Reduction In Load Carrying Capacity Research Articles

Influence of reinforcement reductions on the response of reinforced concrete half-joints

Reinforced concrete half-joints are susceptible to deterioration mechanisms primarily due to the leakage of surface water, often contaminated with chlorides from de-icing salts, through the expansion joint. Due to the joint geometric form, favourable conditions can be created inside the joint for the corrosion of steel reinforcement. To this end, seven reinforced concrete half-joints were tested to failure under three-point bending to investigate the effect of reinforcement reductions that simulate common deterioration scenarios arising from the corrosion of reinforcement. The results were then compared to the predictions of nonlinear finite element analyses and the strut-and-tie method. The results demonstrated that a reduction in the amount of reinforcement close to the re-entrant corner has major influence on the load-deflection response of reinforced concrete half-joints. The largest reductions in load-carrying capacity were obtained from the half-joints with a full removal of diagonal bars and a combined removal of diagonal and U-bars, both showing reductions in load capacity of more than 50 %. The failure mode in each case of simulated deterioration scenarios involved a shear failure at the nib, except one case which displayed a shear failure in the full depth section due to the reduced anchorage of the bottom reinforcement. Furthermore, it was shown that nonlinear finite element analyses provide accurate predictions of the load-deflection response and failure crack patterns. The strut-and-tie method was found to result in overly conservative predictions, with an average observed-to-predicted load ratio of 1.48 and a coefficient of variation (COV) of 10.2 %. This is considerably higher than an average load ratio of 1.05 and a COV of only 3.1 % obtained from the nonlinear finite element analyses.

Fire and post-fire performance of unbonded semi-precast prestressed reinforced concrete beams

The integration of semi-precast concrete beam preparation methods with prestressing structural measures aims to achieve superior mechanical properties while complying with green construction principles. However, the damage mechanism of semi-precast prestressed concrete beams (SP-PCBs) under fire conditions is not clear. In this study, the cross-section temperature distribution, prestressing loss pattern, and residual load-carrying capacity of the SP-PCBs were investigated by conducting standard fire tests. The results show that increasing the thickness of the protective layer of prestressing bars can delay the time of damage by high temperature and thus increase the fire resistance limit of the SP-PCBs. Higher prestressing levels and rebar ratios contribute to the cracking resistance of the SP-PCBs, although the stress loss is obvious. After the fire, the distinct SP-PCBs showed different degrees of reduction in load-carrying capacity and stiffness, but still exhibited excellent fire resistance and avoided brittle damage. Increasing the reinforcing ratio increases the residual load-carrying capacity of the SP-PCBs, while increasing the prestressing level has a relatively small effect. Increasing the height of the post-cast layer slightly reduces the stiffness and ductility of the SP-PCBs, but does not significantly affect the load-bearing capacity. In addition, this paper establishes a theoretical calculation model for the residual load-bearing capacity of the SP-PCBs after the fire, and verifies the accuracy of the model by experimental results, which provides a practical theoretical basis and reference for the design and evaluation of the fire resistance performance of the SP-PCBs.

Behavior of unbonded pre-stressing concrete beams with thermal insulation coating

ABSTRACT Pre-stressing concrete is commonly used in construction. One of the challenges that pre-stressing concrete (PC) faces is that fire exposure reduces the strength and serviceability of PC elements, which requires unique design considerations. The pre-stressing strands are more sensitive to high-temperature, deform larger than mild steel, and break quicker. This research investigates the thermal and structural response of totally unbonded pre-stressing T-beams subjected to increased temperatures and continuous service loads. Thermal coating was proposed to avoid damage and load carrying capacity reduction under fire loading. Seven medium-sized post-tensioned concrete beams were tested in a fire exposure (600°C for 3 h) in order to examine the effect of the following variables: presence of thermal coating, the use of different pre-stressing ratios, increasing the concrete cover, and studying the fire effect at the end anchor, which represents the weakest point at the unbonded system. The proposed insulating technique improved pre-stressing beam behavior during fire exposure by improving crack distribution and lowering strength loss. The thermally insulated beam with a high pre-stressing ratio attained 99.3% of the control specimen load carrying capacity, compared to 86% for the unprotected beam. The deflection of the thermally isolated beam was 7.8 mm, compared to 22.7 mm for the unprotected specimen after 180 min of fire exposure. The use of low pre-stressing ratio caused the insulated pre-stressing strands to rapidly deform with low increases in temperature, which caused rapid crack formation.

