Confinement Reinforcement Research Articles

Experimental analysis of concrete elements under partial area strip loading

AbstractStresses for concrete elements under partial area strip loading are limited to 1.1‐times the concrete compressive strength. In case of particularly small load application areas like at wall supports or segmental tunnel lining longitudinal joints this limitation may be governing the design. Additional load increases due to steel reinforcement confinement are not taken into account. This contribution presents various experimental series on large‐scale reinforced concrete specimens conducted at the Technical University of Munich (TUM) and the Ruhr University Bochum (RUB). It is shown that splitting reinforcements with stiff anchorage (e.g. welded ladders) show distinct load‐bearing capacity increases. Moreover, disregarding the demand for geometric affinity of load application and distribution areas facilitates a more precise estimation of load increase factors. Based upon the experiments and supplemental data from literature, practical design approaches are derived. They distinguish between high‐ and low‐deformation capabilities of the rebar anchorage and—to the most extent—allow pronouncedly increased contact pressures compared to current design approaches.

In-plane cyclic testing of precast concrete wall panels with grouted metal duct base connections

In order to achieve satisfactory seismic performance the connections between precast concrete wall panels and other structural elements should be well-designed to avoid brittle connection failure during an earthquake. Following the 2010/2011 Canterbury (New Zealand) earthquakes it was observed that brittle failure had occurred in some grouted metal duct connections used for precast concrete wall panels, resulting in recommendations for more robust detailing of this connection type. A set of experimental tests was subsequently performed to investigate the in-plane seismic behaviour of both existing and newly recommended detailing for precast concrete wall panel connections, with this testing comprised of seven reversed cyclic in-plane tests of full-scale precast concrete wall panels having wall-to-foundation grouted metal duct connections. Walls with existing connection detailing were found to perform adequately when carrying low axial loads, but performance was found to be less satisfactory as the axial load and wall panel length increased. The use of transverse confinement reinforcement around the grouted metal ducts was observed to prevent brittle connection response and to improve the robustness of the reinforcement splice.

Efficiency of the confinement reinforcement in anchorage zones of posttensioning tendons

In order to study the efficiency of the confinement reinforcement in anchorage zones of posttensioning tendons, using both ordinary reinforced concrete (ORC) and high‐performance fiber reinforced concrete (HPFRC), an experimental research has been performed on the bearing strength of concrete prismatic specimens. This research also intended to assess both ultimate capacity and adequate serviceability of the local anchorage zone when reducing the concrete cross section and the confining reinforcement, both specified by the anchorage device supplier, by using an HPFRC. The experimental program included ORC prismatic specimens with 305 mm × 305 mm × 650 mm reinforced with spirals and a combination of spirals and stirrups, and HPFRC specimens with 210 mm × 210 mm × 420 mm reinforced with stirrups. The reinforcement steel strains were measured to monitor the steel yielding, to assess the relation between the strains of the inner (spiral) and outer (stirrups) levels of reinforcement and the uniformity of the confinement forces along the confined length. A comparison between the bearing strength obtained by experimental tests and by models found in the literature is also presented. From the strain measurements, it can be concluded that in the case where there are, simultaneously, two types of confinement reinforcement, the outer reinforcement is not as effective as the inner one. Therefore, when computing the bearing strength, the linear superposition of contributions of both spiral and stirrups for confinement can be nonconservative, leading to too high estimated load capacity.

Behavior and design of high-strength circular reinforced concrete columns subjected to axial compression

High-strength concrete (HSC) can be of great interest for the construction of lower-stories reinforced-concrete (RC) columns in high-rise buildings. This superior material can reduce the dimensions of the columns, and therefore, can be considered as a more advantageous material than normal-strength concrete (NSC). To compensate for its higher brittleness nature, the confinement reinforcement ratio required for HSC has to be larger than that required for NSC. The aim of this study is to examine the confinement transverse steel reinforcement amounts required for HSC circular columns part of high-rise buildings. The study first compares the confinement reinforcement requirements given by leading standards. Following the comparative research, an experimental study on six HSC columns subjected to axial loading was performed. The results show that in terms of axial capacity, it is recommended to further examine the concrete strength reduction factor and that it is more reasonable to consider a value lower than 0.85 for the design of HSC columns. Moreover, in terms of confinement and ductility, the recommended volumetric transverse steel reinforcement ratio for HSC circular columns not considered as part of the seismic-force-resisting system (SFRS), can be based on the ACI standard requirement and equal to half of the maximum specified volumetric transverse steel reinforcement ratio required for HSC columns considered as part of the SFRS.

