Ultimate Load Capacity Research Articles

Compressive load capacity of CHS X-joints: The Efficacy of doubler plates

This study explores the effects of doubler plates and alterations in joint configuration, on the static characteristics of X-joints made from circular hollow sections (CHS) with slender walls, concentrating on how they withstand compressive forces applied to the braces. A detailed finite element analysis (FEA) was launched. Its accuracy verified through experimental tests carried out by the research team and by comparing it with existing studies. The investigation included an extensive parametric analysis (by generating 204 models) to evaluate changes in initial stiffness, load capacity, and modes of failure, with a focus on the importance of interactions between the chord and plates and the impact of geometric and material nonlinearities. Findings revealed that the doubler plates significantly improve the maximum load bearing capacity and failure modes under various joint geometrical scenarios. While the benefits of doubler plates in enhancing the durability of X-joints are clear, their effectiveness under axial load was not studied. Based on these insights, the research introduces a new theoretical design equation, based on yield volume theory and nonlinear regression, to accurately forecast the ultimate load capacity of the joints.

Experimental study and theoretical prediction of axial compression behavior in PMC-reinforced CFST columns with void defects

Polymer-modified concrete (PMC) is a promising seismic reinforcement material to improve the ultimate load carrying capacity and ductility of structures. This study investigates the reinforcing effects of PMC on voided concrete-filled steel tube (CFST) columns through axial compression tests on 21 specimens. A meticulous analysis, incorporating void arch height, steel tube thickness, and PMC reinforcement, elucidates failure modes, load-deformation behavior, and strain characteristics. The experimental results demonstrate that PMC reinforcements significantly enhance the structural behavior and load-bearing capacity, improve ductility, and prevent material detachment from excellent bonding and collaborative working properties. A novel calculation model for ultimate load capacity and lateral pressure coefficient of voided CFST columns is developed and validated. Results reveal a distinct improvement in specimen performance post PMC reinforcement, with load-displacement curves resembling intact specimens, mitigating the impact of void defects. Furthermore, PMC-reinforced specimens exhibit effective recovery of load-bearing capacity and ductility, offering a cost-effective alternative to steel tube thickening. Changes in strain and Poisson's ratio curves underscore PMC's ability to restore biaxial compression stress, enhancing stability. Prediction models, rooted in the Double Shear Unified Strength Theory, accurately anticipate ultimate bearing capacity and lateral pressure coefficient, bolstering practical engineering design and repair endeavors. In summation, this study provides comprehensive insights into PMC-reinforced voided CFST columns, facilitating informed structural enhancements and repairs.

Experimental study on bond performance of staggered lap rebars in ultra-high performance concrete (UHPC)

Ultra-high performance concrete (UHPC) has received extensive attention worldwide due to its ultra-high mechanical properties and durability. The bond performance between steel bars and UHPC is crucial for the design of Reinforced-UHPC structures. To study the bond performance of overlapping steel bars in UHPC, a total of 13 groups of 39 pull-out tests were conducted with overlapping lengths, cover thickness, steel bar diameter, and clear spacing of steel bars as influencing variables in this study. According to the results, when the lap length increased from 4 times the bar diameter (4db) to 5db and 6db, the maximum bond strength decreased by 10% and 20%, respectively. Moreover, with an increase in the cover thickness from 25 mm to 35 mm and 45 mm, the maximum bond strength increased by 6% and 14%, while the residual bond strength increased by 15% and 48%, respectively. When the diameter of the reinforcing bars increased from 16 mm to 20 mm and 25 mm, the ultimate load capacity increased by 50% and 70%, respectively, while the bond stress decreased by 16% and 27%. Additionally, the bond strength showed less sensitivity to the clear spacing of steel bars, with a decrease of 3% and 10% in bond strength when the clear spacing increased from 1.5db to 2db and 3db, respectively. The ductility of the specimen decreases when the bar diameter or the clear distance between bars is too large. A theoretical calculation formula for splitting bond strength was established, which yielded accurate results. Furthermore, a bond-slip model was fitted based on the test results, providing reference for finite element analysis of steel bar-UHPC structures.