Deterioration law of flexural performance of RC beams with initial cracks under alternating action of salt freeze-thaw cycles and fatigue

Reinforced concrete (RC) bridges in cold regions are continuously exposed to the combined challenges of traffic loads, freeze–thaw cycles, and salt corrosion. This research delves into the deterioration mechanics and flexural performance of damaged RC beams when subjected to the dual stresses of salt freeze–thaw cycles (SFTCs) and fatigue loading. We conducted performance degradation tests on cracked RC beams subjected to alternating SFTCs and fatigue loading, followed by evaluations of their residual flexural capacities. In-depth analysis considered the impact of the number of alternating cycles and the initial crack width. The results indicate that the combined effects of alternating SFTCs, fatigue loading, and initial cracks significantly diminish the RC beams' flexural strength. As the number of alternating cycles and the initial crack width increased, there was a notable rise in mass loss, rebar corrosion, and a reduction in residual load carrying capacity and stiffness. Particularly, beams without initial cracks saw a 3.61 % reduction in load carrying capacity and a 24.06 % decrease in stiffness after four alternating cycles. In contrast, beams with an initial crack width of 0.10 mm experienced an 11.15 % decline in load carrying capacity and a 38.38 % drop in stiffness. The study concludes that while the combined effects of fatigue loading, SFTCs, and initial cracks are significant, initial cracks exhibit a more pronounced negative influence on load carrying capacity than on stiffness and ductility.

Behavior and Performance of Reinforced Concrete Columns Subjected to Accelerated Corrosion

Steel reinforcement corrosion in concrete structures such as bridges, industrial plants, marine structures, and coastal buildings is a growing concern due to its impact on cost, safety, and serviceability. Corrosion leads to spalling, cracking, and reduced reinforcement diameter, which can compromise structural integrity. This study examines the behavior of concrete columns with corroded reinforcement in two phases. In the first phase, 72 columns of 150 × 150 mm cross-sectional dimensions and 300 mm length were cast and subjected to an accelerated corrosion technique. The study examined variables such as concrete cover, concrete strength, and corrosion exposure. The second phase involved studying the axial behavior of corroded columns concerning the effect of column length. Column specimens of 150 × 150 mm cross-sectional dimensions and lengths of 500 mm, 700 mm, and 900 mm were cast, corroded, and tested under axial compressive load. The study revealed that a 30 mm concrete cover offers 10% more protection against corrosion than a 20 mm cover. Continuous exposure to a corrosive environment reduces the load-carrying capacity by 50%, while columns with 28 MPa concrete strength can carry 4% more load. Longer columns are more susceptible to corrosion, leading to a significant reduction in load-carrying capacity and concrete cover damage. Therefore, maintaining adequate concrete cover, strength, and regular inspections are essential to address steel reinforcement corrosion and preserve structural integrity.

Investigation on tensile and creep behaviour of glass fiber reinforced polymer (GFRP) bars: A review

Corrosion has become a global issue primarily responsible for the deterioration of structural capacity of reinforced concrete structures (RCC) and prestressed concrete structures (PSC) leading to its premature failure. Across the globe, corrosion issue is critical in PSC structures, as the cross-sectional area of steel strands gets destroyed leading to the considerable reduction of load carrying capacity. A lot of case studies have been reported regarding the early failure of prestressed box girder bridges prior to their design life. The inspection of corrosion related issues is a complex affair, and it involves huge rehabilitation and maintenance cost. It has been reported that the expenditure estimated for maintenance and rehabilitation of structures due to corrosion is enormous inducing a significant loss in country’s GDP. To overcome this challenge in RCC and PSC structures due to corrosion of conventional steel reinforcement, Fiber reinforced polymer (FRP) bars could be used in place of steel bars. FRP bars distinct characteristics like light weight, excellent corrosion and fatigue resistance have attracted significant attention and priority as substitute over conventional steel reinforcement. The lack of proper design guidelines and specifications restricts the reliability and application of this technology in the construction field. However, the active research on glass fiber reinforced polymer (GFRP) bars indicated that it could be the best alternative due to its lower cost and superior tensile strength. Therefore, it is necessary to understand the preliminary characteristics of GFRP bars prior to its application as reinforcement in RCC and PSC. Hence, a critical review on tensile and creep characteristics of GFRP bars would be presented in this paper to contribute a vivid and detailed documentation for upcoming research on GFRP.

