Vasant Matsagar

During the course of their design life, base isolators may be subjected to elevated temperatures for a variety of reasons, including fire hazards. In such scenarios of elevated temperatures, the vertical load-carrying capacity of base isolators could deteriorate. Therefore, assessment of the stability of fiber-reinforced elastomeric isolators (FREIs) under the vertical loads from the superstructure while under elevated temperatures is important. In this study, the buckling behavior of FREIs is investigated under ambient and elevated temperatures. Available closed-form expressions to predict the buckling load of FREIs at ambient temperatures are extended for applications under elevated temperatures. Under elevated temperatures, the buckling load is derived by considering the thermal expansion of the FREIs and the material degradation of the elastomers with the rise in temperature. Further, nonlinear finite-element analyses are conducted to numerically evaluate the buckling behavior of a wide range of FREIs with various inherent properties. Modified Riks analysis is utilized to estimate the nonlinear buckling behavior of the FREIs. Transient heat transfer analysis within the FREIs is conducted to observe the buckling loads of the FREIs after various time instances, and the steady-state uniform elevated temperature in the FREI is found to be the worst-case condition under the considered thermal boundary conditions. Herein, only the thermal scenarios of uniform elevated temperatures at all the faces of a single FREI are explored. It is observed that the closed-form expressions for buckling load under elevated temperatures could effectively predict the buckling loads of the FREIs, providing slightly conservative values for most cases. Interestingly, the results show that the FREIs with low aspect ratios (such as 1.20) demonstrate the maximum reduction in their vertical load-carrying capacity with the rise in temperature.

Basalt fiber–reinforced polymer (BFRP) composites have recently been introduced in civil engineering applications, yet research on their behavior at elevated temperatures remains limited. A comprehensive understanding of BFRP behavior is crucial for practical and cost-effective fire-safety design applications. This study investigates the performance of basalt fiber–reinforced polymer rods at elevated temperatures. Tension tests were conducted at temperatures up to 450°C, and the changes in mechanical properties were assessed. The findings indicated that the BFRP rods exhibited marginal degradation in mechanical properties at temperatures below 300°C, retained 58% of their tensile strength at 400°C, and lost all tensile strength at 450°C. Scanning electron microscopy analyses revealed fiber discreteness and resin decomposition at high temperatures. Additionally, a semiempirical constitutive law was developed to correlate the mechanical properties of the BFRP rods with the exposure temperature. The proposed model is novel and flexible and demonstrates good applicability to existing literature data sets within the investigated range of material properties. This model can predict the thermomechanical behavior of fiber-reinforced polymer bars using fundamental parameters typically known during manufacturing, potentially eliminating the need for elevated temperature testing.

Base isolation is an attractive technique for protection of structures against earthquakes. Especially, lifeline structures such as hospitals need to remain operational during and after natural disasters like earthquakes or cyclones. However, various environmental factors gradually degrade the performance of the base-isolated buildings in the form of deterioration of the material properties utilized in the base isolation as well as in the primary structure itself. Therefore, the present study aims to investigate the service-life performance of a base-isolated hospital building situated in New Delhi, India under multiple hazards. A detailed numerical study is conducted wherein the lead rubber bearing (LRB)-isolated hospital building is subjected to nonconcurrent earthquake and wind excitations. The effect of chloride-induced degradation of the structural elements and the oxidation-based degradation of the rubber in the LRBs is investigated over the service-life of the building. Interestingly, due to the addition of the LRBs, the hospital building could attain operational performance under earthquakes even with reduced structural member sizes, which in turn diminishes the carbon footprint of the entire project. Therefore, this study further compares the multi-hazard service-life performance of a regular base-isolated structure against a base-isolated structure with reduced carbon footprint.

Long-span cable-stayed bridges present significant engineering challenges due to their susceptibility to dynamic excitations across multiple frequency ranges. This study develops an innovat...

In this study, the comparative residual performance of fire-exposed reinforced concrete (RC) beams with rectangular and T-shaped cross-sections is investigated. Two concrete beams, one with a T-section and the other with a rectangular section, were tested under the combined effects of fire exposure and structural loading. Data generated in the tests during and following fire exposure is utilized to compare the thermal and structural response of the beams. The results indicate a notable difference in the temperature evolution, mid-span deflection, and the residual capacity of the beams. The T-beam experienced greater deflection and stiffness degradation due to its larger exposed surface area (approximately 17% higher than the rectangular beam) and flange geometry, despite comparable peak rebar temperatures. A simplified approach, based on the maximum concrete and rebar temperatures and corresponding strength reductions, is proposed to evaluate the residual capacity of fire-exposed RC beams. For equal cover depth to reinforcement, peak rebar temperature is unaffected by cross-section shape as long as the web of the T-beam is not slender. T-shaped beams with similar overall depth exhibit greater post-fire strength retention than rectangular beams when the neutral axis lies within the flange. A 20% reduction in the web thickness and a combined reduction of 20% in web and 37% in flange thickness result in a comparable decrease in the flexural capacity to that of the rectangular beams of similar depth, indicating that the flange plays a key role in maintaining post-fire performance.