Behavior of concrete voussoir flexible arch bridges reinforced with FRP composites

Flexible arch bridges, which can be pre-fabricated, transported and assembled on-site, have become increasing popular. This study presents an experimental investigation into the behavior of concrete voussoir flexible arch bridges reinforced with fiber-reinforced polymer (FRP) sheets by loading four arch specimens to failure at their left third-spans. The variables included the concrete voussoir strengths, bond quality between FRP and concrete voussoirs, and the FRP reinforcement locations. The results showed that two specimens with good bonding between FRP sheets and concrete voussoirs failed from sudden FRP rupture, while the other two specimens experienced FRP debonding and ultimately exhibited a four-hinge collapse mechanism. For the specimens with good FRP bonding, the typical load-deflection curve obtained at the loading point was an approximately monotonic increasing line, while load reductions and recoveries, as well as slope deteriorations were noted for the specimens experienced FRP debonding. It is also compared that bond quality could be more important than concrete voussoir strength, as the specimens with good bonding had higher ultimate load capacities. Applying one additional FRP sheet at intrados of arch could significantly enhance the initial ascending slope by 100%, but it cannot enhance the peak load as the FRP sheet at extrados of arch was more efficiently utilized in preventing more hinge formations at extrados joints.

Strengthening of reinforced concrete columns incorporating different configurations of stainless-steel plates

Reinforced concrete columns may need to be strengthened to support additional load arising from structural upgrades of existing structures or for retrofitting purposes. There is an increasing demand for sustainable and durable construction materials and techniques for strengthening and retrofitting purposes. Existing studies proposed additional jacketing using steel tubes or fiber-reinforced polymer (FRP). However, steel tubes can corrode when exposed to harsh environments whereas jacketing using FRP is very expensive. This study proposes innovative strengthening techniques using exterior bonding of stainless-steel plates (SSP) strips. SSP offers higher strength and corrosion resistance compared to steel and FRP materials. This paper presents an experimental and numerical study on strengthening reinforced concrete columns by innovative exterior bonding of SSP strips. A total of nine reinforced concrete column specimens are experimentally tested under axial compression loading to failure. The columns are strengthened using two different innovative techniques namely bonding stainless-steel plates to the exterior of the columns in flat as well as spirally wrapped around the columns. The cracking load, ultimate load and energy absorption capacity of the strengthened columns are found to be increased within a range of 45%− 162%, 26%− 112% and 34%− 190%, respectively when compared to the unstrengthened control column. The spacing of the SSP significantly effects the performance of strengthened columns. The ultimate load of the columns with reduced spacing increased as high as 44.9%. Additionally, employing a continuous full-height stainless steel spiral sheet yielded the most significant ultimate strength gains, calculated as high as 112% compared to the unstrengthened column although this led to an increase in the cost of the columns. A nonlinear finite element model (FEM) is also performed of the tested columns and validated the numerical prediction against the test results. The FEM is found to accurately predict the performance of such a column experimentally observed. This study provides crucial knowledge to understand the behavior of such a column and provides numerical tools for design engineers.

Secondary flexural behaviour of reinforced concrete beams strengthened with special-shaped rivet bonded steel plates and prestressed CFRP bars

Special-shaped rivet and glued steel plate reinforcement is an innovative structural reinforcement technology. A riveted glued steel plate primarily relies on the rivet to transfer shear. Prestressed carbon fibre-reinforced polymer (CFRP) reinforcement is a new technique for strengthening concrete structures. These studies focus on the ‘primary load’, overestimate the ultimate flexural load of the components by neglecting the ‘secondary load’ of the components in real engineering. In this study, the flexural properties of concrete beams strengthened using special-shaped rivet steel plates and CFRP prestressed bars were studied theoretically and experimentally. The cracking load, ultimate load capacity, and strain of the steel plate, steel bar and CFRP bars were recorded during the tests. In addition, the failure mode of the beams was observed, and the effect of secondary stress on the flexural capacity of the beams was analysed. The failure load of the beams strengthened by CFRP prestressed tendons increased by 67.8% and 46.1% for beams with primary and active secondary loads, respectively. The failure load of the special-shaped rivet and glued steel plate strengthened beam increased by 115.7% and 160.5%, for beams with primary and active secondary loads, respectively. Both methods have a strong guiding significance for engineering practice.