Gaussian process regression-based load-carrying capacity models of corroded prestressed concrete bridge girders for fast-screening and reliability-based evaluation

Fast screening and reliability-based evaluation of corroded prestressed concrete (PC) bridge girders for safety assessment requires efficient capacity prediction models. This paper aims at developing data-based prediction models to quantify corrosion effects on load-carrying capacity of PC girders that are precast and standardized for short-span bridges. The load-carrying capacity of corroded bridge girders depends on their initial design configuration (e.g., those characterized by the standardized PC girders), loading condition (e.g., shear-span-to-effective-depth ratio), and corrosion conditions (e.g., corrosion degree). To develop data-based prediction models, generating sufficient data through physical experimental tests of full-scale corroded PC girders is prohibitively costly. Thus, a virtual experimental database is generated numerically using two-dimensional continuum-based finite element (FE) models for corroded PC girders, after being validated using 9 corroded PC girders tested in the literature with flexure or shear failure. To this end, a total of 4,165 PC girders under point loading are simulated to consider various design, loading, and corrosion conditions to estimate their load-carrying capacities. With this database, probabilistic machine learning, specifically Gaussian process regression or kriging, is used to develop (1) a residual capacity factor model (i.e., the ratio between load-carrying capacities from corroded and uncorroded girders), and (2) a load-carrying capacity prediction model (i.e., to predict the load-carrying capacity of uncorroded/corroded girders). The first model is used to study the load-carrying capacity reduction of PC girders due to corrosion compared to their uncorroded counterparts; this can reveal how the increasing corrosion condition affects the load-carrying capacity of corroded PC girders together with other design and loading parameters. The second model is developed to predict the load-carrying capacity of corroded PC girders as a function of design, loading, and corrosion parameters; its application to conditional reliability analysis provides insights into corrosion effect on the probability of failure of corroded PC girders at given load levels when the capacity is affected by corrosion. The application results of the two models enable engineers to quantify the corrosion effect on PC girders in terms of (1) reduction in load-carrying capacity for fast screening and (2) increase in probability of failure for reliability-based evaluation.

Foreword to the special issue on new developments in structural stability.

Foreword to the special issue on new developments in structural stability.

Strengthening of Recycled Aggregate Concrete Slender Column with CFRP

This piece provides an overview of an experimental program that tests the structural performance of slender recycled aggregate RAC columns that are externally restrained by carbon fiber reinforced polymer (CFRP composite system). To demonstrate that the CFRP strengthening system is one of the recommended effective techniques for making up for the reduction in load-carrying capacity caused by the use of 100% RCA in combination with the slenderness of column specimens, eight slender circular RC columns were modeled and tested. To more accurately predict the structural features of the RC thin column (the ultimate carrying weight, first cracking load, load-displacement curve, and load-strain response), the findings from experiments have been analyzed and monitored. The findings indicated that the type of transverse reinforcement and the amount of external strengthening impact the degree of improvement in column performance. The strength for the tied RC columns with 100% RCA confined by (25, 50, and 100) % CFRP increased by 5.5, 44.97, and 112.85%, respectively, compared to control columns with no CFRP confinement. Similar strength improvements are seen in spirally RC columns with 100% RCA and the same external confinement coverage ratio: 10.32, 42.81, and 113.51%.

Experimental study on the tensile load-carrying capacity of steel/GFRP bonding in moisture and acidic environments at high temperature

Steel plates are damaged in harsh environments, such as moisture and acidic environments, especially at high temperatures. Damaged areas in steel plates can be strengthened by bonding fiber reinforced polymer (FRP) composites. This paper investigates the effect of harsh environment on the load-carrying capacity of damaged steel specimens reinforced by the GFRP patch. The results of the patched samples immersed in accelerated harsh environments consisting of distilled water and strong sulfuric acid solution are compared to dry ones in the room and high-temperature conditions. The results show about 13% reduction in load-carrying capacity after 8 weeks of immersion in both harsh environments at room temperature. Moreover, the results of high-temperature tension test for patched samples immersed in high-temperature acidic solution show a significant reduction in displacement and load-carrying capacity even after 1 week. The failure mode investigation of dry specimens by numerical analyses shows good consistency with the experimental results.

Compressive Behavior of Pultruded GFRP Boxes with Concentric Openings Strengthened by Different Composite Wrappings.

