Normal Reinforced Concrete Research Articles

Experimental and numerical investigation on normal strength and high strength RC arches subjected to underwater explosions

As a common structure in engineering, reinforced concrete (RC) arch may be subjected to explosion load in its life cycle. However, there are few studies on the blast resistance of RC arch against underwater explosion. A normal strength reinforced concrete (NSRC) arch and a high strength reinforced concrete (HSRC) arch were designed, and two sets of underwater explosion tests were carried out. Multi-media coupling models of the two RC arches subjected to underwater explosions were established based on the Arbitrary-Lagrangian-Eulerian (ALE) algorithm. The propagation characteristics of shock wave, the acceleration response and damage evolution of the arches were experimentally and numerically investigated. The reliability of the numerical method was verified by comparing the numerical results with the test results. Employing the verified numerical method, the effects of standoff distance and explosive weight on the dynamic response and damage distribution of the NSRC and HSRC arches were further studied. Based on extensive numerical simulations, the prediction formulas for the peak displacement of the given NSRC and HSRC arches due to specific underwater explosions were proposed. The results show that the arch vault and both sides of hance are the most vulnerable to failure when suffering the explosions centrally above the arch. The blast resistance of the HSRC arch is much stronger than that of NSRC arch. The failure modes of RC arches can be summarized as: arch vault cracking, global bending failure, combination of global bending failure and local damage, combination of global bending failure and penetration failure.

Improving flexural response of rubberized RC beams with multi-dimensional sustainable approaches

This research presents a sustainable solution to waste tire disposal and raw material depletion by incorporating recycled rubber into concrete mixtures. To mitigate the reduction in mechanical properties, a novel slag pretreatment of rubber particles with controlled temperature is proposed. The study also investigates the effects of pouring concrete in layers with rubberized concrete (RuC) in tension side and normal concrete in compression side, as well as evaluating the use of GFRP compared to conventional steel, thereby introducing multiple innovative dimensions to enhance structural performance. The experimental study included a total of 27 specimens, consisting of normal concrete, untreated rubberized concrete, and treated rubberized concrete mixtures with 15 % rubber content. The study investigated both compression and tension mechanical properties of the concrete mixtures and assessed the flexural response of reinforced concrete (RC) beams. Parameters explored included rubber treatment, utilization of steel and GFRP as tensile reinforcement, and layered concrete pouring. Subsequently, a numerical study was conducted to address the impact of reinforcement ratio and layer depth on the behavior of slag-treated rubberized RC beams. The findings reveal a significant recovery of concrete compressive strength by 23 %, along with a 28 % enhancement in toughness and a 17 % increase in splitting tensile strength attributed to the application of slag treatment to rubberized concrete. The effect of rubber treatment was more pronounced in GFRP RC beams, as they showed similar load capacity as normal concrete. Furthermore, utilizing layered concrete beams with a 67 % depth of slag-treated RuC showed a comparable load capacity to normal RC beams, demonstrating only a 1 % reduction for steel-reinforced beams and a 2.4 % improvement for GFRP-reinforced beams. Notably, the numerical model emphasized this outcome and suggested that increasing the layer depth to 72 % of slag-treated depth displayed better performance.

Combined nomograms for calculating the bearing capacity and reinforcement of high-strength and normal concrete RC columns

PurposeThis paper aims to obtain a calculation method by hand without iteration.Design/methodology/approachThis paper adopts strains as known quantities to solve the internal forces and deformations of the section, simplifies the deflection curve of the column and obtains nomograms that can calculate the bearing capacity and reinforcement of circular reinforced concrete (RC) columns by hand.FindingsNomograms include five variables: mechanical reinforcement ratio, relative normal force, dimensionless bending moment, slenderness ratio and ultimate dimensionless curvature. Nomograms corresponding to all classes of concrete have been drawn, and their dimensionless form makes them widely applicable. The calculation results of nomograms are compared and analysed with numerical calculation results, and the difference is within 5%, meeting the engineering requirements.Originality/valueCalculating the bearing capacity of compression bending components requires considering second-order effects. Therefore, the calculation of the bearing capacity of circular RC columns requires iterative calculation, as it includes dual nonlinearity of material and geometry, and the two are coupled with each other. To calculate the bearing capacity of the section adopting ordinary concrete, it is necessary to solve the transcendental equation iteratively. For high-strength concrete, it can only be solved by numerical integration. A fast calculation method by hand is proposed in this paper.

