minimum steel amount. In addition, regarding the strength-to-cracking moment ratio (Mn/Mcr), although related to the growth of tensile strains, there is no specific value that can be recommended for all wall cross-sections.

Perforation of carbon fiber reinforced plastic laminates struck transversely by hemispherical-nosed projectiles

This study focuses on perforation of carbon fiber reinforced plastic (CFRP) laminates struck transversely by hemispherical-nosed projectiles. Global deformation with local rupture failures for thin laminates and localized response failures for thick laminates are two common categories of the ballistic perforation of CFRP laminates. An analytical model is proposed considering these two failure modes and their transition conditions. The ballistic limit predicted for laminates in global deformation with a local rupture failure mode is given based on the energy dissipation method, and an ultimate perforation failure criterion is derived based on the bottom surface tensile fracture of the laminate. A critical transition condition of the two failure modes is obtained by combing the localized response failure model and Von Karman’s critical impact velocity concept. Model predictions agree with the experimental and numerical results regarding ballistic limits in a wide ratio range of laminate thickness H and hemispherical-nosed projectile diameter d.

Stiffness evaluation of UHPC-filled socket column-foundation joints: Numerical investigation and analytical model

Socket connections are widely used to connect precast columns to the foundation and the initial stiffness of the socket joints is of great significance for seismic design. The connection efficiency of precast socket column has an important influence on its initial stiffness. Therefore, based on the previous experiment research on socket column by authors’ team, a finite element model (FEM) of ultra-high performance concrete (UHPC)-filled socket precast bridge column-foundation joints was established and verified by the local damages, failure mode and hysteresis curves. The key parameters that influencing the initial stiffness of socket joints were studied by numerical analysis, and a simplified calculation formula of initial stiffness was proposed. In addition, based on the theory of elastic foundation beam, an analysis model for predicting the initial stiffness of socket joints considering rotating stiffness of the connection was developed. The theoretical results are verified by the proposed simplified equations and experiments results in the literature. The method presented in this paper can conveniently predict the initial stiffness of RC socket column-foundation joints with reasonable accuracy.

Model for calculating local bearing capacity of concrete with spiral stirrups

This study evaluates the mechanical and failure modes of 30 concrete specimens under local compression. The experimental results indicate that the specimens undergo three types of local compressive failure modes. These modes primarily depend on the strengths of the tensile and compression regions. Based on the test results, a calculation model for the local bearing capacity of concrete with spiral stirrups Fl is formulated. In the model, the local compressive failure of concrete with spiral stirrups is classified into tension and compression. The yielding of spiral stirrups in the tensile region is regarded as tensile failure, and compressive failure is considered to have occurred when the strain value in the compression region reaches 0.002. To simplify the model calculation, the spacing s, diameter d, and yield strength fy of spiral stirrup as well as the local compression area ratio Ab/Al (ratio of the concrete bearing area Ab to the loading area Al) are comprehensively analyzed. Based on the analysis results, a formula for the bearing capacity of the reinforcement Ns is derived. The independent variables of the formula are yield force of spiral stirrup fyAssl, stirrup spacing s, and ratio of specimen side length to loading plate side length h/a. A simplified formula for calculating the tensile failure of the specimen is derived. To ensure simultaneous tensile and compressive failures, a critical reinforcement ratio of the spiral stirrup ρvu is proposed based on the calculation model. Test data from similar axial local compression tests are collected to verify the accuracy of the calculation model. The local bearing capacity of concrete is recalculated according to the calculation method proposed in this study. Results show that the calculation model is highly accurate. Accordingly, it may be used as reference for calculating the local bearing capacity.

Bioinspired Hierarchical Ceramic Sutures for Multi‐Modal Performance

AbstractNatural suture structures, characterized by hard segments joined along a patterned weak interface, are found to provide unique toughening mechanisms for brittle bulk biological materials. Hierarchical ceramic sutures inspired by white‐tailed deer crania and diabolical ironclad beetle exoskeletons are developed using a biomimetic approach. Overlapping geometries unlock twin energy absorption mechanisms. Ceramics with Surlyn‐infiltrated precision laser‐cuts are fabricated using a semi‐automated and smart advanced manufacturing platform. A parametric study comprising four‐point bending, fracture toughness, and tensile tests is conducted to evaluate toughness, strength, and stiffness with geometrical interlocking in two hierarchical orders. Digital image correlation is utilized to analyze the local toughening mechanisms and failure modes in the fracture tests. For all three metrics, the panels with second‐order hierarchy outperform the anti‐trapezoidal equivalents. The ceramic sutures show up to 590%, 340%, and 700% improvements in energy absorption in the tensile, bending, and fracture tests, respectively, owing to the optimal first‐ and second‐order interlocking angles. The high‐order fractal interlocking at multiple scales and overlapping teeth are found to provide high flexibility and failure resistance, whereas progressive fracture mechanisms delay catastrophic failure by up to 50%. The concept of hierarchical suture can lead to industrially applied ceramic systems with tailored mechanical performances.