Covalent-supramolecular hybrid polymers as muscle-inspired anisotropic actuators

Skeletal muscle provides inspiration on how to achieve reversible, macroscopic, anisotropic motion in soft materials. Here we report on the bottom-up design of macroscopic tubes that exhibit anisotropic actuation driven by a thermal stimulus. The tube is built from a hydrogel in which extremely long supramolecular nanofibers are aligned using weak shear forces, followed by radial growth of thermoresponsive polymers from their surfaces. The hierarchically ordered tube exhibits reversible anisotropic actuation with changes in temperature, with much greater contraction perpendicular to the direction of nanofiber alignment. We identify two critical factors for the anisotropic actuation, macroscopic alignment of the supramolecular scaffold and its covalent bonding to polymer chains. Using finite element analysis and molecular calculations, we conclude polymer chain confinement and mechanical reinforcement by rigid supramolecular nanofibers are responsible for the anisotropic actuation. The work reported suggests strategies to create soft active matter with molecularly encoded capacity to perform complex tasks.

Uniaxial behavior of circular ultra-high-performance fiber-reinforced concrete columns confined by spiral reinforcement

This paper presents results from the uniaxial tests of six large-scale ultra-high-performance fiber-reinforced concrete (UHPFRC) circular columns confined by spirals. The UHPFRC used in this study had 1.5% of hybrid micro-steel fibers (1.0% of 19.5 mm fibers and 0.5% of 16.3 mm fibers) in the mixture and had compressive strengths varying from 163 to 181 MPa. The effects of the volumetric ratio of spiral reinforcement, compressive strength of concrete, and presence of hybrid micro-steel fibers on the axial load responses, including post-peak deformability, were investigated. In addition, the ductility level reached by circular UHPFRC columns designed according to the minimum spiral reinforcement of current design provisions of the CSA A23.3-14 Standard and the ACI 318-14 Code were evaluated to investigate the applicability of these equations to UHPFRC columns. Test results showed that the combined effect of the minimum spiral reinforcement and steel fibers resulted in sufficient post-peak ductility of the UHPFRC columns. To investigate the efficiency of the shape of the confinement reinforcement, the test results of the circular UHPFRC columns confined by spirals were compared with those from equivalent-sized square UHPFRC columns confined by hoops. The test results demonstrate the superior performance of circular spirals for developing the ductile behavior of UHPFRC columns than the same volumetric ratio of rectilinear hoops. A design recommendation for spiral reinforcement that ensures the ductile behavior of UHPFRC columns in moderate seismic regions is proposed.

Seismic performance of FRP-reinforced concrete-filled thin-walled steel tube considering local buckling

The objective of this study is to investigate the seismic performance of fiber-reinforced polymer-reinforced concrete-filled thin-walled steel tube (CFTST). Twelve specimens with different fiber-reinforced polymer types (glass fiber-reinforced polymer and carbon fiber-reinforced polymer) and reinforcing modes were tested under constant axially compressive load and cyclic lateral load. The failure mode and lateral load versus displacement relationship for each specimen were recorded during testing. The strength, ductility, and energy dissipation capacity were analyzed accordingly. Further, a stress–strain relationship and a restoring force model of the fiber-reinforced polymer confining steel tube with local buckling were proposed. A hysteretic model for the fiber-reinforced polymer-reinforced CFTST was developed subsequently. The results indicate that the seismic performance of fiber-reinforced polymer-reinforced CFTST can be effectively improved by optimizing the fiber-reinforced polymer type and corresponding reinforcing scheme. Carbon fiber-reinforced polymer and glass fiber-reinforced polymer are suitable materials for the confinement and bending reinforcement of the column, respectively. The modeling results show the energy imported into the column is mainly dissipated by the thin-walled steel tube. The energy dissipation proportion of the steel tube, concrete core, and longitudinal fiber-reinforced polymer are >80%, 10%–20%, and <8%, respectively. The energy dissipation value of the steel tube can be improved more than 40% after effectively restraining the local buckling.

Response of reinforced concrete beams to high‐velocity fluid impact. Part I: Experiments

Thirty‐two reinforced concrete beams were tested under static and fluid impact loads. Hoop (rectangular) and spiral transverse reinforcement of various configurations were used to confine the specimens. The objectives were to observe the effect of shape of beams and configuration of confinement reinforcement on the impact resistance, and to estimate the limiting fluid velocity that causes total failure.

