Carbon Fiber Reinforced Polymer Wrapping Research Articles

Shear contribution of beams of different sizes strengthened in shear with anchored CFRP strips

Carbon-fibre-reinforced polymer (CFRP) materials can be used as structural reinforcement in engineering projects, but its effectiveness is jeopardised by debonding of the CFRP. Anchoring of the CFRP is thus crucial for efficient shear strengthening. The effect of anchoring on the shear resistance of nine CFRP U-wrapped concrete beams with varying shear span-to-depth (SSD) ratios (1.0, 1.5 and 2.0) and depths of 300–900 mm was investigated in this work. Nine unanchored beams and nine plain (without CFRP wrapping) concrete beams were also included in the comparison, considering the influence of the beam effective depth and the SSD ratio, with reference to prior research. An evaluation of the shear contribution of the CFRP wrapping was conducted, particularly for cases involving large dimensions and diverse SSD ratios. The anchoring effect was found to be most pronounced in small-scale beams with a large SSD ratio, demonstrating an improvement of over 60% compared with the CFRP shear-strengthened beam without anchoring. In contrast to beams without CFRP wrapping, the shear performance was enhanced by approximately 90%. Additionally, formulas for calculating the shear capacity from different national specifications were analysed and compared. A new calculation method for CFRP shear resistance was established and its accuracy was verified.

Torsion and Combined Torsion-Axial Load Behaviour of Concrete Filled Steel Tube Columns with and without ECC/CFRP Wrap

ABSTRACT Concrete-filled tube columns may experience coupled torsion and axial compression under seismic and wind loading. Fifteen square, rectangular, and circular concrete filled steel/aluminium tube (CFST/CFAT) are tested under pure torsion to understand the behaviour and develop/validate finite element (FE) models. Parametric studies under pure torsion are conducted using FE models to study the effect of geometric (tube cross-section, length, and thickness) and tube/concrete material parameters on torsional strength, stiffness, and tube-concrete composite interaction. FE models are used to study strength, stiffness, and failure modes of CFST columns under combined torsion and axial compression load at various preload levels of axial and torsion. Coupled torsional preloading and subsequent axial load reduce the axial load capacity significantly, while coupled axial preloading and subsequent torsional loading have shown no significant influence on the torsional strength of CFST columns. Implementation of FE models developed for CFST columns with engineered cementitious composite (ECC) and carbon fibre reinforced polymer (CFRP) wraps showed significant enhancement of axial strength and stiffness compared to control (without wrap) even under high torsional preload level. The energy absorption capacity and ductility of the CFRP wrapped CFST column are about 1.38 and 1.1 times higher than its counterpart with ECC wrap of same axial load capacity. Overall, the results suggest that use of both CFRP and ECC wrap is an effective approach to enhance the torsional behaviour and ductility of CFST columns under combined torsion and axial loading conditions. However, high crack resistance and better post-peak ductility of ECC wrapped CFST compared to sudden CFRP rupture failure in CFRP-wrapped counterpart should be taken into consideration for seismic applications.

Studying the effect of using CFRP warping on strength of husk rice concrete columns

Abstract This research presents the effect of carbon fiber-reinforced polymer (CFRP) on a strength of concrete containing rice husk. Two shapes of columns (circular and square) were used to compare these two types in terms of resistance axial loading. Twelve concrete columns were casting; six are square and others are circular cross-section. All columns of each shape were divided into three groups, and each group consisted of two columns: the first group without CFRP, the second group covered with one layer of CFRP, and the last group covered with two layers of CFRP. The dimensions of the square columns were 300 mm × 300 mm and the height was 900 mm, with reinforced 4–6 mm steel bars. The circular columns were 300 mm in diameter with same height 900 mm and reinforced with 6–6 mm steel bars. Burnt rice husks are added at a rate of 10% of the amount of cement that should be added to the concrete mix. The test results showed the circular columns were the strongest and most resistant to axial loading than square columns. Also, the CFRP wrapping is very effective in strengthening circular concrete columns but significantly less effective in strengthening square concrete columns because the latter have sharp corners and flat sides.

