Concrete Sections Research Articles

Study on influencing factors of hysteretic performance of cantilever fully-bolted prefabricated beam-column joint

In order to improve the construction efficiency and integrity of prefabricated RC frames, a cantilever fully-bolted prefabricated beam-column joint is proposed. Through the reciprocating loading test, the change rules of rotation characteristics, mechanical properties and stiffness degradation of this type of joint were obtained. The failure mode of the joint is found: the steel plate in the connection area undergoes a slight flexural deformation, the concrete on the outside of the connection area forms a plastic region of about 1/3 beam length, the concrete crack develops obliquely from horizontal cracking with the increase of stiffness, and the damage characteristic develops from bending damage to shear damage. The initial stiffness of the precast joint is about 1.5 times that of the cast-in-place joint, the yield load is increased by 31 %, the peak load by 52 % and the ductility coefficient by a maximum of 96 %, with significantly better mechanical properties than the cast-in-place joint. Parametric analysis was carried out based on the tests. When the flexural stiffness ratio of the cantilevered section to the reinforced concrete beam section is less than 0.5, it is a weak connection. Damage to the section cantilever section occurs, and the stiffness degrades significantly. It is recommended that the joint be designed for a strong connection, with a stiffness ratio of around 0.6. The cantilever section's length greatly influences the joint's stress transfer. It is recommended that the length be taken to be about 0.6 and no greater than 0.75 for the width of the precast reinforced concrete beam. The design process of a prefabricated RC frame is given on this basis. A research basis has been laid for the engineering application of this new type of connection.

Biaxial bending of RC rectangular column sections: Improved ‘load contour’ formulation

AbstractIn design practice, the safety of any given rectangular reinforced concrete column section is checked by ensuring that all possible combinations of axial compression (Pu) and biaxial moments (Mux, Muy) at the ultimate limit state lie within its three‐dimensional load–moment interaction failure surface. Although such a check is facilitated by commercial software packages, it is traditionally carried out with the help of an approximate formulation of the ‘load contour’ at any given axial load level, first proposed by Bresler. The present study proposes an efficient algorithm, using a ‘modified thick layer integration’ approach and a ‘nested bisection’ method, to generate the ‘exact’ load contour (and thereby, the complete interaction surface) for any symmetrically reinforced column section, complying with the strength design requirements of ACI 318 (or EC2 or IS 456). The algorithm also generates a measure of the safety margin, called ‘demand‐to‐capacity ratio’ (DCR), defined as the ratio of the resultant design moment (Mu) to the moment capacity (Muθ) at a given axial load level (Pu). For an optimal code‐compliant design, the peak value of DCR generated from various factored load combinations (obtained from frame analyses) must be close to 1.0. The extent to which the peak DCR is less (or greater) than 1.0 provides a measure of over‐design (or under‐design) in a given context. After validating the algorithm, a parametric study was carried out on a spectrum of 36 different cross‐sections having different aspect ratios, bar arrangements and reinforcement percentages. The study reveals that the exponent in the approximate load contour formulation depends not only on the axial load (as currently assumed in ACI: SP17, EC2 and IS 456), but also on the percentage of longitudinal reinforcement. Accordingly, modifications have been suggested to improve the accuracy in these code‐prescribed approximate formulations of the load contour, for more economical and safe design.

Evaluation of detrimental effects in concrete specimens due to the oxidation of sulfide-bearing aggregates after electrochemical treatment

Sulfide-bearing aggregates can cause significant damage when concrete has been produced without considering their potential deleterious oxidation reactivity. This study aims to find a reliable quantitative approach for assessing the impact of the harmful reaction of sulfide minerals (essentially pyrrhotite) in concrete specimens produced under laboratory conditions. To achieve this objective, different parameters such as an electrochemical treatment have been applied over 14, 28, 35 and 56-day periods on a series of concrete specimens made in the laboratory with a reactive sulfide-bearing aggregate (MSK 0.9) and non-reactive aggregate (PKA) After the treatment, the concrete specimens were tested with different tools such as non-destructive (Ultrasonic Pulse Velocity), semi destructive (expansion, modulus of elasticity and stiffness damage test) and destructive (concrete polished section and compression) methods to evaluate the impact of the deleterious reaction of the sulfide-bearing aggregates. The results show that concrete with the reactive aggregate can lose a significant amount of its mechanical performance exhibited principally by a significant reduction in modulus of elasticity (decreasing around 28% after 35 days of electrochemical treatment). Signs of damage associated with the use of the MSK aggregate were identified within concrete polished sections and under the SEM, which allowed to better describe the mechanisms of the oxidation reaction of the sulfide minerals. Ideal parameters/conditions can be achieved to evaluate the potential oxidation reaction of sulfide-bearing aggregates using the electrochemical treatment and the reduction of the modulus of elasticity of the concrete in a reasonable period of time.