Thermal energy storage performance of biaxial voided RCC roof slab integrated with macroencapsulated PCM for passive cooling of buildings

Building space heating and cooling power consumption is growing due to population and economic growth. Integrating phase change materials (PCMs) into various building envelope components is being explored to enhance thermal energy storage capacities. Specifically, roofs exposed to direct sunlight significantly promote thermal energy transfer to the interior, increasing the space heating and cooling requirements. In this study, thermal energy storage performance of a biaxial voided roof slab integrated with PCM is experimentally investigated under ambient conditions and compared with a normal reinforced concrete (RCC) without PCM. PCM selection, characterization, and metal void former development are performed, followed by macroencapsulation and integration into the roof slab. Thermal performance measures are evaluated, including temperature profile, heat flux, thermal load, time lag, and decrement factor. Financial viability indicators such as electricity cost savings, payback period, and CO2 emissions savings are also assessed. The results show PCM integrated biaxial voided roof slab reduces interior temperature by upto 7.2 °C during sunny hours, heat transfer to the interior by upto 60.6 %, and thermal load by upto 54 %. In addition, considering heating and cooling, it offers an average daily saving of 0.06 USD/kWh/m2 and a payback period of about 5.7 years. Further, it gives CO2 emissions savings of upto 13.7, 12.3, and 4.3 kgCO2/kWh for lignite-, coal-, and natural gas-fired power plants. Furthermore, its mean time lag is 4.2 h, with a decrement factor of 0.75 compared to 3.9 h and 0.85 for the normal RCC unit. The study makes significant contribution to knowledge by providing a unique, simple yet highly effective PCM macroencapsulation integration technique for roof slabs and insights into its thermal performance under the hot weather conditions.

A comprehensive review of ultra-high performance concrete (UHPC) behaviour under blast loads

Blasts resulted from industrial/residential accidents and deliberate attacks can impose extremely hazardous loading conditions upon nearby structures. The repercussions of these blasts encompass not only direct effects such as blast overpressure and fragments but also indirect outcomes like progressive collapse of structures. In the pursuit of enhanced protection for concrete structures, substantial endeavors have been directed towards developing innovative construction materials with outstanding properties, among which the ultra-high performance concrete (UHPC) has emerged as a notable representative. Drawing from existing experimental, numerical and theoretical studies, this paper presents an inclusive overview of recent progress in UHPC structural members (slabs, beams and columns) and UHPC-based composite structures (mesh reinforced UHPC, UHPC-filled steel tube and UHPC strengthening of normal reinforced concrete (NRC) structures) in their ability to withstand blast loads. While discussing the exceptional material and structural dynamic performance of UHPC, recommendations are offered for the further research directions in utilising UHPC structures to resist blast loads, which include exploring eco-friendly UHPC, integrating 3D printing technology and employing machine learning analytical methods.

Probabilistic capacity models and fragility estimate for NRC and UHSC panels subjected to contact blast

A Performance-based Design (PBD) framework for protective structural walls/slabs susceptible to contact blast has been developed. Performance-based capacity models are predicted for three performance levels namely, operation with minimum damage (P1), medium damage (P2) and collapse prevention (P3) allied to four damage states. The current study examines multi-level PBD instead of single-level conventional collapse-based design. All these probabilistic models are developed by combining mechanical models with dimensionless explanatory functions. Bayesian inference based on numerical data is used to evaluate the unknown model parameters. The constructed models take into account all inherent aleatoric and epistemic uncertainties of material and geometry. For Normal Reinforced Concrete (NRC) and Ultra-high Strength Concrete (UHSC) panels subjected to contact blast, finite element (FE) modelling (LS-DYNA) is used to obtain the necessary data. The validated models have a high level of agreement with chosen experimentation. In addition, local damage formulations, such as crater diameter, crater depth, spall diameter, spall depth, and perforation diameter, are also developed. The developed capacity models are used to estimate fragility, and the obtained plots demonstrate the consistency of the evaluated equations. When subjected to a contact blast, these probabilistic models can be used to construct protective structures based on the expected demand.