Effect of the CFRP length and beam curvature on the strength gain of CFRP-strengthened vertically curved circular hollow sections: an experimental study

ABSTRACT The effects of CFRP wrapping length and the beam curvature on the ultimate strength of carbon fibre reinforced polymer (CFRP)-strengthened in-plane curved steel circular hollow sections (SCHS) were studied by means of an experimental study. A total of 16 beams having four curvatures 0 mm, 2000 mm, 4000 mm and 6000 mm, which were strengthened with three CFRP lengths 500 mm, 750 mm and 1000 mm, were tested under three-point bending. Failure loads, failure mechanisms, strain variations and load-deflection responses were observed. Four types of failure modes were observed in CFRP-strengthened vertically curved SCHS depending on the CFRP wrapping length. The best performance was noted in strengthened beams when the ratio between CFRP wrapping length and beam span is 0.625.

Axial compressive behavior of pre-damaged concrete-filled square steel tube columns repaired with section circularization and CFRP composites

This study focused on repair treatments for the effective reuse of damaged concrete-filled square steel tube (CFSST) columns with carbon fiber-reinforced polymer (CFRP) composites. Forty specimens were designed to investigate the effects of pre-damage levels, section circularization, and the number of CFRP layers on the compressive behavior of the repaired CFSST columns. Test results indicated that the method of section circularization and CFRP wrapping effectively restored the degraded initial axial stiffness of the pre-damaged CFSST columns and increased the ultimate bearing capacity of the pre-damaged CFSST columns by 49–180 % compared to their undamaged condition. Considering the influence of the pre-damage level and the contribution of section circularization, the ultimate bearing capacity calculation model was suggested for predicting the compressive behavior of the repaired CFSST columns. The experimental results and collected test data have well verified the accuracy and applicability of the calculation model.

Performance assessment of buried steel pipelines reinforced with carbon fibre-reinforced polymer under reverse fault movement

Buried oil and gas pipelines are often affected by the active zones across faults, and the failure of pipeline functions owing to relative fault movements has attracted widespread attention. Carbon fibre-reinforced polymer (CFRP) was proposed as a reinforcement measure for buried continuous pipelines crossing faults to mitigate the structural damage to pipelines subjected to large permanent ground deformations. In this study, the lamina model and Hashin failure criterion were used to simulate the CFRP material in a three-dimensional nonlinear finite element model of the pipeline-soil interaction. The peak strain and cross-sectional ovalization of the pipeline were used to quantify the nonlinear response of the steel pipeline subjected to reverse fault movement. Parametric studies in terms of the CFRP wrapping angle, thickness, length, as well as internal pressure were conducted to comprehensively assess overall performance of CFRP-wrapped steel pipelines. Results indicated that the CFRP wrapping in direction of 0°/90° with respect to the axial direction of the pipeline exhibit the optimum effects in improving the performance of pipelines. For steel pipelines subjected to reverse fault, increase of the CFRP wrapping thickness effectively reduces the development of compressive strain on the pipeline wall, thereby delay the local buckling failure of the pipeline. Besides, CFRP is effective in increasing the bending curvature radius and preventing the local buckling of the pipeline, but insufficient wrapping length of CFRP can lead to local buckling of steel pipelines under same fault displacement. For pipelines with internal pressures internal pressure can enhance the overall performance of CFRP wrapped pipelines against reverse fault movement.

Efficiency of rapid repairing for composites and structural fibre-reinforced plastic waste aggregate concrete members