A Review: On Self Compacting Concrete

A Review: On Self Compacting Concrete

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.

The Effect of Printing Direction on the Strength Characteristics of a 3D Printed Concrete Wall Section

The Effect of Printing Direction on the Strength Characteristics of a 3D Printed Concrete Wall Section

Providing a strategy to restore damaged RC beam-column joints with the combination of CFRP and HPFRCC

This paper endeavors to assess the seismic performance of 3D reinforced concrete (RC) beam-column joints situated on the exterior of buildings, but lacking special ductility requirements. The joints have been rehabilitated by High-Performance Fiber-Reinforced Cement Composites (HPFRCC) and retrofitted using Carbon Fiber Reinforced Polymer (CFRP) wrap methodology. In this context, five beam-column joints located on the exterior of a structure have been subjected to cyclic lateral loading, while being scaled down to half their original size. The present study entailed an investigation into the cyclic behavior of three control specimens in its initial stage. Following the initial examination, it was observed that the control specimens, lacking any designated ductility standards, experienced significant core damage. During the subsequent phase of experimentation, the impaired concrete sections of the control samples were remediated through substitution with HPFRCC matter. Additionally, CFRP sheets were implemented for retrofit purposes. The modified specimens were then exposed to comparable cycles of loading. An analysis is conducted on the empirical findings of the specimens under investigation. The findings of this study indicate that the utilization of HPFRCC materials and CFRP sheets in the restoration and enhancement of deteriorated joints has led to a notable enhancement of their strength and displacement capacity. Specifically, this approach has facilitated the creation of a flexural plastic hinge and impeded the occurrence of shear failure within the core, leading to an improved overall behavior of the repaired damaged joint, which is comparable to that of undamaged seismic joints. The application of this technique demonstrates a high degree of efficacy in the rehabilitation and enhancement of edifices with deficient seismic details that have sustained damage subsequent to an earthquake event.

Pre-tensioned concrete beams optimized with a unified function of objective (UFO) using ANN-based Hong-Lagrange method

ABSTRACT The present study simultaneously optimizes the three objective functions of pre-tensioned concrete (PT) beams, such as construction and material cost, beam weights, and beam depth, where multiple objectives optimizations (MOO) conflicting with each other are performed. MOO is performed based on 21 input parameters including tendon parameters and the 21 output parameters. Preassigned input parameters are defined by 16 equalities and design requirements are also implemented during the optimization through 19 code-based inequalities. Finally, the five-step ANN-based algorithms are presented to find optimized design parameters subject to external loads within ranges prescribed by inequalities. A Pareto frontier is presented based on the combinations of weight fractions representing contributions made by the three objective functions. ANN-based optimizations are capable of quantifying tendon ratios and rebar areas when concrete sections crack under service loads while optimizing multi-design targets and objective functions at the same time. The ANN-based optimized designs are verified with a structural mechanics-based software, AutoPT. Reductions of 9.1%, 30.1%, and 10.4% in beam depths, costs, and weights, respectively, obtained based on a Pareto frontier which simultaneously optimizes multi-objective functions are compared with probable designs by human engineers, demonstrating a design efficiency for a pre-tensioned concrete (PT) beam.

Implications of loss of stability of deformation sequences of reinforced concrete sections

The paper analyses the strain of reinforced concrete sections of flexural and eccentrically compressed sections up to and including failure.

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.

Segmentation of Long Concrete Pavement Sections Based on Concrete Strength

Segmentation of Long Concrete Pavement Sections Based on Concrete Strength

Seismic behavior of irregular shaped beam-column connections

This paper reports test results and numerical analysis of special-shaped beam-column connections based on a frame-shear wall structure. Four connections of 1/5 scale ratio were tested under constant axial force and reversed lateral load on the top of column. The experiment investigated the effect of steel reinforced concrete (SRC) beam, in-plane and out of-plane reinforced concrete (RC) wall on the connections’ seismic behavior. The failure modes, hysteresis curves, ductility, strength degradation and energy-dissipating capacity of test specimens are reported. The results indicated that test joints were susceptible to suffer more brittle failure caused by formation of plastic hinge on column, which is considered unfavorable compared to conventional joint with regular shape in earthquake resisting. Adding in-plane shear walls to the connection switched column failure to beam failure mode, and significantly improved the connection’s strength, stiffness and ductility. Finite element models were detailed established and validated through experiment data. Influence of parameters including axial load ratio, concrete strength grade, section area and steel ratio of upper column, transverse hoops volumetric, RC wall of two orthogonal directions on connection’s seismic behavior were studied through modeling results.