Structural behavior of steel-concrete-steel and steel-ultra-high-performance-concrete-steel composite panels subjected to near-field blast load

In this paper, field blast tests and numerical simulations were conducted to investigate the structural behavior of steel-concrete-steel (SCS) composite panels with shear studs and tie bars as connectors under near-field blast load. Four specimens, including two SCS panels, one steel-ultra-high-performance-concrete-steel (S-UHPC-S) and one normal reinforced concrete (NRC) panel, were fabricated with the same geometric dimensions and tested in the field with cylinder charges under the scaled distances of 0.4 m/kg1/3 and 0.6 m/kg1/3. Finite element models with the implementation of multi-material Arbitary-Lagrangian-Eulerian (MM-ALE) algorithm were built to demonstrate the spatial distribution of shock waves with adequate validation, and the calculated blast load was then simplified and used to compute the dynamic response and the failure mode of SCS and S-UHPC-S panels. After validation of the numerical models, the parametric studies were conducted to investigate the effects of thickness and yield strength of faceplates, ratio of shear connector spacing to the faceplate thickness, section depth of the panels and scaled distance on the structural behavior of SCS and S-UHPC-S panels against near-field blast load. The results indicate that the structural response of SCS and S-UHPC-S panels under the near-field blast load is dominated by global flexural response with the scaled distance (Z) ranging from 0.3 m/kg1/3 to 0.6 m/kg1/3, but shear cracks form near the supports and local damage occurs at Z = 0.3 m/kg1/3. Replacing normal concrete core with UHPC or enlarging the section depth is an effective way to mitigate shear cracking and potential shear failure. In addition, the blast resistance of SCS panel is much superior to that of NRC panel with the same geometric dimensions and is also much greater than that of NRC panel with the similar section strength under close-in scaled distance.

Projectile impact-induced spalling damage on carbon fiber reinforced polymer strengthened RC plates

As the most widely used material in protective structures, a better understanding of the resistance of reinforced concrete (RC) to high-speed projectile striking is needed. It has been accepted that concrete material possesses limited impact resistance in virtue of its poor energy absorption capacity. To improve the performance of RC structures under impulsive loading, affixing externally-bonded Fiber Reinforced Polymer (FRP) sheets on structural elements is a practical method. Due to the emphasis of most existing literature on the penetration behavior of projectiles, the studies of impact-induced spalling damage on normal and FRP strengthened RC plates are not sufficient and in-depth. In this paper, the local response of un-strengthened and FRP strengthened RC plates under projectile impact is systematically investigated with experimental approaches. In consideration of the complexity of transient behavior as well as multiply parameters involved, empirical approaches based on dimensionless analysis are proposed to predict the diameter and depth of spalling craters on normal RC plates and strengthened ones with frontal CFRP layers, which fill current research gap and are potential tools for damage assessment and repair. The validity of the proposed approaches is verified by test results from the present and published studies.

Shear strengthening of reinforced concrete T-beams with anchored fiber-reinforced polymer composites

T-shaped beams are widely used in reinforced concrete (RC) structures, both buildings and bridges. Under-designed shear reinforcement and long-term aging make these structural elements susceptible to shear failure during earthquakes. The currenlty availalbe experimental work investigating the retrofit of these beams against shear failure is very limited. In this work, the external strengthening of RC T-beams with splay anchored strips of fiber reinforced polymer (FRP) composites under cyclic shear loading for the cases of normal and high strength concrete was studied. Six beams with 3.05 m length and 0.46 m that were conservatively reinforced against flexural failure were designed. The shear reinforcement of the beams was sufficiently high to ensure the dominance of shear failure. Three of the beams were built using a normal strength concrete and the other three were built using a high strength concrete with 28-day strengths of 30.5 MPa and 44.0 MPa, respectively. From each group of normal and high strength RC beams, one beam served as the reference. The other two beams were retrofitted with external strips of FRP composites that were bonded on the web and anchored under the flange of the beams. The beams were tested under cyclic four-point loading to evaluate the performance of the FRP retrofitting system against shear failure under simulated seismic loading. The deflection and the strain in the FRP composites were recorded while monitoring the strain of the longitudinal reinforcement to ensure an elastic response in flexure. The reference beams failed by shear cracking and the retrofitted beams failed by shear cracking and FRP delamination. The retrofitting technique increased the shear capacity of the beams by up to 37% and 20% for the normal and high strength beams, respectively, and promoted the beam ductility prior to failure.