Web openings often need to be created in structural elements for the passage of utility ducts and/or pipes. Such web openings reduce the cross-sectional area of the structural element in the affected region, leading to a decrease in its load-carrying capacity and stiffness. This paper experimentally studies the effect of web openings on the response of pultruded fiber-reinforced polymer (PFRP) composite profiles under compressive loads. A number of specimens have been processed to examine the behavior of PFRP profiles strengthened with one or more web openings. The effects of the size of the web opening and the FRP-strengthening scheme on the structural performance of PFRP profiles with FRP-strengthened web openings have been thoroughly analyzed and discussed. The decrease in load-carrying capacity of un-strengthened specimens varies between 7.9% and 66.4%, depending on the diameter of the web holes. It is observed that the diameter of the hole and the type of CFRP- or GFRP-strengthening method applied are very important parameters. All CFRP- and GFRP-strengthening alternatives were successful in the PFRP profiles, with diameter-to-width (D/W) ratios between 0.29 and 0.68. In addition, the load-carrying capacity after reinforcements made with CFRP and GFRP increased by 3.1–30.2% and 1.7–19.7%, respectively. Therefore, the pultruded profiles with openings are able to compensate for the reduction in load-carrying capacity due to holes, up to a D/W ratio of 0.32. The capacity significantly drops after a D/W ratio of 0.32. Moreover, the pultruded profile with CFRP wrapping is more likely to improve the load-carrying capacity compared to other wrappings. As a result, CFRP are recommended as preferred composite materials for strengthening alternatives.

Prediction of Damage in Non-Crimp Fabric Composites Subjected to Transverse Crushing: A Comparison of Two Constitutive Models

Non-crimp fabrics (NCFs) are increasingly used in industry for manufacturing of composite structures due to a combination of high mechanical properties and excellent manufacturability. As with other composites, in-service damage can be a cause for severe reduction in load-carrying capacity of NCF-reinforced plastics. In this experimental and numerical study, two constitutive material models previously used only for damage prediction in unidirectional (UD) tape and woven fabric-reinforced materials (LS-DYNA’s *MAT_ENHANCED_COMPOSITE_DAMAGE—MAT54 and *MAT_LAMINATED_COMPOSITE_FABRIC—MAT58) were evaluated for simulating transverse crushing of composite parts processed from a non-crimp carbon fabric. For this purpose, UD NCF components of tubular shape were subjected to transverse crushing through a controlled indentation of a metallic cylinder, and results of the experiment were compared with numerical modeling. Considered verification metrics included the observed and the predicted patterns of interlaminar damage, the extent of delamination, as well as the ability of the models to replicate force-displacement response exhibited by the tested specimens.

Evaluation of Resilience Parameters of Soybean Oil-Modified and Unmodified Warm-Mix Asphalts—A Way Forward towards Sustainable Pavements

The sustainable design and construction of highways is indispensable for the economic growth and progress of any region. Highway pavements are one of the core transportation infrastructures that require energy efficient materials with durability and an optimized lifecycle. Recent research has proven that warm-mix asphalt pavements prepared with renewable bio-binders are less susceptible to distresses. This study aims to investigate the resilience characteristics (load time, deformation time) of soybean oil modified and unmodified warm-mix asphalts. Aggregates, asphalt binders and asphalt mixes were characterized in accordance with the Superpave Mix Design Criteria. The resilient modulus tests were performed as per ASTM D7369. The test results indicated that the soybean-modified warm asphalt mix samples showed a 20% to 32% reduction in load-carrying capacity than unmodified warm asphalt mixes. The values of the horizontal and vertical recoverable deformations observed in the soybean-modified mixes were found to be 3% to 7% more than in the unmodified mixes. A slight variability (up to 7%) was also observed in the time-response spectra, i.e., peak load, unload and rest periods, in the soybean-modified mixes compared with the unmodified mixes. The Pearson correlation coefficient showed a significant trend between the resilient modulus test parameters for the soybean-modified warm asphalt mixes, i.e., load deformation, load time and deformation time. Soybean oil showed sustainable behavior as a bio-binder, particularly in the deformation-time response for the warm asphalt mixes. However, the effect of soybean in terms of the reduction of the load-carrying capacity from a sustainability perspective needs to be investigated.