Effect of confinement on behavior of short concrete column

In this experimental program a series of nine one-third scale square reinforced concrete columns specimens having cross sectional dimension as 150mm x 150mm with height of 960 mm were tested. The experiment is performed for control column, columns with ferromesh jacket as confinement reinforcement in addition to stirrups and column with ferromesh jacket only as confinement reinforcement. The overall response of the specimens was investigated in terms of load carrying capacity, axial displacement, stress, strain, lateral displacement and ductility. The test results indicated that column wrapped with additional ferromesh as confinement gives 20% increase in axial strength compared to regular control column. It is observed that columns with ferromesh jacket as confinement reinforcement in addition to stirrups gives better ductility and the column wrapped only with ferromesh as additional confinement fails in ductile manner.

Material Modeling in the Dynamic Nonlinear Analysis for Recycled Aggregate Concrete Structures

ABSTRACTDynamic mechanical tests of recycled aggregate concrete (RAC) test units confined by transverse hoop reinforcement are carried out. The effects of the strain rate, hoop reinforcement confinement, and replacement ratio of recycled coarse aggregate (RCA) on the mechanical properties of confined recycled aggregate concrete (CRAC) are thoroughly analyzed and assessed. The strain-rate-dependent constitutive model of CRAC is proposed for the high strain rate representative of seismic conditions. A three-dimensional discrete numerical model, based on the proposed rate-dependent material model of CRAC, is established to investigate and evaluate the dynamic nonlinear behaviors of RAC structures.

21.04: Vibration characteristics of an existing high‐rise building in Montreal and the effects of retrofit

ABSTRACTThe study described in this paper refers to seismic assessment and retrofit of an existing 10‐storey reinforced concrete office building designed and built at the beginning of the 20 century. When this building with a height of 38.95 m was completed it was the highest in downtown Montreal. According to FEMA 547 classification, the typology of this building structure is associated to model building type “C3”. Consequently, this type of non‐ductile frame building with an insignificant amount of masonry walls is relatively weak and unable to carry the seismic forces when subjected to ground motions from a potential earthquake magnitude. The main deficiencies of this structural system are: poor lateral confinement and shear resistance of columns, the location of lap splices and the number of reinforcing bars often inadequate, the lack of confinement and shear reinforcement in joints, poor anchorage of longitudinal reinforcement of beams into joints and shear resistance of beams. Due to lack of seismic detailing, the common retrofit measure recommended in ASCE/SEI 41–13 for this building is to add new lateral force‐resisting systems designed according to current code and standard provisions. Hence, in this case, the most cost‐effective retrofit solution is to add a steel structure designed to withstand seismic forces while responding to serviceability criteria required to preserve the non‐reinforced masonry facades facing the main streets and the facades ornaments.

08.13: Structural performance assessment of steel frames with reinforced concrete walls

ABSTRACTIn recent years, there has been a growing interest towards the use of a composite structural system consisting of steel frames with reinforced concrete walls (SRCWs) as an economical alternative within earthquake resistant wall systems. The SRCW system is classified as Composite Structural Systems Type 1 in EN 1998‐1:2004. It has been shown that the SRCW system has the potential to be applicable as a lateral‐resistance system for low‐to‐moderate rise buildings located in earthquake‐prone regions as it has the potential to offer strength appropriate for resisting the lateral forces from earthquakes and stiffness adequate for controlling drift. Within the frame of this paper, analytical studies are conducted in order to obtain a better understanding of the SRCW system structural performance. Numerous three dimensional (3D) nonlinear Finite Element (FE) models have been developed using ANSYS software package. The detailed developed 3D FE models include the horizontal and vertical boundary steel elements, the discrete reinforcing bars, discrete stirrups as longitudinal and transverse confinement reinforcement, the shear connectors, the top and seat angles and the web angles including the bolts. Results and findings of this study are indicative of effectiveness of the headed studs geometry and material properties.

