Maximum Mid-span Deflection Research Articles

Research on and Model Analysis of Flexural Mechanical Properties of Basic Magnesium Sulfate Cement Concrete Beams.

This study presents a comprehensive investigation into the mechanical properties of Basic Magnesium Sulfate Cement Concrete (BMSC) in comparison to Ordinary Portland Cement Concrete (OPC) within reinforced concrete components. The main objective is to evaluate BMSC's applicability for practical engineering purposes, with a focus on its with early high strength, improved toughness, and superior crack resistance compared to conventional concrete. Experimental procedures involved fabricating beam specimens using OPC concrete with a C40 strength grade, alongside BMSC beams with varying strength grades (C30, C40, and C50). These specimens underwent bending resistance tests to analyze crack patterns and mechanical characteristics. The findings reveal that BMSC beams demonstrate enhanced bending and tensile properties at equivalent strength grades compared to OPC beams. Particularly, cracking mainly occurred at the mid-span region of BMSC beams, characterized by narrower cracks, indicating superior crack resistance. However, it was noted that the toughness of BMSC beams decreases as the strength grade increases. The maximum mid-span deflection of the BMSC test beam was smaller than that of the OPC test beam, which was 3.8 mm and 2.6 mm, respectively. The maximum crack width of the OPC beam was 4.7 times that of the BMSC beam. To facilitate practical implementation, the study developed calculation models for estimating the crack bending distance and ultimate bending distance in BMSC beams, offering valuable tools for engineering design and optimization. Overall, this research provides significant insights into the mechanical behavior of BMSC, presenting potential advantages for structural engineering applications.

Prediction of mechanical response of hexagonal honeycomb SPS blast wall under explosive loading: In-depth review and empirical formula

Despite comprehensive prevention strategies, offshore operations consistently grapple with health, safety, and environmental (HSE) challenges. Though explosions on offshore structures are rare, their devastating impact cannot be understated. Blast walls, functioning as pivotal passive barriers, play a crucial role in protecting the topsides of these structures by dissipating explosive energy. Sandwich panel structures (SPS), with their lightweight attributes, enhanced bending rigidity and exceptional energy absorption, are a cost-effective countermeasure. This study introduces a groundbreaking design guideline, anchored in the LS-Dyna nonlinear finite-element method (NLFEM), tailored for hexagonal SPS offshore blast walls under explosive strains. Our rigorous numerical simulations, encompassing 450 varied scenarios, meticulously evaluated an array of geometric configurations and explosive strengths (spanning from 1 kg to 3 kg of TNT). From these simulations, crucial parameters affecting maximum mid-span plate deflection were discerned. In addition to these simulations, our research offers in-depth technical reviews, shedding light on the nuances of the subject. An empirical formula was subsequently formulated to anticipate this deflection, corroborating its efficacy by FE simulation outcomes. This work provides invaluable guidance for refining early-stage offshore blast wall design.

Magnetic Alignment of Micro Steel Fibers Embedded in Self-Compacting Concrete

Steel fiber reinforced cementitious composites (SFRCC) have emerged as one of the most efficient techniques to improve the flexural capacity and ductility performance of concrete. However, one of the most significant shortcomings is the randomness of steel fibers direction in the concrete matrix, which influences the extent of mechanical enhancement for a limited fiber content. An experimental approach to control the direction of steel fibers embedded in self-compacting concrete is presented in this study, which is based on generating a driving rotating force to overcome the viscous impeding forces acting onto the embedded fiber. The mechanical performance of micro steel fiber reinforced self-compacting concrete members was investigated. A uniform magnetic field of 9.8×10-3 Tesla generated by a cylindrical powered coil was capable of aligning micro steel fibers embedded in fresh self-compacting concrete along the desired direction. The testing program included seven beam specimens of size of 100 ×100 x 500 mm3. The micro steel fiber contents considered were 0.35%, 0.70%, and 1.05% by volume. Fiber volume fraction of 0.35% was the optimum dosage for magnetic alignment as it achieved the highest extents of mechanical enhancement. The concrete specimens reinforced with 0.35% of steel fiber content have exhibited enhancement rates of 5%, 28%, and 30% in four-point failure load, maximum mid-span deflection, and compressive strength, respectively. Based on the visual analysis of cross-sectional images, the highest orientation factor achieved was 0.91 when steel fiber dosage was 0.35%, whereas the random non-magnetized steel fiber reinforced beams achieved an orientation factor ranging from 0.30 to 0.50.