Mechanical properties of geopolymer concrete specimens exposed to fire retrofitted with glass and basalt fiber reinforced polymer laminates

AbstractExposure of concrete to elevated temperature affects its mechanical and physical properties. One of the important reasons for the use of fiber‐reinforced polymer (FRP) composite materials is because of its superior mechanical properties. These mechanical properties include impact resistance, strength, stiffness, flexibility, and also it is enhanced ability to carry loads. The high strength–weight ratio, and corrosion resistance of FRPs made them suitable for repair. For strengthening and retrofitting of concrete structures confinement with FRP has received considerable attention in recent years. Geopolymer concrete (GPC) can be expressed as “concrete without cement.” GPC is environmentally friendly and an inventive way to replace the conservative concrete which contributes 7%–8% of total CO2 production in the world. “The concrete which entails of the source materials and the alkaline solution.” The composite material made of fiber‐reinforced polymer (FRP) has recently gained attention as a potential repair method for concrete structures that have been damaged. This study investigates the performance of glass and basalt fiber‐reinforced polymer (GFRP and BFRP) laminates as a retrofit solution for fire‐damaged GPC specimens. The specimens were subjected to temperatures of 200°C, 400°C, 600°C, and 800°C for a period of 1, 2, and 3 h, followed by retrofitting with FRP laminates. The results indicated an increase in the ultimate load‐carrying capacity of GPC specimens when subjected to 200°C for 1 h, beyond which it decreased. However, a fall in ultimate load capacity was observed for higher ranges of temperature and duration of the fire. In this project, geopolymer specimens that had been damaged by fire are wrapped with GFRP and BFRP laminates to study the effect of confinement on the strength of GPC specimens. The fiber laminate used was bi‐directional glass and bi‐directional basalt. Based on the analysis of test data, there was the conclusion that the fire‐damaged GPC was strengthened when retrofitted with GFRP and BFRP laminates was attainable.

Behavior of Reinforced Lightweight Concrete Slab with Initial Cracks

The flexural behavior of lightweight concrete two-way slabs repaired or strengthened with externally bonded carbon fiber-reinforced polymer (CFRP) sheets is the subject of this study. The experiment included five reinforced lightweight concrete slab specimens with dimensions of 1000 mm in length, 1000 mm in width, and 120 mm in thickness. Tested one specimen without any strengthening and reinforced another specimen with a single layer of CFRP. The other specimens were repaired with a single layer of CFRP, applying damage ratios of 50%, 60%, or 70% of the ultimate load. Intentionally designed each slab to collapse under bending forces and maintained comparable dimensions. According to the experiment results, changing the degree of damage from 70% to 50% increases the ultimate load capacity by about 17.7%, and the ultimate deflection decreases by about 31.4%. CFRPs have the potential to fix structural damage under static stress testing conditions. However, it is essential to make sure that they stick well to surfaces that do not have suitable geometric properties or have been deformed. CFRP sheets effectively repaired the specimens, increasing the failure stress of the reinforced concrete slabs and preventing the spread of cracks.

Study on ultimate capacity and design method of cold-formed steel equal lipped angle components under axial compression

This study focuses on evaluating the load-bearing capacity of cold-formed steel (CFS) equal lipped angle components. It delves into the structural behavior and design methods, taking into account various edge conditions and buckling modes. By considering the key parameters, which are component length, component thickness, total lip length, and lip bending angle, a total of 555 numerical models are developed for a systematic analysis on the components with two types of cross-sectional shapes. Since the coefficients within the direct strength method (DSM) inadequately capture the ultimate load-bearing capacity of lipped angle components, we introduce a design methodology rooted in the DSM framework to address global and global-local coupling buckling modes while imposing constraints to prevent local-distortion coupling buckling modes. The machine learning models (XGBoost, BPNN, and 1D-CNN) are adopted to predict the structural behavior of the two types of lipped angle components. These models can integrate the analysis of the components with two types of cross-section shapes in predictions of ultimate load capacity, axial deformation, and buckling modes. Meanwhile, the prediction accuracy of the machine learning models surpasses that of the analytical design methodology, offering more accurate prediction for ultimate load capacity, axial deformation and buckling modes.