In densely populated urban areas, the spread of fire between buildings is a significant risk. Many urban spaces have evolved with a preference for quick and cheap construction in deference to fire safety and adherence to any applicable local building regulations. With the increasing use of combustible and flammable materials inside and on our buildings, exacerbating the potential for building‐to‐building fire spread, it is therefore necessary to re‐evaluate the threat to the built environment due to this scenario. In order to address this research gap, computational fluid dynamics is implemented as a tool to simulate the behaviour of a fire and to determine the spatial evolution of the external temperature and heat flux away from the burning compartment's external openings under varied fuel load, fire growth rate and ventilation modes. It is shown that these outputs are a function of the heat release inside of the compartment as well as the internal ventilation conditions, with internal doors being closed increasing the intensity and extent of external conditions. This gives insight into factors which could lead to subsequent secondary ignition away from the compartment of origin. We also show that for a given heat release rate, the criteria for window breakage and therefore the time at which window breakage occurs is irrelevant to the ultimate magnitude and extent of the external conditions. These reflect essential considerations, necessary for ignition criteria of novel/new material consideration in the context of building‐to‐building fire spread in high density housing stock.

The confined explosion is a very complex and is a critical problem in various sectors such as defense, petrochemicals, important structures, and industrial structures. The explosives are generally enclosed in a casing. Steel is a commonly used explosive casing material and exhibits intricate and disastrous effects on the container structure, after the detonation of explosive sealed in it. The rupture of casing material develops shards, and these shards are responsible for damage to the container structure. Structure geometry and the material used for the explosive casing, affect the response of the structure subjected to explosions. The cubical or rectangular-shaped structures are generally used for blast resistance of structures. In this study, a finite element-based numerical investigation is conducted to estimate the dynamic response of steel cubical structure subjected to confined explosion. The influence of different lightweight explosive casing materials such as carbon fiber-reinforced polymer (CFRP), glass fiber-reinforced polymer (GFRP), and steel material on the response of the structure is assessed and compared. The initial velocities of the shards generated from explosive casings after the explosion are estimated and compared with code-based guidelines. Furthermore, the response of the un-stiffened and stiffened cubical structure with different stiffener configurations i.e., cross, plus vertical, horizontal, and v-type is compared, and an effective configuration of the stiffener is proposed with the highest blast resistance of the structure. It is observed that the CFRP and GFRP explosive casings show an enhanced energy dissipation ability compared to the steel explosive casing. Edge tearing and maximum central deflections are identified as the dominant failure modes, which can be controlled by using adequate stiffener configurations on the structure. The v-type stiffener and vertical stiffener configurations are found to be the most effective in resisting the effect of confined explosion compared to other configurations considering the strength and serviceability criteria.

This study presents a generalized mathematical formulation and performance evaluation of an energy‐based predictive (EBP) control algorithm for mitigating the seismic response of base‐isolated (BI) multistory buildings equipped with distributed multiple semiactive tuned mass dampers (DM‐SATMDs). Although base isolation effectively limits superstructure accelerations, it often results in large isolator displacements, particularly under strong or near‐fault ground motions. To address this limitation, the EBP algorithm—originally developed for a single semiactive TMD—is extended herein to an arbitrary number of semiactive units distributed across multiple floor levels. The coupled equations of motion for BI buildings with DM‐SATMDs are derived, and a comprehensive parametric study is performed considering different isolation periods, TMD parameters, and number of stories under real earthquake records. Four configurations are examined: BI without TMDs, BI with a single SATMD (S‐SATMD), BI with multiple SATMDs (M‐SATMDs) placed on the same floor, and BI with DM‐SATMDs. The proposed strategy is further evaluated through floor response spectra (FRS), comparisons with existing passive and semiactive control strategies, robustness analyses, and a nonlinear lead–rubber bearing model accounting for heating‐induced lead‐core strength degradation. The results show that the proposed control algorithm is generally more effective for taller BI structures across all evaluated parameters. Notably, the BI + DM‐SATMDs configuration promotes an effective redistribution of seismic energy between the isolation system and the auxiliary dampers. Further, the proposed EBP‐controlled DM‐SATMDs largely outperform S‐SATMD and conventional DM‐PTMDs in mitigating FRS across all considered earthquake records, enhancing floor acceleration control and secondary systems performance. Overall, the proposed EBP‐based DM‐SATMDs framework offers an efficient and adaptable strategy for improving the seismic resilience of BI structures.

In current days, sandwich structures have become popular due to their flexibility with design requirements and excellent performance under extreme loads, such as blast. There are different strategies for enhancing the blast resistance of such sandwich structures. Including an additional layer of polyurea and stiffeners are widely used techniques that may enhance the performance of the panels under high-rate loadings. In this study, the effects of polyurea and stiffeners on the protection of a steel and aluminum foam sandwich panels is studied. Effective configuration of the panels with both polyurea and stiffeners are investigated. Here, different configuration cases of the sandwich panels: (a) panel without polyurea and stiffeners, (b) with polyurea applied on the rear face, (c) with stiffeners applied on the rear face, and (d) with stiffeners and polyurea on the rear face are investigated and compared. The finite element models of sandwich panels are developed, where steel facesheets, steel stiffeners, and polyurea are modeled with shell elements, and aluminum foam core is modeled with solid elements. Elastic-plastic, crushing foam, and hyperelastic material behaviors are implemented for steel, aluminum, and polyurea layers of the sandwich panels, respectively. The performance of the different configurations of the panels are compared in terms of the response quantities, i.e., deformation, equivalent von-Mises stresses, and energy absorption. Moreover, the damage patterns with fragmentation effect are depicted for all the considered sandwich panels. The results of the study show that both polyurea and stiffeners are the most effective configurations in protecting the sandwich structures; however, with the same thickness of polyurea and stiffener, the stiffeners show better performance than polyurea against blast load. Furthermore, it is observed that the deflection values across the configurations follow a logarithmic decay pattern.