In underdeveloped countries, improperly disposed of electronic waste material (E-waste) causes environmental deterioration and health hazards. The previous related work focused on the axial performance of concrete compressive members reinforced with glass fibre reinforced polymer (GFRP), rather than the efficacy of repairing them after minor damage. The present work has endeavored to deliberate the structural performance of partially damaged E-waste aggregate concrete (EAC) compressive members reinforced with structural synthetic fibres reinforced with GFRP bars and GFRP spirals. Carbon fibre-reinforced polymer (CFRP) sheets were utilized to quickly restore the damaged samples. Twelve circular samples with diameters of 250 mm and heights of 1000 mm were constructed. Six samples were reinforced with GFRP bars and spirals (SSEAC compressive members) while the others had steel reinforcement. Following concentric and eccentric compression, which caused a 30% reduction in axial load-carrying capacity in the stage following peak loading, the samples were repaired using CFRP sheets. Before and after their rapid repair, samples' axial load-carrying capacity, load-shortening response, stiffness index, axial shortening, strength index, ductility index, and failure modes were assessed. These factors included spiral pitch, CFRP wrapping, structural synthetic fibres, E-waste concrete, and reinforcement type. The findings showed that as compared to the original compressive members, both restored SSEAC and GSEAC compressive members had good structural behavior in terms of studied parameters due to the efficiency of CFRP wraps. A new theoretical model is also suggested to predict the axial load-carrying capacity of CFRP-repaired members.

Numerical Analysis on Dynamic Response of CFRP-Wrapped RC Columns under Lateral Impact Loading

This paper presents a numerical study examining the dynamic response and resistance mechanism of reinforced concrete (RC) columns strengthened with or without carbon-fiber-reinforced polymer (CFRP) wraps under lateral impact loading by using the software LS-DYNA. First, the information of eight column models was briefly introduced as part of the laboratory experimental program from the literature. Secondly, finite element (FE) models were established in terms of the geometries of impact tests. Then, a detailed comparison between numerical results and experimental results was made, and FE models showed a relatively high simulation accuracy. Subsequently, a series of parametric analyses were carried out with a focus on the effects of axial compression ratio, the boundary condition at the column top, the layer number of CFRP wraps, and the impact velocity and impact height on the dynamic responses of plain and strengthened columns. The results demonstrated that the CFRP retrofit mechanism was not activated during the initial Stage-I when the impact force rapidly increased to the first peak and then decreased to zero. CFRP strengthening came into play in the second stage, Stage-II, and affected the response of the shear force and moment along the column height, as well as had a great influence on the control of shear damage. The dynamic response of RC columns was more sensitive to the impact velocity than to other parameters, regardless of whether CFRP wrapping was applied. The axial compression ratio would have a different influence on the column failure mode if the impact velocity was varied. The variation in impact height and boundary condition at the column top had little influence on the damage mode of strengthened columns.

Study of structural behavior of retrofit beam column junction using Ansys

The beam-column joint is a critical component of reinforced concrete buildings, responsible for effectively transferring loads between connected members while withstanding gravity and seismic forces. However, these joints are often the weakest link in the structure due to insufficient shear strength. To ensure structural integrity, Carbon Fiber Reinforced Polymer (CFRP) materials are widely utilized for retrofitting beam-column joints. CFRP offers high strength, stiffness, and corrosion resistance without significantly increasing the joint's dimensions. ANSYS Workbench is a powerful software tool that enables detailed analysis and design of beam-column joints. By providing advanced simulation capabilities, it reduces the necessity for physical testing and streamlines the retrofitting process, thereby enhancing project efficiency and cost-effectiveness. This study focuses on the analysis and retrofitting of beam-column joints using CFRP materials in ANSYS Workbench, specifically in the 2022 R2 Student and 2022 R1 Teaching versions. The findings of this study reveal significant improvements in the retrofitted beam-column joints compared to their original condition. Notably, the use of CFRP wrapping reduces deformation and increases the maximum principal stress in various reinforcement patterns. The study also includes a comparison between manual and analytical results, further validating the effectiveness of the retrofitting approach using CFRP materials.

External Confined Concrete Cylinders Behavior under Axial Compression Using CFRP Wrapping.