Study on Bonding Behavior between High Toughness Resin Concrete with Steel Wire Mesh and Concrete

This paper investigates the interfacial bonding behavior between high toughness resin concrete with steel wire mesh (HTRCS) and concrete. A total of five sets of fifteen double shear specimens were tested for parameters including concrete strength and material properties of HTRCS composites. The test results showed that the failure mode of DS1 specimens was partial debonding and fracture, and the rest of the specimens were the fracture of HTRCS. The concrete strength and reinforcement ratios of HTRCS composites were positively correlated with interfacial adhesion properties. When the concrete strength was increased from C30 to C40 and C50, the ultimate load increased by 43.4% and 43.2%, respectively. The ultimate load capacity increased by 32.1%, with the reinforcement ratio of HTRCS composites increasing from 1.05% to 1.83%. Moreover, the bonding slip model and the bearing capacity formula for the interface between HTRCS composites and concrete were proposed, and the calculation values were in good agreement with the test values, with an average value of 0.978.

BEHAVIOR OF HYBRID REINFORCED CONCRETE BEAMS ON FLEXURAL STRENGTH

The objective of this research is to experimentally study the flexural behavior of hybrid reinforced concrete beams. Three test beams, each with dimensions of (2200 X 150 X 240) mm, were fabricated for this purpose. The first beam was constructed using ordinary concrete, while the second beam consisted of two layers of high-strength concrete in the compression zone and normal concrete in the tension zone. The third beam was entirely cast using high-strength concrete. In terms of reinforcement, all beams were equipped with 2φ12 steel bars in the tension zone and 2φ12 steel bars in the compression zone. Additionally, φ12 steel bars were employed to resist shear forces, distributed along the length of the beams with a spacing of 125 mm c/c. Two-point loading was applied to all beams until failure occurred. The results obtained from the experimental tests reveal that the use of hybrid concrete beams enhances the ultimate load capacity by approximately 20.93%. On the other hand, beams constructed entirely from high-strength concrete exhibited an increase in failure load capacity by approximately 28.68%.

Numerical Simulation Analysis of the Bending Performance of T-Beams Strengthened with Ultra-High-Performance Concrete Based on the CDP Model

Numerical Simulation Analysis of the Bending Performance of T-Beams Strengthened with Ultra-High-Performance Concrete Based on the CDP Model

Mechanical Characterization of Pultruded GFRP Round Tube under Axial Loading

Abstract: Pultruded Fibre‐Reinforced Polymer profiles are widely used as structural elements in many civil infrastructure applications. However, the anisotropic elasticity and the application‐driven slenderness make these profiles prone to local buckling failure, well below their ultimate load capacity. In this paper, an experimental study was undertaken to characterise the tensile and compressive failure of GFRP round tube under axial loading. Based on the research focus of GFRP structures, this work will present a comprehensive study of the mechanical properties of GFRP tubes in terms of both tensile and compressive loads and investigate the mechanical parameters. This paper presents an investigation on the mechanical properties of pultruded Glass fiber reinforced polymer (GFRP) round tubes for structures subjected to tensile and compressive axial loading. The tensile and compressive strength of GFRP round tubes were first tested. For the stability under compression, the slenderness ratio 6 is adopted. The results show that the tensile strength of GFRP tube could reach 580 MPa, while the compressive strength has been around 72% of tensile strength. Also Experimental results showed that specimens exhibited linearly elastic up to failure. Compared with the single tensile failure mode of GFRP tubes, two types of compressive failure modes, including micro-buckling and local buckling were observed. Moreover, a finite element (FE) analysis was carried to simulate the tensile and compressive behaviours of round tube specimen. The comparison between the tensile and compressive peak load values obtained experiment and FE methods revealed that their difference is less than 5%. These indicated that FE analysis predicted reasonably the actual tensile and compressive behaviours of the pultruded GFRP round tube.