Performance analysis of the ultra high performance concrete composite beam subjected to impact loads

Ultra High Performance Concrete (UHPC) has gradually become the most promising high-performance material, and has achieved good results in the field of impact and explosion protection engineering. In general, normal reinforced concrete (NC) beams subjected to impact load are prone to local punching shear failure. Although pure UHPC beams can improve their impact performance, their further application is limited by the high cost. In order to achieve the balance between impact resistance and economy, this study puts forward the design scheme of local replacement and wrapping with UHPC to improve the impact resistance of reinforced concrete beams. In this work, the different research conditions including NC beam, UHPC beam and NC-UHPC composite beam are designed, and the impact resistance of specimens is compared and analyzed. The results show that UHPC local replacement scheme can effectively avoid local punching shear failure of beams. As for the UHPC wrapping scheme, the failure mode of the beam changes from punching shear failure to bending failure. Compared with NC beams, two schemes can effectively reduce the peak displacement and residual displacement in the mid-span. The peak displacement and residual displacement in the mid-span of the UHPC local replacement beam are smaller than that of UHPC wrapping schemes, and the mid-span bearing capacity is better. In this work, it is recommended to take a local replacement length greater than 2 times the beam height to avoid local punching shear failure.

Experimental Investigation on Shear Behavior of Dune Sand Reinforced Concrete Deep Beams

An experimental study on the shear behavior of dune sand reinforced concrete (DSRC) deep beams was conducted to determine the feasibility of using dune sand (DS) in engineering. Nine DSRC deep beams were designed and thoroughly analyzed for failure modes, diagonal cracks, and load–deflection curves in this study. The results showed that the shear strength and ductility of DSRC deep beams increased when the DS replacement rate was 30%, but the opposite effect occurred when the DS replacement rate was 50%. To analyze the differences in the effects of the DS replacement rate, shear span-to-depth ratio, concrete strength, and stirrup ratio on the shear strength of DSRC and normal reinforced concrete (NRC) deep beams, a total of 227 shear experimental tests of NRC deep beams were conducted. Furthermore, four national codes were evaluated and compared based on experimental data. The evaluation results showed that the four codes underestimated the shear strength of DSRC and NRC deep beams. Among them, ACI 318–11 provided more reliable predictions for both NRC and DSRC deep beams. It is in this regard that a new empirical model for predicting the shear strength of DSRC deep beams is proposed, in which a reduction coefficient of the DS replacement rate is incorporated. The verification results indicates that the predicted results of the proposed model are in good agreement with the experimental results.

Damage assessment of normal reinforced concrete panels strengthened with polyurea after explosion

Polyurea can effectively improve the anti-blast performance of normal reinforced concrete (NRC) panels. However, there are very limited studies on the damage assessment of polyurea strengthening NRC (PU-NRC) panels after near-field explosion. In this paper, a high-fidelity finite element (FE) model of PU-NRC panel was developed and validated by the results from near-field explosion and static loading tests. Subsequently, the deterioration of the bearing capacity was selected as a damage criterion to assess the damage of the PU-NRC panel after explosion. The impacts of polyurea thickness, panel thickness, compressive strength of concrete and longitudial reinforcement ratio on the damage levels of the PU-NRC panel were further discussed. Finally, the empirical formulas of P-I diagram were developed to assess the damage level of the PU-NRC panel after varied blast loads. The results showed that spraying polyurea can improve the stiffness of NRC panel under blast load. In addition, the closer the standoff distance, the better the strengthening effectiveness of polyurea. Increasing polyurea thickness was more effective to increase the value of overpressure asymptote, and spraying polyurea had little contribution to improve the shear resistance of the NRC panel. This research has significant implications for practitioners and scholars in protective engineering.

