Concrete Cross-section Research Articles

Analytical model for RC coupling beam considering axial restraint

A novel three-dimensional distributed plasticity model element is formulated and implemented into an open-source computational platform (OpenSees) to enhance nonlinear modeling approaches for lateral force resisting systems utilizing diagonally reinforced concrete coupling beams. The model incorporates a fiber-based concrete cross-section along with truss elements to represent the diagonal reinforcement and contact elements to model reinforcing bar slip at the beam-wall interface. The model is validated using test results from five different experiments that include variations in cross-section geometries, reinforcement configurations, and boundary conditions. Notably, two test specimens shared identical attributes except for their cross-sectional shapes (with and without a slab), whereas another pair were identical except for the degree of axial restraint provided. The final specimen utilized both longitudinal and diagonal reinforcement along the length of the beam. The model accurately predicted overall shear versus chord rotation responses with errors < 5 % and axial growth responses with errors < 30 %. The proposed model provides enhanced modeling options for nonlinear analysis by enabling sensitivity studies to address the potential impacts of coupling beam axial restraint on coupling beam and coupled wall behavior.

EVALUATING THE STRUCTURAL EFFICACY OF ANGLE AND CHANNEL SHEAR CONNECTORS IN BRICK AGGREGATE CONCRETE AND STONE AGGREGATE CONCRETE AND COMPARISON

Composite structure is becoming prominent for its economy, less time consumption, and higher stiffness-mass ratio. Composite action of the steel-concrete composite structure mainly depends on the connector's geometry and materials. Proper choice of shear connector could make steel beam and concrete slab cross-section minimal. This study carries out push-out tests to evaluate the structural efficiency of channel and angle shear connectors in brick aggregate concrete and stone aggregate concrete. It specifically looks at the failure mode, ductility, load-slip behavior, and energy absorption capacity. In brick aggregate concrete, results show that under monotonic loading, channel connectors have been found to have 15.27% more shear capacity &amp; 28.38% more slip than angle connectors. Similarly, in stone aggregate concrete, channel connectors have been found to have 14% more shear capacity &amp; 12.97% higher slip than angle connectors. On average, stone aggregate concrete has been found to have 34.84% higher shear capacity and 6.7% greater slip than brick aggregate concrete. Strain energy and plastic energy were found 78% and 17.6% less in brick aggregate specimens than those in stone aggregate specimens, respectively. Experimental results were slightly lower for both shear connectors than the empirical values.

Research regarding the influence of size on the compressive strength of spontaneous combustion coal gangue concrete utilizing the diffusion model

This passage employs the U2-Net model to segment images of spontaneous combustion gangue coarse aggregate (SCGCA) concrete cross-section and randomly placed aggregate library. These methods are used to construct the dataset and subsequently establish and train the diffusion model. Based on this model, a two-dimensional micro-mechanical model of SCGCA concrete was constructed, accurately reproducing the distribution, grading, and shape of the aggregate in the concrete. The size effect of SCGCA concrete is analyzed through experimentation and numerical simulation of two-dimensional micro-models. The findings of the study reveal that the dimension conversion factors for the 100 mm and 200 mm cubic specimens are 0.92 and 1.12 respectively, which demonstrates the evident size effect of SCGCA concrete. The remarkable coherence between the empirical results and the computational simulation results serves as a powerful validation of the durability and efficacy of the model delineated in this paper. In accordance with the theory of Bažant's size effect, this paper elucidates the size effect law of uniaxial compressive strength in SCGCA concrete models ignited spontaneously at different dimensions.

Bond Shear Tests to Evaluate Different CFRP Shear Strengthening Strategies for I-Shaped Concrete Cross-Sections.