Experimental study on the mechanical properties of longitudinal joints of shield tunnels under large deformation conditions

Known to be the weakest part of the shield tunnel lining rings, the longitudinal joints render the lining rings prone to large deformation and related diverse defects under nonuniform pressure loading, thereby seriously compromising the safety, serviceability and durability of the tunnel structure. In light of the paucity of studies regarding the performance of joints under large deformation, this paper presents a series of experiments examining the damage mechanism of longitudinal joints under large deformation and investigating the effects of the bolt strength, initial joint configuration, and loading level on the mechanical properties of longitudinal joints. Moreover, a finite element model was developed for the joint, capable of simulating large deformation and bolt yielding. Results show that the specimen’s failure is characterized by concrete cracking and spalling at the compression side of the joint, and/or the thread stripping or fracture failure of the bolts. Besides, an increase in bolt strength can increase the bending capacity of the joint. The discontinuous joint configuration determines the compression height of the joint section cannot be continuously changed, which results in an abrupt change in structural stiffness and a four-stage change in bolt strain. Changes in the loading level not only affect the joint’s bending capacity to some extent, but also alter how cracks develop near the joint. Furthermore, the relationship between the joint opening angle and the segmental rotation angle proves the rigid body deformation characteristics of the segment before the bolts yielded. With the segmental rotation angle increased, the maximum joint opening width and mid-span deflection increased linearly, but the compression height decreased meantime. In addition, the relationship between the bolt strain and the segmental rotation angle exhibited a two-stage linearity after the bolt began to be stressed.

Enhancement of Mechanical Behaviour of Functionally Graded Viscoelastic Materials Parts Reinforced by Hybrids Nanoparticles

This paper studies the mechanical behavior of functionally graded material viscoelastic (FGVE) products employed in automotive, chemical industry, and biomedical appliances. Various experimental models describe and simulate nanobeams with viscoelastic layers subjected to tensile loading, 3-point bending, tear, and impact. All specimens were prepared using the 3D printing method. Tensile, hardness, tear, impact, and bending specimens reinforced with different volume fractions (1-5)% of Al2O3, TiO2, and a hybrid of the nanomaterials Al2O3 /TiO2 were arranged via a mixing process with an extruder and then fabricated by a 3D printing machine. The experimental results of maximum bending load, midspan deflection, impact, and tear resistance were validated by finite element methods (FEM) with the assistance of commercial software (Ansys Workbench 2021 R1). Furthermore, the influence of various parameters on the mechanical performance of reinforced samples has been thoroughly investigated, for example, volume fraction index, nanoparticles content, and FG properties. Based on the findings, the most successful results were obtained by adding 1.5 % Al2O3 and 3% TiO2 hybrid nanoparticles. The experimental and numerical results were in reasonable agreement. The discrepancy did not exceed 10.25% for maximum bending load and no difference over 5% for maximum impact load, indicating that the strengthened nanoparticle specimens were properly fabricated. Also, a significant improvement in mechanical and viscoelastic properties was achieved by incorporating hybrid nanoparticles. Flexural bending load increased by about 17 % with hybrid nanoparticles, while tear resistance increased by 27.5 % and impact resistance increased by 7.5%.