Effectiveness of Combined Confinement with Metal Meshes and Ties for Preloaded and Post-Heated RC Short Columns

Recently, innovative materials are used as lateral confinement reinforcement to increase concrete core contribution to load carrying capacity of reinforced concrete (RC) columns. This paper presents experimental assessment for the effectiveness of practical lateral confinement that utilizes metal meshes combined with typical steel ties for RC columns. The experimental plan comprises thirty square short column specimens and investigates two metal meshes types: expanded metal mesh (EMM) and welded wire mesh (WWM). Preloading and post-heating were considered in the experimental study to provide realistic assessment for proposed confinement in real and fire conditions. Prior to testing under monotonic axial compression, all column specimens were subjected to preloading with 65% (of reference column capacity) in addition to post-heating for only fourteen specimens. The lateral reinforcement consisted of metal mesh layers (either EMM or WWM) wrapped above steel ties of various volumetric ratios (\(\rho =0.333\), 0.167% and zero). Results showed that column load capacity was increased (49.15–2.72%) for all specimens enclosing proposed lateral reinforcement with respect to reference specimens whose lateral reinforcement comprising only ties (\(\rho =0.333\)%). Also, the ductility was noticeably improved. Results revealed that metal mesh strength had the upper hand in magnifying ultimate load and ductility. Moreover, optimum lateral reinforcement (that develops significant improvement in load capacity and ductility without degradation of stiffness) was determined. Metal meshes enhanced fire resistance by dropping concrete core temperature and mitigating ultimate load reduction of post-heated RC columns compared to reference specimens.

Numerical investigation on compressive performance of CFST columns with encased built-up lattice-angles

This paper presents a numerical investigation on the compressive behaviour of thin-walled concrete-filled steel tube (CFST) columns with encased built-up latticed angles. The additional confinement provided by encased angles was considered in the finite element (FE) model, in addition to the contact between tube wall and inner concrete and the effect of tube-wall confinement on concrete model. The established FE model is verified against the existing test results that it can well predict the behaviour of reinforced composite columns under axial compression. The composite action between encased angles and concrete and the efficiency of built-up angle configurations on performance improvement are extensively analyzed through the validated FE models. The influence of three parameters, namely confinement factor (ξ), reinforcement ratio (ρsr) and slenderness ratio (λ), to the angle-contributions on lateral confining pressure and the ultimate strength are evaluated and quantified. It is found the relationship between the strengths of CFST columns and built-up member can be defined as an exponential equation. Finally the design equation based on AISC 360-10 design provisions with consideration of angle-contributions is proposed, and the comparison results show it has a desirable accuracy and satisfactory correlation with both experimental and numerical results.

Finite Element Analysis of Square RC Columns Confined by Different Configurations of Transverse Reinforcement

Introduction:Square reinforced concrete (RC) columns with the confinement effect of transverse reinforcement perform well in ductility and have been used widely in RC structures. Its behavior is the classic topic of anti-seismic and anti-collapse analysis of RC structures. With the advancement of the finite element (FE) analysis technology, the general-purpose simulation tools such as ABAQUS and ANSYS have been universally used to analyze the behavior of structures and members, where the material constitutive model is a key problem in the analysis.Methods:In this study, a new uniaxial compressive stress-strain curve of the confined concrete considering confinement effect of transverse reinforcement in square RC columns was proposed for the concrete damaged plasticity model in ABAQUS to solve the problem that there is no proper uniaxial compressive stress-strain curve for the concrete damaged plasticity model to describe the behavior of concrete confined by transverse reinforcement. Based on the proposed stress-strain relationship, a FE model was developed to analyze the behaviour of laterally confined RC columns under concentric loading.Results:The finite element model is able to predict the response of the confined RC columns from different experiments with reasonable accuracy. Finally, a parametric study was conducted in order to evaluate the effect of confinement reinforcement configuration on the behavior of core concrete in square section.

Study of composite steel frame with reinforced-concrete infill

This paper describes the development of a three-dimensional, non-linear finite-element model for evaluating the response of composite structural systems consisting of steel frames with reinforced-concrete infill walls subjected to a combination of gravity and in-plane lateral loading. Several sensitivity studies, taking into account both material characteristics and geometrical non-linearities were performed in order to investigate parameters such as the shear retention factors, Coulomb's coefficient for steel–concrete contacts and different load–slip relationships for modelling the shear behaviour of headed studs. Appropriate experimental data sourced from the literature were utilised to verify the proposed numerical model. A series of parametric studies was conducted to explore the effect of transverse and longitudinal confinement reinforcement, reinforcing bar diameter and steel strength. In order to investigate the composite interaction effect, several numerical models were developed, with emphasis on the configuration of shear connectors along the interface between the steel members and the reinforced-concrete infills. The analysis results demonstrated that the developed finite-element model captured and predicted the force–drift response of the system and revealed that the presence of shear connectors had a critical effect on the overall behaviour of the system.