Lateral Distortional Buckling Resistance Predictions of Composite Alveolar Beams: A Review

Few studies have investigated the structural behavior of steel-concrete composite alveolar beams in hogging bending regions. Their resistance can be reached by lateral distortional buckling (LDB), coupling LDB and local failure modes, or limit states of cracking or crushing in the concrete slab. This case is characteristic of continuous or cantilever elements. Another critical issue is that the design and calculation recommendations only address the LDB verification on steel-concrete composite beams without web openings, thus disregarding the interaction between the buckling modes. Furthermore, it is necessary to use adaptations of these formulations for beams with web openings. This review paper aims to evaluate the different approaches for standard code adaptations to verify the LDB resistance of the beams in question and to highlight the investigations that addressed this issue. The addressed adaptations consist of different approaches which determine the cross-section geometric properties in the central region of the openings, the so-called double T section, in the region of the web posts (solid section), and the averages between the solid section and double T section. The accuracy of the formulations in question is verified against experimental results from the literature. Furthermore, discussions and suggestions for further studies are presented.

Shake-table testing and numerical simulation to select the FRCM retrofit solution for flexure/shear deficient RC frames

This paper presents shake-table and numerical investigations to select a retrofit strategy for reinforced concrete (RC) frame structures using fiber-reinforced cementitious matrix (FRCM) composites. Two FRCM alternatives are investigated, namely polyparaphenylene benzobisoxazole (PBO) and carbon FRCM composites, denoted as ‘P-FRCM’ and ‘C-FRCM’, respectively. The study focuses on implementing the selected retrofit material with spike anchorage systems to delay the debonding failure and addresses different failure modes of RC framing systems, including shear or flexure failure. The first phase of this study involves pre shake-table test (STT) simulation to investigate the effectiveness of the selected retrofit technique in delaying local and global damage states and failure modes. STT campaigns are undertaken in the second phase to assess the seismic performance of framing systems retrofitted with different FRCM materials and verify their fiber-based modeling approach. The verified numerical modeling approach of the retrofit techniques is utilized in the third phase to upgrade a benchmark RC moment-resisting frame (MRF) building. A parametric study involving inelastic pushover analyses (IPAs) and multi-record incremental dynamic analyses (IDAs) is finally conducted to assess the vulnerability of the retrofitted building with different FRCM alternatives. It is concluded that the adopted two retrofit techniques significantly reduced the collapse damage state at the design and maximum considered earthquake intensities by up to 59% and 46%, respectively. Although the P-FRCM composite has 38% higher tensile strength and 76% higher ultimate tensile strain than C-FRCM, it slightly improves the overall seismic performance by up to 9% based on the adopted seismic performance index. Owing to the higher cost of P-FRCM compared with its counterpart, a performance-to-cost index confirmed that the C-FRCM composite is the preferred retrofit technique for MRF structures.

ANÁLISE TEÓRICA PELO MÉTODO DA RESISTÊNCIA DIRETA DE SEÇÕES DUPLAS DE PERFIS DE AÇO FORMADOS A FRIO SOB COMPRESSÃO

The need for lighter, lower-cost construction has intensified, so the presence of cold-formed profiles has become common in civil construction, offering greater efficiency in the ability to withstand the current demands. The present article aimed at the theoretical study on the stability of double U and U lipped sections, composed of cold formed steel profiles, submitted to compression. Under the justification of analyzing the effectiveness of this type of structural element, with the help of the CUFSM Software that uses the Finite Strip Method, and verify the resistance by the Direct Strength Method (DSM). The objectives of this study were: to investigate the modeling in the CUFSM software for a double section with profiles connected to each other; and apply the DSM to the theoretical analysis of double sections with Brazilian commercial profiles. It was found that the variation in the number of connections influences the analysis and can reproduce the partial connection behavior. The application of folds proved to be efficient, with little influence on local instability and considerable influence on distortion instability. The DSM showed a loss of resistance for the models that presented a local failure mode, being, therefore, the most important factor regarding the resistance.