Structural Performance of Reinforced Concrete Slab with Sugarcane Bagasse Ash and Plastic Flakes as Partial Replacement

This research aims to reduce the weight of concrete structural members and promote the use of eco-friendly concrete. To achieve this, plastic flakes and sugarcane bagasse are used as additional materials in concrete production, which can partially replace fine aggregates and cement respectively. This makes structural members lighter, reducing the overall load transmitted to the foundation and the construction cost. The study investigates the effect of plastic flakes and sugarcane bagasse ash on the performance of a reinforced concrete slab. It includes workability, compressive, flexural, tensile strengths, and water absorption of different mix proportions in the fresh state. Various sugarcane and plastic flake percentage replacements of cement and fine aggregates are also investigated. The results show that the 5% SCBA and 5% plastic flake replacement ratio has better mechanical properties compared to the control concrete and other mix ratios. This ratio is used in casting the reinforced concrete slab, whose structural behavior is then investigated in terms of ultimate load, ultimate deflection, load-deflection relationship, and crack patterns. The study shows that the incorporation of sugarcane bagasse ash and plastic flakes as partial replacements improves the bearing of ultimate load capacity. Still, the slab portrays higher deflection than the control slab. The crack patterns appear in the tension zone of the slab, and the slab fails in flexion.

Effect of different anchorage schemes on the flexural behavior of RC slabs strengthened with CFRP sheets

This research investigated the behavior of RC slabs subjected to four points loading with five different CFRP sheet numbers (1, 2, 3, 4, 5) and three different anchorage systems (Type 1 used CFRP strips in the transverse direction, Type 2 used galvanized steel end plates without grooving, Type 3 used galvanized steel end plates with grooving). A total of twenty reinforced concrete (RC) solid slabs were cast to fulfill the study objectives. Results showed that the presence of CFRP strips enhanced the slab's ultimate load capacity by 102 %, reduced mid-span deflection by 12 %, also improved energy absorption capacity and stiffness by 36 % and 32 %, respectively. Type 2 anchorage system without grooves and type 3 anchorage system with grooves both used galvanized steel end plates and enhanced the flexural capacity of the slabs by 119 % and 125 %, respectively, also improved the RC slab properties and shifted the failure mode from delamination to a CFRP strips rupture. The introduced anchorage system without grooving was found to be an efficient and easily applied technique with high efficiency in terms of capacity and serviceability.

Experimental investigation and evaluation of shear performance of hollow slab beams strengthened by cavity grouting method

After 20 years of service, multiple web shear cracks were observed in 20 m-span prestressed concrete hollow slab beams. Shear enhancement is required to improve structural safety. To evaluate the strengthening effect of the new material on the hollow slab beam structure, fiber-reinforced cementitious composites (FRCC) were used to fill the cavities at the beam ends, and a comprehensive field load test was carried out on the shear-resistant performance of the actual bridge. The web principal stresses changed before and after strengthening under various working conditions, which were analyzed and compared with the performance of the traditional channel steel technique. The findings show that the web principal stresses are significantly reduced by more than 50 % after filling with FRCC, notably superior to the channel steel technique. In addition, both methods can reduce mid-span deflections by 10–20 %. The channel steel technique specifically enhances transverse connection capabilities. Furthermore, strain responses in the beam end sections were reduced by about 30–45 %. Finally, finite element simulations of single beam strengthening were also conducted to complement the experimental analysis. The simulation results show that the shear span ratio (λ), FRCC length and strand prestress loss remarkably impact the strengthening effect. The ultimate load capacity of the strengthened specimens decreases with the increase of λ and prestress loss and increases with the increase of FRCC length. In conclusion, the utilization of FRCC presents a superior alternative for shear enhancement in prestressed concrete hollow slab beams, offering substantial reductions in web principal stresses and enhanced structural performance compared to the traditional strengthening method.