An investigation on the effect of hybrid fiber reinforced on the flexural behavior of RC beams having different lap‐spliced lengths

AbstractThere are only a few studies related to the effect of the hybrid fiber reinforcement on the flexural behavior of full‐scale beam specimens having lap‐spliced length. Thus, this study will ensure important experimental data about the effect of macro steel fibers blended with micro steel fibers on lap‐spliced length. The aim of this study was to investigate the influence of hybrid steel fiber reinforcement on the flexural behavior of full‐scale reinforced concrete beams having different lap‐spliced bars. A sum of three traditional concrete mixtures including a total of 1% fiber by volume fraction was adopted: control mixture without steel fiber, only macro steel fiber and hybrid steel fiber reinforced mixtures. For this purpose, 18 full‐scale beams (200 × 300 × 2000 mm) having three different lap‐spliced length (15, 25, and 35Ø) as tension steel bars were produced and tested under four‐point bending to examine flexural behavior, mode of failure, ductility, and energy absorption capacity properties. In conclusion, the hybrid fiber reinforcement caused the highest increase in the load carrying capacity of the beam specimens. Besides, the hybrid fiber reinforced beam specimens exhibited excellent ductility and energy absorption capacity compared to single fiber reinforced beam specimens. On the other hand, it can be addressed that the hybrid fiber reinforced structural elements had a vital important to compensate the application errors and carelessness in steel bar workmanship, inadequate the lap‐spliced length as per the codes. It can be emphasized that the lap‐spliced length as per the building codes can be reduced in 40% by containing hybrid steel fiber (0.8% macro‐0.2% micro) reinforced concrete without a reduction in load carrying capacity, ductility, and energy absorption capacity compared to control beam specimens without fiber.

Residual post fire strength of non-prismatic perforated beams

The main aim of this study is to assess the performance and residual strength of post-fire non-prismatic reinforced concrete beams (NPRC) with and without openings. To do this, nine beams were cast and divided into three major groupings. These groups were classified based on the degrees of heating exposure temperature chosen (ambient, 400, and 700°C), with each group containing three non-prismatic beams (solid, 8 trapezoidal openings, and 8 circular openings). Experimentally, given the same beam geometry, increasing burning temperature caused degradation in NPRC beams, which was reflected in increased mid-span deflection throughout the fire exposure period and also residual deflection after cooling. But on the other hand, the issue with existing openings was exacerbated. The burned NPRC beams were then gradually cooled down by leaving them at ambient temperature in the laboratory, and the beams were loaded until failure to examine the effect of burning temperature degree on the residual ultimate load-carrying capacity of each beam by comparing them to unburned reference beams. It was found, increasing the exposure temperature leads to a reduction in ultimate strength about (5.7 and 10.84%) for solid NPRC beams exposed to 400 and 700°C, respectively related to unburned one, (21.13 -32.8) % for NPRC beams with eight trapezoidal openings, and (10.5 - 12.8) % for those having 8 circular openings. At higher loading stage the longitudinal compressive strain of Group ambient in mid-span of solid beams reach 2700 με, while the others with openings exhibit divergent strain higher than that, it’s about 3300 με meanwhile, the lower chord main reinforcements have been pass beyond yielding stress. Exposure to high temperatures reduces rafters’ stiffness causing a reduction in load carrying capacity, companion with premature failure consequently reduce the strain at the ultimate stage.

Environmental durability of epoxy-bonded CFRP-to-steel joints in mode I fracture

Exposure to environmental stresses can weaken the connection of epoxy-bonded CFRP-strengthened steel elements. As a result, designers often express concern about possible premature delamination arising from combined peel and shear effects at the CFRP-steel interface. This study was undertaken to further knowledge in relation to the peel failure of epoxy-bonded CFRP-to-steel joints subjected to hygrothermal conditioning. The effect of the bond-line thickness on the bond strength was also examined in this study. A total of 54 specimens were tested including 30 adhesive CFRP-to-steel specimens and 24 adhesive coupons. Two commercially available structural epoxy adhesives were examined. Hygrothermal conditioning may cause the adhesion failure near to the edges of the adhesive joints. The load-carrying capacity and strain energy release rate of adhesive joints depend on the adhesive and hygrothermal environment, and can be degraded up to 15%. The statistical analysis using two-way ANOVA method was applied and showed that the wet conditioning has a significant effect on the maximum failure load of CFRP-to-steel bonded specimens. Reducing the bond-line thickness to less than 1 mm can result in a major reduction in load-carrying capacity and strain energy release rate of CFRP-to-steel bonded specimens. Humid and wet conditioning cause up to 44% and 63% drop in elastic modulus, 31% and 55% reduction in tensile strength, and 32% and 44% increase in average maximum strain of adhesive materials, respectively.