A novel analytical framework for assessing the impact response of SFRC beam

This paper presents a novel model for predicting the impact response of steel fiber reinforced concrete (SFRC) beams. The model utilizes the principles of energy conservation and impulse-momentum theorem to calculate the maximum reaction force and peak impact force. A tensile behavior model for simulating the concrete behavior is proposed considering the effect of volume fraction of steel fibers and the effect of strain rate on the concrete properties. Additionally, the conventional beam theory, along with a cross-section-layered approach, is used to express the total beam's reaction forces vs deflection relationship. Afterwards, the model calculates the maximum midspan deflection of SFRC beams subjected to impact loading by applying the principle of conservation of energy and considering the effect of strain rate. The proposed model is compared with 121 impact tests, and the results show that the model can estimate the maximum reaction force of SFRC beams with acceptable accuracy.

Finite Element Analysis of Reinforced Concrete T-Beams with Multiple Web Openings under Impact Loading

In this study, a three-dimensional finite element analysis using ANSYS 12.1 program had been employed to simulate simply supported reinforced concrete (RC) T-beams with multiple web circular openings subjected to an impact loading. Three design parameters were considered, including size, location and number of the web openings. Twelve models of simply supported RC T-beams were subjected to one point of transient (impact) loading at mid span. Beams were simulated and analysis results were obtained in terms of mid span deflection-time histories and compared with the results of the solid reference one. The maximum mid span deflection is an important index for evaluating damage levels of the RC beams subjected to impact loading. Three experimental T-beams were considered in this study for calibration of the program. All models had an identical cross-section and span similar to those of the experimental beams. The diameter of the openings of the experimental beams was 110 mm. Three other diameters were varied (50, 80 and 130) mm. The location of the face of the opening with respect to the location of impact loading was investigated (the face of the opening at distance varied 0d, 0.5d, 1d and 1.5d from the location of loading, where d is the effective depth) and the number of web openings was varied (2,4 and 6) openings. All modeled beams subjected to dropping mass of 24.5 kg with height of drop of 250 mm (as for the experimental beams). Results obtained from this study showed that the behavior of beams with circular openings of diameter equal to 22% the web depth has a small effect on the response of the RC T-beams. On the other hand, introducing circular openings with a diameter equal to 35% and 57% of the web depth (80 and 130 mm) increases the maximum mid span deflection by 23% and 43% respectively. Results also showed that, openings with a distance greater than or equal to 1.5 d from the location of impact loading have no effect on the deflection of the RC beams.

Dynamic Monitoring of Structural Deformations utilizing an Experimentally Validated Efficient Technique

Up-to-date detection of a building's responses under various load situations is essential to generate data used to assess its capacity to bear crucial loads. This study presents an innovative and effective method to detect structural displacements and provide a more accurate alternative to existing approaches such as trigonometry leveling and angle intersecting. The least squares method was used to produce a concurrent solution that includes all the observed data to improve precision and retrieve the data needed for statistical analysis. The proposed method was validated experimentally and compared with the total station, conventional structural analysis, and displacement gauges to test and monitor a three-point loaded Reinforced Concrete (RC) beam at seven discrete points. The displacement gauge measurements were used as a baseline for comparing the outcomes from the other methods. The maximum mid-span deflection of the tested RC beam showed that the variation between the recorded displacement using displacement gauges and the suggested approach was below 0.31mm, resulting in a 3.7% inaccuracy, while the total station observations and the ACI-Code deflection provisions provided deflections of 0.62 and 3.64mm, resulting in 7.4% and 43.4% inaccuracies, respectively. Furthermore, comparing the results using root-mean-square error, the suggested method's precision in detecting displacements was much superior to the total station. The proposed approach was effective for detecting horizontal and vertical deformations and offers a viable option for building monitoring across both the element and whole building stages.