I-shaped concrete girders are widely used in precast bridge and roof construction, making them a common structural component in existing infrastructure. Despite well-established strengthening techniques using various innovative materials, such as externally bonded carbon fibre reinforced polymer (CFRP) reinforcement, the shear strengthening of an I-shaped concrete girder is not straightforward. Several research studies have shown that externally bonded CFRP reinforcement might exhibit early debonding at the concave corners of the I-shape, resulting in a marginal increase in shear capacity. This research study aims to assess the performance of two different CFRP shear strengthening strategies for I-shaped concrete cross-sections. In the first strategy, CFRP was bonded along the I-shape of the cross-section with the provision of additional anchorage. In the second strategy, the I-shape was transformed into a rectangular shape by using in-fill blocks over which the CFRP was bonded in a U-configuration. In addition to the strengthening strategies, the investigated parameters included two different materials for the in-fill blocks (conventional and aerated concrete) and two different anchoring schemes (bolted steel plate anchor and CFRP spike anchor). To avoid testing on large-scale girders, a new test methodology has been implemented on concrete I-sections. The test results demonstrate the feasibility of comparing different shear strengthening configurations dedicated to I-sections. Among other findings, the results showed that the local transformation of the I-shape to an equivalent rectangular shape could be a viable solution, resulting in shear strength enhancement of 12% to 53% without and with the anchorages, respectively.

Redundancy and reliability levels of post-tensioned and grouted concrete cross-section in case of tendon failure

Since the 1960 s and 1970 s, the prestressing steel used on post-tensioned concrete (PTC) bridges has been known to be susceptible to stress corrosion cracking (SCC). This can result in brittle rupture of the prestressing steel. Objective of this study is to evaluate the reliability levels achieved with assessment method developed for verifying crack behaviour before failure in cross-section of PTC bridges with cross-section loss of prestressing steel. Additionally, the study aims to investigate of tendon loss on crack before failure behaviour. This paper applies a reliability analysis for methodology based on robustness analysis on crack before failure behaviour in PTC with deteriorating prestressing steel. The analysis involves examining cross-sections with various design criteria. The effects of choices made in designing the PTC structure are analysed and noted to have a significant impact on the safety margin of the structure, while the deterioration of prestressing steel does not significantly decrease the ductility of the cross-section if certain conditions are met. The use of stricter serviceability limit-state (SLS) criteria used in past design results the greater safety margin for the structure in the event of tendon loss, which therefore makes it beneficial for structural redundancy in the ultimate limit state (ULS).

Evaluation of moment-curvature response and curvature ductility of reinforced UHPC cross-sections

This study deals with the evaluation of moment-curvature response and curvature ductility of reinforced ultra high performance concrete (R-UHPC) cross-sections. Curvature ductility is calculated based on six definitions. The impact of these definitions is demonstrated through the calculation of strength reduction factors and comparisons of factored flexural strength of R-UHPC and reinforced normal strength concrete (R-NSC) cross-sections. Strategies for improving the curvature ductility of R-UHPC cross-sections are presented. A versatile framework to predict the complete moment curvature response of R-UHPC cross-sections is proposed. The proposed procedure is used to study the effect of tension reinforcement ratio, UHPC strain at crack localization, UHPC tension model, UHPC ultimate tensile strain, and compression reinforcement ratio on curvature ductility and complete moment curvature response. It is determined that for a given cross-section, changing the material from NSC to UHPC causes notable reductions in curvature ductility. This reduction applies to: 1) tension and compression reinforcement ratios that range from 0.69–2.78 % and 0 – 1.37 %, respectively; 2) UHPC tension models that feature elasto-plastic and linear strain hardening responses with and without residual branches; and 3) UHPC ultimate tensile strains that range from 0.005–0.015. Such reductions in curvature ductility render the considered R-UHPC cross-sections as members in the transition zone – a classification currently prohibited for R-NSC sections according to ACI 318–19 (22) - while their R-NSC counterparts qualify as tension-controlled. This results in lower strength reduction factors for R-UHPC cross-sections and limits the benefits of UHPC when flexural strength controls design. It is concluded that R-UHPC cross-sections that feature either the highest or the lowest reinforcement ratios provide the highest added benefit from the point of view of enhancing factored flexural strength compared to R-NSC sections. The most effective method to elevate curvature ductility is an increase in the UHPC strain at crack localization. A minimum UHPC strain at crack localization of 0.006 is required to change the classification of cross-sections from the transition zone to tension-controlled. The use of compression reinforcement - an established technique for R-NSC members to induce a change in the flexural failure mode by elevating curvature ductility - was determined to have almost no influence on the curvature ductility of R-UHPC cross-sections.