Study on the residual performance of RC beams exposed to processed temperatures and fire

PurposeThe Reinforced Concrete(RC) elements are known to perform well during exposure to elevated temperatures. Hence, RC elements are widely used to resist the extreme heat developing from accidental fires and other industrial processes. In both of the scenarios, the RC element is exposed to elevated temperatures. However, the primary differences between the fire and processed temperatures are the rate of temperature increase, mode of exposure and exposure durations. In order to determine the effect of two heating modalities, RC beams were exposed to processed temperatures with slow heating rates and fire with fast heating rates.Design/methodology/approachIn the present study, RC beam specimens were exposed to 200 °C, to 800 °C temperature at 200 °C intervals for 2 h' duration by adopting two heating modes; Fire and processed temperatures. An electrical furnace with low-temperature increment and a fire furnace with standard time-temperature increment is adapted to expose the RC elements to elevated temperatures.FindingsIt is observed from test results that, the reduction in load-carrying capacity, first crack load, and thermal crack widths of RC beams exposed to 200 °C, and 600 °C temperature at fire is significantly high from the RC beams exposed to the processed temperature having the same maximum temperature. As the exposure temperature increases to 800 °C, the performance of RC beams at all heating modes becomes approximately equal.Originality/valueIn this work, residual performance, and failure modes of RC beams exposed to elevated temperatures were achieved through two different heating modes are presented.

Story Stability of a Structure- A Literature Review

Column is a slender beam, which carries load. Failure pattern of a column varies with different parameters such as buckling, compression, shear and tension. The initial imperfections in a column increases deflection and reduction in load carrying capacity. To accomplish stability, the key engineering elements such as connection and rigidity governs the effective length and width of the members. The researchers, covering the key engineering elements with different loading patterns, established numerous comprehensive studies. Further, advancement in the research were carried out to determine lateral stiffness, inter-story displacement and deflected beam shape under various loading patterns. The present study focuses on various literatures on effective length and governing factors, which determine the stability of the structure.

Structural performance of laminated-bamboo lumber nailed connection

ABSTRACT The aim of this paper was to provide a better understanding of the mechanical behaviour of laminated-bamboo lumber nailed connection loaded monotonically. The specimens varied in nail diameter, edge distance of nail and loading angle to the grain. For edge distance less than six times the nail diameter (6d), the specimens failed prematurely at a lower load and exhibited moderate ductility behaviour. Two plastic hinges formed inside the side and core members, with crushing of the laminated bamboo lumber fibres, if the minimum construction requirements of nail edge distance were satisfied. It is found that the load increases significantly with the increase of nail diameter. Reductions in load-carrying capacity are witnessed with the increase in loading angle to grain, but the influence is small. The experimental results, such as stiffness and yield load, are compared against those predictions obtained from the existing design standards. A two-parameter theoretical model, related to the initial stiffness and yield load, is suggested to characterise the load-slip relationship of LBL nailed connections loaded monotonically, with the aim of deriving a mathematical relationship to represent this behaviour. There is a good agreement between the curves predicted by the theoretical model and the experimental results.

The Effects of Steel Core Imperfection, Gap Size and Friction Coefficient on the Behavior of All-Steel Buckling Restrained Braces

Buckling restrained braces (BRBs) which are generally composed of a steel core and a encasing(buckling restrainers) are utilized to resist lateral forces in high seismic regions since BRBs exhibit high energy dissipation capacity, ductility and stiffness. The steel core carries both compressive and tensile forces. During the compression, the core starts buckling and the encasing tries to prevent this buckling. However, due to the unbonding layer/gap between the encasing and steel core, the steel core eventually buckles and contacts with the encasing. Buckling phenomenon is also associated with the initial imperfection and gap size. In this study, the effects of the initial imperfectionof steel core, gap size (1-5 mm)and friction coefficient (0.01-0.5)between the encasing and steel core on the behavior of BRBs are investigated. Pursuant to this goal, numerical analyses using a finite element tool ABAQUS were conducted. A total of 19 numerical models were developed and monotonically loaded. Initial imperfection was implemented to the models using buckling mode shapes.The results revealed that increasing gap size leads to a reduction in load-carrying capacity. It is recommended to keep gap sizes between 1 and 2 mm. On the other hand, initial imperfection does not significantly affect load-carrying capacity and global behavior. However, it was also observed that the fluctuations in load increase as the amplitude of the mode shape and gap size increase. Moreover, the friction coefficient should be kept between 0.01 and 0.05; otherwise, undesired behaviors can be observed.