Static and multi-impact performances of RC beams strengthened with large rupture-strain FRP composites

To solve the problem of inadequate plastic deformation capacity and energy dissipation of traditional fiber-reinforced polymer (FRP) strengthened structures under impact loading, this study proposes the use of novel large-rupture-strain fiber-reinforced polymer (LRS-FRP) materials combined with different strengthening schemes to improve the impact resistance of existing structures. This study conducted three-point bending and drop hammer tests to investigate the static and dynamic behaviors of flexure-dominated LRS-FRP-strengthened beams. Experiment results showed that the end-anchored FRP strengthening system at the beam soffit significantly improved the load capacity of beams under static loading and reduced the maximum mid-span deflection under impact loading, and the ductility factor of LRS-FRP strengthened beams under static loading was 2.7 times higher than that of the carbon-FRP (CFRP) counterpart. Specimens strengthened with a mid-span LRS-FRP wrapping scheme presented improved ductility and multi-impact performance. Specimens strengthened with a combined scheme enhanced the static load capacity and ductility of by 71.9 % and 159.7 %, respectively, compared to the unstrengthened beam, and exhibited the best energy dissipation capacity (23.8 kJ) under multiple impact loads. These findings from the test investigations can facilitate design guidance and evaluation methods for strengthening schemes for RC structures under impact loading.

Fatigue behavior and calculation methods of high strength steel fiber reinforced concrete beam

Adding steel fibers into concrete was considered as one of the most effective ways to restrain the crack development and improve the stiffness for reinforced concrete (RC) structures. To explore the reinforcement mechanism of steel fibers on the fatigue behavior of high-strength RC beam, eight high-strength steel fiber reinforced concrete (HSSFRC) beams subjected to fatigue loading were tested in this study. The main design parameters considered in this work were stress level and steel fiber content. The failure mode, crack patterns, fatigue life, crack width, and stiffness degradation of HSSFRC beams under fatigue loading were discussed. The results showed that steel fibers could significantly increase the fatigue life, restrain crack development, and improve crack patterns of HSSFRC beams under fatigue loading compared to ordinary RC beams. Both the crack width and stiffness degradation rate of beams decrease with increasing steel fiber content. Besides, the empirical formulas for calculating the maximum crack width and midspan deflection of HSSFRC beam under fatigue loading were proposed and validated using experimental results.

Study on hybrid fibre reinforced UHPC beams under single and repeated lateral impact loading

This paper investigates the dynamic response of hybrid fibre reinforced ultra-high performance concrete (UHPC) beams against single and repeated low-velocity impact loads. A brief description of the drop weight impact tests on the UHPC beams was presented first followed by the development of the material and structural model in finite element analysis. A plasticity-based concrete material model with validated compressive and tensile strength surface and damage algorithm was adopted for hybrid fibre reinforced UHPC material. Based on the test results, the bond-slip behaviour between steel rebar and UHPC matrix was developed in an empirical form and incorporated in the model. Compared to the model with the bond-slip definition, the model with perfect bonding was found to underestimate the maximum mid-span deflection, which highlighted the necessity of considering the bond-slip behaviour in dynamic analysis where large deflection occurs. The repeated impact tests were performed numerically, and the results were validated with experimental data. A parametric study was then performed to investigate the effect of key parameters, including different impact energy and the same impact energy but different impact numbers. The results indicated when the total energy increased, the repeated impact loads became more hazardous than the single impact load. With the validated model, the dynamic shear force and bending moment distribution diagrams were compared to study the failure mechanism in single and repeated impact loads.

Structural damage assessment of RC slab strengthened with POZD coated steel plate under contact explosion

To reveal the anti-explosion capacity of polyisocyanate oxazodone (POZD)-coated steel RC composite structural slabs, a explosion test was carried out for 2 test models. Using ANSYS/LS-DYNA, the damage mode and maximum mid-span deflection of steel plate-RC plate and POZD coated steel plate-RC plate were explored, and the experimental results were compared. Parametric analysis of the charge, POZD, steel plate and concrete slab thickness on the anti-explosion performance of the POZD-steel plate-RC slab. The results show that increasing the thickness of POZD, steel plate and RC slab can effectively reduce the POZD-steel – RC slab mid-span deflection. The POZD coating and steel plates increased the tensile area of concrete and improved the flexural and load carrying ability of the concrete slabs.