Diagnostics of premature damage to surface-hardened industrial concrete floors

The article presents the diagnostic results on surface-hardened industrial concrete floors. Selected examples of floors showcased premature damage to surface layers, characterized by intense dusting, delamination, and local spalling, while the structural system remained unaffected. Quantitative petrographic analysis of concrete was applied to core specimens from the floors, involving the examination of digital images from a polarizing optical microscope and a scanning electron microscope. The hardening compound and powdered specimens of the cement matrix were characterized using differential thermal analysis and X-ray diffraction. A multiple microindentation method was employed to assess local variations in mechanical properties. Concrete cross-section analysis revealed areas with a non-uniform distribution of air voids, identified regions exhibiting increased porosity, highlighted areas of cracking in the concrete, indicated local variability in the phase composition of cement hydration products, and pointed out the presence of carbonated areas. The causes of the damage were discussed based on these findings,. The crucial role of quantitative petrographic analysis in diagnosing premature surface damage to industrial floors was demonstrated.

The Influence of e-glass epoxy composite laminate material application on the crack pattern of cylinder concrete column cross-section

In order to better understand the phenomenon of applying GEC reinforcement to RCC based on the percentage of surface crack pattern (PCP), this research will use e-glass epoxy composite laminate (GEC) to obtain the damage pattern of reinforced concrete column specimens (RCC) utilizing GEC. Additionally, it will compare the splitting tensile strength (STS) and SCP. In accordance with ASTM C496 guidelines, the RCC specimens used in this investigation had a cylindrical shape and measured 150 mm in length and 50 mm in diameter. GEC material, consisting of 0–4 layers of woven e-glass fiber sheets, was applied as an extra layer on top of the RCC. In compliance with ASTM C496 guidelines, a Universal Testing Machine (UTM) was used to perform the split tensile test. With the aid of Adobe Photoshop software, the Histogram approach was used to calculate the crack pattern's proportion. The study's findings demonstrated that the specimens reinforced with four layers of GEC exhibited the highest damage pattern. This suggests that the reinforced specimens must be subjected to a sizable load in order to be damaged. Hence, the damage that occurs in the specimens can be lessened by applying GEC layers on RCC. Further information about the performance of RCC reinforced with GEC is also provided by a comparison of the splitting tensile strength and the percentage of fracture pattern

Systematic Calculation of Yield and Failure Curvatures of Reinforced Concrete Cross-Sections

This paper examines and provides a robust solution to the problem of yield and failure curvatures of reinforced concrete (RC) cross-sections, taking into account cracking. At the same time, it calculates the corresponding necessary reinforcement or the moment of resistance in both yield and failure limit states. Computationally, the problem of determining the actual curvatures is reduced to the bending design problem of the cross-section in the yield and failure limit states. This study shows the researcher and the designer how to systematically calculate the strains for different concrete and steel grades and for standard or random cross-sections. This complex process is quite necessary to determine the respective curvatures. The main concept is presented with an emphasis on the “solution regions” as well as the critical cases of the “asymptotic regions”, both in yield and failure limit states. Our wide-ranging research on RC element design under biaxial bending with axial force for both yield and failure limit states has been completed and validated via sophisticated algorithms and is available for publication.

Tensile Load-Bearing Behaviour of Concrete Components Reinforced with Flax Fibre Textiles.

In recent years, the use of natural flax fibres as a reinforcement in composite building structures has witnessed a growing interest amongst research communities due to their green, economical, and capable mechanical properties. Most of the previous investigations on the load-bearing behaviour of concrete components reinforced with natural flax fibres include inorganic impregnations (or even no impregnation) and exclude the use of textile fabrics. Also, the mechanical behaviour of textiles made of natural flax fibres produced as leno fabrics remains to be investigated. In this paper, the results of tensile tests on concrete components reinforced with bio-based impregnated leno fabrics are presented. For comparison, multilayer non-impregnated and impregnated textiles were considered. The results demonstrated that reinforced textiles yielded an increase in the failure loads compared to the concrete cross-sections without reinforcement. The stress-strain diagrams showed that the curves can be divided into three sections, which are typical for reinforced tensile test specimens. For the impregnated textiles, a narrowly distributed crack pattern was observed. The results showed that impregnated textiles tend to support higher failure stresses with less strains than non-impregnated textiles. Moreover, an increase in the reinforcement ratio alongside larger opening widths of the warp yarns enables higher failure loads.