Evaluation of Design Parameters (α and β) for Analysis and Design of Piles on Soft Clays

This paper presents the analyses of 12 prestressed concrete instrumented test piles (TPs) that were driven in different bridge construction projects of Louisiana as part of a load testing program. The 12 TPs were driven mainly in cohesive soils. Detailed soil characterizations including both laboratory and in situ tests were conducted to determine the different soil properties. The TPs were instrumented with vibrating wire strain gauges to be able to calculate the distribution of skin friction and end-bearing capacities separately. Static load tests and dynamic load tests were conducted on each TP after end of driving to calculate the ultimate load capacity. Fifty six soil layers exhibiting clayey soil behavior and sandy soil behavior dominated the remaining 15 soil layers. The total stress parameter (α) and the effective stress parameter (β) were back-calculated for each soil layer. The α values ranged from 0.22 to 1.80, and the β values ranged from 0.11 to 0.83. Regression analyses were performed on 42 soil layers (75% data) to develop an empirical model to predict α as a function of undrained shear strength. The remaining 25% of the data were used to verify the developed model, and good agreement was observed between the measured and predicted values.

Numerical Investigation on Strengthening of Steel Beams for Corrosion Damage or Web Openings Using Carbon Fiber Reinforced Polymer Sheets

Fiber-reinforced polymers (FRPs) have been widely used to strengthen steel structures, which could suffer from corrosion or the introduction of web openings, for utilities such as ductwork, plumbing, electrical conduits, and HVAC systems. The present numerical study involves the application of unidirectional carbon FRP (CFRP) sheets to steel I-beams, damaged due to corrosion or web openings, to regain their lost load-carrying capacity. Finite element analysis (FEA) was utilized to develop and validate three beam models against existing experimentally tested specimens. Subsequently, a parametric study was conducted investigating the effect of various corrosion levels and the number of circular web openings on the yield and ultimate load capacities of the beams. The optimum number of CFRP layers needed to strengthen corroded beams was determined and six CFRP strengthening scenarios were adopted to determine the best configurations to retrofit steel beams with openings (SBWOs). The results revealed that corrosion, introduced by thinning the bottom flange, reduced both yield and ultimate load capacities, with a nearly perfect linear reduction in ultimate load for each 2.5% thickness loss. The optimum number of CFRP layers depended on the level of corrosion damage. Furthermore, while maintaining a constant total opening area, beams with a greater number of smaller circular web openings demonstrated higher yield and ultimate load capacities than those with fewer larger openings. Out of the six adopted CFRP strengthening scenarios, three configurations that involved applying CFRP sheets to both flanges and the web effectively restored the strength of SBWOs, when adequate CFRP layers were used.

Predicting the Ultimate Load Capacity of Extradosed Cable-Stayed Bridges: A Novel Method

Predicting the Ultimate Load Capacity of Extradosed Cable-Stayed Bridges: A Novel Method

The effects of pre-loading on structural behavior of reinforced concrete beams under fire condition: a review

PurposeThis review paper seeks to enhance knowledge of how pre-loading affects reinforced concrete (RC) beams under fire. It investigates key factors like deflection and load capacity to understand pre-loading's role in replicating RC beams' actual responses to fire, aiming to improve fire testing protocols and structural fire engineering design.Design/methodology/approachThis review systematically aggregates data from existing literature on the fire response of RC beams, comparing scenarios with (WP) and without pre-loading (WOP). Through statistical tools like the two-tailed t-test and Mann–Whitney U-test, it assesses deflection extremes. The study further examines structural responses, including flexural and shear behavior, ultimate load capacity, post-yield behavior, stiffness degradation and failure modes. The approach concludes with a statistical forecast of ideal pre-load levels to elevate experimental precision and enhance fire safety standards.FindingsThe review concludes that pre-loading profoundly affects the fire response of RC beams, suggesting a 35%–65% structural capacity range for realistic simulations. The review also recommended the initial crack load as an alternative metric for determining the pre-loading impact. Crucially, it highlights that pre-loading not only influences the fire response but also significantly alters the overall structural behavior of the RC beams.Originality/valueThe review advances structural fire engineering with an in-depth analysis of pre-loading's impact on RC beams during fire exposure, establishing a validated pre-load range through thorough statistical analysis and examination of previous research. It refines experimental methodologies and structural design accuracy, ultimately bolstering fire safety protocols.