Experimental Studies on Blast Performance of Unreinforced Masonry Walls: A state-of-the-art review

A large proportion of India’s residential buildings is of unreinforced masonry (URM) and falls under the category of non-engineered structures. URM walls in the residential buildings, customarily constructed from clay bricks or concrete blocks and cut stones, are found to be braced and therefore able to carry some out-of-plane loads produced by wind and earthquake, and survive. However, they are found to be more vulnerable to high air-pressure generated by explosive-induced detonations. Sufficient amount of investigations has been made by engineers to study the effect of brick strength, mortar strength, boundary conditions, wall thickness, and Young’s modulus of masonry on the blast performance of the URM walls. In this paper, available experimental studies on clay-brick and concrete block URM walls subjected to explosive-induced blast loading are briefly reviewed and summarized in tabular form. Studies conducted to improve the blast resistance of the walls using GFRP strips, GFRP rods, and Polyurea coating, and their effect on mid-span deflection, damage, and cracks have also been reviewed. It has been observed that the effect of brick strength and mortar strength on maximum mid-span deflection and damage resistance of the walls is insignificant under higher peak reflected blast pressures (> 2 MPa). Besides, the walls strengthened with the GFRP strips or Polyurea coating performed better with regards to mid-span deflection, damage, and cracking. The influence of Young’s modulus of masonry on the blast response of the walls is found to be more effective in reducing the maximum mid-span deflection. Also, the failure mechanism of the walls is found to be highly dependent upon the peak overpressure, duration of the blast, and support conditions.

Experimental Study on Flexural Behavior of Seawater Sea-Sand Concrete Beams Reinforced with Superelastic Shape Memory Alloy Bars

In order to research the flexural behavior of shape memory alloy (SMA)-reinforced seawater sea-sand concrete (SWSSC) beams and improve their self-healing ability, three SMA SWSSC beams and one anti-corrosive steel bar SWSSC beam were designed. The influence of the reinforcement ratio, strength grade of SWSSC and type of reinforcement on the flexural performance of the beam were considered. The failure process, maximum crack width, mid-span deflection, displacement ductility and stiffness degradation of beams were studied by cyclic loading tests. The test results showed that the number of cracks in SMA-reinforced beams were significantly smaller than that in anti-corrosive-reinforced beams, and the crack width and mid-span deflection recovery effect were better after unloading. However, the effect of increasing the SMA reinforcement ratio on crack recovery was not obvious. The increase in SMA reinforcement ratio and the strength grade of SWSSC can significantly improve the bearing capacity of the beam and the stiffness, but the stiffness degradation rate decreased. Moreover, the ductility of concrete beams with SMA bars was significantly increased.

Dynamic response of cross steel reinforced concrete filled steel tubular columns under impact under fire

To explore the impact response of cross steel-reinforced concrete-filled steel tubular (CSRCFST) columns under fire, a finite element model using ABAQUS software was generated. After validation against test results, parametric studies were carried out to investigate the effects of impact load as well as time of fire exposure on the impact resistance of CSRCFST columns. The numerical results show that the impact behavior of post-fire CSRCFST columns can be divided into three stages: peak stage, plateau stage, and softening stage. For CSRCFST columns, the peak and plateau stages are important, which absorbed 32.4% and 67.6% of the impact kinetic energy, respectively. After two hours of fire exposure, the stiffness and peak impact load of the column decreased by 93.7% and 71.7%, respectively. However, the peak mid-span deflection and residual deflection increased by 6.5% and 20.1%, respectively. When the drop weight tripled, the maximum deflection and residual deformation of the midspan increased by 2.8 and 3.2 times, respectively. However, the peak impact load increases only by 14.5%. When the impact energy is the similar, the maximum midspan deflection of the specimen is almost identical, whereas a larger impact momentum reduces the peak impact force but increases the impact force at the plateau stage. By increasing fire duration, the behaviors of the column deteriorate seriously, with 85% reductions in peak impact force and 39% increase in maximum midspan deflection. In addition, the effects of impact velocity are also significant regarding each stage.