PROBABILISTIC ANALYSIS OF FLEXURAL OVERSTRENGTH FACTOR FOR SEISMICALLY DESIGNED REINFORCED CONCRETE BEAMS AND COLUMNS

The study presented here aims to address some issues related to seismic design of structures, with special focus on the probabilistic modeling of reinforced concrete (RC) cross-sections capacity. It aims to validate the overstrength factors provided in Eurocode 8 for the design RC beams and columns. A statistical analysis is carried out to determine the uncertainty in the reinforcing steel properties. Uncertainties in concrete properties, geometry of cross-sections and mechanical model are also considered. Assessing the flexural overstrength of RC beams and columns designed according to Eurocode 8 involves ensuring that the structural members meet the capacity design specifications. This research studied 128 cross-sections of beams and columns with different geometry and reinforcement areas by performing Monte Carlo simulation. The code provisions are evaluated through a comparison with the simulation results. In particular, the analyses suggest using an overstrength factor of 1.5 for beams and columns with 95% probability of exceedance (or 1.3 with 50% probability of exceedance). Eurocode 8 provisions, adopting an overstrength factor of 1.3, does not seem conservative enough.

Dimenzioniranje armiranobetonskih pravokutnih presjeka prema drugoj generaciji Eurokoda

This paper describes the design procedure for reinforced concrete rectangular cross-sections according to the standard FprEN 1992-1-1 (second generation of Eurocode 2). Design was carried out in two ways: using design tables for reinforced concrete rectangular sections and using a direct analytical procedure. The stress-strain diagram in the form of a parabola-rectangle was used for concrete, while for the reinforcing steel a bilinear stress-strain diagram with a horizontal post-elastic branch without strain limit was applied. For this reason, when designing the reinforced concrete cross-section, it is necessary to limit the strain in the compression zone of the concrete. Tables for the design of reinforced concrete rectangular sections were obtained using a new procedure in which the mechanical reinforcement ratio is varied. A direct analytical procedure was used for comparison, which can be used for the design of reinforced concrete rectangular sections without the need to use tables. The limit values of the coefficient of the height of the compression zone for pure bending were calculated according to the standard FprEN 1992-1-1.

Behaviour of embedded H-profile balcony-to-slab connection

This paper investigates experimentally and numerically the behaviour of a balcony-to-slab connection made by an H-profile embedded in the concrete slab. A large-scale test was performed on a specimen of the connection system in order to determine the moment-bearing capacity, the deformation behaviour, the cracking patterns, the distribution of the bending moment along the axis of the embedded steel H-profile as well as the failure mode of the connection system. The test results showed that the failure mode was governed by the concrete shear of the slab. In addition, a 3D finite element model of the experimental test was also carried out and successfully validated against the experimental results. For a practical design of the connection system, a model based on Timoshenko beam on elastic foundation (BEF) was investigated and verified against the results obtained from the validated FE model. The Winkler modulus of the BEF model was determined by considering the local deformation of the concrete based on a strut-and-tie model. The results demonstrate that the BEF model with this value of the Winkler modulus provides a conservative estimation of the shear and bending forces applied to both the embedded H-profile and the concrete cross-sections. This method is a first tentative design basis using linear elastic theory for such a system.