Structural behaviour of the strengthened reinforced concrete beams using ultra high-performance fibre reinforced concrete layer

PurposeDamage to reinforced concrete (RC) structural elements is inevitable. Such damage can be the result of several factors, including aggressive environmental conditions, overloading, inadequate design, poor work execution, fire, storm, earthquakes etc. Therefore, repairing and strengthening is one way to improve damaged structures, so that they can be reutilized. In this research, the use of an ultra high-performance fibre-reinforced concrete (UHPFRC) layer is proposed as a strengthening material to rehabilitate damaged-RC beams. Different strengthening schemes pertaining to the structural performance of the retrofitted RC beams due to the flexural load were investigated.Design/methodology/approachA total of 13 normal RC beams were prepared. All the beams were subjected to a four-point flexural test. One beam was selected as the control beam and tested to failure, whereas the remaining beams were tested under a load of up to 50% of the ultimate load capacity of the control beam. The damaged beams were then strengthened using a UHPFRC layer with two different schemes; strip-shape and U-shape schemes, before all the beams were tested to failure.FindingsBased on the test results, the control beam and all strengthened beams failed in the flexural mode. Compared to the control beam, the damaged-RC beams strengthened using the strip-shape scheme provided an increase in the ultimate load capacity ranging from 14.50% to 43.48% (or an increase of 1.1450 to 1.4348 times), whereas for the U-shape scheme beams ranged from 48.70% to 149.37% (or an increase of 1.4870–2.4937 times). The U-shape scheme was more effective in rehabilitating the damaged-RC beams. The UHPFRC mixtures are workable, as well easy to place and cast into the formworks. Furthermore, the damaged-RC beams strengthened using strip-shape scheme and U-shape scheme generated ductility factors of greater than 4 and 3, respectively. According to Eurocode8, these values are suitable for seismically active regions. Therefore, the strengthened damaged-RC beams under this study can quite feasibly be used in such regions.Research limitations/implicationsObservations of crack patterns were not accompanied by measurements of crack widths due to the unavailability of a microcrack meter in the laboratory. The cost of the strengthening system application were not evaluated in this study, so the users should consider wisely related to the application of this method on the constructions.Practical implicationsRehabilitation of the damaged-RC beams exhibited an adequate structural performance, where all strengthened RC beams fail in the flexural mode, as well as having increment in the failure load capacity and ductility. So, the used strengthening system in this study can be applied for the building construction in the seismic regions.Social implicationsAside from equipment, application of this strengthening system need also the labours.Originality/valueThe use of sand blasting on the surfaces of the damaged-RC beams, as well as the application of UHPFRC layers of different thicknesses and shapes to strengthen the damaged-RC beams, provides a novel innovation in the strengthening of damaged-RC beams, which can be applicable to either bridge or building constructions.

Experimental and numerical investigations of hybrid-fibre engineered cementitious composite panels under contact explosions

In this study, the blast response of hybrid-fibre engineered cementitious composite (HFECC) panels with 1.75% polyvinyl alcohol and 0.58% steel fibres (by volume) is experimentally and numerically evaluated for the first time. For blast testing, HFECC and normal reinforced concrete (NRC) panels were tested under contact explosions generated by Plastic Explosive 4 (PE4) on a demolition range. The crater diameter, spalling diameter and fragment size were measured and compared. The averaged crater and spalling diameters of the NRC panels were 173.55 mm and 272.87 mm, respectively, while those of the HFECC panels were 91.16 mm and 178.93 mm, respectively. The fragment size of the HFECC panels was larger than 19 mm, whereas the fragments of the NRC panels had a wide size distribution ranging from < 1.7 mm to > 19 mm. An effective finite element model is also developed to reproduce the responses of the HFECC and NRC panels under blast loads. In the numerical model, a dynamic increase factor formula newly developed by the authors is incorporated to describe the rate sensitivity of HFECC in tension. A particle-based approach is employed, for the first time, to explicitly model the blast load applied on the concrete panels. The efficiency and accuracy of the numerical model are validated by comparing the numerical prediction with the experimental data. The validated model is then used to explore the blast resistance of a reinforced HFECC panel. It is found that the crater and spalling diameters obtained for the reinforced HFECC panel are decreased by 53.6% and 41.1% compared with those of the NRC panel. The damage distribution in the reinforced HFECC panel becomes less localised with the increase of the ductility of HFECC. The numerical results also show that the blast resistance of the distal surface relies more on the ductility of the matrix than that of the proximal surface.