Displacement-based model to predict lateral drift capacities of concrete-filled FRP tube columns

Abstract It has been shown over the past three decades that fiber reinforced polymer (FRP) composite tubes offer an attractive alternative to conventional confinement reinforcement to enhance strength and deformability of concrete columns. Concrete-filled FRP tube (CFFT) columns have been shown to exhibit highly ductile behavior under simulated seismic loading, making them suitable for use in earthquake-resistant construction. For the design of CFFT columns in new construction there is need for a rational procedure that enables the prediction of lateral drift capacities of these columns. This paper presents such a procedure for displacement-based design of circular and square CFFT columns. The approach incorporates influences of experimentally observed confinement parameters while also including axial load level and lateral drift capacity as design variables. The expression derived as part of the proposed design procedure has been validated using available experimental data, and it has been shown that the predicted capacities are in good agreement with the experimental results.

Confinement of ultra-high-performance fiber reinforced concrete columns

This study investigates the axial load response of ultra-high-performance fiber-reinforced concrete (UHPFRC) columns with compressive strengths of 163 and 181MPa (design strengths of 150 and 180MPa). The UHPFRC used in this study had 1.5% of hybrid micro-steel fibers (1.0% of 19.5mm fibers and 0.5% of 16.3mm fibers) and did not contain coarse aggregate. A total of nine UHPFRC columns confined by transverse reinforcement with volumetric ratios of 0.9–9.9% and two different configurations (Types A and C) were tested under pure axial load to investigate the influence of these variables. The overall behavior of the UHPFRC columns was compared with the response of similar strength ultra-high-strength concrete (UHSC) columns having coarse aggregate. Test results showed a pronounced effect of the volumetric ratio of the transverse reinforcement on the confinement. Hybrid micro-steel fibers controlled brittle cover spalling very well and assisted the transverse confinement reinforcement after the peak load. Applicability of the confinement reinforcement equations in the current seismic design provisions for developing ductile behavior of the UHPFRC columns was investigated. The analytical study examined the ability of the existing high-strength concrete (HSC) confinement models for predicting the axial load response of the UHPFRC columns, and a prediction model that accounts for the effects of steel fibers and the stress-strain relationship of UHPFRC is proposed.

Ductility design of RC columns. Part 2: extent of critical zone and confinement reinforcement

ABSTRACTThe current Hong Kong concrete design code (HKConcrete2013), which is a non-seismic design code, includes provisions of the design of confinement zone in reinforced concrete (RC) columns. Whether or not these provisions can be adopted in the development of the new design code of structures for seismic resistance remains uncertain. A thorough scientific investigation with a comprehensive statistical analysis on the seismic behaviour of RC columns under different levels of the axial compression ratio (ACR) and concrete confinement has been conducted and presented in the companion paper [1], where the use of the ACR limits for controlling the seismic performance of various types of RC columns is proposed. The present paper addresses the important aspect of the confinement zone length and the design of confinement reinforcement in RC columns under different levels of the ACR. The theoretical background of the confinement zone is presented and the requirements of the prevailing design standards for des...

Ultimate Compressive Strength and Its Deformation of Normal and High Strength Concrete Cylinder Confined With External Lateral Pre-Stressing

Confining reinforcement for concrete columns have been standardized in building standards ACI 318-11 and SNI 03-2847-2013. The observation of building collapse by earthquake normally caused by malfunction of the building columns as bearing elements. The columns were failed because they did not meet the standard of confining reinforcement. In most cases, external confinement is necessary to strengthen the existing columns of old buildings. This research focused on the methods to strengthen the existing columns. Three types of pre-stressed steel rings were used to confine the concrete cylinders of 10× 20 cm and 10 × 30 cm. Several concrete strengths of 50 MPa, 70 MPa and 100 MPa were selected for constructing 18 specimens of concrete cylinders. The first type of pre-stressed is with zero pre-stressing force represented passive confinement while the second and third types were given different prestressing forces on the steel ring represented active confinement. Prestressing force on the steel ring will cause radial stress that compress the concrete cylinders. Load test were conducted on concrete cylinders to measure the strength and the relationship of stress strain concrete cylinders which was confined by varied external lateral pre-stressing. The testing results showed that the external lateral prestressing increases the ductility and strength of concrete columns. It proved the method of external lateral pre-stressing can be used effectively for retrofitting and strengthening existing columns in order to meet the requirement of ductility and strength.