Force Transfer Mechanism and Behavior Insights for a Large-Diameter CFST Column to Steel Beam Connection

Concrete-filled steel tube (CFST) columns with internal ring-plate-reinforced connections are increasingly used in high-rise buildings. However, the behavior and optimal design of such large-scale connections is not well established. This study presents a numerical investigation of the structural performance of a ring-plate-reinforced CFST column to steel beam connection. The paper begins by reviewing a previous experimental study. Subsequently, nonlinear finite element models were developed and validated using the test results. Parametric analyses were conducted to evaluate the effects of the ring plate dimensions, friction coefficient, and concrete defects on the load transfer mechanism. The results showed that the ring plate and friction force together effectively transferred the beam load to the concrete core. An optimal ring plate width of 75 mm was identified. Concrete defects significantly reduced the load carrying capacity of the ring plate. The stress distribution in the concrete cross section transitioned from nonuniform to uniform over a length approximately equal to the column diameter. The connection design was found adequate for the prototype structure analyzed. The study provides valuable guidance for improving ring-plate-reinforced connection design in future construction.

Influence of fiber dosage, fiber type, and level of prestressing on the shear behaviour of UHPFRC I-girders

Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) has excellent mechanical and durability properties compared to conventional concrete. It offers lightweight structures compared to reinforced concrete. In this study, the shear behaviour of post-tensioned UHPFRC girders is experimentally studied. The parameters considered in this study are (i) the level of prestressing, i.e., 0%, 35%, and 70% of ultimate tensile strength of strand (fpu), (ii) the volume fraction of fibers (Vf), i.e., 1.0%, and 2.0%, and (iii) different types of steel fibers; straight fibers, hybrid fibers (straight and hooked ended). The principal tension and compression strain of beams along and across the cracks were measured throughout the loading and compared with localization strains from the direct tension test. Due to increase in prestress from 0% to 70% of fpu, the ultimate load-carrying capacity increased from 18% to 39% in girders with a 1% fiber volume fraction. Similarly, it increased from 24% to 50% for 2% fiber reinforced girders. This is due to increased active stress transfer across the concrete cross-section, which reduces the crack angle from 44° to 34°. Similarly, the shear cracking load increased, and the post-cracking reserve capacity reduced with an increase in fiber dosage. Digital image correlation analysis reveals that strain distribution across the crack is uniformly distributed at all loading stages.

Nonlinear Deformation Model for Analysis of Temperature Effects on Reinforced Concrete Beam Elements

The results of the study are aimed at developing a nonlinear strain model for reinforced concrete beam elements in the general case of force actions and temperature effects for different durations. As a rule, temperature effects on structures involve temperature drops, causing heterogeneity of mechanical and rheological properties of concrete and reinforcement. The article has approximating expressions needed to take into account the effects of temperature and heating time on the values of temperature-induced strain and mechanical and rheological properties of heavy concretes with C30–C60 strength classes. The properties of concrete and rebars are heterogeneous from top to bottom and across the width of the cross section. A physically nonlinear problem is solved using the method of elastic solutions combined with the method of stepwise increases in temperature and force loading. The cooling of a heated reinforced concrete element to normal temperature is considered a short-term effect. Strength criteria of portions of a concrete cross section, crack closure conditions, and the ability of cracked sections to take loads in compression amid a change in the sign of stresses are determined. The stress–strain state (SSS) analysis of reinforced concrete beams, made according to the proposed method, is compared with the experimental studies using (i) values of thermal bending moments in statically indeterminate structures, (ii) cracking forces, and (iii) values of deformations (elongations and curvatures) of the elements in the longitudinal axis. Good agreement between the calculated and experimental values of controllable criteria confirms the reliability of physical relationships (i) developed for heterogeneous reinforced concrete beam elements and (ii) applied to the complex cases of temperature and force effects.

Cracking in Reinforced Concrete Cross-Sections Due to Non-Uniformly Distributed Corrosion.

Corrosion affecting reinforced concrete (RC) structures generates safety and economical problems. This paper is focused on the simulation of corrosion-induced fractures in concrete, whereby non-uniform corrosion growth is taken into account. In particular, the volumetric expansion of rust accumulated around reinforcement bars causes cracking of the surrounding concrete. This phenomenon is simulated using the finite element (FE) method. In the analyses, concrete is described as a fracturing material by using a damage-plasticity model, steel is assumed to be elastic-plastic and rust is modeled as an interface between concrete and steel. The behavior of corrosion products is simulated as interface opening. Two-dimensional FE models of RC cross-sections with 2, 4 or 6 reinforcing bars are considered. Crack formation and propagation is examined. Moreover, interactions between cracks and patterns of possible failure are predicted. The most developed and complex crack pattern occurs around the side reinforcing bar. Conclusions concerning the comparison of results for uniform and non-uniform corrosion distribution as well as the prediction of concrete spalling are formulated.