Cyclic performance of RC bridge piers retrofitted with UHPC jackets: Experimental investigation

Many existing reinforced concrete (RC) bridge piers do not have sufficient seismic-resistant capacities during the long-term service period. Seismic retrofitting of these piers will be an impending problem. In this study, quasi-static cyclic tests were conducted to investigate the efficiency of ultra-high performance concrete (UHPC) in strengthening the seismic performance of RC bridge piers. Three test specimens, among which one is a normal RC pier and the others are UHPC jackets-retrofitted RC piers, were used for the cyclic tests. Based on the experimental results, the effects of UHPC jackets on hysteresis response, strength, ductility, stiffness degradation, energy dissipation, residual displacement, and curvature distribution, are analyzed and discussed. The results show that after being retrofitted by UHPC jackets, the curvature distribution and damage modes of the RC pier are changed, and the strength and stiffness are improved. Furthermore, 50 mm-thick UHPC jackets contribute to a significant reduction of residual displacement and equivalent viscous ratio, indicating improving post-earthquake serviceability of retrofitted piers. Numerical simulation was conducted to further investigate the influence of size of UHPC jacket on the envelope curve for the RC pier. It was found that for a fixed thickness or height of UHPC jacket, the strength of retrofitted pier would not increase with the UHPC jacket volume when it reached to a certain value.

Performance of reinforced concrete beam with cushion subjected to impact loading

Many countries are developing new ways to protect Reinforced Concrete (RC) structures under specific risks such as rockfall hazards. Cushioning materials, for example, are using to improve the impact resistance of the RC structures. Applying cushions improves the strength of RC structures under aging of materials and deteriorations, therefore, it improves the safety of people, buildings, and infrastructure systems. However, the impact resistance of RC structures with cushions have not yet been clarified. This study aims to clarify the effect of four types of high strength expanded materials, three are Polystyrene and one is Polycarbonate, which were set on RC beams to enhance impact resistance of the beams. Drop weight tests were employed to investigate the mechanical behavior of RC beams with cushions. The following conclusions were found based on the results of this study: 1) High energy absorbing cushions should be used to protect RC beams subjected to impact loadings as it significantly reduced the maximum deflection and crack opening process of the beams. 2) The hardening effect of concrete at upper cover surface of RC beam during collision were confirmed by using yielding static test. It is used to calibrate static fiber model of normal RC beam to obtain the maximum deflection due to impact loadings. 3) The impact absorbing energy of the cushions were verified to establish simplified equation of maximum deflections of the beam with cushions. 4) The estimated maximum deflections of RC beams with and without cushions are in agreement with the measured values.

Explainable machine learning using real, synthetic and augmented fire tests to predict fire resistance and spalling of RC columns

This paper presents the development of systematic machine learning (ML) approach to enable explainable and rapid assessment of fire resistance and fire-induced spalling of reinforced concrete (RC) columns. The developed approach comprises an ensemble of three novel ML algorithms namely; random forest (RF), extreme gradient boosted trees (ExGBT), and deep learning (DL). These algorithms are trained to account for a wide collection of geometric characteristics and material properties, as well as loading conditions to examine fire performance of normal and high strength RC columns by analyzing a comprehensive database of fire tests comprising of over 494 observations. The developed ensemble is also capable of presenting quantifiable insights to ML predictions; thus, breaking free from the notion of “black-box” ML and establishing a solid step towards transparent and explainable ML. Most importantly, this work tackles the scarcity of available fire tests by proposing new techniques to leverage the use of real, synthetic, and augmented fire test observations. The developed ML ensemble has been calibrated and validated for standard and design fire exposures and one-, two-, three- and four-sided fire exposures thus; covering a wide range of practical scenarios present during fire incidents. When fully deployed, the developed ensemble can analyze over 5,000 RC columns in under 60 s; thus, providing an attractive solution for researchers and practitioners. The presented approach can also be easily extended for evaluating fire resistance and spalling of other structural members under varying fire scenarios and loading conditions and hence paves the way to modernize the state of this research area and practice.