Carbon-fiber-reinforced polymer (CFRP) is a composite material used to mend and strengthen concrete structural elements in civil engineering. The prime aim of this experimental study is to investigate the comportment of confined concrete cylinders (CCC) under uniaxial loads by altering the concrete strength, the CFRP angle orientation, and the volumetric ratio, following the externally bonded reinforcement technique (EBR). We present the results of the confinement effect and failure mechanisms issue of more than 150 specimens of CFRP confined concrete cylinders that have been undertaken and in which several parameters were altered. Totally and partially confined concrete cylinders were tested for failure under axial compressive loads and indirect tensile tests. Four different ratios of water/cement (0.33, 0.36, 0.401, and 0.522) were investigated. In addition, three sand-resin ratios were prepared to improve the mechanical properties and the adhesion of the CFRP and the concrete. The obtained results revealed a clear improvement in the compressive strength of the specimens made with low strength concrete (from 38% to 66%) compared to those made of high strength concrete (from 11% to 31%), where the improvements are relatively low. Furthermore, the transversally confined concrete cylinders presented significant gains in strength over those confined longitudinally. Lastly, adding sand to the resin increases the compressive strength of confined concrete cylinders (1.19% to 54.62%) and reduces the cost of the resin used for fixing CFRP materials.

Experimental study on compressive behavior of intermediate slender timber columns with local damage and the retrofitting techniques for the damaged columns

The existing historic timber constructions are often affected by local damage such as decay, and their mechanical properties are significantly reduced. In order to explore the influence of local decay on the compression behavior of timber columns, this work conducted experimental investigations of 10 intermediate slender columns with different damaged conditions under axial compression. Damaged areas, damaged positions and damaged forms of the columns were considered. Based on the failure mechanism of damaged timber columns, the retrofitting technique for locally damaged columns using the combination of wood block, profile and carbon fiber reinforced polymer (CFRP) wrap was proposed, compared with the traditional methods of using wood block only, and both wood block and CFRP wrap. Experimental investigations of 10 retrofitted columns with 4 retrofitting techniques were also conducted. The compressive performances and effect among these retrofitting techniques had been compared based on the failure modes and ultimate load-carrying capacity stiffness and ductility. The results indicated that the compressive performance of the damaged columns was significantly reduced which magnified with the increase of damaged area, and the loss of the load-carrying capacity was much larger than the loss of the cross-section area. The load-carrying capacity and stiffness of the damaged columns were appreciably restored by these retrofitting techniques. The load-carrying capacity of the bilaterally damaged column retrofitted by the combination of wood block, GFRP profile and CFRP wrap was the highest, reaching 98.30% of the intact column.

Axial compression behavior of CFRP-confined square concrete-filled double skin tube stub columns with stainless steel outer tube

Concrete-filled double skin tube (CFDST) stub columns with a stainless steel outer tube is a new kind of composite columns and potential to be widely utilized in ocean engineering owing to the excellent performance characterized by high corrosion resistance. To improve the ultimate bearing capacity and delay the local buckling of stainless steel tube, confining materials such as carbon fiber reinforced polymer (CFRP) can be adopted in these composite columns. Thus, this study conducted an experimental investigation on the axial compression behavior of CFRP-confined square CFDST stub columns with a stainless steel outer tube. The main variables were the width-to-thickness ratio of stainless tube and the number of CFRP layers. The typical failure modes, load-shortening curves, and load-strain curves of the CFDST and CFRP-confined CFDST columns were obtained. The test results indicated that the local buckling of CFDST columns can be well suppressed with CFRP wrapping, prior to CFRP rupturing. The CFRP can provide an effective confinement on the sandwich concrete and the ultimate bearing capacity enhancement increased with increasing the number of CFRP layers. Based on theoretical analysis a design model for the inner steel tube has been proposed to prevent the premature failure of the inner steel tube which can leads serious ultimate bearing capacity lose. Additionally, new methods for predicting the ultimate bearing capacity of the square CFDST and CFRP-confined CFDST are proposed based on the limit equilibrium method and twin shear unified strength theory. The predicted results are in good agreement with the experimental results and collected test data.