Pore structure profile of ambient temperature-cured geopolymer concrete and its effect on engineering properties

Ambient temperature-cured geopolymer concrete (GPC) with solid alkali activators are attracting attention as an eco-friendly alternative to OPC-based concrete (OPCC) for industrial applications. This research investigates the pore structure and microstructural characteristics of GPC via porosimetry and micrography and strives to connect the micro-scale characteristics to macro-scale engineering properties. The dominance of slag and low water content resulted in a denser and more homogenous microstructure in the binder with fewer microcracks and voids. Furthermore, a refined pore structure was observed when the fly ash/slag ratio was 60/40. The porosimetry analysis demonstrated that OPCC possessed a uniform pore structure with a similar porosity profile throughout the concrete cross-section. GPC showed a descending pore gradation profile from top to bottom. The difference in the pore structure profiles can explain the previously witnessed shrinkage behaviour of GPC and OPCC in restrained conditions.

Moment curvature response of composite UHPC filled hollow structural steel cross-sections

A mechanics based analytical method for obtaining the complete moment–curvature response of composite hollow structural steel (HSS) and ultra high performance concrete (UHPC) cross-sections is presented. Flexural response at the cross-sectional level is traced past the local buckling of the steel elements and up to the exhaustion of UHPC and steel material capacity. The proposed method is validated using experimental data from seven flexural tests on composite HSS-UHPC beams. Flexural failure mode is classified as either a UHPC compression-controlled failure, UHPC fiber tension-controlled failure, or a balanced failure. Behavioral differences between the cross-sections that fall into these three categories are discussed in terms of flexural capacity, curvature ductility, and relative contributions of HSS and UHPC to flexural capacity. Flexural response of the composite HSS-UHPC cross-section is compared to that of the bare HSS cross-section. The enhancement in flexural capacity and curvature ductility, for UHPC fiber tension-controlled sections compared to the bare HSS cross-section, was 52% and 79%, respectively. For composite cross-sections that feature a balanced failure, the increase in flexural capacity and curvature ductility, compared to the bare HSS cross-section, was 37% and 35%, respectively. Closed form formulations are proposed to identify the flexural failure mode and predict flexural capacity. The influence of various parameters, such as HSS material grade, size of cross-section, and UHPC material characteristics on the complete flexural response of the cross-section is investigated. The average ratio and corresponding coefficient of variation (COV) of tested to computed flexural strength obtained using the proposed procedure was 1.06 and 21.28%, respectively. Similarly, the average ratio and COV of tested to calculated flexural strength obtained using the proposed closed form formulations was 1.07 and 22.18%, respectively.

Reliability-Based Selection of Retrofit Works for Schools under Seismic Hazard

A reliability-based procedure is proposed to assess and compare the economic effectiveness of three retrofit alternatives for actual schools located in three zones with different seismic hazards. The procedure calculates the school failure probability under the damaged conditions, by considering the damages produced by the 2017 earthquake in Mexico, and the failure probability under each retrofit alternative, from the seismic spectra corresponding to the seismic hazard of each site. The best retrofit alternative is the one with the minimum expected life-cycle cost for each school. The global failure probability is calculated according to the Ditlevsen’s bounds, and the limit states consist of the event in which the maximum moment exceeds the bending capacity for beams, and the combined axial and bending forces exceed the capacity of the columns; the maximum responses are obtained through nonlinear analyses. The proposed retrofit alternatives are column and beam jacketing with steel angles and plates, increment of the concrete cross sections of columns and beams, and the addition of bracing. The effectiveness of each alternative, in terms of failure probability reduction and expected life-cycle cost, was assessed for each school. The procedure may be used to update the current retrofit specifications for schools.