Numerical simulation methods for reinforced concrete columns considering parameter stochasticity

Reinforced concrete column specimens with the same parameters often show differences in bearing capacity and deformation under the same loading path. Most of the existing studies attribute the causes to recording instrumentation errors or randomness in material and bond dimensions, but the method to improve the accuracy of numerical simulation of the reinforced concrete components is still unclear. For a given member, the randomness of material and geometry is an important cause of simulation error, which should be taken into account to improve the simulation accuracy. A weighted least squares estimation (WLS) method is used to fuse the test samples of reinforced concrete member section sizes, reinforcement and concrete with confidence factors as weights. The probability distribution functions of reinforced concrete member section sizes, reinforcement and concrete are calculated by a genetic algorithm method. Based on the existing seismic performance test data of reinforced concrete columns, a stochastic finite element model of reinforced concrete columns is developed for seismic performance analysis using Monte Carlo method through a mixture of two software programs, MATLAB and OpenSees. The numerical seismic performance indexes of eight types of reinforced concrete columns were compared with the test results to verify the importance of introducing stochastic parameters into the model. The results demonstrate the simulation accuracy of the finite element model considering parameter randomness is 88% higher than that of the finite element model without considering parameter randomness, which proves the effectiveness of the numerical simulation method for reinforced concrete columns considering parameter randomness.

Designing reinforced HSC rectangular beams using optimization techniques

AbstractThe current work discusses optimizing the structural design of reinforced high strength concrete rectangular sections under design loads. Using a least-cost design criterion and minimal design variables, an analytical approach to the problem is devised. A nonlinear mathematical programming format for the formulation of the problem is among the things that are demonstrated. To demonstrate how the formulation can be used in line with the ACI 318-08 standard, several typical cases are given. The outcomes are compared to those obtained from existing design practice. The ideal solution demonstrates unequivocally that significant reductions in the anticipated absolute costs of the building materials to be employed are possible and without making significant changes, this method may be expanded to address other portions.

Axial compressive behavior of corroded double-steel-plate composite shear wall with binding bars

Steel structure is susceptible to corrosion, and corrosion will seriously affect its own load-bearing capacity and service life. In this paper, the axial compressive behavior of double-steel-plate composite shear wall (DSCW) with binding bars under different corrosion degrees is experimentally studied. The typical failure modes include the steel plate local buckling, binding bars fracture, concrete crushing, and steel plate weld tearing. The increase of corrosion rate has unfavorable influence on the axial compressive bearing capacity, initial stiffness, and ductility of DSCW. Finite element (FE) models are established to further investigate the axial compressive behavior of DSCW. It is concluded that the concrete and steel plate strength grade, the concrete section area, the steel plate thickness, and the binding bars diameter and spacing significantly affect the axial compressive bearing capacity of DSCW. A formula calculating the axial compressive bearing capacity of corroded DSCW with binding bars is proposed. The formula agrees well with the test results and can provide a reference for the engineering application.

Fast and Accurate Generation Method of Geometric Digital Twin Model of RC Bridge with Box Chambers Based on Terrestrial Laser Scanning

Digital Twin (DT) plays a crucial role in intelligent bridge management, and the geometric DT (gDT) serves as its foundation. Notably, the fast and high-precision generation of bridge gDT models has gained increasing attention. This research presents a method for generating high-precision and fast RC bridges with chambers for gDT using terrestrial laser scanning. The method begins with a proposed fast point cloud data collection technique designed specifically for bridges with internal chambers. Subsequently, Euclidean clustering and grid segmentation algorithms are developed to automatically extract contour features from the sliced point clouds. Finally, a framework based on the Dynamo–Revit reverse modelling method is introduced, enabling the automatic generation of gDT models from the identified point cloud features. To validate the feasibility and accuracy of the proposed method, a concrete variable section bridge is used. A comparison is made between the generated gDT model and the point cloud model in terms of 3D deviation, revealing a maximum deviation of 6.6 mm and an average deviation of 3 mm. These results affirm the feasibility of the proposed method.