Investigation on efficiency of cathodic protection applied on steel in concrete cylinder with CFRP wrap serving as anode

The combination of strengthening and corrosion protection by using multi-functional material is an attractive topic recently. In this paper, carbon fiber reinforced polymer (CFRP) was utilized as a repair material and an anode of impressed current cathodic protection (ICCP) owing to its excellent mechanical and electrochemical properties. The effects of protection methods (non-protection, epoxy coating, CFRP wrapping, CFRP wrapping and ICCP), pre-corrosion degrees (3 %, 6 %, and 12 %), and ICCP current densities (5, 20, and 80 mA/m2) on corrosion performance of reinforced concrete (RC) cylinders were investigated by means of electrochemical measurements. The results showed that the double protection provided by CFRP wrapping and ICCP worked much better than the sole epoxy coating or the sole CFRP wrapping when an appropriate current density was applied. The optimal ICCP current density depended on the pre-corrosion severity of RC specimen. A current density of 20 mA/m2 resulted in the greatest improvements in charge transfer resistance for the 6 % and 12 % pre-corroded specimens while the optimal current density was 5 mA/m2 for the 3 % pre-corroded specimen. Moreover, CFRP wrapping led to greater increases in charge transfer resistance than epoxy coating. It suggested that, besides the contribution of epoxy to isolate harmful substances, confinement provided by CFRP wrapping may benefit corrosion alleviation in a further step by densifying the core concrete and consequently impeding ion transport and oxygen availability. This work provides a basis for further optimization design of ICCP-strengthening technique applied on corroded RC components to achieve higher efficiency.

Parametric investigation on behaviour of carbon fiber reinforced polymers wrapped reinforced concrete columns under eccentric loads

AbstractThe use of carbon fiber reinforced polymer (CFRP) has proved to be significantly efficient in improving the overall behaviour of reinforced concrete columns. The use of high‐strength concrete in columns not only reduces the size but also gives adequate durability to the structure. The behaviour of reinforced concrete columns depends on numerous parameters, including concrete compressive strength, percentage of steel, cross‐section dimensions, ties spacing and the slenderness ratio. In this work the following parameters are investigated: Concrete compressive strength, percentage of steel, and the slenderness ratio. The focus of experimental investigation was to study the influence of carbon fiber reinforced polymer wrapping on the behaviour of plain concrete columns. Following the experimental investigation, a detailed numerical investigation was conducted to study the influence of the above parameters on the behaviour of eccentrically loaded plain and reinforced concrete columns. The influence of carbon fiber reinforced polymer wrapping on the overall performance was also studied using the available models for predicting the load‐moment interaction of columns to confirm the findings of the numerical investigations. Based on the detailed experimental and numerical investigation it was found that the concrete compressive strength significantly influences the overall behaviour of the reinforced concrete columns subjected to eccentric loadings.

Vehicular Impact Resistance of FRP-Strengthened RC Bridge Pier

As-built bridge piers are likely to be subjected to vehicular collisions, causing severe damage to the bridge substructure and even resulting in the collapse of the entire bridge. This study aimed to evaluate the effectiveness of fiber-reinforced polymer (FRP) strengthening in enhancing the vehicular impact resistance of as-built bridge piers. A typical local, refined finite-element (FE) model of a simply supported two-span, double-column, reinforced-concrete (RC) bridge was established. The adopted material constitutive models and the FE analytical approaches were then validated through reduced vehicle model lateral impact tests on bare and carbon fiber–reinforced polymer (CFRP)-strengthened RC columns. The effective schemes for FRP strengthening of bridge piers against vehicle impact are discussed from the aspects of fiber orientation, number of layers, and strengthened height as well as by FRP type. Based on the FRP strengthening scheme, 48 vehicle–bridge collision scenarios were designed to evaluate the collapse of bridges with/without FRP-strengthened piers. It was found that (1) external FRP wrapping can effectively enhance vehicular impact-resistance of as-built bridge piers (e.g., reducing the degree of damage and deformation of the impacted pier); (2) for typical bridge piers, the effective strengthening scheme comprised a fiber orientation of 0° in reference to the circumferential direction, a 3-m strengthened height, and four-layer CFRP wrapping; (3) compared with bare bridge piers, FRP-strengthened piers could improve the vehicular impact-resistant safety redundancy of as-built bridges and, to some extent, avoid bridge collapses under truck collisions at high speed. Furthermore, through introducing the dynamic increase factors of concrete strength, reinforcement rebars, and FRP, and considering the nonuniform distributions of the strain rate of FRP-strengthened bridge piers caused by vehicular collision, the dynamic shear capacity of strengthened bridge pier was formulated.