Lateral impact behaviour of square CFST columns under fire condition

This paper reports a numerical investigation into the lateral impact behaviour of concrete-filled steel tubular (CFST) columns in fire. A coupled finite element (FE) model of square CFST columns under fire condition subjected to lateral impact is developed and verified. The full-range analysis on the impact behaviour of CFST columns under fire condition is carried out, namely the impact process, the development and distribution of the internal forces, the damage evolution, and the energy absorption. The impact responses of columns under different fire damage are also compared in detail. It shows that increasing the fire time causes a significant reduction in the impact resistance and energy absorption capacity of CFST columns that have the smaller plateau impact force and dynamic bending moment but larger mid-span deflection and impact duration. Various parameters affecting the impact responses of CFST columns under fire condition are further analyzed, and the simplified methods are finally proposed to evaluate the impact responses of CFST columns under fire condition, i.e., the dynamic flexural capacity, the maximum mid-span deflection and plateau impact force.

Experimental Study on Bonding CFRP to Fiber Concrete Beam Considering the Effect of using Nanographene Oxide in Improving the Mechanical Properties of Polyamine Resin

This research examined the effect of nanographene oxide in enhancing the mechanical properties of polyamine resin for better adhesion of carbon-fiber-reinforced polymer (CFRP) to a fiber-reinforced concrete beam. To this purpose, 33 fiber-reinforced concrete beams retrofitted with CFRP of lengths 50 cm, 35 cm, and 20 cm and widths 3 cm, 6 cm, and 10 cm were experimentally studied. Graphene oxide weight percentages of 1, 2, and 3 percent were considered, and the corresponding cases were compared with the case of a retrofitted beam without graphene oxide. According to the results of experiments on 12 of the beams, as the nanomaterial in the adhesive increases from 1 to 2 and 3%, the values of maximum load-carrying capacity, maximum mid-span deflection, beam stiffness, and beam toughness exhibited 46,19, 27, and 5 %, respectively, relative to the case of the beam reinforced with CFRP and without graphene oxide. Subsequently, given the close results of the beams reinforced with 2 and 3% graphene oxide. The 2% graphene oxide was used in the rest of the samples to investigate the effect changes in the number of layers, length, and width of the CFRP on the mechanical properties of the concrete beam. The results indicated that an increase in the number of layers, length, and width of CFRP results in an increase in the load-carrying capacity and deformability of the fiber-reinforced concrete beam

Mechanical and fiber/matrix interfacial behavior of ultra-high-strength and high-ductility cementitious composites incorporating waste glass powder

Most of the waste glass is landfilled, which is not conducive to the sustainability of the environment. However, waste glass powder (WGP) with sufficient fineness and high alkali reactivity exhibits excellent pozzolanic behavior, promoting its potential application in the concrete industry. This work evaluated the feasibility of replacing cement with WGP ranging from 0 to 30% to produce Ultra-High-Strength and High-Ductility Cementitious Composites (UHS-HDCC). The influences of WGP on the fresh flowability, mechanical properties, and fiber/matrix interfacial behavior of UHS-HDCC were investigated. The introduction of WGP enhanced the flowability of fresh UHS-HDCC mixtures. UHS-HDCC incorporating 10% WGP achieved incredible compressive strength, ultimate four-point bending stress, and ultimate uniaxial tensile stress, reaching around 158.4 MPa, 43.22 MPa, and 12.47 MPa, respectively. Moreover, all UHS-HDCCs exhibited strain-hardening features and multiple cracking behaviors. The maximum mid-span deflection and ultimate tensile strain capacity of UHS-HDCCs with WGP were distributed in 9.84 mm–13.83 mm and 5.88%–7.47%, respectively. Compared with WGP0, WGP10 and WGP20, the crack distribution in the WGP30 was more saturated and the number of narrow cracks was the largest. The results of the single-fiber pullout test indicated that the interface frictional bonding stress of WGP10 was reached 2.22 MPa, which represented a high ultimate four-point bending stress and ultimate uniaxial tensile stress. Furthermore, the average slip hardening coefficient of UHS-HDCCs ranged from 0.0032 to 0.0041. Based on the micromechanical model, the fiber ruptured fraction of WGP10 in the development of crack opening was calculated to reach 31.5%, which explained the decrease in maximum mid-span deflection and tensile strain capacity. Therefore, the experimental research will provide preliminary data for the scientific and efficient use of waste glass in engineering construction.