Built-Up Fiber-Reinforced Polymers (FRP) Profiles with Improved Shear Performance for FRP–Concrete Hybrid Section

Fiber-reinforced polymer (FRP)–concrete hybrid sections, composed of FRP profiles and a concrete slab, have gathered attention in construction due to their lightweight, easy installation, and high durability. However, the low shear strength and brittle behavior of commercially available pultruded FRP profiles often leads to brittle shear failure at low load levels. To enhance the shear strength and ductility, this study proposes a novel H-shaped FRP profile that is built from two U-shaped pultruded FRP profiles and a hand lay-up sandwiched core of multi-directional fibers. Direct shear tests showed that the built-up FRP profiles failed in pseudo-ductile mode while the U-shaped pultruded FRP profiles failed in brittle mode. Built-up FRP had 1.5 times the capacity and 2.8 times the ultimate redundancy compared to pultruded FRP. Additionally, flexural tests of FRP–concrete hybrid beams revealed that the webs of the built-up FRP profiles failed in a higher shear capacity with smeared cracks.

Material and construction solutions in the construction of civil defence shelters

An analysis is presented of the use of material and construction solutions used in construction, mainly residential, for the construction of OC (civil defence) shelters.The article presents procedures for designing reinforced concrete structures that make it possible to properly determine the load capacity of critical sections. In the present work, a study of the deformation stability of a zone of reinforced concrete sections that is subjected to compression is used. Computational methods based on Drucker's postulate were used to solve the problem. The proposed approach enables the determination of the values of ultimate and failure strains based on the analysis of the loading path of a reinforced concrete section.Generally, shelters built into residential buildings are analysed, intended to be constructed in the rooms of the basement floor. A reduced need for ancillary space, the basement room, is observed. Garage functions are located on the basement floor. The plan contours of the basement are often larger than those of the ground floor. It is possible to design a shelter for the residents of the building, which ensures the greatest efficiency in its use. It is desirable to maintain uniform material and construction solutions while maintaining technological and organisational solutions during the erection of the entire building.The paper indicates the possibility of using some of the material and structural solutions of the housing construction in the realisation of OC shelters built into the basement floor. The construction of free-standing shelters was not analysed separately, but the proposals presented in the paper can also be applied to the type of OC shelters. Some results of the analysis of the adaptation of material and structural solutions of the housing construction to the needs of OC shelters construction will be presented during the symposium.It is advisable to develop models for the construction of OC shelters using contemporary technologies used in the construction industry.Useful tool can be the proposed scheme for improving activities based on the EFQM model.

Refined simulation of bond-slip behavior between ribbed steel and concrete: Effects of initial stress and temperature

The bond performance between steel and concrete exposed to fire is influenced by many factors, including the presence of an initial load before the temperature increase. To investigate such effect, a 3-D refined simulation model is presented accounting for the heterogeneity of concrete at the mesoscopic level and the external geometry of ribbed steel bars. The rationality and validity of the refined simulation model and of the multi-step analysis were verified by comparison with existing experimental data. Subsequently, the effects of aggregate gradation and distribution, initial loading level and temperature on the bond behavior were analyzed. The load transfer mechanism at the steel–concrete interface as a function of temperature under different loading levels is captured and discussed. It is found that the influence of aggregate grading and distribution on the bond-slip curve can be ignored under the aggregate volume fraction set in this work. Additionally, results show that the damage initially concentrates at the rib tip of the deformed steel bars, with an increase across the concrete section as the slip increases, as it could be expected. However, the bond stress and both stress and strain of steel at the same position decrease as the temperature increases. Finally and most importantly, it is found that the heating and loading sequence induce a different damage evolution inside the specimen, with a significant effect on the bond stiffness, the plateau portion of the bond stress-slip curve and the bond strength associated to a given critical temperature.

Neural Networks Applicability for Design of Reinforced Concrete Sections for Bending

Solving engineering design tasks requires the use of analytical formulas and dependencies. The direct inclusion of mathematical expressions in the artificial neural network (ANN) is not possible. This research studies the possibility of applying the neural networks method for designing of single or double-side reinforced concrete sections. A Visual Basic for Applications (VBA) macro was developed in the MS Excel environment to solve the task of determining the required area of the reinforcement by given geometric dimensions and bending moment and applying classical analytical formulas for reinforced concrete sections design. The training of the pre-configured neural network is performed by approximately 34000 sets of matching input parameters. The presented results from the trained ANN are compared and analysed against the exact analytical solutions. The study presents an approach to the application of structural design calculations. The results suggest that the approach is applicable to more complicated structural design problems.