LONG TERM PERFORMANCE OF REHABILITATED CONCRETE BEAMS STRENGTHENED FOR TORSION USING CFRP

The paper presents long term performance of reinforced concrete floor beams that were rehabilitated in 2007 for torsion using carbon fiber reinforced polymer (CFRP). The two rehabilitated beams were members of the concrete beam and slab floor system of a new parking garage near Boston in Massachusetts, USA. Without this rehabilitation, the new garage could not be accepted. The paper recapitulates the causes that led to the cracking and the rehabilitation of the beams for torsion, and the choice between strengthening by reinforced concrete jacket and by CFRP wrap. It was probably the first time and ahead of the Codes of Practice that CFRP was used to resist torsion in real as-built concrete structure and for total torsion. In previous practices, CFRP was ever used for flexure and shear strengthening in partial supplement to the original strength, not for total strength. The methodology for CFRP for torsion was given. Pictures depicting the rehabilitation in 2007 are illustrated. The recent pictures of the beams taken in December 2021 are given. The long term monitoring and observation, on the author’s own time and duty of care, for the past 14 years on this real structure confirms the reliability, durability and efficiency of CFRP wrap for torsion of concrete beams under sustained dynamic live loading and vibration from motor vehicles. The paper concludes with discussion of the advantages of CFRP wrap over the reinforced concrete jacket strengthening.

LONG TERM PERFORMANCE OF REHABILITATED CONCRETE BEAMS STRENGTHENED FOR TORSION USING CFRP

The paper presents long term performance of reinforced concrete floor beams that were rehabilitated in 2007 for torsion using carbon fiber reinforced polymer (CFRP). The two rehabilitated beams were members of the concrete beam and slab floor system of a new parking garage near Boston in Massachusetts, USA. Without this rehabilitation, the new garage could not be accepted. The paper recapitulates the causes that led to the cracking and the rehabilitation of the beams for torsion, and the choice between strengthening by reinforced concrete jacket and by CFRP wrap. It was probably the first time and ahead of the Codes of Practice that CFRP was used to resist torsion in real as-built concrete structure and for total torsion. In previous practices, CFRP was ever used for flexure and shear strengthening in partial supplement to the original strength, not for total strength. The methodology for CFRP for torsion was given. Pictures depicting the rehabilitation in 2007 are illustrated. The recent pictures of the beams taken in December 2021 are given. The long term monitoring and observation, on the author’s own time and duty of care, for the past 14 years on this real structure confirms the reliability, durability and efficiency of CFRP wrap for torsion of concrete beams under sustained dynamic live loading and vibration from motor vehicles. The paper concludes with discussion of the advantages of CFRP wrap over the reinforced concrete jacket strengthening.

Response of strengthened unreinforced brick masonry wall with (1) mild steel wire mesh and (2) CFRP wrapping, under close-in blast

In the past few decades, the world is experiencing a number of frequent and unanticipated blast explosions. Property loss and casualties caused by these blasts are of great concern to state authorities and are of sufficient interest to the structural engineers and researchers. A common structural member in the buildings used for both commercial and residential formats is load-bearing brick masonry walls. For the safety of a structure, the masonry walls which are more vulnerable against such loadings are required to be strengthened. Many retrofitting techniques to strengthen the masonry walls are in vogue. In the present study, a detailed micro-model of 1600 mm × 2100 mm × 240 mm (length × height × thickness) clay brick unreinforced masonry wall has been developed, analyzed, and validated with the available experiment results, using the ABAQUS/Explicit software under the 5 kg-TNT blast load at scaled distance 0.58 m/kg1/3. The Concrete Damage Plasticity (CDP) model including the strain rate effects is used to model the masonry material behavior to blast loading. To improve the response of the wall, it has been strengthened with (1) mild steel wire mesh of different thicknesses 2.50, 3.50, and 4.50 mm (i) on the rear face only, and (ii) on both the faces of the wall; and (2) carbon fiber-reinforced polymer (CFRP) wrapping (i) 0.50 and 0.60 mm thick on the rear face only, and (ii) 0.30 mm thick on both the faces of the wall. Response of the strengthened walls is discussed and compared. The equivalent thickness of the wrapping to the steel wire mesh from displacement and damage point of view has been evaluated.