Reinforced Concrete Circular T-Shaped Deep Beams – Finite Element Investigation

The current work investigates the behavior and strength of T-shaped cross section ring deep beams through a Finite element parametric study. Currently, ring diameter, loading type, concrete compressive strength and number of supports are taken into consideration. It is found that increasing ring diameter of beam by 12.5-25% leads to increase the maximum positive moment, maximum negative moment, maximum torsional moment and midspan deflection by 1.1-2.2%, 2.2-4.3%, 3-6% and 16-33%, respectively, while the load ultimate capacity increases by 11-17%. The positive and torsional moments at midspan and midspan deflection decrease by 23-36%, 3-11% and 6-14%, respectively when the loading type varies from concentered to full uniformly load over a span length of 33, 50, 67 and 100%, respectively. In a related context, this change in load type leads the negative moment at support and the load ultimate capacity to increase by 2-21% and 6-85%, respectively. The midspan positive moment, negative moment, torsional moment and load ultimate capacity increase by 20.4-71.3%, 20-69.7%, 15.6-43.8% and 21-73%, respectively, whereas deflection decreases by 1.4-11%, when increasing the compressive concrete strength by 45-190%. Finally, it is found that the load ultimate capacity increases by 82-348%, when number of supports increases by 25-100%, while torsional moment, maximum positive moments, maximum negative moments and midspan deflection decrease by 11-50%, 38-76.4%, 38.6-76.8% and 14-39%, respectively due to this increase in the number of supports.

Study on explosion-resistance performance of concrete-filled steel tubular columns considering the influence of elevated temperatures

Fire and explosion often occur together that seriously threatens the safety of engineering structures. In order to investigate the explosion resistance of concrete-filled steel tubular (CFST) columns at elevated temperatures, the finite element (FE) model of explosion resistance performance for circular CFST columns at elevated temperatures was established using the ABAQUS software. The fire and blast loads were simulated using ISO 834 standard fire and ConWep model, respectively. In the model, the static implicit and dynamic explicit analysis was coupled using “Restart” and “Import” commands and the strain-rate effect was considered. The experiment results of related literatures, including the temperature field, fire resistance duration and explosion resistance of CFST columns, were used to verify the feasibility of the method. Based on the validated FE models, the explosion mechanism of CFST columns subjected to standard fire was analyzed, including the failure modes, full-range analysis, development of stress and strain, interaction between steel tube and concrete and energy consumption. The influence of duration time, material strength, steel ratio and explosion equivalent on the explosion resistance were studied. The maximum mid-span deflection (Δpeak) was employed to quantitatively analyze the explosion-resistance performance of the CFST columns. The results show that shear failure firstly occurs at both fixed ends, and then the whole column presents flexural failure mode when subjected to explosion load under fire condition. With the increase of duration time, the proportion of energy consumption of steel tube decreases, and plastic deformation of concrete gradually becomes the main energy consumption mechanism. The concrete strength, explosion equivalent and axial load ratio have significant influence on the explosion resistance of CFST at high temperatures. After 0 min and 90 min fire duration, the explosion resistance is improved by approximately 21% and 42% respectively when the concrete cubic compressive strength increases from 30 MPa to 50 MPa.