Experimental Study on Performance of Steel Fiber-Reinforced Concrete V-Shaped Columns

Structural engineers have used V-shaped columns based on technical requirements. The inclination of the V-shaped column underlines the individual purpose of the base floor. However, there is no any specification or guidance on the design of V-shaped columns to date. The aim of this study is to investigate the behavior of V-shaped reinforced concrete columns with three angles between columns (30°, 60°, and 90°) in order for the results to be used in the design and analysis of the V-shaped column. The impact of using a 1.5% dosage of micro-straight-steel fiber (MSSF) in the concrete mixture was also studied. The results showed that the V-shaped column with 30°, regardless of the concrete type (with and without MSSFs), exhibited crushing at legends when the sample reached the ultimate load, while no cracks occurred at the legends during the test for the other V-shaped columns. Upon increasing the angle of inclination of the V-shaped columns, the ultimate load capacity was decreased by 24%, 23%, and 20% for V-shaped columns with 30°, 60°, and 90° angles of inclination, respectively. The addition of MSSFs in the concrete significantly improved the ultimate axial load and the bending moment compared to the reference specimens with the normal reinforced concrete (NRC). The steel-fiber-reinforced concrete (SFRC) vertical column specimen demonstrated the highest increase in axial load, and the other SFRC V-shaped and flexural specimens showed a minor increase compared to the NRC specimens.

Experimental and numerical investigation of normal reinforced concrete panel strengthened with polyurea under near-field explosion

In this paper, field blast tests and numerical simulations were conducted to investigate the strengthening effect of polyurea on the blast resistance of the normal reinforced concrete (NRC) panels under near-field explosion. Five specimens were fabricated and tested, including two NRC panels, and three NRC panels sprayed with polyurea at the rear side. The experimental results showed that polyurea could effectively improve the blast resistance of the NRC panel with less damage and smaller residual displacement. Furthermore, with the existence of the polyurea, the integrity of the specimen could be maintained, and the deadly fragments of the concrete panel were captured, thereby reducing the secondary damage to surrounding personnel and structures. The finite element (FE) model of NRC panels strengthened with polyurea under near-field explosion was established using the Arbitrary-Lagrangian-Eulerian (ALE) method, and validated with the experimental results. Thereafter, the validated FE models were used to investigate the effects of scaled distances and polyurea thickness on the blast resistance of the NRC panel. This research is of direct importance to both practitioners and researchers involved with strengthening design for NRC components against explosion.

ASSESSMENT OF NOMINAL SHEAR STRENGTH OF REINFORCED CONCRETE COLUMN

: SNI 2847-2019 and ACI 318-19 have regulated the use of materials in the design for shear strength. This study presents an evaluation of nominal shear strength in Reinforced Concrete (RC) column from SNI 2847-2019 and ACI 318-19 by variants of the RC columns experimental database. RC column variants consist of normal strength and high strength RC column with a total of 162 specimens. Furthermore, the database also provides a variety of shear span to depth ratio and axial-load ratio. In this study, the calculation was carried out the mean and the coefficient of variation of measured to calculated strength ratio which is according to SNI, ACI, and other experimental models. Both SNI 2847-2019 and ACI 318-19 have 2 different (concrete nominal shear strength) equations. The calculation results show that the equation is more conservative in both SNI and ACI compared to other nominal shear strength equations. Overall, the combination of both normal strength and high strength RC columns, the calculation using ACI 318-19 with the first nominal shear strength equation can be said to be more conservative than any other calculations models. This study also shows that by using the ACI 318-19 model in the second equation which is used the size effect modification factor , the results do not have a significant effect because the value is close to 1.