Strengthening of braced unreinforced brick masonry wall with (i) C-FRP wrapping, and (ii) steel angle-strip system under blast loading

Accidental detonations, and explosions made by extremists are major threats to human life and building structures. The vulnerability of the load-bearing masonry structures is more as compared to the reinforced concrete structures against explosion-induced loadings. Such events weaken the socio-economic stability and therefore necessitates the evaluation and effective strengthening strategies of masonry structures to improve their blast performance. Unreinforced masonry (URM) walls have little flexural resistance against out-of-plane loadings and exhibit a brittle mode of failure. In this research work, the clay brick masonry wall braced with two transverse walls one at each end, tested experimentally under the explosive loads of 4.34 and 7.49 kg-TNT equivalent at scaled distances 2.19 and 1.83 m/kg1/3, has been numerically analyzed using a high-fidelity commercial FEM-based dynamic computer program, ABAQUS/Explicit-v.6.15 considering micro-modeling technique and concrete-damaged-plasticity (CDP) model with strain rate effect. Damage in the exposed masonry wall in the form of (i) vertical mortar joint cracks at the center and next to the bracing transverse walls, (ii) flexural cracks near the ground; and diagonal cracking in the lower part of the bracing walls, is observed at a scaled distance, Z = 2.19 m/kg1/3. For Z = 1.83 m/kg1/3, out-of-plane catastrophic collapse of the walls occurs. The computed damage patterns are found quite similar to the experimental ones in the open literature. A novel strategy other than commonly used carbon fiber reinforced polymer (C-FRP) wrapping technique, consisting of steel angle-strip system has been devised and used to strengthen the wall against the considered blast levels. CFRP wrapping of 2mm thickness, and steel strip mesh of thickness (a) 3mm, and (b) 5mm with angles along the edges of the walls, are considered to improve the wall response and analyses are carried out. The blast load-carrying mechanisms of the walls strengthened with the two techniques are explained.

Performance of axially loaded square RC columns with single/double confinement layer(s) and strengthened with C-FRP wrapping under close-in blast

Very recently a new variant of reinforced concrete (RC) columns confined with a double layer of transverse steel has been introduced by researchers and investigated its performance under axial compression and seismic loading. Analysis of blast performance of such columns is of considerable interest. Most of the columns in a building structure are found to be of square or rectangular cross-section. Being axisymmetric, the circular columns perform better than square/rectangular ones under impulsive loadings. The stability of a structure supported mainly on columns subjected to such loadings depends upon the performance of the columns. Therefore, it is important to enhance the response of supporting RC compression members of square or rectangular cross-sections of a structure subjected to high intense loadings. In this research work, one 3000 mm long, 300 mm × 300 mm square RC column with conventional transverse steel carrying an axial working load of 950kN subjected to 82 kg-TNT-equivalent close-in blast loading at scaled distance 1.0 m/kg1/3 tested experimentally has been first analyzed using the high-fidelity dynamic computer code, ABAQUS/Explicit-v6.15. For comparison, another singly confined concrete column with seismic reinforcement over its entire length is also analyzed. By comparing the numerical results with the experimental results in the open literature, the accuracy of the numerical model is verified. To improve the response, doubly confined RC columns having outer transverse confining steel stirrups of square and inner ones’ diamond/circular geometry with different combinations of stirrup spacing have been considered and investigated. The columns are of the same area of compression steel and carry the same axial load (950kN). Carbon-fiber-reinforced-polymer (C-FRP) wrapping of 2 mm thickness is also considered and modeled using Hashin’s damage initiation criteria and energy-based damage evolution to investigate the blast resistance of the columns. Blast performance in terms of displacement, damage dissipation energy, concrete crushing, and cracking are compared and discussed.